On 06/03/2010 10:00 AM, Jim Vickroy wrote:
> I want to generate a 2-d figure with a (fixed) color scale that does
> not vary with the range of the data being plotted.
>
> How do I do this? Attempts to specify vimin and vmax appear to be ignored.
>
> The following example:
>
> #<code>
> import numpy
> data = numpy.zeros(shape=(240,240),dtype=int)
> data[ 0: 80] = -1
> data[ 80:160] = 0
> data[160:] = 1
>
> import matplotlib.pyplot as plot
> figure = plot.figure()
> ax = figure.add_subplot(111)
> cax = ax.imshow(data, interpolation='bilinear')
> ax.set_title('test data with fixed colorbar')
Adding to what JJ said, note that setting the ticks on the colorbar has
no effect on the norm used in color mapping. The vmin and vmax kwargs
to imshow get passed to the norm, so they do set the mapping range.
> colorbar = figure.colorbar(cax, ticks=[-1, 0, 1])
> colorbar.ax.set_yticklabels(['-1', '0', '1'])
Please avoid setting the ticklabels directly--it is almost always
unnecessary, and it is too easy to shoot yourself in the foot. If the
default tick label formatting is inadequate, you can use the format
kwarg in colorbar.
From the docstring:
*ticks* [ None | list of ticks | Locator object ]
If None, ticks are determined automatically from the
input.
*format* [ None | format string | Formatter object ]
If None, the
:class:`~matplotlib.ticker.ScalarFormatter` is used.
If a format string is given, e.g. '%.3f', that is
used. An alternative
:class:`~matplotlib.ticker.Formatter` object may be
given instead.
Eric
> plot.show()
> #</code>
>
> produces a figure with 3 color bands (blue,green,red) and matching color
> bar with labels (-1,0,1) as expected.
>
> if the data[160:]=1 specification is deleted, in the above code, the
> resulting figure has 2 color bands (blue,red) and the associated color
> bar is identical to the original, but the labels are (-1,0).
>
> What I want, in this second case, is a blue-green figure and a color bar
> with labels identical to the original example.
>
> -- jv
>
>
>
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