contrast.m

function contrast()
    I = imread('AtlasMercury.tiff');
    J=I;
    [r,c,l] = size(I);
    a = 1.5;%transformed value
    I = double(I);
    for i=1:l
      for j =1:r
        for k=1:c
          t = ceil(((a*I(j,k,i))-127)+127);
          if t<0
            I(j,k,i)=0;
          elseif t>=0 && t<256
            I(j,k,i)=t;
          else
            I(j,k,i)=255;
          end
       end
      end 
    end
    %imshow(I);
    %decrease contrast
    a = 0.7;%transformed value
    for i=1:l
      for j =1:r
        for k=1:c
          t = ceil(((a*I(j,k,i))-127)+127);
          if t<0
            I(j,k,i)=0;
          elseif t>=0 && t<256
            I(j,k,i)=t;
          else
            I(j,k,i)=255;
          end
        end
      end 
    end
    imshow(I);
    subplot(1,2,1)
    imhist(J);
    title('Original');
    subplot(1,2,2)
    imhist(uint8(I));
    title('Modified');
    saveas(gcf,'con_hist.jpg');
end