Antti-Pekka Virjonen wrote: >> I think the actual sensors do have the 14-16 bits you mention - [ ... ] >> >> > > Hi, > > Yes, actually I was talking about usable bits, taking the noise into > account, thus giving 14-16bits of usable data. > > This is so at least with the good quality astronomical ccd sensors but I > > am sure the DSLR camera sensors are coming close nowadays (or am I just > hoping?). > As has also been mentioned many times, the max. charge or "full-well" capacity of the sensor depends directly on the pixel area. Apparently it's approximately 1000 electrons per square micrometer in a normal CCD
I'm not sure about astronomical sensors, but in the linear CCDs I've used at work, the pixels are 12x12 or 14x14 micrometers, which should give you 2-3 times the data required for 16 bits. That may not be quite enough to leave you with 16 "good" bits after you've thrown away the noise, but 14 should be no problem. On a DSLR, on the other hand, the pixel size has been something like 8x8 microns for a while now, but on the latest (10MP) cameras, it's down to 6x6 or so. In other words, the DSLRs cameras are not "coming close"; they are actually moving further away in that the pixels keep getting smaller! A different side of this is obviously the noise situation. You can also improve the number of usable bits by reducing the noise, and this is an area where the DLSRs probably are getting better - but they also have to, in order to compensate for the smaller pixels. And it wouldn't surprise me if the astronomical sensors have very low noise, too. > In any case, when designing measuring systems (using amplifiers and a/d > converters) it is a good thing to have plenty of more bits and precision > compared to the original signal. This way you will minimize the added > noise. When having a 22 bits a/d converter on the K10D you can also > measure and analyze the "noise" of the low expusure pixels. You will get > all the available information out of the sensor. > Yes. It definitely seems like I good thing to keep *all* the info for the early image processing stages. Also, having some extra bits around will minimise round-off errors that might accumulate across multiple pixel value adjustment steps. You may think of extra bits as more decimals in intermediate results. I think this may be the most important consideration behind the choice of 22 bits. - Toralf -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
