eee330图像处理实验报告任务1eeelab5 xuluo.pdfVIP

Task1:

Inthistask,itrequirestowriteafunctiontocompresstheimagewithasimilarwayto

JPEG.Inthisfunction,itfirstevaluatesthe2D-DCToftheinputimagebymultiple8×8

macroblocks,andthenquantizestheDCTcoefficientswithgivenqualityfactor(QP)and

quantizationmatrix(Qmat).Afterquantization,the2D-DCTcoefficientsarearithmetic

encodedandthefunctionreturnsthebitrate.

Thefunctionforimagecompressionisshownbelow,andtheexplanationforeachstep

wasnotedbycomments.

function[rate]=compress_im(im,Qmat,QP,file_name)

%definetheblockoperationofDCT

dct_block=@(block_struct)dct2(block_struct.data);

%evaluate2D-DCTblockbyblock

im_dct=blockproc(im,[88],dct_block);

%definetheblockoperationofquantization

quantization_block=@(block_struct)quantization(block_struct.data,Qmat,QP);

%quantizingtheDCTcoefficientsblockbyblock

quantized_dct=blockproc(im_dct,[88],quantization_block);

%encodethequantizedDCTcoefficients

encoded=entropy_enc(quantized_dct);

%converttheencodednumberstobinarystringandwriteintofile

[x,y]=size(encoded);

fid=fopen(file_name,w);

fori=1:x

binary_encoded=dec2bin(encoded(i));

fprintf(fid,%s\n,binary_encoded);

end

fclose(fid);

%calculatethebitrate(thelinebreakcountsfor1bit,hencelinenumber

%xshouldbesubtracted);

rate=(fsize(file_name)-x)/(512^2);

end

%thisfunctionisusedforquantization

function[quantized]=quantization(block,Qmat,QP)

ifQP50

S=(100-QP)/50;

else

S=50/QP;

end

[r,c]=size(block);

fori=1:r

forj=1:c

quantized(i,j)=round(block(i,j)/(S*Qmat(i,j)));

end

end

end

ThenweuseQP=50totestthisfunction.Andwegettheresultantbitrateis0.8586bpp.

Andthefilewhichholdstheencodedcoefficientsisshownby:

Task2:

towriteafunctiontodecompressan