Determine if Alpha Channel is Used in an Image

Question

As I\'m bringing in images into my program, I want to determine if:

1. they have an alpha-channel
2. if that alpha-channel is used

#1

Answer 1

The simplest method using ImageMagick (command line) is to test the alpha channel if the mean is less than 1 (on a scale of 0 to 1). 1 is fully opaque. So

convert image -channel a -separate -format "%[fx:(mean<1)?1:0]" info:

If the return value is 1, then at least one pixel is transparent; otherwise (if 0), the image is fully opaque.