Log Scaled Contour Plot

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Thu, 08/13/2009 - 06:50 am

I'm trying to make a log scaled contour plot. That is, a contour plot that has the colors (for say the rainbow256 option) logarithmically spaced instead of linearly spaced. It would be great if igor could do this for me. I see that I can do this manually by creating a matrix with a column for the z-values, and columns for the RGB specifications. Even if igor could give me a matrix with the RGB numbers for the rainbow256, and then allow me to change the z-values that correspond to the different colors, that would be helpful. Does anyone have any advice on doing this?

Thanks
You can get the RGB values of a built in color table by doing this:

ColorTab2Wave Rainbow

August 13, 2009 at 04:22 pm - Permalink

Thanks, that's a start at least. But now that I have that, I realize that I'd need to either change the wave scaling to be logarithmic (which I don't think is possible), or space the colors in the wave to be log scaled (which would require a bit of work). Does anyone have any advice on either one of these options?

Thanks

August 14, 2009 at 08:59 am - Permalink

I know that it's probably not the best way, but I just make a copy of the data, log it, and display the copy. (all the 0 and -ve numbers go to -Inf/NaN).

August 14, 2009 at 10:00 am - Permalink

I second the request for a log-scaled color table. I have 2D spectral data with peaks that vary by an order of magnitude and I would like to switch between linear and log scales easily. Origin can do this with a simple option in the color table dialog, and I'd like to see Igor keep up with the competition! (I'm an Igor fan in a group of mostly Origin users).

November 13, 2009 at 09:55 am - Permalink

MarkKeller wrote:
I second the request for a log-scaled color table. I have 2D spectral data with peaks that vary by an order of magnitude and I would like to switch between linear and log scales easily. Origin can do this with a simple option in the color table dialog, and I'd like to see Igor keep up with the competition! (I'm an Igor fan in a group of mostly Origin users).


Are you still talking about Contour Plots or generally?
Did you notice the "lookup table" feature for Image Plots, which allows you to apply e.g. Gamma corrections?

see DisplayHelpTopic "Color Table Ranges - Lookup Table (Gamma)"

November 13, 2009 at 12:55 pm - Permalink

Have you tried
#include <WMImageLogColorTable>
?
It creates a logarithmic color lookup table for a image, a new entry appears in the graph menu. ( Has to be updated manually if display settings were changed). See
DisplayHelpTopic "Image and Contour Plots"

I often use it for displaying LEED images without changing the data, dont know if it works for contour plots though.

Christian

November 16, 2009 at 04:04 am - Permalink