This is a name for the contrast or picture control used in this book. It describes a function that is otherwise not clearly spelled out in names of controls used on monitors. It is not a term that is found on a monitor control. (As "black level" clearly defines the brightness control function, "white level" more clearly defines the contrast or picture control function.)
WHITE LEVEL CONTROL
Meaning of WHITE LEVEL CONTROL in English
Film and video English vocabulary. Английский словарь фильмов и видео. 2012