"Neutral" tonemapping darkens the image considerably #4825

hybridherbst · 2024-06-27T12:54:27Z

Description

For one of our viewers, I was using an earlier version of Neutral / Khronos PBR Tonemapper as it was in use by model-viewer. In that version, there was no/almost no darkening on surfaces compared to Linear/None, and only a curve in the highlights to prevent clipping, to the best of my understanding.

To my surprise, switching to the current version of "Neutral" now darkens the image considerably – which doesn't feel intended, and is different to before. Darker areas are now so dark that it loses detail entirely compared to the Linear look (see for example the exhaust area in the pictures below, or the rubber pipes in the back).

I see the same behavior in both three.js and model-viewer, so I think raising the issue here as the "source" of the tonemapper is appropriate.

Long story short – is this intended? Does the shipped version of the Khronos PBR Tonemapper now resemble ACES so much more than previous in-progress versions? To me, that feels like a step back – previously my understanding was that Neutral is designed to keep albedo data as much as possible, but now it feels the goal is to be as close as possible to ACES without having the same hue shifts?

Live Demo – Damaged Helmet

Open https://modelviewer.dev/editor
Load DamagedHelmet (DamagedHelmet (3).glb.zip)
Load Venice Sunrise for comparison (venice_sunrise_1k.hdr.zip)
Open https://threejs.org/examples/webgl_tonemapping.html in parallel

Alternative reproduction: Neutral also darkens "Damaged Helmet" considerably on https://tone-mapping.glitch.me/.

Tone Mapping	model-viewer	three.js
Linear
Neutral
ACES

Since the model-viewer editor doesn't support switching to None/Linear for comparison (#4541), you can paste and run this code snippet in the chrome console to switch to Linear:

const mv = document.querySelector("model-viewer-preview").shadowRoot.querySelector("model-viewer");
const sc = mv[Object.getOwnPropertySymbols(mv).find((x) => x.description === "scene")];
sc.toneMapping = 1;
sc.queueRender();

Live Demo – Caterpillar Work Boot

Here's another real-world scanned PBR model that fares even worse with Neutral tonemapping – I'd say Neutral looks the worst of all tonemapping options, heavily deviating from the intended look of the model: