How to render only one material in color, rest in grayscale?

Development Rendering
1

I am working on a shooter FPS game, similar to Serious Sam or Painkiller. What I would like to achieve looks like this:

[Album]

So basically, renders the whole image in grayscale, and renders in a specific color only materials which are marked by it.
How is this achievable? I’ve watched post-process tutorials, I can make the image grayscale, but how to filter a few materials so it renders them normally, just like in those 2 images?

2

I’m looking for a similar function but object based.
Basically have the post-process ignore certain objects.

Hopefully some wise and old UE wizard responds to this thread and hopefully the solution can be implemented in my scene as well!

3

You could use the Custom Depth buffer to filter what you want in colour. Take a look at some of the post process Outline tutorials on how to use the custom depth and simply use its value in a lerp between PostProcessInput0 and PostProcessInput0 > Desaturation.

4

Thanks Dec1234!
Just found one and it seems pretty straight forward.

5

I still don’t know how to do this. Can anyone else help me please?