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Rick Parent - CIS68 Background Perception Display Considerations Video Technology
Rick Parent - CIS681
Background
Perception
Display Considerations
Video Technology
Rick Parent - CIS681
Persistence of Vision
Refresh rate v. update rate
Perception of Motion
Flicker, flicker rate
Positive Afterimage
Perception
Rick Parent - CIS681
Double buffering
CompositingAlpha channel
Shadows, drop shadows
Motion Blur
Display Issues
Rick Parent - CIS681
Double Buffering
AWrite into buffer
Rick Parent - CIS681
Double Buffering
AWrite into buffer
BDisplay buffer
A
Rick Parent - CIS681
Double Buffering
CClear and write into buffer
BDisplay buffer
B
Rick Parent - CIS681
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
Rick Parent - CIS681
Shadows
Rick Parent - CIS681
Shadows
Rick Parent - CIS681
Shadows
Rick Parent - CIS681
Shadows
Rick Parent - CIS681
Motion Blur
•Sample the pixel over single frame time
•Move objects during frame time
•Blend colors
•Usually jitter the samples in time
Rick Parent - CIS681
Motion Blur
Rick Parent - CIS681
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 ChannelCombined partial coverage and transparency
Rick Parent - CIS681
Compositing - example
Rick Parent - CIS681
Analog Image Technology
Video (raster scan)Interlace v. progressive scanNumber of scanlines (e.g. 525, 625)Aspect ratio (e.g. 4:3, 16:9)Field rate (e.g., 59.94 Hz, 50 Hz)
FilmVarious formats (e.g. mm widths of 8, 16, 35, 65, 70)Vary by placement of sound track, performations, frameSpeeds18 fps or, more usually, 24fpsUsually doubly projected
Rick Parent - CIS681
Video - Raster Pattern
Rick Parent - CIS681
Interlaced Raster Pattern
Frame v.
Field
Rick Parent - CIS681
Video
NTSC: 29.97Hz, interlaced4:3 aspect ratio ~480 scanlines~640 (square) pixels
HDTV: 60Hzprogressive scan16:9 aspect ratio
Video InformationRGB YUV (Betamax)Y-C (S-VHS)NTSC
Rick Parent - CIS681
Video
Analog
Digital
Binary
Rick Parent - CIS681
Codecs
TradeoffsSymmetry v. asymmetryLossy v. losslessSpeedSpace (compression ratio)Video v. Television
Compression techniquesRun-length encodingLZWDiscrete cosine transformWavelet compressionFractal compressionVector quantization
Rick Parent - CIS681
Digital Formats
Movie formatsQuicktimeVideo for Windows
File formatsMPEGMJPEGGif89a
CodecsGIFMotion JPEGMPEGCinepakSorensonIndeo 3.2RLEVideo ISorenson
Rick Parent - CIS681
Digital Video Formats
D1D2D3D5D6DVCamDVCPRODigital8Ampex DCTDigital Betacam
