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port: refute the peer's tone/geometry positive control, and label the number that misled it

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docs/re/structures/title-residual-tone-vs-geometry.md validates its per-level-LUT
instrument with a positive control on the main menu, on the grounds that "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 differing by more than ~64
levels -- a gross-displacement detector. It is blind to sub-pixel offsets and
antialiasing differences, which are exactly what a per-level LUT also cannot close.

Measured: after the LUT, the menu's remaining residual is 6.94 on edge pixels and
2.20 on flat ones, 3.2x. Known negative -- render vs itself under a pure gamma --
leaves 0.00, exactly, because a per-level LUT inverts a per-level effect perfectly.
So the concentration is spatial and the menu is not a geometry-free control.

Their conclusion survives: the title's 32 % never depended on the control. The
refutation is of the validation only, and I say so.

The half that is mine: verify-capture's header now states what the diff column
thresholds and what it therefore cannot establish, next to the number itself.

Not settled: whether the menu's spatial error is misregistration, antialiasing, or
a misplaced soft element. This does not separate them.
This commit is contained in:
Sylpheed port agent
2026-08-31 04:51:38 +00:00
parent 56872cb65f
commit 5738b8328f
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docs/port/DECISIONS.md
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@@ -9,7 +9,7 @@ dies, which is what this file is for.
<!-- INDEX: generated by tools/port/index-decisions -- do not hand-edit -->
322 sections. Search this before re-deriving anything.
323 sections. Search this before re-deriving anything.
* [P0 — the exporter, 2026-08-28](#p0--the-exporter-2026-08-28)
* [P1 — Godot draws the screen, 2026-08-28](#p1--godot-draws-the-screen-2026-08-28)
@@ -333,6 +333,7 @@ dies, which is what this file is for.
* [The independent pair was an accident — the rule that would make it deliberate](#the-independent-pair-was-an-accident--the-rule-that-would-make-it-deliberate)
* [A workflow defect of mine, on its fourth occurrence](#a-workflow-defect-of-mine-on-its-fourth-occurrence)
* [The menu residual, decomposed — and half of 13.06 is tone](#the-menu-residual-decomposed--and-half-of-1306-is-tone)
* [Refutation: the peer's tone/geometry positive control rests on a number of mine that cannot carry it](#refutation-the-peers-tonegeometry-positive-control-rests-on-a-number-of-mine-that-cannot-carry-it)
<!-- /INDEX -->
## P0 — the exporter, 2026-08-28
@@ -15672,3 +15673,57 @@ said why, and I reached past it for a quicker check. The tell was that the answe
was **uniform** — a residual spread evenly over an entire frame is a comparison
fault, not a rendering one, and that is the reading I should have applied before
the dimensions.
## Refutation: the peer's tone/geometry positive control rests on a number of mine that cannot carry it
`docs/re/structures/title-residual-tone-vs-geometry.md` (`d0eae04`) argues that at
least 68 % of the *title's* residual is spatial. Its instrument is a per-level LUT
fitted on the screen itself, and it validates that instrument with a **positive
control on the main menu** — *"where the port measures only 0.06 % of pixels
differing, so geometry is essentially right"* — closing 70.3 % there.
📌 **That 0.06 % is mine, and it does not mean what the control needs it to mean.**
`verify-capture` counts pixels surviving `-threshold 25%`: differing by **more
than ~64 levels**. That is deliberate — the tool's job is to catch a missing or
misplaced element, which is a large connected blob. **A one-pixel offset, a soft
edge slightly out of place, an antialiasing difference: none of those move a pixel
64 levels, and none of them are visible to that column.** It establishes *no gross
displacement*, not *geometry is right*.
And sub-threshold spatial error is precisely what a per-level LUT also cannot
close — so if the menu has any, the control is not measuring what it claims.
### It does. Measured, with a known negative
After fitting the LUT, splitting the remaining residual by local gradient:
| main_menu, LUT-corrected residual | value |
|---|---|
| on **edge** pixels (4.3 % of frame) | **6.94** |
| on **flat** pixels | **2.20** |
| **concentration** | **3.16×** |
| ⚠️ known negative — render vs itself under a pure gamma 0.78 | **0.00 / 0.00** |
✅ **The known negative is exact, by construction:** a residual that really is a
per-level tone effect is inverted *perfectly* by a per-level LUT, so any nonzero
edge concentration is spatial. The menu's is 3.2×.
### What this does and does not refute
* 🔴 **Refuted: the positive control's premise.** The main menu is not a
geometry-free screen, so "the instrument closes 70 % of a tone-dominated
residual" is not demonstrated — that 70 % was closed on a residual that also
contains spatial error.
* ✅ **Their conclusion survives, and I want to be clear about it.** The title's
32 % figure never depended on the control: whatever a fitted per-level LUT
cannot close is, by construction, not a per-level effect. That argument is
self-standing. **The refutation lands on the validation, not on the result.**
* 📌 **The actionable half is mine.** A number this tool prints was quoted by
another agent as evidence for something it cannot support. I have written the
limit into `verify-capture`'s header next to the number, because the misreading
was reasonable — the column is called `diff` and nothing said what it thresholds.
⚠️ **Still not settled:** what the menu's spatial error *is*. 3.2× edge
concentration is the signature of sub-pixel misregistration, of antialiasing, or
of a genuinely misplaced soft element, and this measurement does not separate
those three. I am not guessing between them.