Advanced digital effects generators and paint systems currently in use tend to operate on the video signal as if it were not an interlaced system. These devices produce a new image every field instead of every frame. While resulting in much smoother motion of video tape, this method can result in a film image that is fragmented and sometimes blurred.
Because of the throwaway field sequence (see Fig. 5), an apparently smooth video effect generated in field mode rendering can appear disjointed and unnatural when transferred to film. The amount of degradation depends upon the type of video effect. Very slow horizontal or vertical movement is usually acceptable. As the rate of movement is increased, the artifacts become more objectionable.
The best way to avoid these temporal related artifacts is to refrain from using the more ambitious digital effects that are available. Any effect that is characterized by rapid vertical, horizontal or temporal motion will cause these discontinuities. They will be very noticeable in the film and should be avoided, if at all possible. Some of the more recent digital effects devices offer two modes of rendering motion — field and frame mode. When generating material that will be transferred to film, use the frame rendering mode.
Note that vertically crawling title sequences (such as credits) represent about the absolute worst case, and illustrate all of the problems noted above. When editing in the credits, fade them in and out rather than having them crawl vertically.
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