[R] Asking Favor For the Script of Median Filter

[Mike Marchywka]

( sorry if this is a duplicate, I am not sure if hotmail is
dropping some of my posts. Thanks )





>
 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,
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 http://www.google.com/search?sclient=psy&hl=en&q=R+cran+median+filter
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>> Date: Sun, 27 Mar 2011 07:56:11 -0700
>> From: chuan_zl at hotmail.com
>> To: r-help at 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