JpegLoader: Add support for the CMYK color space

Fixes #221 (GitHub).
hpjansson · Oct 11, 2024 · 9530836 · 9530836
1 parent 3145d05
commit 9530836
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Showing 2 changed files with 63 additions and 3 deletions.
diff --git a/tests/data/good/pixel-cmyk.jpeg b/tests/data/good/pixel-cmyk.jpeg
diff --git a/tools/chafa/jpeg-loader.c b/tools/chafa/jpeg-loader.c
@@ -272,6 +272,38 @@ jpeg_loader_new (void)
  return g_new0 (JpegLoader, 1);
 }
 
+static gint
+convert_cmyk_ch_to_rgb (gint k, gint cmy)
+{
+ gint v = k * cmy + 128;
+ v = ((v >> 8) + v) >> 8;
+ return CLAMP (k - v, 0, 255);
+}
+
+static void
+convert_cmyk_pixel_to_rgb (const guchar *cmyk, guchar *rgb)
+{
+ gint c, m, y, k;
+
+ c = cmyk [0];
+ m = cmyk [1];
+ y = cmyk [2];
+ k = cmyk [3];
+
+ rgb [0] = convert_cmyk_ch_to_rgb (k, 255 - c);
+ rgb [1] = convert_cmyk_ch_to_rgb (k, 255 - m);
+ rgb [2] = convert_cmyk_ch_to_rgb (k, 255 - y);
+}
+
+static void
+convert_cmyk_row_to_rgb (const guchar *cmyk, guchar *rgb, gint width)
+{
+ gint i;
+
+ for (i = 0; i < width; i++)
+ convert_cmyk_pixel_to_rgb (cmyk + 4 * i, rgb + 3 * i);
+}
+
 JpegLoader *
 jpeg_loader_new_from_mapping (FileMapping *mapping)
 {
@@ -281,6 +313,8 @@ jpeg_loader_new_from_mapping (FileMapping *mapping)
  struct my_jpeg_error_mgr my_jerr;
  JpegLoader * volatile loader = NULL;
  gpointer frame_data = NULL;
+ volatile gboolean convert_cmyk_to_rgb = FALSE;
+ guchar *cmyk_buf = NULL;
  volatile gboolean have_decompress = FALSE;
  volatile gboolean success = FALSE;
 
@@ -321,7 +355,17 @@ jpeg_loader_new_from_mapping (FileMapping *mapping)
  my_jpeg_mem_src (&cinfo, loader->file_data, loader->file_data_len);
  (void) jpeg_read_header (&cinfo, TRUE);
 
- cinfo.out_color_space = JCS_RGB;
+ if (cinfo.jpeg_color_space == JCS_CMYK
+ || cinfo.jpeg_color_space == JCS_YCCK)
+ {
+ convert_cmyk_to_rgb = TRUE;
+ cinfo.out_color_space = JCS_CMYK;
+ }
+ else
+ {
+ cinfo.out_color_space = JCS_RGB;
+ }
+
  cinfo.output_components = 3;
 
  jpeg_start_decompress (&cinfo);
@@ -339,11 +383,25 @@ jpeg_loader_new_from_mapping (FileMapping *mapping)
 
  /* Decoding loop */
 
+ if (convert_cmyk_to_rgb)
+ cmyk_buf = g_malloc (width * 4);
+
  while (cinfo.output_scanline < height)
  {
  guchar *row_data = ((guchar *) frame_data) + cinfo.output_scanline * rowstride;
- if (jpeg_read_scanlines (&cinfo, &row_data, 1) < 1)
- goto out;
+
+ if (convert_cmyk_to_rgb)
+ {
+ if (jpeg_read_scanlines (&cinfo, &cmyk_buf, 1) < 1)
+ goto out;
+
+ convert_cmyk_row_to_rgb (cmyk_buf, row_data, width);
+ }
+ else
+ {
+ if (jpeg_read_scanlines (&cinfo, &row_data, 1) < 1)
+ goto out;
+ }
  }
 
  /* Orientation and cleanup */
@@ -361,6 +419,8 @@ jpeg_loader_new_from_mapping (FileMapping *mapping)
  success = TRUE;
 
 out:
+ g_free (cmyk_buf);
+
  if (have_decompress)
  jpeg_destroy_decompress (&cinfo);