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The Universi
The
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o
vember 7, 2007
ty of Michigan
ty
of
Michigan
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PA2: LZ78/LZW Data Compression at University of Michigan - Prof. Sugih Jamin, Exams of Algorithms and Programming
A class agenda for a data compression lecture at the university of michigan. It covers the lz78/lzw encoding and decoding techniques using huffman tree and trie. The process of creating minheap, trie, and compressing code table, as well as the encoding and decoding methods.
Typology: Exams
Pre 2010
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Discussion: No
The UniversiThe
Universi
o
vember 7, 2007
ty of Michiganty
of Michigan
Agenda
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Questions on anything
z
Quick Huffman Review
z
PA2: LZ78/LZW
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Specific questions
Quick Huffman Review
Review of what we need to do (remem1.) Create minheap class: can have <k2.) Create trie class3.) Read in input data (M&Ms) 4.) Put input data into minheap “keyed
- This means lowest key at root
5.) Construct trie (keep pulling off the
- Remember: have to put sub-trie b
6.) When trie is built, we can create the7.) Create compressed code table8.) For encoded data, just use the code
ber this is ONE way):
key,object> paird” by frequency
root of minheap to get pairs)
b
ack onto minheap sometimes!
e codes for each symbol e table to determine what goes where
PA2: LZ78/LZW Encoding
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Encoding process
−
Quick review of exam question
PA2: LZ78/LZW Encoding
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Magic Cookie: 16-bits
z
LZW: 0010
z
Original Sym Size: 8-bits (If ASCII,
l S
S
h
b
l
z
Initial Sym Size*: It is the symbol sstring=256 ,
then initial sym size =
−
Size will increase dynamically
−
Use trie to do the encoding
−
Reserve 2^k-1 symbol for transi
then 8-bits)
h ( f
f
d
ize you start with (If your first code
ition to next symbol size
PA2: LZ78/LZW Decoding
PA2: LZ78/LZW Encoding
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Visit this website for issues regardinstrings
htt
k
l
http://marknelson.us/1989/10/
Strings are stored in a reveRetrieve characters and sto
Retrieve characters and stothem to get the string
g use of stack for getting the decoded 01/l
d
t
i
01/lzw-data-compression/ erse order in our string bufferore them in our stack buffer and popore them in our stack buffer and pop