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Old Sep 11, 2003, 9:55 AM   #1
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Default it doesn't swing both ways

hi everyone,

new member, first post! hope you guys can share your wisdom with me about a few questions i have...

- if a camcorder displays 520 lines, and a conventional tv is approximately 640x480 resolution, that would be 307,200 pixels. if the 520 lines are horizontal lines, would that mean vertically it would have 590-591 lines?

- if a tv shows 640x480 resolution, wouldn't a ccd for a camcorder capable of 1.3 megapixels really be overkill? does it actually reduce the resolution before recording the video? if so, why can't we get the raw footage (at 1.3 megapixels instead of 640x480) to work with?

- finally, if a digital photo camera (such as the minolta dimage z1) states it can film video at 640x480 at 30fps, isn't that roughly the same quality as broadcast-quality tv? on paper, it certainly seems to be much better than mpeg-1. zooming and feature issues aside (most can be done in after-effects i assume), is there really that much of a quality difference between a digital camera's footage (such as the one described) from that of a camcorder's footage?

i know that a camcorder cannot take photos as well as a digital camera, but i am really unsure when the opposite applies when digital cameras claim they are capable of 640x480x30fps. i do not care about features - if i can zoom (and eschew the audio) and the quality is fine, after-effects can handle all my other needs. my purposes are more for taking great photos and video good enough for vcd creation and raw avi or divx conversion to pc.

really appreciate any insight on this. cheers!
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Old Sep 14, 2003, 12:01 AM   #2
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As a rule, digicam movies aren't that great. Also, it would take vast amounts of memory in order to record 640x480 movies for any appreciable length of time. dcresource.com includes sample movies in the reviews if you want to check the 30 fps out.
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Old Sep 14, 2003, 12:19 AM   #3
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Check out my Canon A70 sample photo page. There's a 10 second clip taken in 640x480. It also consumes 8.5MB. There is definitely something to be said about MPEG encoding and compression as used in regular video.


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Old Sep 14, 2003, 5:04 AM   #4
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MPEGG2 coding for TV uses motion prediction to reduce bit rate and this needs very fast real time processing. In the compression world you can get higher quality lower size files, but the penalty is always more and faster processing at the time of capture, and when decoding.

Since most cameras use JPEG as their still image capture, it's relatively straightforward to join still images together and produce motion JPEG. There is no motion prediction and you will notice that movement and particularly pans and zoom are to stressful for MJPEG whilst the compression algorithm isn't as efficient producing really big files. Unfortunately, whereas you can convert a large MJPEG file to MPEG2 in software, the motion artefacts (judder and loss of sharpness resolution on moving images) introduced at the time of capture will still be there.

The low bitrates used in consumer dv cams rely on us not noticing artifacts produced during motion. If you look at a single frozen MPEG frame you will see what I mean, and it would never make a good still print.

At the moment, current still cameras work well producing high res JPEG images, and movie cams work well in MPEG2 for low res output to TV's. I haven't found a dvcam yet that offers the same performance as a 5Mpix still cam or vice versa!
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Old Sep 14, 2003, 8:07 PM   #5
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Another thing I've noticed - and this applies in that DVD's are supposedly high quality video - is that if you go through it in freeze frame, you very rarely get a sharp still if the subject is moving at all. It appears perfectly sharp when moving, but you'll see that every frame actually suffers from motion blur. I'd suspect this could be a big problem with every kind of video camera :S
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Old Sep 15, 2003, 11:51 AM   #6
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thanks for the replies - your comments were useful. i guess what they say is true: "jack of all trades, master of none". i'm better off with buying a decent camcorder and a good camera...
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