SSS Amount

SSS amount maps determine where on your model SSS is going to be applied. A white value will alow 100% SSS, where as a High value which is regarded a darker colour i.e Black will have no effect on SSS.

The Low value of white, or light colours can have a setting of 0%, this means that the map is 100% reasonable for producing its lightest tone. The High value on the other hand is set to 100% to be at its normal darkest value according to the map. Essentially a 0% low is netural and a 100% for the darkest part of the map is also its nutural basis.

When we want to tone down either the light values of the light part of the map, or darker parts of the map, we use these two vales higher and lower to dominate each other. If the lighter value for instance is way too bright, we can get the darker value to tone down the light value by simply moving the high value anything lower than 100%, this starts to saturuate into the lighter tones.

From the lighter tone of the map, it also can be used to dominate the dark part, by having a value anythink above 0%. As to what strength effect this lighter values has over the dark, will be to how much the darker shade took from the lighter shade before hand, if any. The overal amount will determined how much of the SSS colour will spread on your model along with the scatterng distance.


Diffuse Amount

The diffuse amount has a major effect on how the diffuse colour or Diffuse colour map is applied to the amount of light saturation. Even more, difuse amount effects greatly how SSS and colour diffuse work together.

When we have a low diffuse amount, hardly any diffuse colour or a colour map gets applied to the model in the areas that has SSS, this has got be taken into account as to how much SSS amount is applied, more on that later. A low diffuse amount setting shows fade out your texture map on areas that havem more sss applied like ears, nose etc.

In order to get a balanced colour or colored texture map, we have to have the diffuse at 100%, or tone down the SSS amount. The negative effect is that now the diffuse colour or colour map completely dominates the SSS colour when the diffuse is set to 100%. To combat this we use conserve energy function.

Conserve energy now allows the sss colour to be mixed with 100% diffuse colour, more evenly spread across the model. There is a negative effect however, and that is a new colour can be made that you didn't want. As a example if you have green ears on the diffuse colour map and blue sss colour with 100% diffuse amount, plus conserve energy, your get a purple sss effect on the ears. Being consistent of the colour in the SSS areas of the diffuse colour map and the SSS colour will avoid new tones being generated, and remember the diffuse colour doesn't need to be hard in SSS areas, as when the light isn't effecting the SSS the model will have this colour always applied. Let the red of the ears get redder with light from sss colour, not totally diffuse colour.


Scattering Distance

The scattering distance controls how deep into the model the lights penetrates to produce the sss colour. A setting of a very high amount produces a stronger colour closer to the SSS sellected colour sellected. Setup your scene lights how your scene will be for your final render otherwise you can over or under do the SSS distance.

A example would be if you wanted a soft glow to the face but the ears to be translucent in red sss colour. Have the lights set as close to the geometry or as intense as they are needed for the scene before hand. If the SSS distance is set more than the thickness of the models thickness area in question, then it will have no more effect past that thickness limit. A 100mm thick ear can't be penetrated more that 100mm SSS distance, at 100% value the model will have a glow effect.


Front Weighting

This acts like a gradient effect. Basically how the sss colour fades out into the non effected area that was determined by the sss amount. If the sss amount is set correct then use the front weighting to determind the ovarall fall off of colour.


Samples

Sometimes the sss settings can have a speckled effect, This happens when light is skipping certain amounts of the surface area. Higher samples allows more photons of light to pass into the model thus giving a smoother effect. Don't take the samples too high as there is a diminishing point when nothing makes a visual difference, other than longer rendering times.

The first example shows SSS for skin. We see how the maps are applied and do their job. The Model has no detail or projected diffuse colour map. A projected colour map can sometimes give a cheat result as some SSS has been captured in the photo used for projection type texturing. Although this is not bad, it would not show what the SSS maps and settings really are doing in my tests. This example is relatively setup quick, with some time a better balance can be achieved.