why filament doesn't use opencolorio to implement color grading

[dandingol03]

Hi, i met a problem recently. The model rendered in blender has huge chromatic compared to filament .
   After a while, i finally find the reason why there is a lot chromatic when i use the same model and same hdr to provide environment indirect-light.
   The reason is blender use opencolorio to implement color management, and i found the unreal engine also use it to do so. So why filament doesn't use opencolorio? This difference makes the artist must do the same work to make model rendering right after they have do the same stuff in blender

[romainguy]

OCIO is a large and complex system that is not well suited for Filament. More importantly, OCIO itself doesn't solve what you are describing. The difference you are observing is most likely due to a difference in tone mapping between Blender and Filament. Filament offers several tone mapping algorithms, including the ACES reference, that can help you get closer to Blender (Blender now uses its "Filmic" by default).

[dandingol03]

  No, i have choose the tonemapping to filmic in filament. However there is still difference between them. Here is some screenshot:

  The left picture is the rendered result in blend and the right picture is belong to filament. You can see the right picture is more saturated when the model is placed in same indirect light environment.

[dandingol03]

If i baked the lut in opencolorio in advance which has the same ocio config with blender, can i fix chromatic difference by sampling the lut in colorgrading.mat?

[romainguy]

Filmic is a generic term it doesn't mean it's the same tone mapper.

And setting aside saturation, it looks like the lighting is different, or the materials are different (less rough with filament)

[dandingol03]

  I agree your first opinion, the implementation must be different. I think the biggest reason which make chromatic exist is the filmic implementation. Here is some picture for contrast:

  The left part is the render result in filament, and the other is rendered in blender. The most obvious chromatic is the curtain's color, and the curtain's is part of the skybox. Because the rendering result of skybox donot take light result into account, so different implementation of filmic tonemapper have most impact on chromatic problem.
The most i wanna know is how to fix this chromatic problem. How if i replace lut texture in colorgrading.mat by the lut which is generated by blender.
  Thanks