Different Colours When Using GetResourcesWithRects_RenderThread in 5.5 vs 5.6

Development Rendering
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I realize that I have already made two posts about this that went nowhere but it’s still an issue and any info would help. Links to the previous posts:

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For context I have a plugin that captures frames from Unreal through nDisplay. Specifically the function call used to grab the resources is

ViewportProxy->GetResourcesWithRects_RenderThread(resourceType, Resources, Rects);

With the resource type in this case being EDisplayClusterViewportResourceType::InputShaderResource. Now with versions 5.5 and prior this would return a texture with correct looking colours when using OCIO. In 5.6 & 5.7 however the colours look off. This time I made a function to save the texture to disk right after it was retrieved so I could look at it. I’ve attached those captures so you can take a look for yourself. As you can see the colours are noticeably different. I am using a UE project that was created in 5.5 and upgraded to 5.7.

NOTE: I did the capture with 5.7 but this issue first started with 5.6

So what could be the problem here ? It seems clear to me that something has changed behind the scenes but I have no idea what. My OCIO settings are:

Input transform: Linear Rec.709 (sRGB)

Output Transform: Rec.2100-PQ - Display - Un-tone-mapped

Any advice or insight for this problem would be appreciated.

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Hi,

I checked the git repository and there have been a number of changes from 5.5 to 5.6 which are related to nDisplay and OCIO. Below is a list of what I believe are the most important ones (the full list can be found here, only the first two pages are relevant given that the issue occurs only in 5.6 and later versions):

+ HoldoutComposite integration 2/3: New TextureUtils API (RDG/RHI) and color encoding (Gamma, Premultiply). https://github.com/EpicGames/UnrealEngine/commit/6eb4508cffaecdecd7a805faa291a1a527eca1b5

+ [nDisplay] [Virtual Production] UV Lightcards not getting OCIO applied in preview.

Reworked the logic to always call FDisplayClusterViewport::SetupSceneView() for viewports, even if they are not rendered (uvLC).

https://github.com/EpicGames/UnrealEngine/commit/04fbd4f751c920859fa1e3658f8fff90d8f8bda4

+ nDisplay: Fixed issue where color grading and white balance settings would reset to zero instead of desirable default values when the color grading or white balace structs were elements of an array.

https://github.com/EpicGames/UnrealEngine/commit/a2772a31b52f1b3b8482e936935d66cd650d25d7

+ nDisplay: Added option to disable OCIO in preview (this one introduces a new setting, “Enable OCIO on Preview” or bPreviewEnableOCIO, which is set to false by default)

https://github.com/EpicGames/UnrealEngine/commit/8fb09e6aefec77570f1a6eecad3c96752d5a7065

+ [nDisplay] Fixed incorrect colors with late OCIO

- There were multiple issues when the senders have no OCIO configured. Starting from rgb10 (instead of float16) and finishing with incorrect colors regardless of OCIO settings on the receiving side.

- The problem was caused by a logical error that prevented SVF to be prepared for OCIO properly (no tonecurve, linear sRGB)

https://github.com/EpicGames/UnrealEngine/commit/9e3bc03a576292c7379bb4c0153dc7c3a9eab1a3

+ [nDisplay] Late OCIO has no effect if OCIO is disabled completely

- Previously, if OCIO is disabled and “Receivers Apply OCIO” is on, the sender used to multicast a no tone curve linear sRGB texture to the receivers. That looked confusing because the colors are different compared to the outer views. There was an illusion that the same OCIO conversion is applied on all the nodes.

- With this fix, when OCIO is diabled, the “Receivers Apply OCIO” is ignored, and the inner view remains untouched (same colors as non-OCIO outers have)

https://github.com/EpicGames/UnrealEngine/commit/b30f8e056d196847394a17ede884c7a03731cc5e

+ [nDisplay] Late OCIO improvements

- Added ability to manipulate late OCIO live

- Added ability to use PQ for transfer

- Restructured nDisplay media adapters

https://github.com/EpicGames/UnrealEngine/commit/22c459113b9632ac983be8b00b7590e2de5f1fb9

Without a repro project, it’s hard to tell if any of these changes is responsible for the change in colour you are noticing. It is possible that some default settings were changed or new ones were introduced. If you suspect that is the case and are familiar with building the engine from source, you can try to perform git regression and/or bisection testing on the engine source by checking out specific commits to narrow down the range of commits or even pinpoint the commit where the change occurs.

Let me know if this helps or if you have any further questions or comments. If you have a simple repro case, I can try to help debug and narrow down the possible range as well.

Best,

Sam

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Ok thank you I will check these out

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Thanks, please let us know if you find out more.

Best regards,

Sam

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