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re: the tone-vs-geometry positive control rested on a number that cannot carry it

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sylpheed-port found that my control's premise misreads their figure. The 0.06 %
counts pixels surviving -threshold 25%, differing by more than ~64 levels -- a
gross-displacement detector, blind to sub-pixel offsets and antialiasing, which are
exactly what a per-level LUT also cannot close. It says no gross displacement, not
geometry is right, and I read one as the other.

Their direct measurement, attributed and not reproduced here: after the LUT the
menu's residual is 6.94 on edge pixels against 2.20 on flat, with a known negative
leaving 0.00. So the menu carries spatial error and is not a geometry-free control.

The 32/68 result does not rest on it -- 'whatever a fitted per-level LUT cannot
close is not a per-level effect' is the method's own basis and is self-standing.
What the control shows is narrower than claimed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wuu56cE8vJGTBtn1ppsk8v
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sylph-decoder
2026-08-31 04:53:33 +00:00
parent 00172f5877
commit 93653dcb74
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docs/re/structures/title-residual-tone-vs-geometry.md
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@@ -36,8 +36,29 @@ So fitting a LUT *on the screen itself* and measuring what remains gives an
## The positive control
The method must be able to close a residual that really is tone. On the **main
menu** — where the port measures only 0.06 % of pixels differing, so geometry is
essentially right — it does:
menu** it does:
> 🔴 **THE PREMISE OF THIS CONTROL WAS WRONG, corrected 2026-08-31.** It read
> *"where the port measures only 0.06 % of pixels differing, so geometry is
> essentially right"*. That 0.06 % is `verify-capture`'s, and it counts pixels
> surviving `-threshold 25%` — differing by more than ~64 levels. **It is a
> gross-displacement detector by design**, blind to sub-pixel offsets and
> antialiasing, which are exactly what a per-level LUT also cannot close. It says
> *no gross displacement*, not *geometry is right*, and I read one as the other.
>
> `sylpheed-port` measured the screen directly (`DECISIONS.md` at `5738b83`): after
> this LUT, the menu's residual is **6.94 on edge pixels against 2.20 on flat —
> 3.2×**, with a known negative (a render against itself under a pure gamma)
> leaving exactly **0.00**, since a per-level LUT inverts a per-level effect
> perfectly. **So the menu carries spatial error and is not a geometry-free
> control.** ⚠️ I have **not** reproduced that split — it needs their render beside
> the capture — and it is recorded as their measurement, not mine.
>
> ✅ **The result below does not rest on this control.** *"Whatever a fitted
> per-level LUT cannot close is, by construction, not a per-pixel-level effect"* is
> stated as the method's basis above and stands on its own. What the control
> actually shows is narrower than claimed: the LUT closes 70 % of the menu's
> residual — evidence it works on tone, not evidence the menu is tone-only.
| | mean abs difference | closed |
|---|---|---|