Mental Ray Alpha Map get Bitchy: notes!

 The only other thing that comes to mind is on the Quality tab, at the bottom under Framebuffer, make sure your Data Type is a type of 'RGBA'. If it is just 'RGB', you won't get the alpha channel.(choose 16bit!!!)

and also, check "Alpha is luminance"....stupid feature.




found some basic along the way, good to have

Maya (and mental ray) both regard Black = 0, White = 1.  When applied to a “Transparency” attribute, 0 = no transparency (opaque) and 1 = full transparency. 

I would make three separate files in Photoshop - one with the picture of the leaf, one with the leaf filled in completely with black and the background completely white, and the third would be a grayscale image of the leaf against a black background.

In Maya, create a file texture node; import the picture of the leaf as the image, and connect it to the color attribute of your shader (I was using a blinn). 

In the hypershade, select the file texture node, select “Edit - Duplicate - Duplicate with connections to the network”.  (Use the “Edit” menu command from the hypershade, not the main menu).  This gives you a new leaf, but it is connected to the same placement node as the original.  Replace the image with the picture of the black leaf against the white background.

Drag this on top of your blinn material, and from the drop-down menu that appears, select “other”.  This brings up the connection editor.  In the left column, find the “color” attribute, and connect that to the “transparency” attribute on the right.  Maya wants to connect alpha or transparency by default- you have to force this connection.

Finally, duplicate this again in the same way, replace the image with the grayscale image, and connect that to the “specular” attribute of the shader.  You can adjust the specular by using the “Color Gain” slider for the image in the attribute editor.