What good is 30-bit color scanning if PSP (and most other programs) only use 24-bit color?
This is actually a fairly complex question. The answer has to do with how the eye and film see light, versus how electronics see light. The eye (and film) have a “logarithmic” response. That is, the eye sees the same difference between 4 units and 8 units as between 16 units and 32 units. Electronic devices have a linear response – that is, the difference between 4 units and 8 units is the same as the difference between 16 units and 20 units. A 24-bit-color scanner detects 256 different levels each of red, blue, and green, then performing some kind of transformation to make those linear levels more closely approximate the logarithmic response we expect. By scanning an extra two bits per channel, the scanner can make finer distinctions in the dark end of each range, and deliver better scan quality. For some images, this will matter. For others, it won’t. Think about what you will use your scanner for when evaluating various features and claims before you buy one.
