Archived posting to the Leica Users Group, 2001/04/27
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]>on 4/27/01 5:09 AM, Malcolm McCullough at MM4@mm-croy.mottmac.com wrote: > >> John Brownlow wrote (probably without thinking, 'cos I'm sure he knows >> this): >> >> 'The same is NOT true of digital cameras! I have been through SO many >> digital >> formats, moving and still... eg Umatic, 1" reel to reel, Betamax, VHS, >> S-VHS, 8mm, Hi-8, Beta, Beta SP,...' >> >> Nine video formats - none of which are digital (though the cameras may use >> digital signal processing). > At 09:21 AM 4/27/01 -0400, Johnny Deadman wrote: > >Yeah you're right but you get the point, I hope. ALL video cameras since >they phased out the vacuum tube type are digital, since they rely on a CCD >for image acquisition. > >John Brownlow John, Data (pixels) captured in a CCD is an analog process. They are stored as a minute voltage level in a capacitive junction associated with each pixel. The voltage level stored between black (no light/no voltage) and white (saturated pixel) is a few hundred millivolts. Typically between 10 and 350 mv. Reading the data out of a CCD is an "analog" process and the signal IS an analog signal that could be recorded onto analog tape. If you look at it on a scope, it looks like any audio signal. The CCD signal has to be run through an analog to digital converter before it becomes a digital signal. This is just one of the many reasons why pixels cannot, with current technology, get any smaller. They could not produce enough analog signal (voltage level captured in the even more teeny weeny capacitor) to be separated from the noise. As the pixel size goes down, the noise level goes up. As the light level goes down (same problem, not many electrons stored in the capacitors) the noise level goes up. When thinking about digital cameras (still or video) you still have to think "analog". Digitizing happens later. This is like film. Digitizing happens later. Only with film, you have a good master. With a digital camera, you have no master so you cannot redo the analog to digital process. But you can PhotoShop it until you have what you wanted in the first place. Jim