Alpha channel for transparency in shaders:

When you put an image with an alphachannel on the color of a shader assigned to an object, Maya will use this as transparency in the interactive viewport (and hardware renderer)

This is a simple texturefile with an alpha (mask) channel:


Result in the interactive viewport (the shader with the texturemap is assigned to a nurbsplane):


but if you render it in the software renderer you don't get the same result:
rendered in the sw-renderer, no transparency...


Ok so lets take a look at the shadernetwork:
Currently only the 'Out Color' of 'file1' is connected to 'color' of 'blinn1'


Since alphachannels are opacity based and maya's shaders are transparency based (opposites) you cannot just connect the Alpha (alpha out) to the transparency of the shader, you need to invert it first.
This is done with the 'reverse node':



Now mmb-drag the file-node (file1) onto the reverse-node, this opens the 'connection editor' (this can also be opened manually through window->connectioneditor):


Here you need to connect the 'Out Alpha' of the file-node to the X,Y,Z components of the 'input' on the reverse-node:


This updates the hypershade:


Now you need to connect the output of the reverse-node to the Transparency of the shader-node (blinn1).
This can be done either by the connection editor, or by mmb-dragging the reversenode onto the transparency parameter of the shadernode in the AttributeEditor.

The result in the connection editor/hypershade is:


Ok lest do a testrender:


Ok thats better but you can still see the result of the specular-reflection, to get rid of this you can connect the 'Out Alpha' of the file-node directly to the R,G and B components of the 'Specular Color' on the shader-node:


And heres the resulting render:


The resulting hypershade looks like:


The shader can be downloanded, and so can the circle-image

Good luck with it.