What are Alpha only icons?

问题:

As per Android L developers guide here,

The system ignores all non-alpha channels in action icons and the main notification icon. You should assume that these icons are alpha-only.

So my question is very simple: what are alpha-only icons? and how does it affect the UI? What are the things that I have to update in my project which was targeted previously for jelly bean?

I searched on google but couldn't find any answer for this.

回答1:

Alpha is from a graphical background, and in Google docs it refers to Icons with transparent Background

Graphical definition

Alpha channels are masks through which you can display images. The alpha channel is an 8-bit channel, which means it has 256 levels of gray from 0 (black) to 255 (white). White acts as the visible area; black acts as the transparent area