Change the compositor after the image has finished rendering and save the result

Is it possible to tweak the compositor nodes after the render is complete and then re-apply the post processing?

I’m asking this as I made a mistake in a couple of the nodes and I want to just re-process them without having to wait forever to re-render the image! If this is possible, what are the steps that would allow me to save the output from the re-processed image?



Node setup (your “noodle”) will have some effect on this, but usually if you alter a node setting, the Compositor will take it through the nodes one-by-one (status bar reads “Compositing”) and you will see the change in one of the output options – a Viewer node or the Composite node, depending on how you’ve set up the Compositor and/or the UV/Image Editor. Unless there is a change in the Scene setup (lights, position, frame number, etc.), there should be no need to re-render.

If using Render Layer nodes you have a bit more flexibility even if something in the Scene changes. Each Render Layer node has a camera-icon button that will render only the Scene layers assigned to that particular Render Layer node. This can be real handy for complex compositing setups.