DVL-Digest 756 - Postings: Index - (3) - (4) FW: Resolution - Engineering vs. Marketing - "Perry" Kevin Marks posted: >Each CCD element is a little bucket that has hard edges and counts photons. Each LCD element is 3 little coloured rectangles with variable polarisers on top. They output and input analog voltages for each element, but the elements have hard edges. When your input device is an electron gun sweeping across a surface then it doesn't make sense to talk about pixels. When it is a CCD it does. How many CCD elements across do the cameras in question use?. Does the camera convert their digital signals into analog and then sample the analog one to derive the DV bitstream?< For reasons we discussed earlier, it is good to 'sample' the image in a CCD at a higher rate than the subsequent sampling in the DSP and DV codec. Typically a CCD will have between 800-1000 pixels width. The output of the CCD is indeed an analog signal that subsequently goes into an AtoD converter. If the signal is converted directly at the output of the CCD, it can be shown to need as many as 14 bits to allow accurate gamma processing. 14 bits are not currently practical, so the gamma is compromised or some pre AtoD processing occurs in the analog domain. It is not clear whether all DSP is done at the DV sample rate of 13.5MHz. LCD devices have usually been fed with an analog signal (via VGA or video connection) but Apple and others do now make displays with a wholly digital connection. The 'sample rate' or resolution is wholly unconnected to anything pertaining to DV video of course. Perry Mitchell Video Facilities http://www.perrybits.co.uk/ FW: Resolution - Engineering vs. Marketing - "Perry" Blain: As an ex Camera Product Manager I understand the theory of camera resolution very well. Trying to find EXACTLY how manufacturers obtain their specifications is an entirely different thing! Most broadcasters who care will create their own minimum specifications in proper engineering terms that all can understand. Some will insist that the manufacturer test the cameras against this spec before the broadcaster will accept them. In other words they completely ignore the manufacturers Marketing numbers. This leaves normal customers in no mans land! The situation was not dissimilar a few years ago with cars, where manufacturers used to claim ridiculous numbers for fuel consumption. In Europe the Government agencies forced them to use standardised tests so that customers could get proper comparable and realistic figures. The manufacturers hated it of course, because the gas consumption appeared to double or more overnight!! As I think Jan Crittenden's splendidly honest post on the subject shows, any connection between camera marketing specs and engineering tests are very loose to say the least. Perry Mitchell Video Facilities http://www.perrybits.co.uk/ (diese posts stammen von der DV-L Mailingliste - THX to Adam Wilt and Perry Mitchell :-) [up] |
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