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# local mean and standard deviation

Asked by Elysi Cochin on 19 Jan 2013

sir is there any difference between local mean and mean of a pixel?????????? i need to calculate the local mean and standard deviation of a pixel..... how to do it.... please do reply.....

## Products

Answer by Matt J on 19 Jan 2013
Edited by Matt J on 19 Jan 2013

For example, if you want sliding means and stds in all 3x3 neighborhoods

```slidingmean=conv2(A,ones(3)/9,'same');
```
```slidingstd=stdfilt(A);
```

or if you don't have the Image Processing Toolbox

` slidingstd=sqrt( conv2(A.^2,ones(3)/9,'same') - slidingmean.^2 );`

Answer by Image Analyst on 19 Jan 2013

I'm not sure you got the terminology right, but the mean of a pixel is just the value of the pixel, because a pixel has a single value unless you're talking about the pixel going across different color channels (in a true color or multispectral image) or across the z dimension in a volumetric image where each slice or plane is the image at a different depth. I don't think you're talking about such images and that you're talking about a normal gray scale 2D image. Correct me if I'm wrong.

The local mean is the mean of several pixels in a region (for example a rectangular 3 by 3 window) around the pixel. The code Matt gave you will do that.

Answer by Sapam Jaya on 4 Sep 2013

regarding the local mean..how to find the local mean of an image from a user defined window of size n by n

## 1 Comment

Image Analyst on 4 Sep 2013

Did you see Matt's answer? Just replace 3 by n and 9 by n^2.

Answer by Sapam Jaya on 4 Sep 2013

and also the local std deviation over the n by n window

## 1 Comment

Image Analyst on 4 Sep 2013

See the documentation for stdfilt().

Answer by Sapam Jaya on 5 Sep 2013

thanx