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Re: Color table question [message #436 is a reply to message #435]

Mon, 10 August 1992 16:59

thompson
Messages: 584
Registered: August 1991

Senior Member

In article <1992Aug10.223854.14071@news2.cis.umn.edu>,
patel@sparky.drad.umn.edu () writes...

> In PV-WAVW, I need to display a gray scale image(256 grays). I need
> few colors for graphics. I did the following to accomplish this:
>
>
> loadct,0 ; load a gray scale color table.
> ; Load the color table with 7 colors.
> Tvlct, 140, 140, 140, 1
> Tvlct, 130, 140, 220, 2
> Tvlct, 90, 80, 160, 3
> Tvlct, 255, 255, 255, 4
> Tvlct, 200, 200, 60, 5
> Tvlct, 50, 170, 80, 6
> Tvlct, 200, 70, 70, 7
>
> ; Byte scale the image in 'im'
> imb=bytscl(im)
> ;to avoid funny colors in the image, set all pixels with value <10 to 10
> imb(where(imb lt 10))=10
> tvscl,imb
> end
>
>
> with this segment of the program, I donot expect to see any colors
> in my image. But I do see scattered pixels with different colors.
> What am I doing wrong here.

First of all, since you've already scaled the image with BYTSCL, you don't need
to rescale it with TVSCL. Use TV instead. Also, you don't need to go to all
that much trouble to make sure that the scaled image has no values <10; you can
simply say

imb = bytscl(im) > 10b
tv, imb

Even better would be to scale the image to exactly the number of colors
available after reserving the 10 colors you're using elsewhere. At the same
time, we can also take care of the fact that your display may have less than
256 colors available:

imb = bytscl(im,top=!d.n_colors-11) + 10b
tv, imb

In fact, you simplify this to one line

tv, bytscl(im,top=!d.n_colors-11) + 10b

Bill Thompson

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[Message index]

		Color table question By: patel on Mon, 10 August 1992 15:38
		Re: Color table question By: thompson on Mon, 10 August 1992 16:59
		Re: color table question By: R.Bauer on Sat, 16 March 2002 12:19
		Re: color table question By: David Fanning on Fri, 15 March 2002 17:19
		Re: color table question By: Rick Towler on Thu, 14 March 2002 10:58

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