> >> In theory I think you could gain 4 stops. One stop is x2 more light, so x2^4 >> should translate to 4 stops. >> > > That's quite a lot. I don't find the raw files from *istD to lack much > in dynamic range as it is, so an increase of just 2 stops would > probably make me a very happy man. > > >> However, that requires a linear intensity response from the sensor and the >> same size of the steps. If you just put 16bit within the same dynamic range >> that is covered by the 12 bit you may get better nuances but not dynamic >> range.... >> > > That's understood. :-) > > I assume the CCD itself, or maybe its surroundig circuitry, has a > theoretical maximum dynamic range as well. IIRC, this has been > mentioned on PDML recently too, but, alas for my attention...:-( > I always mention this when the sensor size and/or dynamic range discussion comes up ;-)
According to sources on the Net, the current 6MP sensors have a range corresponding to slightly more than 60000 "steps", or somewhat less that the full range of 16 bits. However, the full range is not really usable due to noise; noise essentially means that the output for the same exposure level may vary between several steps next to each other. Apparently, the noise in the sensors used up to now will typically correspond to 10 levels or so, equivalent to 3 or 4 bits. In other words, if you were to use 16 bits, the lower 4 would probably contain little more than random data caused by the noise. This means you are left with a usable range corresponding to 12 bits. With a 10MP sensor of the same size, the number of levels should be reduced to something like 35000, meaning that the range even before you consider the noise is closer to 15 bits than 16. And with the "old" amount of noise, even 12 bits would be stretching things... So, 16 "real" bits seems unrealistic to me. The noise can probably be reduced, but I'm sure it will never be 0, and to change the actual number of steps in the sensor, I'm assuming you have to do something radical e.g. to the material used. I'm not 100% sure that the numbers I found are reliable, though. Here is one of my sources http://micro.magnet.fsu.edu/primer/digitalimaging/concepts/dynamicrange.html - Toralf -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
