Composite two rendered images

To get rid of fireflies I’m trying to combine two Cycles renders with different seeds into one final image. What is unclear to me is how I have to set up the rendering (Render layer, slot, …) and how to access that output in the compositor.
I’m sure there is a way, I just cannot see.


Are you rendering an animation or still images?

If it is still images… render one… and save it out as a multilayer EXR… then render the second one with a different seed… save it out as a multilayer exr…

then in a seperate file all together, go into the compositor, add in two file input nodes, open the two files… add a colour mix node, and (provided they have the same amount of samples) mix them together at a factor of .5 (that will use .5 of the first slot and .5 of the second)…

Sure. Note that png store only values between 0 and 1. Moreover it’s 8 bpc (bits per channel), which means that only 256 values for R, G and B can be stored, but this is not the problem here.
If you are looking for fireflies you have to find values like 999999999999999 or so and png stores no greater value than 1.
Value of 1 for all three channels is displayed as white. Everything greater than 1 will also appear as white, so you’ll not see the difference, but computer sees it. You need those crazy high values to use the technique you’re trying to use, so you have to store images in format that can handle such values.
To make the story short - png stores about 0.0000000000000000000000000001% of the information you need :slight_smile: