Actually making use of the "persistent images" and "save buffers" features

The internet seems to be full of vaguery and guessing regarding the “persistent images” feature in the render settings panel, and the manual is also a bit vague. Clearly I’m not quite understanding how they work, but they SEEM like they might help me do what I would like to.

Here is a simple hypothetical scenario:

I have a blender scene, all nicely broken up into render layers and compositing nodes to piece everything together. I’ve done what was meant to be a final render. "Whoops, I see a problem! That’s okay though, I just need to re-render the layer with the furniture, and nothing else. "

In my experience: “Well, time to render that layer to some EXRs, just like my other layers… then re-create my compositing setup in another blend file that is just for compositing, or change every render layer node in my original file temporarily to an image node. Ho boy.”

What I would love to achieve: Having blender re-render the layer(s) I have specified, and use the existing rendered data for everything else, as if it was all rendered at the same time. No need to redo anything.

Now, if I enable “persistent images” and “save buffers” I CAN do this, but only if I have not restarted Blender. It does remember what it previously rendered in a given session. However, if I’ve shutdown or crashed, or am rendering from the command-line, I appear to be out of luck.

Is this do-able? Am I totally misunderstanding something key?

Thanks for taking the time to read this :slight_smile:

This behaviour would be great. Plus be able to resume render after computer restart like in Corona.

Only thing I know about “Save Buffers” is that when it is ON, I don’t see progress of my rendering, only the final image. This is really annoying when you don’t know why.