Paint over Render in compositor I am trying to figure out the proper workflow setup to manually paint onto a render within Blender.

I want to:


Render an Image
Run it through a compositor node setup
Be able to manually paint on it afterwards, but non-destructively.


For it to be non-destructive, I need some sort of new layer. I want to be able to paint on top to add more light/shadow, lineart, color correction, etc. My first thought was to make a blank image and alpha-over it over the whole render in the compositor, and then paint on that. However, I don't seem to be able to have it overlay the render visually while painting, so I can't tell what I'm doing (the image editor showing the render is in one window, and the paint mode with my new image is in another, but I need them superimposed.)

I could also make new images or masks and combine them with the render in the compositor, but then I end up limited by mix modes, and still have the problem of super imposing over the render. If I just wanted to darken areas, then I could make a new image and combine it with multiply in a mixRGB node. But if I want to also lighten some areas, change color in others, etc, then I end up needing tons of new images.

Is it possible to make a proper multi-layer painting setup in Blender similar to what you can do in Photoshop or Sai? (I could take it into Photoshop or something, but I want to see if I can keep it all within Blender.)
By creating a new image in the UV/Image editor and using a mixRGB node to mix it with the render layer you can get the same result as a photoshop layer. Each image created and mixed in using the compositor will correspond to one layer in PS. You will find each blend type of the mix node will correspond to a layer mode in PS. The alpha of the image or a separate image can be connected to the fac of the mix node for a layer mask. We can also create and animate a mask. While the render result or viewer node preview doesn't update as you paint, it does update after you complete each stroke.

So while we don't get the simplicity of the way layers are presented and edited in the same location, we can get the same end results, even with some extra flexibility in how they are combined by using blenders compositor node system. The other factor to differentiate PS and blender will be the amount of painting tools available.