Storing multiple render passes into the output image

I figured I’d make a separate thread for this question as it’s technically a different issue with other beneficial use cases, even if it’s partly a continuation of this discussion. I’d like to know if Blender allows resizing an output image beyond the scale of the render, in order to add custom render passes into the same output.

For example: I’m making a render at 1920 x 1080 resolution. When saving the final image, I want the image file to be 3840 x 1080 instead. On the left side I have a normal version of the render… on the right side I can add different pass, like alpha or depth or normal, which a custom player can use for special effects.

The issue is that as far as I’m aware, the output image is forced to have the same dimensions as the size of the render, I don’t see any option to resize the output from the compositor or post-render. This is only ever done for multi-view when choosing side-by-side stereoscopic rendering, which is not customizable to my knowledge. If that can be bypassed, sorting the passes from the compositor would be a piece of cake.

Also please don’t suggest ImageMagick as it’s been brought up in other places: I only use Blender to render and ffmpeg to compile to an animation. If Blender can’t do this I’ll try it from ffmpeg or find another way.

Hi. According to your example try this:

Note that it’ll fail with Depth and likely other passes as it is.

Oh… yes. I was thinking of just setting the render size to be twice bigger, then scaling each pass in the compositor to half. But there’s a huge problem there: Blender will still render at that resolution, and you’re essentially doubling your render time for pixels you’ll be throwing away. Especially with Cycles which is so slow on CPU rendering, it’s not price that can be easily paid. Blender needs to be “convinced” to render at the intended resolution, even if the output will be larger than that resolution.

Yeah, it’s inefficient for sure. I think I managed to scale up a render just through compositor nodes but the node tree is eluding me at the moment. Will have to look through some old files.

Hi @MirceaKitsune . Using a scene per pass plus an extra scene to composite a mosaic of passes seems like a viable way to meet your needs (each scene can hold different resolutions). See the answer here for an example: