# py_colorize.py

  def _limit(x):
      if x > 255.: x = 255
      if x < 0.:   x = 0
      return chr(int(x))

  def adduv(bwdata, uvdata):
      size = len(bwdata)
      x = []
      for i in xrange(size):
          r = float(ord(uvdata[i*3]))
          g = float(ord(uvdata[i*3+1]))
          b = float(ord(uvdata[i*3+2]))
          u = -0.169 * r - 0.331 * g + 0.500 *b;
          v =  0.500 * r - 0.419 * g - 0.081 *b;
          y = float(ord(bwdata[i]))
          r = _limit(y             + 1.402 * v)
          g = _limit(y - 0.344 * u - 0.714 * v)
          b = _limit(y + 1.772 * u)
          x.append(r+g+b)
      return ''.join(x)

  # Cython test
  # cy_colorize.pyx

  def _limit(x):
      if x > 255.: x = 255
      if x < 0.:   x = 0
      return chr(int(x))

  def adduv(bwdata, uvdata):
      cdef int size, i
      size = len(bwdata)
      x = []
      for i in xrange(size):
          r = float(ord(uvdata[i*3]))
          g = float(ord(uvdata[i*3+1]))
          b = float(ord(uvdata[i*3+2]))
          u = -0.169 * r - 0.331 * g + 0.500 *b;
          v =  0.500 * r - 0.419 * g - 0.081 *b;
          y = float(ord(bwdata[i]))
          r = _limit(y             + 1.402 * v)
          g = _limit(y - 0.344 * u - 0.714 * v)
          b = _limit(y + 1.772 * u)
          x.append(r+g+b)
      return ''.join(x)

  /* c_colorize.c */
  #include <Python.h>
  #include <stdlib.h>
  #include <math.h>

  static unsigned char
  limit(double x)
  {
      if (x > 255.) x = 255.;
      if (x < 0.)   x = 0.;
      return (unsigned char)x;
  }

  static PyObject *
  c_colorize_adduv(PyObject *self, PyObject *args)
  {
      long i, size, dummy;
      double r, g, b, u, v, y;
      unsigned char *bwdata, *uvdata, *cldata, *cl;

      if (!PyArg_ParseTuple(args, "s#s#", 
                              &bwdata, &size, &uvdata, &dummy))
          return NULL;
      if ((cldata = malloc(3*size)) == NULL)
          return NULL;
      cl = cldata;
      for (i = 0; i < size; i++) {
          r = (double)(*uvdata++);
          g = (double)(*uvdata++);
          b = (double)(*uvdata++);
          u = -0.169 * r - 0.331 * g + 0.500 *b;
          v =  0.500 * r - 0.419 * g - 0.081 *b;
          y = (double)(*bwdata++);
          *cldata++ = limit(y             + 1.402 * v);
          *cldata++ = limit(y - 0.344 * u - 0.714 * v);
          *cldata++ = limit(y + 1.772 * u);
      }
      return Py_BuildValue("s#", cl, size*3);
  }

  static PyMethodDef c_colorizeMethods[] = {
      {"adduv", c_colorize_adduv, METH_VARARGS, "adduv(bwdata, uvdata)"},
      {NULL, NULL, 0, NULL}
  };

  PyMODINIT_FUNC
  initc_colorize(void)
  {
      (void) Py_InitModule("c_colorize", c_colorizeMethods);
  }

  import Image
  from py_colorize import adduv as py_adduv
  from cy_colorize import adduv as cy_adduv
  from c_colorize import adduv as c_adduv
  import time

  m = Image.open('sample.gif')
  m = m.convert('L')
  c = Image.open('sample.jpg')
  md = m.tostring()
  cd = c.tostring()
  # python
  t = time.time()
  xd = py_adduv(md, cd)
  print time.time() - t 
  x = Image.fromstring('RGB', m.size, xd)
  x.save('sample-py.jpg')
  # cython
  t = time.time()
  xd = cy_adduv(md, cd)
  print time.time() - t
  x = Image.fromstring('RGB', m.size, xd)
  x.save('sample-cy.jpg')
  # c
  t = time.time()
  xd = c_adduv(md, cd)
  print time.time() - t
  x = Image.fromstring('RGB', m.size, xd)
  x.save('sample-c.jpg')

  $ python testcol.py 
  1.12569904327
  0.657740831375
  0.00496792793274