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 C B
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. Shadows

13. Shadows

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

15. 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
Use transparancy values (alpha) in addition to partial coverage

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., 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 Compression techniques 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
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