[wip] low overhead icc for jpeg

third_party/iccjpeg/iccjpeg.c

 /*
  * iccprofile.c
  *
  * This file provides code to read and write International Color Consortium
  * (ICC) device profiles embedded in JFIF JPEG image files.  The ICC has
  * defined a standard format for including such data in JPEG "APP2" markers.
  * The code given here does not know anything about the internal structure
  * of the ICC profile data; it just knows how to put the profile data into
  * a JPEG file being written, or get it back out when reading.
  *
@@ skipping 228 matching lines @@
         *dst_ptr++ = *src_ptr++;
       }
     }
   }
 
   *icc_data_ptr = icc_data;
   *icc_data_len = total_length;
 
   return TRUE;
 }
+
+
+/*
+ * ICCbis color profile: one APP2 marker containing the following data:
+ *  Identifying string  ASCII "ICC_BIS\0"  (8 bytes)
+ *  Profile data (remainder of APP2 data)  (2 bytes) being:
+ *    <id> (1 byte) and a <rendering-intent> (1 byte)
+ *  where <id> is non-zero, <rendering-intent> values are:
+ *  0 Perceptual - for images preferring good adaptation to output device
+ *      gamut at the expense of colorimetric accuracy, such as photographs.
+ *  1 Relative Colorimetric - for images requiring color appearance matching
+ *      (relative to the output device white point), such as logos.
+ *  2 Saturation - for images preferring preservation of saturation at the
+ *      expense of hue and lightness, such as charts and graphs.
+ *  3 Absolute Colorimetric - for images requiring preservation of absolute
+ *      colorimetry, such as previews of images destined for a different
+ *      output device (proofs).
+ * A JPEG image can contain an implicit profile (ICC_BIS marker), or an
+ * explicit profile (ICC_PROFILE markers), but not both.

[Noel Gordon, 2016/04/04 08:37:54]

Another option here might be to allow both markers, but make one trump the other
if both are given.

+ */
+
+#define ICCBIS_OVERHEAD_LENGTH  8  /* length of non-profile data in APP2 */
+#define ICCBIS_PROFILE_LENGTH  2  /* length of profile data in APP2 */
+#define ICCBIS_MARKER ICC_MARKER
+
+
+/*
+ * Write the given ICCbis profile data into a JPEG file.
+ * It *must* be called AFTER calling jpeg_start_compress() and BEFORE
+ * the first call to jpeg_write_scanlines().
+ * (This ordering ensures that the APP2 marker(s) will appear after the
+ * SOI and JFIF or Adobe markers, but before all else.)
+ */
+
+void
+write_icc_profile_bis (j_compress_ptr cinfo,
+       JOCTET profile,
+       JOCTET intent)
+{
+  if (profile) {
+    /* Write the JPEG marker header (APP2 code and marker length) */
+    jpeg_write_m_header(cinfo, ICCBIS_MARKER,
+      (unsigned int) (ICCBIS_OVERHEAD_LENGTH + ICCBIS_PROFILE_LENGTH));
+
+    /* Write the identifier string "ICC_BIS" (null-terminated) */
+    jpeg_write_m_byte(cinfo, 0x49);
+    jpeg_write_m_byte(cinfo, 0x43);
+    jpeg_write_m_byte(cinfo, 0x43);
+    jpeg_write_m_byte(cinfo, 0x5F);
+    jpeg_write_m_byte(cinfo, 0x42);
+    jpeg_write_m_byte(cinfo, 0x49);
+    jpeg_write_m_byte(cinfo, 0x53);
+    jpeg_write_m_byte(cinfo, 0x0);
+
+    /* Write the ICCbis profile info */
+    jpeg_write_m_byte(cinfo, profile);
+    jpeg_write_m_byte(cinfo, intent);
+  }
+}
+
+
+/*
+ * Subroutine to test whether a saved marker is an ICCbis marker.
+ */
+
+static boolean
+marker_is_icc_bis (jpeg_saved_marker_ptr marker)
+{
+  return
+    marker->marker == ICCBIS_MARKER &&
+    marker->data_length >= ICCBIS_OVERHEAD_LENGTH &&
+    /* verify the identifying string */
+    GETJOCTET(marker->data[0]) == 0x49 &&
+    GETJOCTET(marker->data[1]) == 0x43 &&
+    GETJOCTET(marker->data[2]) == 0x43 &&
+    GETJOCTET(marker->data[3]) == 0x5F &&
+    GETJOCTET(marker->data[4]) == 0x42 &&
+    GETJOCTET(marker->data[5]) == 0x49 &&
+    GETJOCTET(marker->data[6]) == 0x53 &&
+    GETJOCTET(marker->data[7]) == 0x0;
+}
+
+
+/*
+ * See if there was an ICCbis profile in the JPEG file being read; the
+ * ICCbis profile is returned (0 for invalid / not found). If found,
+ * write the rendering-intent to *intent (if given).
+ */
+
+unsigned int
+read_icc_profile_bis (j_decompress_ptr cinfo, unsigned int *intent)
+{
+  jpeg_saved_marker_ptr marker;
+  JOCTET FAR *src;
+
+  for (marker = cinfo->marker_list; marker != NULL; marker = marker->next) {
+    /* find ICCbis marker */
+    if (marker_is_icc_bis(marker)) {
+      unsigned int length = marker->data_length - ICCBIS_OVERHEAD_LENGTH;
+      if (length < ICCBIS_PROFILE_LENGTH)
+        return 0;   /* bogus bis profile data length */
+
+      /* return the profile info */
+      src = marker->data + ICCBIS_OVERHEAD_LENGTH;
+      if (intent && GETJOCTET(src[0]))
+        *intent = GETJOCTET(src[1]);

[Noel Gordon, 2016/04/04 08:37:54]

Should we write the following here?

  *intent = GETJOCTET(src[1]) & 3;

+      return GETJOCTET(src[0]);
+    }
+  }
+
+  return 0;
+}