I don't understand about this row and column??

who know about this code? if N=8 and L=512

for i= N:N:L-N
   for j = 1:L

and this one

for i= 1:L
   for j= N:N:L-N

what is the different? thanx for any advance.

Answer 1

[Image Analyst]

Well the first one starts at row (or column) 8 while the second one starts at 1. There are some other differences but you can just print them out to see:

N=8
L=512

i= N:N:L-N
j = 1:L

i= 1:L
j= N:N:L-N

Then look in the command window to see what they are.

[troy]

ok i actually want value for pixel image by divide 8x8 and then want to find threshold. then i use this code

I2 = imread('......');
I2 = rgb2gray (I2);
N=8; %N= window size (8x8)
[L,L]=size(I2);
L2=L/N;
S=zeros(L,L);

for i=1:L2
for j=1:L2
S=I2((i-1)*N+1:i*N,(j-1)*N+1:j*N);
S= sum((I2(i,j)-I2(i,j+1))+(I2(i+2,j)-I2(i+2,j+1))+(I2(i+4,j)-I2(i+4,j+1)));
end;
end;

then, why the ans in the workspace only show value 82? why not the answer is in 64x64? i mean, like row 2 and column 2 have value, row 3 and column 3 have value until 64. the workspace only show for row 1 and column 1 only. i hope u understand what i mean.

[troy]

u mean for the second it star form 1 then do loop until 512?

[Image Analyst]

S is the rectangular sub-image at that location. So to get the sum at each location, you'd do

theSum(i, j) = sum(S(:));

Not sure how you want to find the threshold though.

[troy]

how to modify the for loop of i and j to get value odd number? thanks sir.