PhilFX looks at the layer texture node in maya with a particular look at alphas, transparencies, and using luminance as an alpha and how file format affects each.

Maya – Using the Layered Texture Node with alpha layers from Phil Hoppes on Vimeo.

This is a brief tutorial that discusses using the layered texture node within maya in conjunction with jpg and png files. The tutorial covers the subtle differences of using true alpha channel data vs derived alpha channels from luma data.