Hello,
I got a mismatch from Houdini render view and Nuke when the background image is enable in Houdini.
The smoke look correctly comped if I disable the OCIO or if I turn off the ‘Toggle Transparency’.

The value of the smoke are over 10 and the alpha is around 0.7. I would expect a final value of 7 over BG but I got value around 0.4 instead. (BG value are pretty low {0.03, 0.02, 0.02})

I'm a bit confuse on how Houdini compose the render over a background image.
It seem different from Nuke ‘over’ (A+B(1-a))

Thanks for your help,
Gabriel

It's because the OCIO correction is being done on each image separately, then they are composited together. What needs to happen is that they should be composited together first, then OCIO correction run on the result. The two are the same until transparency comes into play, then they differ quite a bit. The display pipeline is rather old and hasn't been upgraded to support this yet, but hopefully will get some attention soon.

That all make sense. If you ever got a workaround for this issue, please let me know.
Thank you for your quick answer.