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CP2022 - Lecture 8

PC and Media exchange standards

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Standards

Two opposing (extreme) views All diversity in computing is to be

encouraged and any differences between systems can be accommodated by translation software or special devices.

All diversity in computing should be discouraged and standards should be rigorously defined and used.

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User requirements

Users have a requirement to process Video Audio Image Text

at different quality levels. (e.g. video at 15 or 30 fps)

The end-user system should work at a faster speed than any communication connection available.

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System specification- MPC3

Processor Pentium (75 MHz)Memory 8 Mb RAMStorage 540 Mb hard disc drive Audio 16-bit digital sound; wave table

Graphics Colour space conversion and scaling capability Video MPEG1 CD-ROM drive 600 kbps transfer rate - 250 ms max. average seek

timeUser input 101-key IBM-style keyboard - Two-button mouseI/O MIDI; joystick; serial; parallelSystem software Windows 3.11, DOS 6.0, or binary compatible

MPC attempted to standardise PCs – but failed.

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Current

The MPC specification became redundant and all current systems are far better than this!!

Hardware systems depend on software performance

Particularly Operating system performance

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Operating system influence Operating systems range from Single-tasking to Multi-tasking

one or more simultaneous processes Single-user to Multi-user

one or more simultaneous users with one or more simultaneous processes

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Communication channel requirement MPC 3 could achieve the following processing

Video 352 x 240 at 30 fps & 15 bits/pixel = 38 016 000 bps

Audio 8 kHz samples of 16 bits (stereo) = 256 000 bpsText up to 9600 bps =

9600 bpsTotal = 38.3 Mbps

with compression this can be transmitted at around 1.2 Mbps.

assuming about 30:1 compression

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Text standards

Character formats ASCII (IA5) -7/8 bit Unicode - 16 bit

Text formats Various word processing forms (inc.

RTF) Tex, Latex,Postscript

Document formats PDF, SGML, XML

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Image standards

The International standard is JPEGInternational Standard 10918 Digital compression and coding of continuous

tone still images Many other formats in widespread

use See assessment 1 !! For example

BMP, GIF, TIFF, PCX, TGA, EPS, DIB, IMG, PIC, WPG etc...

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Image standards

Colour depth can change8-bit = 256 colours16-bit = 64K colours24-bit = 16M colours

Some have compression lossy or lossless

Application will determine use e.g WWW uses JPG and GIF

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JPEG compression ratios

Quality Bits per pixelModerate to good 0.25 - 0.5Good to very good 0.5 - 0.75Excellent 0.75 - 1.5Near original quality 1.5 - 2.0

Example - Image (352 x 240) pixels x 16-bit colourUncompressed size 168 960 bytesCompressed size

From 2640 bytesTo 21120 bytes

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Audio standards

Audio is based on PCM pulse code modulation

Analogue wave

Sampled version

Levels

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Audio quality

Sampling creates errors Higher sample rates give less errors Lower sample rates need less data

Quality CD quality needs over 1 Mbps Voice quality audio PCM needs 64 kbps

Lower sample rates use Adaptive PCM More efficient 12-bit quality with 8-bit

samples

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Video standards

The International standard is MPEG M-JPEG can be used but compression is less

MPEG frames

Time

I

I

P

BB

B

BB

B

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MPEG

I, P and B frames I frame is a full image (most

information) P is a predicted frame

Uses an I frame and predicts using motion compensation

B is interpolated from I and P frames (least information)

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Summary

Standards affect all areas of computing and communication

Some standards are not the best technology

Some technology is non-standard Application and use will determine

need for standards