output of subtract node different for image input and renderlayer input

Hey,

I have a node setup where 2 renderlayers are inverted and subtracted from one another:



The output is not as I expected, so I saved the output of the “Invert” nodes in 2 images.
If I know change the node setup so that these images are subtracted, I get a different result:


Unfortantly the output for when using images is what I want.

Why is there a difference?

Thanks!
Nathan

It might be that the outputs are HDR so you would have values above 1 (which wouldn’t be immediately visible in the preview).

You might want to try to string both images through a color-ramp node first so you have all the values mapped between 0 and 1 (removing the dynamic range).