Hi Eric,
thanks for answering. I updated the attached figure.
The idea is, we want to show the tree cover difference, but to make
the negative and positive values very contrastive, we would like to
assign the values falling in small range of change (in the figure, it’s -1 to 1)
as blank (or gray), in order to make the remaining data constrasting different.
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?
Then I notice in the colormap methos there is one called “set_bad”, I guess this
is for this purpose, as in the case of “set_over” and “set_under”, which will
influence the colors in the colorbar when you later call the colorbar method.
But is it not like this?
I invented an example like below:
import numpy as np
import matplotlib as mat
import matplotlib.pyplot as plt
data = np.random.random(10000).reshape(100,100) - 0.5
data_masked = np.ma.masked_inside(data,-0.05,0.05)
cmap = mat.cm.jet
cmap.set_bad(‘0.5’)
fig,ax = plt.subplots(1,1)
lev = [-0.5,-0.4,-0.3,-0.2,-0.1,-0.05,0,0.05,0.1,0.2,0.3,0.4,0.5]
cas = ax.contourf(data_masked,levels=lev,cmap=cmap)
plt.colorbar(cas,ticks=lev)
In this example, how can I make the colors between -0.05 to 0.05 as white,
if I don’t want to bother write a new colormap.
Thanks a lot for your time, I hope this case could be useful for others as I
am sure it’s very widely used in geographic related sciences.
Cheers,
Chao
colorbar_eg.png (74K) Download Attachment
···
On Sat, Mar 1, 2014 at 9:16 PM, Eric Firing [via matplotlib] <[hidden email]> wrote:
On 2014/03/01 9:57 AM, Chao YUE wrote:
Dear all,
In many cases in geoscience mapping we want to show the some missing values
as some special color in the colorbar. like attached one.
I know there is one method in matplotlib colormap called “set_bad”, official
docs says:
Set color to be used for masked values.
But I don’t know how to make this work when I call the colorbar method.
It is not a matter of calling the colorbar method, but of setting up the
colormap used on the color-mapped plot for which the colorbar is made.
The one wrinkle to this is that if you are using contourf, the masked
regions are not filled at all, so they take on the color of the
background. To give them the color you assigned to the colormap with
set_bad, you need to assign that same color to the background, e.g.
ax.set_axis_bgcolor("#bdb76b")
On re-reading your message, however, I think you are asking something
else, but it is not clear to me from your example exactly what you are
trying to do.
The colorbar is strictly for a range or sequence of colors, which can
include triangle regions for the “over” and “under” values; there is no
place on the colorbar for a “bad” or “missing” value. Where would you
put one? I don’t see any such region on the example colorbar you attached.
Eric
Is there anyone who have the some successful experience?
Thanks a lot in advance!
Chao
–
Chao YUE
Laboratoire des Sciences du Climat et de l’Environnement (LSCE-IPSL)
UMR 1572 CEA-CNRS-UVSQ
Batiment 712 - Pe 119
91191 GIF Sur YVETTE Cedex
Tel: (33) 01 69 08 29 02; Fax:01.69.08.77.16
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Chao YUE
Laboratoire des Sciences du Climat et de l’Environnement (LSCE-IPSL)
UMR 1572 CEA-CNRS-UVSQ
Batiment 712 - Pe 119
91191 GIF Sur YVETTE Cedex
Tel: (33) 01 69 08 29 02; Fax:01.69.08.77.16
