| about color table [message #66904] |
Thu, 18 June 2009 14:40  |
Hu
Messages: 35
Registered: January 2009
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Member |
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Hi, folks
I want to do something like this: I got an 2-D array with values range
from 0.0 to 1.0. and I want to display the array using different
colors. for example, if the value is greater than 0.8, the elements
will be displayed as red, if the values is between 0.5 and 0.8, the
color will be blue, and the relationship can be listed as follows:
> 0.8 red
0.5-0.8 blue
0.3-0.5 yellow
0.2-0.3 green
<0.2 white
I know I need to set up a color table, and the book 'IDL Programming
techniques' demostrate how to set up a color table, and I set up the
table including those above colors.
The question is , How can I set up the relationship between the color
table and the different ranges? I mean how to 'tell' the computer
display the array using this relationship?
Thanks
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| Re: about color table [message #67118 is a reply to message #66904] |
Sun, 21 June 2009 12:46  |
Michael Galloy
Messages: 1114
Registered: April 2006
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Senior Member |
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David Fanning wrote:
> Jeremy Bailin writes:
>
>> Yeah, value_locate is very handy for problems like this! I
>> particularly like using it as a precursor to histogram - i.e. if you
>> want to do something fancy using reverse_indices but don't have
>> uniformly-spaced bins, first use value_locate to get integer indices
>> and then use histogram to do the heavy lifting.
>
> All right, I'll bite. Let's see an example of this.
> Maybe you can write an article and become the JD Smith
> of Value_Locate. :-)
No article, but I think this is what Jeremy is talking about:
IDL> ; get some random data
IDL> d = randomu(12345678L, 20)
IDL> print, d
0.765989 0.0234537 0.589727 0.535102 0.982231
0.693016 0.328147
0.295642 0.849918 0.592262 0.558133 0.534926
0.541119 0.594831
0.410172 0.928598 0.161021 0.928724 0.952072
0.522173
IDL> ; specify cutoffs
IDL> cutoffs = [0.3, 0.4, 0.8]
IDL> ; compute index of "bin" to put each value into
IDL> bins = value_locate(cutoffs, d) + 1L
IDL> print, ind
2 0 2 2 3
2 1 0
3 2 2 2 2
2 2 3
0 3 3 2
IDL> ; compute histogram of bins
IDL> h = histogram(bins, reverse_indices=r)
IDL> print, h
3 1 11 5
IDL> ; values less than 0.3
IDL> print, d[r[r[0]:r[1] - 1]]
0.0234537 0.295642 0.161021
IDL> ; values between 0.3 and 0.4
IDL> print, d[r[r[1]:r[2] - 1]]
0.328147
IDL> ; values between 0.4 and 0.8
IDL> print, d[r[r[2]:r[3] - 1]]
0.765989 0.589727 0.535102 0.693016 0.592262
0.558133 0.534926
0.541119 0.594831 0.410172 0.522173
IDL> ; values greater than 0.8
IDL> print, d[r[r[3]:r[4] - 1]]
0.982231 0.849918 0.928598 0.928724 0.952072
Mike
--
www.michaelgalloy.com
Associate Research Scientist
Tech-X Corporation
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| Re: about color table [message #67119 is a reply to message #66904] |
Fri, 19 June 2009 20:58 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Jeremy Bailin writes:
> Yeah, value_locate is very handy for problems like this! I
> particularly like using it as a precursor to histogram - i.e. if you
> want to do something fancy using reverse_indices but don't have
> uniformly-spaced bins, first use value_locate to get integer indices
> and then use histogram to do the heavy lifting.
All right, I'll bite. Let's see an example of this.
Maybe you can write an article and become the JD Smith
of Value_Locate. :-)
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.")
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