On 13/12/06, Cory Papenfuss <[EMAIL PROTECTED]> wrote: > 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.
Other arguments I've heard raised were that even if the last 8 bits of the 22bit ADC were recording purely noise the remaining bits would record more linear steps given that the ADCs imprecision lies mainly in the low bit range. > 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). If Pentax are using the Nucore NDX-2240 AFE on the front end of their PRIME Image Processor (which hasn't been denied and was rumored to be confirmed) the it provides what they deem as a "color sensitive PGA" prior to the input to the 22 bit ADC. You can read up more here: http://www.nucoretech.com/nu3/images/80_downloads/pres_technology.ppt.us.pdf -- Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://home.swiftdsl.com.au/~distudio//publications/ Pentax user since 1986, PDMLer since 1998 -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
