pir - 1 year ago 220

Python Question

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

`N`

In the code below I've used

`cmap._segmentdata`

`N`

`N`

`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()

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Answer Source

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):
rgb = cmap(i)[:3] # will return rgba, we take only first 3 so we get rgb
print(matplotlib.colors.rgb2hex(rgb))
```

The output is:

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

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