When you paint on a model, you actually paint on a file texture that has been assigned to the model. You can assign a file texture in Hypershade, or you can create and assign it from the 3D Paint Tool.
When you select the 3D Paint Tool, Maya checks to see if there are any file textures already assigned to the selected surfaces for the current attribute (such as color or bump maps). If any of the surfaces do not have file textures assigned, Maya prompts you to assign textures to them. Maya creates the textures, assigns them to the surfaces, names the new textures based on the current scene, shape and attribute names, and places them in a subdirectory of the current project’s 3dPaintTextures directory.
If there are existing file textures, Maya checks to see if their names match the current shape, scene and attribute names. If they do not, Maya copies the textures to the correct names. This prevents you from overwriting existing file textures, and makes it easier for the tool to keep track of the textures.
When you Assign Textures you can save the file in any of the following formats:
(Windows and Linux) Maya IFF (the default) Autodesk PIX, EPS, GIF, JPEG, RLA, SGI, SoftImage, Targa, and Tiff.
(Mac OS X) Maya IFF (the default), Windows Bitmap, JPEG, MacPaint, Photoshop, PNG, QuickDraw, QuickTime Image, Targa, SGI, and Tiff.
