Controlling Alphas with ProEXR

One of the more unique features of ProEXR is that it lets you choose how alpha channels are treated. Usually Photoshop takes an alpha channel and makes a layer with transparency, but some people would prefer to have the alpha channel kept seperate, particularly if they plan to use it for something unrelated to transparency like a bump map.

In ProEXR, holding down the option (Mac) or alt (Win) keys as the file loads causes any alpha channel(s) to show up on separate layers.

Update: In ProEXR 1.3, holding down option or alt now brings up a dialog with these import options and more.

Under ProEXR naming conventions (see the manual), a layer named "RGBA" will save layers "R", "G", "B", and "A" in the file, but a layer "RGB" will skip the alpha. Then if you have a separate layer called "*A", the red channel in that layer will become "A".

Or to put it simply, if you separate the alpha by holding down option/alt, save the file without changing the layer names and you'll get the RGBA file you expect.