Archived posting to the Leica Users Group, 1999/10/13
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]At 08:15 PM 10/13/99 +0200, Erwin Puts wrote: >snip< > >In fact "Digital" means using only the digits 0 and 1, these numbers >producing the simplest scale (binary scale) that uses positional >notation where the value of each digit is multiplied by a power of >the base depending on its position. >A symbolic representation refers to anything that can carry a meaning >and acts as a proxy to that meaning. > >snip< > >Any CCD sensor signal can be recorded as an analogue signal, >no need for a digital capture here. So digital and analogue can be >mixed as it is in the eye. > >Erwin Yes. People talk about "digital photography", "digital sensors", etc... but in reality, a "digital" sensor is really an "analog" sensor. Each pixel position has an associated capacitor "bucket" to hold the number of electrons that were allowed to flow in, based upon the number of photons that the receptor received during the "exposure." The number of electrons held at the pixel site can be from zero (no exposure) to I suspect billions. The net effect is that the more electrons, the higher the charge, the closer to white. This is clearly an "analog" event. Like volume control or dimmer switch. The way that this analog value gets "converted" to a digital value, is by sending the charge value through an "analog to digital converter." It takes an analog voltage on the input (the charge value of the pixel) and outputs a number. This "number" is stored in the computer's memory. The number can be 8-bits, 12-bits, 16-bit, 24-bits, whatever. All this means is that the number of binary bits that can be used to represent the pixel charge, can give you from coarse gradation (8-bits) to fine gradation (24-bits). Like dynamic range in film. In a current consumer level 2 megapixel sensor, there is only one analog to digital converter. When a picture is taken, all 2 million pixel charges must be sequentially run through the A/D converter and the output numbers stored sequentially in computer memory. Then the correction and compression process starts via computer software. It's a wonder that the resulting image actually looks like what you photographed. So you see, digital cameras aren't really digital at all. The analog light value collected in each pixel is electronically "converted" to a digital value. The electron buckets (capacitor) in each pixel has to have a large enough range from 0 (black) to billions (pure white) or the differences between various shades of grey cannot be ascertained. This puts size constraints on the manufacturing of each pixel. Make them smaller, the noise data goes up and the good image data goes down. You get more pixels per inch, but a crappy image. As I said, the wall is in sight. Time to leave this train and get on one going in another direction. Jim