Add support for scan optimisation of monochrome pictures

jcapistd.c

@@ -3,6 +3,8 @@
  *
  * Copyright (C) 1994-1996, Thomas G. Lane.
  * This file is part of the Independent JPEG Group's software.
+ * mozjpeg Modifications:
+ * Copyright (C) 2014, Mozilla Corporation.
  * For conditions of distribution and use, see the accompanying README file.
  *
  * This file contains application interface code for the compression half
@@ -43,6 +45,10 @@ jpeg_start_compress (j_compress_ptr cinfo, boolean write_all_tables)
   if (write_all_tables)
     jpeg_suppress_tables(cinfo, FALSE);	/* mark all tables to be written */
 
+  /* setting up scan optimisation pattern failed, disable scan optimisation */
+  if (cinfo->num_scans_luma == 0)
+    cinfo->optimize_scans = FALSE;
+  
   /* (Re)initialize error mgr and destination modules */
   (*cinfo->err->reset_error_mgr) ((j_common_ptr) cinfo);
   (*cinfo->dest->init_destination) (cinfo);

jcmaster.c

@@ -644,7 +644,9 @@ select_scans (j_compress_ptr cinfo, int next_scan_number)
     for (i = 0; i < cinfo->num_scans_luma; i++)
       free(cinfo->scan_buffer[i]);
     
-  } else if (next_scan_number == cinfo->num_scans_luma+cinfo->num_scans_chroma_dc) {
+  } else if (cinfo->num_scans > cinfo->num_scans_luma) {
+    
+    if (next_scan_number == cinfo->num_scans_luma+cinfo->num_scans_chroma_dc) {
       base_scan_idx = cinfo->num_scans_luma;
       
       if (cinfo->scan_size[base_scan_idx] <= cinfo->scan_size[base_scan_idx+1] + cinfo->scan_size[base_scan_idx+2])
@@ -732,6 +734,7 @@ select_scans (j_compress_ptr cinfo, int next_scan_number)
         free(cinfo->scan_buffer[i]);
     }
   }
+}
 
 /*
  * Finish up at end of pass.

jcparam.c

@@ -612,12 +612,15 @@ fill_dc_scans (jpeg_scan_info * scanptr, int ncomps, int Ah, int Al)
  * cinfo->num_components and cinfo->jpeg_color_space must be correct.
  */
 
-LOCAL(void)
+LOCAL(boolean)
 jpeg_search_progression (j_compress_ptr cinfo)
 {
   int ncomps = cinfo->num_components;
   int nscans;
   jpeg_scan_info * scanptr;
+  int Al;
+  int frequency_split[] = { 2, 8, 5, 12, 18 };
+  int i;
   
   /* Safety check to ensure start_compress not called yet. */
   if (cinfo->global_state != CSTATE_START)
@@ -627,19 +630,11 @@ jpeg_search_progression (j_compress_ptr cinfo)
   if (ncomps == 3 && cinfo->jpeg_color_space == JCS_YCbCr) {
     /* Custom script for YCbCr color images. */
     nscans = 64;
+  } else if (ncomps == 1) {
+    nscans = 23;
   } else {
-    /* All-purpose script for other color spaces. */
+    cinfo->num_scans_luma = 0;
-    if (cinfo->use_moz_defaults) {
+    return FALSE;
-      if (ncomps > MAX_COMPS_IN_SCAN)
-        nscans = 5 * ncomps;	/* 2 DC + 4 AC scans per component */
-      else
-        nscans = 1 + 4 * ncomps;	/* 2 DC scans; 4 AC scans per component */
-    } else {
-      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.
@@ -650,7 +645,7 @@ jpeg_search_progression (j_compress_ptr cinfo)
    * 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_size = MAX(nscans, 64);
     cinfo->script_space = (jpeg_scan_info *)
     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
                                 cinfo->script_space_size * SIZEOF(jpeg_scan_info));
@@ -659,15 +654,8 @@ jpeg_search_progression (j_compress_ptr cinfo)
   cinfo->scan_info = scanptr;
   cinfo->num_scans = nscans;
   
-  if (ncomps == 3 && cinfo->jpeg_color_space == JCS_YCbCr) {
-    int Al;
-    int frequency_split[] = { 2, 8, 5, 12, 18 };
-    int i;
-    
   cinfo->Al_max_luma = 3;
-    cinfo->Al_max_chroma = 2;
   cinfo->num_scans_luma_dc = 1;
-    cinfo->num_scans_chroma_dc = 3;
   cinfo->num_frequency_splits = 5;
   cinfo->num_scans_luma = cinfo->num_scans_luma_dc + (3 * cinfo->Al_max_luma + 2) + (2 * cinfo->num_frequency_splits + 1);
   
@@ -697,6 +685,12 @@ jpeg_search_progression (j_compress_ptr cinfo)
     scanptr = fill_a_scan(scanptr, 0, frequency_split[i]+1, 63, 0, 0);
   }
   
+  if (ncomps == 1) {
+    cinfo->Al_max_chroma = 0;
+    cinfo->num_scans_chroma_dc = 0;
+  } else {
+    cinfo->Al_max_chroma = 2;
+    cinfo->num_scans_chroma_dc = 3;
     /* 41 scans for chroma */
     
     /* chroma DC combined */
@@ -726,9 +720,9 @@ jpeg_search_progression (j_compress_ptr cinfo)
       scanptr = fill_a_scan(scanptr, 2, 1, frequency_split[i], 0, 0);
       scanptr = fill_a_scan(scanptr, 2, frequency_split[i]+1, 63, 0, 0);
     }
-  } else {
-    /* TODO */
   }
+  
+  return TRUE;
 }
 
 /*
@@ -740,9 +734,10 @@ GLOBAL(void)
 jpeg_simple_progression (j_compress_ptr cinfo)
 {
   if (cinfo->optimize_scans) {
-    jpeg_search_progression(cinfo);
+    if (jpeg_search_progression(cinfo) == TRUE)
       return;
   }
+  
   int ncomps = cinfo->num_components;
   int nscans;
   jpeg_scan_info * scanptr;