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By now, I’m sure you’ve all at least heard of Worley Labs new Lightwave plugin, G2, and I’d be willing to bet that most of you already have your own copies, and have been playing around with it for some time now. Isn’t it cool? I’ve been beta-testing it for a while, and I still find myself discovering features I hadn’t played with before, or new ways of using it. Trying to go through it all would be a nightmare, so luckily I’ve only been asked to talk about the Subsurface Scattering in G2 - also known as SSS.

Subsurface Scattering works on the principle that for many materials, light doesn’t bounce right off the surface, but actually manages to penetrate a certain extent and is eventually absorbed, bounces back out again or continues straight through. SSS is a hot topic these days and there are some incredible things you can do with it which would have been virtually impossible before.

Imagine a marble statue, lit from the side and slightly behind very dramatically. Notice that the version shown here without Scattering (pic01) just doesn’t look as real as the one with it turned on(pic02). The thin nose and collar allow more light to escape than from the thicker regions like Beethoven’s hair, and the sides facing away from the light are illuminated accordingly. Notice how much more detail is evident in the region around the neckline(pic03). This is not caused by radiosity effects, but by G2 simulating the way light would enter the bust, and be diffused, virtually illuminating it from within.

Substances like wax, marble, jade, milk, plastics and skin all share this property of internal light scattering, and being able to reproduce it will become increasingly vital for all 3D artists. In some cases you can fake it, or use very simplified effects like lightwave’s native translucency. But eventually you’ll find the need for depth attenuation, realistic falloff, and more subtle aspects that require more complicated algorithms like that used by G2.

Since SSS is so dependent on the actual physical geometry of the object to which G2 is applied, it would not make very much sense for me to simply give you a list of numbers to enable you to produce the perfect surfaces. Instead we’ll walk through a couple of examples, and I’ll explain G2’s Scattering controls in that context.

Let’s start simple with a candle. First, you should get a real candle and light it in a dark room and study how the light interacts with the wax of the candle itself. Depending on how thick your candle is, the top should glow, even where the light from the flame cannot directly illuminate it. Keeping that image firmly in mind, let’s turn to lightwave. First, model a candle. This should be fairly easy, but obviously the more detail you add, the more realistic your final image will appear. You can get away with a point light, but a linear or area light would be more realistic. I’ve made my lights a little orange, and given them some falloff since a single candle doesn’t light up a room a whole bunch. The flame is a simple image map.(pic04)

Preparing a surface before you apply G2 is important, since we want to utilize the preview function as much as possible, and minimize the F9s, AND have the G2 numbers make some kind of sense. Therefore, I turn everything I think I might need in the Lightwave surface panel up to 100%. Diffuse, specularity, even glossiness and reflectivity. I can always use G2’s boosts to bring them down later with instant updates, and numbers that make sense. (A glossiness of 52% in LW combined with a G2 boost of 16% is a bit unwieldy. If possible, I ONLY want to change numbers in the G2 panel.) I’ll also open a G2 preview window and apply G2 to the candle surface right away.

Now since the Scattering operations are a bit more computationally intensive, if Transparency Absorption or Translucent Lighting are at 0%, G2 ignores those factors when you render. This means that G2 doesn’t capture any information pertaining to those functions when you F9, so turn Translucency on now, even though we have no clue what to set the values to quite yet.(pic05) Remember, we want to minimize how many F9’s we do since they’re slllloooooowwwwwww. G2’s instant feedback is much more user-friendly. But we do need to F9 at least once, so go ahead and do it now.(pic06)

Not a bad start. Depending on your reference candle and the model you’ve built, you’ll want to tweak differently than I did, but let me explain what you’re tweaking. In this case, the important controls are Translucent Lighting, Subsurface Scattering and Falloff Distance. Falloff Distance tells G2 how far light can penetrate a material before all its energy is absorbed. Turn it towards 0 for wax that doesn’t glow so much. Notice that since we have a falloff on the light, higher levels eventually produce no change. Subsurface Scattering determines how diffuse the light becomes once it enters the material. At 0%, the light passes right through, and maintains a tight coherent beam. At 100%, it’s bouncing around all over the place, and the glow is much more even. And obviously, Translucent Lighting simply controls the intensity of the effect.

Nonlinear Scattering and Surface Refraction adjust how the light is spread as it travels through the medium. This can help you wrap the internal glows around corners, and modify the falloff to get it just right. This version (pic08) feels much better, and looks more like the candle I have sitting at my desk right now. The most important and hardest change to get just right was the highlight on the fat yellow candle. Now the translucency is not so vague and the internal glow is clearly being caused by the candle flame.

Before we get into some of the other controls, we’re going to have to try making something else. How about a little crystal figurine so we can show off the Transparency Absorption controls? I’m using a little elephant model I made a while back. Animals are great for this exercise because they have complicated, organic shapes and regions with varying degrees of thickness. (pic09)

Once again, I start with 100’s in LW’s surface panel, including transparency. Also since I’ll be using G2’s backside poly trick, I need to turn on double sided and in G2, I click on the options in the transparency tab, and turn Transparency Absorption to 100% on the Scattering tab.(pic10) This should get me a smoky glass effect where the thicker parts of the elephant are not as transparent as the thin bits.

Falloff Distance is again the important control here. Low values get you glass like welder’s goggles you could use to look at the sun.(pic10b) Complementary Color goes hand-in-hand with Falloff distance and helps determine which wavelengths of light are being absorbed. At 0%, only light the same color as the surface can get through, tinting everything that color. At 100%, all colors get through. Finding just the right balance helps when your crystal elephant needs to be mainly blue, except where the very thin parts let through light of all colors, and so don’t get tinted at all and show up white or clear.(pic11)

What’s really fun is when you combine both Transparency Absorption and Translucent Lighting to make complex materials like jade. Transparency Absorption usually winds up darkening your surface. Here are the settings I’m using and the result.(pic12) (pic13) Just remember that the thing about translucency is that you usually don’t notice it until the object in question is backlit, but G2 is great for seeing what your work looks like no matter how it’s lit. Move your lights around and watch the preview window.

Also remember to use G2’s SSS features in moderation. They’re designed to add subtle effects. Setting G2’s preview to only show the effects of Scattering is an easy way to dial your settings in quickly without getting confused by other effects.(pic14) In this case, I was trying to get the light to appear like it could penetrate just the very outermost layers before it was completely absorbed and scattered by the minerals that make up the stone. But look at the different materials I get simply by changing the Falloff Distance and Subsurface Scattering.(pic15)

Well, hopefully that helped you understand the power and usefulness of G2’s scattering tab. It’s certainly one of the ones I find myself playing with most often. I could easily keep giving you sample after sample of cool things I’ve been building lately, but I’ll stop here and let you go explore and discover it all for yourself.

A professional Lightwave 3D user since 1996, Rich Helvey’s work history includes UFO Films, Art F/X, and Entertainment Tonight. Rich is currently the lead animator for NBC’s Access Hollywood, in Burbank California, and was an active member of the G2 beta-testing team.

	By now, I’m sure you’ve all at least heard of Worley Labs new Lightwave plugin, G2, and I’d be willing to bet that most of you already have your own copies, and have been playing around with it for some time now. Isn’t it cool? I’ve been beta-testing it for a while, and I still find myself discovering features I hadn’t played with before, or new ways of using it. Trying to go through it all would be a nightmare, so luckily I’ve only been asked to talk about the Subsurface Scattering in G2 - also known as SSS. Subsurface Scattering works on the principle that for many materials, light doesn’t bounce right off the surface, but actually manages to penetrate a certain extent and is eventually absorbed, bounces back out again or continues straight through. SSS is a hot topic these days and there are some incredible things you can do with it which would have been virtually impossible before. Imagine a marble statue, lit from the side and slightly behind very dramatically. Notice that the version shown here without Scattering (pic01) just doesn’t look as real as the one with it turned on(pic02). The thin nose and collar allow more light to escape than from the thicker regions like Beethoven’s hair, and the sides facing away from the light are illuminated accordingly. Notice how much more detail is evident in the region around the neckline(pic03). This is not caused by radiosity effects, but by G2 simulating the way light would enter the bust, and be diffused, virtually illuminating it from within. Substances like wax, marble, jade, milk, plastics and skin all share this property of internal light scattering, and being able to reproduce it will become increasingly vital for all 3D artists. In some cases you can fake it, or use very simplified effects like lightwave’s native translucency. But eventually you’ll find the need for depth attenuation, realistic falloff, and more subtle aspects that require more complicated algorithms like that used by G2. Since SSS is so dependent on the actual physical geometry of the object to which G2 is applied, it would not make very much sense for me to simply give you a list of numbers to enable you to produce the perfect surfaces. Instead we’ll walk through a couple of examples, and I’ll explain G2’s Scattering controls in that context. Let’s start simple with a candle. First, you should get a real candle and light it in a dark room and study how the light interacts with the wax of the candle itself. Depending on how thick your candle is, the top should glow, even where the light from the flame cannot directly illuminate it. Keeping that image firmly in mind, let’s turn to lightwave. First, model a candle. This should be fairly easy, but obviously the more detail you add, the more realistic your final image will appear. You can get away with a point light, but a linear or area light would be more realistic. I’ve made my lights a little orange, and given them some falloff since a single candle doesn’t light up a room a whole bunch. The flame is a simple image map.(pic04) Preparing a surface before you apply G2 is important, since we want to utilize the preview function as much as possible, and minimize the F9s, AND have the G2 numbers make some kind of sense. Therefore, I turn everything I think I might need in the Lightwave surface panel up to 100%. Diffuse, specularity, even glossiness and reflectivity. I can always use G2’s boosts to bring them down later with instant updates, and numbers that make sense. (A glossiness of 52% in LW combined with a G2 boost of 16% is a bit unwieldy. If possible, I ONLY want to change numbers in the G2 panel.) I’ll also open a G2 preview window and apply G2 to the candle surface right away. Now since the Scattering operations are a bit more computationally intensive, if Transparency Absorption or Translucent Lighting are at 0%, G2 ignores those factors when you render. This means that G2 doesn’t capture any information pertaining to those functions when you F9, so turn Translucency on now, even though we have no clue what to set the values to quite yet.(pic05) Remember, we want to minimize how many F9’s we do since they’re slllloooooowwwwwww. G2’s instant feedback is much more user-friendly. But we do need to F9 at least once, so go ahead and do it now.(pic06) Not a bad start. Depending on your reference candle and the model you’ve built, you’ll want to tweak differently than I did, but let me explain what you’re tweaking. In this case, the important controls are Translucent Lighting, Subsurface Scattering and Falloff Distance. Falloff Distance tells G2 how far light can penetrate a material before all its energy is absorbed. Turn it towards 0 for wax that doesn’t glow so much. Notice that since we have a falloff on the light, higher levels eventually produce no change. Subsurface Scattering determines how diffuse the light becomes once it enters the material. At 0%, the light passes right through, and maintains a tight coherent beam. At 100%, it’s bouncing around all over the place, and the glow is much more even. And obviously, Translucent Lighting simply controls the intensity of the effect. Nonlinear Scattering and Surface Refraction adjust how the light is spread as it travels through the medium. This can help you wrap the internal glows around corners, and modify the falloff to get it just right. This version (pic08) feels much better, and looks more like the candle I have sitting at my desk right now. The most important and hardest change to get just right was the highlight on the fat yellow candle. Now the translucency is not so vague and the internal glow is clearly being caused by the candle flame. Before we get into some of the other controls, we’re going to have to try making something else. How about a little crystal figurine so we can show off the Transparency Absorption controls? I’m using a little elephant model I made a while back. Animals are great for this exercise because they have complicated, organic shapes and regions with varying degrees of thickness. (pic09) Once again, I start with 100’s in LW’s surface panel, including transparency. Also since I’ll be using G2’s backside poly trick, I need to turn on double sided and in G2, I click on the options in the transparency tab, and turn Transparency Absorption to 100% on the Scattering tab.(pic10) This should get me a smoky glass effect where the thicker parts of the elephant are not as transparent as the thin bits. Falloff Distance is again the important control here. Low values get you glass like welder’s goggles you could use to look at the sun.(pic10b) Complementary Color goes hand-in-hand with Falloff distance and helps determine which wavelengths of light are being absorbed. At 0%, only light the same color as the surface can get through, tinting everything that color. At 100%, all colors get through. Finding just the right balance helps when your crystal elephant needs to be mainly blue, except where the very thin parts let through light of all colors, and so don’t get tinted at all and show up white or clear.(pic11) What’s really fun is when you combine both Transparency Absorption and Translucent Lighting to make complex materials like jade. Transparency Absorption usually winds up darkening your surface. Here are the settings I’m using and the result.(pic12) (pic13) Just remember that the thing about translucency is that you usually don’t notice it until the object in question is backlit, but G2 is great for seeing what your work looks like no matter how it’s lit. Move your lights around and watch the preview window. Also remember to use G2’s SSS features in moderation. They’re designed to add subtle effects. Setting G2’s preview to only show the effects of Scattering is an easy way to dial your settings in quickly without getting confused by other effects.(pic14) In this case, I was trying to get the light to appear like it could penetrate just the very outermost layers before it was completely absorbed and scattered by the minerals that make up the stone. But look at the different materials I get simply by changing the Falloff Distance and Subsurface Scattering.(pic15) Well, hopefully that helped you understand the power and usefulness of G2’s scattering tab. It’s certainly one of the ones I find myself playing with most often. I could easily keep giving you sample after sample of cool things I’ve been building lately, but I’ll stop here and let you go explore and discover it all for yourself. A professional Lightwave 3D user since 1996, Rich Helvey’s work history includes UFO Films, Art F/X, and Entertainment Tonight. Rich is currently the lead animator for NBC’s Access Hollywood, in Burbank California, and was an active member of the G2 beta-testing team.
	The Japanese version of this tutorial was printed in the Japanese Computer Graphics World magazine.