我正在尝试读取图像，对其进行 DCT 变换，对其进行量化，然后将量化后的系数保存到将被读入分形编码程序的文件中。
当我解码文件（使用量化系数）时，我得到的只是一些灰屏。这是由于文件的内容还是我错过了其他东西？
%% 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;