Emgu learning (4) use pointers to access image memory

Draw a color bar 10 in the first row of the original image

 

 

 

   class Program
    {
        static void Main(String[] args)
        {
            Mat img = CvInvoke.Imread(@"C:\Users\dell\Pictures\mach.jpg");

            CvInvoke.Imshow("draw", img);
            Mat dst = img.Clone();
            int row = img.Rows;
            int col = img.Cols * img.NumberOfChannels;
            Console.WriteLine("DepthType is " + dst.Depth+"and elementSize is"+dst.ElementSize);

            for (int i = 0; i < 20; i++)
                for (int j = 0; j < img.Cols;j++)
                {
                    SetAtB(dst, i, j, 0);
                    SetAtG(dst, i, j, 255);
                    SetAtR(dst, i, j, 0);

                }

            CvInvoke.Imshow("hello", dst);
                    CvInvoke.WaitKey(0);
            

        }
        private static IntPtr GetAt(Mat mat,int row,int col)
        {
            return mat.DataPointer + (row * mat.Cols + col) * mat.ElementSize;
        }
        private static void SetAtB(Mat mat, int row, int col, byte value)
        {
            Marshal.Copy(new byte[] { value }, 0, GetAt(mat, row, col), 1);
        }
        private static void SetAtG(Mat mat, int row, int col, byte value)
        {
            Marshal.Copy(new byte[] { value }, 0, GetAt(mat, row, col)+1, 1);
        }
        private static void SetAtR(Mat mat, int row, int col, byte value)
        {
            Marshal.Copy(new byte[] { value }, 0, GetAt(mat, row, col)+2, 1);
        }
    }

 

Similar requirements two methods in C ++

method 1

 

#include <opencv2 / opencv.hpp> 
#include <the iostream>
 the using  namespace CV;
 the using  namespace STD; 

void main () {
     // Dynamic Address access 
    Mat imread IMG = ( " E: //green.png " ); 
    imshow ( " the src " , IMG); 
    Mat DST = img.clone ();
     int rowNumber = img.rows; // get the number of rows 
    int colNumber = img.cols; // Get the number of columns 
    for ( int I = 0 ; I <rowNumber ; I ++ ) {
         for( Int J = 0 ; J <colNumber; J ++ ) 
        { 
            dst.at <Vec3b> (I, J) [ 0 ] = 255 ; // blue channel 
            dst.at <Vec3b> (I, J) [ . 1 ] = 0 ; // green channel 
            dst.at <Vec3b> (I, J) [ 2 ] = 0 ; // red channel
             // dst.at <UCHAR> (I, J) = 255; // gray image 
        } 
    } 
    imshow ( " DST " , DST); 
    waitKey ( 0 ); 
}

Method 2:

#include <opencv2 / opencv.hpp> 
#include <the iostream>
 the using  namespace CV;
 the using  namespace STD; 

void main () { 
        Mat IMG = imread ( " E: //green.png " ); 
    imshow ( " the src " , IMG ); 
    Mat DST = img.clone ();
     int rowNumber = img.rows; // get the number of rows 
    int colNumber = img.cols img.channels * (); // number of columns in each row × number of channel elements = 
    for ( int I = 0 ; I <rowNumber; I ++ ) { 
        UCHARData = dst.ptr * <UCHAR> (I); // get the first address of each row, ptr address of the image function can be any of the first row 
        for ( int J = 0 ; J <colNumber; J ++ ) 
        { 
            // Data [J ] = 255; // grayscale 
            Switch (J% . 3 ) 
            { 
            Case  0 : // blue channel 
                Data [J] = 255 ;
                 BREAK ;
             Case  . 1 : // green channel 
                Data [J] = 0 ;
                 BREAK ;
             Case  2 :// red channel 
                Data [J] = 255 ;
                 BREAK ; 
            } 
        } 
    } 
    imshow ( " DST " , DST); 
    waitKey ( 0 );     
}