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Philosophical Scaling Question [message #51605]

Mon, 04 December 2006 08:15

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Folks,

With no answers to my weekend questions about logarithmic
color bars I'm flying blind this morning. And I seem to be
running into theoretical difficulties. Can anyone help?

Suppose I had a color table (color table 33 comes to mind)
where each color vector had a min of 0 and a max 0f 255.

IDL> Loadct, 33, /Silent
IDL> TVLCT, r, g, b, /Get
IDL> MinMax, r
0 255
IDL> MinMax, g
0 255
IDL> MinMax, b
0 255

And suppose I also have an image that is scaled in
the same way:

IDL> image = Loaddata(7)
IDL> MinMax, image
0 255

And finally, suppose I have a way to scale such data
sets in a logametric way, say a function LOGSCL.

IDL> .compile LOGSCL
Compiled module: LOGSCL.

My hypothesis is that there are two ways to display this
data "logarithmically". I can leave the color table vectors
alone, and scale the image data. Or, I can leave the image
alone and scale the color vectors. Either way should result
in exactly the same display.

The problem is, it doesn't. :-(

Window, XSize=400, YSize=350, 0
Loadct, 33, /Silent
TVImage, image

Window, XSize=400, YSize=350, 1
Loadct, 33, /Silent
TVImage, LogScl(image)

Window, XSize=400, YSize=350, 2
Loadct, 33, /Silent
TVLCT, r, g, b, /Get
TVLCT, LogScl(r), LogScl(g), LogScl(b)
TVImage, image

Does anyone have a good idea for why not?

Cheers,

David

P.S. And please don't tell me there is something wrong
with LOGSCL, as this is *not* the answer I want to
hear. :-(

--
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.")

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[Message index]

		Philosophical Scaling Question By: David Fanning on Mon, 04 December 2006 08:15
		Re: Philosophical Scaling Question By: David Fanning on Tue, 05 December 2006 11:57
		Re: Philosophical Scaling Question By: news.qwest.net on Tue, 05 December 2006 11:37
		Re: Philosophical Scaling Question By: Paul Van Delst[1] on Tue, 05 December 2006 13:49
		Re: Philosophical Scaling Question By: David Fanning on Tue, 05 December 2006 07:34
		Re: Philosophical Scaling Question By: Paul Van Delst[1] on Tue, 05 December 2006 07:12
		Re: Philosophical Scaling Question By: David Fanning on Mon, 04 December 2006 11:21
		Re: Philosophical Scaling Question By: Braedley on Mon, 04 December 2006 11:13
		Re: Philosophical Scaling Question By: David Fanning on Mon, 04 December 2006 10:45
		Re: Philosophical Scaling Question By: Brian Larsen on Mon, 04 December 2006 10:30

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