Normal distribution

Hi, i need to calculate the normal distribution value for an image. for that,i used the following coding,

    I=imread('image1.jpg');

    K = double(I(:));

    mu=mean(K);

    sigma=std2(K);

    P=normpdf(K, mu, sigma);

    Z = norminv(P,mu,sigma);
when i use some images it is giving the values. but sometimes it is giving like 'NaN'.I don't know how to solve this problem. Please help me.

Answer 1

[Christopher Kanan]

Instead of casting the image as a zero, you might consider using im2double. Otherwise your image values may be very large causing a floating point problem.

You should check to see if any non-finite values ( see isfinite) are present in mu, sigma, P, or just Z. Since you are treating K as a vector, you could use std instead of std2 as well.

    I=im2double(imread('image1.jpg'));
    K = I(:);
    mu=mean(K);
    sigma=std(K);
    P=normpdf(K, mu, sigma);
    Z = norminv(P,mu,sigma);

[Jaanu]

still i am getting NaN value. could you please suggest any other solution.

Answer 2

[Walter Roberson]

Check to see whether the images that work (or do not work) are all RGB images and the others grayscale ?

Also, check to see if sigma is perhaps coming out 0.

Note: You might as well use std(K) instead of std2(K) as std2(K) is just std(K(:)) but K is already a column vector in your code.

[Jaanu]

sometimes, why is mean value giving zero? even if i apply your hint too?