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LibGfx/TIFF: Add support for the differencing predictor

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The differencing predictor is a different way to encode pixels in TIFF
images. Every pixel is encoded as a difference with the previous column
of the image, except the first column, obviously.

This parameter is materialized by a new tag for which reading was also
implemented.
This commit is contained in:
Lucas CHOLLET 2023-11-04 22:47:24 -04:00 • committed by Andreas Kling
parent 86ee7d219e
commit 4f5a0227e2
1 changed files with 34 additions and 1 deletions
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35
Userland/Libraries/LibGfx/ImageFormats/TIFFLoader.cpp
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@ -102,6 +102,11 @@ private:
PackBits = 32773,
};
enum class Predictor {
None = 1,
HorizontalDifferencing = 2,
};
template<typename ByteReader>
ErrorOr<void> loop_over_pixels(ByteReader&& byte_reader)
{
@ -112,8 +117,18 @@ private:
if (scanline >= static_cast<u32>(m_size.height()))
break;
Optional<Color> last_color {};
for (u32 column = 0; column < static_cast<u32>(m_size.width()); ++column) {
auto const color = Color { TRY(byte_reader()), TRY(byte_reader()), TRY(byte_reader()) };
auto color = Color { TRY(byte_reader()), TRY(byte_reader()), TRY(byte_reader()) };
if (m_predictor == Predictor::HorizontalDifferencing && last_color.has_value()) {
color.set_red(last_color->red() + color.red());
color.set_green(last_color->green() + color.green());
color.set_blue(last_color->blue() + color.blue());
}
last_color = color;
m_bitmap->set_pixel(column, scanline, color);
}
}
@ -528,6 +543,23 @@ private:
});
}
break;
case 317:
// Predictor
if (type != Type::UnsignedShort || count != 1)
return Error::from_string_literal("TIFFImageDecoderPlugin: Invalid tag 317");
TRY(value[0].visit(
[this](u16 const& predictor) -> ErrorOr<void> {
if (predictor != 1 && predictor != 2)
return Error::from_string_literal("TIFFImageDecoderPlugin: Invalid predictor value");
m_predictor = static_cast<Predictor>(predictor);
return {};
},
[&](auto const&) -> ErrorOr<void> {
VERIFY_NOT_REACHED();
}));
break;
default:
dbgln_if(TIFF_DEBUG, "Unknown tag: {}", tag);
}
@ -545,6 +577,7 @@ private:
Array<u16, 3> m_bits_per_sample {};
Compression m_compression {};
Predictor m_predictor {};
Vector<u32> m_strip_offsets {};
u32 m_rows_per_strip {};
Vector<u32> m_strip_bytes_count {};