Re: [Matplotlib-users] contourf() color mapping

[James C. <jco...@uc...>]

Great. Just what I needed. I appreciate it. 

- James



On Feb 2, 2010, at 1:56 PM, Eric Firing wrote:

> James Conners wrote:
>> Hi, 
>> 
>> I'm having some trouble producing a filled contour how I want it. 
>> 
>> Say I'm plotting data over the range [1.2, 20] using 15 level lines evenly spaced
>> over that interval. I'd like the min of that interval to map to the min of the color spectrum (say "jet" so dark blue)
>> and the max of that interval to map to the max of the spectrum (so red). It doesn't seem to work that way. 
>> When I do filled contours, sometimes the low values are mapped to black or dark gray and 
>> sometimes they're mapped to blue. 
>> 
>> I always want the endpoints of the spectrum to map to the endpoints of the plotted values. Can this be done? 
>> Any help is appreciated. Thanks. 
> 
> The root of the problem is a questionable choice I made in the 
> _process_colors method of ContourSet; I will investigate either changing 
> it, or making it an option.  In the meantime, there is an easy 
> workaround: just use the set_clim method of the ContourSet, or the 
> pyplot.clim function.  In ipython -pylab:
> 
> z = rand(10,10)
> cs = contourf(z)
> cb = colorbar()
> cs.set_clim(cs.layers.min(), cs.layers.max())
> draw()
> 
> The idea behind the present default choice for clim within contourf is that
> the range of colors covers values from the lowest contour level to the 
> highest; the color of a *layer* is then the color of the midpoint 
> between its bounding levels.  This has some logic to it (and is more 
> consistent with pcolor and image color mapping), but I agree that it 
> probably makes more sense to use the full color range by default; most 
> often, this is likely to be what one wants, and for the exceptions one 
> can always use set_clim.
> 
> Eric
> 
>> 
>> - James
>> 
>> 
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