LZW compression using easy method(Dictionary-based coding)in DIP & its Implementation in MATLAB

[@pravinbhoi3121]

The best channel, and the only one, that covers both theoretical as well as practical concepts in such a easy way. Thank you.

[@StudywithDrDafda]

Thank you.

[@tahseenali5609]

Dear Sir, I am very very thank full to you. I entered the code and successfully run. I am very happy thanks a lotttttttt.

[@tahseenali5609]

Very very very nice Sir.

[@tahseenali5609]

Sir i sm doing PhD in Telecom. What is your research field....

[@StudywithDrDafda]

I have done my PhD on Satellite Communications.

[@tahseenali5609]

@@StudywithDrDafda I am doin research... Resource allocation in 5g and 6g...can you help me Sir in this regard?

[@StudywithDrDafda]

Yes, you can mail me your queries on my email [e-mail]

[@kartikforwork]

why are we putting last char value in the encoded output?
like at 7:28, the 7 output value has fda in dictonary, so decoding it will give fda directly, so why 1 in the end

[@StudywithDrDafda]

At 7:28, the 7 output value has FD in the dictionary, and not FDA. Check dictionary location number 7, it is FD and therefore always last character is required for correct decoding.

[@yousefeldewik3027]

if I want to do this but instead of Image compression, voice compression and calculate the equivalent probability of each symbol what will be the code
could you provide me with some help

[@tuananhvu5398]

Can you sum up all the code, I'm new so I don't know how to arrange it properly
Thank you

[@StudywithDrDafda]

function [output,table, Alphabet] = LZW_encoder_string(vector)
% LZW Data Compression for string (encoder)
% For vectors, LZW_encoder_string(X) is the compressed vector
% of X using the LZW algorithm.
% [...,T] = LZW_encoder_string(X) returns also the table
% that the algorithm produces.
% For matrices, X(:) is used as fprintf.
% fprintf must be of uint8 type, while the output is a uint16.
%Table is a cell array, each element_k containing the resp.code.
% How it encodes:
% STRING = get fprintf character
% WHILE there are still fprintf characters DO
% CHARACTER = get fprintf character
% IF STRING+CHARACTER is in the string table then
% STRING = STRING+character
% ELSE
% output the code for STRING
% add STRING+CHARACTER to the string table
% STRING = CHARACTER
% END of IF
% END of WHILE
% output the code for STRING
% ensure to handle uint8 fprintf vector
if ~isa(vector,'uint8'),
error('fprintf argument must be a uint8 vector')
end
% vector as uint16 row
vector = uint16(vector(:)');
%initialize table (don't use cellstr because char(10) will be turned to empty!!!)
fprintf('Initialising Table
');
table = [];
Alphabet = unique(vector);
for i = 1:numel(Alphabet)
[table, code] = addcode(table, (double(Alphabet(i))));
fprintf('Table Entry %d : %s
', i, char(Alphabet(i)));
end
fprintf('
');
% initialize output
output = vector;
% main loop
outputindex = 1;
startindex = 1;
element_k = vector(1);
substr_w = [];
fprintf('w k output index symbol
');
fprintf('------------------------------------
');
fprintf('NIL\t\t%s
', char(element_k));

for index=2:length(vector),
element_k = vector(index);
substr_w = vector(startindex:(index-1));
code = getcodefor([substr_w element_k],table);

if isempty(code),
% add it to the table
output(outputindex) = getcodefor(substr_w,table);
[table,code] = addcode(table,[substr_w element_k]);
fprintf('%s\t\t%s\t\t%d\t\t%d\t\t%s
', ...
char(substr_w), char(element_k), output(outputindex), code,...
char([substr_w element_k]));
outputindex = outputindex+1;
startindex = index;
else
fprintf('%s\t\t%s
', char(substr_w), char(element_k));
end
end
substr_w = vector(startindex:index);
output(outputindex) = getcodefor(substr_w,table);
% remove not used positions
output((outputindex+1):end) = [];
% ###############################################
function code = getcodefor(substr,table)
code = uint16([]);
for index=1:length(table),
if isequal(substr,table{index}),
code = uint16(index); % start from 0
break
end
end
% ###############################################
function [table,code] = addcode(table,substr_w)
code = length(table)+1; % start from 1
table{code} = substr_w;
code = uint16(code); % start from 1

[@doaajawad2379]

When I run this program in maylab there are,an error ??

[@StudywithDrDafda]

First, please save the functions given in above comments in MATLAB folder, then run the programs.

[@doaajawad2379]

LZW_encoder string ;error in this step

[@StudywithDrDafda]

First, please save the functions given in above comments in MATLAB folder, then run the programs.

[@StudywithDrDafda]

function [output,table] = LZW_decoder_string(vector, alphabet)
% LZW Data Compression for string(decoder)
% For vectors, LZW_decoder_string(X) is the uncompressed
% vector of X using the LZW algorithm.
% [...,T] = LZW_decoder_string(X) returns also the table
% that the algorithm produces.
% For matrices, X(:) is used as input.
% Input must be of uint16 type, while the output_w is a uint8.
%Table is a cell array, each element_k containing the resp.code.
% How it decodes:
% Read OLD_CODE
% output_w OLD_CODE
% CHARACTER = OLD_CODE
% WHILE there are still input characters DO
% Read NEW_CODE
% IF NEW_CODE is not in the translation table THEN
% entry = get translation of OLD_CODE
% entry = entry+CHARACTER
% ELSE
% entry = get translation of NEW_CODE
% END of IF
% output_w entry
% CHARACTER = first character in entry
%add translation of OLD_CODE + CHARACTER to the translation table
% OLD_CODE = NEW_CODE
% END of WHILE
% ensure to handle uint8 input vector
if ~isa(vector,'uint16'),
error('input argument must be a uint16 vector')
end
% vector as a row
vector = vector(:)';
%Intialise Table
fprintf('Initialising Table
');
table = [];
% Alphabet = unique(vector);
for i = 1:numel(alphabet)
[table,code] = addcode(table, uint16(double(i)));
end
for index = 1:numel(table),
fprintf('Table Entry %d : %s
',index, alphabet(table{index}));
end
% initialize output_w
output = uint8([]);
code = vector(1);
output(end+1) = table{code};
character = code;
fprintf('Input + code_w k (w=k): %d
', code);
fprintf('w k output index symbol
');
fprintf('------------------------------------
');
fprintf('NIL\t\t%s
', alphabet(code));
for index=2:length(vector),
element_k = vector(index);
%k_pos = getcodefor(element_k,table)
% fprintf('Input k: %d
', code);
% element_k
if (element_k)>length(table),
% add it to the table
entry = table{double(code)};
entry = [entry character];
else
entry = element_k;
end

if code > numel(alphabet)
ow = num2str(code);
else
ow = alphabet(code);
end

if element_k > numel(alphabet)
ok = num2str(element_k);
else
ok = alphabet(element_k);
end
character = table{entry};
[table,code] = addcode(table,[table{code} character(1)]);
fprintf('%s\t\t%s\t\t%s\t\t%d\t\t%s', ow, ok, char(alphabet(table{entry})), ...
code, alphabet([table{code}]));
warning off
output = [output table{entry}];
warning on
code = element_k;
end
% ###############################################
function code = getcodefor(substr,table)
code = uint16([]);
for index=1:length(table),
if isequal(substr,table{index}),
code = uint16(index); % start from 0
break
end
end
% ###############################################
function [table,code] = addcode(table,substr)
code = length(table)+1; % start from 1
table{code} = substr;
code = uint16(code); % start from 1

[@StudywithDrDafda]

function [output,table] = LZW_decoder_image(vector, alphabet)
% LZW Data Compression (decoder)
% For vectors, LZW_decoder_image(X) is the uncompressed
% vector of X using the LZW algorithm.
% [...,T] = LZW_decoder_image(X) returns also the table
% that the algorithm produces.
% For matrices, X(:) is used as input.
% Input must be of uint16 type, while the output_w is a uint8.
%Table is a cell array, each element_k containing the resp. code.
% How it decodes:
% Read OLD_CODE
% output_w OLD_CODE
% CHARACTER = OLD_CODE
% WHILE there are still input characters DO
% Read NEW_CODE
% IF NEW_CODE is not in the translation table THEN
% entry = get translation of OLD_CODE
% entry = entry+CHARACTER
% ELSE
% entry = get translation of NEW_CODE
% END of IF
% output_w entry
% CHARACTER = first character in entry
%add translation of OLD_CODE + CHARACTER to the translation table
% OLD_CODE = NEW_CODE
% END of WHILE
% ensure to handle uint8 input vector
if ~isa(vector,'uint16'),
error('input argument must be a uint16 vector')
end
% vector as a row
vector = vector(:)';
%Intialise Table
fprintf('Initialising Table
');
table = [];
% Alphabet = unique(vector);
for i = 1:numel(alphabet)
[table,code] = addcode(table, uint16(double(i)));
end
for index = 1:numel(table),
fprintf('Table Entry %d: %d
',index, alphabet(table{index}));
end
fprintf('
');
% initialize output_w
output = uint8([]);
code = vector(1);
output(end+1) = table{code};
character = code;
fprintf('Input + code_w k (w=k): %d
', code);
fprintf('w k output index symbol
');
fprintf('------------------------------------
');
fprintf('NIL\t\t%d
', alphabet(code));

for index=2:length(vector),
element_k = vector(index);
%k_pos = getcodefor(element_k,table)
% fprintf('Input k: %d
', code);
% element_k
if (element_k)>length(table),
% add it to the table
entry = table{double(code)};
entry = [entry character];
else
entry = element_k;
end

if code > numel(alphabet)
ow = num2str(code);
else
ow = alphabet(code);
end

if element_k > numel(alphabet)
ok = num2str(element_k);
else
ok = alphabet(element_k);
end


character = table{entry};
[table,code] = addcode(table,[table{code} character(1)]);
fprintf('%d\t\t%d\t\t%d\t\t%d\t\t%d
',ow,ok,char(alphabet(table{entry})),...
code, alphabet([table{code}]));
warning off
output = [output table{entry}];
warning on
code = element_k;
end
% ###############################################
function code = getcodefor(substr,table)
code = uint16([]);
for index=1:length(table),
if isequal(substr,table{index}),
code = uint16(index); % start from 0
break
end
end
% ###############################################
function [table,code] = addcode(table,substr)
code = length(table)+1; % start from 1
table{code} = substr;
code = uint16(code); % start from 1

[@StudywithDrDafda]

function [output,table, Alphabet] = LZW_encoder_image(vector)
% LZW Data Compression (encoder)
% For vectors, LZW_encoder_image(X) is the compressed vector
% of X using the LZW algorithm.
% [...,T] = LZW_encoder_image(X) returns also the table
% that the algorithm produces.
% For matrices, X(:) is used as fprintf.
% fprintf must be of uint8 type, while the output is a uint16.
% Table is a cell array, each element_k containing resp.code.
% How it encodes:
% STRING = get fprintf character
% WHILE there are still fprintf characters DO
% CHARACTER = get fprintf character
% IF STRING+CHARACTER is in the string table then
% STRING = STRING+character
% ELSE
% output the code for STRING
% add STRING+CHARACTER to the string table
% STRING = CHARACTER
% END of IF
% END of WHILE
% output the code for STRING
% ensure to handle uint8 fprintf vector
if ~isa(vector,'uint8'),
error('fprintf argument must be a uint8 vector')
end
% vector as uint16 row
vector = uint16(vector(:)');
% initialize table (don't use cellstr because char(10)
% will be turned to empty!!!)
fprintf('Initialising Table
');
table = [];
Alphabet = unique(vector);
for i = 1:numel(Alphabet)
[table, code] = addcode(table, (double(Alphabet(i))));
fprintf('Table Entry %d : %d
', i, char(Alphabet(i)));
end
fprintf('
');
% initialize output
output = vector;
% main loop
outputindex = 1;
startindex = 1;
element_k = vector(1);
substr_w = [];
fprintf('w k output index symbol
');
fprintf('------------------------------------
');
fprintf('NIL\t\t%d
', char(element_k));

for index=2:length(vector)
element_k = vector(index);
substr_w = vector(startindex:(index-1));
code = getcodefor([substr_w element_k],table);

if isempty(code)
% add it to the table
output(outputindex) = getcodefor(substr_w,table);
[table,code] = addcode(table,[substr_w element_k]);
fprintf('%d\t\t%d\t\t%d\t\t%d\t\t%d
',...
char(substr_w), char(element_k), output(outputindex), code, ...
char([substr_w element_k]));
outputindex = outputindex+1;
startindex = index;
else
% go on looping
fprintf('%d\t\t%d
', char(substr_w), char(element_k));
end
end
substr_w = vector(startindex:index);
output(outputindex) = getcodefor(substr_w,table);
% remove not used positions
output((outputindex+1):end) = [];
% ###############################################
function code = getcodefor(substr,table)
code = uint16([]);
for index=1:length(table),
if isequal(substr,table{index}),
code = uint16(index); % start from 0
break
end
end
% ###############################################
function [table,code] = addcode(table,substr_w)
code = length(table)+1; % start from 1
table{code} = substr_w;
code = uint16(code); % start from 1