pkg load image

clear
clc

I = imread('Lena256color.jpg');
I2 = uint8(zeros(256));
I3 = uint8(zeros(256));

for i = 1 : 256
  if (rem(i,3)==1)
    I2(i,:) = I(i,:,1);
    I3(:,i) = I(:,i,1);
  elseif (rem(i,3)==2)
    I2(i,:) = I(i,:,2);
    I3(:,i) = I(:,i,2);
  elseif (rem(i,3)==0)
    I2(i,:) = I(i,:,3);
    I3(:,i) = I(:,i,3);
  endif
endfor

I4 = (0.5)*I2 + (0.5)*I3;

subplot(2,4,1), imshow(I,[0 255]), title('Original')
subplot(2,4,2), imshow(I2,[0 255]), title('Combined rows')
subplot(2,4,3), imshow(I3,[0 255]), title('Combined columns')
subplot(2,4,4), imshow(I4,[0 255]), title('Average')
subplot(2,4,6), imhist(I2), axis([0 256 0 700])
subplot(2,4,7), imhist(I3), axis([0 256 0 700])
subplot(2,4,8), imhist(I4), axis([0 256 0 700])