Opencv之saturate_cast防止數據溢出

原創

小木匠_

2020-02-20 21:30

在OpenCV學習中經常看見saturate_cast的使用，下面的代碼會展示它的作用，這個功能實現的是兩個圖像融合，作者提供了saturate_case的作用，同時比較了兩個方法的運行時間，後面會給出代碼和結果。

也可以原文 http://blog.csdn.net/mjlsuccess/article/details/12401839

一、staturate_cast的原理

大致的原理應該如
if(data<0) 
        data=0; 
elseif(data>255) 
    data=255;

二、關鍵語句，同時保護與不保護可以自己修改

//使用圖像混合例子中的C語言版本演示 
for (int i=0; i<src1.rows; i++) 
{ 
   const uchar* src1_ptr = src1.ptr<uchar>(i); 
   const uchar* src2_ptr = src2.ptr<uchar>(i); 
   uchar* dst_ptr  =dst.ptr<uchar>(i); 
   for (int j=0; j<src1.cols*nChannels; j++) 
   { 
       dst_ptr[j] = saturate_cast<uchar>(src1_ptr[j]*alpha +src2_ptr[j]*beta + gama);//gama = -100, alpha = beta = 0.5 
//     dst_ptr[j] = (src1_ptr[j]*alpha + src2_ptr[j]*beta + gama); 
   } 
} 
imshow("output2",dst);

//沒加入溢出保護 
   for (int i=0; i<src1.rows; i++) 
   { 
       const uchar* src1_ptr = src1.ptr<uchar>(i); 
       const uchar* src2_ptr = src2.ptr<uchar>(i); 
       uchar* dst_ptr  =dst.ptr<uchar>(i); 
       for (int j=0; j<src1.cols*nChannels; j++) 
       { 
//         dst_ptr[j] = saturate_cast<uchar>(src1_ptr[j]*alpha +src2_ptr[j]*beta + gama);//gama = -100, alpha = beta = 0.5 
           dst_ptr[j] = (src1_ptr[j]*alpha + src2_ptr[j]*beta + gama); 
       } 
   } 
imshow("output2",dst);

三、整體代碼

#include "StdAfx.h"  
#include "blending.h"  
using namespace std;  
using namespace cv;  
void blending_test()  
{  
    Mat src1, src2, dst;  
    double alpha = 0.5;  
    double beta = 1-alpha;  
  
    src1 = imread("LinuxLogo.jpg");  
    src2 = imread("WindowsLogo.jpg");  
  
    if(!src1.data) cout<<"error loading src1"<<endl;  
    if(!src2.data) cout<<"Error loading src2"<<endl;  
  
    addWeighted(src1, alpha, src2, beta, 0.0, dst);  
  
    imshow("output1", dst);  
  
//  waitKey(0);  
}  
//C語言自己實現  
void blending()  
{  
    Mat src1, src2, dst;  
    double alpha = 0.5;  
    double beta = 1-alpha;  
    double gama = 0;  
  
    src1 = imread("LinuxLogo.jpg");  
    src2 = imread("WindowsLogo.jpg");  
    //判斷兩幅圖片是否相同  
    CV_Assert(src1.depth() == CV_8U);  
    CV_Assert(src1.depth() == src2.depth());  
    CV_Assert(src1.size() == src2.size());  
    //爲dst申請內存  
    dst.create(src1.size(), src1.type());  
  
    const int nChannels = src1.channels();  
  
    if(!src1.data) cout<<"error loading src1"<<endl;  
    if(!src2.data) cout<<"Error loading src2"<<endl;  
  
    for (int i=0; i<src1.rows; i++)  
    {  
        const uchar* src1_ptr = src1.ptr<uchar>(i);  
        const uchar* src2_ptr = src2.ptr<uchar>(i);  
        uchar* dst_ptr  = dst.ptr<uchar>(i);  
        for (int j=0; j<src1.cols*nChannels; j++)  
        {  
            dst_ptr[j] = src1_ptr[j]*alpha + src2_ptr[j]*beta + gama;  
        }  
    }  
    imshow("output2",dst);  
  
//  cvWaitKey(0);  
}

int main(int argc, char* argv[])   
{   
    double t;  
    t = (double)getTickCount();   
    blending_test();      
    t = 1000*((double)getTickCount() - t)/getTickFrequency();  
    cout<<"庫函數時間："<<t<<endl;  
  
    t = (double)getTickCount();  
    blending();  
    t = 1000*((double)getTickCount() - t)/getTickFrequency();  
    cout<<"C語言實現："<<t<<endl;  
  
    cvWaitKey(0);  
    return 0;  
}

結果如下：第一副是加保護，第二幅是不加保護，第三幅是運行時間的對比