Dirty Glass

[cheesemcboots]

Hey mate. First of all I just want to say i dont know how to do alpha maps (I cant model so I dont know how to make them or bake them or whatever is required) but as a texture artist in the making I should know. If I was making this, I would look into how decals are made. The file format here is crucial. So basically, I am saying I would like to know to.

[Magnus3D]

It could be helpful if you provided information about what renderengine you are using so people would be able to give you better feedback that matches your tool.

/ Magnus

[soulburn3d]

It depends on what 3d app and renderer you're using. But in general, make a glass material, make a dirt material, then blend between the two using a mask that's your dirt pattern.

- Neil

[Cloudless]

Paint a dirt map for the refraction color.

[sundialsvc4]

Look carefully at the reference photos and consider how many distinct visual characteristics are affected by the "dirt":

Transparency. "Shininess" (specularity). others ...
Next consider what characteristics of the glass are not affected by the dirt... i.e. they are fundamental to "it looks like glass" whether or not it is "dirty glass."

Now, starting with the "spotlessly clean glass" that is underneath all that dirt, build one or more texture layers for these. (In the case of glass at this distance, it's mostly specularity, general reflection/color, and the alpha of each of these.) Ponder a piece of glass carefully: look at the light.

The various "dirt" layers, which undoubtedly will use some kind of image-map or procedural texture as their inputs, are put on top of that. They're blended with each other and with the "pristine glass" layers. Somehow. Somehow that looks good.

For instance: the dirt-and-grime is greyish, it dampens the reflection quite a bit, it's modestly opaque. And, on top of that basic "dirtiness," we notice that there's a certain definite pattern to it, especially in the center pane. So we might contemplate an approach of "build the base 'dirt', then modify the degree to which that is applied, using some kind of image-based map."

Now, I can't tell you how (many ways there are) to do this in "your package of choice," but I would like you to get the big-picture of where I'm going with this. "The visual appearance" of almost anything in this world is made up of several simpler characteristics, somehow combined. If the object is, say, "dirty," then the characterstics pertaining to "dirtiness" are added on top of that. You can now "tweak" the various influences, rearrange them, add some, remove some, until you get it "just right." You are building up layers, or perhaps a system of, discrete visual elements and filters.

Sometimes (but not always), you can employ the same layers in building-up the textures of different parts of your model: the "dirtiness" might be applied both to the glass and to the surrounding metal frame. Whether it's exactly the same "dirtiness" or not, the principle is the same.

You can make this "easy" or you can make it "over-complicated." The choice is yours, but the choices in modern software packages are limitless. At some point (preferably "soon"), you'll draw a line in the sand and say, "that's good enough."

The trick is: look at the light. What is the light doing? No matter how you wrestle with the features of your package (or, choose to avoid doing so), the biggest determinant of a satisfactory result are: your powers of observation.

[Nidirhab]

Thank you guys for response!
sundialsvc4 (http://forums.cgsociety.org/member.php?u=93006)
cheesemcboots (http://forums.cgsociety.org/member.php?u=383376)
Magnus3D (http://forums.cgsociety.org/member.php?u=216022)
soulburn3d (http://forums.cgsociety.org/member.php?u=4754)
and MikeJohnson (http://forums.cgsociety.org/member.php?u=110997)

Thanks once again!

I'm using 3ds max 9 and Vray 1.5

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