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The World of HD Dr. Hayden So Department of Electrical and Electronic Engineering 24 Oct, 2008
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Area You Ready?
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What does HD really mean? High Definition Full HD 1080p 1920 x 1080 pixels + progressive scan PAL: 768x576 Supposedly higher quality video, TV More Pixels = Higher Quality?
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Three Characteristics of Display Panel Size The physical dimension of the panel A 42” panel has a diagonal measurement of 42” Display Resolution The number of picture-elements (pixels) along each X-Y direction In a HD panel: 1920 x 1080 pixels Dot Pitch The distance between two pixel of the screen Panel Size = Display Resolution * Dot Pitch
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More Pixel = Good? Human eye can identify 120 pixels per degree of visual arc i.e. if 2 dots are closer than 1/120 degree, then our eyes cannot tell the difference At a distance of 2m (normal distance to a TV) our eyes cannot differentiate 2 dots 0.4mm apart. Closer to TV => easier to differentiate pixels Far away => cannot tell the difference screen Minimum: 2 arc minute
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Image courtesy of www.carltonbale.com
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Why is HD difficult? One major problem is bandwidth The amount of video data needed to be processed for each frame HD: 1920 x 1080 x 50 Hz x 24 bits = 2.48 Gb/s PAL (progressive, digital) 768 x 576 x 25 Hz x 24 bits = 133 Mb/s 10x more data needed to be processed, stored
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HDTV Transmission Digital Broadcast Vs conventional Analog transmission Over-the-air transmission of HD content Began in Dec 31, 2007
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DTT in Hong Kong DTMB – Digital Terrestrial Multimedia Broadcast (formerly DMB-T/H) Same as mainland China Different from rest of the world Two standards MPEG-2 for Standard Definition TV - Basic H.264 for HDTV – Higher-tier Higher-tier supports full H.264 + interactive
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Storing and Playing HD Movies DVD was not capable The standard Physically infeasible A double-layer DVD-9 can store around 8 GB of data ~= 4 hours of PAL video compressed using MPEG2 720 x 576 @ 25 fps, < 10 Mbps variable video bitrate About 2 hours on a DVD-5 Using the same encoding for HD video 1080p24 requires ~5 times the storage Need new storage + new encoding
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Blu-ray Discs Next generation DVD Same form factor New Storage Single side: 25 GB Double side: 50 GB New encoding Uses MPEG2 or H.264/AVC Using MPEG2: 2 hours on single side Using H.264/AVC: ~4 hours single side, 8 hours DL
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Enabling Technology Blue-violet laser Blu-ray uses violet 405nm laser DVD: 650nm near infrared CD: 780nm Shorter wavelength allows more information to be stored per unit area Why not use it in DVD? It was very expensive to produce blue laser Until him…
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Story of Shuji Nakamura A research scientist at Nichia Chemical Industries Ltd. in Tokushima, Japan Graduated with a PhD but decided to stay in Tokushima, instead of Tokyo, to raise his child A research team that shrinks from 3 people in 1979 down to 1 in 1991 Invented the world’s first commercially viable blue-violet solid state laser diode Beat all major research universities Beat all big companies: RCA and Hewlett- Packard to Matsushita and Sony
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Summary Given the right condition, HD does give better quality video Over the air broadcast is achieved through digital broadcasting Need new equipments For stored video, Blu-ray is the next standard Blu-ray was only made possible by discovery of Shuji Nakamura
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