On Tue, Dec 12, 2006 at 08:54:25PM -0500, Cory Papenfuss wrote: > > 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.
But 22 bits is enough to measure 4 million discrete signal levels. That's far more than is needed - even the most optimistic estimates of the full well capacity of the sensor don't go beyond 100,000 or so electrons. You need 17 bits to count that high. Add one or two guard bits to take care of round-off errors in the calculations, and you'd still be OK with 19. In fact if you're going to end up with a 12-bit RAW output file I'd bet nobody would see the difference between the 22-bit PRIME processor of the K10D and a 16-bit processing engine. At best, this is for design compatibility with future systems (such as the 645D, or maybe a K1D) that will use the 16-bit output version of the processing chip; alternatively, it's just meaningless marketing. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
