Gray-scale operation on nodes While I was  playing with nodes I wanted to check which gray-scale algorithm blender use. And i came up with this node system: 
 
But I got this strange result. Where did i make mistake?
The luminance weights are intended to be summed. That is, for any given colourspace, multiply each light by its luminance position, and sum the result with the other two. You will end up with equal values across all three channels.

For REC.709 lights, which are the lights that define the sRGB specification, the formula would be:

Y = 0.2126*R + 0.7152*G + 0.0722*B