matlab function

I have write a code to find the first pixel that not equal to zero and store the pixel position to M and N respectively as follow:

 j=1;
    while (j>=1&&j<=size(I,1) )
        for i=1:size(I,2)
            if I(i,j) >= 0
               M=j
               N=i  
            break; 
            else 

            end
        end
        j=j+1;
     end    
where I is the image;
 when the code find the first pixel that not equal to zeros,however , the loop can not stop, the break seems do not help to stop the loop; 
Can you please help me on this?

Answer 1

[Walter Roberson]

The break is breaking out of the "for", but then you are still within the "while". You need to set a flag before you break and test it after the "for" loop code, using break when the flag is set.

[LIU WEIHUA]

can you give me some detail about how to set the flag?

[Walter Roberson]

j=1;

breakout = false;

while (j>=1&&j<=size(I,1) )

for i=1:size(I,2)

if I(i,j) >= 0

M=j

N=i

breakout = true;

break;

else

end

end

if breakout; break; end

j=j+1;

end

[Image Analyst]

I think you meant

while (j >= 1 && j <= size(I, 2) )

for i = 1 : size(I, 1)

Answer 2

[Richard Brown]

Why not just

[M, N] = find(I, 1, 'first')

?

Answer 3

[Image Analyst]

Um, did you notice that your "i" variable is the first dimension (row) in the matrix but you are going to the second dimension max (the max column, not row)? Similarly for your j variable. Thus your code will bomb for anything but square matrices.

And what do you define as the "first" pixel? Starting at the upper left pixel, do you want to go across columns, then down to the next row, or go down rows then over to the next column, or do you want to find the pixel that is closest to the upper left? Those might (probably) give three different pixels as the answer.