A/D Conversion Explained:
Simply put, an A/D converter samples the analogue electric signals from the camera’s CMOS or CCD image sensor (N.B. He doesn't state it is recorded digitally like you have?), which vary in intensity based on the number of photons captured in each pixel, and converts them into digital data consisting of 0’s and 1’s. In the case of the EOS 5D Mark II and 50D cameras, the raw digital data produced by the A/D converter is fed directly to the DIGIC 4 image processing circuit, which does the mathematical “heavy lifting” of converting the data to a usable image.
Here is a very simple analogy: The original analog signals are like an old-fashioned clockface -- the moving hands progress through the second markers, indicating every instant of passing time: In other words, the signal is stepless. For a digital camera to function, these analog ('stepless') signals must be converted into digital signals with definite, distinct steps. Using the clock analogy again: This digital signal acts more like a modern digital clockface, with a numeric display changing to indicate the passage of time, but without continuous movement between seconds.
Several factors may affect the strength or purity of the analogue signals reaching the A/D converter, such as electronic noise generated by the image sensor or its readout circuitry, or electronic noise generated by the signal amplification which occurs at high ISO speed settings (No........are you sure Mr Canon, that means you agree with me!). These factors primarily affect the dynamic range of the image. (What 'utter rubbish' according to Mr Bollygum on the TP Forum)
