diff -r 26c8c43dd774 Lib/colorsys.py
--- a/Lib/colorsys.py	Fri Mar 16 22:51:00 2012 -0400
+++ b/Lib/colorsys.py	Fri Mar 16 21:10:01 2012 -0700
@@ -33,17 +33,26 @@
 # YIQ: used by composite video signals (linear combinations of RGB)
 # Y: perceived grey level (0.0 == black, 1.0 == white)
 # I, Q: color components
+#
+# There are a great many versions of the constants used in these
+# formulae.  The ones in this library provide results which are 
+# compatible with similar functions in Matlab.
+#
+# Ref:
+#   http://www.mathworks.com/help/toolbox/images/ref/ntsc2rgb.html
+#   http://www.mathworks.com/help/toolbox/images/ref/rgb2ntsc.html
 
 def rgb_to_yiq(r, g, b):
-    y = 0.30*r + 0.59*g + 0.11*b
-    i = 0.60*r - 0.28*g - 0.32*b
-    q = 0.21*r - 0.52*g + 0.31*b
+    y = 0.299*r + 0.587*g + 0.114*b
+    i = 0.596*r - 0.274*g - 0.322*b
+    q = 0.211*r - 0.523*g + 0.312*b
     return (y, i, q)
 
 def yiq_to_rgb(y, i, q):
-    r = y + 0.948262*i + 0.624013*q
-    g = y - 0.276066*i - 0.639810*q
-    b = y - 1.105450*i + 1.729860*q
+    r = y + 0.956*i + 0.621*q
+    g = y - 0.272*i - 0.647*q
+    b = y - 1.106*i + 1.703*q
+    
     if r < 0.0:
         r = 0.0
     if g < 0.0:
diff -r 26c8c43dd774 Lib/test/test_colorsys.py
--- a/Lib/test/test_colorsys.py	Fri Mar 16 22:51:00 2012 -0400
+++ b/Lib/test/test_colorsys.py	Fri Mar 16 21:10:01 2012 -0700
@@ -8,12 +8,43 @@
 
 class ColorsysTest(unittest.TestCase):
 
-    def assertTripleEqual(self, tr1, tr2):
+    def assertTripleEqual(self, tr1, tr2, places=7):
         self.assertEqual(len(tr1), 3)
         self.assertEqual(len(tr2), 3)
-        self.assertAlmostEqual(tr1[0], tr2[0])
-        self.assertAlmostEqual(tr1[1], tr2[1])
-        self.assertAlmostEqual(tr1[2], tr2[2])
+        self.assertAlmostEqual(tr1[0], tr2[0], places)
+        self.assertAlmostEqual(tr1[1], tr2[1], places)
+        self.assertAlmostEqual(tr1[2], tr2[2], places)
+
+    def test_rgb_to_yiq(self):
+        self.assertTripleEqual((0.0, 0.0, 0.0),
+                               colorsys.rgb_to_yiq(0.0, 0.0, 0.0))
+        self.assertTripleEqual((0.0747, 0.1490, 0.0529),
+                               colorsys.rgb_to_yiq(0.25, 0.0, 0.0), 3)
+        self.assertTripleEqual((0.1468, -0.0686, -0.1307),
+                               colorsys.rgb_to_yiq(0.0, 0.25, 0.0), 3)
+        self.assertTripleEqual((0.0285, -0.0804, 0.0779),
+                               colorsys.rgb_to_yiq(0.0, 0.0, 0.25), 3)
+
+    def test_yiq_to_rgb(self):
+        self.assertTripleEqual((0.0, 0.0, 0.0), 
+                               colorsys.yiq_to_rgb(0.0, 0.0, 0.0))
+        self.assertTripleEqual((0.25, 0.0, 0.0),
+                               colorsys.yiq_to_rgb(0.0747, 0.1490, 0.0529), 3)
+        self.assertTripleEqual((0.0, 0.25, 0.0),
+                               colorsys.yiq_to_rgb(0.1468, -0.0686, -0.1307), 3)
+        self.assertTripleEqual((0.0, 0.0, 0.25),
+                               colorsys.yiq_to_rgb(0.0285, -0.0804, 0.0779), 3)
+
+    def test_yiq_roundtrip(self):
+        for r in frange(0.0, 1.0, 0.2):
+            for g in frange(0.0, 1.0, 0.2):
+                for b in frange(0.0, 1.0, 0.2):
+                    rgb = (r, g, b)
+                    self.assertTripleEqual(
+                        rgb,
+                        colorsys.yiq_to_rgb(*colorsys.rgb_to_yiq(*rgb)),
+                        2
+                    )
 
     def test_hsv_roundtrip(self):
         for r in frange(0.0, 1.0, 0.2):