Further partial image decompression fixes

- Referring to 073b0e8 and #185, the
  reason why BMP and RLE didn't (and won't) work with partial image
  decompression is that the output engines for both formats maintain a
  whole-image buffer, which is used to reverse the order of scanlines.
  However, it was straightforward to add -crop support for GIF and
  Targa, which is useful for testing partial image decompression along
  with color quantization.
- Such testing reproduced a bug reported by Mozilla (refer to PR #182)
  whereby jpeg_skip_scanlines() would segfault if color quantization was
  enabled.  To fix this issue, read_and_discard_scanlines() now sets up
  a dummy quantize function in the same manner that it sets up a dummy
  color conversion function.

Closes #182

ChangeLog.md

@@ -10,9 +10,16 @@ image planes and allocates memory for the image planes.
 2. Fixed an issue whereby the Java version of TJUnitTest would fail when
 testing BufferedImage encoding/decoding on big endian systems.
 
-3. djpeg will now exit gracefully if an output image format other than PPM/PGM
-is selected along with the `-crop` option.  That option does not currently work
-with other output image formats.
+3. Fixed a segfault in djpeg that would occur if an output format other than
+PPM/PGM was selected along with the `-crop` option.  The `-crop` option now
+works with the GIF and Targa formats as well (unfortunately, it cannot be made
+to work with the BMP and RLE formats due to the fact that those output engines
+write scanlines in bottom-up order.)  djpeg will now exit gracefully if an
+output format other than PPM/PGM, GIF, or Targa is selected along with the
+`-crop` option.
+
+4. Fixed an issue whereby `jpeg_skip_scanlines()` would segfault if color
+quantization was enabled.
 
 4. TJBench (both C and Java versions) will now display usage information if any
 command-line argument is unrecognized.  This prevents the program from silently

cdjpeg.h

@@ -3,8 +3,8 @@
  *
  * This file was part of the Independent JPEG Group's software:
  * Copyright (C) 1994-1997, Thomas G. Lane.
- * It was modified by The libjpeg-turbo Project to include only code relevant
- * to libjpeg-turbo.
+ * libjpeg-turbo Modifications:
+ * Copyright (C) 2017, D. R. Commander.
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
  *
@@ -54,6 +54,14 @@ struct djpeg_dest_struct {
                           JDIMENSION rows_supplied);
   /* Finish up at the end of the image. */
   void (*finish_output) (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo);
+  /* Re-calculate buffer dimensions based on output dimensions (for use with
+     partial image decompression.)  If this is NULL, then the output format
+     does not support partial image decompression (BMP and RLE, in particular,
+     cannot support partial decompression because they use an inversion buffer
+     to write the image in bottom-up order.) */
+  void (*calc_buffer_dimensions) (j_decompress_ptr cinfo,
+                                  djpeg_dest_ptr dinfo);
+
 
   /* Target file spec; filled in by djpeg.c after object is created. */
   FILE *output_file;

djpeg.1

@@ -1,4 +1,4 @@
-.TH DJPEG 1 "8 November 2017"
+.TH DJPEG 1 "13 November 2017"
 .SH NAME
 djpeg \- decompress a JPEG file to an image file
 .SH SYNOPSIS
@@ -205,7 +205,7 @@ with width W and height H.  If necessary, X will be shifted left to the nearest
 iMCU boundary, and the width will be increased accordingly.  Note that if
 decompression scaling is being used, then X, Y, W, and H are relative to the
 scaled image dimensions.  Currently this option only works with the
-PBMPLUS (PPM/PGM) output format.
+PBMPLUS (PPM/PGM), GIF, and Targa output formats.
 .TP
 .B \-verbose
 Enable debug printout.  More

djpeg.c

@@ -31,7 +31,6 @@
 #include "cdjpeg.h"             /* Common decls for cjpeg/djpeg applications */
 #include "jversion.h"           /* for version message */
 #include "jconfigint.h"
-#include "wrppm.h"
 
 #include <ctype.h>              /* to declare isprint() */
 
@@ -173,7 +172,7 @@ usage (void)
 
   fprintf(stderr, "  -skip Y0,Y1    Decompress all rows except those between Y0 and Y1 (inclusive)\n");
   fprintf(stderr, "  -crop WxH+X+Y  Decompress only a rectangular subregion of the image\n");
-  fprintf(stderr, "                 [requires PBMPLUS (PPM/PGM) output format]\n");
+  fprintf(stderr, "                 [requires PBMPLUS (PPM/PGM), GIF, or Targa output format]\n");
   fprintf(stderr, "  -verbose  or  -debug   Emit debug output\n");
   fprintf(stderr, "  -version       Print version information and exit\n");
   exit(EXIT_FAILURE);
@@ -714,11 +713,10 @@ main (int argc, char **argv)
     }
 
     jpeg_crop_scanline(&cinfo, &crop_x, &crop_width);
-    if (requested_fmt != FMT_PPM)
+    if (dest_mgr->calc_buffer_dimensions)
+      (*dest_mgr->calc_buffer_dimensions) (&cinfo, dest_mgr);
+    else
       ERREXIT(&cinfo, JERR_UNSUPPORTED_FORMAT);
-    ((ppm_dest_ptr) dest_mgr)->buffer_width = cinfo.output_width *
-                                              cinfo.out_color_components *
-                                              sizeof(JSAMPLE);
 
     /* Write output file header.  This is a hack to ensure that the destination
      * manager creates an output image of the proper size.

jdapistd.c

@@ -4,7 +4,7 @@
  * This file was part of the Independent JPEG Group's software:
  * Copyright (C) 1994-1996, Thomas G. Lane.
  * libjpeg-turbo Modifications:
- * Copyright (C) 2010, 2015-2016, D. R. Commander.
+ * Copyright (C) 2010, 2015-2017, D. R. Commander.
  * Copyright (C) 2015, Google, Inc.
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
@@ -293,6 +293,14 @@ noop_convert (j_decompress_ptr cinfo, JSAMPIMAGE input_buf,
 }
 
 
+/* Dummy quantize function used by jpeg_skip_scanlines() */
+LOCAL(void)
+noop_quantize (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
+               JSAMPARRAY output_buf, int num_rows)
+{
+}
+
+
 /*
  * In some cases, it is best to call jpeg_read_scanlines() and discard the
  * output, rather than skipping the scanlines, because this allows us to
@@ -308,14 +316,22 @@ read_and_discard_scanlines (j_decompress_ptr cinfo, JDIMENSION num_lines)
   void (*color_convert) (j_decompress_ptr cinfo, JSAMPIMAGE input_buf,
                          JDIMENSION input_row, JSAMPARRAY output_buf,
                          int num_rows);
+  void (*color_quantize) (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
+                          JSAMPARRAY output_buf, int num_rows) = NULL;
 
   color_convert = cinfo->cconvert->color_convert;
   cinfo->cconvert->color_convert = noop_convert;
+  if (cinfo->cquantize && cinfo->cquantize->color_quantize) {
+    color_quantize = cinfo->cquantize->color_quantize;
+    cinfo->cquantize->color_quantize = noop_quantize;
+  }
 
   for (n = 0; n < num_lines; n++)
     jpeg_read_scanlines(cinfo, NULL, 1);
 
   cinfo->cconvert->color_convert = color_convert;
+  if (color_quantize)
+    cinfo->cquantize->color_quantize = color_quantize;
 }
 
 

wrbmp.c

@@ -5,7 +5,7 @@
  * Copyright (C) 1994-1996, Thomas G. Lane.
  * libjpeg-turbo Modifications:
  * Copyright (C) 2013, Linaro Limited.
- * Copyright (C) 2014-2015, D. R. Commander.
+ * Copyright (C) 2014-2015, 2017, D. R. Commander.
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
  *
@@ -437,6 +437,7 @@ jinit_write_bmp (j_decompress_ptr cinfo, boolean is_os2)
                                   sizeof(bmp_dest_struct));
   dest->pub.start_output = start_output_bmp;
   dest->pub.finish_output = finish_output_bmp;
+  dest->pub.calc_buffer_dimensions = NULL;
   dest->is_os2 = is_os2;
 
   if (cinfo->out_color_space == JCS_GRAYSCALE) {

wrgif.c

@@ -4,7 +4,7 @@
  * This file was part of the Independent JPEG Group's software:
  * Copyright (C) 1991-1997, Thomas G. Lane.
  * libjpeg-turbo Modifications:
- * Copyright (C) 2015, D. R. Commander.
+ * Copyright (C) 2015, 2017, D. R. Commander.
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
  *
@@ -355,6 +355,16 @@ finish_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
 }
 
 
+/*
+ * Re-calculate buffer dimensions based on output dimensions.
+ */
+
+METHODDEF(void)
+calc_buffer_dimensions_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
+{
+}
+
+
 /*
  * The module selection routine for GIF format output.
  */
@@ -372,6 +382,7 @@ jinit_write_gif (j_decompress_ptr cinfo)
   dest->pub.start_output = start_output_gif;
   dest->pub.put_pixel_rows = put_pixel_rows;
   dest->pub.finish_output = finish_output_gif;
+  dest->pub.calc_buffer_dimensions = calc_buffer_dimensions_gif;
 
   if (cinfo->out_color_space != JCS_GRAYSCALE &&
       cinfo->out_color_space != JCS_RGB)

wrppm.c

@@ -4,8 +4,8 @@
  * This file was part of the Independent JPEG Group's software:
  * Copyright (C) 1991-1996, Thomas G. Lane.
  * Modified 2009 by Guido Vollbeding.
- * It was modified by The libjpeg-turbo Project to include only code and
- * information relevant to libjpeg-turbo.
+ * libjpeg-turbo Modifications:
+ * Copyright (C) 2017, D. R. Commander.
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
  *
@@ -20,7 +20,6 @@
  */
 
 #include "cdjpeg.h"             /* Common decls for cjpeg/djpeg applications */
-#include "wrppm.h"
 
 #ifdef PPM_SUPPORTED
 
@@ -63,6 +62,21 @@
  */
 
 
+/* Private version of data destination object */
+
+typedef struct {
+  struct djpeg_dest_struct pub; /* public fields */
+
+  /* Usually these two pointers point to the same place: */
+  char *iobuffer;               /* fwrite's I/O buffer */
+  JSAMPROW pixrow;              /* decompressor output buffer */
+  size_t buffer_width;          /* width of I/O buffer */
+  JDIMENSION samples_per_row;   /* JSAMPLEs per output row */
+} ppm_dest_struct;
+
+typedef ppm_dest_struct *ppm_dest_ptr;
+
+
 /*
  * Write some pixel data.
  * In this module rows_supplied will always be 1.
@@ -196,6 +210,20 @@ finish_output_ppm (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
 }
 
 
+/*
+ * Re-calculate buffer dimensions based on output dimensions.
+ */
+
+METHODDEF(void)
+calc_buffer_dimensions_ppm (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
+{
+  ppm_dest_ptr dest = (ppm_dest_ptr) dinfo;
+
+  dest->samples_per_row = cinfo->output_width * cinfo->out_color_components;
+  dest->buffer_width = dest->samples_per_row * (BYTESPERSAMPLE * sizeof(char));
+}
+
+
 /*
  * The module selection routine for PPM format output.
  */
@@ -211,13 +239,13 @@ jinit_write_ppm (j_decompress_ptr cinfo)
                                   sizeof(ppm_dest_struct));
   dest->pub.start_output = start_output_ppm;
   dest->pub.finish_output = finish_output_ppm;
+  dest->pub.calc_buffer_dimensions = calc_buffer_dimensions_ppm;
 
   /* Calculate output image dimensions so we can allocate space */
   jpeg_calc_output_dimensions(cinfo);
 
   /* Create physical I/O buffer */
-  dest->samples_per_row = cinfo->output_width * cinfo->out_color_components;
-  dest->buffer_width = dest->samples_per_row * (BYTESPERSAMPLE * sizeof(char));
+  dest->pub.calc_buffer_dimensions (cinfo, (djpeg_dest_ptr) dest);
   dest->iobuffer = (char *) (*cinfo->mem->alloc_small)
     ((j_common_ptr) cinfo, JPOOL_IMAGE, dest->buffer_width);
 

wrrle.c

@@ -3,8 +3,8 @@
  *
  * This file was part of the Independent JPEG Group's software:
  * Copyright (C) 1991-1996, Thomas G. Lane.
- * It was modified by The libjpeg-turbo Project to include only code and
- * information relevant to libjpeg-turbo.
+ * libjpeg-turbo Modifications:
+ * Copyright (C) 2017, D. R. Commander.
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
  *
@@ -286,6 +286,7 @@ jinit_write_rle (j_decompress_ptr cinfo)
                                   sizeof(rle_dest_struct));
   dest->pub.start_output = start_output_rle;
   dest->pub.finish_output = finish_output_rle;
+  dest->pub.calc_buffer_dimensions = NULL;
 
   /* Calculate output image dimensions so we can allocate space */
   jpeg_calc_output_dimensions(cinfo);

wrtarga.c

@@ -3,8 +3,8 @@
  *
  * This file was part of the Independent JPEG Group's software:
  * Copyright (C) 1991-1996, Thomas G. Lane.
- * It was modified by The libjpeg-turbo Project to include only code and
- * information relevant to libjpeg-turbo.
+ * libjpeg-turbo Modifications:
+ * Copyright (C) 2017, D. R. Commander.
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
  *
@@ -211,6 +211,19 @@ finish_output_tga (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
 }
 
 
+/*
+ * Re-calculate buffer dimensions based on output dimensions.
+ */
+
+METHODDEF(void)
+calc_buffer_dimensions_tga (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
+{
+  tga_dest_ptr dest = (tga_dest_ptr) dinfo;
+
+  dest->buffer_width = cinfo->output_width * cinfo->output_components;
+}
+
+
 /*
  * The module selection routine for Targa format output.
  */
@@ -226,12 +239,13 @@ jinit_write_targa (j_decompress_ptr cinfo)
                                   sizeof(tga_dest_struct));
   dest->pub.start_output = start_output_tga;
   dest->pub.finish_output = finish_output_tga;
+  dest->pub.calc_buffer_dimensions = calc_buffer_dimensions_tga;
 
   /* Calculate output image dimensions so we can allocate space */
   jpeg_calc_output_dimensions(cinfo);
 
   /* Create I/O buffer. */
-  dest->buffer_width = cinfo->output_width * cinfo->output_components;
+  dest->pub.calc_buffer_dimensions (cinfo, (djpeg_dest_ptr) dest);
   dest->iobuffer = (char *)
     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
                                 (size_t) (dest->buffer_width * sizeof(char)));