[libpng16] Changed ICC profile support to allow use of an external color

management system (CMS). In practice it is not possible to obtain cHRM
information reliably using just the end-point tags because they do not exist
in the vast majority of profiles.  Instead it is necessary to run the endpoints
through the ICC colorimetric intent transform (as described in the v4
spec).  Since this is likely to be too much code inside libpng for too
little gain (it implies a fairly complete CMS implementation) the code
has been changed to allow an external CMS to be used.  This code is
temporarily disabled until a suitable set of test cases using one or more
external CMS implementations have been implemented.

png.h

@@ -1,7 +1,7 @@
 
 /* png.h - header file for PNG reference library
  *
- * libpng version 1.6.0beta31 - October 24, 2012
+ * libpng version 1.6.0beta31 - October 26, 2012
  * Copyright (c) 1998-2012 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
@@ -11,7 +11,7 @@
  * Authors and maintainers:
  *   libpng versions 0.71, May 1995, through 0.88, January 1996: Guy Schalnat
  *   libpng versions 0.89c, June 1996, through 0.96, May 1997: Andreas Dilger
- *   libpng versions 0.97, January 1998, through 1.6.0beta31 - October 24, 2012: Glenn
+ *   libpng versions 0.97, January 1998, through 1.6.0beta31 - October 26, 2012: Glenn
  *   See also "Contributing Authors", below.
  *
  * Note about libpng version numbers:
@@ -198,7 +198,7 @@
  *
  * This code is released under the libpng license.
  *
- * libpng versions 1.2.6, August 15, 2004, through 1.6.0beta31, October 24, 2012, are
+ * libpng versions 1.2.6, August 15, 2004, through 1.6.0beta31, October 26, 2012, are
  * Copyright (c) 2004, 2006-2012 Glenn Randers-Pehrson, and are
  * distributed according to the same disclaimer and license as libpng-1.2.5
  * with the following individual added to the list of Contributing Authors:
@@ -310,7 +310,7 @@
  * Y2K compliance in libpng:
  * =========================
  *
- *    October 24, 2012
+ *    October 26, 2012
  *
  *    Since the PNG Development group is an ad-hoc body, we can't make
  *    an official declaration.
@@ -378,7 +378,7 @@
 /* Version information for png.h - this should match the version in png.c */
 #define PNG_LIBPNG_VER_STRING "1.6.0beta31"
 #define PNG_HEADER_VERSION_STRING \
-     " libpng version 1.6.0beta31 - October 24, 2012\n"
+     " libpng version 1.6.0beta31 - October 26, 2012\n"
 
 #define PNG_LIBPNG_VER_SONUM   16
 #define PNG_LIBPNG_VER_DLLNUM  16
@@ -3204,6 +3204,90 @@ PNG_EXPORT(242, void, png_set_check_for_invalid_index,
     (png_structrp png_ptr, int allowed));
 #endif
 
+/*******************************************************************************
+ *  CMS (Color Management System) SUPPORT
+ *******************************************************************************
+ *
+ * The PNG file format supports embedding of ICC profiles, however libpng
+ * provides only limited support for handling these profiles.  In particular
+ * libpng includes no support for using the profile to transform data into a
+ * different color space.  If PNG_ICC_SUPPORTED is set, however, libpng allows
+ * an external CMS to be registered into the png_struct after it is created.
+ * This simply records a single callback function to transform samples between
+ * two color spaces.
+ */
+typedef struct png_cms_data *png_cms_datap, * PNG_RESTRICT png_cms_datarp;
+   /* An opaque type defined by a specific implementation to hold whatever data
+    * is required.  The implementation is responsible for all storage management
+    * of this data.
+    */
+
+typedef PNG_CALLBACK(png_uint_32, *png_cms_transform_ptr,
+   (png_const_structrp png_ptr, png_cms_datarp data_ptr, png_const_voidp input,
+   png_alloc_size_t input_bytes, png_voidp output,
+   png_alloc_size_t output_bytes, int format, int intent));
+   /* Transform input[input_bytes] of samples to output[output_bytes].  The
+    * format of the input and output is given by 'format'.  The function shall
+    * transform only so much input as there is space for in the output buffer.
+    * 'intent' is the ICC intent required for the transformation.
+    *
+    * The connection space data (which may be either the input or output) is
+    * always either 16-bit achromatic data (as described in Annex F.2 of the v4
+    * ICC specification) for grayscale PNG files or 16-bit PCSXYZ data for RGB
+    * PNG files.  Any alpha channel may be present in the connection space, in
+    * which case it is a 16-bit channel and the alpha value follows each sample.
+    * Samples are not pre-multiplied by the alpha.  The connection space data
+    * is stored as an array of png_uint_16 values in the native representation
+    * of the machine.
+    *
+    * For transforms to the connection space the input is in the PNG format
+    * using either 8-bit or big-endian 16-bit components.  16-bit quantities use
+    * the PNG layout - big-endian in two bytes.
+    *
+    * By default a transform from the connection space will be to 8-bit sRGB
+    * (with an optional alpha value) or 8-bit gray encoded with the inverse of
+    * the sRGB transfer function.  If png_set_cms_output is called, however, the
+    * transform may produce arbitrary output in a format potentially not handled
+    * by libpng.
+    *
+    * It is valid to register a CMS when writing a PNG image, however the CMS
+    * will only be used to generate appropriate values for cHRM and gAMA of the
+    * profile.
+    *
+    * The format parameter is made up of the following flags:
+    */
+#define PNG_CMS_FORMAT_FLAG_ALPHA 0x01 /* data has alpha channel */
+#define PNG_CMS_FORMAT_FLAG_16BIT 0x02 /* 16-bit image components else 8-bit */
+#define PNG_CMS_FORMAT_FLAG_PCS   0x04 /* input is PCS data, else image data */
+
+#ifdef PNG_ICC_SUPPORTED
+PNG_EXPORT(243, void, png_set_cms, (png_structrp png_ptr,
+   png_cms_datap cms_data_ptr, png_cms_transform_ptr cms_transform_function));
+   /* Register the CMS transform function.  The given pointer will be passed to
+    * every call to the function.
+    */
+
+#ifdef PNG_READ_SUPPORTED
+PNG_EXPORT(244, void, png_set_cms_output, (png_structrp png_ptr,
+   int bytes_per_pixel, int rendering_intent));
+   /* Inform libpng that the transform function will write output requiring
+    * bytes_per_pixel bytes for each sample.  The output need not be in any
+    * particular format, for example the transform could produce a print
+    * separation.  libpng will provide a buffer equal in size to the row width
+    * of the image times the bytes_per_pixel value (and the application must
+    * provide this size buffer.)
+    *
+    * This also forces the CMS transform to be used even when it is apparently
+    * not necessary (e.g. for sRGB input data, or for PNG files with no ICC
+    * profile information and no sRGB data.)  The intent overrides the default,
+    * which is perceptual.
+    */
+#endif
+#endif
+/*******************************************************************************
+ *  END OF CMS (Color Management System) SUPPORT
+ ******************************************************************************/
+
 /* Maintainer: Put new public prototypes here ^, in libpng.3, and project
  * defs
  */
@@ -3213,7 +3297,7 @@ PNG_EXPORT(242, void, png_set_check_for_invalid_index,
  * scripts/symbols.def as well.
  */
 #ifdef PNG_EXPORT_LAST_ORDINAL
-  PNG_EXPORT_LAST_ORDINAL(242);
+  PNG_EXPORT_LAST_ORDINAL(244);
 #endif
 
 #ifdef __cplusplus