CS 414 Multimedia Systems Design Lecture 5 Digital Video Representation Klara Nahrstedt Spring 2011 CS 414 Spring 2011 Administrative MP1 is out January 28 Deadline of MP1 is February 16 Wednesday midnight submit via compass Help session for MP1 Monday February 2 7pm Room 1111 SC CS 414 Spring 2011 Outline Human Visual System Visual Perception Resolution Brightness Temporal Resolution Television 3D Video CS 414 Spring 2011 Color and Visual System Color refers to how we perceive a narrow band of electromagnetic energy source object observer Visual system transforms light energy into sensory experience of sight Human Visual System Eyes optic nerve parts of the brain Transforms electromagnetic energy Human Visual System Image Formation cornea sclera pupil iris lens retina fovea Transduction retina rods and cones Processing optic nerve brain Retina and Fovea Retina has photosensitive receptors at back of eye Retina Fovea is small dense region of receptors only cones no rods gives visual acuity Outside fovea fewer receptors overall larger proportion of rods Fove a Transduction Retina Transform light to neural impulses Receptors signal bipolar cells Bipolar cells signal ganglion cells Axons in the ganglion cells form optic nerve Bipolar cells Rods Ganglion Cones Optic nerve Rods vs Cones Cones Rods Contain photo pigment Respond to high energy Enhance perception Concentrated in fovea exist sparsely in retina Three types sensitive to different wavelengths Contain photo pigment Respond to low energy Enhance sensitivity Concentrated in retina but outside of fovea One type sensitive to grayscale changes CS 414 Spring 2011 Tri stimulus Theory 3 types of cones 6 to 7 million of them Red L cones Green M cones Blue S cones Ratio differentiates for each person E g Red 64 Green 32 rest S cones E g L 75 8 M 20 rest S cones E g L 50 6 M 44 2 rest S cones Source of information Each type most responsive to a narrow band See cone cell in wikipedia www colorbasics com tristimulus index php red and green absorb most energy blue the least Light stimulates each set of cones differently and the ratios produce sensation of color Color Perception Color Theory Hue distinguishes Hue Scale named colors e g RGB dominant wavelength of the light Saturation intensity of a specific color how far color is from a gray of equal intensity Brightness lightness perceived Saturation Original Perceived intensity lightness Source Wikipedia CS 414 Spring 2011 Visual Perception Resolution and Brightness Spatial Resolution depends on Brightness Image size Viewing distance Perception of brightness is higher than perception of color Different perception of primary colors Relative brightness green red blue 59 30 11 B W vs Color CS 414 Spring 2011 Source wikipedia Visual Perception Temporal Resolution Effects caused by inertia of human eye Perception of 16 frames second as continuous sequence Special Effect Flicker CS 414 Spring 2011 Temporal Resolution Flicker Perceived if frame rate or refresh rate of screen too low 50Hz Especially in large bright areas Higher refresh rate requires Higher scanning frequency Higher bandwidth CS 414 Spring 2011 Visual Perception Influence Viewing distance Display ratio width height 4 3 for conventional TV Number of details still visible Intensity luminance CS 414 Spring 2011 Television History 1927 Hoover made a speech in Washington while viewers in NY could see hear him AT T Bell Labs had the first television 18 fps 2 x 3 inch screen 2500 pixels Television Concepts Production capture 2D array of light energy to electrical signals signals must adhere to known structured formats Representation and Transmission popular formats include NTSC PAL SECAM HDTV Re construction CRT technology and raster scanning display issues refresh rates temporal resolution relies on principles of human visual system CS 414 Spring 2011 Video Representations Composite NTSC 6MHz 4 2MHz video 29 97 fps PAL 6 8MHz 4 2 6MHz video 25 fps Component Maintain separate signals for color Color spaces RGB YUV YCRCB YIQ CS 414 Spring 2011 Color Coding YUV PAL video standard Y is luminance UV are chrominance Y YUV from RGB Y 299R 587G 114B U 0 492 B Y V 0 877 R Y U V plane at Y 0 5 U V CS 414 Spring 2011 Source wikipedia YCrCb Subset of YUV that scales and shifts the chrominance values into range 0 1 Y 0 299R 0 587G 114B Cr B Y 2 0 5 Cb R Y 1 6 0 5 CS 414 Spring 2011 YIQ NTSC standard YIQ from RGB Y 299R 587G 114B I 74 R Y 27 B Y Q 0 48 R Y 0 41 B Y CS 414 Spring 2011 YIQ with Y 0 5 Source wikipedia NTSC Video 525 scan lines per frame 29 97 fps 33 37 msec frame 1 second 29 97 frames scan line lasts 63 6 usec 33 37 msec 525 aspect ratio of 4 3 gives 700 horizontal pixels 20 lines reserved for control information at the beginning of each field so only 485 lines of visible data CS 414 Spring 2011 NTSC Video Interlaced scan lines divide each frame into 2 fields each of which is 262 5 lines phosphors in early TVs did not maintain luminance long enough caused flicker scanning also interlaced can cause visual artifacts for high motion scenes CS 414 Spring 2011 HDTV Digital Television Broadcast DTB System Twice as many horizontal and vertical columns and lines as traditional TV Resolutions 1920x1080 1080p Standard HDTV Frame rate options 50 or 60 frames per second CS 414 Spring 2011 Pixel Aspect Ratio Computer Graphics parameter Mathematical ratio describing horizontal length of a pixel to its vertical height Used mainly in digital video editing software to properly scale and render video Into a new format CS 414 Spring 2011 Source wikipedia Resolution WxH Pixels Aspect Ratio Pixel aspect ra tio Video Format Description 1024 768 786 432 16 9 Standard 16 9 4 3 720p XGA 1280 720 921 600 16 9 1 1 square 720p WXGA Used on PDP HDTV Used on Digital television 1366 768 1 049 088 16 9 Approx 1 1 square 720p WXGA Used on LCD HDTV PDP HDTV standard displays format 1024 1080 1 105 920 16 9 15 8 1080p 1280 1080 1 382 400 16 9 3 2 1920 1080 2 073 600 16 9 1 1 square 3840x2160 8 294 400 16 9 1 1 square CS 414 Spring 2011 Used on PDP displays HDTV Used on PDP 1080p HDTV displays 1080p HDTV Used on all types standard of HDTV format technologies 2160p Quad HDTV HDTV Interlaced and or progressive formats Conventional TVs use interlaced formats Computer displays LCDs use progressive scanning MPEG 2 compressed streams In Europe Germany MPEG 4 compressed streams CS 414 Spring 2011 Aspect Ratio and Refresh Rate Aspect ratio Conventional TV is 4 3 1 33 HDTV is 16
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