compression data files compression music compression image and video compression

Compression

Data files compression

Music compression

Image and video compression

Introduction

File CompressionAsk not what your country can do for you -- ask what you can do for your country.

79 characters

Dictionnary

1. Ask2. What3. Your4. Country5. Can6. Do7. For8. you

Compressed sentence

1 not 2 3 4 5 6 7 8 -- 1 2 8 5 6 7 3 4

Dictionnary + Compressed sentence : 72 characters

File CompressionAsk not what your country can do for you -- ask what you can do for your country.

79 characters

Dictionnary

1. ask_2. what_3. you4. r_country5. _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 - 1961

LZ adaptive dictionnary-based algorithm

Audio Compressing

Digital soundSound compression techniquesHuffman algorithmMP3

Digital Sound

Sampling– A song is a frequency– Shannon theorem

Exemple sampling rate

Sampling Rate Sound quality

44,100 Hz CD quality

22,000 Hz Radio quality

8000 Hz Phone 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

letters occurencies

frenquency

coding

Space 4 2 00

A 3 2 01

E 2 3 100

N 2 3 101

C 1 4 1100

I 1 4 1101

M 1 4 1110

S 1 4 1111

total 120bits 42bits

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

…1001011…

Picture compression

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 compressionJPEG 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 Bytes 1512 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