Ah - very interesting. But I'm probably still missing something. I thought I followed your suggestion, looks OK when the size is 1, but I can see the square of the decal image if I set the scale to 0.2.

"I paint that which comes from the imagination or from dreams, or from an unconscious drive. I photograph the things that I do not wish to paint, the things which already have an existence."
Man Ray, modernist painter
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