[转]OpenCV学习--saturate_cast防止数据溢出

//使用图像混合例子中的C语言版本演示  
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);  

这里加入了溢出保护，结果如下

 

//没加入溢出保护  
    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); 

大致的原理应该如下

if(data<0)  
        data=0;  
else if(data>255)  
    data=255;