We just had a client flag issues with the alpha channels in our renders. Our Path Traced renders for vehicle configurators have nearly invisible “Ghost pixels” around the edges of the actual alpha channel of the render, in the range of 0.00049 - 0.0024. They are present around any objects in the scene, as well as around the edge of the render frame.
These artifacts are present in Path Traced renders from 5.5 and 5.6, rendered with Movie Render Queue.
The artifacts are not visible to the naked eye when viewed in Nuke, until you crank the exposure up nearly 1000%. This was only caught because the client is doing a QA step on renders with an Outer-Glow action in Photoshop. Anywhere a Ghost Pixel was detected, the outer glow made them visible. This is mainly an issue for our client because they are programmatically cropping assets using alpha channels for various web deployments.
It’s an extremely niche issue, and our solution was to clamp pixels below a certain threshold in Nuke to 0.
See image below for alpha channel artifacts viewed at extreme exposure.
