MATLAB: Error in function ‘var’ while calculating variance

submatrixvarvariance

Hello everyone!

I'm new with Matlab, so I hope you're understanding with me.

I'm trying to calculate the variance of a submatrix. So, I do the following:

IMG = imread('figure13.tif');
Sxy = IMG(top_x:top_x+k-1, top_y:top_y+k-1); 
local_var = var(var(Sxy));

But, it prints me this error:

Error using var (line 65)
First argument must be single or double.

I don't write the variables top_x , top_y and k in order to make it simple but it takes the submatrix correctly.

I make the same with mean function and it works perfectly. Why is 'var' different? How can I calculate the local variance?

Thanks in advance!

Best Answer

Your image data is stored in one of the integer data types. Convert the data to single precision using the single function or to double precision using the double function before calling var on it.

Related Solutions

MATLAB: Lighthouse.jpg imread into matrix and calculate mean and std? – Homework

The standard deviation of the standard deviation of the columns is not the standard deviation of the entire image! It's not like the max, min, and mean functions. Try a simple example and you'll see. Just do

imsr = std(imr(:));

to get the standard deviation of an entire array (a single color channel). imr(:) converts the 2D array into a 1D array.

MATLAB: How to find the variance of an image

var requires a double or single argument. This will work:

img = double(imread('eight.tif'));
v = var(img);

But note that will give a vector, with one value for the variance of each column of the image. To get the variance of all the pixels in the image, you'll need

v = var(img(:));

Best Answer

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