> Thats not true. Nikon and Canon both do a lot of their own sensor to > digital representation processing too, ya know? And their RAW data is > just as much RAW as anyone else's. I don't know what quantization > they use in their A-D converter; I suspect it's greater than 12 bits > at least in the higher end cameras ... I suspect 14 or 16 bit, it > would have to be if they're concerned with round-off error in > modeling the voltages for a good 12 bit representation. Pentax has > gone beyond that with a 22 bit A-D, which makes much more accurate 12 > bit output. 22 bit quantization vs other cameras' 12, 14 or 16 bit > quantization renders better modeling of the voltages regardless of > whether the output digital representation is further reduced to 12 > bit or not. > Umm... sorry. I'll have to throw the "bullshit flag" on that play. If one measures and analog voltage at 22-bits, does nothing to it, and then throws away the least-significant 10 bits to produce 12-bits, the results are absolutely identical to another who quantizes at 12-bits to begin with. Only if "mid-processing" (i.e. processing between the data measurement and RAW file writing) is done is there a difference. That "mid-processing" is precisely the unknown that I'm talking about, but one would assume that some was done.
Most likely the reason for using 22-bits was so that variable-gain analog amplifiers and fixed-full-scale-voltage A/D's were NOT used. For ISO 100, choose bits 10-22. For ISO 200 choose bits 9-21. ISO 400 choose 8-20, etc, etc. Now, for example, if one were to apply a cloudy WB vs. a tungsten WB, the red channel gain would likely be at least a bit (i.e. f-stop) or two different. It makes sense to chose a different "dynamic range" for each channel based on things like WB (and by association colorspace). > I don't presume to know what Pentax did in tuning the A->D converter > and subsequent 22->12 bit transformation, but whatever the body > writes to the RAW format file as sensor date is, by definition, the > camera's RAW format data. > Yes, but no longer presumed to be an unaltered digitized version of exactly what the sensor sees. > You can't get at or use anything more anyway so there's no point in > debating it. > If you get the white-balance wrong, you only get 10 or 11 (linear) bits of the red channel in the example I proposed above. That does make a difference. For the most part, this is speculation since nobody but the image-processing software guys at Pentax know for sure. I'm just saying that not only is what I'm suggesting possible, it's rather *likely* given that they're trying to exploit the additional data available. -Cory -- ************************************************************************* * Cory Papenfuss, Ph.D., PPSEL-IA * * Electrical Engineering * * Virginia Polytechnic Institute and State University * ************************************************************************* -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net