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Ensure background is premultiplied when compositing #2858

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Lovell Fuller
2021-08-29 16:40:40 +01:00
parent 2031d7d112
commit 60adc110f5
5 changed files with 51 additions and 17 deletions
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24
src/common.cc
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@@ -759,23 +759,27 @@ namespace sharp {
/*
Convert RGBA value to another colourspace
*/
std::vector<double> GetRgbaAsColourspace(std::vector<double> const rgba, VipsInterpretation const interpretation) {
std::vector<double> GetRgbaAsColourspace(std::vector<double> const rgba,
VipsInterpretation const interpretation, bool premultiply) {
int const bands = static_cast<int>(rgba.size());
if (bands < 3 || interpretation == VIPS_INTERPRETATION_sRGB || interpretation == VIPS_INTERPRETATION_RGB) {
if (bands < 3) {
return rgba;
} else {
VImage pixel = VImage::new_matrix(1, 1);
pixel.set("bands", bands);
pixel = pixel.new_from_image(rgba);
pixel = pixel.colourspace(interpretation, VImage::option()->set("source_space", VIPS_INTERPRETATION_sRGB));
return pixel(0, 0);
}
VImage pixel = VImage::new_matrix(1, 1);
pixel.set("bands", bands);
pixel = pixel
.new_from_image(rgba)
.colourspace(interpretation, VImage::option()->set("source_space", VIPS_INTERPRETATION_sRGB));
if (premultiply) {
pixel = pixel.premultiply();
}
return pixel(0, 0);
}
/*
Apply the alpha channel to a given colour
*/
std::tuple<VImage, std::vector<double>> ApplyAlpha(VImage image, std::vector<double> colour) {
std::tuple<VImage, std::vector<double>> ApplyAlpha(VImage image, std::vector<double> colour, bool premultiply) {
// Scale up 8-bit values to match 16-bit input image
double const multiplier = sharp::Is16Bit(image.interpretation()) ? 256.0 : 1.0;
// Create alphaColour colour
@@ -799,7 +803,7 @@ namespace sharp {
alphaColour.push_back(colour[3] * multiplier);
}
// Ensure alphaColour colour uses correct colourspace
alphaColour = sharp::GetRgbaAsColourspace(alphaColour, image.interpretation());
alphaColour = sharp::GetRgbaAsColourspace(alphaColour, image.interpretation(), premultiply);
// Add non-transparent alpha channel, if required
if (colour[3] < 255.0 && !HasAlpha(image)) {
image = image.bandjoin(