pkg load image
clear
clc

I = imread('lena.bmp');

% generate upper triangular
upperTriangular = zeros(256);
j = 256;
for i = 1 : 128
  upperTriangular(i,257-j:j) = I(i,257-j:j);
  j = j - 1;
endfor

% generate lower triangular
lowerTriangular = zeros(256);
j = 1;
for i = 256 : (-1) : 129
  lowerTriangular(i,j:257-j) = I(i,j:257-j);
  j = j + 1;
endfor
upperTriangular = uint8(upperTriangular);
lowerTriangular = uint8(lowerTriangular);

% generate left triangular
leftTriangular = zeros(256);
i = 256;
for j = 1 : 128
  leftTriangular(257-i:i,j) = I(257-i:i,j);
  i = i - 1;
endfor

% generate right triangular
rightTriangular = zeros(256);
i = 1;
for j = 256 : (-1) : 129
  rightTriangular(i:257-i,j) = I(i:257-i,j);
  i = i + 1;
endfor
upperTriangular = uint8(upperTriangular);
lowerTriangular = uint8(lowerTriangular);

subplot(3,3,2), imshow(upperTriangular,[0 255]), title('Up')
subplot(3,3,4), imshow(leftTriangular,[0 255]), title('Left')
subplot(3,3,5), imshow(I,[0 255]), title('Original')
subplot(3,3,6), imshow(rightTriangular,[0 255]), title('Right')
subplot(3,3,8), imshow(lowerTriangular,[0 255]), title('Down')