Bit depth

To capture details in shadow or highlight areas of an image, the correct bit depth is needed. Different sources have a wide range of brightness ranges. The higher the number of bits captured per pel, the larger the contrast range. The figure may also be given as an optical density value (O.D.), this is a logarithmic scale of brightness:
Optical Density % Transmitted/Reflected Contrast Range Approximate Bit Equivalent (Greyscale)
0 100 0 -
1 10 10:1 3-4
2 1 100:1 7
3 0.1 1000:1 10
Comparison of Optical Density, transmittance, contrast range and bit depth.

good photographic print: 100:1 so 24 bits is OK
Negatives/Transparencies: around 300:1
X-rays: >= 500:1.