PC-Online 1996 May/PCOnline_05_1996.bin/linux/source/contrib/seejpeg/seejpeg-.4/seejpeg-/seejpeg-1.4.3/jpeg.c

C/C++ Source or Header | 1994-03-19 | 15KB | 367 lines

/*
 * Previously example.c from the JPEG distribution.
 */

#include "seejpeg.h"
#include <setjmp.h>
#include <vga.h>

/******************** JPEG DECOMPRESSION SAMPLE INTERFACE *******************/

/* This half of the example shows how to read data from the JPEG decompressor.
 * It's a little more refined than the above in that we show how to do your
 * own error recovery.  If you don't care about that, you don't need these
 * next two routines.
 */


/*
 * These routines replace the default trace/error routines included with the
 * JPEG code.  The example trace_message routine shown here is actually the
 * same as the standard one, but you could modify it if you don't want messages
 * sent to stderr.  The example error_exit routine is set up to return
 * control to read_JPEG_file() rather than calling exit().  You can use the
 * same routines for both compression and decompression error recovery.
 */

/* These variables are needed by the error routines. */
jmp_buf setjmp_buffer;    /* for return to caller */
external_methods_ptr emethods; /* needed for access to message_parm */


/* This routine is used for any and all trace, debug, or error printouts
 * from the JPEG code.  The parameter is a printf format string; up to 8
 * integer data values for the format string have been stored in the
 * message_parm[] field of the external_methods struct.
 */

/*METHODDEF*/ void
trace_message (const char *msgtext)
{
  fprintf(stderr, msgtext,
      emethods->message_parm[0], emethods->message_parm[1],
      emethods->message_parm[2], emethods->message_parm[3],
      emethods->message_parm[4], emethods->message_parm[5],
      emethods->message_parm[6], emethods->message_parm[7]);
  fprintf(stderr, "\n");    /* there is no \n in the format string! */
}

/*
 * The error_exit() routine should not return to its caller.  The default
 * routine calls exit(), but here we assume that we want to return to
 * read_JPEG_file, which has set up a setjmp context for the purpose.
 * You should make sure that the free_all method is called, either within
 * error_exit or after the return to the outer-level routine.
 */

/*METHODDEF*/ void
error_exit (const char *msgtext)
{
  trace_message(msgtext);    /* report the error message */
  (*emethods->free_all) ();    /* clean up memory allocation & temp files */
  display_shutdown();
  longjmp(setjmp_buffer, 1);    /* return control to outer routine */
}



/*
 * To accept the image data from decompression, you must define four routines
 * output_init, put_color_map, put_pixel_rows, and output_term.
 *
 * You must understand the distinction between full color output mode
 * (N independent color components) and colormapped output mode (a single
 * output component representing an index into a color map).  You should use
 * colormapped mode to write to a colormapped display screen or output file.
 * Colormapped mode is also useful for reducing grayscale output to a small
 * number of gray levels: when using the 1-pass quantizer on grayscale data,
 * the colormap entries will be evenly spaced from 0 to MAX_JSAMPLE, so you
 * can regard the indexes are directly representing gray levels at reduced
 * precision.  In any other case, you should not depend on the colormap
 * entries having any particular order.
 * To get colormapped output, set cinfo->quantize_colors to TRUE and set
 * cinfo->desired_number_of_colors to the maximum number of entries in the
 * colormap.  This can be done either in your main routine or in
 * d_ui_method_selection.  For grayscale quantization, also set
 * cinfo->two_pass_quantize to FALSE to ensure the 1-pass quantizer is used
 * (presently this is the default, but it may not be so in the future).
 *
 * The output file writing modules (jwrppm.c, jwrgif.c, jwrtarga.c, etc) may be
 * useful examples of what these routines should actually do, although each of
 * them is encrusted with a lot of specialized code for its own file format.
 */

METHODDEF void
output_init (decompress_info_ptr cinfo)
/* This routine should do any setup required */
{
  /* This routine can initialize for output based on the data passed in cinfo.
   * Useful fields include:
   *    image_width, image_height    Pretty obvious, I hope.
   *    data_precision            bits per pixel value; typically 8.
   *    out_color_space            output colorspace previously requested
   *    color_out_comps            number of color components in same
   *    final_out_comps            number of components actually output
   * final_out_comps is 1 if quantize_colors is true, else it is equal to
   * color_out_comps.
   *
   * If you have requested color quantization, the colormap is NOT yet set.
   * You may wish to defer output initialization until put_color_map is called.
   */

  display_init(cinfo->image_width, cinfo->image_height,
           cinfo->final_out_comps);
}


/*
 * This routine is called if and only if you have set cinfo->quantize_colors
 * to TRUE.  It is given the selected colormap and can complete any required
 * initialization.  This call will occur after output_init and before any
 * calls to put_pixel_rows.  Note that the colormap pointer is also placed
 * in a cinfo field, whence it can be used by put_pixel_rows or output_term.
 * num_colors will be less than or equal to desired_number_of_colors.
 *
 * The colormap data is supplied as a 2-D array of JSAMPLEs, indexed as
 *        JSAMPLE colormap[component][indexvalue]
 * where component runs from 0 to cinfo->color_out_comps-1, and indexvalue
 * runs from 0 to num_colors-1.  Note that this is actually an array of
 * pointers to arrays rather than a true 2D array, since C does not support
 * variable-size multidimensional arrays.
 * JSAMPLE is typically typedef'd as "unsigned char".  If you want your code
 * to be as portable as the JPEG code proper, you should always access JSAMPLE
 * values with the GETJSAMPLE() macro, which will do the right thing if the
 * machine has only signed chars.
 */

METHODDEF void
put_color_map (decompress_info_ptr cinfo, int num_colors, JSAMPARRAY colormap)
/* Write the color map */
{
  display_set_palette(num_colors, colormap, cinfo->color_out_comps);
}


/*
 * This function is called repeatedly, with a few more rows of pixels supplied
 * on each call.  With the current JPEG code, some multiple of 8 rows will be
 * passed on each call except the last, but it is extremely bad form to depend
 * on this.  You CAN assume num_rows > 0.
 * The data is supplied in top-to-bottom row order (the standard order within
 * a JPEG file).  If you cannot readily use the data in that order, you'll
 * need an intermediate array to hold the image.  See jwrrle.c for an example
 * of outputting data in bottom-to-top order.
 *
 * The data is supplied as a 3-D array of JSAMPLEs, indexed as
 *        JSAMPLE pixel_data[component][row][column]
 * where component runs from 0 to cinfo->final_out_comps-1, row runs from 0 to
 * num_rows-1, and column runs from 0 to cinfo->image_width-1 (column 0 is
 * left edge of image).  Note that this is actually an array of pointers to
 * pointers to arrays rather than a true 3D array, since C does not support
 * variable-size multidimensional arrays.
 * JSAMPLE is typically typedef'd as "unsigned char".  If you want your code
 * to be as portable as the JPEG code proper, you should always access JSAMPLE
 * values with the GETJSAMPLE() macro, which will do the right thing if the
 * machine has only signed chars.
 *
 * If quantize_colors is true, then there is only one component, and its values
 * are indexes into the previously supplied colormap.  Otherwise the values
 * are actual data in your selected output colorspace.
 */


METHODDEF void
put_pixel_rows (decompress_info_ptr cinfo, int num_rows, JSAMPIMAGE pixel_data)
/* Write some rows of output data */
{
  display_rows(num_rows, pixel_data, cinfo->image_width,
           cinfo->final_out_comps);
}


METHODDEF void
output_term (decompress_info_ptr cinfo)
/* Finish up at the end of the output */
{
  /* This termination routine may not need to do anything. */
  /* Note that the JPEG code will only call it during successful exit; */
  /* if you want it called during error exit, you gotta do that yourself. */

  scroll_until_end();
}


/*
 * That's it for the routines that deal with writing the output image.
 * Now we have overall control and parameter selection routines.
 */


/*
 * This routine gets control after the JPEG file header has been read;
 * at this point the image size and colorspace are known.
 * The routine must determine what output routines are to be used, and make
 * any decompression parameter changes that are desirable.  For example,
 * if it is found that the JPEG file is grayscale, you might want to do
 * things differently than if it is color.  You can also delay setting
 * quantize_colors and associated options until this point.
 *
 * j_d_defaults initializes out_color_space to CS_RGB.  If you want grayscale
 * output you should set out_color_space to CS_GRAYSCALE.  Note that you can
 * force grayscale output from a color JPEG file (though not vice versa).
 */

METHODDEF void
d_ui_method_selection (decompress_info_ptr cinfo)
{
  /* set 256 colour, colourmapped,  1 pass quantizing if greyscale
   * else we'll use 32768 colour, 2 pass quantizing.
   * this may change later if we want to add using a colourmap in
   * colour modes.
   */
  if (cinfo->jpeg_color_space == CS_GRAYSCALE || opt_greyscale) {
    cinfo->out_color_space = CS_GRAYSCALE;
    cinfo->quantize_colors = TRUE;
    cinfo->desired_number_of_colors = 256;
    cinfo->two_pass_quantize = FALSE;
  } else if (opt_quantize || opt_onepass || !vga_hasmode(TESTMODE)) {
    cinfo->quantize_colors = TRUE;
    cinfo->desired_number_of_colors = 256;
    if (opt_onepass) {
      cinfo->two_pass_quantize = FALSE;
    } else {
      cinfo->two_pass_quantize = TRUE;
    }
  } else {
    cinfo->quantize_colors = FALSE;
    cinfo->two_pass_quantize = TRUE;
  }

  /* select output routines */
  cinfo->methods->output_init = output_init;
  cinfo->methods->put_color_map = put_color_map;
  cinfo->methods->put_pixel_rows = put_pixel_rows;
  cinfo->methods->output_term = output_term;
}


/*
 * OK, here is the main function that actually causes everything to happen.
 * We assume here that the JPEG filename is supplied by the caller of this
 * routine, and that all decompression parameters can be default values.
 * The routine returns 1 if successful, 0 if not.
 */

GLOBAL int
read_JPEG_file (char * filename)
{
  /* These three structs contain JPEG parameters and working data.
   * They must survive for the duration of parameter setup and one
   * call to jpeg_decompress; typically, making them local data in the
   * calling routine is the best strategy.
   */
  struct Decompress_info_struct cinfo;
  struct Decompress_methods_struct dc_methods;
  struct External_methods_struct e_methods;

  /* Select the input and output files.
   * In this example we want to open the input file before doing anything else,
   * so that the setjmp() error recovery below can assume the file is open.
   * Note that cinfo.output_file is only used if your output handling routines
   * use it; otherwise, you can just make it NULL.
   * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
   * requires it in order to read binary files.
   */

  if ((cinfo.input_file = fopen(filename, "rb")) == NULL) {
    fprintf(stderr, "can't open %s\n", filename);
    return 0;
  }

  cinfo.output_file = NULL;    /* if no actual output file involved */

  /* Initialize the system-dependent method pointers. */
  cinfo.methods = &dc_methods;    /* links to method structs */
  cinfo.emethods = &e_methods;
  /* Here we supply our own error handler; compare to use of standard error
   * handler in the previous write_JPEG_file example.
   */
  emethods = &e_methods;    /* save struct addr for possible access */
  e_methods.error_exit = error_exit; /* supply error-exit routine */
  e_methods.trace_message = trace_message; /* supply trace-message routine */
  e_methods.trace_level = 0;    /* default = no tracing */
  e_methods.num_warnings = 0;    /* no warnings emitted yet */
  e_methods.first_warning_level = 0; /* display first corrupt-data warning */
  e_methods.more_warning_level = 3; /* but suppress additional ones */

  /* prepare setjmp context for possible exit from error_exit */
  if (setjmp(setjmp_buffer)) {
    /* If we get here, the JPEG code has signaled an error.
     * Memory allocation has already been cleaned up (see free_all call in
     * error_exit), but we need to close the input file before returning.
     * You might also need to close an output file, etc.
     */
    fclose(cinfo.input_file);
    return 0;
  }

  /* Here we use the standard memory manager provided with the JPEG code.
   * In some cases you might want to replace the memory manager, or at
   * least the system-dependent part of it, with your own code.
   */
  jselmemmgr(&e_methods);    /* select std memory allocation routines */
  /* If the decompressor requires full-image buffers (for two-pass color
   * quantization or a noninterleaved JPEG file), it will create temporary
   * files for anything that doesn't fit within the maximum-memory setting.
   * You can change the default maximum-memory setting by changing
   * e_methods.max_memory_to_use after jselmemmgr returns.
   * On some systems you may also need to set up a signal handler to
   * ensure that temporary files are deleted if the program is interrupted.
   * (This is most important if you are on MS-DOS and use the jmemdos.c
   * memory manager back end; it will try to grab extended memory for
   * temp files, and that space will NOT be freed automatically.)
   * See jcmain.c or jdmain.c for an example signal handler.
   */

  /* Here, set up the pointer to your own routine for post-header-reading
   * parameter selection.  You could also initialize the pointers to the
   * output data handling routines here, if they are not dependent on the
   * image type.
   */
  dc_methods.d_ui_method_selection = d_ui_method_selection;

  /* Set up default decompression parameters. */
  j_d_defaults(&cinfo, TRUE);
  /* TRUE indicates that an input buffer should be allocated.
   * In unusual cases you may want to allocate the input buffer yourself;
   * see jddeflts.c for commentary.
   */

  /* At this point you can modify the default parameters set by j_d_defaults
   * as needed; for example, you can request color quantization or force
   * grayscale output.  See jdmain.c for examples of what you might change.
   */

  /* Set up to read a JFIF or baseline-JPEG file. */
  /* This is the only JPEG file format currently supported. */
  jselrjfif(&cinfo);

  /* Here we go! */
  jpeg_decompress(&cinfo);

  /* That's it, son.  Nothin' else to do, except close files. */
  /* Here we assume only the input file need be closed. */
  fclose(cinfo.input_file);

  /* You might want to test e_methods.num_warnings to see if bad data was
   * detected.  In this example, we just blindly forge ahead.
   */
  return 1;            /* indicate success */

  /* Note: if you want to decompress more than one image, we recommend you
   * repeat this whole routine.  You MUST repeat the j_d_defaults()/alter
   * parameters/jpeg_decompress() sequence, as some data structures allocated
   * in j_d_defaults are freed upon exit from jpeg_decompress.
   */
}