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Re: Median filter the hard way [message #36725]

Tue, 21 October 2003 16:51

Dick Jackson
Messages: 347
Registered: August 1998

Senior Member

"JD Smith" <jdsmith@as.arizona.edu> wrote in message
news:pan.2003.10.21.23.29.45.108433.5869@as.arizona.edu...
> On Tue, 21 Oct 2003 15:52:28 -0700, Dick Jackson wrote:
>
>
>> "JD Smith" <> wrote in message
>> news:pan.2003.10.17.22.22.14.73337.24537@as.arizona.edu...
>>> On Fri, 17 Oct 2003 14:34:30 -0700, Dick Jackson wrote:
>>>
>>>> Here's an array, a:
>>>>
>>>> IDL> a=Float(Byte(RandomU(seed,7,7)*10)) IDL>
>> a[2:4,2:4]=!values.F_nan
>>>
>>> [...]
>>>
>>>> The Convol function can be used to count up neighborhoods. If you
>> need
>>>> better counting around the edge, you could pad the array before
>> calling
>>>> Convol.
>>>>
>>>> IDL> print,Convol(Finite(a),Replicate(1B,3,3))
>>>
>>> Looks good, Dick. CONVOL's a bit heavy-handed for just counting:
I'd
>> use
>>> smooth instead:
>>>
>>> IDL> print,smooth(finite(a)*9,3,/EDGE_TRUNCATE)
>>>
>>> [...]
>>>
>>> Notice it treats edges better (as far as this problem is
concerned),
>>
>> Granted, if edge pixels are not going to be dropped anyway for
having
>> too few 'good' neighbors...
>>
>>> and should definitely be faster.
>>
>> A good guess, but in this case, I guess Convol can keep everything
as
>> Byte type and it is indeed faster:
>
> This is the key (byte type). Change it to smooth(finite(a)*9b... and
you
> should see similar performance. Obviously, in this case, we're
limited
> by something other than the details of the addition.

Argh, you're right. (I don't know why I thought Smooth wouldn't do
bytes, but it does!) I think you win on the edge-handling, nice one!

Cheers,
--
-Dick

Dick Jackson / dick@d-jackson.com
D-Jackson Software Consulting / http://www.d-jackson.com
Calgary, Alberta, Canada / +1-403-242-7398 / Fax: 241-7392

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[Message index]

		Re: Median filter the hard way By: Dick Jackson on Tue, 21 October 2003 16:51
		Re: Median filter the hard way By: JD Smith on Tue, 21 October 2003 16:29
		Re: Median filter the hard way By: Dick Jackson on Tue, 21 October 2003 15:52
		Re: Median filter the hard way By: the_cacc on Fri, 17 October 2003 23:08
		Re: Median filter the hard way By: Peter Payzant on Fri, 17 October 2003 15:50
		Re: Median filter the hard way By: JD Smith on Fri, 17 October 2003 15:22
		Re: Median filter the hard way By: Dick Jackson on Fri, 17 October 2003 14:34
		Re: Median filter the hard way By: mmiller3 on Thu, 16 October 2003 18:21

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