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The World of HD. Dr. Hayden So Department of Electrical and Electronic Engineering 24 Oct, 2008. Area You Ready?. What does HD really mean?. H igh D efinition Full HD 1080p 1920 x 1080 pixels + progressive scan PAL: 768x576 Supposedly higher quality video, TV.

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The World of HD

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The World of HD

Dr. Hayden So

Department of Electrical and Electronic Engineering

24 Oct, 2008


Area You Ready?


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?


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


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


Image courtesy of www.carltonbale.com


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


HDTV Transmission

  • Digital Broadcast

    • Vs conventional Analog transmission

  • Over-the-air transmission of HD content

  • Began in Dec 31, 2007


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


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 x576 @ 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


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


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…


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


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 ShujiNakamura


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