comp.lang.idl-pvwave archive: archive » Re: Variance in sub-sections?

Home » Public Forums » archive » Re: Variance in sub-sections?

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: Variance in sub-sections? [message #29383 is a reply to message #29381]

Mon, 18 February 2002 07:41

Alex Schuster
Messages: 124
Registered: February 1997

Senior Member

Joshua Nipper wrote:

> I have a 512x512 image, and I would like to calculate the mean/variance
> in a 3x3 neighborhood around every pixel. What would be the easiest way
> to do this w/out for loops?

For the mean, you can use smooth() : m = smooth( img, 3 ).
Or using convol:
k = ( intarr( 3, 3 ) + 1 ) / 9.0 ; 3x3 kernel, all elements set to 1/9
m = convol( img, k )

The variance is total( (x_mean-x_i)^2 ) / n, so just subtract the mean
image, square all elements, and use convol() to sum up 3x3 local pixels
around each element:

v = convol( (img-m)^2, k )

Alex
--
Alex Schuster Wonko@netcologne.de
alex@pet.mpin-koeln.mpg.de

Report message to a moderator

[Message index]

		Re: Variance in sub-sections? By: Joshua Nipper on Mon, 18 February 2002 13:04
		Re: Variance in sub-sections? By: David Fanning on Mon, 18 February 2002 10:31
		Re: Variance in sub-sections? By: Jaco van Gorkom on Mon, 18 February 2002 10:12
		Re: Variance in sub-sections? By: David Fanning on Mon, 18 February 2002 08:42
		Re: Variance in sub-sections? By: Alex Schuster on Mon, 18 February 2002 07:41
		Re: Variance in sub-sections? By: Jaco van Gorkom on Mon, 18 February 2002 06:04

Previous Topic:	broken country borders in map_continents
Next Topic:	Re: debug IDL DLM in Visual C++

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Sun Oct 12 05:49:47 PDT 2025

Total time taken to generate the page: 1.60516 seconds