const lowp float a7contrast   = %contrast%;    // modify to adjust contrast (default: 1.0, lower: <1.0, higher: >1.0)
const lowp float a7brightness = %brightness%;    // modify to adjust brightness (default: 0.0, darker: <0.0, brighter: >0.0)
const lowp float a7gamma      = %gamma%;    // modify to adjust gamma correction (default: 1.0, darker: <1.0, brighter: >1.0)

