I am trying to create a script, that would allow me to merge multiple images, rendered with different seeds and different sample amounts into one image with a higher sample amount.
The script is using blender compositor nodes. At start it seemed to work, but upon closer inspection, some brighter parts of the rendered image are noisier than one image rendered with the same sample amount, as the combined image.
Below i'm attaching two renders from the Blender classroom scene, the first one is rendered with 1000 samples, and the second is a merge of 300, 300, 200, 100 and 100 samples.
At first glance, the images are similar, but the difference can be spotted if you zoom in at the top of the board, where it is lit up.
Also, below i'm attaching the node setup, that my script generated. The number in the name of the files shows with how many samples it was rendered.
My question is, is there some "magic" that blender does to make those large samples renders look better, and if yes, can i mimic it somehow in compositing? Or do i have to tweak some render settings when rendering those images for merging.
The images were rendered with direct clamping set to 0, and indirect to 10.
Also it was rendered in blender 3.0.0, with Cycles X.