Understanding 24 bit PNG generated with Photoshop

Question

A 24 bit .png file with transparency, as those that can be generated with Photoshop, has really 24 bits distributed across each color plus the alpha ? or the 24 bit refer only to the colors and ignores the alpha (RGBA 8888).

Is there any tool to examine a PNG file and verify this kind of information? Does Photoshop have any options to verify or configure this?

Answer 1

24 bit + alpha is actually 32 bits per pixel. Meaning you have the Red, Green, Blue and Alpha channels, each being 8 bit, allowing for 256 shades per channel translating to 256 x 256 x 256 x 256 possible colour combinations. That's what the "millions of colours" and "billions of colours" mean in certain graphics and video software.