Image Matte ...
 

Is there a way to create a mask of an object limited to the camera view ONLY. As an example ... lets say you have a box with an object placed in it. The object sticks out the top of the open box, it could be a board or what ever. If I render out alpha channels for both objects the masks are of the complete object. Can I also create a alpha of only what the camera sees sticking out of the box and not include what is hidden inside the box.

Yes

Have a look into using the matte opacity settings for the materials, that should get you going in the right direction as well as rendering in layers.

Rendering in layers gives me the entire object. I then have to go into PhotoShop and outline the areas the camera wouldn't see and delete them. I want to generate a mask of only what the camera sees of an object. Can a mask be created for only specific faces of an object ... just the faces the camera sees. Like "Camera Based Selection".

do an ID pass, its when you assign a surface shader of a different color to each mask you want in your scene. Then in your compositing package you can select that color and use it as a mask as you wish.

Normally, like LP just said, in post you would use the Alpha/ID of the occluding object(s) to "cut-away" the alpha of your target object.

However, you seem to want to make a single pass with this operation already done.

So, below is the fastest and easiest way this can be achieved directly in Maya rather than the normal way of using matte or ID passes:

-Select the shader that you have applied to the box, and open its' attribute editor and under Matte Opacity, change the drop-down box to BLACK HOLE.

This will do exactly what you require to both the color and the alpha of the result.

There are also other ways to achieve this directly in Maya, but like I said normally in production one would do this operation in post and simply use the alpha or ID pass of the "occluding" object to remove/occlude the contents of your box:)

Thats it. Thanks to all. I'm looking for a way to separate complex CAD components from each other pre-post. Like engine components, and do it all at once.