Data compression Data compression lossless looking for unicolor
- Slides: 19
Data compression
Data compression • lossless – looking for unicolor areas or repeating patterns – Run length encoding – Dictionary compressions • Lossy – reduction of colors - approximating methods (JPEG)
Grid graphics formats • • BMP – no compression PCX – lossless compression RLE PNG – lossless dictionary compression LZW GIF – lossless dictionary compression LZW + reduction to 256 color (adaptive palette) • JPG – approximating compression JPEG
JFIF format (JPEG File Interchange format) sequential, common known progressive, more effective, for computer net transmissions lossless, not known and not widely supported hierarchic, more resolutions in one file, quick preview
Sequential JFIF encoding
Color model transofmation RGB → Y Cb Cr Y= 0, 299*R + 0, 587*G + 0, 114*B (brightness) Cb = - 0, 1687*R - 0, 3313*G + 0, 5*B + 128 Cr = 0, 5*R - 0, 4187*G - 0, 0813*B + 128 R=Y + 1. 402*(Cr-128) G = Y - 0. 34414*(Cb-128) - 0. 71414*(Cr-128) B = Y + 1. 772*(Cb-128)
Subsampling of Cb, Cr Computing of average value for the block • 2 x 1 pixels (6 bits sample), – 6 bits -> 4 bits (compression 67%) • or 2 x 2 pixels (12 bits sample), – 12 bits -> 6 bits (compression 50%)
DCT transformation
Example 139 144 149 153 155 155 144 151 153 156 159 156 156 150 155 160 163 158 156 156 159 161 162 160 159 159 160 161 162 155 155 161 161 160 157 157 162 161 163 162 157 157 162 161 163 158 158
DCT coefficients AC coefficient (= 8 x average brightness
Quantization matrix – example for 90% “qality”
Quantization matrices Defined by standardization committee JPEG. Separately for brightness and for color components. • Defined matrices for quality 10% and 90%. • For other values of quality between 10% and 90%obtained by linear interpolation. • For values under 10% or over 90% extrapolation can be used but it is not recommended. •
Coefficients after quantisation
AC coefficients • Stored separately • Not compressed • Possibility used for quick preview •
Huffman encoding
Example 0, -2, -1, -1, 0, 0, 0…. .
Reconstruction of DCT coeffients
After inverse DCT transformation
Table of differences
- Examples of lossy and lossless compression
- Lossless compression algorithms in multimedia
- 472
- Objective fidelity criteria
- Gzip vs bzip
- Lossless compression
- Lossless compression in multimedia
- Looking out looking in summary
- Looking out looking in chapter 9
- Lossless transmission line examples
- Lossless network s parameters
- Characteristic impedance of transmission line
- An example for lossless propagation is___________________.
- Lossless join decomposition adalah
- Lossless join
- Scattering matrix for a reciprocal network is
- Discrete memoryless channel
- Decomposition in dbms ppt
- Lossless transmission line
- Data compression in data mining