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colour.py
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colour.py
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from bisect import bisect
from PIL import ImageColor
def getrgba(s):
"""Get an RGBA colour tuple from a string"""
if s.lower() == 'transparent': # add a name for fully transparent
s = '#0000'
c = ImageColor.getrgb(s)
if len(c) == 3:
return c + (255,)
return c
def _interpolate(vals, x):
# handle out of range values
if x < vals[0][0]:
return vals[0][1]
if x >= vals[-1][0]:
return vals[-1][2]
# get index in colour component map
i = bisect(vals, [x])
# if we are exactly on a value, return that
if x == vals[i][0]:
return vals[i][2]
# otherwise interpolate between values on either side
d0 = vals[i][0] - vals[i - 1][0]
d1 = vals[i][1] - vals[i - 1][2]
return int(vals[i - 1][2] + d1 * (x - vals[i - 1][0]) / d0)
class ColourScale:
def __init__(self, cols):
self.cols = cols
def __call__(self, x):
return tuple(_interpolate(col, x) for col in self.cols)
def is_flat(self):
for c in self.cols:
v = c[0][1]
for a in c:
if a[1] != v or a[2] != v:
return False
return True
def scale(*args):
"""Get a colour scale, either by name or by building a scale from a list of points
The magma, plasma, inferno & viridis scales are approximations of their matplotlib namesakes"""
if len(args) == 1:
if isinstance(args[0], ColourScale):
return args[0]
try:
return scales[args[0]]
except KeyError:
pass
return _scale(*args)
def _scale(*args):
"""Build a colour scale from a list of colour points on the scale"""
cols = [[], [], [], []]
if len(args) == 1:
# Make single colour be a constant scale
args = args * 2
# Populate known values
for c in args:
if isinstance(c, str):
for i, v in enumerate(getrgba(c)):
cols[i].append([None, v, v])
elif len(c) == 1:
for i, v in enumerate(getrgba(c[0])):
cols[i].append([None, v, v])
elif len(c) == 2:
for i, v in enumerate(getrgba(c[1])):
cols[i].append([c[0], v, v])
else:
for i, [v, w] in enumerate(zip(getrgba(c[1]), getrgba(c[2]))):
cols[i].append([c[0], v, w])
# Fill in missing range values
for i in range(4):
if cols[i][0][0] is None:
cols[i][0][0] = 0
if cols[i][-1][0] is None:
cols[i][-1][0] = 1
last = 0
for j in range(1, len(cols[i])):
if cols[i][j][0] is not None:
if j > last + 1:
d = cols[i][j][0] - cols[i][last][0]
n = j - last
for k in range(last + 1, j):
cols[i][k][0] = cols[i][last][0] + d * (k - last) / n
last = j
# Find and remove redundant values
for col in cols:
j = 1
while j < len(col) - 1:
dv = col[j + 1][1] - col[j - 1][2]
dx = col[j + 1][0] - col[j - 1][0]
c = col[j-1][2] + (col[j][0] - col[j - 1][0]) * dv / dx
if col[j][1] == col[j][2] and abs(c - col[j][1]) < 1:
del col[j]
else:
j += 1
return ColourScale(cols)
def show(*args):
"""Show a colour scale on screen"""
from PIL import Image
w = 1000
h = 100
sc = scale(*args)
img = Image.new('RGBA', (w, h))
pix = img.load()
for x in range(w):
c = sc(x/w)
for y in range(h):
pix[x, y] = c
img.show()
scales = dict(flame=_scale('transparent', [0.4, 'red'], [0.7, 'yellow'], 'white'),
magma=ColourScale([[[0, 0, 0],
[0.1, 17, 17],
[0.65, 238, 238],
[0.9, 255, 255],
[1, 252, 252]],
[[0, 0, 0],
[0.17, 17, 17],
[0.25, 15, 15],
[0.6, 76, 76],
[1, 253, 253]],
[[0, 3, 3],
[0.055, 29, 29],
[0.19, 107, 107],
[0.23, 120, 120],
[0.37, 130, 130],
[0.7, 92, 92],
[0.8, 112, 112],
[1, 191, 191]],
[[0, 255, 255],
[1, 255, 255]]]),
plasma=ColourScale([[[0, 12, 12],
[0.01, 22, 22],
[0.05, 42, 42],
[0.5, 208, 208],
[0.9, 254, 254],
[1, 240, 240]],
[[0, 7, 7],
[0.2, 0, 0],
[0.3, 9, 9],
[1, 249, 249]],
[[0, 135, 135],
[0.04, 146, 146],
[0.23, 169, 169],
[0.94, 36, 36],
[0.98, 39, 39],
[0.99, 36, 36],
[1, 33, 33]],
[[0, 255, 255],
[1, 255, 255]]]),
inferno=ColourScale([[[0, 12, 12],
[0.01, 22, 22],
[0.05, 42, 42],
[0.5, 208, 208],
[0.9, 254, 254],
[1, 240, 240]],
[[0, 7, 7],
[0.2, 0, 0],
[0.3, 9, 9],
[1, 249, 249]],
[[0, 135, 135],
[0.04, 146, 146],
[0.2, 169, 169],
[0.94, 36, 36],
[0.98, 39, 39],
[0.99, 36, 36],
[1, 33, 33]],
[[0, 255, 255],
[1, 255, 255]]]),
viridis=ColourScale([[[0, 68, 68],
[0.1, 72, 72],
[0.55, 30, 30],
[0.65, 44, 44],
[0.75, 85, 85],
[1, 254, 254]],
[[0, 1, 1],
[0.4, 112, 112],
[1, 231, 231]],
[[0, 84, 84],
[0.1, 121, 121],
[0.5, 142, 142],
[0.7, 104, 104],
[0.95, 24, 24],
[0.98, 28, 28],
[1, 36, 36]],
[[0, 255, 255],
[1, 255, 255]]]))