1. RUN LENGTH
ENCODING
Praseetha S Nair
M.Tech(CS)

2. COMPRESSION
 Data compressed by eliminating redundant elements.
 Purpose of compression:-
-save storage space
-reduce communications capacity requirements
 Some code must be substituted for eliminated element.
 Based on this code receiver can reconstruct original
data.

3.  Categories:-
1.lossless compression
-no information lost
-decompressed data are identical to original
uncompressed
data
2.lossy compression
-decompressed data may be an
approximation to the
original uncompressed data

4. Null Suppression
 Oldest and simplest
 Long string of blanks , nulls etc cause
redundancy.
 At transmitter:
-scans data for string of blanks.
-substitute two character code for any string
that is encountered.

5.  Example :
the string
XYZbbbbbQRX
is replaced by
XYZSC5QRX
where Sc is a special compression indication
character
b is symbol for a blank space

6.  At receiver:
-scan incoming character for special indication
character
-reconstruct original data

7. Run-Length Encoding
 Compress any type of repeating data sequence
 At transmitter:
-identify repeating characters to replace
-if found, eliminate and replace by three- character code

8. Sc X Cc
Sc-Special character indicating compression follows
X-Any repeated data character
Cc-Character count
(a) Compression format
Original data string Encoded data string
$******55.72 $c*655.72
--------- Sc-9
GunsScb9Butter
(b)Examples
Fig: Run-Length Encoding

9.  Efficiency depends on
-number of repeated character occurrences in data to be
compressed
-average repeated character length.
 Compression ratio=length of uncompressed data
length of compressed data
 Any compression scheme will have variable performance
as the content of the input varies.

10.  It is used as an element in more complex
image compression technique.
 For run-length encoding on an image,
transmission of digital line scan is replaced
by transmission of a quantity count of each of
successive run of black or white scanned
picture element.

11. 0000000000
0000000000
0001111000
0001001000
0001111000
0000001000
0000001000
0001111000
0000000000
0000000000
Length:100 bit
23W 4B 6W 1B 2W 1B
6W 4B 9W 1B 9W 1B
6W 4B 23W
(a)Image
or:
Fig: Run-Length Code for a 100-pixel 23 4 6 1 6 4 9 1 916 4
image 23
Length:15characters=1
20bit

12.  Application of run length encoding to a 10X10
image.
 10X10 representation is converted to a 100-
bit code.
 Each pixel is represented by a single bit
indicate black or white.
 Run-length code consist of length of alternate
black or white sequence.
 Encoded data stream is a string of number
that indicate length of alternate black or
white runs.

13. THANK YOU