sane-project-website/old-archive/1998-11/0080.html

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<!-- name="Stefan Illy" -->
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<!-- subject="Output filters for xscanimage: a simple attempt" -->
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<title>sane-devel: Output filters for xscanimage: a simple attempt</title>
<h1>Output filters for xscanimage: a simple attempt</h1>
<b>Stefan Illy</b> (<a href="mailto:stefan.illy@itp.fzk.de"><i>stefan.illy@itp.fzk.de</i></a>)<br>
<i>Tue, 10 Nov 1998 10:13:23 +0100 (MET)</i>
<p>
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Hello,<br>
<p>
I wondered why there is no possibility to use other output formats than<br>
PNM in xscanimage. So I decided to implement output filters for other<br>
formats in a simple way without changing too much of xscanimage.<br>
<p>
This was done by replacing the `fopen' and `fclose' commands in<br>
xscanimage.c by functions called `pfopen' and `pfclose'. Both functions<br>
are implemented in `pfopen.c' appended below. Please look at the<br>
comments in this file for more details, it should be not too complicated.<br>
<p>
The conversion can be done by `netpbm' filters, ImageMagick's `convert'<br>
command or `cjpeg'. Compression using `gzip' is also possible.<br>
<p>
If you want to test it, replace `fopen' and `fclose' in xscanimage.c<br>
by `pfopen' and `pfclose', respectively. Don't forget to provide<br>
prototypes for both functions. Provide pfopen.c in the `frontend' path<br>
and add an entry for pfopen.o in the corresponding Makefile.<br>
<p>
I tested it both with the 0.74 and the pre-1.00 version and had no<br>
problems (on Linux, kernel 2.0.35, libc5).<br>
<p>
<p>
Please tell me what you think about this attempt, if it worked for you<br>
and what could be done in a better way.<br>
<p>
Stefan<br>
<p>
----8&lt;-------8&lt;-------8&lt;-------8&lt;-------8&lt;-------8&lt;-------8&lt;-------8&lt;---<br>
/* <br>
 *  pfopen.c: A simple way to provide output filters for xscanimage.<br>
 *<br>
 *  Author: Stefan Illy &lt;<a href="mailto:stefan.illy@itp.fzk.de">stefan.illy@itp.fzk.de</a>&gt;<br>
 *<br>
 */<br>
<p>
#include &lt;stdio.h&gt;<br>
#include &lt;string.h&gt;<br>
#include &lt;sys/stat.h&gt;<br>
#include &lt;unistd.h&gt;<br>
<p>
#define STRLEN 256<br>
<p>
<p>
/*<br>
 *  List of output filters.<br>
 *  This should be provided in a configuration file (e.g. `filters.conf')<br>
 */<br>
char* filter_list[] = {<br>
  ".eps: convert pnm:- eps2:-",<br>
  ".eps.gz: convert pnm:- eps2:- | gzip",<br>
  ".ps: convert pnm:- ps2:-",<br>
  ".ps.gz: convert pnm:- ps2:- | gzip",<br>
  ".jpg: cjpeg -quality 75",<br>
  ".png: pnmtopng",<br>
  ".pnm.gz: gzip",<br>
  NULL};<br>
<p>
<p>
/*<br>
 *  Returns one if `str' ends with `expr', otherwise zero.<br>
 */<br>
int<br>
strends(const char* str, const char* expr)<br>
{<br>
  char* pos;<br>
  if ((pos = strstr(str, expr)) == NULL) return 0;<br>
  if (strlen(str) - strlen(expr) == (int)(pos - str)) return 1; else return 0;<br>
}<br>
<p>
<p>
/*<br>
 *  pfopen: replacement for fopen in `xscanimage.c'.<br>
 *  <br>
 *  If `path' starts with the pipe symbol `|' or the extension of the<br>
 *  file name is in `filter_list', popen will be used instead of<br>
 *  fopen.<br>
 *  <br>
 */<br>
FILE*<br>
pfopen(const char* path, char* mode)<br>
{<br>
  FILE* stream;<br>
  char filter[STRLEN] = "";<br>
<p>
  if (path[0] == '|')                   /* Output filter directly specified. */<br>
  {<br>
    strcpy(filter, &amp;path[1]);<br>
  }<br>
  else                                  /* Search filter_list for extension. */<br>
  {<br>
    int i;<br>
    for (i = 0; filter_list[i] != NULL; i++)<br>
    {<br>
      char* pos;<br>
      if ((pos = strchr(filter_list[i], ':')) != NULL)<br>
      {<br>
	char ext[STRLEN] = "";<br>
	strncpy(ext, filter_list[i], (int)(pos - filter_list[i]));<br>
	if (strends(path, ext))<br>
	{<br>
	  strcpy(filter, pos + 1);<br>
	  strcat(filter, " &gt; ");<br>
	  strcat(filter, path);<br>
	  break;<br>
	}<br>
      }<br>
    }<br>
  }<br>
<p>
  if (strcmp(filter, "") == 0)<br>
  {<br>
    fprintf(stderr, "pfopen: using fopen(%s).\n", path);<br>
    stream = fopen(path, mode);<br>
  }<br>
  else<br>
  {<br>
    fprintf(stderr, "pfopen: using popen(%s).\n", filter);<br>
    stream = popen(filter, mode);<br>
  }<br>
<p>
  return stream;<br>
}<br>
<p>
<p>
/*<br>
 *  pfclose: replacement for fclose in `xscanimage.c'.<br>
 *<br>
 *  Uses fstat to determine if `stream' belongs to a regular file.<br>
 *  If this is not the case, pclose will be used instead of<br>
 *  fclose.<br>
 *<br>
 *  Maybe there are better (and more secure) methods to do this.<br>
 */<br>
int<br>
pfclose(FILE* stream)<br>
{<br>
  struct stat statinfo;<br>
<p>
  if (fstat(fileno(stream), &amp;statinfo) != 0)<br>
  {<br>
    fprintf(stderr, "pfclose: fstat was not successful, using fclose.\n");<br>
    return fclose(stream);<br>
  }<br>
<p>
  if (S_ISREG(statinfo.st_mode))<br>
  {<br>
    fprintf(stderr, "pfclose: S_ISREG==true, using fclose.\n");<br>
    return fclose(stream);<br>
  }<br>
  else<br>
  {<br>
    fprintf(stderr, "pfclose: S_ISREG==false, using pclose.\n");<br>
    return pclose(stream);<br>
  }<br>
}<br>
----8&lt;-------8&lt;-------8&lt;-------8&lt;-------8&lt;-------8&lt;-------8&lt;-------8&lt;---<br>
<p>
<pre>
-- 
Stefan Illy                     |  Institut fuer Technische Physik (ITP)
e-mail: <a href="mailto:stefan.illy@itp.fzk.de">stefan.illy@itp.fzk.de</a>  |  Forschungszentrum Karlsruhe GmbH
phone:  (+49) 07247/82-4165     |  Hermann-von-Helmholtz-Platz 1
fax:    (+49) 07247/82-2849     |  D-76344 Eggenstein-Leopoldshafen, Germany
<p>
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