image-compress.zip

% COMPRESSION_JPEG contains the implementation of the main routine for Part 2 of % Assignment 3, which is a part of JPEG lossy encoder/decoder using DCT. % You need to implement step 3 & 4 in compression and step 2 & 3 in decompression. % function compression_jpeg() % Read the image Im = imread('taio.tif'); % convert the image type to double Im = double(Im); OriginalIm=Im; % % Start compression % % (1)Subtract the image intensity by 128. Im = Im -128; % (2)Partition the input image into 8x8 blocks for r=1:32 for c=1:32 B((r-1)*32+c, 1:8, 1:8) = Im( (r-1)*8+1:r*8 , (c-1)*8+1:c*8 ); end end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % TODO: % (3)Apply DCT to each 8x8 block tem=zeros(8,8); C=zeros(1024,8,8); for i=1:1024 tem(1:8,1:8)=B(i,1:8,1:8); C(i,:,:)=dct2(tem); end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Q=[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]; %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % TODO: % (4) Perform quantisation with Quantisation Table and convert all the % quantized coefficients into integer. tem=zeros(8,8); D=zeros(1024,8,8); for i=1:1024 tem(1:8,1:8)=C(i,:,:); D(i,:,:)=round(tem./Q); end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % (5) Follow zig-zag order (?Zig-zag? Order Coefficients in lecture notes % Image compression), convert all 8x8 blocks into vectors with 64 elements. Z=[0 1 5 6 14 15 27 28; 2 4 7 13 16 26 29 42; 3 8 12 17 25 30 41 43; 9 11 18 24 31 40 44 53; 10 19 23 32 39 45 52 54; 20 22 33 38 46 51 55 60; 21 34 37 47 50 56 59 61; 35 36 48 49 57 58 62 63]; Z=Z+1; C1=D; for k=1:1024 tmpCS(Z)=C1(k, 1:8, 1:8); CS(k, 1:64)=tmpCS; end % % Finish compression, start decompression % % (1) Convert the vectors back to 8x8 blocks % for k=1:1024 tmpCS=CS(k, 1:64); tmpDC1=tmpCS(Z); DC1(k, 1:8, 1:8)=tmpDC1; end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % TODO: %(2) Multiply the blocks with quantization table. % E=zeros(1024,8,8); for i=1:1024 tem(1:8,1:8)=DC1(i,1:8,1:8); E(i,1:8,1:8)=tem.*Q; end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % TODO: %(3) Apply Inverse DCT to each block, (use command "IDCT2" of matlab) % temp=zeros(8,8); F=zeros(1024,8,8); for i=1:1024 temp(1:8,1:8)=E(i,1:8,1:8); F(i,1:8,1:8)=idct2(temp); end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %(4) Group all 8x8 blocks back to form an image % DB=F; for r=1:32 for c=1:32 tmpIm=DB((r-1)*32+c, 1:8, 1:8); Im( (r-1)*8+1:r*8 , (c-1)*8+1:c*8 ) = tmpIm; end end % %(5) Add 128 to each pixel of the image. % Im = Im + 128; Im = uint8(Im); Im = double(Im); % % Finish Decompression % figure; subplot(1,3,1);imshow(OriginalIm, [0 255]);title('Original Image'); subplot(1,3,2);imshow(Im, [0 255]);title(['After DCT/Quantisation']); %, MSE = ' num2str(sum(sum((Im-OriginalIm).^2)))]); subplot(1,3,3);imshow((OriginalIm-Im), []);title(['Difference image, MSE= ' num2str(mean(mean( ( (Im-OriginalIm) .^2 )) ))]);