problem in finding Mean value
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Vennila Gangatharan
on 6 Jan 2013
Edited: Walter Roberson
on 26 Jun 2017
Hi,
I want to find mean value of a mammogram only by choosing the values greater than zero. I used for loops with condition but it gives 255 as answer constantly. I don't know what's the mistake i have done.
Code:
[x,y] = size(I);
s = 0;
for i = 1:x
for j = 1:y
if I(i,j) > 0
s = s + I(i,j);
end
end
end
disp('s = ');
disp(s);
0 Comments
Accepted Answer
Walter Roberson
on 6 Jan 2013
Change to
s = s + double(I(i,j));
Question: when you are calculating the mean, are you going to be dividing by the number of values in I, or by the number of non-negative values?
Also are you sure that I will be two-dimensional and not 3 dimensional?
More Answers (2)
Image Analyst
on 6 Jan 2013
Why are you doing two loops, which will make it slow? Why not just do:
nonZeroPixels = yourImage > 0;
meanValue = mean(yourImage(nonZeroPixels));
The way above is vectorized, faster, and very MATLABish.
0 Comments
Jan
on 6 Jan 2013
Alternative method without loops:
s = mean(double(I(I > 0)));
2 Comments
Jan
on 6 Jan 2013
Yes, Walter, because the underlying SUM uses the DOUBLE format as default, when 'native' is not specified. I would prefer to let functions reply the same type as the input as default, therefore I tend to cast more often than needed.
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