This patch is a continuation of the work done in D1082
In a private email from Charles Poynton:
Using [0.299, 0.587, 0.114] as _luminance_ coefficients (that is, with radiometric quantities) would be unwise, as modern displays typically do not have the highly chromatic green of 1953, and Ill. C is deprecated today.
So basically everywhere in Blender we are using BT.709 but here we are using BT.601
Here is a sample file: