I'm a programmer, not a graphic designer. I'm writing a custom
View for Android that requires the ability to apply an alpha mask to an image. I want to make it easy for graphic designers (specifically, those who specialize in UI widgets like buttons and icons) to produce media for this software.
Is there any standard or conventional file format for an alpha mask? In other words, if I were to ask a UI designer to give me an alpha mask, what would it look like? The most common example I find on the web is a bitmap with black indicating complete transparency and white indicating complete opacity. Is that a format that graphic designers would be familiar with?
If the answer differs by application, I'm most interested in what would be familiar to a designer using Photoshop.