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.