kopia lustrzana https://gitlab.com/sane-project/frontends
1870 wiersze
75 KiB
TeX
1870 wiersze
75 KiB
TeX
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\title{\huge SANE Standard Version 1.01}
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\author{}
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\date{October 17, 2000}
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\makeindex
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\begin{document}
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\maketitle
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\tableofcontents
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\listoffigures
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\listoftables
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\chapter{Preface}
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The SANE standard is being developed by a group of free-software
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developers. The process is open to the public and comments as well as
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suggestions for improvements are welcome. Information on how to join
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the SANE development process can be found in Chapter
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\ref{chap:contact}.
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The SANE standard is intended to streamline software development by
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providing a standard application programming interface to access
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raster scanner hardware. This should reduce the number of different
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driver implementations, thereby reducing the need for reimplementing
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similar code.
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\section{About This Document}
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This document is intended for developers who are creating either an
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application that requires access to raster scanner hardware and for
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developers who are implementing a SANE driver. It does not cover
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specific implementations of SANE components. Its sole purpose is to
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describe and define the SANE application interface that will enable
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any application on any platform to interoperate with any SANE backend
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for that platform.
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The remainder of this document is organized as follows.
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Chapter~\ref{chap:intro} provides introductional material.
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Chapter~\ref{chap:environ} presents the environment SANE is designed
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for. Chapter~\ref{chap:api} details the SANE Application Programmer
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Interface. Chapter~\ref{chap:net} specifies the network protocol that
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can be used to implement the SANE API in a network transparent
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fashion. Finally, Chapter~\ref{chap:contact} gives information on how
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to join the SANE development process.
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\subsection{Typographic Conventions}
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\chapter{Introduction}\label{chap:intro}
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SANE is an application programming interface (API) that provides
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standardized access to any raster image scanner hardware. The
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standardized interface allows to write just one driver for each
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scanner device instead of one driver for each scanner and application.
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The reduction in the number of required drivers provides significant
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savings in development time. More importantly, SANE raises the level
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at which applications can work. As such, it will enable applications
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that were previously unheard of in the UNIX world. While SANE is
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primarily targeted at a UNIX environment, the standard has been
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carefully designed to make it possible to implement the API on
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virtually any hardware or operating system.
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SANE is an acronym for ``Scanner Access Now Easy.'' Also, the hope is
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that SANE is sane in the sense that it will allow easy implementation
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of the API while accommodating all features required by today's
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scanner hardware and applications. Specifically, SANE should be broad
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enough to accommodate devices such as scanners, digital still and
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video cameras, as well as virtual devices like image file filters.
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\section{Terminology}
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An application that uses the SANE interface is called a SANE {\em
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frontend}. A driver that implements the SANE interface is called a
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SANE {\em backend}. A {\em meta backend\/} provides some means to
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manage one or more other backends.
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\chapter{The SANE Environment}\label{chap:environ}
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SANE is defined as a C-callable library interface. Accessing a raster
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scanner device typically consists of two phases: first, various
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controls of the scanner need to be setup or queried. In the second
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phase, one or more images are acquired.
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Since the device controls are widely different from device to device,
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SANE provides a generic interface that makes it easy for a frontend to
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give a user access to all controls without having to understand each
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and every device control. The design principle used here is to
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abstract each device control into a SANE {\em option\/}. An option is
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a self-describing name/value pair. For example, the brightness
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control of a camera might be represented by an option called
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\code{brightness} whose value is an integer in the range from 0 to
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255.
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With self-describing options, a backend need not be concerned with
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{\em presentation\/} issues: the backend simply provides a list of
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options that describe all the controls available in the device.
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Similarly, there are benefits to the frontend: it need not be
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concerned with the {\em meaning\/} of each option. It simply provides
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means to present and alter the options defined by the backend.
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\section{Attaching to a SANE backend}
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The process through which a SANE frontend connects to a backend is
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platform dependent. Several possibilities exist:
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\begin{itemize}
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\item {\bf Static linking:} A SANE backend may be linked directly into
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a frontend. While the simplest method of attaching to a backend, it
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is somewhat limited in functionality since the available devices is
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limited to the ones for which support has been linked in when the
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frontend was built. But even so static linking can be quite useful,
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particularly when combined with a backend that can access scanners
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via a network. Also, it is possible to support multiple backends
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simultaneously by implementing a meta backend that manages several
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backends that have been compiled in such a manner that they export
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unique function names. For example, a backend called \code{be}
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would normally export a function called \code{sane\_read()}. If
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each backend would provide such a function, static linking would
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fail due to multiple conflicting definitions of the same symbol.
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This can be resolved by having backend \code{be} include a
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header file that has lines of the form:
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\begin{quote}
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\begin{verbatim}
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#define sane_read be_sane_read
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\end{verbatim}
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\end{quote}
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With definitions of this kind, backend \code{be} will export
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function name \code{be\_sane\_read()}. Thus, all backends will
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export unique names. As long as a meta backend knows about these
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names, it is possible to combine several backends at link time and
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select and use them dynamically at runtime.
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\item {\bf Dynamic linking:} A simpler yet more powerful way to
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support multiple backends is to exploit dynamic linking on platforms
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that support it. In this case, a frontend is linked against a
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shared library that implements any SANE backend. Since each
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dynamically linked backend exports the same set of global symbols
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(all starting with the prefix \code{sane\_}), the dynamic library
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that gets loaded at runtime does not necessarily have to be the same
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one as one the frontend got linked against. In other words, it is
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possible to switch the backend by installing the appropriate backend
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dynamic library.
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More importantly, dynamic linking makes it easy to implement a meta
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backend that loads other backends {\em on demand}. This is a
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powerful mechanism since it allows adding new backends merely by
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installing a shared library and updating a configuration file.
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\item {\bf Network connection:} Arguably the ultimate way to attach to
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a scanner is by using the network to connect to a backend on a
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remote machine. This makes it possible to scan images from any host
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in the universe, as long as there is a network connection to that
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host and provided the user is permitted to access that scanner.
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\end{itemize}
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\begin{figure}[htbp]
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\begin{center}
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\leavevmode
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\psfig{file=figs/hierarchy.eps,angle=270,width=\textwidth}
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\caption{Example SANE Hiearchy}
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\label{fig:hierarchy}
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\end{center}
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\end{figure}
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The above discussion lists just a few ways for frontends to attach to
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a backend. It is of course possible to combine these solutions to
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provide an entire hierarchy of SANE backends. Such a hierarchy is
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depicted in Figure~\ref{fig:hierarchy}. The figure shows that machine
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A uses a dynamic-linking based meta backend called \code{dll} to
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access the backends called \code{pnm}, \code{mustek}, and \code{net}.
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The first two are real backends, whereas the last one is a meta
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backend that provides network transparent access to remote scanners.
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In the figure, machine B provides non-local access to its scanners
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through the SANE frontend called \code{saned}. The \code{saned} in
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turn has access to the \code{hp} and \code{autolum} backends through
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another instance of the \code{dll} backend. The \code{autolum} meta
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backend is used to automatically adjust the luminance (brightness) of
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the image data acquired by the camera backend called \code{qcam}.
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Note that a meta backend really is both a frontend and a backend at
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the same time. It is a frontend from the viewpoint of the backends
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that it manages and a backend from the viewpoint of the frontends that
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access it. The name ``meta backend'' was chosen primarily because the
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SANE standard describes the interface from the viewpoint of a (real)
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frontend.
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\section{Image Data Format}\label{sec:imageformat}\index{image data format}
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Arguably the most important aspect of an image acquisition system is
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how images are represented. The SANE approach is to define a simple
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yet powerful representation that is sufficient for vast majority of
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applications and devices. While the representation is simple, the
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interface has been defined carefully to allow extending it in the
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future without breaking backwards compatibility. Thus, it will be
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possible to accommodate future applications or devices that were not
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anticipated at the time this standard was created.
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A SANE image is a rectangular area. The rectangular area is
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subdivided into a number of rows and columns. At the intersection of
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each row and column is a quadratic pixel. A pixel consists of one or
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more sample values. Each sample value represents one channel (e.g.,
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the red channel). Each sample value has a certain bit depth. The bit
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depth is fixed for the entire image and can be as small as one bit.
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Valid bit depths are 1, 8, or 16 bits per sample. If a device's
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natural bit depth is something else, it is up to the driver to scale
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the sample values appropriately (e.g., a 4 bit sample could be scaled
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by a factor of four to represent a sample value of depth 8).
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\subsection{Image Transmission}
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The SANE API transmits an image as a sequence of frames. Each frame
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covers the same rectangular area as the entire image, but may contain
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only a subset of the channels in the final image. For example, a
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red/green/blue image could either be transmitted as a single frame
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that contains the sample values for all three channels or it could be
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transmitted as a sequence of three frames: the first frame containing
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the red channel, the second the green channel, and the third the blue
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channel.
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Conceptually, each frame is transmitted a byte at a time. Each byte
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may contain 8 sample values (for an image bit depth of 1), one full
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sample value (for an image bit depth of 8), or a partial sample value
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(for an image bit depth of 16 or bigger). In the latter case, the
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bytes of each sample value are transmitted in the machine's native
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byte order.
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\begin{quote}
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\begin{center}
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{\bf Backend Implementation Note}
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\end{center}
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A network-based meta backend will have to ensure that the byte order
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in image data is adjusted appropriately if necessary. For example,
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when the meta backend attaches to the server proxy, the proxy may
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inform the backend of the server's byte order. The backend can then
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apply the adjustment if necessary. In essence, this implements a
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``receiver-makes-right'' approach.
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\end{quote}
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\begin{figure}[htbp]
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\begin{center}
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\leavevmode
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\psfig{file=figs/xfer.eps,width=0.5\textwidth}
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\caption{Transfer order of image data bytes}
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\label{fig:xfer}
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\end{center}
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\end{figure}
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The order in which the sample values in a frame are transmitted is
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illustrated in Figure~\ref{fig:xfer}. As can be seen, the values are
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transmitted row by row and each row is transmitted from left-most to
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right-most column. The left-to-right, top-to-bottom transmission
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order applies when the image is viewed in its normal orientation (as
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it would be displayed on a screen, for example).
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If a frame contains multiple channels, then the channels are
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transmitted in an interleaved fashion. Figure~\ref{fig:pixels}
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illustrates this for the case where a frame contains a complete
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red/green/blue image with a bit-depth of 8. For a bit depth of 1,
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each byte contains 8 sample values of a {\em single\/} channel. In
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other words, a bit depth 1 frame is transmitted in a byte interleaved
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fashion.
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\begin{figure}[htbp]
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\begin{center}
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\leavevmode
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\psfig{file=figs/image-data.eps,width=0.8\textwidth}
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\caption{Bit and byte order or image data}
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\label{fig:pixels}
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\end{center}
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\end{figure}
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When transmitting an image frame by frame, the frontend needs to know
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what part of the image a frame represents (and how many frames it
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should expect). For that purpose, the SANE API tags every frame with
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a type. This version of the SANE standard supports the following
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frame types:
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\begin{quote}
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\begin{description}
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\item[\code{\defn{SANE\_FRAME\_GRAY}}:] The frame contains a single
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channel of data that represents sample values from a spectral band
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that covers the human visual range. The image consists of this
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frame only.
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\item[\code{\defn{SANE\_FRAME\_RGB}}:] The frame contains three
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channels of data that represent sample values from the red, green,
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and blue spectral bands. The sample values are interleaved in the
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order red, green, and blue. The image consists of this frame only.
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\item[\code{\defn{SANE\_FRAME\_RED}}:] The frame contains one channel
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of data that represents sample values from the red spectral band.
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The complete image consists of three frames:
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\code{SANE\_\-FRA\-ME\_RED}, \code{SANE\_FRAME\_GREEN}, and
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\code{SANE\_FRAME\_BLUE}. The order in which the frames are
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transmitted chosen by the backend.
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\item[\code{\defn{SANE\_FRAME\_GREEN}}:] The frame contains one
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channel of data that represents sample values from the green
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spectral band. The complete image consists of three frames:
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\code{SANE\_\-FRA\-ME\_RED}, \code{SANE\_FRAME\_GREEN}, and
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\code{SANE\_FRAME\_BLUE}. The order in which the frames are
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transmitted chosen by the backend.
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\item[\code{\defn{SANE\_FRAME\_BLUE}}:] The frame contains one channel
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of data that represents sample values from the blue spectral band.
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The complete image consists of three frames:
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\code{SANE\_\-FRA\-ME\_RED}, \code{SANE\_FRAME\_GREEN}, and
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\code{SANE\_FRAME\_BLUE}. The order in which the frames are
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transmitted chosen by the backend.
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\end{description}
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\end{quote}
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In frames of type SANE\_FRAME\_GRAY, when the bit depth is 1 there are
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only two sample values possible, 1 represents minimum intensity
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(black) and 0 represents maximum intensity (white). For all other bit
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depth and frame type combinations, a sample value of 0 represents
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minimum intensity and larger values represent increasing intensity.
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\chapter{The SANE Application Programmer Interface (API)}\label{chap:api}
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This Section defines version 1 of the SANE application
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programmer interface (API). Any SANE frontend must depend on the
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interface defined in this section only. Converseley, any SANE backend
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must implement its functionality in accordance with this
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specification. The interface as documented here is declared as a C
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callable interface in a file called \filename{sane/sane.h}. This file should
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normally be included via a C pre-processor directive of the form:
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\begin{verbatim}
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#include <sane/sane.h>
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\end{verbatim}
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\section{Version Control}
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The SANE standard is expected to evolve over time. Whenever a change
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to the SANE standard is made that may render an existing frontend or
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backend incompatible with the new standard, the major version number
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must be increased. Thus, any frontend/backend pair is compatible
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provided the major version number of the SANE standard they implement
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is the same. A frontend may implement backwards compatiblity by
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allowing major numbers that are smaller than the expected major number
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(provided the frontend really can cope with the older version). In
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contrast, a backend always provides support for one and only one
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version of the standard. If a specific application does require that
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two different versions of the same backend are accessible at the same
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time, it is possible to do so by installing the two versions under
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different names.
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SANE version control also includes a minor version number and a build
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revision. While control of these numbers remains with the implementor
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of a backend, the recommended use is as follows. The minor version is
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incremented with each official release of a backend. The build
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revision is increased with each build of a backend.
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The SANE API provides the following five macros to manage version
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numbers.
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\begin{quote}
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\begin{description}
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\item[\code{\defn{SANE\_CURRENT\_MAJOR}}:] The value of this macro is the
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number of the SANE standard that the interface implements.
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\item[\code{\defn{SANE\_VERSION\_CODE}(\var{maj},\var{min},\var{bld})}:]
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\label{sec:saneversioncode}
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This macro can be used to build a monotonically increasing version
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code. A SANE version code consists of the SANE standard major
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version number (\var{maj}), the minor version number \var{min},
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and the build revision of a backend (\var{bld}). The major and
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minor version numbers must be in the range 0\ldots255 and the
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build revision must be in the range 0\ldots65535.
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Version codes are monotonic in the sense that it is possible to
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apply relational operators (e.g., equality or less-than test)
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directly on the version code rather than individually on the three
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components of the version code.
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Note that the major version number alone determines whether a
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frontend/backend pair is compatible. The minor version and the
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build revision are used for informational and bug-fixing purposes
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only.
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\item[\code{\defn{SANE\_VERSION\_MAJOR}(\var{vc})}:] This macro returns the
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major version number component of the version code passed in
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argument \var{vc}.
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\item[\code{SANE\_VERSION\_MINOR(\var{vc})}:] This macro returns the
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minor version number component of the version code passed in
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argument \var{vc}.
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\item[\code{SANE\_VERSION\_BUILD(\var{vc})}:] This macro returns the
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build revision component of the version code passed in argument
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\var{vc}.
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\end{description}
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\end{quote}
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\section{Data Types}
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\subsection{Base Types}
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The SANE standard is based on just two SANE-specific base types: the
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SANE byte and word.
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\begin{quote}
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\code{typedef \var{some-scalar-type\/} \defn{SANE\_Byte};} \\
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\code{typedef \var{some-scalar-type\/} \defn{SANE\_Word};}
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\end{quote}
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\verb|SANE_Byte| must correspond to some scalar C type that is capable
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of holding values in the range 0 to 255. \verb|SANE_Word| must be
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capable of holding any of the following:
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\begin{itemize}
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\item the truth values \verb|SANE_FALSE| and \verb|SANE_TRUE|
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\item signed integers in the range $-2^{31}\ldots2^{31}-1$
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\item fixed point values in the range $-32768\ldots32767.9999$ with
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a resolution of $1/65536$
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\item 32 bits (for bit sets)
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\end{itemize}
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Note that the SANE standard does not define what C type
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\verb|SANE_Byte| and \verb|SANE_Word| map to. For example, on some
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platforms, the latter may map to \verb|long int| whereas on others it
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may map to \verb|int|. A portable SANE frontend or backend must
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therefore not depend on a particular mapping.
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\subsection{Boolean Type}
|
|
|
|
\code{\defn{SANE\_Bool}} is used for variables that can take one of
|
|
the two truth values \code{\defn{SANE\_FALSE}} and
|
|
\code{\defn{SANE\_TRUE}}. The former value is defined to be 0,
|
|
whereas the latter is 1.\footnote{This is different from ANSI C where
|
|
any non-zero integer value represents logical TRUE.} The C
|
|
declarations for this type are given below.
|
|
\begin{quote}
|
|
\begin{verbatim}
|
|
#define SANE_FALSE 0
|
|
#define SANE_TRUE 1
|
|
typedef SANE_Word SANE_Bool;
|
|
\end{verbatim}
|
|
\end{quote}
|
|
Note that \verb|SANE_Bool| is simply an alias of \verb|SANE_Word|. It
|
|
is therefore always legal to use the latter type in place of the
|
|
former. However, for clarity, it is recommended to use
|
|
\verb|SANE_Bool| whenever a given variable or formal argument has a
|
|
fixed interpretation as a boolean object.
|
|
|
|
\subsection{Integer Type}
|
|
|
|
\code{\defn{SANE\_Int}} is used for variables that can take integer
|
|
values in the range $-2^{32}$ to $2^{31}-1$. Its C declaration is
|
|
given below.
|
|
\begin{quote}
|
|
\begin{verbatim}
|
|
typedef SANE_Word SANE_Int;
|
|
\end{verbatim}
|
|
\end{quote}
|
|
Note that \verb|SANE_Int| is simply an alias of \verb|SANE_Word|. It
|
|
is therefore always legal to use the latter type in place of the
|
|
former. However, for clarity, it is recommended to use
|
|
\verb|SANE_Int| whenever a given variable or formal argument has a
|
|
fixed interpretation as an integer object.
|
|
|
|
|
|
\subsection{Fixed-point Type}
|
|
|
|
\code{\defn{SANE\_Fixed}} is used for variables that can take fixed
|
|
point values in the range $-32768$ to $32767.9999$ with a resolution
|
|
of $1/65535$. The C declarations relating to this type are given
|
|
below.
|
|
\begin{quote}
|
|
\begin{verbatim}
|
|
#define SANE_FIXED_SCALE_SHIFT 16
|
|
typedef SANE_Word SANE_Fixed;
|
|
\end{verbatim}
|
|
\end{quote}
|
|
The macro \code{\defn{SANE\_FIXED\_SCALE\_SHIFT}} gives the location
|
|
of the fixed binary point. This standard defines that value to be 16,
|
|
which yields a resolution of $1/65536$.
|
|
|
|
Note that \verb|SANE_Fixed| is simply an alias of \verb|SANE_Word|.
|
|
It is therefore always legal to use the latter type in place of the
|
|
former. However, for clarity, it is recommended to use
|
|
\verb|SANE_Fixed| whenever a given variable or formal argument has a
|
|
fixed interpretation as a fixed-point object.
|
|
|
|
For convenience, SANE also defines two macros that convert fixed-point
|
|
values to and from C double floating point values.
|
|
\begin{quote}
|
|
\begin{description}
|
|
|
|
\item[\code{\defn{SANE\_FIX}(\var{d})}:] Returns the largest SANE
|
|
fixed-point value that is smaller than the double value \var{d}.
|
|
No range checking is performed. If the value of \var{d} is out of
|
|
range, the result is undefined.
|
|
|
|
\item[\code{\defn{SANE\_UNFIX}(\var{w})}:] Returns the nearest
|
|
double machine number that corresponds to fixed-point value
|
|
\var{w}.
|
|
|
|
\end{description}
|
|
\end{quote}
|
|
SANE does {\em not\/} require that the following two expressions hold
|
|
true (even if the values of \var{w} and \var{d} are in range):
|
|
\begin{quote}
|
|
\begin{verbatim}
|
|
SANE_UNFIX(SANE_FIX(d)) == d
|
|
SANE_FIX(SANE_UNFIX(w)) == w
|
|
\end{verbatim}
|
|
\end{quote}
|
|
In other words, conversion between fixed and double values may be
|
|
lossy. It is therefore recommended to avoid repeated conversions
|
|
between the two representations.
|
|
|
|
|
|
\subsection{Text}
|
|
|
|
\subsubsection{Character Type}
|
|
|
|
Type \code{\defn{SANE\_Char}} represents a single text character or
|
|
symbol. At present, this type maps directly to the underlying C
|
|
\verb|char| type (typically one byte). The encoding for such
|
|
characters is currently fixed as ISO LATIN-1. Future versions of this
|
|
standard may map this type to a wider type and allow multi-byte
|
|
encodings to support internationalization. As a result of this, care
|
|
should be taken to avoid the assumption that
|
|
\verb|sizeof(SANE\_Char)==sizeof(char)|.
|
|
\begin{quote}
|
|
\begin{verbatim}
|
|
typedef char SANE_Char;
|
|
\end{verbatim}
|
|
\end{quote}
|
|
|
|
\subsubsection{String Type}
|
|
|
|
Type \code{\defn{SANE\_String}} represents a text string as a sequence
|
|
of C \verb|char| values. The end of the sequence is indicated by a
|
|
\verb|'\0'| (\defn{NUL}) character.
|
|
\begin{quote}
|
|
\begin{verbatim}
|
|
typedef SANE_Char *SANE_String;
|
|
typedef const SANE_Char *SANE_String_Const;
|
|
\end{verbatim}
|
|
\end{quote}
|
|
The type \code{\defn{SANE\_String\_Const}} is provided by SANE to
|
|
enable declaring strings whose contents is unchangable. Note that in
|
|
ANSI C, the declaration
|
|
\begin{quote}
|
|
\begin{verbatim}
|
|
const SANE_String str;
|
|
\end{verbatim}
|
|
\end{quote}
|
|
declares a string pointer that is constant (not a string pointer that
|
|
points to a constant value).
|
|
|
|
|
|
\subsection{Scanner Handle Type}
|
|
|
|
Access to a scanner is provided through an opaque type called
|
|
\code{\defn{SANE\_Handle}}. The C declaration of this type is given
|
|
below.
|
|
\begin{quote}
|
|
\begin{verbatim}
|
|
typedef void *SANE_Handle;
|
|
\end{verbatim}
|
|
\end{quote}
|
|
While this type is declared to be a void pointer, an application must
|
|
not attempt to interpret the value of a \verb|SANE_Handle|. In
|
|
particular, SANE does not require that a value of this type is a legal
|
|
pointer value.
|
|
|
|
|
|
\subsection{Status Type}
|
|
|
|
Most SANE operations return a value of type \code{\defn{SANE\_Status}}
|
|
to indicate whether the completion status of the operation. If an
|
|
operation completes successfully, \verb|SANE_STATUS_GOOD| is returned.
|
|
In case of an error, a value is returned that indicates the nature of
|
|
the problem. The complete list of available status codes is listed in
|
|
Table \ref{tab:status}. It is recommended to use function
|
|
\code{sane\_strstatus()} to convert status codes into a legible
|
|
string.
|
|
|
|
\begin{table}[htbp]
|
|
\begin{center}
|
|
\begin{tabular}{|l|r|l|}
|
|
\hline
|
|
\multicolumn{1}{|c|}{\bf Symbol} & \multicolumn{1}{c|}{\bf Code} &
|
|
\multicolumn{1}{c|}{\bf Description} \\
|
|
\hline\hline
|
|
\code{\defn{SANE\_STATUS\_GOOD}}
|
|
& 0 & Operation completed succesfully. \\
|
|
\code{\defn{SANE\_STATUS\_UNSUPPORTED}}
|
|
& 1 & Operation is not supported. \\
|
|
\code{\defn{SANE\_STATUS\_CANCELLED}}
|
|
& 2 & Operation was cancelled. \\
|
|
\code{\defn{SANE\_STATUS\_DEVICE\_BUSY}}
|
|
& 3 & Device is busy---retry later. \\
|
|
\code{\defn{SANE\_STATUS\_INVAL}}
|
|
& 4 & Data or argument is invalid. \\
|
|
\code{\defn{SANE\_STATUS\_EOF}}
|
|
& 5 & No more data available (end-of-file). \\
|
|
\code{\defn{SANE\_STATUS\_JAMMED}}
|
|
& 6 & Document feeder jammed. \\
|
|
\code{\defn{SANE\_STATUS\_NO\_DOCS}}
|
|
& 7 & Document feeder out of documents. \\
|
|
\code{\defn{SANE\_STATUS\_COVER\_OPEN}}
|
|
& 8 & Scanner cover is open. \\
|
|
\code{\defn{SANE\_STATUS\_IO\_ERROR}}
|
|
& 9 & Error during device I/O. \\
|
|
\code{\defn{SANE\_STATUS\_NO\_MEM}}
|
|
& 10 & Out of memory. \\
|
|
\code{\defn{SANE\_STATUS\_ACCESS\_DENIED}}
|
|
& 11 & Access to resource has been denied. \\
|
|
\hline
|
|
\end{tabular}
|
|
\caption{Status Codes}\label{tab:status}
|
|
\end{center}
|
|
\end{table}
|
|
|
|
|
|
\subsection{Device Descriptor Type}
|
|
|
|
Each SANE device is represented by a structure of type
|
|
\code{\defn{SANE\_Device}}. The C declaration of this type is given
|
|
below.
|
|
\begin{quote}
|
|
\begin{verbatim}
|
|
typedef struct
|
|
{
|
|
SANE_String_Const name;
|
|
SANE_String_Const vendor;
|
|
SANE_String_Const model;
|
|
SANE_String_Const type;
|
|
}
|
|
SANE_Device;
|
|
\end{verbatim}
|
|
\end{quote}
|
|
\index{device-name}
|
|
The structure provides the unique name of the scanner in member
|
|
\code{name}. It is this unique name that should be passed in a call
|
|
to \code{sane\_open()}. The format of this name is completely up to
|
|
the backend. The only constraints are that the name is unique among
|
|
all devices supported by the backend and that the name is a legal SANE
|
|
text string. To simplify presentation of unique names, their length
|
|
should not be excessive. It is {\em recommended\/} that backends keep
|
|
unique names below 32 characters in length. However, applications
|
|
{\em must\/} be able to cope with arbitrary length unique names.
|
|
|
|
The remaining members in the device structure provide additional
|
|
information on the device corresponding to the unique name.
|
|
Specifically, members \code{vendor}, \code{model}, and \code{type} are
|
|
single-line strings that give information on the vendor
|
|
(manufacturer), model, and the type of the device. For consistency's
|
|
sake, the following strings should be used when appropriate (the lists
|
|
will be expanded as need arises):
|
|
|
|
\begin{table}[htbp]
|
|
\begin{center}
|
|
\leavevmode
|
|
\hspace{\fill}
|
|
\begin{tabular}[t]{|ll|}
|
|
\hline
|
|
\multicolumn{2}{|c|}{\bf \defn{Vendor Strings}} \\
|
|
\hline\hline
|
|
\code{AGFA} & \code{Logitech} \\
|
|
\code{Artec} & \code{Microtek} \\
|
|
\code{Connectix} & \code{Minolta} \\
|
|
\code{Epson} & \code{Mustek} \\
|
|
\code{Hewlett-Packard} & \code{UMAX} \\
|
|
\code{Kodak} & \code{Noname} \\
|
|
\hline
|
|
\end{tabular}
|
|
\hspace{\fill}
|
|
\begin{tabular}[t]{|l|}
|
|
\hline
|
|
\multicolumn{1}{|c|}{\bf \defn{Type Strings}} \\
|
|
\hline\hline
|
|
\code{flatbed scanner} \\
|
|
\code{frame grabber} \\
|
|
\code{handheld scanner} \\
|
|
\code{still camera} \\
|
|
\code{video camera} \\
|
|
\code{virtual device} \\
|
|
\hline
|
|
\end{tabular}
|
|
\hspace{\fill}
|
|
\caption{Predefined Device Information Strings}
|
|
\label{tab:devinfo}
|
|
\end{center}
|
|
\end{table}
|
|
Note that vendor string \code{Noname} can be used for virtual devices
|
|
that have no physical vendor associated. Also, there are no
|
|
predefined model name strings since those are vendor specific and
|
|
therefore completely under control of the respective backends.
|
|
|
|
|
|
\subsection{Option Descriptor Type}\label{sec:odesc}
|
|
|
|
Option descriptors are at the same time the most intricate and
|
|
powerful type in the SANE standard. Options are used to control
|
|
virtually all aspects of device operation. Much of the power of the
|
|
SANE API stems from the fact that most device controls are completely
|
|
described by their respective option descriptor. Thus, a frontend can
|
|
control a scanner abstractly, without requiring knowledge as to what
|
|
the purpose of any given option is. Conversely, a scanner can
|
|
describe its controls without requiring knowledge of how the frontend
|
|
operates. The C declaration of the
|
|
\code{\defn{SANE\_Option\_Descriptor}} type is given below.
|
|
\begin{quote}
|
|
\begin{verbatim}
|
|
typedef struct
|
|
{
|
|
SANE_String_Const name;
|
|
SANE_String_Const title;
|
|
SANE_String_Const desc;
|
|
SANE_Value_Type type;
|
|
SANE_Unit unit;
|
|
SANE_Int size;
|
|
SANE_Int cap;
|
|
SANE_Constraint_Type constraint_type;
|
|
union
|
|
{
|
|
const SANE_String_Const *string_list;
|
|
const SANE_Word *word_list;
|
|
const SANE_Range *range;
|
|
}
|
|
constraint;
|
|
}
|
|
SANE_Option_Descriptor;
|
|
\end{verbatim}
|
|
\end{quote}
|
|
|
|
\subsubsection{Option Name}
|
|
|
|
Member \code{name} is a string that uniquely identifies the option.
|
|
The name must be unique for a given device (i.e., the option names
|
|
across different backends or devices need not be unique). The option
|
|
name must consist of lower-case ASCII letters (\code{a}--\code{z}),
|
|
digits (\code{0}--\code{9}), or the dash character (\code{-}) only.
|
|
The first character must be a lower-case ASCII character (i.e., not a
|
|
digit or a dash).
|
|
|
|
\subsubsection{Option Title}
|
|
|
|
Member \code{title} is a single-line string that can be used by the
|
|
frontend as a title string. This should typically be a short (one or
|
|
two-word) string that is chosen based on the function of the option.
|
|
|
|
\subsubsection{Option Description}
|
|
|
|
Member \code{desc} is a (potentially very) long string that can be
|
|
used as a help text to describe the option. It is the responsibility
|
|
of the frontend to break the string into managable-length lines.
|
|
Newline characters in this string should be interpreted as paragraph
|
|
breaks.
|
|
|
|
\subsubsection{Option Value Type}
|
|
|
|
Member \code{type} specifies the type of the option value. The
|
|
possible values for type \code{\defn{SANE\_Value\_Type}} are described
|
|
in Table \ref{tab:valuetype}.
|
|
|
|
\begin{table}[htbp]
|
|
\begin{center}
|
|
\leavevmode
|
|
\begin{tabular}{|l|l|p{0.6\textwidth}|}
|
|
\hline
|
|
\multicolumn{1}{|c|}{\bf Symbol} &
|
|
\multicolumn{1}{c|}{\bf Code} &
|
|
\multicolumn{1}{c|}{\bf Description} \\
|
|
\hline\hline
|
|
|
|
\code{\defn{SANE\_TYPE\_BOOL}} & 0 & Option value is of type
|
|
\verb|SANE_Bool|. \\
|
|
|
|
\code{\defn{SANE\_TYPE\_INT}} & 1 & Option value is of type
|
|
\verb|SANE_Int|. \\
|
|
|
|
\code{\defn{SANE\_TYPE\_FIXED}}&2 & Option value is of type
|
|
\verb|SANE_Fixed|. \\
|
|
|
|
\code{\defn{SANE\_TYPE\_STRING}}&3 & Option value is of type
|
|
\verb|SANE_String|. \\
|
|
|
|
\code{\defn{SANE\_TYPE\_BUTTON}} & 4 & An option of this type has no value.
|
|
Instead, setting an option of this type has an option-specific
|
|
side-effect. For example, a button-typed option could be used by a
|
|
backend to provide a means to select default values or to the tell an
|
|
automatic document feeder to advance to the next sheet of paper. \\
|
|
|
|
\code{\defn{SANE\_TYPE\_GROUP}} & 5 & An option of this type has no value.
|
|
This type is used to group logically related options. A group option
|
|
is in effect up to the point where another group option is encountered
|
|
(or up to the end of the option list, if there are no other group
|
|
options). For group options, only members \code{title} and
|
|
\code{type} are valid in the option descriptor. \\
|
|
|
|
\hline
|
|
\end{tabular}
|
|
\caption{Option Value Types (\code{SANE\_Value\_Type})}
|
|
\label{tab:valuetype}
|
|
\end{center}
|
|
\end{table}
|
|
|
|
\subsubsection{Option Value Unit}
|
|
|
|
Member \code{unit} specifies what the physical unit of the option
|
|
value is. The possible values for type \code{\defn{SANE\_U\-nit}} are
|
|
described in Table \ref{tab:units}. Note that the specified unit is
|
|
what the SANE backend expects. It is entirely up to a frontend as to
|
|
how these units a presented to the user. For example, SANE expresses
|
|
all lengths in millimeters. A frontend is generally expected to
|
|
provide appropriate conversion routines so that a user can express
|
|
quantities in a customary unit (e.g., inches or centimeters).
|
|
|
|
\begin{table}[htbp]
|
|
\begin{center}
|
|
\leavevmode
|
|
\begin{tabular}{|l|l|l|}
|
|
\hline
|
|
\multicolumn{1}{|c|}{\bf Symbol} &
|
|
\multicolumn{1}{|c|}{\bf Code} &
|
|
\multicolumn{1}{|c|}{\bf Description} \\
|
|
|
|
\hline\hline
|
|
|
|
\code{\defn{SANE\_UNIT\_NONE}} & 0 & Value is unit-less (e.g., page count).\\
|
|
\code{\defn{SANE\_UNIT\_PIXEL}} & 1 & Value is in number of pixels. \\
|
|
\code{\defn{SANE\_UNIT\_BIT}} & 2 & Value is in number of bits. \\
|
|
\code{\defn{SANE\_UNIT\_MM}} & 3 & Value is in millimeters. \\
|
|
\code{\defn{SANE\_UNIT\_DPI}} & 4 & Value is a resolution in dots/inch. \\
|
|
\code{\defn{SANE\_UNIT\_PERCENT}}& 5 & Value is a percentage. \\
|
|
\code{\defn{SANE\_UNIT\_MICROSECOND}}& 6 & Value is time in $\mu$-seconds. \\
|
|
|
|
\hline
|
|
\end{tabular}
|
|
\caption{Physical Units (\code{SANE\_Unit})}
|
|
\label{tab:units}
|
|
\end{center}
|
|
\end{table}
|
|
|
|
\subsubsection{Option Value Size}\label{sec:valuesize}
|
|
|
|
Member \code{size} specifies the size of the option value (in bytes).
|
|
This member has a slightly different interpretation depending on the
|
|
type of the option value:
|
|
\begin{quote}
|
|
\begin{description}
|
|
\item[\code{SANE\_TYPE\_STRING}:] The size is the maximum size of
|
|
the string. For the purpose of string size calcuations, the
|
|
terminating \code{NUL} character is considered to be part of the
|
|
string. Note that the terminating \code{NUL} character must
|
|
always be present in string option values.
|
|
\item[\code{SANE\_TYPE\_INT}, \code{SANE\_TYPE\_FIXED}:] The size
|
|
must be a positive integer multiple of the size of a
|
|
\verb|SANE_Word|. The option value is a vector of length
|
|
\[ \code{size}/\code{sizeof(SANE\_Word)}. \]
|
|
\item[\code{SANE\_TYPE\_BOOL}:] The size must be set to
|
|
\code{sizeof(SANE\_Word)}.
|
|
\item[\code{SANE\_TYPE\_BUTTON}, \code{SANE\_TYPE\_GROUP}:] The
|
|
option size is ignored.
|
|
\end{description}
|
|
\end{quote}
|
|
|
|
\subsubsection{Option Capabilities}
|
|
|
|
Member \code{cap} describes what capabilities the option posseses.
|
|
This is a bitset that is formed as the inclusive logical OR of the
|
|
capabilities described in Table \ref{tab:capabilities}. The SANE API
|
|
provides the following to macros to test certain features of a given
|
|
capability bitset:
|
|
\begin{quote}
|
|
\begin{description}
|
|
|
|
\item[\code{\defn{SANE\_OPTION\_IS\_ACTIVE}(\var{cap})}:] This macro
|
|
returns \code{SANE\_TRUE} if and only if the option with the
|
|
capability set \var{cap} is currently active.
|
|
|
|
\item[\code{\defn{SANE\_OPTION\_IS\_SETTABLE}(\var{cap})}:] This
|
|
macro returns \code{SANE\_TRUE} if and only if the option with the
|
|
capability set \var{cap} is software settable.
|
|
\end{description}
|
|
\end{quote}
|
|
|
|
\begin{table}[htbp]
|
|
\begin{center}
|
|
\leavevmode
|
|
\begin{tabular}{|l|r|p{0.59\textwidth}|}
|
|
\hline
|
|
\multicolumn{1}{|c|}{\bf Symbol} &
|
|
\multicolumn{1}{c|}{\bf Code} &
|
|
\multicolumn{1}{c|}{\bf Description} \\
|
|
\hline\hline
|
|
|
|
\code{\defn{SANE\_CAP\_SOFT\_SELECT}} & 1 & The option
|
|
value can be set by a call to \code{sane\_con\-trol\_opt\-ion()}.\\
|
|
|
|
\code{\defn{SANE\_CAP\_HARD\_SELECT}} & 2 & The option value can be set by
|
|
user-intervention (e.g., by flipping a switch). The user-interface
|
|
should prompt the user to execute the appropriate action to set such
|
|
an option. This capability is mutually exclusive with
|
|
SANE\_CAP\_SOFT\_SELECT (either one of them can be set, but not both
|
|
simultaneously). \\
|
|
|
|
\code{\defn{SANE\_CAP\_SOFT\_DETECT}} & 4 & The option
|
|
value can be detected by software. If
|
|
\code{SANE\_\-CAP\_\-SO\-FT\_SEL\-ECT} is set, this capability {\em must\/}
|
|
be set. If \code{SANE\_CAP\_HARD\_SELECT} is set, this capability
|
|
may or may not be set. If this capability is set but neither
|
|
\code{SANE\_CAP\_SO\-FT\_SEL\-ECT} nor \code{SANE\_CAP\_HA\-RD\_SEL\-ECT}
|
|
are, then there is no way to control the option. That is, the
|
|
option provides read-out of the current value only. \\
|
|
|
|
\code{\defn{SANE\_CAP\_EMULATED}} & 8 & If set, this capability indicates
|
|
that an option is not directly supported by the device and is
|
|
instead emulated in the backend. A sophisticated frontend may
|
|
elect to use its own (presumably better) emulation in lieu of an emulated
|
|
option. \\
|
|
|
|
\code{\defn{SANE\_CAP\_AUTOMATIC}} & 16 & If set, this capability indicates
|
|
that the backend (or the device) is capable to picking a reasonable
|
|
option value automatically. For such options, it is possible to
|
|
select automatic operation by calling \code{sane\_control\_option()}
|
|
with an action value of \code{SANE\_ACTION\_SET\_AUTO}. \\
|
|
|
|
\code{\defn{SANE\_CAP\_INACTIVE}} & 32 & If set, this capability indicates
|
|
that the option is not currently active (e.g., because it's
|
|
meaningful only if another option is set to some other value). \\
|
|
|
|
\code{\defn{SANE\_CAP\_ADVANCED}} & 64 &
|
|
If set, this capability indicates that the option should be
|
|
considered an ``advanced user option.'' A frontend typically
|
|
displays such options in a less conspicuous way than regular options
|
|
(e.g., a command line interface may list such options last or a
|
|
graphical interface may make them available in a seperate ``advanced
|
|
settings'' dialog).
|
|
\\
|
|
|
|
\hline
|
|
\end{tabular}
|
|
\caption{Option Capabilities}
|
|
\label{tab:capabilities}
|
|
\end{center}
|
|
\end{table}
|
|
|
|
\subsubsection{Option Value Constraints}
|
|
|
|
It is often useful to constrain the values that an option can take.
|
|
For example, constraints can be used by a frontend to determine how to
|
|
represent a given option. Member \code{constraint\_type} indicates
|
|
what constraint is in effect for the option. The constrained values
|
|
that are allowed for the option are described by one of the union
|
|
members of member \code{constraint}. The possible values of type
|
|
\code{\defn{SANE\_Constraint\_Type}} and the interpretation of the
|
|
\code{constraint} union is described in Table~\ref{tab:constraints}.
|
|
|
|
\begin{table}[htbp]
|
|
\begin{center}
|
|
\leavevmode
|
|
\begin{tabular}{|l|r|p{0.5\textwidth}|}
|
|
\hline
|
|
\multicolumn{1}{|c|}{\bf Symbol} &
|
|
\multicolumn{1}{|c|}{\bf Code} &
|
|
\multicolumn{1}{|c|}{\bf Description} \\
|
|
|
|
\hline\hline
|
|
|
|
\code{\defn{SANE\_CONSTRAINT\_NONE}} & 0 & The value is unconstrained.
|
|
The option can take any of the values possible for the option's
|
|
type. \\
|
|
|
|
\code{\defn{SANE\_CONSTRAINT\_RANGE}} & 1 & This constraint is
|
|
applicable to integer and fixed-point valued options only. It
|
|
constrains the option value to a possibly quantized range of
|
|
numbers. Option descriptor member \code{constraint.range} points to
|
|
a range of the type \code{\defn{SANE\_Range}}. This type is illustrated
|
|
below:
|
|
\begin{quote}
|
|
\begin{verbatim}
|
|
typedef struct
|
|
{
|
|
SANE_Word min;
|
|
SANE_Word max;
|
|
SANE_Word quant;
|
|
}
|
|
SANE_Range;
|
|
\end{verbatim}
|
|
\end{quote}
|
|
All three members in this structure are interpreted according to the
|
|
option value type (\verb|SANE_TYPE_INT| or \verb|SANE_TYPE_FIXED|).
|
|
Members \code{min} and \code{max} specify the minimum and maximum
|
|
values, respectively. If member \code{quant} is non-zero, it
|
|
specifies the quantization value. If $l$ is the minimum value, $u$
|
|
the maximum value and $q$ the (non-zero) quantization of a range,
|
|
then the legal values are $v=k\cdot q+l$ for all non-negative
|
|
integer values of $k$ such that $v<=u$. \\
|
|
|
|
\code{\defn{SANE\_CONSTRAINT\_WORD\_LIST}} & 2 & This constraint is applicable
|
|
to integer and fixed-point valued options only. It constrains the
|
|
option value to a list of numeric values. Option descriptor member
|
|
\code{constraint.word\_list} points to a list of words that
|
|
enumerates the legal values. The first element in that list is an
|
|
integer (\verb|SANE_Int|) that specifies the length of the list (not
|
|
counting the length itself). The remaining elements in the list are
|
|
interpreted according to the type of the option value
|
|
(\verb|SANE_TYPE_INT| or \verb|SANE_TYPE_FIXED|). \\
|
|
|
|
\code{\defn{SANE\_CONSTRAINT\_STRING\_LIST}} & 3 & This constraint is
|
|
applicable to string-valued options only. It constrains the option
|
|
value to a list of strings. The option descriptor member
|
|
\code{con\-strai\-nt.str\-ing\_list} points to a \code{NULL} terminated
|
|
list of strings that enumerate the legal values for the option
|
|
value.
|
|
\\\hline
|
|
\end{tabular}
|
|
\caption{Option Value Constraints}
|
|
\label{tab:constraints}
|
|
\end{center}
|
|
\end{table}
|
|
|
|
|
|
\section{Operations}
|
|
|
|
\subsection{\code{sane\_init}}
|
|
|
|
This function must be called before any other SANE function can be
|
|
called. The behavior of a SANE backend is undefined if this function
|
|
is not called first. The version code of the backend is returned in
|
|
the value pointed to by \code{version\_code}. If that pointer is
|
|
\code{NULL}, no version code is returned.
|
|
Argument \code{authorize} is either a pointer to a function that is
|
|
invoked when the backend requires authentication for a specific
|
|
resource or \code{NULL} if the frontend does not support
|
|
authentication.
|
|
\begin{quote}\index{sane\_init}
|
|
\begin{verbatim}
|
|
SANE_Status sane_init (SANE_Int * version_code,
|
|
SANE_Authorization_Callback authorize);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
|
|
The authorization function may be called by a backend in response to
|
|
any of the following calls:
|
|
\begin{quote}
|
|
\code{sane\_open}, \code{sane\_control\_option}, \code{sane\_start}
|
|
\end{quote}
|
|
If a backend was initialized without authorization function, then
|
|
authorization requests that cannot be handled by the backend itself
|
|
will fail automatically and the user may be prevented from accessing
|
|
protected resources. Backends are encouraged to implement means of
|
|
authentication that do not require user assistance. E.g., on a
|
|
multi-user system that authenticates users through a login process a
|
|
backend could automatically lookup the apporpriate password based on
|
|
resource- and user-name.
|
|
|
|
The authentication function type has the following declaration:
|
|
\begin{quote}\index{SANE\_Authorization\_Callback}
|
|
\index{domain}\index{username}\index{password}
|
|
\begin{verbatim}
|
|
#define SANE_MAX_USERNAME_LEN 256
|
|
#define SANE_MAX_PASSWORD_LEN 256
|
|
|
|
typedef void (*SANE_Authorization_Callback)
|
|
(SANE_String_Const resource,
|
|
SANE_Char username[SANE_MAX_USERNAME_LEN],
|
|
SANE_Char password[SANE_MAX_PASSWORD_LEN]);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
Three arguments are passed to the authorization function:
|
|
\code{resource} is a string specifying the name of the resource that
|
|
requires authorization. A frontend should use this string to build a
|
|
user-prompt requesting a username and a password. The \code{username}
|
|
and \code{password} arguments are (pointers to) an array of
|
|
\code{SANE\_MAX\_USERNAME\_LEN} and \code{SANE\_MAX\_PASSWORD\_LEN}
|
|
characters, respectively. The authorization call should place the
|
|
entered username and password in these arrays. The returned strings
|
|
{\em must\/} be ASCII-NUL terminated.
|
|
|
|
\subsection{\code{sane\_exit}}
|
|
|
|
This function must be called to terminate use of a backend. The
|
|
function will first close all device handles that still might be open
|
|
(it is recommended to close device handles explicitly through a call
|
|
to \code{sane\_clo\-se()}, but backends are required to release all
|
|
resources upon a call to this function). After this function returns,
|
|
no function other than \code{sane\_init()} may be called (regardless
|
|
of the status value returned by \code{sane\_exit()}. Neglecting to
|
|
call this function may result in some resources not being released
|
|
properly.
|
|
\begin{quote}\index{sane\_exit}
|
|
\begin{verbatim}
|
|
void sane_exit (void);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
|
|
|
|
\subsection{\code{sane\_get\_devices}}
|
|
|
|
This function can be used to query the list of devices that are
|
|
available. If the function executes successfully, it stores a pointer
|
|
to a \code{NULL} terminated array of pointers to \verb|SANE_Device|
|
|
structures in \code{*device\_list}. The returned list is guaranteed
|
|
to remain unchanged and valid until (a) another call to this function
|
|
is performed or (b) a call to \code{sane\_exit()} is performed. This
|
|
function can be called repeatedly to detect when new devices become
|
|
available. If argument \code{local\_only} is true, only local devices
|
|
are returned (devices directly attached to the machine that SANE is
|
|
running on). If it is false, the device list includes all remote
|
|
devices that are accessible to the SANE library.
|
|
\begin{quote}\index{sane\_get\_devices}
|
|
\begin{verbatim}
|
|
SANE_Status sane_get_devices (const SANE_Device *** device_list,
|
|
SANE_Bool local_only);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
|
|
This function may fail with \code{SANE\_STATUS\_NO\_MEM} if an
|
|
insufficient amount of memory is available.
|
|
|
|
\begin{quote}
|
|
\begin{center}
|
|
{\bf Backend Implementation Note}
|
|
\end{center}
|
|
SANE does not require that this function is called before a
|
|
\code{sane\_open()} call is performed. A device name may be
|
|
specified explicitly by a user which would make it unnecessary and
|
|
undesirable to call this function first.
|
|
\end{quote}
|
|
|
|
|
|
\subsection{\code{sane\_open}}
|
|
|
|
This function is used to establish a connection to a particular
|
|
device. The name of the device to be opened is passed in argument
|
|
\code{name}. If the call completes successfully, a handle for the
|
|
device is returned in \code{*h}. As a special case, specifying a
|
|
zero-length string as the device requests opening the first available
|
|
device (if there is such a device).
|
|
\begin{quote}\index{sane\_open}
|
|
\begin{verbatim}
|
|
SANE_Status sane_open (SANE_String_Const name, SANE_Handle * h);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
|
|
This function may fail with one of the following status codes.
|
|
\begin{quote}
|
|
\begin{description}
|
|
\item[\code{SANE\_STATUS\_DEVICE\_BUSY}:] The device is currently
|
|
busy (in use by somebody else).
|
|
\item[\code{SANE\_STATUS\_INVAL}:] The device name is not valid.
|
|
\item[\code{SANE\_STATUS\_IO\_ERROR}:] An error occured while
|
|
communicating with the device.
|
|
\item[\code{SANE\_STATUS\_NO\_MEM}:] An insufficent amount of memory
|
|
is available.
|
|
\item[\code{SANE\_STATUS\_ACCESS\_DENIED}:] Access to the device has
|
|
been denied due to insufficient or invalid authentication.
|
|
\end{description}
|
|
\end{quote}
|
|
|
|
|
|
\subsection{\code{sane\_close}}
|
|
|
|
This function terminates the association between the device handle
|
|
passed in argument \code{h} and the device it represents. If the
|
|
device is presently active, a call to \code{sane\_cancel()} is
|
|
performed first. After this function returns, handle \code{h} must
|
|
not be used anymore.
|
|
|
|
\begin{quote}\index{sane\_close}
|
|
\begin{verbatim}
|
|
void sane_close (SANE_Handle h);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
|
|
\subsection{\code{sane\_get\_option\_descriptor}}
|
|
|
|
This function is used to access option descriptors. The function
|
|
returns the option descriptor for option number \code{n} of the device
|
|
represented by handle \code{h}. Option number 0 is guaranteed to be a
|
|
valid option. Its value is an integer that specifies the number of
|
|
options that are available for device handle \code{h} (the count
|
|
includes option 0). If $n$ is not a valid option index, the function
|
|
returns \code{NULL}. The returned option descriptor is guaranteed to
|
|
remain valid (and at the returned address) until the device is closed.
|
|
|
|
\begin{quote}\index{sane\_get\_option\_descriptor}
|
|
\begin{verbatim}
|
|
const SANE_Option_Descriptor *
|
|
sane_get_option_descriptor (SANE_Handle h, SANE_Int n);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
|
|
\subsection{\code{sane\_control\_option}}\label{sec:control}
|
|
|
|
This function is used to set or inquire the current value of option
|
|
number \code{n} of the device represented by handle \code{h}. The
|
|
manner in which the option is controlled is specified by parameter
|
|
\code{a}. The possible values of this parameter are described in more
|
|
detail below. The value of the option is passed through argument
|
|
\code{v}. It is a pointer to the memory that holds the option value.
|
|
The memory area pointed to by \code{v} must be big enough to hold the
|
|
entire option value (determined by member \code{size} in the
|
|
corresponding option descriptor). The only exception to this rule is
|
|
that when setting the value of a string option, the string pointed to
|
|
by argument \code{v} may be shorter since the backend will stop
|
|
reading the option value upon encountering the first \code{NUL}
|
|
terminator in the string. If argument \code{i} is not \code{NULL},
|
|
the value of \code{*i} will be set to provide details on how well the
|
|
request has been met. The meaning of this argument is described in
|
|
more detail below.
|
|
\begin{quote}\index{sane\_control\_option}
|
|
\begin{verbatim}
|
|
SANE_Status sane_control_option (SANE_Handle h, SANE_Int n,
|
|
SANE_Action a, void *v,
|
|
SANE_Int * i);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
|
|
The way the option is affected by a call to this function is
|
|
controlled by parameter \code{a} which is a value of type
|
|
\code{\defn{SANE\_Action}}. The possible values and their meaning is
|
|
described in Table~\ref{tab:actions}.
|
|
|
|
\begin{table}[h]
|
|
\begin{center}
|
|
\leavevmode
|
|
\begin{tabular}{|l|r|p{0.5\textwidth}|}
|
|
\hline
|
|
\multicolumn{1}{|c|}{\bf Symbol} &
|
|
\multicolumn{1}{|c|}{\bf Code} &
|
|
\multicolumn{1}{|c|}{\bf Description} \\
|
|
|
|
\hline\hline
|
|
|
|
\code{\defn{SANE\_ACTION\_GET\_VALUE}} & 0 & Get current option value. \\
|
|
|
|
\code{\defn{SANE\_ACTION\_SET\_VALUE}} & 1 & Set option value. The
|
|
option value passed through argument \code{v} may be modified by the
|
|
backend if the value cannot be set exactly. \\
|
|
|
|
\code{\defn{SANE\_ACTION\_SET\_AUTO}} & 2 & Turn on automatic mode. Backend
|
|
or device will automatically select an appropriate value. This mode
|
|
remains effective until overridden by an explicit set value request.
|
|
The value of parameter \code{v} is completely ignored in this case and
|
|
may be \code{NULL}. \\
|
|
|
|
\hline
|
|
\end{tabular}
|
|
\caption{Action Values (\code{SANE\_Action})}
|
|
\label{tab:actions}
|
|
\end{center}
|
|
\end{table}
|
|
|
|
After setting a value via an action value of
|
|
\verb|SANE_ACTION_SET_VALUE|, additional information on how well the
|
|
request has been met is returned in \code{*i} (if \code{i} is
|
|
non-\code{NULL}). The returned value is a bitset that may contain any
|
|
combination of the values described in Table~\ref{tab:info}.
|
|
\begin{table}[htbp]
|
|
\begin{center}
|
|
\leavevmode
|
|
\begin{tabular}{|l|r|p{0.5\textwidth}|}
|
|
\hline
|
|
\multicolumn{1}{|c|}{\bf Symbol} &
|
|
\multicolumn{1}{|c|}{\bf Code} &
|
|
\multicolumn{1}{|c|}{\bf Description} \\
|
|
|
|
\hline\hline
|
|
|
|
\code{\defn{SANE\_INFO\_INEXACT}} & 1 & This value is returned when
|
|
setting an option value resulted in a value being selected that does
|
|
not exactly match the requested value. For example, if a scanner
|
|
can adjust the resolution in increments of 30dpi only, setting the
|
|
resolution to 307dpi may result in an actual setting of 300dpi.
|
|
When this happens, the bitset returned in \code{*i} has this member
|
|
set. In addition, the option value is modified to reflect the
|
|
actual (rounded) value that was used by the backend. Note that
|
|
inexact values are admissible for strings as well. A backend may
|
|
choose to ``round'' a string to the closest matching legal string
|
|
for a constrained string value. \\
|
|
|
|
\code{\defn{SANE\_INFO\_RELOAD\_OPTIONS}} & 2 & The setting of an
|
|
option may affect the value or availability of one or more {\em
|
|
other\/} options. When this happens, the SANE backend sets this
|
|
member in \code{*i} to indicate that the application should reload
|
|
all options. This member may be set if and only if at least one
|
|
option changed. \\
|
|
|
|
\code{\defn{SANE\_INFO\_RELOAD\_PARAMS}} & 4 & The setting of an option may
|
|
affect the parameter values (see \code{sane\_get\_parameters()}).
|
|
If setting an option affects the parameter values, this member will
|
|
be set in \code{*i}. Note that this member may be set even if the
|
|
parameters did not actually change. However, it is guaranteed that
|
|
the parameters never change without this member being set. \\
|
|
|
|
\hline
|
|
\end{tabular}
|
|
\caption{Additional Information Returned When Setting an Option}
|
|
\label{tab:info}
|
|
\end{center}
|
|
\end{table}
|
|
|
|
This function may fail with one of the following status codes.
|
|
\begin{quote}
|
|
\begin{description}
|
|
\item[\code{SANE\_STATUS\_UNSUPPORTED}:] The operation is not
|
|
supported for the specified handle and option number.
|
|
\item[\code{SANE\_STATUS\_INVAL}:] The option value is not valid.
|
|
\item[\code{SANE\_STATUS\_IO\_ERROR}:] An error occured while
|
|
communicating with the device.
|
|
\item[\code{SANE\_STATUS\_NO\_MEM}:] An insufficent amount of memory
|
|
is available.
|
|
\item[\code{SANE\_STATUS\_ACCESS\_DENIED}:] Access to the option has
|
|
been denied due to insufficient or invalid authentication.
|
|
\end{description}
|
|
\end{quote}
|
|
|
|
|
|
|
|
\subsection{\code{sane\_get\_parameters}}
|
|
|
|
This function is used to obtain the current scan parameters. The
|
|
returned parameters are guaranteed to be accurate between the time a
|
|
scan has been started (\code{sane\_start()} has been called) and the
|
|
completion of that request. Outside of that window, the returned
|
|
values are best-effort estimates of what the parameters will be when
|
|
\code{sane\_start()} gets invoked. Calling this function before a
|
|
scan has actually started allows, for example, to get an estimate of
|
|
how big the scanned image will be. The parameters passed to this
|
|
function are the handle \code{h} of the device for which the
|
|
parameters should be obtained and a pointer \code{p} to a parameter
|
|
structure. The parameter structure is described in more detail below.
|
|
|
|
\begin{quote}\index{sane\_get\_parameters}
|
|
\begin{verbatim}
|
|
SANE_Status sane_get_parameters (SANE_Handle h,
|
|
SANE_Parameters * p);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
|
|
The scan parameters are returned in a structure of type
|
|
\code{\defn{SANE\_Parameters}}. The C declaration of this structure
|
|
is given below.
|
|
\begin{quote}
|
|
\begin{verbatim}
|
|
typedef struct
|
|
{
|
|
SANE_Frame format;
|
|
SANE_Bool last_frame;
|
|
SANE_Int lines;
|
|
SANE_Int depth;
|
|
SANE_Int pixels_per_line;
|
|
SANE_Int bytes_per_line;
|
|
}
|
|
SANE_Parameters;
|
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\end{verbatim}
|
|
\end{quote}
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|
|
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Member \code{format} specifies the format of the next frame to be
|
|
returned. The possible values for type \code{\defn{SANE\_Frame}} are
|
|
described in Table~\ref{tab:frameformat}. The meaning of these
|
|
values is described in more detail in Section~\ref{sec:imageformat}.
|
|
\begin{table}[htbp]
|
|
\begin{center}
|
|
\leavevmode
|
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\begin{tabular}{|l|r|l|}
|
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\hline
|
|
\multicolumn{1}{|c|}{\bf Symbol} &
|
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\multicolumn{1}{|c|}{\bf Code} &
|
|
\multicolumn{1}{|c|}{\bf Description} \\
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|
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\hline\hline
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|
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\code{\defn{SANE\_FRAME\_GRAY}} & 0 & Band covering human visual range. \\
|
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\code{\defn{SANE\_FRAME\_RGB}} & 1 & Pixel-interleaved red/green/blue bands. \\
|
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\code{\defn{SANE\_FRAME\_RED}} & 2 & Red band of a red/green/blue image. \\
|
|
\code{\defn{SANE\_FRAME\_GREEN}} & 3 & Green band of a red/green/blue image. \\
|
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\code{\defn{SANE\_FRAME\_BLUE}} & 4 & Blue band of a red/green/blue image. \\
|
|
|
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\hline
|
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\end{tabular}
|
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\caption{Frame Format (\code{SANE\_Frame})}
|
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\label{tab:frameformat}
|
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\end{center}
|
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\end{table}
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|
|
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Member \code{last\_frame} is set to \code{SANE\_TRUE} if and only if
|
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the frame that is currently being acquired (or the frame that will be
|
|
acquired next if there is no current frame) is the last frame of a
|
|
multi frame image (e.g., the current frame is the blue component of a
|
|
red, green, blue image).
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|
|
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Member \code{lines} specifies how many scan lines the frame is
|
|
comprised of. If this value is -1, the number of lines is not known a
|
|
priori and the frontend should call \code{sane\_read()} until it
|
|
returns a status of \code{SANE\_STATUS\_EOF}.
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|
|
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Member \code{bytes\_per\_line} specifies the number of bytes that
|
|
comprise one scan line.
|
|
|
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Member \code{depth} specifies the number of bits per sample.
|
|
|
|
Member \code{pixels\_per\_line} specifies the number of pixels that
|
|
comprise one scan line.
|
|
|
|
Assume $B$ is the number of channels in the frame, then the bit depth
|
|
$d$ (as given by member \code{depth}) and the number of pixels per
|
|
line $n$ (as given by this member \code{pixels\_per\_line}) are
|
|
related to $c$, the number of bytes per line (as given by member
|
|
\code{bytes\_per\_line}) as follows:
|
|
\[
|
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c >= \left\{
|
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\begin{array}{ll}
|
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\lceil B\cdot n / 8\rceil & \mbox{if $d=1$}\\
|
|
B\cdot n \cdot \lceil (d + 7)/8 \rceil & \mbox{if $d>1$}
|
|
\end{array}
|
|
\right.
|
|
\]
|
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Note that the number of bytes per line can be larger than the minimum
|
|
value imposed by the right side of this equation. A frontend must be
|
|
able to properly cope with such ``padded'' image formats.
|
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|
|
|
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\subsection{\code{sane\_start}}
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|
|
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This function initiates aquisition of an image from the device
|
|
represented by handle \code{h}.
|
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\begin{quote}\index{sane\_start}
|
|
\begin{verbatim}
|
|
SANE_Status sane_start (SANE_Handle h);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
This function may fail with one of the following status codes.
|
|
\begin{quote}
|
|
\begin{description}
|
|
\item[\code{SANE\_STATUS\_CANCELLED}:] The operation was cancelled through
|
|
a call to \code{sane\_cancel}.
|
|
\item[\code{SANE\_STATUS\_DEVICE\_BUSY}:] The device is busy. The
|
|
operation should be retried later.
|
|
\item[\code{SANE\_STATUS\_JAMMED}:] The document feeder is jammed.
|
|
\item[\code{SANE\_STATUS\_NO\_DOCS}:] The document feeder is out of
|
|
documents.
|
|
\item[\code{SANE\_STATUS\_COVER\_OPEN}:] The scanner cover is open.
|
|
\item[\code{SANE\_STATUS\_IO\_ERROR}:] An error occurred while communicating
|
|
with the device.
|
|
\item[\code{SANE\_STATUS\_NO\_MEM}:] An insufficent amount of memory
|
|
is available.
|
|
\end{description}
|
|
\end{quote}
|
|
|
|
|
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\subsection{\code{sane\_read}}
|
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|
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This function is used to read image data from the device represented
|
|
by handle \code{h}. Argument \code{buf} is a pointer to a memory area
|
|
that is at least \code{maxlen} bytes long. The number of bytes
|
|
returned is stored in \code{*len}. A backend must set this to zero
|
|
when the call fails (i.e., when a status other than
|
|
\code{SANE\_STA\-TUS\_GOOD} is returned). When the call succeeds, the
|
|
number of bytes returned can be anywhere in the range from 0 to
|
|
\code{maxlen} bytes.
|
|
\begin{quote}\index{sane\_read}
|
|
\begin{verbatim}
|
|
SANE_Status sane_read (SANE_Handle h, SANE_Byte * buf,
|
|
SANE_Int maxlen, SANE_Int * len);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
If this function is called when no data is available, one of two
|
|
things may happen, depending on the I/O mode that is in effect for
|
|
handle \code{h}.
|
|
\begin{enumerate}
|
|
\item If the device is in blocking I/O mode (the default mode), the
|
|
call blocks until at least one data byte is available (or until some
|
|
error occurs).
|
|
|
|
\item If the device is in non-blocking I/O mode, the call returns
|
|
immediately with status \code{SANE\_STA\-TUS\_GOOD} and with
|
|
\code{*len} set to zero.
|
|
\end{enumerate}
|
|
The I/O mode of handle \code{h} can be set via a call to
|
|
\code{sane\_set\_io\_mode()}.
|
|
|
|
This function may fail with one of the following status codes.
|
|
\begin{quote}
|
|
\begin{description}
|
|
\item[\code{SANE\_STATUS\_CANCELLED}:] The operation was cancelled through
|
|
a call to \code{sane\_cancel}.
|
|
\item[\code{SANE\_STATUS\_EOF}:] No more data is available for the
|
|
current frame.
|
|
\item[\code{SANE\_STATUS\_JAMMED}:] The document feeder is jammed.
|
|
\item[\code{SANE\_STATUS\_NO\_DOCS}:] The document feeder is out of
|
|
documents.
|
|
\item[\code{SANE\_STATUS\_COVER\_OPEN}:] The scanner cover is open.
|
|
\item[\code{SANE\_STATUS\_IO\_ERROR}:] An error occurred while communicating
|
|
with the device.
|
|
\item[\code{SANE\_STATUS\_NO\_MEM}:] An insufficent amount of memory
|
|
is available.
|
|
\item[\code{SANE\_STATUS\_ACCESS\_DENIED}:] Access to the device has
|
|
been denied due to insufficient or invalid authentication.
|
|
\end{description}
|
|
\end{quote}
|
|
|
|
|
|
\subsection{\code{sane\_cancel}}
|
|
|
|
This function is used to immediately or as quickly as possible cancel
|
|
the currently pending operation of the device represented by handle
|
|
\code{h}.
|
|
\begin{quote}\index{sane\_cancel}
|
|
\begin{verbatim}
|
|
void sane_cancel (SANE_Handle h);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
This function can be called at any time (as long as handle \code{h} is
|
|
a valid handle) but usually affects long-running operations only (such
|
|
as image is acquisition). It is safe to call this function
|
|
asynchronously (e.g., from within a signal handler). It is important
|
|
to note that completion of this operaton does {\em not\/} imply that
|
|
the currently pending operation has been cancelled. It only
|
|
guarantees that cancellation has been {\em initiated}. Cancellation
|
|
completes only when the cancelled call returns (typically with a
|
|
status value of \code{SANE\_STATUS\_CANCELLED}). Since the SANE API
|
|
does not require any other operations to be re-entrant, this implies
|
|
that a frontend must {\em not\/} call any other operation until the
|
|
cancelled operation has returned.
|
|
|
|
|
|
\subsection{\code{sane\_set\_io\_mode}}
|
|
|
|
This function is used to set the I/O mode of handle \code{h}. The I/O
|
|
mode can be either blocking or non-blocking. If argument \code{m} is
|
|
\code{SANE\_TRUE}, the mode is set to non-blocking mode, otherwise
|
|
it's set to blocking mode.
|
|
\begin{quote}\index{sane\_set\_io\_mode}
|
|
\begin{verbatim}
|
|
SANE_Status sane_set_io_mode (SANE_Handle h, SANE_Bool m);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
By default, newly opened handles operate in blocking mode. A backend
|
|
may elect not to support non-blocking I/O mode. In such a case the
|
|
status value \code{SANE\_STATUS\_UNSUPPORTED} is returned. Blocking
|
|
I/O must be supported by all backends, so calling this function with
|
|
argument \code{m} set to \code{SANE\_FALSE} is guaranteed to complete
|
|
successfully.
|
|
|
|
This function may fail with one of the following status codes:
|
|
\begin{quote}
|
|
\begin{description}
|
|
\item[\code{SANE\_STATUS\_INVAL}:] No image acquisition is pending.
|
|
\item[\code{SANE\_STATUS\_UNSUPPORTED}:] The backend does not support
|
|
this operation.
|
|
\end{description}
|
|
\end{quote}
|
|
|
|
|
|
\subsection{\code{sane\_get\_select\_fd}}
|
|
|
|
This function is used to obtain a (platform-specific) file-descriptor
|
|
for handle \code{h} that is readable if and only if image data is
|
|
available (i.e., when a call to \code{sane\_read()} will return at
|
|
least one byte of data). If the call completes successfully, the
|
|
select file-descriptor is returned in \code{*fd}.
|
|
\begin{quote}\index{sane\_get\_select\_fd}
|
|
\begin{verbatim}
|
|
SANE_Status sane_get_select_fd (SANE_Handle h, SANE_Int *fd);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
This function can be called only after a call to \code{sane\_start()}
|
|
has been performed and the returned file-descriptor is guaranteed to
|
|
remain valid for the duration of the current image acquisition (i.e.,
|
|
until \code{sane\_cancel()} or \code{sane\_start()} get called again
|
|
or until \code{sane\_read()} returns with status
|
|
\code{SANE\_STA\-TUS\_EOF}). Indeed, a backend must guarantee to
|
|
close the returned select file descriptor at the point when the next
|
|
\code{sane\_read()} call would return \code{SANE\_STA\-TUS\_EOF}.
|
|
This is necessary to ensure the application can detect when this
|
|
condition occurs without actually having to call \code{sane\_read()}.
|
|
|
|
A backend may elect not to support this operation. In such a case,
|
|
the function returns with status code
|
|
\code{SANE\_STATUS\_UNSUPPORTED}.
|
|
|
|
Note that the only operation supported by the returned file-descriptor
|
|
is a host operating-system dependent test whether the file-descriptor
|
|
is readable (e.g., this test can be implemented using \code{select()}
|
|
or \code{poll()} under UNIX). If any other operation is performed on
|
|
the file descriptor, the behavior of the backend becomes
|
|
unpredictable. Once the file-descriptor signals ``readable'' status,
|
|
it will remain in that state until a call to \code{sane\_read()} is
|
|
performed. Since many input devices are very slow, support for this
|
|
operation is strongly encouraged as it permits an application to do
|
|
other work while image acquisition is in progress.
|
|
|
|
This function may fail with one of the following status codes:
|
|
\begin{quote}
|
|
\begin{description}
|
|
\item[\code{SANE\_STATUS\_INVAL}:] No image acquisition is pending.
|
|
\item[\code{SANE\_STATUS\_UNSUPPORTED}:] The backend does not support
|
|
this operation.
|
|
\end{description}
|
|
\end{quote}
|
|
|
|
|
|
\subsection{\code{sane\_strstatus}}
|
|
|
|
This function can be used to translate a SANE status code into a
|
|
printable string. The returned string is a single line of text that
|
|
forms a complete sentence, but without the trailing period
|
|
(full-stop). The function is guaranteed to never return \code{NULL}.
|
|
The returned pointer is valid at least until the next call to this
|
|
function is performed.
|
|
\begin{quote}\index{sane\_strstatus}
|
|
\begin{verbatim}
|
|
const SANE_String_Const sane_strstatus (SANE_Status status);
|
|
\end{verbatim}
|
|
\end{quote}
|
|
|
|
\section{Code Flow}\index{code flow}
|
|
|
|
The code flow for the SANE API is illustrated in
|
|
Figure~\ref{fig:flow}. Functions \code{sane\_init()} and
|
|
\code{sane\_exit()} initialize and exit the backend, respectively.
|
|
All other calls must be performed after initialization and before
|
|
exiting the backend.
|
|
|
|
\begin{figure}[htb]
|
|
\begin{center}
|
|
\leavevmode
|
|
\psfig{file=figs/flow.eps,height=0.5\textheight}
|
|
\caption{Code flow}
|
|
\label{fig:flow}
|
|
\end{center}
|
|
\end{figure}
|
|
|
|
Function \code{sane\_get\_devices()} can be called any time after
|
|
\code{sane\_init()} has been called. It returns the list of the
|
|
devices that are known at the time of the call. This list may change
|
|
over time since some devices may be turned on or off or a remote host
|
|
may boot or shutdown between different calls. It should be noted that
|
|
this operation may be relatively slow since it requires contacting all
|
|
configured devices (some of which may be on remote hosts). A frontend
|
|
may therefore want to provide the ability for a user to directly
|
|
select a desired device without requiring a call to this function.
|
|
|
|
Once a device has been chosen, it is opened using a call to
|
|
\code{sane\_open()}. Multiple devices can be open at any given time.
|
|
A SANE backend must not impose artificial constraints on how many
|
|
devices can be open at any given time.
|
|
|
|
An opened device can be setup through the corresponding device handle
|
|
using functions \code{sane\_get\_opt\-ion\_desc\-riptor()} and
|
|
\code{sane\_control\_option()}. While setting up a device, obtaining
|
|
option descriptors and setting and reading of option values can be
|
|
mixed freely. It is typical for a frontend to read out all available
|
|
options at the beginning and then build a dialog (either graphical or
|
|
a command-line oriented option list) that allows to control the
|
|
available options. It should be noted that the number of options is
|
|
fixed for a given handle. However, as options are set, other options
|
|
may become active or inactive. Thus, after setting an option, it
|
|
maybe necessary to re-read some or all option descriptors. While
|
|
setting up the device, it is also admissible to call
|
|
\code{sane\_get\_parameters()} to get an estimate of what the image
|
|
parameters will look like once image acquisition begins.
|
|
|
|
The device handle can be put in blocking or non-blocking mode by a
|
|
call to \code{sane\_set\_io\_mode()}. Devices are required to support
|
|
blocking mode (which is the default mode), but support for
|
|
non-blocking I/O is strongly encouraged for operating systems such as
|
|
UNIX.
|
|
|
|
After the device is setup properly, image acquisition can be started
|
|
by a call to \code{sane\_start()}. The backend calculates the exact
|
|
image parameters at this point. So future calls to
|
|
\code{sane\_get\_parameters()} will return the exact values, rather
|
|
than estimates. Whether the physical image acquisition starts at this
|
|
point or during the first call to \code{sane\_read()} is unspecified
|
|
by the SANE API. If non-blocking I/O and/or a select-style interface
|
|
is desired, the frontend may attempt to call
|
|
\code{sane\_set\_io\_mode()} and/or \code{sane\_get\_select\_fd()} at
|
|
this point. Either of these functions may fail if the backend does
|
|
not support the requested operation.
|
|
|
|
Image data is collected by repeatedly calling \code{sane\_read()}.
|
|
Eventually, this function will return an end-of-file status
|
|
(\code{SANE\_STATUS\_EOF}). This indicates the end of the current
|
|
frame. If the frontend expects additional frames (e.g., the
|
|
individual channels in of a red/green/blue image or multiple images),
|
|
it can call \code{sane\_start()} again. Once all desired frames have
|
|
been acquired, function \code{sane\_cancel()} must be called. This
|
|
operation can also be called at any other time to cancel a pending
|
|
operation. Note that \code{sane\_cancel()} must be called even if the
|
|
last read operation returned \code{SANE\_STATUS\_EOF}.
|
|
|
|
When done using the device, the handle should be closed by a call to
|
|
\code{sane\_close()}. Finally, before exiting the application,
|
|
function \code{sane\_exit()} must be called. It is important not to
|
|
forget to call this function since otherwise some resources (e.g.,
|
|
temporary files or locks) may remain unclaimed.
|
|
|
|
|
|
\section{Well-Known Options}\index{well-known options}
|
|
|
|
While most backend options are completely self-describing, there are a
|
|
cases where a user interface might want to special-case the handling
|
|
of certain options. For example, the scan area is typically defined
|
|
by four options that specify the top-left and bottom-right corners of
|
|
the area. With a graphical user interface, it would be tedious to
|
|
force the user to type in these four numbers. Instead, most such
|
|
interfaces will want to present to the user a preview (low-resolution
|
|
scan) of the scanner surface and let the user pick the scan area by
|
|
dragging a rectangle into the desired position. For this reason, the
|
|
SANE API specifies a small number of option names that have
|
|
well-defined meanings.
|
|
|
|
\subsection{Option Number Count}\index{option count}
|
|
|
|
Option number 0 has an empty string as its name. The value of this
|
|
option is of type \code{SANE\_TYPE\_INT} and it specifies the total
|
|
number of options available for a given device (the count includes
|
|
option number 0). This means that there are two ways of counting the
|
|
number of options available: a frontend can either cycle through all
|
|
option numbers starting at one until
|
|
\code{sane\_get\_option\_descriptor()} returns \code{NULL}, or a
|
|
frontend can directly read out the value of option number 0.
|
|
|
|
\subsection{Scan Resolution Option}\index{scan resolution}\index{resolution option}
|
|
|
|
Option \code{resolution} is used to select the resolution at which an
|
|
image should be acquired. The type of this option is either
|
|
\code{SANE\_TYPE\_INT} or \code{SANE\_TYPE\_FIXED}. The unit is
|
|
\code{SANE\_UNIT\_DPI} (dots/inch).
|
|
|
|
This option is not mandatory, but if a backend does support it, it
|
|
must implement it in a manner consistent with the above definition.
|
|
|
|
\subsection{Preview Mode Option}\index{preview mode}
|
|
|
|
The boolean option \code{preview} is used by a frontend to inform the
|
|
backend when image acquisition should be optimized for speed, rather
|
|
than quality (``preview mode''). When set to \code{SANE\_TRUE},
|
|
preview mode is in effect, when set to \code{SANE\_FALSE} image
|
|
acquisition should proceed in normal quality mode. The setting of
|
|
this option \emph{must not\/} affect any other option. That is, as
|
|
far as the other options are concerned, the preview mode is completely
|
|
side effect free. A backend can assume that the frontend will take
|
|
care of appropriately setting the scan resolution for preview mode
|
|
(through option \code{resolution}). A backend is free to override the
|
|
\code{resolution} value with its own choice for preview mode, but it
|
|
is advised to leave this choice to the frontend wherever possible.
|
|
|
|
This option is not mandatory, but if a backend does support it, it
|
|
must implement it in a manner consistent with the above definition.
|
|
|
|
\subsection{Scan Area Options}\index{scan area options}
|
|
|
|
The four most important well-known options are the ones that define
|
|
the scan area. The scan area is defined by two points (x/y coordinate
|
|
pairs) that specify the top-left and the bottom-right corners. This
|
|
is illustrated in Figure~\ref{fig:area}. Note that the origin of the
|
|
coordinate system is at the top-left corner of the scan surface as
|
|
seen by the sensor (which typically is a mirror image of the scan
|
|
surface seen by the user). For this reason, the top-left corner is
|
|
the corner for which the abscissa and ordinate values are
|
|
simultaneously the {\em smallest} and the bottom-right corner is the
|
|
corner for which the abscissa and ordinate values are simulatenously
|
|
the {\em largest}. If this coordinate system is not natural for a
|
|
given device, it is the job of the backend to perform the necessary
|
|
conversions.
|
|
\begin{figure}[tbp]
|
|
\begin{center}
|
|
\leavevmode
|
|
\psfig{file=figs/area.eps,height=0.3\textheight}
|
|
\caption{Scan area options}
|
|
\label{fig:area}
|
|
\end{center}
|
|
\end{figure}
|
|
|
|
The names of the four options that define the scan area are given in
|
|
the table below:
|
|
\begin{center}
|
|
\begin{tabular}{ll}
|
|
{\bf Name} & {\bf Description} \\
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|
\code{\defn{tl-x}} & Top-left $x$ coordinate value \\
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|
\code{\defn{tl-y}} & Top-left $y$ coordinate value \\
|
|
\code{\defn{br-x}} & Bottom-right $x$ coordinate value \\
|
|
\code{\defn{br-y}} & Bottom-right $y$ coordinate value \\
|
|
\end{tabular}
|
|
\end{center}
|
|
There are several rules that should be followed by front and backends
|
|
regarding these options:
|
|
\begin{itemize}
|
|
|
|
\item Backends must attach a unit of either pixels
|
|
(\code{SANE\_UNIT\_PIXEL}) or millimeters (\code{SANE\_UNIT\_MM}) to
|
|
these options. The unit of all four options must be identical.
|
|
|
|
\item Whenever meaningful, a backend should attach a range or a
|
|
word-list constraint to these options.
|
|
|
|
\item A frontend can determine the size of the scan surface by first
|
|
checking that the options have range constraints associated. If a
|
|
range or word-list constraints exist, the frontend can take the
|
|
minimum and maximum values of one of the x and y option
|
|
range-constraints to determine the scan surface size.
|
|
|
|
\item A frontend must work properly with any or all of these options
|
|
missing.
|
|
|
|
\end{itemize}
|
|
|
|
\input{net.tex}
|
|
|
|
\chapter{Contact Information}\label{chap:contact}
|
|
|
|
The SANE standard is discussed and evolved via a mailing list.
|
|
Anybody with email access to the Internet can automatically join and
|
|
leave the discussion group by sending mail to the following address.
|
|
\begin{quote}\index{mailing list}
|
|
\begin{verbatim}
|
|
majordomo@mostang.com
|
|
\end{verbatim}
|
|
\end{quote}
|
|
To subscribe, send a mail with the body ``\verb|subscribe sane-devel|'' to the
|
|
above address.
|
|
|
|
A complete list of commands supported can be obtained by sending a
|
|
mail with a subject of ``\code{help}'' to the above address. The
|
|
mailing list is archived and available through the SANE home page at
|
|
URL:
|
|
\begin{quote}
|
|
\url{http://www.mostang.com/sane/}
|
|
\end{quote}
|
|
|
|
\newpage
|
|
\input{sane.ind}
|
|
|
|
\end{document}
|