removing fields

[Steve Roberts]

Each frame of interlaced digital video shows two slices of time at once, 1/60th of a second apart for NTSC. The odd lines of the image were shot in the first 1/60th, while the even lines were shot in the second 1/60th. Or the other way around — that’s field order. So that those fields don’t get mushed up, often you have to ask AE to “separate” them, and create a frame that shows only one slice of time, not two. At high quality, those two sets of lines (fields) are interpolated, but at draft quality, one set of lines is simply duplicated.

If you expect to move, rotate, scale, blur or otherwise distort imported footage, you must make sure that fields are separated on import, or interpret the footage as lower field first (DV and most interlaced footage) or upper field first (other footage).

If your interlaced footage will not be altered as mentioned above, you don’t need to separate fields. This is for footage that will just sit happily in the center of the frame, filling the frame. If you haven’t animated anything else in the frame, you can render with no fields, and the result will be unchanged interlaced footage. By rendering progressive (frames, or no fields) in this case, you are leaving the interlaced frames as is.

However, if you add moving graphics over the interlaced footage, you should render with fields, in the same order as your footage. Rendering with (or without) fields affects the appearance of objects that have been animated in AE. Basically, you should make the graphics match the footage, field-wise.

Regarding the look of the overall piece, rendering with or without fields is an aesthetic choice. However, if you choose to render with fields, the field order (not DOMINANCE, Apple!) must be appropriate for your format and equipment. I rarely render with fields, since I don’t like the look.

For more info, you might want to buy “Videosyncrasies” by Chris and Trish Meyer.

Hope that helps.