Extract matplotlib colormap in hex-format

Question

I am trying to extract discrete colors from a matplotlib colormap by manipulating this example. However, I cannot find the N discrete colors that are extracted from the colormap.

In the code below I've used cmap._segmentdata, but I've found that it is the definition of the entire colormap. Given a colormap and an integer N, how do I extract N discrete colors from the colormap and export them in hex-format?

from pylab import *  delta = 0.01 x = arange(-3.0, 3.0, delta) y = arange(-3.0, 3.0, delta) X,Y = meshgrid(x, y) Z1 = bivariate_normal(X, Y, 1.0, 1.0, 0.0, 0.0) Z2 = bivariate_normal(X, Y, 1.5, 0.5, 1, 1) Z = Z2 - Z1 # difference of Gaussians  cmap = cm.get_cmap('seismic', 5)    # PiYG cmap_colors = cmap._segmentdata  def print_hex(r,b,g):                if not(0 <= r <= 255 or 0 <= b <= 255 or 0 <= g <= 255):                               raise ValueError('rgb not in range(256)')                print '#%02x%02x%02x' % (r, b, g)   for i in range(len(cmap_colors['blue'])):                r = int(cmap_colors['red'][i][2]*255)                b = int(cmap_colors['blue'][i][2]*255)                g = int(cmap_colors['green'][i][2]*255)                print_hex(r, g, b)    im = imshow(Z, cmap=cmap, interpolation='bilinear',             vmax=abs(Z).max(), vmin=-abs(Z).max()) axis('off') colorbar()  show() 

Answer 1

You can get a tuple of rgba values for the segment with index i by calling cmap(i). There is also already a function that turns rgb values into hex. As Joe Kington wrote in the comments, you can use matplotlib.colors.rgb2hex. Therefore, a possible solution would be:

from pylab import *  cmap = cm.get_cmap('seismic', 5)    # PiYG  for i in range(cmap.N):     rgba = cmap(i)     # rgb2hex accepts rgb or rgba     print(matplotlib.colors.rgb2hex(rgba)) 

The output is:

#00004c #0000ff #ffffff #ff0000 #7f0000 

Answer 2

For future reference: My CMasher package provides a function called take_cmap_colors() (https://cmasher.readthedocs.io/user/usage.html#taking-colormap-colors), which allows one to take any number of discrete colors from a given colormap and return them in any format (8-bit, normalized or HEX) they want.

So, if you for example wanted to take 5 colors in HEX from the viridis colormap, you could do this with:

import cmasher as cmr  colors = cmr.take_cmap_colors('viridis', 5, return_fmt='hex') 

or if you want all colors in HEX from a colormap in a specific value range, you can do that with:

colors = cmr.take_cmap_colors('viridis', None, cmap_range=(0.2, 0.8), return_fmt='hex')