fix(hcg): return chroma/grayness on [0..1] so rgb2hcg round-trips (#250) - #393
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fix(hcg): return chroma/grayness on [0..1] so rgb2hcg round-trips (#250)#393chatman-media wants to merge 2 commits into
chatman-media wants to merge 2 commits into
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rgb2hcg scaled chroma and grayness to [0..100] and computed grayness with a mismatched denominator, while hcg2rgb (and the existing tests) treat both channels as [0..1]. As a result rgb -> hcg -> rgb did not round-trip, notably when all three channels were non-zero (gka#250). Normalize RGB to [0..1], return delta as chroma and min/(1-delta) as grayness (0 when delta is 1, where min is necessarily 0).
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Closes #250.
rgb2hcgreturned chroma and grayness on a[0..100]scale (and computed grayness with a mismatched255 - deltadenominator), whilehcg2rgband the existinghcg2rgbtests treat both channels as[0..1]. Sorgb -> hcg -> rgbdid not round-trip — e.g.rgb2hcg([255,0,0])returned[0, 100, NaN]instead of[0, 1, 0], and the breakage was most visible when all three channels were non-zero.Fix: normalize RGB to
[0..1], returndeltaas chroma andmin / (1 - delta)as grayness (0whendelta === 1, whereminis necessarily0, avoiding a0/0NaN). The new cases are the exact inverse of the existinghcg2rgbtest cases, so the two functions now agree.test/io/rgb2hcg.test.js: per-color conversions + arbitrary-RGB round-trip; fails without the fix (25/28), passes with it