How can I include vertex color information in .OBJ files?

Question

The .obj files I export are missing data for vertex colors. Is there a way to include color information in the .obj file? If not, what are the alternatives?

Answer 1

Blender can export PLY files (.ply), which are text-based, very easy to parse, and include vertices colors. The hard way is to change the OBJ exporter code so that it includes the vertices colors (thus breaking obj compatibility).

Answer 2

Wavefront OBJ supports materials, which color groups of meshes the same color.

Material statements look like this:

newmtl redMtl
Kd 1.00 0.00 0.00
Ks 0.50 0.50 0.50
Ns 18.00

So, Kd is the diffuse component, Ks specular.

These would be specified inside a .mtl file that accompanies the .obj file. Inside the .obj file are statements like

usemtl redMtl
f 1/5/1 30/39/2 20/29/3
f 20/29/4 30/39/5 31/41/6
f 35/48/7 26/35/8 2/6/9

This means the faces specified there are to use the redMtl material. When you're parsing the obj file, this translates down to per-vertex color.

If there are lots of different colors, you will have a lot of different materials, but you can do it.

Here's a video of how to assign a particular group of faces a different material. You can assign a different material to each face in a mesh if you wish.