Color space conversion in the UI composition is incorrect on DX12 HDR.

In the main() function In CompositeUIPixelShader.usf, you can see the following color space transform.

	// sRGB -> RRT -> ODT = ColorLookupTable(;

But it seems that the input of ColorLookupTable() must be linear color space. So it makes UI color incorrect on HDR.
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Adding sRGB->Linear transform before the function fix this problem.

	// sRGB -> Linear -> RRT -> ODT = sRGBToLinear(; = ColorLookupTable(;

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Steps to Reproduce
  1. Open the attached repro project
  2. Play Standalone Game, you can see SDR result.
  3. set r.HDR.EnableHDROutput to 1 via console command.
  4. Play Standalone Game, you can see HDR result. and you can find the result slight brighter than SDR

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ComponentUE - Graphics Features
Affects Versions4.264.275.0-early access5.0
Target Fix5.1
Fix Commit19918995
CreatedJun 11, 2021
ResolvedApr 26, 2022
UpdatedMay 6, 2022