灰度拉伸是分段进行线性变换，对红色，绿色，蓝色三分量进行统一的分段线性变换，以增强图像对比度-Gray-scale stretch is sub-linear transformation of the red, green, blue three-component unified piecewise linear transformation, to enhance the image contrast

灰度图像 对比度增强 线性拉伸 只针对8比特图像-Gray-scale image contrast enhancement linear stretch

实现影像镶嵌，并且进行反差调整和线性拉伸-Achieve image mosaic, and the contrast adjustment and linear stretch