第二节记录一下自己学习图像遍历的一点点代码，摘自《opencv2编程手册》（张静译）

第一个代码是最简单的强行修改像素（添加椒盐噪声）

1 #include 
     
       2 #include 
      
        3  4 void salt(cv::Mat &image, int n) { 5  6     int i,j; 7     for (int k=0; k
       
        (j,i)= 255; 17 18         } else if (image.channels() == 3) { // color image19 20             image.at
        
         (j,i)[0]= 255; 21             image.at
         
          (j,i)[1]= 255; 22             image.at
          
           (j,i)[2]= 255; 23 }24 }25 }26 27 int main()28 {29 srand(cv::getTickCount()); // init random number generator30 31 cv::Mat image= cv::imread("../cat.jpg",0);32 33 salt(image,3000);34 35 cv::namedWindow("Image");36 cv::imshow("Image",image);37 38 cv::imwrite("salted.bmp",image);39 40 cv::waitKey(5000);41 42 return 0;43 }
          
         
        
       
      
     

书上的注释为image.<unchar>(j,i)=255，将i行j列的数据变为白色。

第二个程序才开始真正的遍历

 

1 #include 
     
       2 #include 
      
        3  4 void colorReduce0(cv::Mat &image, int div=64) { 5  6       int nl= image.rows; // 每行的像素数目 7       int nc= image.cols * image.channels(); // total number of elements per line 8                9       for (int j=0; j
       
        (j);//此句返回j行的首地址12 13           for (int i=0; i
       
      
     

这个程序写的是对小猫的颜色进行缩减,效果如下

另，对像素的操作可以采用

*data++ =*data/div*div + div/2

来书写

 接下来，我就继续看第二种颜色缩进的算法

1 void colorReduce1(cv::Mat &image, int div=64) { 2  3       int nl= image.rows; // number of lines 4       int nc= image.cols * image.channels(); // total number of elements per line 5                6       for (int j=0; j
     
      (j); 9 10           for (int i=0; i
     

效果如下

到这里我就整个人变傻了。两个算法不是一样的吗-  -，为什么效果差别这么大-  -

算了，还是将人家给的代码放出吧，希望有大神指正

#include 
     
      #include 
      
       #include 
       
        // using .ptr and []void colorReduce0(cv::Mat &image, int div=64) {      int nl= image.rows; // number of lines      int nc= image.cols * image.channels(); // total number of elements per line                    for (int j=0; j
        
         (j);          for (int i=0; i
         
          (j);          for (int i=0; i
          
           (j); for (int i=0; i
           
            (log(static_cast
            
             (div))/log(2.0)); // mask used to round the pixel value uchar mask= 0xFF<
             
              (j); for (int i=0; i
              
               (log(static_cast
               
                (div))/log(2.0)); int step= image.step; // effective width // mask used to round the pixel value uchar mask= 0xFF<
                
                 (log(static_cast
                 
                  (div))/log(2.0)); // mask used to round the pixel value uchar mask= 0xFF<
                  
                   (j); for (int i=0; i
                   
                    (log(static_cast
                    
                     (div))/log(2.0)); // mask used to round the pixel value uchar mask= 0xFF<
                     
                      (j); for (int i=0; i
                      
                       (log(static_cast
                       
                        (div))/log(2.0)); // mask used to round the pixel value uchar mask= 0xFF<
                        
                         (j); for (int i=0; i
                         
                          ::iterator it= image.begin
                          
                           (); cv::Mat_
                           
                            ::iterator itend= image.end
                            
                             (); for ( ; it!= itend; ++it) { // process each pixel --------------------- (*it)[0]= (*it)[0]/div*div + div/2; (*it)[1]= (*it)[1]/div*div + div/2; (*it)[2]= (*it)[2]/div*div + div/2; // end of pixel processing ---------------- }}// using Mat_ iterator and bitwisevoid colorReduce9(cv::Mat &image, int div=64) { // div must be a power of 2 int n= static_cast
                             
                              (log(static_cast
                              
                               (div))/log(2.0)); // mask used to round the pixel value uchar mask= 0xFF<
                               
                                ::iterator it= image.begin
                                
                                 (); cv::Mat_
                                 
                                  ::iterator itend= image.end
                                  
                                   (); // scan all pixels for ( ; it!= itend; ++it) { // process each pixel --------------------- (*it)[0]= (*it)[0]&mask + div/2; (*it)[1]= (*it)[1]&mask + div/2; (*it)[2]= (*it)[2]&mask + div/2; // end of pixel processing ---------------- }}// using MatIterator_ void colorReduce10(cv::Mat &image, int div=64) { // get iterators cv::Mat_
                                   
                                     cimage= image; cv::Mat_
                                    
                                     ::iterator it=cimage.begin(); cv::Mat_
                                     
                                      ::iterator itend=cimage.end(); for ( ; it!= itend; it++) { // process each pixel --------------------- (*it)[0]= (*it)[0]/div*div + div/2; (*it)[1]= (*it)[1]/div*div + div/2; (*it)[2]= (*it)[2]/div*div + div/2; // end of pixel processing ---------------- }}void colorReduce11(cv::Mat &image, int div=64) { int nl= image.rows; // number of lines int nc= image.cols; // number of columns for (int j=0; j
                                      
                                       (j,i)[0]= image.at
                                       
                                        (j,i)[0]/div*div + div/2; image.at
                                        
                                         (j,i)[1]= image.at
                                         
                                          (j,i)[1]/div*div + div/2; image.at
                                          
                                           (j,i)[2]= image.at
                                           
                                            (j,i)[2]/div*div + div/2; // end of pixel processing ---------------- } // end of line }}// with input/ouput imagesvoid colorReduce12(const cv::Mat &image, // input image cv::Mat &result, // output image int div=64) { int nl= image.rows; // number of lines int nc= image.cols ; // number of columns // allocate output image if necessary result.create(image.rows,image.cols,image.type()); // created images have no padded pixels nc= nc*nl; nl= 1; // it is now a 1D array int n= static_cast
                                            
                                             (log(static_cast
                                             
                                              (div))/log(2.0)); // mask used to round the pixel value uchar mask= 0xFF<
                                              
                                               (j); const uchar* idata= image.ptr
                                               
                                                (j); for (int i=0; i
                                                
                                                 (log(static_cast
                                                 
                                                  (div))/log(2.0)); // mask used to round the pixel value uchar mask= 0xFF<