[R] Asking Favor For the Script of Median Filter

[Bert Gunter]

Oops. My error! You wanted a 2D filter.

I suspect a search will find some implementation, but you may wish to consider
?loess instead (there are numerous others, no doubt).

-- Bert

On Sun, Mar 27, 2011 at 3:30 PM, David Winsemius <dwinsemius at comcast.net> wrote:
>
> 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_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
>
>
> --
> David Winsemius, MD
> West Hartford, CT
>
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>



-- 
Bert Gunter
Genentech Nonclinical Biostatistics