2.2. 8 bits per colour value

The GIMP supports 8-bits per RGB colour value and 8-bit grayscale images.
That means pixel values in the range 0 to 255.

Demo:

Open lena_color.jpg.
Select the "Color Picker" tool from the toolbox.
Click on pixels of the image (or drag while holding the mouse button) and see the colour values that exist there.

There's a patch available at film.gimp.org that adds 16-bit precision to the GIMP.
It will be integrated into the main source tree in GIMP 2.0.

Written by Shlomi Fish