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WebP/Lossy: Clamp negative quantization indices to zero
The spec doesn't talk about this happening in the text, but `dequant_init()` in 20.4 stores `q` in an int and clamps that to 0 later.
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3 changed files with 24 additions and 3 deletions
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@ -404,6 +404,27 @@ TEST_CASE(test_webp_extended_lossy_uncompressed_alpha)
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EXPECT_EQ(frame.image->get_pixel(355, 106), Gfx::Color(0, 0, 0, 0));
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}
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TEST_CASE(test_webp_extended_lossy_negative_quantization_offset)
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{
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auto file = MUST(Core::MappedFile::map(TEST_INPUT("smolkling.webp"sv)));
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EXPECT(Gfx::WebPImageDecoderPlugin::sniff(file->bytes()));
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auto plugin_decoder = MUST(Gfx::WebPImageDecoderPlugin::create(file->bytes()));
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MUST(plugin_decoder->initialize());
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EXPECT_EQ(plugin_decoder->frame_count(), 1u);
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EXPECT(!plugin_decoder->is_animated());
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EXPECT(!plugin_decoder->loop_count());
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EXPECT_EQ(plugin_decoder->size(), Gfx::IntSize(264, 264));
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auto frame = MUST(plugin_decoder->frame(0));
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EXPECT_EQ(frame.image->size(), Gfx::IntSize(264, 264));
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// While VP8 YUV contents are defined bit-exact, the YUV->RGB conversion isn't.
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// So pixels changing by 1 or so below is fine if you change code.
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EXPECT_EQ(frame.image->get_pixel(16, 16), Gfx::Color(0x3c, 0x24, 0x1a, 255));
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}
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TEST_CASE(test_webp_lossy_4)
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{
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// This is https://commons.wikimedia.org/wiki/File:Fr%C3%BChling_bl%C3%BChender_Kirschenbaum.jpg,
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BIN
Tests/LibGfx/test-inputs/smolkling.webp
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BIN
Tests/LibGfx/test-inputs/smolkling.webp
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Binary file not shown.
After Width: | Height: | Size: 27 KiB |
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@ -621,7 +621,7 @@ i16 dequantize_value(i16 value, bool is_dc, QuantizationIndices const& quantizat
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y_ac_base = segmentation.quantizer_update_value[segment_id];
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}
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u8 dequantization_index;
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int dequantization_index;
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if (index.is_y2())
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dequantization_index = y_ac_base + (is_dc ? quantization_indices.y2_dc_delta : quantization_indices.y2_ac_delta);
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else if (index.is_u() || index.is_v())
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@ -631,9 +631,9 @@ i16 dequantize_value(i16 value, bool is_dc, QuantizationIndices const& quantizat
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// clamp index
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if ((index.is_u() || index.is_v()) && is_dc)
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dequantization_index = min(dequantization_index, 117);
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dequantization_index = clamp(dequantization_index, 0, 117);
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else
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dequantization_index = min(dequantization_index, 127);
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dequantization_index = clamp(dequantization_index, 0, 127);
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// "the multiplies are computed and stored using 16-bit signed integers."
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i16 dequantization_factor;
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