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Re: Does IDL has histogram matching function? [message #32955 is a reply to message #32803]

Mon, 18 November 2002 15:49

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Paul Sorenson (aardvark62@msn.com) writes:

> There is an undocumented keyword to HIST_EQUAL that looks like it
> might do the same thing as Davids HistoMatch. Here is an example:
>
> filename = filepath('ctscan.dat', subdir=['examples', 'data'])
> image = read_binary(filename, data_dims=[256, 256])
>
> desired_hist = histogram(hist_equal(image), min=0, max=255)
>
> window, xsize=3*256, ysize=256
> tv, image, 0
> tv, hist_equal(image), 1
> tv, hist_equal(image, fcn=total(desired_hist, /cumulative)), 2
> end

I think this is probably right, but I think
both this function and the code that I threw off
in a couple of minutes earlier in the week suffers
from a deficiency.

As it happens, I need a histogram-match-by-region
capability. In other words, the user wants to select
a region in an image, and use the histogram of that
region to adjust the histogram of the entire image.

This example and my previous code work if the histograms
are taken from images of the same size. They do not work
correctly (I think) if the histograms use images of different
sizes. In that case, you must normalize the histograms to the
same "total number" of pixels. I'll probably have this on
my web page soon, with the corrections in it. I just didn't
want anyone getting too far down the wrong road here. :-)

Cheers,

David

--
David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		Does IDL has histogram matching function? By: tianyf_cn on Thu, 07 November 2002 22:36
		Re: Does IDL has histogram matching function? By: David Fanning on Mon, 18 November 2002 15:49
		Re: Does IDL has histogram matching function? By: Paul Sorenson on Thu, 21 November 2002 14:23
		Re: Does IDL has histogram matching function? By: David Fanning on Thu, 21 November 2002 15:57
		Re: Does IDL has histogram matching function? By: aardvark62 on Fri, 06 December 2002 13:37
		Re: Does IDL has histogram matching function? By: David Fanning on Thu, 12 December 2002 15:20

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