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I have system that consumes depth and RGB output of Cycles renderer. I can observe noise in depth maps when I use transparent BSDF with Mix shader and RGBA texture. Let's look at sample simple shader: Sample shader with mix BSDF and transparent BSDF

That shader is giving material that is transparent with level of transparency given by alpha channel of texture. I am not happy with depth image, especially on edges (white dots):

enter image description here Two factor has to be present to "depth" noise appears:

  • There must be some other object behind the part that is transparent.
  • The noise seems to be absent when alpha channel has only value 255 or 0.

A this moment I found some solutions:

  • using mist pass
  • using material override

First solution seems to give depth values in some bizzare scale (I need it linear in meters, like Z-pass) and the noise is still present. Second solution is not acceptable, because removes desired feature.

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I think that it is normal behavior, same issue appears in mist pass. During mist pass / z-pass mixa shaders with transparent shader cause that some of rays do not contribute to image output. I resolved it introducing contrast node before mix shader to keep mixing rate 0 or 1.

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