Stretches contrast on the image and normalize image from 0 to 1 The main difference of this function to the standard streching functions is that standard function finds global minimum and maximum on the image, then uses some low and high

利用差分法检测QRS波，代码完整，可以直接运行-QRSdifference and Tompkinsdifference

基于差分法的QRS波检测算法程序（PAN.J, TOMPKINS. W.J： A Real-Time QRS Detection Algorithm 对应的matlab程序）。-QRS detection algorithm program based difference method (PAN.J, TOMPKINS WJ:. " A Real-Time QRS Detection Algorithm" corresponding matlab program).