You can save the images you paint on the canvas in Maya image format (.iff) only.
If you have specified a name for the image, Maya saves the image to that file.
If you have not specified a name for the image, the Save Image (Linux) or Save (Windows and Mac OS X) window opens.
If you have specified a name for the image, Maya saves the image to that file.
You can set whether or not changes to the alpha channel are saved when you use Save and Save As.
To set Save and Save As options
When you modify textures that are attached to surfaces in your scene, you may want to see the changes on the surface immediately. Whenever you save a texture in the canvas, the texture updates on all the surfaces it is attached to. You can see this update if you have hardware texturing turned on. To update the texture after every stroke, set Paint Effects to save the image after each stroke.