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[alpha] Implementing premultiplied alpha, work in progress

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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.
This commit is contained in:
Glenn Randers-Pehrson
2009-11-28 18:33:19 -06:00
parent 85fbf27733
commit 7aa2927db0
5 changed files with 94 additions and 48 deletions
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103
pngrtran.c
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@@ -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)) &&
png_ptr->gamma != 0.0)
if ((png_ptr->transformations & (PNG_GAMMA |
#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