1. 1 SWE 423 – Multimedia System

2. 2 SWE 423 - Multimedia System Introduction  Compression is the process of coding that will effectively reduce the total number of bits needed to represent certain information.  Data compression seeks to reduce the number of bits used to store or transmit information. A General Data Compression Scheme

3. 3 SWE 423 - Multimedia System Two Types of Data Compression  Lossless Compression  The property that it is always possible to decompress data that has been compressed and retrieve an exact copy of the original data  Lossy Compression  The property that some data has been discarded in the compression process and cannot be restored, so that the decompressed data is only an approximation to the original.

4. 4 SWE 423 - Multimedia System Compression Ratio 

5. 5 SWE 423 - Multimedia System Lossless Techniques  Run-Length Encoding (RLE)  a simple technique to compress digital data by representing successive runs of the same value in the data as the count followed by the value, rather than the original run of values.  This encoding method is frequently applied to images.  For example given the following data: AAAAAHHHHHHHHHHHHHH 5A14H Uncompressed data

6. 6 SWE 423 - Multimedia System  RLE AAAAAHHHHHHHHHHHHHH 19 5

7. 7 SWE 423 - Multimedia System  RLE CORRECTLY 9 16

8. 8 Variants on RLE X-axis Y-axis 2D tiles Diagonal zigzag

9. 9 RLE  Given the following data: a. Apply the X- axis variants on run-length encoding (RLE) data compression algorithm. b. What is the compression ratio when RLE is applied?

10. 10 Solution a. Line1 = 5W2B1W1B4W Line2 = 4W3B5W1B Line3 = 8B5W Line4 = 5W8B Line5 = 13B compression ratio

11. 11 RLE  Given the following data: a. Apply the X- axis variants on run-length encoding (RLE) data compression algorithm. b. What is the compression ratio when RLE is applied?

12. 12 a. Line1 = 70 Line2 = 71 Line3 = 71 Line4 = 71 Line5 = 4130 Line6 = 4130 Line7 = 70 compression ratio Solution

13. 13 Fixed-Length Code (FLC)  Also known as the prefix code.  is a code system that uses same number of bits for each symbol.

14. 14 Another example of FLC

15. 15 Variable-Length Code (VLC)  Variable Length Code is a code which maps source symbols to a variable number of bits.  is a sophisticated lossless techniques  The best known technique of this group is called Huffman coding.  Huffman coding uses variable-length codes where data are re-encoded to make the most frequent values occupy the fewest bits.

16. 16 SWE 423 - Multimedia System Variable-Length Codes A=31 B=18 C=7 D=4 BinaryDec. 11 102 113 1004 1015 1106 1117 10008 10019 101010 101111