exp function is returning zeros
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Hi,
i am trying to compute a normal function for all pixels on the image ,
m = mean(I(:));
segma = std (I(:));
fb1=(exp(-abs((I(i)-m).^2)./2.*segma.^2))% Feature based1
fb2=(exp(-abs((I(j)-m).^2)./2.*segma.^2))% Feature based 2
it returns zeros,am i clculating the mean and the std in wrong way !!
Thanks
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Risposte (3)
Steven Lord
il 27 Apr 2016
Using Symbolic Math Toolbox, we can see what exp(-850) and exp(-950) would be, displayed to 20 digits.
>> vpa(exp(sym([-850; -950])), 20)
ans =
7.0744125465834323713e-370
2.6317352159005409842e-413
The smallest positive double precision number is not quite that small.
>> eps(0)
ans =
4.9407e-324
Star Strider
il 27 Apr 2016
Assuming that ‘I’ is single or double, and not uint8 (that would throw an error for std), the most likely possibility is that the exp argument is very large.
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Star Strider
il 27 Apr 2016
On my computer, the realmin function returns 2.225073858507201e-308, corresponding to exp(-708.396418532264). The exponential function of any value less than -708.396418532264 will return zero. (Even the Symbolic Math Toolbox with its extended resolution returns zero.)
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