Saving quantized coefficients to file - matlab

Question

I am trying to read an image, DCT transform it, quantize it, and then save the quantized coefficients to a file that will be read into a fractal encoding program.
When I decode the file (with the quantized coefficients), all I get is some grey screen. Is this due to the contents of the file or am I missing out on something else?
%% LOSSY COMPRESSION-DECOMPRESSION USNIG DISCRETE COSINE TRANSFORM TECHNIQUE.
function[]=dct11(filename,n,m)
% "filename" is the string of characters including Image name and its
% extension.
% "n" denotes the number of bits per pixel.
% "m" denotes the number of most significant bits (MSB) of DCT Coefficients.
% Matrix Intializations.
N=8; % Block size for which DCT is Computed.
M=8;
I=imread('Lenna.bmp'); % Reading the input image file and storing intensity values in 2-D matrix I.
I_dim=size(I); % Finding the dimensions of the image file.
I_Trsfrm.block=zeros(N,M); % Initialising the DCT Coefficients Structure Matrix "I_Trsfrm" with the required dimensions.
Norm_Mat=[16 11 10 16 24 40 51 61 % Normalization matrix (8 X 8) used to Normalize the DCT Matrix.
12 12 14 19 26 58 60 55
14 13 16 24 40 57 69 56
14 17 22 29 51 87 80 62
18 22 37 56 68 109 103 77
24 35 55 64 81 104 113 92
49 64 78 87 103 121 120 101
72 92 95 98 112 100 103 99];
save('LenaInitial.dat','I');
%% PART-1: COMPRESSION TECHNIQUE.
% Computing the Quantized & Normalized Discrete Cosine Transform.
% Y(k,l)=(2/root(NM))*c(k)*c(l)*sigma(i=0:N-1)sigma(j=0:M-1)y(i,j)cos(pi(2i+1)k/(2N))cos(pi(2j+1)l/(2M))
% where c(u)=1/root(2) if u=0
% = 1 if u>0
for a=1:I_dim(1)/N
for b=1:I_dim(2)/M
for k=1:N
for l=1:M
prod=0;
for i=1:N
for j=1:M
prod=prod+double(I(N*(a-1)+i,M*(b-1)+j))*cos(pi*(k-1)*(2*i-1)/(2*N))*cos(pi*(l-1)*(2*j-1)/(2*M));
end
end
if k==1
prod=prod*sqrt(1/N);
else
prod=prod*sqrt(2/N);
end
if l==1
prod=prod*sqrt(1/M);
else
prod=prod*sqrt(2/M);
end
I_Trsfrm(a,b).block(k,l)=prod;
end
end
% Normalizing the DCT Matrix and Quantizing the resulting values.
I_Trsfrm(a,b).block=round(I_Trsfrm(a,b).block./Norm_Mat);
% save ('LenaCompressed1.txt');
end
end
%Andrew added this
% save ('LenaCompressed.txt');
% zig-zag coding of the each 8 X 8 Block.
for a=1:I_dim(1)/N
for b=1:I_dim(2)/M
I_zigzag(a,b).block=zeros(1,0);
freq_sum=2:(N+M);
counter=1;
for i=1:length(freq_sum)
if i<=((length(freq_sum)+1)/2)
if rem(i,2)~=0
x_indices=counter:freq_sum(i)-counter;
else
x_indices=freq_sum(i)-counter:-1:counter;
end
index_len=length(x_indices);
y_indices=x_indices(index_len:-1:1); % Creating reverse of the array as "y_indices".
for p=1:index_len
if I_Trsfrm(a,b).block(x_indices(p),y_indices(p))<0
bin_eq=dec2bin(bitxor(2^n-1,abs(I_Trsfrm(a,b).block(x_indices(p),y_indices(p)))),n);
else
bin_eq=dec2bin(I_Trsfrm(a,b).block(x_indices(p),y_indices(p)),n);
end
I_zigzag(a,b).block=[I_zigzag(a,b).block,bin_eq(1:m)];
end
else
counter=counter+1;
if rem(i,2)~=0
x_indices=counter:freq_sum(i)-counter;
else
x_indices=freq_sum(i)-counter:-1:counter;
end
index_len=length(x_indices);
y_indices=x_indices(index_len:-1:1); % Creating reverse of the array as "y_indices".
for p=1:index_len
if I_Trsfrm(a,b).block(x_indices(p),y_indices(p))<0
bin_eq=dec2bin(bitxor(2^n-1,abs(I_Trsfrm(a,b).block(x_indices(p),y_indices(p)))),n);
else
bin_eq=dec2bin(I_Trsfrm(a,b).block(x_indices(p),y_indices(p)),n);
end
I_zigzag(a,b).block=[I_zigzag(a,b).block,bin_eq(1:m)];
end
end
end
end
end
% Clearing unused variables from Memory space
clear I_Trsfrm prod;
clear x_indices y_indices counter;
% Run-Length Encoding the resulting code.
for a=1:I_dim(1)/N
for b=1:I_dim(2)/M
% Computing the Count values for the corresponding symbols and
% savin them in "I_run" structure.
count=0;
run=zeros(1,0);
sym=I_zigzag(a,b).block(1);
j=1;
block_len=length(I_zigzag(a,b).block);
for i=1:block_len
if I_zigzag(a,b).block(i)==sym
count=count+1;
else
run.count(j)=count;
run.sym(j)=sym;
j=j+1;
sym=I_zigzag(a,b).block(i);
count=1;
end
if i==block_len
run.count(j)=count;
run.sym(j)=sym;
end
end
% Computing the codelength needed for the count values.
dim=length(run.count); % calculates number of symbols being encoded.
maxvalue=max(run.count); % finds the maximum count value in the count array of run structure.
codelength=log2(maxvalue)+1;
codelength=floor(codelength);
% Encoding the count values along with their symbols.
I_runcode(a,b).code=zeros(1,0);
for i=1:dim
I_runcode(a,b).code=[I_runcode(a,b).code,dec2bin(run.count(i),codelength),run.sym(i)];
end
end
end
% Saving the Compressed Code to Disk.
save ('LenaCompressed.txt','I_runcode');
% Clearing unused variables from Memory Space.
clear I_zigzag run;

Answer 1

Andrew, you use MATLAB's save statement to save the coefficients into a file ending with .txt. What does the "fractal encoding program" assume about the file format?
Your file will not be a text file. Check out the documentation of save. Perhaps you can use the '-ascii' flag.
Otherwise, you may have to write that file of coefficients yourself. To get you started, I'd say fprintf is worth a look.