1 CP Lecture 8 PC and Media exchange standards

2 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.

3 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.

5 System specification- MPC3 Processor Pentium (75 MHz) Memory 8 Mb RAM Storage 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 ms max. average seek time User input 101-key IBM-style keyboard - Two-button mouse I/O MIDI; joystick; serial; parallel System software Windows 3.11, DOS 6.0, or binary compatible MPC attempted to standardise PCs – but failed.

6 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

7 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

8 Communication channel requirement MPC 3 could achieve the following processing Video 352 x 240 at 30 fps & 15 bits/pixel= bps Audio8 kHz samples of 16 bits (stereo)= bps Textup to 9600 bps= 9600 bps Total= 38.3 Mbps with compression this can be transmitted at around 1.2 Mbps. assuming about 30:1 compression

9 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

10 Image standards The International standard is JPEG International Standard 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...

11 Image standards Colour depth can change 8-bit = 256 colours 16-bit = 64K colours 24-bit = 16M colours Some have compression lossy or lossless Application will determine use e.g WWW uses JPG and GIF

12 JPEG compression ratios Quality Bits per pixel Moderate to good Good to very good Excellent Near original quality Example - Image (352 x 240) pixels x 16-bit colour Uncompressed size bytes Compressed size From 2640 bytes To bytes

13 Audio standards Audio is based on PCM pulse code modulation

14 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

15 Video standards The International standard is MPEG M-JPEG can be used but compression is less MPEG frames

16 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)

17 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