Distorted image after DCT compression

Question

Siyomnqoba 2015-10-19

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/249472-distorted-image-after-dct-compression

编辑： Siyomnqoba 2015-10-19

After the image goes through the compression scheme (which does not include an entropy encoder) I get the following blurred image:

I think it has something to do with the way my code inserts an end of block (eob) symbol.

 eob = 500;
 r = zeros(numel(y) + size(y,2),1);
 count = 0;
 for j = 1:xb
     i = find(max(y(:,j)));
     if isempty(i)
         i = 0;
     end
     p = count + 1;
     q = p + i;
     r(p:q) = [y(1:i,j);eob];
     count = count + i + 1;
 end
 r((count + 1):end) = [];

What this code does is that,after the each 8x8 block of coefficients has gone through the DCT and quantization stages it was converted to a column and then a end of block symbol is inserted after 64 entries to indicate that we've reached the end of each block.

the following block of code, which i suspect is what's causing the problem, comes before the blocks go through the de-quantization and inverse DCT stages.

if true
  % code
end
eob = 500;
z = zeros(64,xb);
k = 1;
for j = 1:xb
  for i = 1:64
      if k <8192       
      if x(k) == eob 
          k = k+1;
          break;
      else
          z(i,j) = x(k);
          k = k+1;
      end
      end
  end
end
z = z(rev,:);
x = col2im(z, [8 8], [xm xn], 'distinct');
fun = @(block_struct) (block_struct.data .* m);
y = blockproc(x, [8,8], fun);
t = Cintra(dctmtx(8));
dct = @(block_struct) t' * block_struct.data * t ;
y = blockproc(y, [8,8], dct);
x = uint8(double(y) + 128);

It basically takes the long stream of coefficients removes the end of block symbols,rearrange the stream into 64 columns and then reverses the the zig-zag order done previously.Is there anything fundamentally wrong in the code above that I am currently missing? Please note that the code is designed for images that 512x512 pixels