Definitions for "Solarize"
To injure by too long exposure to the light of the sun in the camera; to burn.
To become injured by undue or too long exposure to the sun's rays in the camera; -- an older term now replaced by overexpose.
become overepxosed; "The film solarized"
verb: reverse some of the tones of an image and introduce pronounced outlines of highlights
reverse some of the tones of (a negative or print) and introduce pronounced outlines of highlights, by exposing it briefly to light, then washing and redeveloping it
Keywords:  negate, threshold, pixels, above, level
negate all pixels above the threshold level