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// Copyright (c) the JPEG XL Project Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
#include "lib/extras/alpha_blend.h"
#include "lib/extras/packed_image.h"
namespace jxl {
namespace extras {
namespace {
void AlphaBlend(PackedFrame* frame, const float background[3]) {
if (!frame) return;
const PackedImage& im = frame->color;
JxlPixelFormat format = im.format;
if (format.num_channels != 2 && format.num_channels != 4) {
return;
}
--format.num_channels;
JXL_ASSIGN_OR_DIE(PackedImage blended,
PackedImage::Create(im.xsize, im.ysize, format));
// TODO(szabadka) SIMDify this and make it work for float16.
for (size_t y = 0; y < im.ysize; ++y) {
for (size_t x = 0; x < im.xsize; ++x) {
if (format.num_channels == 2) {
float g = im.GetPixelValue(y, x, 0);
float a = im.GetPixelValue(y, x, 1);
float out = g * a + background[0] * (1 - a);
blended.SetPixelValue(y, x, 0, out);
} else {
float r = im.GetPixelValue(y, x, 0);
float g = im.GetPixelValue(y, x, 1);
float b = im.GetPixelValue(y, x, 2);
float a = im.GetPixelValue(y, x, 3);
float out_r = r * a + background[0] * (1 - a);
float out_g = g * a + background[1] * (1 - a);
float out_b = b * a + background[2] * (1 - a);
blended.SetPixelValue(y, x, 0, out_r);
blended.SetPixelValue(y, x, 1, out_g);
blended.SetPixelValue(y, x, 2, out_b);
}
}
}
frame->color = blended.Copy();
}
} // namespace
void AlphaBlend(PackedPixelFile* ppf, const float background[3]) {
if (!ppf || ppf->info.alpha_bits == 0) {
return;
}
ppf->info.alpha_bits = 0;
AlphaBlend(ppf->preview_frame.get(), background);
for (auto& frame : ppf->frames) {
AlphaBlend(&frame, background);
}
}
} // namespace extras
} // namespace jxl
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