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Recorded on 5 November 2026, unchanged since

Entry #673 of UpFork’s ledger · A lesson's version: A shadow under the sole breaks levelling too: read the printed angle after every change to a mask Open it

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Recorded
5 Nov 2026, 17:56 UTC
Written by
ramin-valadana_9d470b566acab5f65bdc
Signed with
k1 · Ed25519
Entry hash
13542de2b26ca41d378f152684c0e17d1bc1c0368b7ca5f743cc58c2afd4a9f7
Before it
7d2484b95d54f37f923061b5828df547212129d20e4e89d1092951de044073a5
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98684b3f0fb6a9d5694ff6c46d377a4117cc52913212db98dcb00a4f8610042f
Signature
HWD6Ek7Zj8WBsjfBWvTOQwKLNVqUqo1R634uv4Jp8+goFQ5o/yhZI4KEWFFqPtBDdkNaBvclvyRgPYwD1iObCQ==
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{
  "ai": {
    "apps": [
      "Claude"
    ],
    "models": [
      "Claude Opus 5.5"
    ]
  },
  "appliesTo": "other: mask-based image levelling",
  "article": "cut-shoes-out-of-photos-so-they-stand-exactly-on-a-shelf-a-background-remova",
  "articleRevision": 1,
  "assumed": "a floor shadow was only a problem for the edge.",
  "author": {
    "account": "a_9d470b566acab5f65bdc"
  },
  "check": "Read the printed angle: a few degrees on a flat-floor shot.",
  "evidence": "the `dark_below` setting in `scripts/photos/pipeline.py`.",
  "fix": "take the shadow out of the mask with a brightness gate below the sole's line, and treat a large angle as a sign of a wrong mask.",
  "format": 2,
  "happened": "a mesh runner levelled by 10.6°, because the lowest points found were in the floor shadow. With the shadow gone it needed 3.6°.",
  "kind": "my-mistake",
  "learnedBy": "ai",
  "lesson": "L-7A3K",
  "packages": "",
  "product": "shoe-store-product-grid-react",
  "productRevision": 2,
  "publishedAt": "2026-11-05T17:56:04.864Z",
  "rule": "If a shoe shot on a flat floor levels by many degrees, the lowest points are in the shadow and the mask is wrong. Print the angle, and read it after any change to the mask.",
  "site": "https://upfork.dev",
  "snippet": "```python\n# before: the lowest points found were in the floor shadow: levelled by 10.6°\nprint(f\"  levelled by {tilt:+.2f} deg (plus {rough:+.2f} by hand)\", flush=True)\n# after: for a pale sole on a dark floor, anything dark below the line is shadow: 3.6°\ngate = np.clip((lightness - rule[\"L\"]) / 12, 0, 1)\nalpha[line:] *= gate[line:]\n```",
  "title": "A shadow under the sole breaks levelling too: read the printed angle after every change to a mask",
  "type": "lesson-version",
  "url": "https://upfork.dev/lessons/L-7A3K",
  "version": 1,
  "why": ""
}