On 02/01/2011 02:18 PM, Benjamin Root wrote: > On Tue, Feb 1, 2011 at 6:05 PM, Jeremy Conlin <jlcon...@gmail.com > <mailto:jlcon...@gmail.com>> wrote: > > On Tue, Feb 1, 2011 at 5:00 PM, Benjamin Root <ben.r...@ou.edu > <mailto:ben.r...@ou.edu>> wrote: > > > > > > On Tue, Feb 1, 2011 at 5:48 PM, Jeremy Conlin <jlcon...@gmail.com > <mailto:jlcon...@gmail.com>> wrote: > >> > >> I'm trying to create a custom colormap used with pcolormesh, but the > >> results seem inconsistent to me. I want the following colors > >> > >> -3 < x <= -2 ----- Black > >> -2 < x <= -1 ----- Blue > >> -1 < x <= 0 ----- Yellow > >> 0 < x <= 1 ----- Green > >> 1 < x <= inf ----- Red > >> > >> A minimal example is copied below. I have a 2-D array that > looks like: > >> > >> -1, 6, 2.5 > >> 1.3, -2, 4/3 > >> 2.5, 6, 0 > >> > >> I want to get a pcolormesh that looks like > >> > >> R R Y > >> R K R > >> B R R > >> > >> But instead I get: > >> > >> Y R B > >> Y K Y > >> K R Y > >> > >> I recognize that the pcolormesh is plotted "upside-down" from > how the > >> matrix is printed. I apparently don't understand how to use a > custom > >> colormap. I have tried to follow the example here: > >> > >> http://matplotlib.sourceforge.net/examples/api/colorbar_only.html > >> > >> but haven't been too successful. It seems like there is a > >> normalization going on that I can't seem to track down. Can anyone > >> see what is wrong? > >> > >> Thanks, > >> Jeremy > >> > >> > >> import numpy > >> import matplotlib.pyplot as pyplot > >> import matplotlib.colors > >> > >> C = numpy.array([[-1,6,2.5],[4/3., -2, > 4/3.],[2.5,6,0.0]],dtype=float) > >> > >> cMap = matplotlib.colors.ListedColormap(['k', 'b', 'y', 'g', 'r']) > >> Bounds = [-3.0, -2.0, -1.0, 0.0, 1.0, numpy.inf] > >> > >> # Plot > >> Fig = pyplot.figure() > >> pyplot.pcolormesh(C, cmap=cMap) > >> > > > > Have you given imshow() a try? The pcolor() and family are > really meant for > > more general domain specifications. imshow() is about as basic > as one can > > get for producing an image that shows the colors for particular > values. > > matshow() also does something similar and doesn't interpolate between > > points. > > > > I don't know if it would fix your problem, but it should be a > good start. > > I just tried both imshow and matshow and they gave the same output, > but the plot was rotated -90ยบ. I don't care so much about how it is > oriented, but I do care about consistency, i.e. -1 should be plotted > as blue, but is instead black. I could also accept -1 as yellow since > -1 is on the boundary. pcolor, imshow, and matshow all show the same > inconsistency. > > Jeremy > > > I think I just figured out what is wrong. In your code, you create a > ListedColormap, but you don't assign a Norm object. So, when you call > pcolor or whatever, it will use the default norm using the range of > input values. I see you created a list of boundaries called Bounds, but > you don't do anything with it. > > I believe you want to first make a BoundaryNorm object using Bounds and > pass that object to the ListedColormap using the norm keyword.
Not to the ListedColormap, but to the imshow or whatever. Here is an example of BoundaryNorm: http://matplotlib.sourceforge.net/examples/pylab_examples/image_masked.html And here is another, using a BoundaryNorm with a ListedColormap: http://matplotlib.sourceforge.net/examples/pylab_examples/multicolored_line.html (It is the first of the two line plots.) Note that you need to instantiate it with the number of colors in your colormap. Eric > > That should fix it. > > Ben Root ------------------------------------------------------------------------------ Special Offer-- Download ArcSight Logger for FREE (a $49 USD value)! Finally, a world-class log management solution at an even better price-free! Download using promo code Free_Logger_4_Dev2Dev. Offer expires February 28th, so secure your free ArcSight Logger TODAY! http://p.sf.net/sfu/arcsight-sfd2d _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
