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While all of the images are impressive, I found the hair rendering to be the most interesting. It's very tough to get it right, that is, realistic-appearing.

by jrapdx3 12y ago

While all of the images are impressive, I found the hair rendering to be the most interesting. It's very tough to get it right, that is, realistic-appearing. As presented it's very close to that ideal. An attribute of hair that makes it hard to render is color. At least on my monitor the "blonde" sample seems a bit too reddish. (Blonde is really sort of a dull green.) Another factor is color variation, not only the result of lighting, but also intrinsic to hair growth. (Commonly hair at its "roots" is slightly darker/lighter, and there's natural randomness among individual hairs.) I hope that doesn't sound like picky criticism, it really does look very promising. Portrait artists I know would empathize with the challenge of convincingly depicting the hair of human heads.

Tunabrain 12y ago
You're absolutely right. Getting the hair data right (groom, strand color, little fiber variations) is just as difficult as implementing the right shading model. My renders are currently a bit lacking in that regard - I'm not an artist, but I'll try to look out for that in the future. Adding some subtle random variation between fibers is definitely doable. As far as the hair color goes, I was following measured absorption coefficients of real human hair. Eugene d'Eon's paper "An Energy-Conserving Hair Reflectance Model" contains measured absorption coefficients for the pigments Eumelanin and Pheomelanin, which are responsible for human hair color. By mixing their concentrations, you can reproduce any hair color found in real life. It's difficult to find the mixtures that are just right though, and it's likely that I was a bit off for the blonde hair render :) I'll tweak it some more in the future.