Darken or lighten a color in matplotlib

Question

Say I have a color in Matplotlib. Maybe it\'s a string (\'k\') or an rgb tuple ((0.5, 0.1, 0.8)) or even some hex (#05FA2B). Is there a

Answer 1

A few months ago I had to solve that problem. The idea was for the user to choose a color (any color) and the software automatically generated a colormap (this was part of a package for scientific purposes).

In any case here is the code that I used to achieve it. You won't need most of what the object does but it will give you what you ask:

import math

class Color():
    def __init__(self, color, fmt='rgb'):
        self.__initialize__(color, fmt)

    def __initialize__(self, color, fmt='rgb'):
        if fmt == 'rgb':
            self.rgb = (int(color[0]), int(color[1]), int(color[2]))
            self.hex = self._rgb2hex(self.rgb)
            self.hsv = self._rgb2hsv(self.rgb)
            self.rgb0 = self.rgb[0] / 255, self.rgb[1] / 255, self.rgb[2] / 255
        elif fmt == 'rgb0':
            self.rgb = (int(color[0] * 255), int(color[1] * 255), int(color[2] * 255))
            self.hex = self._rgb2hex(self.rgb)
            self.hsv = self._rgb2hsv(self.rgb)
            self.rgb0 = (color[0], color[1], color[2])
        elif fmt == 'hex':
            self.hex = color
            self.rgb = self._hex2rgb(self.hex)
            self.hsv = self._rgb2hsv(self.rgb)
            self.rgb0 = self.rgb[0] / 255, self.rgb[1] / 255, self.rgb[2] / 255
        elif fmt == 'hsv':
            self.hsv = color
            self.rgb = self._hsv2rgb(self.hsv)
            self.hex = self._rgb2hex(self.rgb)
            self.rgb0 = self.rgb[0] / 255, self.rgb[1] / 255, self.rgb[2] / 255
        self.__automaticPalette__()

    def __automaticPalette__(self):
        self.rgbColors = []
        self.hexColors = []
        self.hsvColors = []
        self.rgb0Colors = []
        hsv = self.hsv
        for i in range(255):
            new_hsv = hsv[0], hsv[1], (1 / 255) * i
            self.rgbColors.append(self._hsv2rgb(new_hsv))
            self.hexColors.append(self._rgb2hex(self.rgbColors[-1]))
            self.hsvColors.append(new_hsv)
            r, g, b = self.rgbColors[-1]
            self.rgb0Colors.append((r / 255, g / 255, b / 255))

    def _testPalette(self, o=1):
        from matplotlib import pyplot as plt
        from matplotlib.patches import Rectangle
        if o == 1:
            someX, someY = 0.5, 0.1
            plt.figure()
            s = 1
            currentAxis = plt.gca()
            for x in range(254):
                currentAxis.add_patch(Rectangle((x * s, someY), s, 0.1, alpha=1, color=self.rgb0Colors[x]))
            currentAxis.add_patch(Rectangle((5 * s, someY + 0.07), 30, 0.02, alpha=1, color=self.rgb0))

            plt.ylim(0.1, 0.2)
            plt.xlim(0, (x + 1) * s)
            plt.show()
        elif o == 2:
            local = self.rgb0Colors[90:190][0:-1:10]
            someX, someY = 0.5, 0.1
            plt.figure()
            s = 1
            currentAxis = plt.gca()
            for x in range(len(local)):
                currentAxis.add_patch(Rectangle((x * s, someY), s, 0.1, alpha=1, color=local[x]))
            currentAxis.add_patch(Rectangle((5 * s, someY + 0.07), 30, 0.02, alpha=1, color=self.rgb0))

            plt.ylim(0.1, 0.2)
            plt.xlim(0, (x + 1) * s)
            plt.show()

    def _hex2rgb(self, value):
        # http://stackoverflow.com/questions/214359/converting-hex-color-to-rgb-and-vice-versa
        value = value.lstrip('#')
        lv = len(value)
        return tuple(int(value[i:i + int(lv / 3)], 16) for i in range(0, lv, int(lv / 3)))

    def _rgb2hex(self, rgb):
        # http://stackoverflow.com/questions/214359/converting-hex-color-to-rgb-and-vice-versa
        r = rgb[0]
        g = rgb[1]
        b = rgb[2]
        return '#%02X%02X%02X' % (r, g, b)

    def _hsv2rgb(self, hsv):
        # http://code.activestate.com/recipes/576919-python-rgb-and-hsv-conversion/
        h, s, v = hsv
        h = float(h)
        s = float(s)
        v = float(v)
        h60 = h / 60.0
        h60f = math.floor(h60)
        hi = int(h60f) % 6
        f = h60 - h60f
        p = v * (1 - s)
        q = v * (1 - f * s)
        t = v * (1 - (1 - f) * s)
        r, g, b = 0, 0, 0
        if hi == 0:
            r, g, b = v, t, p
        elif hi == 1:
            r, g, b = q, v, p
        elif hi == 2:
            r, g, b = p, v, t
        elif hi == 3:
            r, g, b = p, q, v
        elif hi == 4:
            r, g, b = t, p, v
        elif hi == 5:
            r, g, b = v, p, q
        r, g, b = int(r * 255), int(g * 255), int(b * 255)
        return r, g, b

    def _rgb2hsv(self, rgb):
        # http://code.activestate.com/recipes/576919-python-rgb-and-hsv-conversion/
        r, g, b = rgb
        r, g, b = r / 255.0, g / 255.0, b / 255.0
        mx = max(r, g, b)
        mn = min(r, g, b)
        df = mx - mn
        if mx == mn:
            h = 0
        elif mx == r:
            h = (60 * ((g - b) / df) + 360) % 360
        elif mx == g:
            h = (60 * ((b - r) / df) + 120) % 360
        elif mx == b:
            h = (60 * ((r - g) / df) + 240) % 360
        if mx == 0:
            s = 0
        else:
            s = df / mx
        v = mx
        return h, s, v

    def getColor(self, fmt='rgb'):
        if fmt == 'rgb':
            return self.rgb
        elif fmt == 'hex':
            return self.hex
        elif fmt == 'rgb0':
            return self.rgb0
        elif fmt == 'hsv':
            return self.hsv

So if you call it like this:

c = Color((51, 153, 255))
# c = Color((0.5, 0.1, 0.8), fmt='rgb0') # It should work with rgb0
# c = Color('#05d4fa', fmt='hex')        # and hex but I don't remember if it was well tested so be careful (the conversions might be messy).
c._testPalette(1)
print(c.rgbColors)

It will return you this:

, and this:

[(0, 0, 0), (0, 0, 1), (0, 1, 2), (0, 1, 3), (0, 2, 4), (0, 3, 5), (1, 3, 6), (1, 4, 7), (1, 4, 8), (1, 5, 9), (1, 6, 10), (2, 6, 11), (2, 7, 12), (2, 7, 13), (2, 8, 14), (2, 9, 15), (3, 9, 16), (3, 10, 17), (3, 10, 18), (3, 11, 19), (3, 12, 20), (4, 12, 21), (4, 13, 22), (4, 13, 23), (4, 14, 24), (4, 15, 25), (5, 15, 26), (5, 16, 27), (5, 16, 28), (5, 17, 29), (5, 18, 30), (6, 18, 31), (6, 19, 32), (6, 19, 32), (6, 20, 34), (6, 21, 35), (7, 21, 36), (7, 22, 36), (7, 22, 38), (7, 23, 39), (7, 24, 40), (8, 24, 40), (8, 25, 42), (8, 25, 43), (8, 26, 44), (8, 26, 44), (9, 27, 46), (9, 28, 47), (9, 28, 48), (9, 29, 48), (9, 30, 50), (10, 30, 51), (10, 31, 52), (10, 31, 52), (10, 32, 54), (10, 33, 55), (11, 33, 56), (11, 34, 56), (11, 34, 58), (11, 35, 59), (11, 36, 60), (12, 36, 60), (12, 37, 62), (12, 37, 63), (12, 38, 64), (12, 38, 65), (13, 39, 65), (13, 40, 67), (13, 40, 68), (13, 41, 69), (13, 42, 70), (14, 42, 71), (14, 43, 72), (14, 43, 73), (14, 44, 73), (14, 45, 75), (15, 45, 76), (15, 46, 77), (15, 46, 78), (15, 47, 79), (15, 48, 80), (16, 48, 81), (16, 49, 81), (16, 49, 83), (16, 50, 84), (16, 50, 85), (17, 51, 86), (17, 52, 87), (17, 52, 88), (17, 53, 89), (17, 53, 89), (18, 54, 91), (18, 55, 92), (18, 55, 93), (18, 56, 94), (18, 57, 95), (19, 57, 96), (19, 58, 97), (19, 58, 97), (19, 59, 99), (19, 60, 100), (20, 60, 101), (20, 61, 102), (20, 61, 103), (20, 62, 104), (20, 62, 105), (21, 63, 105), (21, 64, 107), (21, 64, 108), (21, 65, 109), (21, 66, 110), (22, 66, 111), (22, 67, 112), (22, 67, 113), (22, 68, 113), (22, 69, 115), (23, 69, 116), (23, 70, 117), (23, 70, 118), (23, 71, 119), (23, 72, 120), (24, 72, 121), (24, 73, 121), (24, 73, 123), (24, 74, 124), (24, 74, 125), (25, 75, 126), (25, 76, 127), (25, 76, 128), (25, 77, 129), (25, 77, 130), (26, 78, 131), (26, 79, 131), (26, 79, 133), (26, 80, 134), (26, 81, 135), (27, 81, 136), (27, 82, 137), (27, 82, 138), (27, 83, 139), (27, 84, 140), (28, 84, 141), (28, 85, 142), (28, 85, 143), (28, 86, 144), (28, 86, 145), (29, 87, 146), (29, 88, 147), (29, 88, 147), (29, 89, 149), (29, 90, 150), (30, 90, 151), (30, 91, 152), (30, 91, 153), (30, 92, 154), (30, 93, 155), (31, 93, 156), (31, 94, 157), (31, 94, 158), (31, 95, 159), (31, 96, 160), (32, 96, 161), (32, 97, 162), (32, 97, 163), (32, 98, 163), (32, 99, 165), (33, 99, 166), (33, 100, 167), (33, 100, 168), (33, 101, 169), (33, 101, 170), (34, 102, 171), (34, 103, 172), (34, 103, 173), (34, 104, 174), (34, 105, 175), (35, 105, 176), (35, 106, 177), (35, 106, 178), (35, 107, 179), (35, 107, 179), (36, 108, 181), (36, 109, 182), (36, 109, 183), (36, 110, 184), (36, 110, 185), (37, 111, 186), (37, 112, 187), (37, 112, 188), (37, 113, 189), (37, 114, 190), (38, 114, 191), (38, 115, 192), (38, 115, 193), (38, 116, 194), (38, 116, 195), (39, 117, 195), (39, 118, 197), (39, 118, 198), (39, 119, 199), (39, 120, 200), (40, 120, 201), (40, 121, 202), (40, 121, 203), (40, 122, 204), (40, 123, 205), (41, 123, 206), (41, 124, 207), (41, 124, 208), (41, 125, 209), (41, 125, 210), (42, 126, 211), (42, 127, 211), (42, 127, 213), (42, 128, 214), (42, 129, 215), (43, 129, 216), (43, 130, 217), (43, 130, 218), (43, 131, 219), (43, 132, 220), (44, 132, 221), (44, 133, 222), (44, 133, 223), (44, 134, 224), (44, 135, 225), (45, 135, 226), (45, 136, 227), (45, 136, 227), (45, 137, 229), (45, 138, 230), (46, 138, 231), (46, 139, 232), (46, 139, 233), (46, 140, 234), (46, 140, 235), (47, 141, 236), (47, 142, 237), (47, 142, 238), (47, 143, 239), (47, 144, 240), (48, 144, 241), (48, 145, 242), (48, 145, 243), (48, 146, 243), (48, 147, 245), (49, 147, 246), (49, 148, 247), (49, 148, 248), (49, 149, 249), (49, 149, 250), (50, 150, 251), (50, 151, 252), (50, 151, 253), (50, 152, 254)]

Which is a list of all the color generated to create that color map. It's custom though, matplotlib was just used to plot it.

EDIT: Just a note to explain how this is achieved. RGB gives you a value for Red, Green and Blue. HSL (HSV) on the other hand gives you hue, saturation, and lightness (value). So if you convert your color from RGB into HSL and than run the whole spectrum of lightness you'll obtain the dark to light values of a color (for example blue will always remain blue, although lighter and darker).