Color scales: Black out the middle range.

Share icon

Thu, 07/25/2013 - 07:23 pm


Hi

I'm making an image plot and, I'm wondering if it's possible to black out only the middle values of the range in a similarly simple way. For example if my scale runs from -10 to 10, I would like to black out a small range of values centered around 0.

Thanks
What do you mean by "black out"? Do you want those pixels to *be* black, or be missing?

If you want them to be black, regardless of the color table, you'll need to create a color index wave from a color table. And you'll need one color index wave per image plot, because Igor uses the color index wave's X scaling to set the color min/max.

If you want to hide the pixels near 0, use a lookup wave with NaN near the middle:
Make/O/N=(20,20) twod= -10 +p
newimage twod
ModifyImage twod ctab= {*,*,CyanMagenta,0}
Make/O/N=41 colorLookup=p/40; colorLookup[19,21]=NaN
ModifyImage twod ctabAutoscale=0,lookup= colorLookup
Colorscale


--Jim Prouty
Software Engineer, WaveMetrics, Inc.
BlackOutMeansMissing.png

July 26, 2013 at 11:16 am - Permalink

Thanks for the reply, Jim.

I was hoping for the pixels to "be" black. So I guess I need to make an index wave. If I'm understanding you and the relevant help file, I can copy an existing colour scheme to a wave using ColorTab2Wave. But then do I need to reset the scale of the new wave to match my desired interval using SetScale before it will work?

Thanks again

July 26, 2013 at 05:39 pm - Permalink

Yes, that's the way to do it.

More info if you enter this Igor command:

DisplayHelpTopic "Linear Indexed Color"


--Jim Prouty
Software Engineer, WaveMetrics, Inc.

July 26, 2013 at 06:25 pm - Permalink