Videomaker – Learn video production and editing, camera reviews › Forums › General › Video and Film Discussion › What’s the real diff. w/ Interlaced and Progressive Scan? › Video is 30 frames per sec
Video is 30 frames per second, period. This means 60 fields per second. (NTSC of course). The 29.97 fps is (more or less) the way timecode labels each frame. Actuality, there is a frame that gets dropped every so often, but they are far apart and no one every actually sees when it happens.
When video gets deinterlaced, an option is sometimes presented as to which field to remove, odd or even? If odd is removed, then 224466 will be the correct drawing method used. The first even line will replace the first odd line, then the first even line is drawn again where it should be. 22 instead of 12. 44 instead of 34, and so on. Thus the loss in resolution.
Converting to progressive won’t change the image shift between odd and even fields. Instead of drawing all the odd and then all the even, it will draw 1 odd then 1 even, then the next odd then the next even. If you could freeze 1 frame of interlaced video and the same frame of converted to progressive, they would look identical. The only difference is the order in which they are drawn. The only real way to get progressive video is to film it that way. This means using a camera that uses progressive image scanning. As like a tv, a video camera utilizes the same method when seeing the image. Behind the camera lens is an image sensor which is basically a grid of light sensitive pixels. In order to save the info onto tape, there must be some type of scanning. If you fish through your camcorders settings, you’ll find the framerate control. This can be set fron 1/30 to 1/4000. Some cameras have a bigger range. This is the actual scan rate. Now don’t think that 1/4000 means 4000 frames per second. It scans at 4000 frames per second but only stores onto tape 1/30. Why? For fast moving action, 4000 will create a very sharp and non-blurred image versus 1/30. Sure, 3999 scans get lost and playback does look a bit choppy, but even with interlaced video, you’ll never see the interlaced lines. Some may even argue that it tends to represent film since film displays 24 fps and there are no line to draw. Just the whole image. Experiment and you’ll see. By the way, you need alot of light at that framerate.
Technology is advancing so fast its tough to keep up. TVs of the future will probably all be progressive scan. Planning for it now is good, but understanding the difference is more important. Once your content is on tape, not much can be done to change it. Conversions work mostly for display purposes only. They really don’t change the content itself. Thats why DVD players usually have options. Until the format is standardized, users have the options to select what’s best for them. It really comes down to trial and error. Now that you have a more than basic understanding of this, experiment with it. You will ALWAYS remember what you’ve done versus reading what others have done!