Re: [Matplotlib-users] color bar with non-linear spacing

[David H. <dav...@gm...>]

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 <bo...@ll...>:
>
> 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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