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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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1
examples/pngdec.c
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@ -267,6 +267,7 @@ int ReadPNG(FILE* in_file, WebPPicture* const pic, int keep_alpha,
pic->width = width;
pic->height = height;
pic->use_argb = 1;
ok = has_alpha ? WebPPictureImportRGBA(pic, rgb, stride)
: WebPPictureImportRGB(pic, rgb, stride);
free(rgb);