John - thanks for that link. It sounds like they come in enough variety to choose from.(posted 8065 days ago)Pete, yes, I meant your previous info, which I couldn't find... even through google with site: specified.
The raw data I get is set for gamma of 1.0 with some unknown brightness and contrast. (note: gamma here is a different stuff from those used for contrast for those not familiar) So it should be pretty linear to light intensity (whether transmitted or reflected) except for the effect of noise, device nonlinearity, etc. However, these are easy to fix as long as I have a good calibration material.
For those who are confused by "log" and "linear" thing. The linear here is meant for intensity-value relation. Strictly speaking, it's not linear because quantization is a non-linear function... I'm sure there are some DSP-heads around here. Gamma in the context of CRT, printing device, etc refer to the exponent g in intensity = (contrast * value)^g + offset (or something more accurate than this). Optical density is defined by common log of ratio of incident and transmitted light intensities. For some reason, I like playing with slide rules but I haven't used log scale plotting paper for years.