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LibGfx/JPEG: Simplify loops walking all pixels in all macroblocks
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When we want to walk everything, we can just do a linear walk.

No behavior change.
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@nico
nico committed Jan 14, 2024
1 parent 84366e4 commit 85bb2da
Showing 1 changed file with 29 additions and 57 deletions.
86 changes: 29 additions & 57 deletions Userland/Libraries/LibGfx/ImageFormats/JPEGLoader.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1631,32 +1631,22 @@ static void undo_subsampling(JPEGLoadingContext const& context, Vector<Macrobloc
}
}

static void ycbcr_to_rgb(JPEGLoadingContext const& context, Vector<Macroblock>& macroblocks)
static void ycbcr_to_rgb(Vector<Macroblock>& macroblocks)
{
// Conversion from YCbCr to RGB isn't specified in the first JPEG specification but in the JFIF extension:
// See: https://www.itu.int/rec/dologin_pub.asp?lang=f&id=T-REC-T.871-201105-I!!PDF-E&type=items
// 7 - Conversion to and from RGB
for (u32 vcursor = 0; vcursor < context.mblock_meta.vcount; vcursor += context.sampling_factors.vertical) {
for (u32 hcursor = 0; hcursor < context.mblock_meta.hcount; hcursor += context.sampling_factors.horizontal) {
for (u8 vfactor_i = 0; vfactor_i < context.sampling_factors.vertical; ++vfactor_i) {
for (u8 hfactor_i = 0; hfactor_i < context.sampling_factors.horizontal; ++hfactor_i) {
u32 macroblock_index = (vcursor + vfactor_i) * context.mblock_meta.hpadded_count + (hcursor + hfactor_i);
auto* y = macroblocks[macroblock_index].y;
auto* cb = macroblocks[macroblock_index].cb;
auto* cr = macroblocks[macroblock_index].cr;
for (u8 i = 0; i < 8; ++i) {
for (u8 j = 0; j < 8; ++j) {
u8 const pixel = i * 8 + j;
int r = y[pixel] + 1.402f * (cr[pixel] - 128);
int g = y[pixel] - 0.3441f * (cb[pixel] - 128) - 0.7141f * (cr[pixel] - 128);
int b = y[pixel] + 1.772f * (cb[pixel] - 128);
y[pixel] = clamp(r, 0, 255);
cb[pixel] = clamp(g, 0, 255);
cr[pixel] = clamp(b, 0, 255);
}
}
}
}
for (auto& macroblock : macroblocks) {
auto* y = macroblock.y;
auto* cb = macroblock.cb;
auto* cr = macroblock.cr;
for (u8 i = 0; i < 64; ++i) {
int r = y[i] + 1.402f * (cr[i] - 128);
int g = y[i] - 0.3441f * (cb[i] - 128) - 0.7141f * (cr[i] - 128);
int b = y[i] + 1.772f * (cb[i] - 128);
y[i] = clamp(r, 0, 255);
cb[i] = clamp(g, 0, 255);
cr[i] = clamp(b, 0, 255);
}
}
}
Expand All @@ -1672,21 +1662,12 @@ static void invert_colors_for_adobe_images(JPEGLoadingContext const& context, Ve
// files: 0 represents 100% ink coverage, rather than 0% ink as you'd expect.
// This is arguably a bug in Photoshop, but if you need to work with Photoshop
// CMYK files, you will have to deal with it in your application.
for (u32 vcursor = 0; vcursor < context.mblock_meta.vcount; vcursor += context.sampling_factors.vertical) {
for (u32 hcursor = 0; hcursor < context.mblock_meta.hcount; hcursor += context.sampling_factors.horizontal) {
for (u8 vfactor_i = 0; vfactor_i < context.sampling_factors.vertical; ++vfactor_i) {
for (u8 hfactor_i = 0; hfactor_i < context.sampling_factors.horizontal; ++hfactor_i) {
u32 mb_index = (vcursor + vfactor_i) * context.mblock_meta.hpadded_count + (hcursor + hfactor_i);
for (u8 i = 0; i < 8; ++i) {
for (u8 j = 0; j < 8; ++j) {
macroblocks[mb_index].r[i * 8 + j] = NumericLimits<u8>::max() - macroblocks[mb_index].r[i * 8 + j];
macroblocks[mb_index].g[i * 8 + j] = NumericLimits<u8>::max() - macroblocks[mb_index].g[i * 8 + j];
macroblocks[mb_index].b[i * 8 + j] = NumericLimits<u8>::max() - macroblocks[mb_index].b[i * 8 + j];
macroblocks[mb_index].k[i * 8 + j] = NumericLimits<u8>::max() - macroblocks[mb_index].k[i * 8 + j];
}
}
}
}
for (auto& macroblock : macroblocks) {
for (u8 i = 0; i < 64; ++i) {
macroblock.r[i] = 255 - macroblock.r[i];
macroblock.g[i] = 255 - macroblock.g[i];
macroblock.b[i] = 255 - macroblock.b[i];
macroblock.k[i] = 255 - macroblock.k[i];
}
}
}
Expand All @@ -1710,29 +1691,20 @@ static ErrorOr<void> cmyk_to_rgb(JPEGLoadingContext& context)
return {};
}

static void ycck_to_cmyk(JPEGLoadingContext const& context, Vector<Macroblock>& macroblocks)
static void ycck_to_cmyk(Vector<Macroblock>& macroblocks)
{
// 7 - Conversions between colour encodings
// YCCK is obtained from CMYK by converting the CMY channels to YCC channel.

// To convert back into RGB, we only need the 3 first components, which are baseline YCbCr
ycbcr_to_rgb(context, macroblocks);
ycbcr_to_rgb(macroblocks);

// RGB to CMY, as mentioned in https://www.smcm.iqfr.csic.es/docs/intel/ipp/ipp_manual/IPPI/ippi_ch15/functn_YCCKToCMYK_JPEG.htm#functn_YCCKToCMYK_JPEG
for (u32 vcursor = 0; vcursor < context.mblock_meta.vcount; vcursor += context.sampling_factors.vertical) {
for (u32 hcursor = 0; hcursor < context.mblock_meta.hcount; hcursor += context.sampling_factors.horizontal) {
for (u8 vfactor_i = 0; vfactor_i < context.sampling_factors.vertical; ++vfactor_i) {
for (u8 hfactor_i = 0; hfactor_i < context.sampling_factors.horizontal; ++hfactor_i) {
u32 mb_index = (vcursor + vfactor_i) * context.mblock_meta.hpadded_count + (hcursor + hfactor_i);
for (u8 i = 0; i < 8; ++i) {
for (u8 j = 0; j < 8; ++j) {
macroblocks[mb_index].r[i * 8 + j] = NumericLimits<u8>::max() - macroblocks[mb_index].r[i * 8 + j];
macroblocks[mb_index].g[i * 8 + j] = NumericLimits<u8>::max() - macroblocks[mb_index].g[i * 8 + j];
macroblocks[mb_index].b[i * 8 + j] = NumericLimits<u8>::max() - macroblocks[mb_index].b[i * 8 + j];
}
}
}
}
for (auto& macroblock : macroblocks) {
for (u8 i = 0; i < 64; ++i) {
macroblock.r[i] = 255 - macroblock.r[i];
macroblock.g[i] = 255 - macroblock.g[i];
macroblock.b[i] = 255 - macroblock.b[i];
}
}
}
Expand All @@ -1756,10 +1728,10 @@ static ErrorOr<void> handle_color_transform(JPEGLoadingContext const& context, V
}
break;
case ColorTransform::YCbCr:
ycbcr_to_rgb(context, macroblocks);
ycbcr_to_rgb(macroblocks);
break;
case ColorTransform::YCCK:
ycck_to_cmyk(context, macroblocks);
ycck_to_cmyk(macroblocks);
break;
}

Expand All @@ -1771,13 +1743,13 @@ static ErrorOr<void> handle_color_transform(JPEGLoadingContext const& context, V
// - 3 components means YCbCr
// - 4 components means CMYK (Nothing to do here).
if (context.components.size() == 3)
ycbcr_to_rgb(context, macroblocks);
ycbcr_to_rgb(macroblocks);

if (context.components.size() == 1) {
// With Cb and Cr being equal to zero, this function assign the Y
// value (luminosity) to R, G and B. Providing a proper conversion
// from grayscale to RGB.
ycbcr_to_rgb(context, macroblocks);
ycbcr_to_rgb(macroblocks);
}

return {};
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