I finally got transparency working on hair cards in LW 2020. However, after running a few test renders, it seems to take just as long as using fiber fx. I thought it would render faster. Anyone have any tips/suggestions?
Without an example, I can only give generalities:
1) Use Clip maps and transparency. This should help cut down on ray recursion.
2) Don't use absolute black for shadows. It introduces way too much noise into the image. I use a very dark grey<.11, .11, .11>/purplish-grey <.11, .12, .10> for shadows. Less noise = less time spent on AA passes.
3) Use the surfacing overrides to increase/decrease reflection and refraction samples instead of the global controls.
4) What material are you using for the hair? Keep in mind that the three hair materials are designed to be used with the hair primitive. I would tweak Principled BSDF to get it close.
5) Make sure you're using fastest under Render Properties -> Render -> Polygon Intersection mode.
6) Is this a radiosity scene? Have you tried it under direct lighting or direct lighting & environment light? direct lighting & a touch of ambient light?
+1 to everything Kryslin wrote above! In my experience, the biggest render time savings should come from using clip maps.
Many years ago (late 1990's - early 2000's), I used cards for hair routinely. That changed when Sasquatch and later FiberFx became more usable for studio production. Using hair cards is still a viable technique but, TBH, I don't think you're going to get much time saving even in the setup stage, compared to generating hair guides for fiber rendering.
Cards might be faster for real-time rendering with a game engine? I don't really know, just starting a conversation.
Thanks for the info guys will check out those points. Yes, I've noticed in LW that it seems to take just as long to render hair cards as using fiber fx. However, I'm also experimenting in Marmoset real-time rendering so the hair cards are needed in that. The problem I'm having with fiber fx is some of the single strands seem to tail off with some gaps in the strand, even after upping the camera samples.
Re: Strands that disappear and re-appear in FiberFX - crank the refraction samples in the hair material. Keep in mind that things multiply (I think), so that setting your hair material's refraction samples to 8 means 8 times the camera samples, which could result in A Lot of render time. You could probably determine the settings by rendering the problem area, I think Lightwave can render a portion of the scene...