On Jul 5, 2006, at 12:11 PM, Toralf Lund wrote: > So, essentially what you are saying is that you want to retain the > data > "exposed to the right" past the gain phase because that can only scale > the values in a linear fashion, while the RAW conversion is non- > linear? > (And non-linear in such a fashion that an input where the low-range of > values are "stretched" is advantageous.) > ... > One minor point, though: Do you actually know that the CCD has 4096 > different values? I mean, the A/D gives you that, and you obviously > expect that to be matched to the CCD, but I've been thinking that > it may > make sense (partly due to the gain etc. involved) to keep the sensor > resolution slightly higher that the one of the A/D. If it is set up > like > that, obviously you want to do as much of the scaling/"exposure > correction" as you can in the analogue domain, as you'll retain > more of > the dynamics in the digital output that way...
The data output by the Pentax DSLR sensor into the RAW format file contains photosite values in the range from 0-4095, that is, in numbers bounded from 0 to 2e12. That data is the output characteristic of a linear sensor device and requires gamma correction to be transformed into a tonal scale normal for the human eye to appropriate. The rest of what you write is incomprehensible and/or irrelevant. Here's what I've said, as succinct as I can make it: The best exposure for a digital capture is obtained by biasing the exposure to capture as much data as possible with respect to the after-gamma-correction tonal scale. This means, in practical terms, use as much exposure as possible without saturating the sensor in highlight areas that contain important detail. Both theoretically and empirically, this strategy returns the best results. Godfrey -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
