gpyros
Key Veteran
Location: On a beach in Mexico
| Rich:
That is just the nature of the beast! The video format in the USA is called NTSC (often referred to as "Never Twice the Same Color", but I digress). It is approximately 30 frames per second (for you purists, 29.97 to be exact). Each frame is composed of two fields, which consist of every other line (the "comb" effect you were talking about). So each field lasts about 1/60th of a second.
When shooting a still object, no big deal, both fields see the same thing and line up well. When shooting a moving object (or if the camera is moving, same end result) each field is recording something that is happening 1/60 of a second later than the last one, so they are all off a bit. When played back in the same order they were recorded on, and at the same speed, they look perfect. Your eye follows the fields just fine. Normally the human eye is considered to be able to differentiate about 48 items per second, so at 60 you appear to have perfectly smooth motion.
So if you are taking this back out to video, you will be fine. However, you said that you were having a problem with it when played back on a computer. Here's the rub - computer playback is not interlaced, like video, each frame is solid. So instead of seeing one field after another, you are seeing both fields together, which looks really bad.
Fixes: Depending on your editing system, you may have a few choices. One is to bring in every other field when you are importing the video to your computer. This gives you a half-size video vertically, so you just have to compress the video horizontally in half to match. Now edit it and play it back, and you will never have that problem. You have introduced another problem, though - you are cutting out half the information, so your playback will be the equivalent of 30 frames per second instead of 60 fields per second, and you will see a little jumping between frames. Usually not too objectionable, and better than the field problems, but there.
Another option is to bring in every field of the video and use them as separate frames, offsetting every other one by one line vertically so they will line up. Now you'll have to play it back at 60 frames per second or you will get a slo-motion effect (which can be very cool with heli shots) but not good for the entire video. If your editing system can speed up the video by 2 times, though, you've got it made. Of course, if it just takes it literally, you haven't accomplished anything more than bringing in every other field.
A better solution if your camera supports it is to have it record in frames instead of fields if you know you will be doing computer playback. My Canon XL-1 has this option, I'm not sure which others do.
So before you go blaming the editing system, remember that the editor is made to go back out to video, where it will probably be fine. If you plan on changing formats (from video playback to computer playback) you need to have a system geared for this, many are not.
Greg Pyros
Video and Visual Effects geek
www.pyros.com
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