Compositing only a certain region within the rendered image

Support Compositing and Post Processing
#1

Hi
I am quite new to blender and am creating my first animation on using text and a logo.
Now in this animation I render each frames and then each frame are fed to a composite glare that adds 4 streaks to it.
My render image consites of a Test in red and white car paint and a logo in red car paint. When I add a glare to this image all the white region get the glare in absolutely perfect manner. However in the logo the glare is of very small amount; to increase that if I reduce the threshold then the glare on the white test increases a lot and makes the image very bad.

So I was wondering if there is a way if only a region of the image could be composited then in that way after adding the glare to whote text I would be able to add approprate amount of the glare to the red logo.

I thought of doing this using Photoshop but doing Photoshop on 3000 frames seems really hard to me.

I’ll be really thankfull if I could be advised on this issue

Thanks a lot. :slight_smile:

#2

You could use layers in the sequenzer and only composite the layer you need to modify.

#3

Can you use object ID pass to isolate the logo? Use the matte to add glare to that part.

#4

Hi

Thanks a lot for the information. I tried using the render layers and rendered the red logo separate. I then added glare to it and added it to the final image. But the problem was that the background color was changed slightly and in the final image the red logo was kind of little translucent ans one could see the background lines :S. I also applied RGB curves but could not obtain anything better.

I am not surehow to do the object ID pass, but would be happy to know more about it.

#5

It is very hard to recommend specific solutions without seeing more about the scene details and how the Render Layers and the nodes are set up. Screenshots help if they show the problem clearly, include a shot of your nodes as well, Best yet, post the .blend file if possible, and a clear explanation of the goals you want to achieve in the composite image.

In general, it sounds like what you want to do is use some method (such as Render Layers or Object ID) to isolate the scene elements that need different kinds of effects, then create a node system for each part of the effect. Bringing it all back together can be a little tricky, because different nodes can be used depending on what precedes them and what effect you want. The most common end-composite nodes are probably Color>Alpha Over and Color>Mix. Sometimes it’s necessary to create masking elements to further restrict or isolate certain portion son the scene. How to do all this is often highly dependent on the details of your scene.