Skin Making Terms

Hello , I have been hearing a number of terms being used in relation to creating skins in Photoshop and I wanted to know exactly what they are and their usefulness while creating skins for Second Life and possibly how they can be used.

I have searched these phrases on the internet but most websites I went to did not explain very well how these can be used for skin making.

They are : Color Map , Bump Map , Spec Map , Reflectivity Map , Transparency Map , Translucence Map , Diffuse Map.

I really appreciate any help that anyone can give me on these terms.

All of those various map types are used in 3d rendering applications (like Blender, Max, Maya, etc) to define various aspects of a material. Depending on the map type, the grayscale or color information of the map is used to influence the way the material is rendered. A map is wrapped around the model according to the UV mapping on the object, which defines where each pixel on the texture map falls on the surface of the objects.

color maps (aka diffuse maps) are used to define the color of the material under diffuse lighting (as opposed to shadow, or specular). Color maps come in various types and depending on the material type there may be different ones for ambient, diffuse, and specular components of the material.

bump maps are used to fake bumps, dents, grain, and other topographical features that aren't actually a part of the model itself. They're grayscale maps that alter the way the surface is rendered. Dark pixels cause the surface to be shaded as if it has indentations. Light pixels cause that area to be shaded like a raised dimple. This is achieved by the rendering engine lightening or darkening the corresponding pixels of the color map according to the bump map as if the light was reacting to features that don't really exist.

Specular maps are also grayscale maps used to define how dull or shiny parts of the surface are. In shiny areas (called specular reflections) the diffuse color is washed out by bright highlights. Most apps have two different kids of specular maps, one to control the specular level (how dull or shiny) and one to control the color of the specular reflections.

Reflection maps are used to define what's reflected by reflective materials. They're used in lieau of raytraced reflections when accurate reflections aren't necessary or when render time is an issue. Depending on the app and material type reflections are sometimes also broken into two different maps, one for how reflective parts of the surface are and one for the reflections themselves.

Transparency maps are just like alpha channels for the material. They grayscale values of each pixel in the map define how opaque or transparent the corresponding part of the surface is.

Translucency maps are used to fake what's known as sub-surface scattering, which is a fancy way of saying how light diffuses and scatters as it moves through a translucent material (like human skin, wax, gelatin, and that sort of thing).

Hope that helps.

Colour map is, well, the colour. For some reason, Max calls this Diffuse. A diffuse map is supposed to be how much the surface scatters light. Now, the Raytrace material in Max the surface scattering dynamic is called Diffusion. This mixing of terms like this can be vexing at times.

I have issue with specular and gloss maps. These were originally intended as hacks for reflect and diffuse with regards to light. The problem I have is that reflect and scatter properties don't reflect just light sources. I've always found it weird that a high specular object will show highlights from light sources but not any reflections from the environment. It's like specular and gloss are only half of the equation. But speed hacks are understandable considering how slow computers used to be.

I got more, but my night is about to begin.
BBL

It's that way in every scan line renderer I've used, probably because glossy reflections are so expensive to calculate and difficult to fake well. In V-ray specularity and reflectivity are the same thing. You use a glossiness value to determine how much it scatters. High gloss is mirror-like with sharp edged specular highlights. Low gloss has diffuse specular highlights and blurry reflections (down to too blurry to be visible). It's a very realistic system. I'm not sure how it is in Mental Ray. I was already a V-Ray user when they added MR to Max and I've just never gotten in to it. V-Ray is much faster and easier to work with imo.

The last dedicated renderer that I used to use was an early version of finalRender. I really like how fR did ambient renders. It made sense and the tweaks were easy for me to get damn close without having to do more than a handful of test renders.

I do play with Mental Ray on occassion, but I haven't really gotten into it. After what you said about V-Ray, you got me kind of curious as to how MR handles these things. Great, now I might have to really dig-in one of these days.

Transparency is basically how transparent (or opaque) the object is in the textured areas.

Translucency is more along the lines of sub-surface scattering as already mentioned. Neil Blevins has a damn good article about this:

http://www.neilblevins.com/cg_education/translucency/translucency.htm

As a matter of fact, read everything by Neil Blevins.

And while you are at it, read everything by Leigh van der Byl:

http://www.leighvanderbyl.com/tutorials.html

Then have some Dr. Julian for dessert:

http://www.3dm3.com/tutorials/maya/texturing/

Looks like I lost my train of thought while I was digging up those links.

That's pretty much how MR handles it too, provided you use the correct MR shaders. You need to raytrace the scene to replicate that type of material quality, so that's why you don't get that in the specular material of a Reyes renderer like the Max scanline.

If you want to dig into Mental Ray I recommend purchasing "Mental ray for Maya, 3ds Max, and XSI" by Boaz Livny.

MR is a powerful general purpose renderer but it can take quite a bit of time and background knowledge of how 3D works under the hood to get it tuned properly. It's similar to PR RenderMan in that it was used in the VFX industry for years before it came into the desktop realm. It's made to be used by professionals and it's easy to shoot yourself in the foot if you don't know what you are doing. This is why you often get statements like MR is slower than other renderers, because it's so hard to optimize the settings properly for beginners. This is why renderers like VRay, Brazil, FinalGather and Turtle are still sold while MR is included the 3d applications - ease of use (at the expense of flexibility). You are given a much smaller box to work in but when time is money that's a commonly accepted trade off. On top of this most of the default settings for MR in Max are horrible, although it has been improved in 2009.

If you can get past that initial investment to get up the steep learning curve it's a thing of beauty on par with PR RenderMan. MR knowledge is also application generic, so if you use MR in Max it's easy to come to terms with rendering in Maya or XSI.

Now that mental images is a subsidiary of Nvidia, I expect to see GPU support for MR in the future, like they did with the Gelato renderer.

Woah!! Way off topic and I should get back to work.

Thank you very much for the detailed explanations and links , these were highly useful!!