Is it possible to use a section of a colormap?

I am using a Matlab gui the has multiple graphs. One of these graphs is a smith chart, which plots coordinates in the complex plane. Each graph is plotted using a custom plot_colorfade(x,y,varargin) function. This function uses the default colormap "jet" and plots the collection of coordinates that are gathered from an external file as a color fade. Right now I have implemented a zoom function that when used on a first graph (tag: handles.del_pwr) it takes the new x (time) limits in a ActionPostCallback and redraws the smith chart with these new time limits.

Whenever I use the zoom feature I can focus on a section of the colorfade. However, when the smith chart is redrawn with the new x limits the colorfades between the two graphs do not match. For example, I can focus on the green-yellow section of the standard blue to red 'jet' colormap. When this happens, the limits of the smith chart are drawn to the new x limits of the handles.del_pwr graph but the color fade remains as the standard "jet" color fade (blue to red) regardless of the starting/ending point.

What I am wondering is if it is possible to use only a section of the "jet" colormap? (From my example above, I would want the green-yellow section for the smith chart starting at the same x coordinates as the handles.del_pwr graph colorfade). If hiding points of a graph without disturbing the colormap is possible that could potentially be a solution too.

Note: Using something such as linkaxes when zooming is not possible in this case because the smith chart and handles.del_pwr graphs don't use the same coordinate systems.

I can post the code for my plot_colorfade function and elaborate more if it is needed.

[Sean de Wolski]

It's certainly possible. If you could provide a simple minimal working example, it would help us a lot.

It sounds to me like you'll need to set a few properties of the various lines, and perhaps change the CDataMapping property in order to force the limits. However, and example would clarify this.

[Matthew]

Here is a link to what I am working on with a large section of my code included: http://www.mathworks.com/matlabcentral/answers/90086-warning-error-during-mode-callback-when-calling-functions-in-zoom-actionpostcallback

The redrawsmithchart function mentioned uses my plot_colorfade(x,y) function in code I have omitted. When it is called x = real gamma values and y = imaginary gamma values. These values are individual coordinates which the jet colormap is used to plot within the plot_colorfade function.

Answer 1

[Jeremy]

you can define a colormap using the jet(n) function where n is the number of steps. Based on the min/max of the current window you could limit the portion of the colormap to use. With a large n, it should work pretty well. You have to figure out exactly how to integrate.

example:

d=rand(100)*100;
image(d);
c=jet(100);
colormap(c(1:50,:)); %only uses the cold portion of the color map
%colormap(c(50:100,:)); %only uses the warmportion of the color map

[Matthew]

Thank you for the answer! I was able to get my code to work by modifying my plot_colorfade function and adding the lines:

CMAP_LENGTH = 256;
colormin = round((newLim(1)/initial_endtime)*256);
colormax = round((newLim(2)/initial_endtime)*256);
d = jet(CMAP_LENGTH);
cmap = colormap(d(colormin:colormax,:));

where newLim is a global variable for the x limits that is set during a zoom actionpostcallback and initial_endtime is the x max before the zoom actionpostcallback.

Answer 2

[John Barber]

The caxis function lets you adjust the axes' color limits ( CLim property), which determine the range of data values that are mapped to the colormap (for plots using 'scaled' CDataMapping, but not 'direct' ). See here for details: www.mathworks.com/help/matlab/ref/caxis.html.