dotCooCoo dd411ec6b4 Image Trace: a JPEG's 8 x 8 blocks no longer trace as staircase steps ...

A JPEG rounds each 8 x 8 block's tone on its own, which leaves a small
step at every block edge. Where a dark ground changes slowly, those steps
decided which of two palette colors a whole block got, and the trace
followed the block edges as a staircase.

The new deblock pass finds the block grid in the image: the mean step
between neighboring opaque pixels must peak at the same one of eight
positions at both block edges of a 16 px span, across and down. Cropped
JPEGs and JPEGs saved in another format are found the same way; pictures
of flat 8 x 8 cells are not. At each block edge, a stretch of eight lines
whose step is under the limit and whose pixels hold no edge has the step
spread over the eight pixels around the edge, as the deblocking filters
of ITU-T H.263 Annex J and MPEG-4 Part 2 Annex F.3.1 do. Larger steps are
kept. The limit, the edge guard and how much of each line's own step is
smoothed depend on the mode: Black and White smooths only the smallest
steps, and traces of more than 16 colors move every line of a stretch
by the same amount. The pass runs before the photo pre-filter and works
in strips of rows, so only its output is as large as the image.

2026-11-13 15:47:30 -08:00

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src

Image Trace: a JPEG's 8 x 8 blocks no longer trace as staircase steps

2026-11-13 15:47:30 -08:00

tests

Fix enhanced_preset Shapes for decorated High Fidelity Photo names

2026-10-31 20:44:04 +07:00

Cargo.toml

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