image - FInd out if PNG is 8 or 24?

Question

Is there a way to find out if a PNG is the 8 or 24 type? Ive tried with windows, fireworks and photoshop but I cant figure this out. Thanks

Answer 1

The quickest way is to just peek at bytes 24 and 25 in the PNG file. They contain the bit depth (1, 2, 4, 8, or 16) and color type

• 0: gray,
• 2: rgb,
• 3: indexed (colormapped),
• 4: gray+alpha, or
• 6: rgba.

If the bitdepth is 8 and the colortype is 3 you have a PNG8, and if the bitdepth is 8 and colortype is 2 you have a PNG24.

On a *nix platform, the "file" command will do this for you, e.g.,

A PNG8:

glenn.rp> file logo.png
logo.png: PNG image data, 640 x 480, 8-bit colormap, non-interlaced

A PNG24:

glenn.rp> file rose.png
rose.png: PNG image data, 70 x 46, 8-bit/color RGB, non-interlaced