帧差法动态获取阈值：灰度直方图分析

int Calculate(IplImage * gray_plane)
{
int * pMax = new int[512];
int max = 0;
     int hist_size = 512;    //直方图尺寸  
     int hist_height = 256;  
     float range[] = {0,255};  //灰度级的范围  
     float* ranges[]={range};  
     //创建一维直方图，统计图像在[0 255]像素的均匀分布  
     CvHistogram* gray_hist = cvCreateHist(1,&hist_size,CV_HIST_ARRAY,ranges,1);  
     //计算灰度图像的一维直方图  
     cvCalcHist(&gray_plane,gray_hist,0,0);
     //归一化直方图  
     cvNormalizeHist(gray_hist,1.0);  
     int scale = 2;  
     //创建一张一维直方图的“图”，横坐标为灰度级，纵坐标为像素个数（*scale）  
     IplImage* hist_image = cvCreateImage(cvSize(hist_size*scale,hist_height),8,3);  
     cvZero(hist_image);  
     //统计直方图中的最大直方块  
     float max_value = 0;  
     cvGetMinMaxHistValue(gray_hist, 0,&max_value,0,pMax);
     //分别将每个直方块的值绘制到图中  
     for(int i=0;i<hist_size;i+=2)  
     {  
         float bin_val = cvQueryHistValue_1D(gray_hist,i); //像素i的概率  
         int intensity = cvRound(bin_val*hist_height/max_value);  //要绘制的高度  
if(i == pMax[0] + 20) max = i;
         cvRectangle(hist_image,  
             cvPoint(i*scale,hist_height-1),  
             cvPoint((i+1)*scale - 1, hist_height - intensity),