I've been trying to do little special effects for some of my videos. For example I create a light emitting object that woud cast light on a black floor, later composit the black out and the finished result would be a light pattern on a transparent background. Using this method I could have a camera tracked scene with an object that would realstically light the floor around it.
The floor is a diffuse node with 0 roughness and white color. The lamp emits pure white light. And the world has its material removed so that it couldn't interrupt anything.
Then I noticed an ugly white blown out clipping area in the middle which was not there when I rendered the image. It reminded me the problem of colors clipping and low dynamic range that we had before Filmic color management was introduced to Blender.
No matter how I moved the colorramp sliders, the white blob in the middle stayed there. I even tried using Separate RGBA node and used one of its outputs as a factor for where the whites should be, but the clipping area in the middle stayed there.
Lastly i added a black background to the image and this made the problem little less obvious, but it didn't solve it. I suppose there is something to do with Blender color management tools, but I let someone more experienced decide.
My question is what is causing this issue and is there some kind of way to maintain this smooth light transition as there was on the render, when composited onto transparent background?