adjust = function(c, thresh) {
            var b = c.brightness();
            if (b > thresh) {
              c.setBrightness(0.1 + b * 0.25);
            } else {
              c.setBrightness(1.0 - b * 0.25);
            }
            return c;
          }
Creates a new instance
@param {Number} [theta] optionally provide an angle in degrees, defaults to 10
@param {Number} [contrast] optionally provide a contrast, defaults to 0.25