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add WebPBlendAlpha() function to blend colors against background

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new option: -blend_alpha 0xrrggbb
also: don't force picture.use_argb value for lossless. Instead,
delay the YUVA<->ARGB conversion till WebPEncode() is called.
This make the blending more accurate when source is ARGB
and lossy compression is used (YUVA).
This has an effect on cropping/rescaling. E.g. for PNG, these
are now done in ARGB colorspace instead of YUV when lossy compression
is used.

Change-Id: I18571f1b1179881737a8dbd23ad0aa8cddae3c6b
This commit is contained in:
Pascal Massimino
2013-04-02 19:14:14 -07:00
parent df4a406d8d
commit e7d9548c9b
8 changed files with 121 additions and 6 deletions
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16
examples/cwebp.c
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@ -594,6 +594,10 @@ static void HelpLong(void) {
printf(" -alpha_filter <string> . predictive filtering for alpha plane.\n");
printf(" One of: none, fast (default) or best.\n");
printf(" -alpha_cleanup ......... Clean RGB values in transparent area.\n");
printf(" -blend_alpha <hex> ..... Blend colors against background color\n"
" expressed as RGB values written in\n"
" hexadecimal, e.g. 0xc0e0d0 for red=0xc0\n"
" green=0xe0 and blue=0xd0.\n");
printf(" -noalpha ............... discard any transparency information.\n");
printf(" -lossless .............. Encode image losslessly.\n");
printf(" -hint <string> ......... Specify image characteristics hint.\n");
@ -656,6 +660,8 @@ int main(int argc, const char *argv[]) {
int short_output = 0;
int quiet = 0;
int keep_alpha = 1;
int blend_alpha = 0;
uint32_t background_color = 0xffffffu;
int crop = 0, crop_x = 0, crop_y = 0, crop_w = 0, crop_h = 0;
int resize_w = 0, resize_h = 0;
int show_progress = 0;
@ -720,6 +726,10 @@ int main(int argc, const char *argv[]) {
config.alpha_compression = strtol(argv[++c], NULL, 0);
} else if (!strcmp(argv[c], "-alpha_cleanup")) {
keep_alpha = keep_alpha ? 2 : 0;
} else if (!strcmp(argv[c], "-blend_alpha") && c < argc - 1) {
blend_alpha = 1;
background_color = strtol(argv[++c], NULL, 16); // <- parses '0x' prefix
background_color = background_color & 0x00ffffffu;
} else if (!strcmp(argv[c], "-alpha_filter") && c < argc - 1) {
++c;
if (!strcmp(argv[c], "none")) {
@ -736,7 +746,6 @@ int main(int argc, const char *argv[]) {
keep_alpha = 0;
} else if (!strcmp(argv[c], "-lossless")) {
config.lossless = 1;
picture.use_argb = 1;
} else if (!strcmp(argv[c], "-hint") && c < argc - 1) {
++c;
if (!strcmp(argv[c], "photo")) {
@ -924,6 +933,11 @@ int main(int argc, const char *argv[]) {
goto Error;
}
picture.progress_hook = (show_progress && !quiet) ? ProgressReport : NULL;
if (blend_alpha) {
WebPBlendAlpha(&picture, background_color);
}
if (keep_alpha == 2) {
WebPCleanupTransparentArea(&picture);
}