Hi Friedrich, Thanks a lot for your response. I think that you are right - using the vmin/vmax args into imshow (as well as into pcolor) does seem to do what I want. Great!
The only thing that remains now is to simultaneously stretch the colormap in the image itself to this range, while also restricting the range of the colorbar which is displayed, to only the part of the colormap which actually has values (in the attached .png, I only want values between 0 and ~0.33 to appear in the colorbar, not from negative -0.33 to +0.33). Does anyone know how to do that? Thanks again - Ariel On Sat, Mar 27, 2010 at 3:29 PM, Friedrich Romstedt < friedrichromst...@gmail.com> wrote: > 2010/3/27 Ariel Rokem <aro...@berkeley.edu>: > > I am trying to make a color-map which will respond to the range of values > in > > the data itself. That is - I want to take one of the mpl colormaps and > use > > parts of it, depending on the range of the data. > > > > In particular, I am interested in using the plt.cm.RdYlBu_r colormap. If > the > > data has both negative and positive values, I want 0 to map to the > central > > value of this colormap (a pale whitish yellow) and I want negative values > to > > be in blue and positive numbers to be in red. Also - I would want to use > the > > parts of the colormap that represent how far away the smallest and > largest > > values in the data are from 0. So - if my data is in the range [x1,x2] I > > would want to use the part of the colormap in indices > > 127-127*abs(x1)/(x2-x1) through 127+127*x2/(x2-x1). If the data only > > includes positive numbers, I would want to only use the blue part of the > > colormap and if there are negative numbers, I would want to only use the > red > > part of the colormap (in these cases, I would also want to take only a > > portion of the colormap which represents the size of the interval > [x1,x2] > > relative to the interval [0,x1] or [x2,0], as the case may be). > > > > I think that this might be useful when comparing matrices generated from > > different data, but with the same computation, such as correlation or > > coherence (see http://nipy.sourceforge.net/nitime/examples/fmri.html to > get > > an idea of what I mean). > > I might miss something important, but why not use pcolor() with kwargs > vmin and vmax, > > http://matplotlib.sourceforge.net/api/axes_api.html#matplotlib.axes.Axes.pcolor > , > e.g.: > > maxval = numpy.abs(C).max() > pcolor(C, vmin = -maxval, vmax = maxval) > > As far as I can judge, this should have the desired effect. > > Friedrich > -- Ariel Rokem Helen Wills Neuroscience Institute University of California, Berkeley http://argentum.ucbso.berkeley.edu/ariel
<<attachment: colorbar.png>>
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