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I have a simple scene where I have simple planes and textures using the alpha channel of the PNG as transparency.
The way I created the files makes the Alpha channel 000 black and 255 pure white. Here is one texture if you want to examine it.
When I prepare a scene using cycles, it works fine.
I can add more planes this way.
But when I add a third one, the intersection of the planes begin to form a shadow.
Stacking 4 planes make the shadow obvious. It is rendered on the spot where the images are combined.
Here is the blend file without textures.
What settings can I change? I changed bounce samples... but this is not about bouncing...