1 / 11

MultiMedia Compression

MultiMedia Compression. Images. Audio. Cryptography - Steganography. }. Movies. Codes' type. Statistic code Giving a presentation in a different length to each item according to its probability. Dictionary code A collection of strings.

kylemore-losty
Download Presentation

MultiMedia Compression

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. MultiMedia Compression • Images. • Audio. • Cryptography - Steganography. } Movies 1. 1

  2. Codes' type • Statistic code • Giving a presentation in a different length to each item according to its probability. • Dictionary code • A collection of strings. • The compressed file contains pointers to those strings. 1. 2

  3. Another division for types • Static code • Two passes on data. • One for gathering information and one for executing the compression. • Adaptive code • One pass on data for both gathering information and compression's executing. • Faster than static. • If file isn't uniform, can be sometimes better since it can "forget". 1. 3

  4. Yet another division for types • Lossless Code • No loss of data • Lossy Code • Some data may lost. • Very common in use for audio, images, video etc. 1. 4

  5. Uniquely Decipherable • Fixed length code can be easily broken into codewords. • How can we split a variable length code? A - 0 B - 10 C - 11 D - 1 • 110 can be “CA” or “DB” or “DDA”. 1. 5

  6. The prefix property • No codeword is the prefix of any other codeword. • Example: • A - 000 • B - 001 • C - 0100 • D - 0101 • E - 011 • F - 10 • G - 11 10011010000000111 F C G E A B 1. 6

  7. Tree of Prefix code 1. 7

  8. A complete prefix code • A prefix code is complete if it fits a complete binary tree. • A prefix code is complete if an insertion of another codeword will make it a not Uniquely Decipherable code. • These two definitions are equivalents. 1. 8

  9. Shannon-Fano coding • Divide the set of symbols into two equal or almost equal subsets based on the probability of occurrence of characters in each subset. • One set is assigned 0. • The other set is assigned 1. • Repeat the procedure until all subsets have a single element. • Each element's code is the concatenation of the sets' bits. 1. 9

  10. An example • A - 5%, B - 15%, C - 20%, D - 25%, E - 35%. 111 A(5%) 01 B(15%) 110 C(20%) 10 D(25%) 00 E(35%) 1. 10

  11. Shannon-Fano is not optimal • This tree will give a better compression: • Shannon-Fano tree: 3*0.05+2*0.15+3*0.20 +2*0.25+2*0.35=2.25 • This better tree: 3*0.05+3*0.15+2*0.20 +2*0.25+2*0.35=2.2 1. 11

More Related