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Re: Butterworth Band-Pass Filter [message #73915 is a reply to message #73914]

Sun, 12 December 2010 08:29

burton449
Messages: 15
Registered: December 2010

Junior Member

On Dec 11, 11:37 pm, David Fanning <n...@dfanning.com> wrote:
> burton449 writes:
>> as mentionned in the topic, i want to do a Butterworth Band-Pass
>> Filter on a 9166 X 4600 pixels image.
>
>> The doc of butterworth.pro in the astrolib explain how to use the
>> script for a lowpass filter, but not for a band-pass and a high-pass.
>
>> Have any idea how to do?
>
> You need to read my new book. In the meantime, you
> can find an explanation here:
>
> http://www.dfanning.com/ip_tips/freqfiltering.html
>
> This describes a low-pass filter, but the equation for
> the high-pass filter is there, too. Just replace the
> low-pass filter with the high-pass version. :-)
>
> Cheers,
>
> David
>
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming:http://www.dfanning.com/
> Sepore ma de ni thui. ("Perhaps thou speakest truth.")

Thank you again David for your help,

According to your documentation, a high-pass butterworth filter will
be defined like that:
filter = 1 / [1 + C(Ro/R)^2n]

So in IDL, for a cuttoff of 15, and freqImage = FFT(image, -1), the
filter will be defined like that:
filter = 1.0 / ( 1.0d + (15.0/freqImage)^2 )

Is it right?
Thanks again
Max

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[Message index]

		Re: Butterworth Band-Pass Filter By: David Fanning on Sun, 12 December 2010 09:24
		Re: Butterworth Band-Pass Filter By: David Fanning on Sun, 12 December 2010 09:19
		Re: Butterworth Band-Pass Filter By: burton449 on Sun, 12 December 2010 09:07
		Re: Butterworth Band-Pass Filter By: David Fanning on Sun, 12 December 2010 09:02
		Re: Butterworth Band-Pass Filter By: David Fanning on Sun, 12 December 2010 08:56
		Re: Butterworth Band-Pass Filter By: burton449 on Sun, 12 December 2010 08:29
		Re: Butterworth Band-Pass Filter By: David Fanning on Sat, 11 December 2010 20:37
		Re: Butterworth Band-Pass Filter By: burton449 on Sun, 12 December 2010 09:28
		Re: Butterworth Band-Pass Filter By: burton449 on Sun, 12 December 2010 09:30

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