I have spent a long time rendering an animation that I do not want to redo. I also want to render a mist pass though. Is there a way to render only the mist pass without rendering the original images? Sorry if this is a dumb question, it's just that in all of the tutorials, they show how to render both the original image and the mist pass.
I guess you could enable the mist pass, and in the compositor, Ctrl+Shift+LMB to view the mist pass and you'll get the viewer node. Press N to open the side panel and in the Item tab there is an option to save that as an image. [the viewer node has to be selected in the last step].
I got this problem too, I have searched all over internet and it seems there's no answer that leads to rendering mistpass only.
So I used a cheap trick, where I just render everything all again, but only output the mistpass to the folder
BUT only using 1 samples
might not be precise but still useable !
best solution for this
I don't believe there is a way to render only a mist pass without diving into code. However, as far as I've experienced, the mist passes in Eevee and Cycles are nearly identical, so if your original render is in Cycles, you can render the mist pass much more efficiently by temporarily switching. Just enable "Mist" in the View Layer Properties panel and grab it in the compositor.
You can also try disabling any other render passes you don't need to see if that speeds it up at all, though I've found disabling "Combined" still renders the full image.