Index: source/blender/compositor/operations/COM_KeyingOperation.cpp
===================================================================
--- source/blender/compositor/operations/COM_KeyingOperation.cpp	(revision 51301)
+++ source/blender/compositor/operations/COM_KeyingOperation.cpp	(working copy)
@@ -50,7 +50,7 @@
 
 	float val = screen_balance * pixelColor[min_channel] + (1.0f - screen_balance) * pixelColor[max_channel];
 
-	return (pixelColor[primary_channel] - val) * fabsf(1.0f - val);
+	return pixelColor[primary_channel] - val;
 }
 
 KeyingOperation::KeyingOperation() : NodeOperation()
@@ -87,35 +87,13 @@
 
 	int primary_channel = get_pixel_primary_channel(screenColor);
 
-	if (pixelColor[primary_channel] > 1.0f) {
-		/* overexposure doesn't happen on screen itself and usually happens
-		 * on light sources in the shot, this need to be checked separately
-		 * because saturation and falloff calculation is based on the fact
-		 * that pixels are not overexposured
-		 */
-		output[0] = 1.0f;
-	}
-	else {
-		float saturation = get_pixel_saturation(pixelColor, this->m_screenBalance, primary_channel);
-		float screen_saturation = get_pixel_saturation(screenColor, this->m_screenBalance, primary_channel);
+	float saturation = get_pixel_saturation(pixelColor, this->m_screenBalance, primary_channel);
+	float screen_saturation = get_pixel_saturation(screenColor, this->m_screenBalance, primary_channel);
 
-		if (saturation < 0) {
-			/* means main channel of pixel is different from screen,
-			 * assume this is completely a foreground
-			 */
-			output[0] = 1.0f;
-		}
-		else if (saturation >= screen_saturation) {
-			/* matched main channels and higher saturation on pixel
-			 * is treated as completely background
-			 */
-			output[0] = 0.0f;
-		}
-		else {
-			/* nice alpha falloff on edges */
-			float distance = 1.0f - saturation / screen_saturation;
-
-			output[0] = distance;
-		}
-	}
+	float key = 1.0f - saturation / screen_saturation;
+	float dR = pixelColor[0] - screenColor[0];
+	float dG = pixelColor[1] - screenColor[1];
+	float dB = pixelColor[2] - screenColor[2];
+	key = MAX4(key, dR, dG, dB);
+	output[0] = CLAMPIS(key, 0.0f, 1.0f);
 }