Saved 32-bit EXR's with LUT enabled in VFB act as 8-bit precision images instead

[Alex_M]

Hi,

I'm not sure if this is a bug or the way it should be, hence my question. When I have a LUT loaded and enabled in the VFB, saving EXR's with 32-bit precision don't retain the 32-bit precision, but act as if they are ordinary 8-bit images such as JPG. As soon as I disable LUT in VFB, saved 32-bit EXR images act as 32-bit precision again. I've tested this with Affinity Photo 1.8.

[theedge]

My understanding is that applying a LUT anywhere will destroy the high dynamic range information and remap it to a 0-1 interval.
Interesting fact : try doing the opposite of what you did : save the raw EXR from VFB without LUT, then apply the LUT in affinity Photo. You'll notice that the image is now 8 bit too.

[Alex_M]

Interesting. Then why does using a LUT in the VFB not destroy the dynamic range?

[theedge]

What you mean is : in the VFB, even with a LUT applied, you can adjust the color corrections controls while still retaining the full dynamic range, right ?
I guess this is because the VFB internally acts as an light compositing app : it loads the RAW 32 bit image, applies all colors corrections in 32 bit and then applies the LUT as a last step.
This is how you would do it in any compositing app, and why there is no reason to bake any correction into the raw 32 bit output.

[Alex_M]

Yes, that's what I meant. Thanks for the explanation! I'll see if I can add the LUT in my compositing app (Affinity Photo) and get the same result.