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Background. Perception. Display Considerations. Video Technology. Perception. Persistence of Vision. Positive Afterimage. Perception of Motion. Flicker, flicker rate. Refresh rate v. update rate. Display Issues. Double buffering. Shadows, drop shadows. Motion Blur. Compositing

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  1. Background Perception Display Considerations Video Technology

  2. Perception Persistence of Vision Positive Afterimage Perception of Motion Flicker, flicker rate Refresh rate v. update rate

  3. Display Issues Double buffering Shadows, drop shadows Motion Blur Compositing Alpha channel

  4. Double Buffering A Write into buffer

  5. Double Buffering A B Write into buffer Display buffer A

  6. Double Buffering B C Clear and write into buffer Display buffer B

  7. Double Buffering • Requires additional memory • Allows for “instantaneous” update of screen • Writing to buffer may not be real-time • May be supported in hardware • Can use more than two buffers

  8. Shadows

  9. Shadows

  10. Shadows

  11. Shadows

  12. Motion Blur • Sample the pixel over single frame time • Move objects during frame time • Blend colors • Usually jitter the samples in time

  13. Motion Blur

  14. Compositing • Z buffer: keep z values with color buffer • Compare z values at corresponding pixels • Keep all or nothing • OR compute partial coverage • Interpolate corner z values • Compare corner values for pixel and blend Alpha Channel Combined partial coverage and transparency

  15. Compositing - example

  16. Analog Image Technology • Film • Various formats (e.g. mm widths of 8, 16, 35, 65, 70) • Vary by placement of sound track, performations, frame • Speeds • 18 fps or, more usually, 24fps • Usually doubly projected • Video (raster scan) • Interlace v. progressive scan • Number of scanlines (e.g. 525, 625) • Aspect ratio (e.g. 4:3, 16:9) • Field rate (e.g., 59.94 Hz, 50 Hz)

  17. Video - Raster Pattern

  18. Interlaced Raster Pattern Frame v. Field

  19. Video • Video Information • RGB • YUV (Betamax) • Y-C (S-VHS) • NTSC • NTSC: • 29.97Hz, interlaced • 4:3 aspect ratio • ~480 scanlines • ~640 (square) pixels • HDTV: • 60Hz • progressive scan • 16:9 aspect ratio

  20. Video Analog Digital Binary

  21. Codecs • Tradeoffs • Symmetry v. asymmetry • Lossy v. lossless • Speed • Space (compression ratio) • Video v. Television • Compression techniques • Run-length encoding • LZW • Discrete cosine transform • Wavelet compression • Fractal compression • Vector quantization

  22. Digital Formats • Codecs • GIF • Motion JPEG • MPEG • Cinepak • Sorenson • Indeo 3.2 • RLE • Video I • Sorenson • File formats • MPEG • MJPEG • Gif89a • Movie formats • Quicktime • Video for Windows

  23. Digital Video Formats D1 D2 D3 D5 D6 DVCam DVCPRO Digital8 Ampex DCT Digital Betacam

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