Change from gamma 2.2 to the slightly more precise 1/0.45 as per BT.709. https://www.itu.int/rec/R-REC-BT.709-5-200204-I/en mentions a value of γ=0.45 for the conceptual non-linear precorrection of video signals. This is approximately the inverse of 2.22, and not 2.20 as the code had been using until now.