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

[@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

[@unmeshdhere1263]

It's says error in line 9
Unrecognised function or variable ... 'LZW_encoder_string'.

[@StudywithDrDafda]

Save the functions written in comments in MATLAB folder and then run the program. The program uses these functions.

[@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_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

[@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