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Interlaced and Progressive Scan
The image to the left was taken with a mini-DV camera in standard (interlaced) mode. when viewed on a television monitor that sort of video looks perfectly smooth, because the television will display every even line of pixel (rows 0,2,4,6 etc) in one pass and in the next pass it will show the odd lines (1,3,5,7 etc). American televisions (NTSC, Never Twice Same Color) thus scan from top to bottom twice per frame, 60 times per second (PAL, europe and elsewhere will scan 50 times when viewed like that). "Interlaced" is smoother only when played back on a television set which uses the same interlace timing as the footage from mini-DV. Due to a few differences video will look different on computer monitors (see left picture). A second, and more significant drawback of interlaced video occurs during editing: if one never crops, zooms in or out and always uses the frame as shot by the camera, then "interlace" fidelity can quite easily be achieved. But, as soon as the signal is moved up by an odd number of lines during editing, the timing goes down the drain because in the end, results will be displaced by 1/50 to 1/60 of a second. Forget about smoothly slowing down or speeding up the video, rotating it, etc... While it is possible to apply such complex manipulation cleanly to an interlaced signal, it is costly in terms of computing resources. it is also behind the times. After all, once editing/compositing is finished, the result may be displayed at the european grandmothers house, down the road in Moosejaw, Canada, on a laptop, desktop, movile phone at frame rates of 15, 24, 25, 29.97 or 30. This is why I only will buy cameras capable of progressive scan. A camera which can deliver 25 or 30 non-interlaced frames per second. All pixel rows are scanned progressively (sequentially) in the sequence 0,1,2,3,4 etc... The above artifacts will never show up, and my freeze frames always look coherent. A lower quality fix for interlace artifacts are the "even field" and "odd field" effect filters in ZS4, which remove the artifacts, by losing some of the vertical resolution. viff_fields viff_even viff_odd |
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