"""
Some simple functions to generate colours.
"""
from Numeric import asarray
from matplotlib.mlab import linspace
from matplotlib.colors import colorConverter
from Numeric import sum
def pastel(colour, weight=2.4):
""" Convert colour into a nice pastel shade"""
rgb = asarray(colorConverter.to_rgb(colour))
# scale colour
maxc = max(rgb)
if maxc < 1.0 and maxc > 0:
# scale colour
scale = 1.0 / maxc
rgb = rgb * scale
# now decrease saturation
total = sum(rgb)
slack = 0
for x in rgb:
slack += 1.0 - x
# want to increase weight from total to weight
# pick x s.t. slack * x == weight - total
# x = (weight - total) / slack
x = (weight - total) / slack
rgb = [c + (x * (1.0-c)) for c in rgb]
return rgb
def get_colours(n):
""" Return n pastel colours. """
base = asarray([[1,0,0], [0,1,0], [0,0,1]])
if n <= 3:
return base[0:n]
# how many new colours to we need to insert between
# red and green and between green and blue?
needed = (((n - 3) + 1) / 2, (n - 3) / 2)
colours = []
for start in (0, 1):
for x in linspace(0, 1, needed[start]+2):
colours.append((base[start] * (1.0 - x)) +
(base[start+1] * x))
return [pastel(c) for c in colours[0:n]]
