While I was working, I used Karma to render smoke. I have to admit that Karma's XPU is really fast, but I encountered some issues when applying object masks. So, I created a small scene to test it out and found that the problem is indeed real.





This is just a simple scene where ordinary smoke is combined with a pig head. Then, using the Render Geometry Settings node, the pig head is used as a mask for rendering.




In Nuke, when combining the smoke and the pig head together, you may not notice anything unusual. However, when examining the alpha channel, the problem arises. There is a small seam between the smoke and the pig head. They don't match perfectly.






I don't know why this is happening. Is it a problem with my settings? Is there any way to solve this issue? If you know, please let me know. I would truly appreciate it.