Reputation: 13
i have a code that averages 4 adjacent values into the elements with double loop, i want to vectorize it how can i achieve this ?
for i=2:99
for j=2:99
T1(i,j)= (T0(i+1,j) + T0(i-1,j) + T0(i,j+1) + T0(i,j-1))/4; %adjacent units avarage
end
end
Upvotes: 1
Views: 146
Reputation: 32144
Here is a vectorized version of your code:
T1(2:end-1, 2:end-1) = (T0(3:end, 2:end-1) + T0(1:end-2, 2:end-1) + T0(2:end-1, 3:end) + T0(2:end-1, 1:end-2))/4;
Following code sample verifies the vectorized code gives the same result as the loops:
T0 = imresize(im2double(imread('cameraman.tif')), [100, 100]); %Read image - used as input for the test.
T1 = T0;
for i=2:99
for j=2:99
T1(i,j)= (T0(i+1,j) + T0(i-1,j) + T0(i,j+1) + T0(i,j-1))/4; %adjacent units avarage
end
end
T2 = T0;
T2(2:end-1, 2:end-1) = (T0(3:end, 2:end-1) + T0(1:end-2, 2:end-1) + T0(2:end-1, 3:end) + T0(2:end-1, 1:end-2))/4;
disp(['Maximum difference = ', num2str(max(abs(T1(:) - T2(:))))]);
Using imfilter (or conv2):
Your code is equivalent to convolution of T0
and [0,1,0;1,0,1;0,1,0]./4
as mentioned by Daniel.
The margins result are different - I replaced the margins with the margins of T0
.
%Filter kernel:
h = [0 1 0
1 0 1
0 1 0]/4;
T3 = imfilter(T0, h);
T4 = T0;
T4(2:end-1, 2:end-1) = T3(2:end-1, 2:end-1); %Fix the margins.
disp(['Maximum T4 difference = ', num2str(max(abs(T1(:) - T4(:))))]);
Upvotes: 1