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Re: Curve Fitting Question [message #82110 is a reply to message #1309]

Tue, 20 November 2012 06:58

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

David Fanning writes:

> Hold off on this a minute. I've been using my version
> of the OTSU_THRESHOLD program for a week now, and I've
> been seeing some strange results. The only thing I did
> in my program was to beef up the keywords and error handling
> for the histogram itself. I didn't change the underlying
> code for OTSU_THRESHOLD.
>
> In fact, just to confirm this, I've now gone back and
> used the VERY same variable names, etc. But, I seem
> to be getting different slightly different results with
> the two programs.
>
> I am trying to track this down now. In fact, I'm using the
> newsgroup in EXACTLY the way Helder describes this morning!
>
> Here is what just occurred to me. One of the things I am
> VERY particular about (long experience, probably) is matching
> the data type of the BINSIZE keyword with the data type of
> the data going into the histogram. The OTSU_THRESHOLD program
> I was using as a model didn't do this. I wonder if this is
> the source of the difference. Back soon! :-)

Humm. There is always something strange going on with Histogram!

The difference in our two programs is that I set the MIN and MAX
keywords on the Histogram call to the minimum and maximum
of the data. OTSU_THRESHOLD doesn't do this. As a result the
output min and max for their histogram of byte data is 0 to 255.
Mine is 1 to 50. If I use the MIN and MAX keywords to set the
histogram range to 0 to 255, my results are identical.

I'm going to have to think about this. I think OTSU_THRESHOLD has
been written *assuming* byte data is coming in. I can't always
be so trusting of the data I work with. So...humm. Any ideas?

I would have thought the OTSU threshold method would work for ANY
bimodal population of values, assuming you could calculate
a histogram.

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")

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[Message index]

		Curve Fitting Question By: ftdwh on Tue, 14 September 1993 11:01
		Re: Curve Fitting Question By: David Fanning on Tue, 13 November 2012 15:24
		Re: Curve Fitting Question By: cgguido on Wed, 14 November 2012 06:22
		Re: Curve Fitting Question By: David Fanning on Tue, 20 November 2012 06:22
		Re: Curve Fitting Question By: Mark Piper on Tue, 13 November 2012 08:31
		Re: Curve Fitting Question By: David Fanning on Mon, 12 November 2012 19:40
		Re: Curve Fitting Question By: ben.bighair on Mon, 12 November 2012 18:47
		Re: Curve Fitting Question By: David Fanning on Mon, 12 November 2012 17:23
		Re: Curve Fitting Question By: David Fanning on Mon, 12 November 2012 17:18
		Re: Curve Fitting Question By: Craig Markwardt on Mon, 12 November 2012 15:51
		Re: Curve Fitting Question By: David Fanning on Tue, 20 November 2012 06:58

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