>>In commercial CCDs, the lowest n bits are always garbage.
>>
>Actually, Peter, CCD's are ANALOGUE devices - the output needs to be
fed
>to an ADC before it can be read by computer. The ultimate limit of
>signal to noise for a CCD (or any other light sensor) is the photon
>noise limit. Most visible CCD's have a storage capacity at each pixel
>of around 10^6 photo-generated carriers, and since the arrival of one
>photon is totally uncorrelated with the arrival of another at the pixel
>(ie. it is a random process) the noise level on this is approximately
>the square root of the carrier capacity - around1000 - as is the signal
>to noise ratio. To prevent saturation, CCD's are normally operated
>closer to 700f saturation, so the SNR is actually lower than this in
>practice. So the limit for a typical high performance CCD detector is
>around 10 bits.
OK ! Thanks for this explanation. At least, now I know why the bit
depth of CCDs is the way it is.
--
Peter Leyssens
Eonic Systems
Personal e-mail : Peter.Leyssens@xxxxxxxxx
Support mail : support@xxxxxxxxx
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