Example 1: Effect of GI on hair
Example 2: The transmission length and width glossiness
Example 3: Strand taper vs transparency mapping
This example shows how important GI (multiple scattering) is for the appearance of hair, especially bright hair. The top row shows several of the presets rendered without GI, and the bottom shows the same scene when GI is enabled. Again GI is brute force and light cache with retrace. The scene GI environment is black so that a spherical area light is the only light source.
GI is disabled GI is enabled
This example shows the effect of the transmission glossiness length and the transmission glossiness width parameters. It shows a number of vertical strands (in this case, produced by VRayFur) lit from behind by a spherical light. Note how each parameter changes the way light scatters along the length and the width of the strands. Higher values for the length glossines compress the transmission highlight along the strand length, while lower values expand it.
This example shows how transparency mapping can be used to simulate hair thinning towards the tips with improved quality. Since transparency also increases render times, the VRayHairMtl material provides two options to optimize this - the opaque for shadows and opaque for GI options allow to skip the transparency calculations for shadow and GI rays, thus speeding up the rendering.
For the first image, the thinning of the strands towards the tips was done by setting the Taper parameter of VRayFur to 1.0. The opacity of the hairs for the 2nd, 3rd and 4th image is done with the VRayHairInfoTex texture in the opacity slot of the VRayHairMtl material, while keeping the Taper parameter in VRayFur to 0.0. The scene is illuminated with one point light with sharp raytraced shadows to better show the difference between the options. Note how opacity mapping improves the antialiasing of the hair, while still preserving the same overall look, at the expense of somewhat increased render times. However, the first image also required increased AA samples compared to the rest.
Note that using transparency for the strands may require increasing of the Max. transp. levels option in the global V-Ray settings, although it was not necessary for this particular case.
Hair geometry with taper, 1m 6s Hair geometry without taper, with opacity mapping, 2m 14s Hair geometry without taper, with opacity mapping, both opaque for shadows and opaque for GI enabled, 1m 46s Hair geometry without taper, with opacity mapping, opaque for GI enabled, 1m 57s