# 🟡 Our composite is brighter than the emulator's frame — measured, not decoded

**Status:** 🟡 **measured, with a narrow reach and a live confound.** Closes an
observation left dangling by
[ui-8ax-fullres-background](ui-8ax-fullres-background.md) ("the capture is ~4×
darker than the render"), and puts a number on the ❔ that
[INDEX](../INDEX.md)'s texture row already carried: *"exact fidelity
(gamma/sRGB curve, premultiplied alpha, per-channel scale) is untested, since a
hue comparison cannot see it."*

⚠️ **This is not a decode.** A port applying it is authoring a value.

## First: the geometry is right

Cross-correlating `live-main-menu.png` against our render over ±6 px finds the
best alignment at exactly **dy = 0, dx = 0**, correlation **0.9466**. So the
composite is in the right place at the right size and only the *tone* differs.
(The capture is 1279×675 and top-aligned; that is the screenshot tool's crop.)

## 🔴 The first two methods were wrong, and both failed visibly

* **Three dark patches** gave "capture ≈ 4× darker". Over the whole frame the
  best linear scale is **0.914**. Three patches from one region are not a
  transfer curve.
* **A pixel-wise fit** over 854 685 pixels produced a non-monotonic transfer
  (render 96–127 → capture *143*, brighter than render 128–159 → 132). That is
  the signature of **edge misalignment**, not of a tone curve: at a 0.947
  correlation a bright render pixel routinely lands on a dark capture pixel.
  Mean abs error was 10–14 for every model, which is the tell that none of them
  fit.

Both are recorded because the second is the interesting failure — a fit whose
*residual* is large everywhere is not a model to choose between, it is a method
to throw away.

## The method that works: flat patches only

16×16 patches where **both** images have `std < 8`, so local edges cannot
contribute. The threshold is not arbitrary — at `std < 3` there are **zero**
patches, and the count runs 0 / 83 / 404 / 1055 / 1788 for `std <`
3 / 5 / 8 / 12 / 20.

| screen | flat patches | gamma exponent | mean abs err | best linear | its err |
|---|---|---|---|---|---|
| main menu | 404 | **1.491** | 0.28 | 0.276 | 0.34 |
| `EXTRAS` | 382 | **1.493** | 0.22 | 0.273 | 0.28 |
| title | 506 | **1.338** | 1.08 | 0.842 | 9.02 |

So `capture ≈ 255·(render/255)^γ` with **γ ≈ 1.34 – 1.49**.

## ⚠️ The reach — and it is narrow

* **The flat patches are almost all dark**: render values ~0–60. Over that range
  a gamma and a linear scale are nearly indistinguishable — on the two menus the
  errors are 0.28 vs 0.34 and 0.22 vs 0.28, which decides nothing. **Only the
  title separates them** (1.08 vs 9.02), because its flat regions reach ~60.
* **The held-out control could not test it.** Running the same fit on the
  developer splash gives 2 918 flat patches whose render range is **0–4** — pure
  black. Every model scores ≈ 0.00 there. That is a control that failed to
  discriminate, not a control that passed.
* **Nothing here constrains midtones or highlights**, which is exactly where a
  γ = 1.4 curve does its visible work.

## ❔ The confound: this may be the emulator, not the game

The comparison is our composite against **what Xenia Canary displays**, and
canary applies its own output transform:
`kernel_display_gamma_type = 2` — BT.709 (HDTV) — in this container's config
(`0` linear, `1` sRGB, `3` a power set by `kernel_display_gamma_power`).

So the measured exponent may belong to canary's display stage rather than to the
game or the console. **The discriminating experiment is cheap and was not run:**
set `kernel_display_gamma_type = 0`, re-capture the same screen, and re-fit. If
the exponent collapses toward 1.0 it is canary's; if it survives it is upstream.
That needs one emulator run reaching the main menu.

## What a port should do with this

Treat it as **authored**, not transcribed. If the goal is to match the emulator —
which is what every capture in this corpus is — a γ ≈ 1.4 darkening of the
composite gets closer, and is best applied where it was measured (the dark
background), not extrapolated to the whole range on this evidence.