HSV color generator

color.py

def rgb2hsv(rgb):
    """Converts RGB to HSV.

    Note that H may be None when S is 0 (for grey colors).
    """
    r, g, b = rgb
    minimum = min(r, g, b)
    maximum = max(r, g, b)

    v = maximum

    delta = maximum - minimum

    if delta != 0:
        s = delta / maximum
    else:
        # h is undefined
        s = 0
        h = None
        return (h, s, v)

    if r == maximum:
        h = (g - b) / delta     # between yellow & magenta
    elif g == maximum:
        h = 2 + (b - r) / delta # between cyan & yellow
    else:
        h = 4 + (r - g) / delta # between magenta & cyan

    h *= 60 # degrees

    if h < 0:
        h += 360

    return (h, s, v)


def hsv2rgb(hsv):
    """Converts HSV to RGB.

    Accepts H=None when S=0.
    """
    h, s, v = hsv

    if s == 0:
        return (v, v, v)

    h /= 60
    i = int(h)
    f = h - i   # factorial part
    p = v * (1 - s)
    q = v * (1 - s * f)
    t = v * (1 - s * (1 - f))

    if i == 0:
        return (v, t, p)
    elif i == 1:
        return (q, v, p)
    elif i == 2:
        return (p, v, t)
    elif i == 3:
        return (p, q, v)
    elif i == 4:
        return (t, p, v)
    else: # i == 5
        return (v, p, q)


class ColorGenerator(object):
    def __init__(self, h=8, v=2):
        self.colors_per_value = h
        self.value_planes = v

    def get_color_hsv(self, pos):
        h = 360.0 / self.colors_per_value * (pos % self.colors_per_value)
        s = 1.0
        v = pos // self.colors_per_value
        if v >= self.value_planes:
            raise ValueError
        v = 1.0 - (1.0/self.value_planes) * v
        print "h, s, v: %f, %f, %f" % (h, s, v)
        return (h, s, v)

    def get_color_rgb(self, pos):
        return hsv2rgb(self.get_color_hsv(pos))

    get_color = get_color_rgb

    def __iter__(self):
        def generator():
            pos = 0
            try:
                while True:
                    yield self.get_color(pos)
                    pos += 1
            except ValueError:
                raise StopIteration
        return generator()


from PyQt4 import QtGui


if __name__ == '__main__':
    app = QtGui.QApplication([])

    w = QtGui.QWidget()
    w.show()

    l = QtGui.QVBoxLayout()
    w.setLayout(l)

    for r, g, b in ColorGenerator(12, 2):
        c = QtGui.QWidget()
        c.setStyleSheet('background-color: rgb(%d, %d, %d);' % (
                r * 255, g * 255, b * 255))
        l.addWidget(c)

    app.exec_()