Background Perception Display Considerations Video Technology Rick Parent

Background Perception Display Considerations Video Technology Rick Parent - CIS 681

Perception Persistence of Vision Positive Afterimage Perception of Motion Flicker, flicker rate Refresh rate v. update rate Rick Parent - CIS 681

Display Issues Double buffering Shadows, drop shadows Motion Blur Compositing Alpha channel Rick Parent - CIS 681

Double Buffering Write into buffer A Rick Parent - CIS 681

Double Buffering A B Write into buffer Display buffer A Rick Parent - CIS 681

Double Buffering B C Clear and write into buffer Display buffer B Rick Parent - CIS 681

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 - CIS 681

Shadows Rick Parent - CIS 681

Shadows Rick Parent - CIS 681

Shadows Rick Parent - CIS 681

Shadows Rick Parent - CIS 681

Shadows Rick Parent - CIS 681

Shadows Rick Parent - CIS 681

Motion Blur • Sample the pixel over single frame time • Move objects during frame time • Blend colors • Usually jitter the samples in time Rick Parent - CIS 681

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 Rick Parent - CIS 681

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, 24 fps 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) Rick Parent - CIS 681

Video - Raster Pattern Rick Parent - CIS 681

Interlaced Raster Pattern Frame v. Field Rick Parent - CIS 681

Video Information RGB YUV (Betamax) Y-C (S-VHS) NTSC: 29. 97 Hz, interlaced 4: 3 aspect ratio ~480 scanlines ~640 (square) pixels HDTV: 60 Hz progressive scan 16: 9 aspect ratio Rick Parent - CIS 681

Video Analog Digital Binary Rick Parent - CIS 681

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 Rick Parent - CIS 681

Digital Formats File formats MPEG MJPEG Gif 89 a Codecs GIF Motion JPEG MPEG Cinepak Sorenson Indeo 3. 2 RLE Video I Sorenson Movie formats Quicktime Video for Windows Rick Parent - CIS 681

Digital Video Formats D 1 D 2 D 3 D 5 D 6 DVCam DVCPRO Digital 8 Ampex DCT Digital Betacam Rick Parent - CIS 681