mirror of
https://github.com/SerenityOS/serenity
synced 2024-10-07 16:40:59 +00:00
69964e10f4
JPEGs can store a `restart_interval`, which controls how many minimum coded units (MCUs) apart the stream state resets. This can be used for error correction, decoding parts of a jpeg in parallel, etc. We tried to use u32 i = vcursor * context.mblock_meta.hpadded_count + hcursor; i % (context.dc_restart_interval * context.sampling_factors.vertical * context.sampling_factors.horizontal) == 0 to check if we hit a multiple of an MCU. `hcursor` is the horizontal offset into 8x8 blocks, vcursor the vertical offset, and hpadded_count stores how many 8x8 blocks we have per row, padded to a multiple of the sampling factor. This isn't quite right if hcursor isn't divisible by both the vertical and horizontal sampling factor. Tweak things so that they work. Also rename `i` to `number_of_mcus_decoded_so_far` since that what it is, at least now. For the test case, I converted an existing image to a ppm: Build/lagom/bin/image -o out.ppm \ Tests/LibGfx/test-inputs/jpg/12-bit.jpg Then I resized it to 102x77px in Photoshop and saved it again. Then I turned it into a jpeg like so: path/to/cjpeg \ -outfile Tests/LibGfx/test-inputs/jpg/odd-restart.jpg \ -sample 2x2,1x1,1x1 -quality 5 -restart 3B out.ppm The trick here is to: a) Pick a size that's not divisible by the data size width (8), and that when rounded to a block size (13) still isn't divisible by the subsample factor -- done by picking a width of 102. b) Pick a huffman table that doesn't happen to contain the bit pattern for a restart marker, so that reading a restart marker from the bitstream as data causes a failure (-quality 5 happens to do this) c) Pick a restart interval where we fail to skip it if our calculation is off (-restart 3B) Together with #22987, fixes #22780. |
||
---|---|---|
.. | ||
test-inputs | ||
BenchmarkGfxPainter.cpp | ||
BenchmarkJPEGLoader.cpp | ||
CMakeLists.txt | ||
TestDeltaE.cpp | ||
TestFontHandling.cpp | ||
TestGfxBitmap.cpp | ||
TestICCProfile.cpp | ||
TestImageDecoder.cpp | ||
TestPainter.cpp | ||
TestParseISOBMFF.cpp | ||
TestRect.cpp | ||
TestScalingFunctions.cpp | ||
TestWOFF.cpp | ||
TestWOFF2.cpp |