Question

DO NOT use the built in function ”histeq” to do the histogram equalization.

Capture an image with low contrast. Write a Matlab program to do histogram equalization and process your image.

Answer 1

Matlab Code:

GIm=imread('tire.tif');

numofpixels=size(GIm,1)*size(GIm,2);

figure,imshow(GIm);

title('Original Image');

HIm=uint8(zeros(size(GIm,1),size(GIm,2)));

freq=zeros(256,1);

probf=zeros(256,1);

probc=zeros(256,1);

cum=zeros(256,1);

output=zeros(256,1);

%freq counts the occurrence of each pixel value.

%The probability of each occurrence is calculated by probf.

%The result is shown in the form of a table

figure('Position',get(0,'screensize'));

dat=cell(256,6);

for i=1:256

dat(i,:)={i,freq(i),probf(i),cum(i),probc(i),output(i)};   

end

columnname = {'Bin', 'Histogram', 'Probability', 'Cumulative histogram','CDF','Output'};

columnformat = {'numeric', 'numeric', 'numeric', 'numeric', 'numeric','numeric'};

columneditable = [false false false false false false];

t = uitable('Units','normalized','Position',...

[0.1 0.1 0.4 0.9], 'Data', dat,...

'ColumnName', columnname,...

'ColumnFormat', columnformat,...

'ColumnEditable', columneditable,...

'RowName',[]);

subplot(2,2,2); bar(GIm);

title('Before Histogram equalization');

subplot(2,2,4); bar(HIm);

title('After Histogram equalization');

for i=1:size(GIm,1)

for j=1:size(GIm,2)

value=GIm(i,j);

freq(value+1)=freq(value+1)+1;

probf(value+1)=freq(value+1)/numofpixels;

end

end

sum=0;

no_bins=255;

%The cumulative distribution probability is calculated.

for i=1:size(probf)

sum=sum+freq(i);

cum(i)=sum;

probc(i)=cum(i)/numofpixels;

output(i)=round(probc(i)*no_bins);

end

for i=1:size(GIm,1)

for j=1:size(GIm,2)

HIm(i,j)=output(GIm(i,j)+1);

end

end

figure,imshow(HIm);

title('Histogram equalization');