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Grayscale fix for Image::premultiply_alpha() and Image::convert(FORMAT_L8) while using REC.709, with added test case

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This commit is contained in:
Kory Postma
2023-05-24 15:00:47 -05:00
parent 2eec9a67d5
commit c8cac39446
2 changed files with 28 additions and 6 deletions
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13
core/io/image.cpp
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@@ -468,7 +468,7 @@ int Image::get_mipmap_count() const {
//using template generates perfectly optimized code due to constant expression reduction and unused variable removal present in all compilers
template <uint32_t read_bytes, bool read_alpha, uint32_t write_bytes, bool write_alpha, bool read_gray, bool write_gray>
static void _convert(int p_width, int p_height, const uint8_t *p_src, uint8_t *p_dst) {
uint32_t max_bytes = MAX(read_bytes, write_bytes);
constexpr uint32_t max_bytes = MAX(read_bytes, write_bytes);
for (int y = 0; y < p_height; y++) {
for (int x = 0; x < p_width; x++) {
@@ -492,8 +492,9 @@ static void _convert(int p_width, int p_height, const uint8_t *p_src, uint8_t *p
}
if constexpr (write_gray) {
//TODO: not correct grayscale, should use fixed point version of actual weights
wofs[0] = uint8_t((uint16_t(rgba[0]) + uint16_t(rgba[1]) + uint16_t(rgba[2])) / 3);
// REC.709
const uint8_t luminance = (13938U * rgba[0] + 46869U * rgba[1] + 4729U * rgba[2] + 32768U) >> 16U;
wofs[0] = luminance;
} else {
for (uint32_t i = 0; i < write_bytes; i++) {
wofs[i] = rgba[i];
@@ -3718,9 +3719,9 @@ void Image::premultiply_alpha() {
for (int j = 0; j < width; j++) {
uint8_t *ptr = &data_ptr[(i * width + j) * 4];
ptr[0] = (uint16_t(ptr[0]) * uint16_t(ptr[3])) >> 8;
ptr[1] = (uint16_t(ptr[1]) * uint16_t(ptr[3])) >> 8;
ptr[2] = (uint16_t(ptr[2]) * uint16_t(ptr[3])) >> 8;
ptr[0] = (uint16_t(ptr[0]) * uint16_t(ptr[3]) + 255U) >> 8;
ptr[1] = (uint16_t(ptr[1]) * uint16_t(ptr[3]) + 255U) >> 8;
ptr[2] = (uint16_t(ptr[2]) * uint16_t(ptr[3]) + 255U) >> 8;
}
}
}