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Old Apr 8, 2008, 6:42 AM   #1
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Hello there,
I have bought the Kodak Easyshare z812is when it came out some months ago, the few reviews then were good. Now I noticed that when I watch the HD Vids on my computer, they show some horrible artifacts. Basically, every time I moved the camera while I was recording in HD, the middle horizontal part of the recorded video images lags behind. It looks as if I have covered the middle part of the viewing field with a piece of window glass thats slightly misaligned, well lagging behind, as if the camera can't prozess fast movement. Do I need the change something on the setup or do I have to live with that? I had a small casio exilim 600s before, it made great vids with good sound, have I made a mistake buying this Kodak? :-(

regards,
markus
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Old Apr 11, 2008, 11:59 AM   #2
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Did you buy the Z812 as a video cam? If so, sorry, it's a still cam.

What you're see is the result of the compression algorithm chosen by Kodak so a short discussion of video compression algorithms is in order. Lossless algorithms such as run-length encodingreproduces the exact image captured upon playback at the expense of large file sizes. Example, 3-4 sec. of video produces about a 100MB of data, run-length encoding will result in about a 40MB file. The next group of compression algorithms are lossy algorithm which, in essence throw away data an on the theory that the eye/brain can fill in the missing data. A sub-type of these algorithms are the intraframe algorithms such as motion jpeg. Each frame is compressed individually using the lossy jpeg compression scheme. This typically will reduce our 100MB of data to a 10MB file. This is used by the Canon S3/S5. Finally the highest level of compression is achieved intraframe compression algorithms where frames are compared andredundant data across frames is discarded. MPEG4, used by Kodak, is one of this type and typically will reduce our 100MB of data to a 1MB file. A more extensive treatment of this can be had in tclune's comments in http://forums.steves-digicams.com/fo...amp;forum_id=9

Both the Canon S5 and the Z812 are still cameras with an added video capability (because they could.) In each case the companies made some assumptions on what the users needs were. Canon assumed that the users would need, at most only a very few minutes of video so selected motion jpeg as the compression algorithm. Kodak on the other hand assumed the users would take longer videos but then would want to upload/share the files so smaller file sizes were an overarching requirement. They selected MPEG4 to achieve that objective. Trade-offs.

MPEG4 handles motion within the frame very well because all the data point remain essentially the same, just in a different location. Panning actually introduces new information into the frame and can cause the algorithm to break down if the new information is introduced too rapidly. This is the smearing you see and is the direct result of providing a fairly long record time with small files.

I have a Z612 which I purchased as a still camera and I am very pleased with the camera. Should I ever need to shot a video with the camera and knowing that it uses MPEG4 I would simply frame and setup the scene so I didn't have to pan, turning off the recording between scenes if need be. Does this upset me? NO. I bought a still camera and the fact that I can shoot a short clip with a relatively small file in an emergency is just fine. If I need to shoot serious videos I will buy a video cam and be pleased that it can shoot still pics in an emergency.

Finally, there is a participant in this forum that will suggest that what you're seeing is the result of Kodak using a CCD sensor rather than a CMOS sensor and the effect you're seeing will go away if Kodak ever goes to a CMOS sensor. Just not so.
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Old Apr 22, 2008, 9:32 AM   #3
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I know nothing about z812 but it sounds like the problem may not be in the video but in your computer being too slow or playing it using bad player, codec or even video drivers. You can tell for sure if it is Z812 fault or not if you resize that video with some software to 640 x 360 and check if you see the same problem again.
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Old Apr 22, 2008, 1:23 PM   #4
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Caldur wrote:
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I know nothing about z812 but it sounds like the problem may not be in the video but in your computer being too slow or playing it using bad player, codec or even video drivers. You can tell for sure if it is Z812 fault or not if you resize that video with some software to 640 x 360 and check if you see the same problem again.
This argument works only if one also makes the argument that all Z612/Z712/Z812 owners have inadequate computers. I can produce the effect thatOP observes when shooting 1280x720 30 fps HD video on my Z612 shooting 640x480 30 fps VGA video. My computer, while not a high end gaming machine is at least a dual core AMD running XP media edition as the OS.
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