for循环的一种加速方法

原文：http://blog.csdn.net/CXP2205455256/article/details/42044107

一、源码如下：

 #include "stdafx.h"
 #include "cv.h"
 #include "highgui.h"
 #include

 using namespace cv;
 using namespace std;


 int _tmain(int argc, _TCHAR* argv[])
 {
     Mat srcImg = imread("D:\\Documents\\Desktop\\图像拼接测试图片\\11-over750.bmp", CV_LOAD_IMAGE_GRAYSCALE);
     Mat dstImg1, dstImg2;
     srcImg.copyTo(dstImg1);
     srcImg.copyTo(dstImg2);

     uchar *srcData = srcImg.data;
     uchar *dstData1 = dstImg1.data;
     uchar *dstData2 = dstImg2.data;

     int size = srcImg.cols * srcImg.rows;
     int threshold = 122;
     int i;

     double ts1 = ( double )getTickCount();

     for(i = 0; i < size; ++i)
     {
         if(srcData[i] < threshold)
             dstData1[i] = 0;
         else
             dstData1[i] = 255;

     }//i

     double te1 = ( double )getTickCount();
     double tim1 = (te1 - ts1) * 1000.0 / getTickFrequency();

     double ts2 = ( double )getTickCount();

     i = 0;
     int size2 = size - 4;
     for(; i < size2; i += 4)
     {
         if(srcData[i] < threshold)
             dstData2[i] = 0;
         else
             dstData2[i] = 255;


         if(srcData[i + 1] < threshold)
             dstData2[i + 1] = 0;
         else
             dstData2[i + 1] = 255;


         if(srcData[i + 2] < threshold)
             dstData2[i + 2] = 0;
         else
             dstData2[i + 2] = 255;


         if(srcData[i + 3] < threshold)
             dstData2[i + 3] = 0;
         else
             dstData2[i + 3] = 255;


     }//i
     for(; i < size; ++i)
     {
         if(srcData[i] < threshold)
             dstData2[i] = 0;
         else
             dstData2[i] = 255;
     }//i

     double te2 = ( double )getTickCount();
     double tim2 = (te2 - ts2) * 1000.0 / getTickFrequency();

     cout << "     one loop:" << tim1 << endl;
     cout << "one four loop:" << tim2 << endl;

     namedWindow("img1");
     namedWindow("img2");
     imshow("img1", dstImg1);
     imshow("img2", dstImg2);

     waitKey(0);
     return 0;
 }

时间对比：

1、Debug下时间：

2、Release下时间：

结论：几乎加速一倍。