Composite BG colour

Hi guys,
I followed a thread on blender.stackexchange

I just want to be able to choose a solid colour for the background (transparent areas) in my renders.
I inverted the alpha of my render layer and plugged that into an Alpha Over factor. It should put the render layer wherever there are rendered pixels and then the “Image” (which has nothing plugged in so it’s just a white colour) wherever there are transparent pixels.

It works but my problem is that the white colour is NOT true white in the result.
Here is the screenshot:

Any ideas how to do this better?

How do you measure the BG color values? My first guess is that you have some tone mapping going on there.

Oh I see, I have it set to Filmic and when I change the “Look” (like low contrast, very high contrast etc.) it affects the background colour from the compositor!

Thank you Kesonmis! So now I know why it’s happening, any ideas how to make a background colour independent of the tone mapping?

You can’t. The best you can do is to push it to full white for current tonemappinng. To do this, you must make the bg so bright that it clips in tonemapper to max white. Another option is to make your composite without adding the bg, render it out with alpha and add the bg later in separate scene with no tonemapping.

Instead of using an sRGB background colour, you could create a high bit depth image of ‘white’, use that as the backplate, and increase it’s luminance in the compositor separately from the rendered data?

Or create a new scene of a ‘white’ background and comp the two scenes. You will be able to edit the background scene on it’s own to be very bright.

hmmm, thanks for the suggestion. I think it might just be easier to save a PNG with transparency and then just comp in any colour I want in post.

Thanks anyways :smiley: