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Some Hints In Using Subsurface Scattering.


rasputin

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I've spent the last two days concentrating solely on SUBSURFACE SCATTERING in C4D. I haven't found a truly thorough discussion of this-- in plain language-- elsewhere.

I've jotted down some notes from my SSS experiments. Perhaps these will be helpful to you in sorting out this rather tricky effect? (If not, please disregard!). God knows there are infinite possibilties and variations on these settings (as with everything in C4D). But here goes:

Keynotes for SUBSURFACE SCATTERING in C4D, where SSS has been entered in the LUMINANCE channel of your Material:

Absorption: How thoroughly the colors in the absorption filter are dissipated and (ultimately) neutralized. As a rule of

thumb, Absorption should be set to just less than half the thickness of your Object in units. e.g., Your Object is 14 units wide in total width.... Your Absorption setting should be around 6.5 units.

Samples: How subtle, delicate and precise is the distribution of your filter gradient. Higher numbers definitely increase rendering time, but look smoother and prettier. A setting of "8" looks OK.... but a setting of "33" looks much better.

Absorption filter gradient works like this:

Leftmost color= Where the light directly strikes your object.

Rightmost color= The glowing color visible in the far penumbra of your object. ["penumbra" means "near the Object's shadow".]

It's implied that the color on the right is the "hidden" interior volumetric color of your Object's substance, while the color on the left has more to do with the Object's surface color. Perhaps the color on the right is the warmer, more saturated one because it reveals the nature of the light itself multiplied through your object's (volumetric) substance. In a human figure, the rightmost color would be red.... for blood. A good rule-of-thumb for starting out is a color gradient running running from cool (left) to warm (right), or from desaturated (left) to highly saturated (right). Adding more colors than the default two to this filter gradient will add fanciness to the translucent effect, but often aren't necessary.

If USE NORMALS is checked, then each portion of your object--- each extrusion or appendage, like, say, an ear, a nostril, a finger--- will become a "microcosm" of the whole filter effect. USE NORMALS greatly slows render time, but diminishes the undesirable glowing of interior polys (like eyeballs or mouth sock).

The more neutral, desaturated and dark is the COLOR setting in your Material, the more your SSS effect will become evident. If a rich, saturated color is chosen under COLOR, then the resulting SSS effect might be too "glowing" and overpowering. A COLOR setting of 50% gray can be just what the doctor ordered; in other words, let the LUMINANCE/SSS do all the work in giving your Material "personality".

Minimum Thickness has much to say about the overall permeability--- translucence--- your Object possesses. High numbers imply a dense Object; low numbers imply high light permeability.

Filter Length darkens and lightens the apparent permeability of your Object. Lower numbers provide greater translucence; higher numbers make a denser, darker Object. Filter Length also determines the exact width and location, on your Object, of your colored penumbra. Thus you might think of it as SSS's "fresnel" effect.

Scattering Length= How far towards the core of your Object the light will travel. Scattering Length operates much as Refraction does under the Transparency Channel.

A Normal setting under your Material's LUMINANCE Channel itself will yield you a milkier appearance; a Multiply setting will yield

you a more translucent effect

P.S. You can often set your SSS object to not cast any shadows at all (by using a C4D COMPOSITING tag), because, as you will discover, SSS really is a form of "shadowing" in itself!. As a trick, use a "dummy" Object, with a simple COLOR Material (no other Channels active), exactly duplicating your SSS one, but set it to be unseen by Camera not receiving shadows, but still casting shadows, with a COMPOSITING tag. Then your SSS object will appear to cast shadows upon surrounding Objects, avoiding too many "busy" shadows within your SSS Object.

P.P.S. Often an SSS object will look fantastic simply illuminated by one scene light, or maybe with a second fill light barely "ghosted". It's often enough. Start adding many lights, a lot of REFLECTION/ENVIRONMENT, or HDRI skylighting, and the whole SSS effect may be spoiled. However, GI, global AO and Caustics, in your RENDER SETTINGS can enhance the look a great deal.

P.P. P.S. Saving your SSS Material for future use can be problematic, because SSS has everything in the world to do with both the unit width of your Object, and the color, strength and directionality of your scene's lighting. This cannot be overemphasized. So don't be surprised if an SSS Material doesn't transfer exactly-- or even approximately-- from one Object (or scene) to another. SSS parameters will need to be tweaked per each new Object.

Hope these are useful. They're the stuff I wish someone had told me! :)

Best, rasputin

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thanks for the guide. So far Ive just got annoyed with c4d sss because of the way objects inside the mesh became visible/cast shadows through the mesh when I used it. I will see if I can stop this happening in future.

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a few minutes of playing and Ive got this, I still dont like the seams Im getting on the shadows inside the shapes. 2 different lighting setups, 1 with no sky just 1 light on omni shadow map 1000 50% density. Other image is using a sky preset.

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Wow, SilverTalon, that is one wild model.... good for showing off SSS.

Some tricks, perhaps for enhancing the SSS effect:

1. Have the object itself neither cast nor receive any shadows and see what happens... use a COMPOSITING tag for that.

2. Wise to keep only one Omni light.... Why not position it as low in the scene as you dare to point up the translucent effect to Camera.

3. Lastly, in the world of visual phenomena, everything is relative: "A" most looks like "A" when you have "B" right next to it to compare it to. That's true in most every aspect of visual phenomena you can think of (color, size, texture, distance, shape, value, saturation, etc.) Therefore, why not have another object sitting next to, or underneath, this one, which is definitely NOT translucent... e.g. made of steel or wood, etc.

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  • 1 year later...

hi

iv been working with SSS myself on my fetus/baby model, but when i use a SSS material on it the mesh gets visible when i render. something that dont happen with an ordinary matterial. Do any one know how i can get this fixed, or were i went wrong to get this result?

-d-

edit: sorry about the rule breach, ill watch out in further posts:)

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  • 1 year later...
  • 3 months later...
Guest mascerrado

I try using SSS to my human head model, but the head become quite translucent, i can see the eyeball, teeth, everything inside the mesh. Is SSS just for solid model such as candle, teeth,etc?

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  • 4 weeks later...

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