tiny tracer no vector class

#tiny-tracer-no-vector-class. 2x speedup.

#original pastebin: http://pastebin.com/F8f5GHJZ
#original thread:   http://www.reddit.com/r/tinycode/comments/169ri9/ray_tracer_in_140_sloc_of_python_with_picture/

from math import sqrt, pow, pi
import Image, sys

def vMul(a,b):  return [ a[0]*b[0], a[1]*b[1], a[2]*b[2] ]
def vMulD(a,b): return [ a[0]*b,    a[1]*b,    a[2]*b    ]
def vAdd(a,b):  return [ a[0]+b[0], a[1]+b[1], a[2]+b[2] ]
def vAddD(a,b): return [ a[0]+b,    a[1]+b,    a[2]+b    ]
def vSub(a,b):  return [ a[0]-b[0], a[1]-b[1], a[2]-b[2] ]
def vSubD(a,b): return [ a[0]-b,    a[1]-b,    a[2]-b    ]
def vNeg(a):    return [-a[0],     -a[1],     -a[2]      ]
def vPow(a,b):  return [ a[0]**b,   a[1]**b,   a[2]**b   ]

def vDot(a,b):  return a[0]*b[0] + a[1]*b[1] + a[2]*b[2]
def vSqr(a):    return vDot(a,a)
def vLen(a):    return sqrt(vSqr(a))
def vNorm(a):   return vMulD(a, 1.0/vLen(a))

class Sphere( object ):

    def __init__(self, center, radius, color):
        self.c = center
        self.r = radius
        self.col = color

    def intersection(self, l):
        q = vDot(l.d, vSub(l.o, self.c))**2 - vSqr(vSub(l.o, self.c)) + self.r**2
        if q < 0:
            return Intersection( [0,0,0], -1, [0,0,0], self)
        else:
            d = -vDot(l.d, vSub(l.o, self.c))
            d1 = d - sqrt(q)
            d2 = d + sqrt(q)
            if 0 < d1 and ( d1 < d2 or d2 < 0):
                return Intersection(vAdd(l.o,vMulD(l.d,d1)), d1, self.normal(vAdd(l.o,vMulD(l.d,d1))), self)
            elif 0 < d2 and ( d2 < d1 or d1 < 0):
                return Intersection(vAdd(l.o,vMulD(l.d,d2)), d2, self.normal(vAdd(l.o,vMulD(l.d,d2))), self)
            else:
                return Intersection( [0,0,0], -1, [0,0,0], self)

    def normal(self, b):
        return vNorm(vSub(b,self.c))

class Plane( object ):

    def __init__(self, point, normal, color):
        self.n = normal
        self.p = point
        self.col = color

    def intersection(self, l):
        d = vDot(l.d, self.n)
        if d == 0:
            return Intersection( [0,0,0], -1, vector[0,0,0], self)
        else:
            d = vDot(vSub(self.p,l.o),self.n) / d
            return Intersection(vAdd(l.o,vMulD(l.d,d)), d, self.n, self)

class Ray( object ):

    def __init__(self, origin, direction):
        self.o = origin
        self.d = direction

class Intersection( object ):

    def __init__(self, point, distance, normal, obj):
        self.p = point
        self.d = distance
        self.n = normal
        self.obj = obj

def testRay(ray, objects, ignore=None):
    intersect = Intersection( [0,0,0], -1, [0,0,0], None)

    for obj in objects:
        if obj is not ignore:
            currentIntersect = obj.intersection(ray)
            if currentIntersect.d > 0 and intersect.d < 0:
                intersect = currentIntersect
            elif 0 < currentIntersect.d < intersect.d:
                intersect = currentIntersect
    return intersect

def trace(ray, objects, light, maxRecur):
    if maxRecur < 0:
        return [0,0,0]
    intersect = testRay(ray, objects)
    if intersect.d == -1:
        col = [AMBIENT,AMBIENT,AMBIENT]
    elif vDot(intersect.n, vSub(light,intersect.p)) < 0:
        col = vMulD(intersect.obj.col, AMBIENT)
    else:
        lightRay = Ray(intersect.p, vNorm(vSub(light,intersect.p)))
        if testRay(lightRay, objects, intersect.obj).d == -1:
            lightIntensity = 1000.0/(4*pi*vLen(vSub(light,intersect.p))**2)
            col = vMulD(intersect.obj.col, max(vDot(vNorm(intersect.n),vMulD(vNorm(vSub(light,intersect.p)),lightIntensity)), AMBIENT))
        else:
            col = vMulD(intersect.obj.col, AMBIENT)
    return col

def gammaCorrection(color,factor):
    return (int(pow(color[0]/255.0,factor)*255),
            int(pow(color[1]/255.0,factor)*255),
            int(pow(color[2]/255.0,factor)*255))

AMBIENT = 0.1
GAMMA_CORRECTION = 1/2.2
MAX_RECURSION = 10

#these are left global so we don't have to pass them to apply_async each pixel
objs = [ Sphere([-2, 0,-10], 2,   [0,255,0]),
         Sphere([ 2, 0,-10], 3.5, [255,0,0]),
         Sphere([ 0,-4,-10], 3,   [0,0,255]),
         Plane([0,0,-12], [0,0,1], [255,255,255]) ]

lightSource = [0,10,0]
cameraPos = [0,0,20]

def main():
    img = Image.new("RGB",(500,500))
    for x in range(500):
        results = []
        for y in range(500):
            ray =  Ray(cameraPos, vNorm(vSub([x/50.0-5, y/50.0-5, 0], cameraPos)))
            col = trace(ray, objs, lightSource, MAX_RECURSION)
            img.putpixel((x,499-y),gammaCorrection(col,GAMMA_CORRECTION))
        print x
        sys.stdout.flush()
    img.save("trace.bmp","BMP")

if __name__ == '__main__':
    main()