Calculate jpeg_simple_progression nscans correctly with respect to dc…

…_scan_opt_mode

jcparam.c

@@ -868,7 +868,13 @@ jpeg_simple_progression (j_compress_ptr cinfo)
  ncomps = cinfo->num_components;
  if (ncomps == 3 && cinfo->jpeg_color_space == JCS_YCbCr) {
  /* Custom script for YCbCr color images. */
- nscans = 10;
+ if (cinfo->master->dc_scan_opt_mode == 0) {
+ nscans = 8; /* 1 DC scan for all components */
+ } else if (cinfo->master->dc_scan_opt_mode == 1) {
+ nscans = 10; /* 1 DC scan for each component */
+ } else {
+ nscans = 9; /* 1 DC scan for luminance and 1 DC scan for chroma */
+ }
  } else {
  /* All-purpose script for other color spaces. */
  if (cinfo->master->compress_profile == JCP_MAX_COMPRESSION) {
@@ -906,14 +912,16 @@ jpeg_simple_progression (j_compress_ptr cinfo)
  if (cinfo->master->compress_profile == JCP_MAX_COMPRESSION) {
  /* scan defined in jpeg_scan_rgb.txt in jpgcrush */
  /* Initial DC scan */
- if (cinfo->master->dc_scan_opt_mode == 0)
+ if (cinfo->master->dc_scan_opt_mode == 0) {
+ /* 1 DC scan for all components */
  scanptr = fill_dc_scans(scanptr, ncomps, 0, 0);
- else if (cinfo->master->dc_scan_opt_mode == 1) {
+ } else if (cinfo->master->dc_scan_opt_mode == 1) {
+ /* 1 DC scan for each component */
  scanptr = fill_a_scan(scanptr, 0, 0, 0, 0, 0);
  scanptr = fill_a_scan(scanptr, 1, 0, 0, 0, 0);
  scanptr = fill_a_scan(scanptr, 2, 0, 0, 0, 0);
- }
- else {
+ } else {
+  /* 1 DC scan for luminance and 1 DC scan for chroma */
  scanptr = fill_dc_scans(scanptr, 1, 0, 0);
  scanptr = fill_a_scan_pair(scanptr, 1, 0, 0, 0, 0);
  }