调整对比度：首先设定一个阀值，通常是128；然后判断像素点的R，G，B值，凡是大于128的， 增加一个值，小于128的，减少一个值-Adjust the contrast: First, set a threshold, usually 128 then determine the pixel R, G, B values, all greater than 128, add a value smaller than 128, reduce the value