jcparam.c

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  /* Use Huffman coding, not arithmetic coding, by default */
  cinfo->arith_code = FALSE;

  /* By default, don't do extra passes to optimize entropy coding */
  cinfo->optimize_coding = FALSE;
  /* The standard Huffman tables are only valid for 8-bit data precision.
   * If the precision is higher, force optimization on so that usable
   * tables will be computed.  This test can be removed if default tables
   * are supplied that are valid for the desired precision.
   */
  if (cinfo->data_precision > 8)
    cinfo->optimize_coding = TRUE;

  /* By default, use the simpler non-cosited sampling alignment */
  cinfo->CCIR601_sampling = FALSE;

  /* No input smoothing */
  cinfo->smoothing_factor = 0;

  /* DCT algorithm preference */
  cinfo->dct_method = JDCT_DEFAULT;

  /* No restart markers */
  cinfo->restart_interval = 0;
  cinfo->restart_in_rows = 0;

  /* Fill in default JFIF marker parameters.  Note that whether the marker
   * will actually be written is determined by jpeg_set_colorspace.
   *
   * By default, the library emits JFIF version code 1.01.
   * An application that wants to emit JFIF 1.02 extension markers should set
   * JFIF_minor_version to 2.  We could probably get away with just defaulting
   * to 1.02, but there may still be some decoders in use that will complain
   * about that; saying 1.01 should minimize compatibility problems.
   */
  cinfo->JFIF_major_version = 1; /* Default JFIF version = 1.01 */
  cinfo->JFIF_minor_version = 1;
  cinfo->density_unit = 0;	/* Pixel size is unknown by default */
  cinfo->X_density = 1;		/* Pixel aspect ratio is square by default */
  cinfo->Y_density = 1;

  /* Choose JPEG colorspace based on input space, set defaults accordingly */

  jpeg_default_colorspace(cinfo);
}


/*
 * Select an appropriate JPEG colorspace for in_color_space.
 */

GLOBAL(void)
jpeg_default_colorspace (j_compress_ptr cinfo)
{
  switch (cinfo->in_color_space) {
  case JCS_GRAYSCALE:
    jpeg_set_colorspace(cinfo, JCS_GRAYSCALE);
    break;
  case JCS_RGB:
    jpeg_set_colorspace(cinfo, JCS_YCbCr);
    break;
  case JCS_YCbCr:
    jpeg_set_colorspace(cinfo, JCS_YCbCr);
    break;
  case JCS_CMYK:
    jpeg_set_colorspace(cinfo, JCS_CMYK); /* By default, no translation */
    break;
  case JCS_YCCK:
    jpeg_set_colorspace(cinfo, JCS_YCCK);
    break;
  case JCS_UNKNOWN:
    jpeg_set_colorspace(cinfo, JCS_UNKNOWN);
    break;
  default:
    ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
  }
}


/*
 * Set the JPEG colorspace, and choose colorspace-dependent default values.
 */

GLOBAL(void)
jpeg_set_colorspace (j_compress_ptr cinfo, J_COLOR_SPACE colorspace)
{
  jpeg_component_info * compptr;
  int ci;

#define SET_COMP(index,id,hsamp,vsamp,quant,dctbl,actbl)  \
  (compptr = &cinfo->comp_info[index], \
   compptr->component_id = (id), \
   compptr->h_samp_factor = (hsamp), \
   compptr->v_samp_factor = (vsamp), \
   compptr->quant_tbl_no = (quant), \
   compptr->dc_tbl_no = (dctbl), \
   compptr->ac_tbl_no = (actbl) )

  /* Safety check to ensure start_compress not called yet. */
  if (cinfo->global_state != CSTATE_START)
    ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);

  /* For all colorspaces, we use Q and Huff tables 0 for luminance components,
   * tables 1 for chrominance components.
   */

  cinfo->jpeg_color_space = colorspace;

  cinfo->write_JFIF_header = FALSE; /* No marker for non-JFIF colorspaces */
  cinfo->write_Adobe_marker = FALSE; /* write no Adobe marker by default */

  switch (colorspace) {
  case JCS_GRAYSCALE:
    cinfo->write_JFIF_header = TRUE; /* Write a JFIF marker */
    cinfo->num_components = 1;
    /* JFIF specifies component ID 1 */
    SET_COMP(0, 1, 1,1, 0, 0,0);
    break;
  case JCS_RGB:
    cinfo->write_Adobe_marker = TRUE; /* write Adobe marker to flag RGB */
    cinfo->num_components = 3;
    SET_COMP(0, 0x52 /* 'R' */, 1,1, 0, 0,0);
    SET_COMP(1, 0x47 /* 'G' */, 1,1, 0, 0,0);
    SET_COMP(2, 0x42 /* 'B' */, 1,1, 0, 0,0);
    break;
  case JCS_YCbCr:
    cinfo->write_JFIF_header = TRUE; /* Write a JFIF marker */
    cinfo->num_components = 3;
    /* JFIF specifies component IDs 1,2,3 */
    /* We default to 2x2 subsamples of chrominance */
    SET_COMP(0, 1, 2,2, 0, 0,0);
    SET_COMP(1, 2, 1,1, 1, 1,1);
    SET_COMP(2, 3, 1,1, 1, 1,1);
    break;
  case JCS_CMYK:
    cinfo->write_Adobe_marker = TRUE; /* write Adobe marker to flag CMYK */
    cinfo->num_components = 4;
    SET_COMP(0, 0x43 /* 'C' */, 1,1, 0, 0,0);
    SET_COMP(1, 0x4D /* 'M' */, 1,1, 0, 0,0);
    SET_COMP(2, 0x59 /* 'Y' */, 1,1, 0, 0,0);
    SET_COMP(3, 0x4B /* 'K' */, 1,1, 0, 0,0);
    break;
  case JCS_YCCK:
    cinfo->write_Adobe_marker = TRUE; /* write Adobe marker to flag YCCK */
    cinfo->num_components = 4;
    SET_COMP(0, 1, 2,2, 0, 0,0);
    SET_COMP(1, 2, 1,1, 1, 1,1);
    SET_COMP(2, 3, 1,1, 1, 1,1);
    SET_COMP(3, 4, 2,2, 0, 0,0);
    break;
  case JCS_UNKNOWN:
    cinfo->num_components = cinfo->input_components;
    if (cinfo->num_components < 1 || cinfo->num_components > MAX_COMPONENTS)
      ERREXIT2(cinfo, JERR_COMPONENT_COUNT, cinfo->num_components,
	       MAX_COMPONENTS);
    for (ci = 0; ci < cinfo->num_components; ci++) {
      SET_COMP(ci, ci, 1,1, 0, 0,0);
    }
    break;
  default:
    ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
  }
}


#ifdef C_PROGRESSIVE_SUPPORTED

LOCAL(jpeg_scan_info *)
fill_a_scan (jpeg_scan_info * scanptr, int ci,
	     int Ss, int Se, int Ah, int Al)
/* Support routine: generate one scan for specified component */
{
  scanptr->comps_in_scan = 1;
  scanptr->component_index[0] = ci;
  scanptr->Ss = Ss;
  scanptr->Se = Se;
  scanptr->Ah = Ah;
  scanptr->Al = Al;
  scanptr++;
  return scanptr;
}

LOCAL(jpeg_scan_info *)
fill_scans (jpeg_scan_info * scanptr, int ncomps,
	    int Ss, int Se, int Ah, int Al)
/* Support routine: generate one scan for each component */
{
  int ci;

  for (ci = 0; ci < ncomps; ci++) {
    scanptr->comps_in_scan = 1;
    scanptr->component_index[0] = ci;
    scanptr->Ss = Ss;
    scanptr->Se = Se;
    scanptr->Ah = Ah;
    scanptr->Al = Al;
    scanptr++;
  }
  return scanptr;
}

LOCAL(jpeg_scan_info *)
fill_dc_scans (jpeg_scan_info * scanptr, int ncomps, int Ah, int Al)
/* Support routine: generate interleaved DC scan if possible, else N scans */
{
  int ci;

  if (ncomps <= MAX_COMPS_IN_SCAN) {
    /* Single interleaved DC scan */
    scanptr->comps_in_scan = ncomps;
    for (ci = 0; ci < ncomps; ci++)
      scanptr->component_index[ci] = ci;
    scanptr->Ss = scanptr->Se = 0;
    scanptr->Ah = Ah;
    scanptr->Al = Al;
    scanptr++;
  } else {
    /* Noninterleaved DC scan for each component */
    scanptr = fill_scans(scanptr, ncomps, 0, 0, Ah, Al);
  }
  return scanptr;
}


/*
 * Create a recommended progressive-JPEG script.
 * cinfo->num_components and cinfo->jpeg_color_space must be correct.
 */

GLOBAL(void)
jpeg_simple_progression (j_compress_ptr cinfo)
{
  int ncomps = cinfo->num_components;
  int nscans;
  jpeg_scan_info * scanptr;

  /* Safety check to ensure start_compress not called yet. */
  if (cinfo->global_state != CSTATE_START)
    ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);

  /* Figure space needed for script.  Calculation must match code below! */
  if (ncomps == 3 && cinfo->jpeg_color_space == JCS_YCbCr) {
    /* Custom script for YCbCr color images. */
    nscans = 10;
  } else {
    /* All-purpose script for other color spaces. */
    if (ncomps > MAX_COMPS_IN_SCAN)
      nscans = 6 * ncomps;	/* 2 DC + 4 AC scans per component */
    else
      nscans = 2 + 4 * ncomps;	/* 2 DC scans; 4 AC scans per component */
  }

  /* Allocate space for script.
   * We need to put it in the permanent pool in case the application performs
   * multiple compressions without changing the settings.  To avoid a memory
   * leak if jpeg_simple_progression is called repeatedly for the same JPEG
   * object, we try to re-use previously allocated space, and we allocate
   * enough space to handle YCbCr even if initially asked for grayscale.
   */
  if (cinfo->script_space == NULL || cinfo->script_space_size < nscans) {
    cinfo->script_space_size = MAX(nscans, 10);
    cinfo->script_space = (jpeg_scan_info *)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
			cinfo->script_space_size * SIZEOF(jpeg_scan_info));
  }
  scanptr = cinfo->script_space;
  cinfo->scan_info = scanptr;
  cinfo->num_scans = nscans;

  if (ncomps == 3 && cinfo->jpeg_color_space == JCS_YCbCr) {
    /* Custom script for YCbCr color images. */
    /* Initial DC scan */
    scanptr = fill_dc_scans(scanptr, ncomps, 0, 1);
    /* Initial AC scan: get some luma data out in a hurry */
    scanptr = fill_a_scan(scanptr, 0, 1, 5, 0, 2);
    /* Chroma data is too small to be worth expending many scans on */
    scanptr = fill_a_scan(scanptr, 2, 1, 63, 0, 1);
    scanptr = fill_a_scan(scanptr, 1, 1, 63, 0, 1);
    /* Complete spectral selection for luma AC */
    scanptr = fill_a_scan(scanptr, 0, 6, 63, 0, 2);
    /* Refine next bit of luma AC */
    scanptr = fill_a_scan(scanptr, 0, 1, 63, 2, 1);
    /* Finish DC successive approximation */
    scanptr = fill_dc_scans(scanptr, ncomps, 1, 0);
    /* Finish AC successive approximation */
    scanptr = fill_a_scan(scanptr, 2, 1, 63, 1, 0);
    scanptr = fill_a_scan(scanptr, 1, 1, 63, 1, 0);
    /* Luma bottom bit comes last since it's usually largest scan */
    scanptr = fill_a_scan(scanptr, 0, 1, 63, 1, 0);
  } else {
    /* All-purpose script for other color spaces. */
    /* Successive approximation first pass */
    scanptr = fill_dc_scans(scanptr, ncomps, 0, 1);
    scanptr = fill_scans(scanptr, ncomps, 1, 5, 0, 2);
    scanptr = fill_scans(scanptr, ncomps, 6, 63, 0, 2);
    /* Successive approximation second pass */
    scanptr = fill_scans(scanptr, ncomps, 1, 63, 2, 1);
    /* Successive approximation final pass */
    scanptr = fill_dc_scans(scanptr, ncomps, 1, 0);
    scanptr = fill_scans(scanptr, ncomps, 1, 63, 1, 0);
  }
}

#endif /* C_PROGRESSIVE_SUPPORTED */