Re: [R] Asking Favor For the Script of Median Filter

[David Winsemius]

On Mar 27, 2011, at 1:07 PM, Mike Marchywka wrote:
You obviously want to delegate inner loops to R packages that
execute as native, hopefully optimized, code.
Generally a google search that starts with "R CRAN" will help.
In this case it looks like a few packages available,

http://www.google.com/search?sclient=psy&hl=en&q=R+cran+median+filter

Did you find any that include a 2D median filter? All the ones I  
looked at were for univariate data.

--
David.



----------------------------------------
Date: Sun, 27 Mar 2011 07:56:11 -0700
From: chuan...@hotmail.com
To: r-help@r-project.org
Subject: [R] Asking Favor For the Script of Median Filter

Hello,everybody. My name is Chuan Zun Liang. I come from Malaysia.  
I am just
a beginner for R. Kindly to ask favor about median filter. The  
problem I
facing as below:


x<-matrix(sample(1:30,25),5,5)
x
[,1] [,2] [,3] [,4] [,5]
[1,] 7 8 30 29 13
[2,] 4 6 12 5 9
[3,] 25 3 22 14 24
[4,] 2 15 26 23 19
[5,] 28 18 10 11 20

This is example original matrices of an image. I want apply with  
median
filter with window size 3X# to remove salt and pepper noise in my  
matric.
Here are the script I attend to writing.The script and output  
shown as
below:

MedFilter<-function(mat,sz)
+ {out<-matrix(0,nrow(mat),ncol(mat))
+ for(p in 1:(nrow(mat)-(sz-1)))
+ {for(q in 1:(ncol(mat)-(sz-1)))
+ {outrow<-median(as.vector(mat[p:(p+(sz-1)),q:(q+(sz-1))]))
+ out[(p+p+(sz-1))/2,(q+q+(sz-1))/2]<-outrow}}
+ out}

MedFilter(x,3)
[,1] [,2] [,3] [,4] [,5]
[1,] 0 0 0 0 0
[2,] 0 8 12 14 0
[3,] 0 12 14 19 0
[4,] 0 18 15 20 0
[5,] 0 0 0 0 0

Example to getting value 8 and 12 as below:

7 8 30 8 30 29
4 6 12 (median=8) 6 12 5 (median=12)
25 3 22 3 22 14

Even the script can give output. However, it is too slow. My image  
size is
364*364. It is time consumption. Is it get other ways to improving  
it?

Best Wishes
Chuan


--
David Winsemius, MD
West Hartford, CT

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