The knee sets the level at which the auto exposure begins dealing with blowouts. If the knee is set to low, then the camera begins reducing exposure well before there is a danger of blowout. High lets the exposure get closure to blowout level and, so, there is a greater danger of blowout. When set to Auto, the camera decides at what point it begins dealing with blowout.
However, if the gamma is set to CINELIKE, the knee is disabled and it doesn't matter what it's setting is.
