2-DCT Image compression matlab - matlab

Question

Problem:
I tried implementing Discrete Cosine Transformation compression using matlab.
Input image would a jpg image (Lena) having a size 512 X 512.
There are two stages namely compression and decompression.
Compression and Quantization:
The input image is converted to YCbCr component. Then Y component is taken up
for compression. Further DCT will quantized.
Quantization and Decompression:
The quantized image is undergoes dequantization for decompression.
Issues:
Rectangular boxes are spotted in the decompressed version of the image. Is anything wrong with the code?
For your inference, below are the sample input and output images and followed by the matlab code.
Input image:
Y Component in YCbCr:
Output image:
Code:
clc;
clear all;
close all;
I = imread('lena512.jpg');
figure, imshow(I);
% Y = I;
YCbCr = rgb2ycbcr(I);
figure, imshow(YCbCr);
Y = YCbCr(:,:, 1);
figure, imshow(Y);
[h, w] = size(Y);
r = h/8;
c = w/8;
s = 1;
q50 = [16 11 10 16 24 40 51 61;
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];
% COMPRESSION
for i=1:r
e = 1;
for j=1:c
block = Y(s:s+7,e:e+7);
cent = double(block) - 128;
for m=1:8
for n=1:8
if m == 1
u = 1/sqrt(8);
else
u = sqrt(2/8);
end
if n == 1
v = 1/sqrt(8);
else
v = sqrt(2/8);
end
comp = 0;
for x=1:8
for y=1:8
comp = comp + cent(x, y)*(cos((((2*(x-1))+1)*(m-1)*pi)/16))*(cos((((2*(y-1))+1)*(n-1)*pi)/16));
end
end
F(m, n) = v*u*comp;
end
end
for x=1:8
for y=1:8
cq(x, y) = round(F(x, y)/q50(x, y));
end
end
Q(s:s+7,e:e+7) = cq;
e = e + 8;
end
s = s + 8;
end
% % % % % % % % % % % % % % %
% % DECOMPRESSION
% % % % % % %
s = 1;
for i=1:r
e = 1;
for j=1:c
cq = Q(s:s+7,e:e+7);
for x=1:8
for y=1:8
DQ(x, y) = q50(x, y)*cq(x, y);
end
end
for m=1:8
for n=1:8
if m == 1
u = 1/sqrt(8);
else
u = sqrt(2/8);
end
if n == 1
v = 1/sqrt(8);
else
v = sqrt(2/8);
end
comp = 0;
for x=1:8
for y=1:8
comp = comp + u*v*DQ(x, y)*(cos((((2*(x-1))+1)*(m-1)*pi)/16))*(cos((((2*(y-1))+1)*(n-1)*pi)/16));
end
end
bf(m, n) = round(comp)+128;
end
end
Org(s:s+7,e:e+7) = bf;
e = e + 8;
end
s = s + 8;
end
imwrite(Y, 'F:\workouts\phd\jpeg\input.jpg');
imwrite(uint8(Org), 'F:\workouts\phd\jpeg\output.jpg');
return;
Can you suggest me where the error is? It would be helpful.