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LibGfx/TIFF: Add support for the differencing predictor
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.
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1 changed files with 34 additions and 1 deletions
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@ -102,6 +102,11 @@ private:
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PackBits = 32773,
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};
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enum class Predictor {
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None = 1,
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HorizontalDifferencing = 2,
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};
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template<typename ByteReader>
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ErrorOr<void> loop_over_pixels(ByteReader&& byte_reader)
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{
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@ -112,8 +117,18 @@ private:
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if (scanline >= static_cast<u32>(m_size.height()))
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break;
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Optional<Color> last_color {};
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for (u32 column = 0; column < static_cast<u32>(m_size.width()); ++column) {
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auto const color = Color { TRY(byte_reader()), TRY(byte_reader()), TRY(byte_reader()) };
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auto color = Color { TRY(byte_reader()), TRY(byte_reader()), TRY(byte_reader()) };
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if (m_predictor == Predictor::HorizontalDifferencing && last_color.has_value()) {
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color.set_red(last_color->red() + color.red());
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color.set_green(last_color->green() + color.green());
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color.set_blue(last_color->blue() + color.blue());
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}
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last_color = color;
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m_bitmap->set_pixel(column, scanline, color);
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}
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}
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@ -528,6 +543,23 @@ private:
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});
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}
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break;
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case 317:
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// Predictor
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if (type != Type::UnsignedShort || count != 1)
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return Error::from_string_literal("TIFFImageDecoderPlugin: Invalid tag 317");
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TRY(value[0].visit(
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[this](u16 const& predictor) -> ErrorOr<void> {
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if (predictor != 1 && predictor != 2)
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return Error::from_string_literal("TIFFImageDecoderPlugin: Invalid predictor value");
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m_predictor = static_cast<Predictor>(predictor);
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return {};
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},
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[&](auto const&) -> ErrorOr<void> {
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VERIFY_NOT_REACHED();
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}));
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break;
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default:
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dbgln_if(TIFF_DEBUG, "Unknown tag: {}", tag);
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}
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@ -545,6 +577,7 @@ private:
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Array<u16, 3> m_bits_per_sample {};
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Compression m_compression {};
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Predictor m_predictor {};
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Vector<u32> m_strip_offsets {};
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u32 m_rows_per_strip {};
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Vector<u32> m_strip_bytes_count {};
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