sane-project-backends/doc/sane-sharp.man

.TH sane-sharp 5 "28 Dec 1999"
.IX sane-sharp
.SH NAME
sane-sharp - SANE backend for SHARP scanners
.SH DESCRIPTION
The
.B sane-sharp
library implements a SANE (Scanner Access Now Easy) backend that
provides access to Sharp SCSI scanners.  This backend should be
considered
.B beta-quality
software!  In the current state it is known to work with JX-610 and JX-250 
scanners. It is prepared for usage with the JX-330 series scanners,
but we are not able to test it with these devices.
.PP
For other Sharp scanners, it may or may not work.
.PP
At present,
the following scanners are known to work with this backend.
.RS
.PP
Vendor	Product id:
.br
-----	-----------
.br
Sharp	JX-610
.br
Sharp	JX-250
.RE
.PP
The following scanners are detected by the backend, but not tested:
.PP
.RS
Vendor	Product id:
.br
-----	-----------
.br
Sharp	JX-320
.br
Sharp	JX-325
.br
Sharp	JX-330

.RE
.SH DEVICE NAMES
This backend expects device names of the form:
.PP
.RS
.I special
.RE
.PP
Where
.I special
is either the path-name for the special device that corresponds to a
SCSI scanner. The special device name must be a generic SCSI device or a
symlink to such a device.  Under Linux, such a device name could be
.I /dev/sga
or
.IR /dev/sge ,
for example.  See sane-scsi(5) for details.

.SH SCAN OPTIONS

.B Scan Mode
(parameter 
.B --mode
for scanimage). Possible settings: 
.RS
.B Lineart
(1 bit black & white scans), 
.br
.B Gray
(8 bit gray scale scans),
.br
.B Lineart Color
(bi-level color scans), 
.br
.B Color
(8 bit RGB scans).
.RE
The default value is
.B Color.

.B Halftone Pattern
(parameter
.B --halftone-pattern
for scanimage). Available only for the JX-330 series scanners.
Possible settings:
.RS
.B none
.br
.B Dither Bayer
.br 
.B Dither Spiral
.br
.B Dither Dispersed
.br 
.B Error Diffusion
.RE
The default value is
.B none.

.B Paper Source
(parameter
.B --source
for scanimage). This option is only available, if an automatic document
feeder or a transparency adapter is installed. Possible settings:
.RS
.B Flatbed
.br
.B Automatic Document Feeder
.br
.B Transparency Adapter
.RE
If an ADF or a transparency adapter is installed, using it is the
default selection. 

.B Custom Gamma
(parameter 
.B --custom-gamma
for scanimage). This option determines whether a builtin or a custom 
gamma-table is used. Possible settings:
.RS
.B yes
enables custom gamma tables
.br
.B no
enables a built gamma table
.RE

.B Gamma
(parameter 
.B --Gamma
for scanimage). This option is only available, if 
.B Custom Gamma
is set to 
.B no.
Possible values:
.RS
.B 1.0
.br
.B 2.2
.RE
The default value is 2.2. (The JX-250 has no built in gamma correction; for
this scanner, a gamma table is downloaded to the scanner by the backend.)

.B Gamma Table
(parameter 
.B --gamma-table
for scanimage). Allowed values: 0..255; 256 numbers must be defined. 
The default values are 0, 1, 2, .. 255 (i.e., gamma == 1). This table 
is only used for gray scale scans.

.B Red Gamma Table
(paramter 
.B --red-gamma-table 
for scanimage). Allowed values: 0..255; 256 numbers must be defined.
The default values are 0, 1, 2, .. 255 (i.e., gamma == 1).

.B Green Gamma Table
(paramter 
.B --green-gamma-table 
for scanimage). Allowed values: 0..255; 256 numbers must be defined.
The default values are 0, 1, 2, .. 255 (i.e., gamma == 1).

.B Blue Gamma Table
(paramter 
.B --blue-gamma-table 
for scanimage). Allowed values: 0..255; 256 numbers must be defined.
The default values are 0, 1, 2, .. 255 (i.e., gamma == 1).

.B Resolution
in pixel per inch (parameter
.B --resolution
for scanimage). Selects the resolution of the scanned image. Allowed values:
.RS
.B 30..600
(JX-330 and JX-610) resp. 
.B 30..400
(JX-250)
.RE
The default value is 150.

.B Scan Window

The possible settings depend on the scanner model and, for the
JX-250, also on the usage of the automatic document feeder resp. the
transparency adapter. Please refer to the values allowed by xscanimage, or
xsane. With scanimage, enter one of the following commands:

.RS
.I scanimage -d sharp --source """Automatic Document Feeder""" --help

.I scanimage -d sharp --source Flatbed --help

.I scanimage -d sharp --source """Transparency Adapter""" --help
.RE

in order to see the allowed parameter values for the scan window.

The scan window parameters are:

.RS
Top-left x position of scan area (parameter 
.B -l
for scanimage);
.br
Top-left y position of scan area (parameter 
.B -t
for scanimage);
.br
bottom right x position of scan area (parameter 
.B -x
for scanimage);
.br
bottom right y position of scan area (parameter 
.B -y
for scanimage);
.RE

.B Edge emphasis
(parameter
.B --Edge emphasis
for scanimage). This option is not available for the JX-250. Possible 
settings:
.RS
.B None
.br
.B Middle
.br
.B Strong
.br
.B Blur
.RE
The default value is 
.B None.

.B Threshold
(parameter 
.B --threshold
for scanimage). Sets the threshold for black and white pixels in lineart
mode. Possible values:
.RS
.B 1..255
.RE
The default value is 
.B 128.
This option is only available in scan mode lineart.

.B Threshold Red
(parameter 
.B --threshold-red
for scanimage). Sets the threshold for the red component of a pixel in
in lineart color scan mode. Possible values:
.RS
.B 1..255
.RE
The default value is 
.B 128.
This option is only available in scan mode color lineart.

.B Threshold Green
(parameter 
.B --threshold-green
for scanimage). Sets the threshold for the green component of a pixel in
in lineart color scan mode. Possible values:
.RS
.B 1..255
.RE
The default value is 
.B 128.
This option is only available in scan mode color lineart.

.B Threshold Blue
(parameter 
.B --threshold-blue
for scanimage). Sets the threshold for the blue component of a pixel in
in lineart color scan mode. Possible values:
.RS
.B 1..255
.RE
The default value is 
.B 128.
This option is only available in scan mode color lineart.

.B Light Color
(parameter 
.B --LightColor
for scanimage). Sets the color of the light source. Possible values:
.RS
.B white
.br
.B red
.br
.B green
.br
.B blue
.RE
The default value is 
.B white.
This option is only available in scan modes lineart color and color.

.SH ADF USAGE
If a paper jam occured, the maintenance cover
.I
must
be opened and closed, even if the jammed paper can be removed without opening
the maintenance cover. Otherwise, the error condition cannot be cleared.

.SH CONFIGURATION
The contents of the 
.I sharp.conf
file is a list of options and device names that correspond to Sharp 
scanners. Empty lines and lines beginning with a hash mark (#) are
ignored. See sane-scsi(5) for details about device names.
.PP
Lines setting an option start with the key word
.B option,
followed by the option's name and the option's value. At present, three
options are defined: 
.B buffers, buffersize, 
and
.B readqueue. 
.PP
Options defined at the start of 
.I sharp.conf
apply to all devices; options defined after a
device name apply to this device.
.PP
The options 
.B buffers
and
.B
readqueue
are only significant if the backend has been compiled
so that for each scan a second process is forked (switch 
.B USE_FORK
in 
.I sharp.c
). This process reads the
scan data from the scanner and writes this data into a block of shared memory.
The parent process reads the data from this memory block and delivers it 
to the frontend. The options control the size and usage of this shared 
memory block.
.PP
.B option buffers
defines the number of buffers used. The smallest number allowed is 2. 
.PP
.B option buffersize
defines the size of one buffer. Since each buffer is filled with a 
single read command sent to the scanner, its size is limited automatically
to the size allowed by the operating system or by the Sane SCSI library
for SCSI read commands. A buffer size of 128 kB or 256 kB is recommended
for scan resolutions of 300 dpi and above.
.PP
.B option readqueue 
defines how many read commands to be sent to the scanner
are queued. At present, the Sane SCSI library supports queued read 
commands only for for Linux. For other operating systems, 
.B option readqueue
should be set to 0. For Linux, 
.B option readqueue
should be set to 2. Larger values than 2 for
.B option readqueue
are not reasonable in most cases.
.B option buffers
should be greater than 
.B option readqueue.

.SH Performance Considarations
This section focuses on the problem of stops of the scanner's carriage
during a scan. Carriage stops happen mainly with the JX-250. This scanner 
has obviously only a small internal buffer compared to its speed. That 
means that the backend must read the data as fast as possible from the 
scanner in order to avoid carriage stops. 
.PP
Even the JX-250 needs only less than 10 seconds for a 400 dpi A4 gray 
scale scan, which results in a data transfer rate of more than 1.6 MB 
per second. This means that the data produced by the scanner must be 
processed fairly fast. Due to the small internal buffer of the JX-250,
the backend must issue a read request for the next data block as soon
as possible after reading a block of data in order to avoid carriage
stops.
.PP
Stops of the carriage can be caused by the following reasons:
.PP
.RS
- too much "traffic" on the SCSI bus
.br
- slow responses by the backend to the scanner,
.br
- a program which processes the data aquired by the backend too slow.
.PP
.RE
Too much "traffic" on the SCSI bus: This happens for example, if hard disks
are connected to the same SCSI bus as the scanner, and when data transfer 
from/to these hard disks requires a considerable part of the SCSI bandwidth
during a scan. If this is the case, you should consider to connect the 
scanner to a separate SCSI adapter.
.PP
Slow responses by the backend to the scanner: Unfortunately,
Unix-like operating systems generally have no real time capabilities.
Thus there is no guarantee that the backend is under any circumstances
able to communicate with the scanner as fast as required. To minimize this
problem, the backend should be compiled so that a separate reader process 
is forked: Make sure that
.B USE_FORK
is defined when you compile 
.I sharp.c.
If slow responses of the backend remain to be problem, you could try to
reduce the load of the system. Even while the backend and the reader 
process need only a minor amount of processor time, other running 
processes can cause an increase in the time delay between two time
slices given to the reader process. On slower systems, such an 
increased delay can be enough to cause a carriage stop with the JX-250.
For Linux, the usage of the SG driver version 2.1.36 or above is
recommended, because it supports, in combination with
the SCSI library of Sane version 1.0.2, command queueing within the kernel.
This queueing implementation, combined with a buffer size of at least
128 kB, should avoid most carirage stops.
.PP
Slow processing of the scan data: An example for this situation is
the access to the scanner via a 10 MBit Ethernet, which is definitely
too slow to transfer the scan data as fast as they are produced by the
scanner. If you have enough memory available, you can increase 
.B option buffers,
so that an entire image can be stored in these buffers. 
.PP
In order to see, if the backend is too slow or if the further processing
of the data is too slow, set the environment variable
.B SANE_DEBUG_SHARP
to 1. When a scan is finished, the backend writes the line "buffer full
conditions: 
.I nn"
to stderr. If
.I nn
is zero, carriage stops are caused by too slow responses of the backend
or too much "traffic" on the SCSI bus. If 
.I nn
is greater than zero, the backend had to wait
.I nn
times until a buffer has been processed by the frontend. (Please note that
.B option buffers
must be greater than
.B option readqueue
in order to get useful output for "buffer full conditions".)

.SH FILES
.TP
.I @CONFIGDIR@/sharp.conf
The backend configuration file.
.TP
.I @LIBDIR@/libsane-sharp.a
The static library implementing this backend.
.TP
.I @LIBDIR@/libsane-sharp.so
The shared library implementing this backend (present on systems that
support dynamic loading).
.SH ENVIRONMENT
.TP
.B SANE_DEBUG_SHARP
If the library was compiled with debug support enabled, this
environment variable controls the debug level for this backend.  E.g.,
a value of 128 requests all debug output to be printed.  Smaller
levels reduce verbosity.
.SH KNOWN PROBLEMS
1. ADF Mode
.RS
After several ADF scans, the scanner moves the carriage back to the idle
position and back to ADF scan position, before a scan starts. We do not 
know, if this is a problem of the scanner, or if this is a bug of the 
backend. At present, the scanner must power off and on to stop this
annoying behaviour.
.RE

2. Threshold level does not work (only JX-610)
.PP
3. The maximum resolution is limited to 600 dpi(JX-610 supported 
to 1200 dpi) resp. 400 dpi (JX-250)
.PP
4. If the JX250 is used with an ADF, the following situation can occur: After
several scans, the scanner moves, after loading a new sheet of paper, the
carriage to the idle position, and then back to the position used for ADF
scans. This happens for 
.I
every
scan, in contrast to the calibration, which is done after 10 scans. (For the
calibration, the carriage is also moved to the idle position.) We do not
know, if this behavior is caused by the backend, or if it is a bug in the
firmware of the scanner.
.PP
5. Usage of a transparency adapter (film scan unit) is supported, but not
tested.

.SH "SEE ALSO"
sane\-scsi(5)
.SH AUTHORS
Kazuya Fukuda, Abel Deuring
.SH CREDITS
The Sharp backend is based on the Canon backend written by Helmut Koeberle
.PP
Parts of this man page are a plain copy of sane-mustek(5) by David
Mosberger-Tang, Andreas Czechanowski and Andreas Bolsch