color bar with non-linear spacing

I am interested in producing a color map and accompanying colorbar with non-linear (arbitrary) spacing. My intent is like the attached color bar in which the increments are monotonic but vary in size. There might be an easy way to do this but it is not apparent to me.

--Jim

pastedGraphic1.tiff (4.46 KB)

Hi Jim,

I guess you’d have to write a custom palette dictionnary do to that. If you already have a GMT file, check the link
www.scipy.org/Cookbook/Matplotlib/Loading_a_colormap_dynamically

You could also take a cpt file you like, see for example

http://pdfb.wiredworkplace.net/cpt-city/www/cb/seq/index.html

tweak it to fit your needs and use the script below to convert it to a format matplotlib will understand. See the example in the docstring.

David

def cpt2seg(file_name, sym=False, discrete=False):
“”"Reads a .cpt palette and returns a segmented colormap.

sym : If True, the returned colormap contains the palette and a mirrored copy.
For example, a blue-red-green palette would return a blue-red-green-green-red-blue colormap.

discrete : If true, the returned colormap has a fixed number of uniform colors.

That is, colors are not interpolated to form a continuous range.

Example :
>>> _palette_data = cpt2seg('palette.cpt')
>>> palette = matplotlib.colors.LinearSegmentedColormap

(‘palette’,
_palette_data, 100)
>>> imshow(X, cmap=palette)

Licence: MIT
Author: David Huard, 2006
"""

dic = {}
f = open(file_name, 'r')

rgb = read_array(f)
rgb = rgb/255.
s = shape(rgb)
colors = ['red', 'green', 'blue']
for c in colors:
    i = colors.index(c)
    x = rgb[:, i+1]

    if discrete:

        if sym:
            dic[c] = zeros((2*s[0]+1, 3), float)
            dic[c][:,0] = linspace(0,1,2*s[0]+1)
            vec = concatenate((x ,x[::-1]))
        else:
            dic[c] = zeros((s[0]+1, 3), float)

            dic[c][:,0] = linspace(0,1,s[0]+1)
            vec = x
        dic[c][1:, 1] = vec
        dic[c][:-1,2] = vec

    else:
        if sym:
            dic[c] = zeros((2*s[0], 3), float)

            dic[c][:,0] = linspace(0,1,2*s[0])
            vec = concatenate((x ,x[::-1]))
        else:
            dic[c] = zeros((s[0], 3), float)
            dic[c][:,0] = linspace(0,1,s[0])

            vec = x
        dic[c][:, 1] = vec
        dic[c][:, 2] = vec

return dic

2006/6/29, James Boyle <boyle5@…99…

···

:
I am interested in producing a color map and accompanying colorbar with
non-linear (arbitrary) spacing. My intent is like the attached color

bar in which the increments are monotonic but vary in size. There might
be an easy way to do this but it is not apparent to me.

–Jim

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I think this may be what you need
http://matplotlib.sourceforge.net/matplotlib.colors.html#LinearSegmentedColormap

As I recall there are some examples floating around somewhere, perhaps
on the wiki...

Cheers
JP

James Boyle wrote:

···

I am interested in producing a color map and accompanying colorbar
with non-linear (arbitrary) spacing. My intent is like the attached
color bar in which the increments are monotonic but vary in size.
There might be an easy way to do this but it is not apparent to me.

--Jim

------------------------------------------------------------------------

Using Tomcat but need to do more? Need to support web services, security?
Get stuff done quickly with pre-integrated technology to make your job easier
Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo
http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642

------------------------------------------------------------------------

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