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Re: Array Subscripting Puzzle [message #30788 is a reply to message #30785]

Fri, 17 May 2002 11:30

Liam E. Gumley
Messages: 378
Registered: January 2000

Senior Member

David Fanning wrote:
> Folks,
>
> I have a 24-bit image. You can interleave it anyway
> you like that will make the problem described below
> trackable. At the moment it is 800 by 600 by 3.
>
> I have the indices of something I want to draw on
> the image. Say they are the indices of the outlines
> of some continents. For example, like this:
>
> window, xsize=800, ysize=600
> map_set, /Cylindrical, position=[0,0,1,1]
> map_continents, /fill
> a = tvrd()
> indices = where(a GT 0)
>
> I want to make all the outline pixels yellow.
> I *could* do this:
>
> r = Reform((image[*,*,0]))
> g = Reform((image[*,*,1]))
> b = Reform((image[*,*,2]))
> r[indices] = 255
> g[indices] = 255
> b[indices] = 0
> image[*,*,0] = r
> image[*,*,1] = g
> image[*,*,2] = b
>
> That seems wasteful and inelegant. There must be
> a way to do this in one go. I'm sure it uses REBIN
> and REFORM, but I'm not sure in which order. :-(
>
> Can anyone help?

Here's a shorcut with no array rearrangment.
Note that the 24-bit image must be in [NCOL, NROW, 3] format:

dims = size(image, /dimensions)
ncol = dims[0]
nrow = dims[1]
chan = 0 ; red channel
image[indices + (chan * ncol * nrow)] = 255
chan = 1 ; green channel
image[indices + (chan * ncol * nrow)] = 255
chan = 2 ; blue channel
image[indices + (chan * ncol * nrow)] = 0

Cheers,
Liam.
Practical IDL Programming
http://www.gumley.com/

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[Message index]

		Re: Array Subscripting Puzzle By: Richard Younger on Fri, 17 May 2002 14:18
		Re: Array Subscripting Puzzle By: James Kuyper on Fri, 17 May 2002 12:45
		Re: Array Subscripting Puzzle By: dmarshall on Fri, 17 May 2002 11:57
		Re: Array Subscripting Puzzle By: Liam E. Gumley on Fri, 17 May 2002 11:30
		Re: Array Subscripting Puzzle By: James Kuyper on Fri, 17 May 2002 11:15
		Re: Array Subscripting Puzzle By: JD Smith on Wed, 22 May 2002 14:12

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