Black and White read every pixel as a blend of "black" and "white", and took for those the mean luminance of
the image's black and white pixels. In blurred or scanned line art most black pixels are part paper, so the
mean black was a gray: the middle of every line counted as more than all ink, and by how much changed as the
line crossed the pixel rows, which put a ripple on its edges that the fit then followed with anchors.
- Black is the image's darkest black (the 2nd percentile of its black pixels' luminance).
- White is the lightest pixel within a few pixels of each crack: the paper as it is there. A scan's paper is
darker in one corner than in another, and read against the image's lightest white it counted as part ink.
On each preset's own inputs, all sizes and variants (docs/image-trace-quality.md), before -> after:
- Line Art: 78 -> 46 anchors, outlines 0.093 -> 0.055 px off on average (blurred lines 168 -> 53 anchors,
scanned 199 -> 70); before sub-pixel edges it was 25 anchors and 0.158 px off
- Technical Drawing: 56 -> 46 anchors, 0.092 -> 0.084 px off
- Sketched Art: 0.197 -> 0.186 px off; Default 0.092 -> 0.090; Black and White Logo 0.063 -> 0.059 with
27 -> 29 anchors
Not kept: reading lines up to six pixels deep by their ink's centroid and width, and a looser tolerance for
straight runs, neither of which measured better.
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