Compression  Data files compression  Music compression  Image and video compression

Introduction

File Compression Ask not what your country can do for you -- ask what you can do for your country. 79 characters Dictionnary 1. Ask 2. What 3. Your 4. Country 5. Can 6. Do 7. For 8. you Compressed sentence 1 not Dictionnary + Compressed sentence : 72 characters

File Compression Ask not what your country can do for you -- ask what you can do for your country. 79 characters Dictionnary 1. ask_ 2. what_ 3. you 4. r_country 5. _can_do_for_you Compressed sentence Dictionnary + Compressed sentence : 59 characters 1not__2345__--__12354

File Compression Ask not what your country can do for you -- ask what you can do for your country. John F. Kennedy LZ adaptive dictionnary-based algorithm

Audio Compressing  Digital sound  Sound compression techniques  Huffman algorithm  MP3

Digital Sound  Sampling –A song is a frequency –Shannon theorem  Exemple sampling rate Sampling RateSound quality 44,100 HzCD quality 22,000 HzRadio quality 8000 HzPhone quality

Digital sound  Example for a 1 minute long song Sampling 44,100 Hz Encoding 16 bits Stereo song –=> (((44100*2o)*2)*60) ≈ 10Mo for CDA –1 Mo for MP3

Sound compression techniques  Destroying compression –Frequencies located between 20 Hz 20 Khz –Human ear can hear between 2 and 5 KHz –Cut higher and lower frequencies  No destroying compression –Generally techniques of coding –Huffman algorithm

Huffman algorithm lettersoccuren cies frenque ncy coding Space4200 A3201 E23100 N23101 C I M S total120bits42bits  Principle –The most frequent information is coded with short symbols, the less frequent one with longs symbols  Example « I can see a man »

MP3  called MPEG Audio Layer-3  a compression system for audio  compress a CD-quality song by a factor of 10 to 14, without losing the CD sound quality

MP3  Procedure –The mask effect –The reserve of bytes –The join stereo –Huffman algorithm

Picture coding Coding -HSL :(Hue,Saturation,Luminance) -RGB :(Red,Green,Blue) Pixel … …

Picture compression RLE method (for BMP TIFF formats) ‘’BBBBBWWBBBBWWWWWWW ‘’  ‘’5B 2W 4B 7W’’ (Black and white) ‘’r1r2r3r4r5r6’’  ‘’ 1r1 1r2 1r3 1r4 1r5 1r6’’ (Colour gradation) Bad effectiveness

Picture compression JPEG Compression -merging per packages of 2x2 pixels -merging per packages of 8x8 packages - calculation of the average color of packages - allocation to each new package of the average color - coding of each colour by HUFFMAN 5169 Bytes1512 Bytes 369 Bytes

Video compression (MPEG) Moving Pictures Expert Group -frame I compression -picture by picture -frame P compression -what differs from the previous (and the following) picture is coded -frame B compression

Video compression MPEG-1:  1988 MPEG-2:  used by DVD MPEG-4:  used by Divx—Xvid—VP3-—3ivX