Apple MA261Z/A User Manual - Page 1049

XIII Early television systems used a different approach for the same result: increased flicker without increasing the necessary electronic bandwidth. Interlaced scanning fills a television frame with only half the video lines of a frame (this is known as a field), and then fills in the remaining lines (the other field). A field effectively fills the television screen with an image, even though it is only half-resolution, and it does so in half the time it would take to draw the full frame. The result is a perceived frame rate which is double the actual frame rate. For NTSC, the frame rate is 29.97 fps, but the perceived frame rate (the field rate) is 59.94 fps. This causes less flicker. PAL, which has a lower frame rate of 25 fps (or 50 fields per second) has a slightly more noticeable flicker. Frame Rate Limits: How Many Frames per Second Is Best? When recording an object in motion, there are practical reasons to limit the camera frame rate: Â The limit of human perception: There is no reason to show more frames per second than the viewer can perceive. The exact limit of human motion perception is still up for scientific debate, but it is generally agreed that there is an upper threshold after which people can't appreciate the difference. Â Media cost and size: Film and video tape stock cost money. Higher frame rates require more footage, and are more expensive to shoot. Editing and media management become more difficult as the amount of raw media increases. Recording High Frame Rates for Slow Motion Effects Despite the increased cost and effort, there are cases where shooting higher frame rates is useful. Slow motion effects are created by recording hundreds of frames per second and then playing the same frames back at a slower rate. For example, a bullet shattering a light bulb may take only a fraction of second, seeming almost instantaneous to anyone watching. If a camera records the light bulb a thousand times per second and then a projector plays the frames back at 24 fps, the movie on screen will take almost 40 times as long (1000 fps / 24 fps = 41.6 seconds). The higher the frame rate, the more temporal (time) resolution your footage has, which means it can be slowed down to show detailed moments that would otherwise be a blur. Shooting at high frame rates also requires more light, because there is less time to expose each frame. Appendix B Frame Rate and Timecode 1049