# ✅ At least two thirds of the title's disagreement is GEOMETRY, not tone

> ⚠️ **The 10.92 title baseline here could not be reproduced on 2026-08-29** —
> `screen render --build 4 --black` against the same capture gives 14.07 both at
> `formats-pin-2026-08-29c` and today. The *ratio* this document argues for may
> well survive; the absolute is in doubt. Separately, part of the title's residual
> is now known to be neither tone nor rotation but `rest()` posing five transient
> flashes at their peaks — [`ui-settle-time.md`](ui-settle-time.md) closes the
> light-arc band from 33.22 to 11.79.

**Classification: measured**, on committed captures. Answers a question the
pending rotation decision needs: *how much would drawing the rotation actually
buy?*

Two separate effects are known to make our renders differ from the console:

* the **tone curve** — the console renders midtones brighter than we do
  ([`ui-render-tone-curve.md`](ui-render-tone-curve.md)), and its single-exponent
  model is refuted above render ≈ 40;
* the **missing rotation** — our blit draws axis-aligned rectangles, so the
  title's two tilted light sweeps land as upright bars
  ([`ui-keyframe-rotation.md`](ui-keyframe-rotation.md)).

They are confounded in any whole-frame number. This separates them.

## Method, and why the split is an upper bound on tone

A **per-level lookup table** fitted on a screen is the most general tone model
there is: it maps every render level to whatever capture level minimises the
error, with no functional form assumed. **Whatever such a LUT cannot close is,
by construction, not a per-pixel-level effect** — it is spatial.

So fitting a LUT *on the screen itself* and measuring what remains gives an
**upper bound on the tone share** and a **lower bound on the geometry share**.

## The positive control

The method must be able to close a residual that really is tone. On the **main
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 |
|---|---|---|
| main menu, uncorrected | 9.26 | — |
| **main menu + LUT fitted on the main menu** | **2.75** | **70.3 %** |

✅ The instrument works: a tone-dominated residual collapses by 70 %.

## The result

| | mean abs difference | closed |
|---|---|---|
| title, uncorrected | 10.92 | — |
| **title + LUT fitted on the title** | **7.42** | **32.0 %** |

🔴 **At most 32 % of the title's disagreement is a tone effect, so at least 68 %
is spatial** — content in the wrong place. That is where the rotation lives, and
it makes the rotation the dominant term by roughly two to one.

⚠️ The same-screen LUT is *fitted*, so 32 % is generous to tone. The true tone
share is smaller and the geometry share larger.

## 🔴 And a claim this refutes: there is no single transferable tone curve

Fitting on one screen and applying to the other:

| | closed |
|---|---|
| main menu + LUT fitted on the **title** | **+29.7 %** |
| title + LUT fitted on the **main menu** | **−24.0 %** ✗ |

**The menu's curve makes the title worse.** A curve fitted on a dark, flat screen
is unconstrained at the bright end — the menu's populated range is levels 5–204
with few bright pixels — and extrapolating it onto the title's planet and
wordmark actively harms.

⚠️ So *"the tone curve"* is not one thing that can be measured once and applied.
This extends [`ui-render-tone-curve.md`](ui-render-tone-curve.md)'s refutation of
the single **exponent**: even a full per-level LUT fails to transfer between
screens. **A consumer must not carry a global tone correction.**

## Reach

* Two screens, one capture each; the title capture is the plate-free frame and
  our render is at rest, so they are **the same screen but not the same
  instant** — a looser pairing than the port's posed comparison, which is why
  the absolute numbers here (10.92) are larger than its 1.81 % of pixels.
  ⚠️ The *ratio* is what this page claims, not the absolute level.
* Our render draws the sweeps' **parent** record only — the pre-leaf-fix state —
  so the geometry share measured here includes both the missing rotation and the
  missing leaf placement. Both are closed by the same decision.

## ✅ The menu's edge residual is NOT global misregistration, and not blur

**Measured by `sylpheed-port`** (`tools/port/edge-residual-kind`, branch
`auto/port-p6-audio` at `f4351b0`), running the discriminator I proposed but could
not execute — it needs their render beside the capture, which I do not have.
Recorded as their measurement.

The test, made concrete: a shift by `(dx,dy)` makes the **signed** residual track
the **gradient**, and the fitted slope *is* the shift in pixels; a blur makes it
track the **laplacian**, symmetric and directionless.

| | |
|---|---|
| **control** — a known +1 px shift | reads back **+0.938 px** (r +0.789) |
| **control** — a known blur | **r −0.896** on the laplacian |
| neither leaked into the other's channel | ✅ |
| **`main_menu` vs the capture** | **−0.010 px** horizontal, **−0.009 px** vertical; laplacian **r +0.103** |

❌ **Global misregistration is excluded**: any whole-frame translation is under a
hundredth of a pixel, against a control that reads a true 1 px at 0.938.
❌ **Blur is excluded**: the weak laplacian term is the **opposite sign** to the
blur control, so the capture is not a softened render either.

⚠️ **The reach is the whole reach: this is a WHOLE-FRAME fit.** One misplaced
element is a small share of 38 752 edge pixels and would not move these numbers. It
excludes a **global** translation, not a **local** one.

📌 **So of the three candidates I named — misregistration, antialiasing, a misplaced
soft element — the third survives, and it is the only one left.** The next test is
necessarily **local**: where does the edge residual concentrate spatially, and does
that region correspond to one element? ⚠️ That needs the residual map, which is on
the port's side; I can state the test and cannot run it.