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tpribanic57
11-11-2003, 03:28 AM
Dear All,

Concerning recent discussion about camera compression/storage issue I'd like to ask you the following question. Frequently I came across expression claiming that some video cameras are able to 'save streaming uncompressed video directly to disk'. What bothers me here is word 'uncompressed'. If we take cameras (effective) CCD to be 640x480 pixels size we end up with 307200 pixels. Then each pixel is granted 3 bytes for color which leads to amount of information 307200*3=921600 bytes, or 921600/1024=900KB, or 900/1024=0.8789MB. That is how much you are going to get if you take still photo (bmp file) with your digital photographic (video)camera. Now, 25frames progressive video camera would need to handle 25 of those images in second, meaning that 0.8789*25=21.97MB need to be sent via firewire on hard disk. Theoretical speed of firewire is 400MBits/seconds which is roughly twice as needed for above data. However to my knowledge realistic read/write speeds of most commercial hard drives can be expected around 20-30MB, which is pretty optimistic (try diagnostic toll SisSoft Sandra). If CCD sensor is of even greater size things becomes even more suspicious.
1. Thus, do 'streaming uncompressed video cameras' really have no compression at all or some takes place right at the CCD sensor?
2. Is it possible to save uncompressed above data on tape too ( I have no idea how inert is tape saving mechanism on cameras ). If so, then it should be no problem to grab those video images on disk, but of course not in real (playback) time if our disks are not ready for it!?
Thank you.
Regards, Tomislav
Tomislav Pribanic, M.Sc., EE
Department for Electronic Systems and Information Processing
Faculty of Electrical Engineering and Computing
3 Unska, 10000 Zagreb, Croatia
tel. ..385 1 612 98 67, fax. ..385 1 612 96 52
E-mail : tomislav.pribanic@fer.hr

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