ch13 - Chapter 13: Creating and Modifying Movies 1 2...

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Chapter 13: Creating and Modifying Movies 1
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Movies, animations, and video …oh my! We’re going to refer generically to captured (recorded) motion as “movies.” This includes motion entirely generated by graphical drawings, which are normally called animations. This also includes motion generated by some kind of photographic process, normally called video. 3
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Psychophysics of Movies: Persistence of Vision What makes movies work is yet another limitation of our visual system: Persistence of vision We do not see every change that happens in the world around us. Instead, our eye retains an image (i.e., tells the brain “This is the latest! Yup, this is still the latest!”) for a brief period of time. If this were not the case, you would be aware of every time that your eye blinks because the world would “go away” for a moment. 4
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16 frames and it’s motion If you see 16 separate pictures in one second, and these pictures are logically sequenced, That is, #2 could logically follow from the scene in #1. 16 pictures of completely different things doesn’t work, You will perceive the pictures as being in motion. 16 frames per second (fps), 16 pictures in a second, is the lower bound for the sensation of motion. 5
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Beyond 16 fps Early silent pictures were 16 fps. Motion picture standards shifted to 24 fps to make sound and picture smoother. Videocameras (digital video) captures 30 fps How high can we go? Air force experiments suggest that pilots can recognize a flash of light in 1/200th of a second! Video game players say that they can discern a difference between 30 fps and 60 fps. Bottomline: Generate at least 16 fps and you provide a sense of motion. If you want to process video, you’re going to have 30 fps to process (unless it’s been modified elsewhere for you.) 6
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Processing movies Our frames are going to be JPEG pictures. One JPEG file per frame. So, if we’re going to be processing movies, we’re going to generating or processing sequences of JPEG files. Three tools for manipulating movies <-> JPEGs MediaTools QuickTime Pro (free QuickTime won’t do it) Windows Movie Maker (for converting image sequences to movies) 7
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Using MediaTools To generate a series of frame pictures in a folder from an MPEG file. To play a folder of frame pictures and to save it as a JMV file. (JPEG Movie format.) To play JMV or MPEG movies. 8
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QuickTime Pro (http://www.apple.com/quicktime) can read a sequence of JPEG images and produce MPEG, AVI, or QuickTime movies. Windows Movie Maker can create WMV (Windows Media Player movies) from image sequences. ImageMagick (open source toolkit) can also read a
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ch13 - Chapter 13: Creating and Modifying Movies 1 2...

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