Re: [Matplotlib-users] How can I put a white area in the middle of colorbar showing the masked data

On 2014/03/02 1:02 AM, ChaoYue wrote:
> Dear Eric,
>
> This solved part of my problem. thanks a lot.
> I think I will revisit this issue when I have time (not promised).
> do you think this could be some feature desirable?

I don't understand what feature you are referring to; evidently I don't 
understand what the problem is, so I don't know what part remains unsolved.

Eric


>
> Cheers,
>
> Chao
>
>
> On Sat, Mar 1, 2014 at 10:39 PM, Eric Firing [via matplotlib] <[hidden
> email] </user/SendEmail.jtp?type=node&node=42956&i=0>> wrote:
>
>     On 2014/03/01 11:03 AM, ChaoYue wrote:
>      > The most correct way might be to design a new colormap with white
>     color
>      > exactly in the middle, however this is very tedious, especially if I
>      > want to try
>      > different colormaps. so the alternative approach would be to set
>     the values
>      > falling in (-1,1) as being masked, so they will be the same as
>     the axes
>      > background color as you mentioned (in our case it's white). My
>     question is,
>      > how can I put this background color (which shows maksed data) in the
>      > colorbar,
>      > by avoiding design a new colormap?
>
>     It's not the answer you want to hear, but I think the correct answer is
>     that you should do this via the colormap, and not by masking the low
>     values.  It doesn't have to be painful.  If, in contourf, you use a
>     diverging colormap with white already in the middle
>     (http://matplotlib.org/examples/color/colormaps_reference.html) and a
>     norm with symmetric limits (vmin and vmax; you can let them be set
>     automatically after you specify your symmetric set of contour
>     boundaries
>     appropriately) then it will be done for you.
>
>     e.g.,
>
>     z = 10 * np.random.randn(20, 30)
>     clevs = [-10, -5, -2, -1, 1, 2, 5, 10]
>     cs = plt.contourf(z, levels=clevs, cmap=plt.get_cmap('PRGn'),
>                         extend='both')
>     cbar = plt.colorbar(cs, spacing='uniform')
>
>     Eric
>
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