Out-of-gamut colors produced by inverse tone mapping cause hue shifts

[grassydragon]

Hello!
As stated in this issue in the maintained Sceneform repository (SceneView/sceneform-android#60) the inverseTonemapSRGB function makes the colors with the full pixel intensity appear incorrectly. Is it because the inverseTonemapSRGB function is an approximation and isn't suitable for converting colors from the sRGB space to the linear space (I think that is why it is used in the ViewRenderable material in Sceneform)?

[romainguy]

Can you define "incorrectly" please? What's the expected output and the actual output?

This function will be exact if you choose the FILMIC tone mapper in the ColorGrading API. It will be an approximation with other tone mappers.

[grassydragon]

Here is what happens when I set the color in the hello-triangle example to #0000ff.
Without inverseTonemapSRGB:

With inverseTonemapSRGB:

I expect the color to be close to blue.

[romainguy]

It should be blue, the approximation should not cause this.

[romainguy]

Oh never mind I understand what's going on. It's a hue skew caused by out of gamut colors. You can workaround the problem for now by using the FILMIC tone mapping operator instead of the default ACES_LEGACY.

[grassydragon]

Thank you for the quick reply!

[alexey-pelykh]

@romainguy any ETA on this issue?

[pixelflinger]

No ETA yet. It's probably going to be a while.

[ThomasGorisse]

Sorry for asking it again but we are updating to the last 1.10.6 and we'd like to know if we can suppress our workaround:

filamentView.setColorGrading(
    new ColorGrading.Builder()
        .toneMapping(ColorGrading.ToneMapping.FILMIC)
        .build(EngineInstance.getEngine().getFilamentEngine())
);