Re: Digital questions: was: Re: Is the New LX Going to Be a Digital Camera
William Robb writes: What I would like to know is what sort of dynamic range in stops (a concept I do understand) does a CCD chip have? Is it variable based on software or is it hardware limited? I have no idea. I do wonder if the in-camera exposure compensation is done in the digital domain or if it sets the gain of an analogue amplifier prior to sampling. The second way will result in more useable data provided you've got enough linearity and dynamic range, and a low enough noise floor in the analogue stage. I am of course assuming that the CCD elements are essentially an analogue device with a DAC somewhere either on the CCD chip itself or separately in the camera. Another thing is that the camera firmware can always interpolate. You can easily sample at (say) 8 bits per channel, then when you're interpolating the extra pixels to fill the gaps left by the CCD, you can add a few bits. This would be very similar to the oversampling process used in expensive CD players that use 20-bit DACs. Is it closer to a short range slide film such as Velvia? Or closer to a long range print film such as Portra NC? Or is the question to general to give a specific answer to? It'll depend on the CCD itself. Someone would have to try it out to be sure (unless you want to read some semiconductor datasheets). Cheers, - Dave David A. Mann, B.E. (Elec) http://www.digistar.com/~dmann/ Why is it that if an adult behaves like a child they lock him up, while children are allowed to run free on the streets? -- Garfield - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Digital questions: was: Re: Is the New LX Going to Be a Digital Camera
- Original Message - From: David A. Mann Subject: Re: Is the New LX Going to Be a Digital Camera William Robb writes: I do have a question about film to digital comparisons. What is the comparative image depth of film to digital capture? I know the digital guys talk about 36 bit depth, but how does that tranlate to the capture depth of a long scale film such as Portra? Is 12 bits per colour the equivalent of 12 stops of tonal range? Not necessarily. Each bit might not represent a doubling of the actual light intensity, even though it will represent a doubling of signal out of the CCD's analogue electronics. 12 bits will represent a range of 4096 levels (per colour). The important part is how the range is scaled. Those 4096 levels might represent a 1-stop tonal range with _heaps_ of tonal detail within that range. Which is great if your lighting is flat. But when the sun comes out it'd respond like lith film :) In reality there's a bit of a tradeoff between tonal range and tonal detail, within the limits of the CCD (dynamic range, linearity and noise). That is sort of where I was going with that question. In digital, we hear lots about image resolution, like as if that is the most important criteria, but not so much about image depth. This is also a concept I am a bit fuzzy on. I know it roughly translates as tonal range, and that more is better (possibly even more important than absolute pixel count). What I would like to know is what sort of dynamic range in stops (a concept I do understand) does a CCD chip have? Is it variable based on software or is it hardware limited? Is it closer to a short range slide film such as Velvia? Or closer to a long range print film such as Portra NC? Or is the question to general to give a specific answer to? Thanks William Robb - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Digital questions: was: Re: Is the New LX Going to Be a Digital Camera
On Fri, 27 Jul 2001 06:30:28 -0600, William Robb wrote: What I would like to know is what sort of dynamic range in stops (a concept I do understand) does a CCD chip have? Is it variable based on software or is it hardware limited? Based on the ads I've seen for film scanners, it appears that Dmax (maximum dynamic range) for CCDs typically runs from about 3.0 to nearly 4.0 ... some scanners actually claim Dmax of 4.0 or a little more, but I have to wonder if those are marketing numbers. IIRC, the Dmax scale is log-10 rather than log-2 like stops. So, Dmax of 3.0 would translate to 9 or 10 stops (log2(10^3)) while a Dmax of 4 would translate to 12 or 13 stops (log2(10^4)) of range, assuming the CCD response is linear. TTYL, DougF - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
