Inkscape - SoftLight Inverse effect

import coloreffect
import math

class C(coloreffect.ColorEffect):
  def colmod(self,r,g,b):
    l = (max(r,g,b)+min(r,g,b))/2

    l = float(l) / 255
    r = float(r) / 255
    g = float(g) / 255
    b = float(b) / 255

    l = 1 - l

    if l < 0.5:
      r = (2 * l - 1) * (r - r * r) + r
    else:
      r = (2 * l - 1) * (math.sqrt(r) - r) + r

    if l < 0.5:
      g = (2 * l - 1) * (g - g * g) + g
    else:
      g = (2 * l - 1) * (math.sqrt(g) - g) + g

    if l < 0.5:
      b = (2 * l - 1) * (b - b * b) + b
    else:
      b = (2 * l - 1) * (math.sqrt(b) - b) + b

    r = int(r * 255)
    g = int(g * 255)
    b = int(b * 255)

    return '%02x%02x%02x' % (r,g,b)

c = C()
c.affect()