[alpha] Implementing premultiplied alpha, work in progress

Always expand pixels to 16-bit samples when premultiplying.
  In pngconf.h, require PNG_GAMMA_SUPPORTED to be defined when defining
    PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
  Eliminated PNG_DIVIDE_BY_255 and PNG_8_BIT_PREMULTIPLY macros
    leaving only PNG_DIVIDE_BY_65535 and PNG_16_BIT_PREMULTIPLY
    because we will always work with 16 bits.

ANNOUNCE

@@ -1,5 +1,5 @@
 
-Libpng 1.4.1alpha02 - November 28, 2009
+Libpng 1.4.1alpha02 - November 29, 2009
 
 This is not intended to be a public release.  It will be replaced
 within a few weeks by a public version or by another test version.
@@ -29,13 +29,19 @@ Changes since the last public release (1.4.0beta107):
 version 1.4.1alpha01 [November 27, 2009]
   Based on 1.4.0beta107
 
-version 1.4.1alpha02 [November 28, 2009]
+version 1.4.1alpha02 [November 29, 2009]
   Restored premultiplied alpha feature from version 1.4.0beta105.
   Added "double gamma" to parameters for png_set_premultiply_alpha().
   Added "float gamma_premultiply" member to the png_struct.
   Moved PNG_DIVIDE_BY_255, PNG_8_BIT_PREMULTIPLY(), etc., from
     png.h to pngpriv.h
   Updated documentation about png_set_premultiply_alpha().
+  Always expand pixels to 16-bit samples when premultiplying.
+  In pngconf.h, require PNG_GAMMA_SUPPORTED to be defined when defining
+    PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
+  Eliminated PNG_DIVIDE_BY_255 and PNG_8_BIT_PREMULTIPLY macros
+    leaving only PNG_DIVIDE_BY_65535 and PNG_16_BIT_PREMULTIPLY
+    because we will always work with 16 bits.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
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CHANGES

@@ -2411,13 +2411,19 @@ version 1.4.0beta107 [November 27, 2009]
 version 1.4.1alpha01 [November 27, 2009]
   Based on 1.4.0beta107
 
-version 1.4.1alpha02 [November 28, 2009]
+version 1.4.1alpha02 [November 29, 2009]
   Restored premultiplied alpha feature from version 1.4.0beta105.
   Added "double gamma" to parameters for png_set_premultiply_alpha().
   Added "float gamma_premultiply" member to the png_struct.
   Moved PNG_DIVIDE_BY_255, PNG_8_BIT_PREMULTIPLY(), etc., from
     png.h to pngpriv.h
   Updated documentation about png_set_premultiply_alpha().
+  Always expand pixels to 16-bit samples when premultiplying.
+  In pngconf.h, require PNG_GAMMA_SUPPORTED to be defined when defining
+    PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
+  Eliminated PNG_DIVIDE_BY_255 and PNG_8_BIT_PREMULTIPLY macros
+    leaving only PNG_DIVIDE_BY_65535 and PNG_16_BIT_PREMULTIPLY
+    because we will always work with 16 bits.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit

png.h

@@ -1,7 +1,7 @@
 
 /* png.h - header file for PNG reference library
  *
- * libpng version 1.4.1alpha02 - November 28, 2009
+ * libpng version 1.4.1alpha02 - November 29, 2009
  * Copyright (c) 1998-2009 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 1.4.1alpha02 - November 28, 2009: Glenn
+ *  libpng versions 0.97, January 1998, through 1.4.1alpha02 - November 29, 2009: Glenn
  *  See also "Contributing Authors", below.
  *
  * Note about libpng version numbers:
@@ -164,7 +164,7 @@
  *
  * This code is released under the libpng license.
  *
- * libpng versions 1.2.6, August 15, 2004, through 1.4.1alpha02, November 28, 2009, are
+ * libpng versions 1.2.6, August 15, 2004, through 1.4.1alpha02, November 29, 2009, are
  * Copyright (c) 2004, 2006-2007 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:
@@ -340,7 +340,7 @@
 /* Version information for png.h - this should match the version in png.c */
 #define PNG_LIBPNG_VER_STRING "1.4.1alpha02"
 #define PNG_HEADER_VERSION_STRING \
-   " libpng version 1.4.1alpha02 - November 28, 2009\n"
+   " libpng version 1.4.1alpha02 - November 29, 2009\n"
 
 #define PNG_LIBPNG_VER_SONUM   14
 #define PNG_LIBPNG_VER_DLLNUM  14
@@ -1339,7 +1339,7 @@ struct png_struct_def
 
 /* New member added in libpng-1.4.1 */
 #ifdef PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
-   float gamma_premultiply;
+   float gamma_premultiply PNG_DEPSTRUCT;
 #endif
 };
 

pngconf.h

@@ -1,7 +1,7 @@
 
 /* pngconf.h - machine configurable file for libpng
  *
- * libpng version 1.4.1alpha02 - November 28, 2009
+ * libpng version 1.4.1alpha02 - November 29, 2009
  * For conditions of distribution and use, see copyright notice in png.h
  * Copyright (c) 1998-2009 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
@@ -524,7 +524,7 @@
 #    define PNG_READ_INVERT_ALPHA_SUPPORTED
 #  endif
 #  ifndef PNG_NO_READ_PREMULTIPLY_ALPHA
-#      define PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
+#    define PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
 #  endif
 #  ifndef PNG_NO_READ_STRIP_ALPHA
 #    define PNG_READ_STRIP_ALPHA_SUPPORTED
@@ -861,6 +861,13 @@
 #  define PNG_TEXT_SUPPORTED
 #endif
 
+#  /* Premultiply will not work without gamma support. */
+#  ifdef PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
+#    ifndef PNG_READ_GAMMA_SUPPORTED
+#      undef PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
+#    endif
+#  endif
+
 #endif /* PNG_READ_ANCILLARY_CHUNKS_SUPPORTED */
 
 #ifndef PNG_NO_READ_UNKNOWN_CHUNKS

pngrtran.c

@@ -1,7 +1,7 @@
 
 /* pngrtran.c - transforms the data in a row for PNG readers
  *
- * Last changed in libpng 1.4.0 [November 28, 2009]
+ * Last changed in libpng 1.4.0 [November 29, 2009]
  * Copyright (c) 1998-2009 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.)
@@ -151,7 +151,7 @@ png_set_premultiply_alpha(png_structp png_ptr, double gamma)
    png_ptr->transformations |=
      (PNG_PREMULTIPLY_ALPHA | PNG_EXPAND_tRNS);
    png_ptr->transformations |=
-     PNG_EXPAND;  /* This shouldn't be necessary */
+     PNG_EXPAND;
    png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
    /* Check for overflow */
    if (gamma == 0 || gamma > 21474.83)
@@ -902,8 +902,11 @@ png_init_read_transformations(png_structp png_ptr)
       png_ptr->transformations &= ~PNG_GAMMA;
    }
 
-   if ((png_ptr->transformations & (PNG_GAMMA | PNG_RGB_TO_GRAY)) &&
+   if ((png_ptr->transformations & (PNG_GAMMA |
-        png_ptr->gamma != 0.0)
+#ifdef PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
+        PNG_PREMULTIPLY_ALPHA |         
+#endif
+        PNG_RGB_TO_GRAY )) && png_ptr->gamma != 0.0)
    {
       png_build_gamma_table(png_ptr);
 #ifdef PNG_READ_BACKGROUND_SUPPORTED
@@ -1298,6 +1301,11 @@ defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
      }
 #endif
 
+#  ifdef PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
+   if (png_ptr->transformations & PNG_PREMULTIPLY_ALPHA)
+      info_ptr->bit_depth = 16;
+#endif
+
    info_ptr->pixel_depth = (png_byte)(info_ptr->channels *
       info_ptr->bit_depth);
 
@@ -1430,8 +1438,17 @@ png_do_read_transformations(png_structp png_ptr)
 #endif
 
 #ifdef PNG_READ_16_TO_8_SUPPORTED
+#  ifdef PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
+   /* Do this after the PREMULTIPLY operation */
+   if (!(png_ptr->transformations & PNG_PREMULTIPLY_ALPHA))
+   {
+     if (png_ptr->transformations & PNG_16_TO_8)
+        png_do_chop(&(png_ptr->row_info), png_ptr->row_buf + 1);
+   }
+#  else
    if (png_ptr->transformations & PNG_16_TO_8)
       png_do_chop(&(png_ptr->row_info), png_ptr->row_buf + 1);
+#  endif
 #endif
 
 #ifdef PNG_READ_BACKGROUND_SUPPORTED
@@ -1513,9 +1530,30 @@ png_do_read_transformations(png_structp png_ptr)
 #endif
 
 #ifdef PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
+
+  /* TO DO: build 16-bit gamma tables */
+
+  /* TO DO: expand pixels to 16 bits either here or (better) inside
+   * png_do_read_premultiply_alpha
+   */
+
    if (png_ptr->transformations & PNG_PREMULTIPLY_ALPHA)
       png_do_read_premultiply_alpha(&(png_ptr->row_info),
          png_ptr->row_buf + 1);
+
+#  ifdef PNG_READ_16_TO_8_SUPPORTED
+   if (!(png_ptr->transformations & PNG_PREMULTIPLY_ALPHA))
+   {
+     if (png_ptr->transformations & PNG_16_TO_8)
+        png_do_chop(&(png_ptr->row_info), png_ptr->row_buf + 1);
+   }
+#  endif
+
+   /* TO DO: apply png_ptr->gamma_premultiply to the premultiplied
+    * samples, using either the 8-bit or 16-bit gamma table as
+    * appropriate.
+    */
+
 #endif
 
 #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
@@ -2008,30 +2046,17 @@ png_do_read_invert_alpha(png_row_infop row_info, png_bytep row)
 void /* PRIVATE */
 png_do_read_premultiply_alpha(png_row_infop row_info, png_bytep row)
 {
+
+  /* TO DO: expand to 16 bits, then apply gamma
+   * before premultiply
+   */
+
    png_debug(1, "in png_do_read_premultiply_alpha");
 
    {
       png_uint_32 row_width = row_info->width;
       if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
       {
-         /* This premultiplies the pixels with the alpha channel in RGBA */
-         if (row_info->bit_depth == 8)
-         {
-            png_bytep sp = row + row_info->rowbytes;
-            png_bytep dp = sp;
-            png_uint_16 a = 0;
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               a = *(--sp); --dp;
-               sp--; *(--dp) = PNG_8_BIT_PREMULTIPLY((*sp), a);
-               sp--; *(--dp) = PNG_8_BIT_PREMULTIPLY((*sp), a);
-               sp--; *(--dp) = PNG_8_BIT_PREMULTIPLY((*sp), a);
-            }
-         }
-         /* This premultiplies the pixels with the alpha channel in RRGGBBAA */
-         else
          {
             png_uint_16p sp = (png_uint_16p)(row + row_info->rowbytes);
             png_uint_16p dp = sp;
@@ -2049,22 +2074,6 @@ png_do_read_premultiply_alpha(png_row_infop row_info, png_bytep row)
       }
       else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
       {
-         /* This premultiplies the pixels with the alpha channel in GA */
-         if (row_info->bit_depth == 8)
-         {
-            png_bytep sp = row + row_info->rowbytes;
-            png_bytep dp = sp;
-            png_uint_16 a = 0;
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               a = *(--sp); --dp;
-               sp--; *(--dp) = PNG_8_BIT_PREMULTIPLY((*sp), a);
-            }
-         }
-         /* This premultiplies the pixels with the alpha channel in GGAA */
-         else
          {
             png_uint_16p sp  = (png_uint_16p) (row + row_info->rowbytes);
             png_uint_16p dp  = sp;
@@ -3880,6 +3889,24 @@ png_do_expand(png_row_infop row_info, png_bytep row,
          row_info->pixel_depth = (png_byte)(row_info->bit_depth << 2);
          row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
       }
+#ifdef PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
+      if (row_info->bit_depth == 8)
+      {
+         if (row_info->bit_depth == 8)
+         {
+            png_bytep sp = row + (png_size_t)row_width;
+            png_bytep dp =  sp + (png_size_t)row_width;
+            for (i = 1; i < row_width; i++)
+            {
+               *(--dp) = *(--sp);
+               *(--dp) = *(sp);
+            }
+         }
+         row_info->pixel_depth *= 2;
+         row_info->rowbytes *= 2;
+      }
+#endif
+
    }
 }
 #endif