Ptex
By Neil Blevins
Created On: Apr 14th 2012
Updated On: Aug 26th 2012

Go here to read this tutorial in Russian.

A Ptex file is an image file format not that unlike a tif, jpg or exr, its main difference is it isn't a purely 2d file format, but contains 2d pixel information on a face by face basis for a 3d model. The format was created at Disney for use in their proprietary paint3d software, but the format was open sourced so that now other 3d applications will be able to take advantage of the format. For a more technical discussion of Ptex, including the original paper and usage videos, visit Disney's Ptex Site.

2D vs Ptex Workflow

When dealing with normal 2d image formats, your 3d workflow would be something like this:

One of the main issues with this scheme is it takes a long time to setup good uvs for a model, especially if it has a lot of separate pieces of geometry. And it's just so darn frustrating, it seems like there should be a way to paint on your model directly without the need for a 2d intermediate. That's where the Ptex format comes into play. Here's a common Ptex workflow...
Advantages & Disadvantages

So there are a number of advantages of using Ptex over the normal 2d mapping method...
There are some disadvantages though...
The Ptex Format
So a Ptex file is basically a list of faces, and all the pixels (also called texels, for texture pixels) on that face. For example, here's a rock texture painted onto a 3d face...



This is what that texture map may look like applied to uvs in 2d...



And this is similar to what would be contained in a Ptex file...



As a 2d map, this is unreadable. But the 3d software reads the Ptex file, and knows which chunk of texels are applied to which faces, and the result in 3d is the proper paint on the proper faces.

Painting And Baking

The two most common ways to use Ptex files in your workflow are as a way to store 3d paint, and as a way to bake various properties into your mesh.
Conclusion

So this may sound a little complex, but try and remember back to when you first learned about uvs. I bet the concept was a little bit difficult to visualize. It's the same with Ptex files, it's just a different way of doing the same thing. But once you understand how it works, it's actually in many ways a simpler process. And as the tech advances, hopefully most of the gotchas will slowly disappear. UVs will never go away fully, but with Ptex, hopefully we can do away with unneeded uv sets and only use uvs when necessary.

Examples

The best way to get into Ptex is to jump in and start using them, so for those of you who own mudbox 2012-2013, here's a tutorial on the Ptex workflow for mudbox: Ptex Use In Mudbox 2013.

And here's some info for people who are interested in using ptex files in mentalray for Maya.

And here's some info for people who are interested in using ptex files in vray for 3dsmax.


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