AHD chose the horizontal or the vertical candidate outright by the larger 3×3 homogeneity sum. In a flat, noisy
area noise alone decides which is larger, so the picture became short horizontal and vertical strokes (a maze,
orange and blue under strong white balance) that noise reduction then made stand out. It now blends the two
linearly while their sums are within 12 of each other (of 36), and takes one alone beyond that.
On an ISO 4000 ILCE-7CM2 ARW under tungsten light the maze measure of a flat region drops ~30 %; PSNR on the
synthetic smooth and edge scenes is unchanged or better (73.0 → 73.7 dB, 37.7 → 37.9 dB). The colour part of the
pattern mostly comes from demosaicing before white balance (#1328, PR #1463), which this does not change.
New test flat_noise_does_not_turn_into_a_maze fails on the outright pick. RENDER_CACHE_VERSION 70.
strebdom
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