How to generate random 'greenish' colors

Question

Anyone have any suggestions on how to make randomized colors that are all greenish? Right now I\'m generating the colors by this:

color = (randint(100, 200),         


        

Answer 1

As others have suggested, generating random colours is much easier in the HSV colour space (or HSL, the difference is pretty irrelevant for this)

So, code to generate random "green'ish" colours, and (for demonstration purposes) display them as a series of simple coloured HTML span tags:

#!/usr/bin/env python2.5
"""Random green colour generator, written by dbr, for
http://stackoverflow.com/questions/1586147/how-to-generate-random-greenish-colors
"""

def hsv_to_rgb(h, s, v):
    """Converts HSV value to RGB values
    Hue is in range 0-359 (degrees), value/saturation are in range 0-1 (float)

    Direct implementation of:
    http://en.wikipedia.org/wiki/HSL_and_HSV#Conversion_from_HSV_to_RGB
    """
    h, s, v = [float(x) for x in (h, s, v)]

    hi = (h / 60) % 6
    hi = int(round(hi))

    f = (h / 60) - (h / 60)
    p = v * (1 - s)
    q = v * (1 - f * s)
    t = v * (1 - (1 - f) * s)

    if hi == 0:
        return v, t, p
    elif hi == 1:
        return q, v, p
    elif hi == 2:
        return p, v, t
    elif hi == 3:
        return p, q, v
    elif hi == 4:
        return t, p, v
    elif hi == 5:
        return v, p, q

def test():
    """Check examples on..
    http://en.wikipedia.org/wiki/HSL_and_HSV#Examples
    ..work correctly
    """
    def verify(got, expected):
        if got != expected:
            raise AssertionError("Got %s, expected %s" % (got, expected))

    verify(hsv_to_rgb(0, 1, 1), (1, 0, 0))
    verify(hsv_to_rgb(120, 0.5, 1.0), (0.5, 1, 0.5))
    verify(hsv_to_rgb(240, 1, 0.5), (0, 0, 0.5))

def main():
    """Generate 50 random RGB colours, and create some simple coloured HTML
    span tags to verify them.
    """
    test() # Run simple test suite

    from random import randint, uniform

    for i in range(50):
        # Tweak these values to change colours/variance
        h = randint(90, 140) # Select random green'ish hue from hue wheel
        s = uniform(0.2, 1)
        v = uniform(0.3, 1)

        r, g, b = hsv_to_rgb(h, s, v)

        # Convert to 0-1 range for HTML output
        r, g, b = [x*255 for x in (r, g, b)]

        print "  " % (r, g, b)

if __name__ == '__main__':
    main()

The output (when viewed in a web-browser) should look something along the lines of:

Edit: I didn't know about the colorsys module. Instead of the above hsv_to_rgb function, you could use colorsys.hsv_to_rgb, which makes the code much shorter (it's not quite a drop-in replacement, as my hsv_to_rgb function expects the hue to be in degrees instead of 0-1):

#!/usr/bin/env python2.5
from colorsys import hsv_to_rgb
from random import randint, uniform

for x in range(50):
    h = uniform(0.25, 0.38) # Select random green'ish hue from hue wheel
    s = uniform(0.2, 1)
    v = uniform(0.3, 1)

    r, g, b = hsv_to_rgb(h, s, v)

    # Convert to 0-1 range for HTML output
    r, g, b = [x*255 for x in (r, g, b)]

    print "  " % (r, g, b)