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Re: strange behaviour of bytscl by large arrays [message #79962 is a reply to message #79961]

Mon, 23 April 2012 07:21

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Klemen writes:

>
> Hi folks,
>
> is there any explanation of why I don't get the same or at least similar results using the code below by:
> a) using DINDGEN in line 3
> b) using FINDGEN in line 3
>
> pro test
> s = 10000
> a = sin(findgen(s, s)/100000.)
> b = bytscl(a)
> write_tiff, 'b.tif', b
> end
>
> The tif file I get using the DINDGEN function has waves all over the image. The option using FINDGEN produces strange results (a couple of waves and then wide bands of constant values). See the following link for the (resized) results.
> https://picasaweb.google.com/112572300011512591455/Eumetsat# 5734593216558178098
>
> I came across this problem as I tried to scale (using HIST_EQUAL and BYTSCL functions) 16-bit 5-band RapidEye data to 24-bit RGB image. Scaling the whole image produced results that were all black, smaller subsets seemed ok.
>
> Does anybody have a suggestion how to handle this issue?

Do you mean other than re-read the Sky Is Falling article again?

http://www.idlcoyote.com/math_tips/sky_is_falling.html

Here are some companion articles that might shed light on this problem:

http://www.idlcoyote.com/math_tips/storenum.html
http://www.idlcoyote.com/math_tips/double.html

I think you should examine the minimum and maximum values in your BytScl
function to see what they are. :-)

Cheers,

David

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

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[Message index]

		Re: strange behaviour of bytscl by large arrays By: David Fanning on Mon, 23 April 2012 10:06
		Re: strange behaviour of bytscl by large arrays By: Lajos Foldy on Mon, 23 April 2012 09:57
		Re: strange behaviour of bytscl by large arrays By: David Fanning on Mon, 23 April 2012 09:50
		Re: strange behaviour of bytscl by large arrays By: Lajos Foldy on Mon, 23 April 2012 09:18
		Re: strange behaviour of bytscl by large arrays By: Lajos Foldy on Mon, 23 April 2012 09:14
		Re: strange behaviour of bytscl by large arrays By: David Fanning on Mon, 23 April 2012 08:32
		Re: strange behaviour of bytscl by large arrays By: Klemen on Mon, 23 April 2012 08:22
		Re: strange behaviour of bytscl by large arrays By: David Fanning on Mon, 23 April 2012 08:10
		Re: strange behaviour of bytscl by large arrays By: Klemen on Mon, 23 April 2012 07:59
		Re: strange behaviour of bytscl by large arrays By: David Fanning on Mon, 23 April 2012 07:21
		Re: strange behaviour of bytscl by large arrays By: Carsten Lechte on Tue, 24 April 2012 00:59
		Re: strange behaviour of bytscl by large arrays By: chris_torrence@NOSPAM on Mon, 23 April 2012 13:22
		Re: strange behaviour of bytscl by large arrays By: Klemen on Mon, 23 April 2012 12:00
		Re: strange behaviour of bytscl by large arrays By: Klemen on Mon, 23 April 2012 13:54

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