[opendtv] Sampling Frequency of Image Signals
- From: dan.grimes@xxxxxxxx
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 29 May 2007 17:43:31 -0700
I have a couple of questions regarding the digitization of the signals
coming from the CCD.
I realize that many cameras out there today process the signal coming from
a CCD in analog and only after completely processing it in analog is the
signal sampled at some frequency to put it on an SDI interface or record it
to some form of digital media. There are some cameras that go to the
digital domain earlier and do much more digital processing. I have several
different cameras that do some processing in the digital domain but at
various stages of the path.
Are there any cameras that are sampling each pixel as they come out of the
CCD, and then processing in a true native matrix in the digital domain? Or
is this not recommended, possible, or perhaps practical? I would think
that if the digitization happened before the compression circuit, it would
require a large number of bits per sample (or the use of a floating point
number) to keep the dynamic range of the CCD, so perhaps it is not
practical at this time. I think what I am asking is when is earliest
practical point in the processing system of a camera that the analog signal
can be digitized in today's high quality HD video cameras?
I know the designation such as 4:4:4 means different things depending on
the video system. For instance, in regards to digitizing an analog signal
it would mean sampling at four times the subcarrier frequency. In the
digital domain I assumed it referenced the spatial frequency, meaning that
it was full resolution and 1920 pixels per line were sampled from 1920
imager or 720 samples were taken from a 720 pixel imager). But considering
that most cameras process an analog signal, perhaps that isn't true. And
the 4:2:2 has been used with so many different formats, I'm a little
confused to its true meaning in today's digital formats.
Dan Grimes
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