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LibGfx/TIFF: Add support for images with UnassociatedAlpha

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UnassociatedAlpha is the one used by GIMP when generating TIFF images
with transparency. Support is added for Grayscale and RGB images as it's
the two that we support right now but managing transparency should be
really straightforward for other types as well.
This commit is contained in:
Lucas CHOLLET 2023-12-16 23:05:41 -05:00 committed by Sam Atkins
parent 796ece7b35
commit 2cfca633ca
Notes: sideshowbarker 2024-07-17 03:35:16 +09:00 
Author: https://github.com/LucasChollet
Commit: https://github.com/SerenityOS/serenity/commit/2cfca633ca
Pull-request: https://github.com/SerenityOS/serenity/pull/22375
Reviewed-by: https://github.com/nico ✅
4 changed files with 58 additions and 9 deletions
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24
Tests/LibGfx/TestImageDecoder.cpp
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@ -465,6 +465,30 @@ TEST_CASE(test_tiff_grayscale)
EXPECT_EQ(frame.image->get_pixel(60, 75), Gfx::Color(130, 130, 130));
}
TEST_CASE(test_tiff_grayscale_alpha)
{
auto file = MUST(Core::MappedFile::map(TEST_INPUT("tiff/grayscale_alpha.tiff"sv)));
EXPECT(Gfx::TIFFImageDecoderPlugin::sniff(file->bytes()));
auto plugin_decoder = TRY_OR_FAIL(Gfx::TIFFImageDecoderPlugin::create(file->bytes()));
auto frame = TRY_OR_FAIL(expect_single_frame_of_size(*plugin_decoder, { 400, 300 }));
EXPECT_EQ(frame.image->get_pixel(0, 0).alpha(), 0);
EXPECT_EQ(frame.image->get_pixel(60, 75), Gfx::Color(130, 130, 130));
}
TEST_CASE(test_tiff_rgb_alpha)
{
auto file = MUST(Core::MappedFile::map(TEST_INPUT("tiff/rgb_alpha.tiff"sv)));
EXPECT(Gfx::TIFFImageDecoderPlugin::sniff(file->bytes()));
auto plugin_decoder = TRY_OR_FAIL(Gfx::TIFFImageDecoderPlugin::create(file->bytes()));
auto frame = TRY_OR_FAIL(expect_single_frame_of_size(*plugin_decoder, { 400, 300 }));
EXPECT_EQ(frame.image->get_pixel(0, 0).alpha(), 0);
EXPECT_EQ(frame.image->get_pixel(60, 75), Gfx::Color::NamedColor::Red);
}
TEST_CASE(test_tiff_16_bits)
{
auto file = MUST(Core::MappedFile::map(TEST_INPUT("tiff/16_bits.tiff"sv)));

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Tests/LibGfx/test-inputs/tiff/grayscale_alpha.tiff Normal file
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Tests/LibGfx/test-inputs/tiff/rgb_alpha.tiff Normal file
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41
Userland/Libraries/LibGfx/ImageFormats/TIFFLoader.cpp
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@ -100,6 +100,18 @@ private:
}
}
Optional<u8> alpha_channel_index() const
{
if (m_metadata.extra_samples().has_value()) {
auto const extra_samples = m_metadata.extra_samples().value();
for (u8 i = 0; i < extra_samples.size(); ++i) {
if (extra_samples[i] == ExtraSample::UnassociatedAlpha)
return i + samples_for_photometric_interpretation();
}
}
return OptionalNone {};
}
ErrorOr<Color> read_color(BigEndianInputBitStream& stream)
{
auto bits_per_sample = *m_metadata.bits_per_sample();
@ -107,19 +119,32 @@ private:
// Section 7: Additional Baseline TIFF Requirements
// Some TIFF files may have more components per pixel than you think. A Baseline TIFF reader must skip over
// them gracefully, using the values of the SamplesPerPixel and BitsPerSample fields.
auto discard_unknown_channels = [&]() -> ErrorOr<void> {
auto const unknown_channels = *m_metadata.samples_per_pixel() - samples_for_photometric_interpretation();
for (u8 i = bits_per_sample.size() - unknown_channels; i < bits_per_sample.size(); ++i)
auto manage_extra_channels = [&]() -> ErrorOr<u8> {
// Both unknown and alpha channels are considered as extra channels, so let's iterate over
// them, conserve the alpha value (if any) and discard everything else.
auto const number_base_channels = samples_for_photometric_interpretation();
auto const alpha_index = alpha_channel_index();
Optional<u8> alpha {};
for (u8 i = number_base_channels; i < bits_per_sample.size(); ++i) {
if (alpha_index == i)
alpha = TRY(read_component(stream, bits_per_sample[i]));
else
TRY(read_component(stream, bits_per_sample[i]));
return {};
}
return alpha.value_or(NumericLimits<u8>::max());
};
if (m_metadata.photometric_interpretation() == PhotometricInterpretation::RGB) {
auto const first_component = TRY(read_component(stream, bits_per_sample[0]));
auto const second_component = TRY(read_component(stream, bits_per_sample[1]));
auto const third_component = TRY(read_component(stream, bits_per_sample[2]));
TRY(discard_unknown_channels());
return Color(first_component, second_component, third_component);
auto const alpha = TRY(manage_extra_channels());
return Color(first_component, second_component, third_component, alpha);
}
if (*m_metadata.photometric_interpretation() == PhotometricInterpretation::WhiteIsZero
@ -129,8 +154,8 @@ private:
if (m_metadata.photometric_interpretation() == PhotometricInterpretation::WhiteIsZero)
luminosity = ~luminosity;
TRY(discard_unknown_channels());
return Color(luminosity, luminosity, luminosity);
auto const alpha = TRY(manage_extra_channels());
return Color(luminosity, luminosity, luminosity, alpha);
}
return Error::from_string_literal("Unsupported value for PhotometricInterpretation");