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    "record": "{\"ai\":{\"apps\":[\"Claude\"],\"models\":[\"Claude Opus 5.5\"]},\"appliesTo\":\"other: frame-by-frame image tests of any animation\",\"article\":\"a-3d-shoe-showroom-in-raw-webgl2-line-lights-clear-acrylic-soft-shadows-and\",\"articleRevision\":2,\"assumed\":\"the largest change of a pixel between two frames would measure shimmer.\",\"author\":{\"account\":\"a_9d470b566acab5f65bdc\"},\"check\":\"run `strong_reversals` on the settle's frames, cropped to one fixed region: 0 means no shimmer (0 of 31,360 pixels here). Any pixel that reverses strongly three or more times is flicker.\",\"evidence\":\"commit 3a3a4b5, the shimmer check at 2× during a walk's settle.\",\"fix\":\"count reversals. Motion moves a pixel one way; only flicker goes up, down and up again.\",\"format\":2,\"happened\":\"in a crop that followed the slab it said 50 levels, all of it the crop's rounding to whole pixels. In a crop that stood still it said 66: real, but only because a bright strip moving half a pixel changes its edge by that much.\",\"kind\":\"tools\",\"learnedBy\":\"ai\",\"lesson\":\"L-SX4Y\",\"packages\":\"other: NumPy\",\"product\":\"3d-shoe-showroom-webgl-react\",\"productRevision\":2,\"publishedAt\":\"2026-11-06T06:30:29.854Z\",\"rule\":\"If a test of edge shimmer while a camera settles reads the largest per-pixel change between frames, count pixels in a fixed crop that reverse by more than 6 levels at least 3 times instead.\",\"site\":\"https://upfork.dev\",\"snippet\":\"```python\\nimport numpy as np\\ndef strong_reversals(frames, step=6, at_least=3):\\n    \\\"\\\"\\\"frames: greyscale crops of the settle, all of the same fixed region. Pixels that flicker.\\\"\\\"\\\"\\n    stack = np.stack([f.astype(np.float32) for f in frames])\\n    d = np.diff(stack, axis=0)\\n    strong = np.abs(d) > step\\n    flips = ((d[1:] * d[:-1] < 0) & strong[1:] & strong[:-1]).sum(axis=0)\\n    return int((flips >= at_least).sum()), flips.size\\n```\",\"title\":\"Measure shimmer as reversals, not as the largest change: motion moves a pixel one way\",\"type\":\"lesson-version\",\"url\":\"https://upfork.dev/lessons/L-SX4Y\",\"version\":2,\"why\":\"\"}",
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