Marr-Hildreth Program not Giving Desired Result

Hi Experts,

The c++ code below on the lena image in .pgm format is not giving very good edge detection. The threshold value of 100 yields the best result; however, this is quite inferior to the results of the matlab edge detection using the same algorithm.

I am not sure where I am going wrong in the algorithm. Below a threshold value of 100, the resulting image doesn't detect edges anymore.

Thanks,

Dennis

#include <iostream>
#include <fstream>
#include <string>
#include <math.h>
#include <time.h>
 
 
using namespace std;
 
/*** New Data Types ***/
typedef unsigned char BYTE;
 
// create data structure to hold image
struct PIC
{
    unsigned int nChannel;
    bool InterLeaved;
    unsigned int Width, Height, Maxval;
    BYTE *img;
};
 
template <typename T>
 
T **AllocateDynamicArray( int nRows, int nCols)
{
 
    T **dynamicArray;
    dynamicArray = new T*[nRows];
    for( int i = 0 ; i < nRows ; i++ )
    dynamicArray[i] = new T [nCols];
    return dynamicArray;
}
 
template <typename T>
 
void FreeDynamicArray(T** dArray)
{
    delete [] *dArray;
    delete [] dArray;
}
 
 
 
//function that loads in the header
bool LoadP5Header(ifstream &infile, PIC &pic)
{
    bool rtv = true;
    char buf[16];
    int bufIndex;
    int width, height, maxval;
 
    infile.read(buf, 2); // get the magic number
    buf[2]='\0';
 
    if(buf[0] == 'P' && buf[1] == '5')
	{
        infile.read(buf, 1);
        while(isspace(buf[0])) // Skip white space(s)
		{
            infile.read(buf,1);
		}
 
        // get width
        bufIndex = 0;
        while(bufIndex < 15 && !isspace(buf[bufIndex]))
		{
            bufIndex++;
            infile.read(buf+bufIndex, 1);
        }
        buf[bufIndex] = NULL;  // null terminated string
        width = atoi(buf);
 
        // get height
        infile.read(buf,1);
        while(isspace(buf[0])) // Skip white space(s)
		{
            infile.read(buf,1);
        }
        bufIndex = 0;  //line 
        while(bufIndex < 15 && !isspace(buf[bufIndex]))
		{
            bufIndex++;
            infile.read(buf+bufIndex, 1);
        }
        buf[bufIndex] = NULL;  // null terminated string
        height = atoi(buf);
 
       // get Maxval
		infile.read(buf,1);
        while(isspace(buf[0])) // Skip white space(s)
		{
            infile.read(buf,1);
        }
        bufIndex = 0;
        while(bufIndex < 15 && !isspace(buf[bufIndex]))
		{
            bufIndex++;
            infile.read(buf+bufIndex, 1);
        }
        buf[bufIndex] = NULL;  // null terminated string
        maxval = atoi(buf);
 
		// Skip white space(s)
		//infile.read(buf,1);
 
        // set the image information in the struct
        pic.InterLeaved = false;
        pic.Width = width;
        pic.Height = height;
		pic.Maxval = maxval;
 
    }
    else rtv = false;
 
    return rtv;
}; // end of LoadP5Header()
 
//function that accepts an infile object and a PIC Object
//and reads in the PIC object
void LoadImage(ifstream &infile, PIC &pic)
{
    infile.read(reinterpret_cast<char *>(pic.img), pic.Width*pic.Height);
}
 
//function that accepts an outstream file and a PIC object to
//and writes the output stream to the PIC object
void WritePGM(ofstream & outfile, PIC pic)
{
    outfile << "P5" << endl;
    outfile << pic.Width << " " << pic.Height << endl;
	outfile << pic.Maxval << endl;
 
    outfile.write(reinterpret_cast<char *>(pic.img), pic.Width*pic.Height);
}
 
 
void MaskFiltering(PIC Pin_t, int Mask[5][5], char *outFileName_Pout)
{
    
        ofstream outfile_Pout;
 
        outfile_Pout.open(outFileName_Pout, ios::binary);
        
        int **IMG_matrix = AllocateDynamicArray<int>(Pin_t.Width+6,Pin_t.Height+6);
        int **IMG_temp_matrix = AllocateDynamicArray<int>(Pin_t.Width,Pin_t.Height);
   
        int Npixels, pixelCnt, LoGValue;
        int threshVal = 100;
            
		Npixels = Pin_t.Width*Pin_t.Height;
		Pin_t.Maxval = 255;
 
		        //create a two pixel layer of black border around the original image to apply the mask to boundary values
 
        for(int j = 0; j <= Pin_t.Height+3; j++)
        {
             IMG_matrix[0][j] = 0;
             IMG_matrix[1][j] = 0;
             IMG_matrix[Pin_t.Width+2][j] = 0; 
             IMG_matrix[Pin_t.Width+3][j] = 0; 
        }
        
        for(int k = 0; k <= Pin_t.Width+3; k++)
        {
             IMG_matrix[k][0] = 0;
             IMG_matrix[k][1] = 0;
             IMG_matrix[k][Pin_t.Height+2] = 0;
             IMG_matrix[k][Pin_t.Height+3] = 0;
        }
 
        pixelCnt = 0;
        //make 2D matrix of input
 
        for(int j = 2; j < Pin_t.Height + 2; j++)
        {
              for(int k = 2; k < Pin_t.Width + 2; k++)
              {
                    IMG_matrix[k][j] = (int) Pin_t.img[pixelCnt];
                    pixelCnt++;
              }
         }
 
        
        for(int j=2; j <= Pin_t.Height+1; j++)
        {           
            for(int k=2; k <= Pin_t.Width+1; k++)
            {      
 
                      LoGValue = Mask[2][2]*IMG_matrix[k][j] + Mask[3][2]*IMG_matrix[k+1][j] + Mask[4][2]*IMG_matrix[k+2][j] + Mask[1][2]*IMG_matrix[k-1][j] + Mask[0][2]*IMG_matrix[k-2][j]
                                     + Mask[2][3]*IMG_matrix[k][j+1] + Mask[2][4]*IMG_matrix[k][j+2] + Mask[2][1]*IMG_matrix[k][j-1] + Mask[2][0]*IMG_matrix[k][j-2]
                                     + Mask[3][1]*IMG_matrix[k+1][j-1] + Mask[3][4]*IMG_matrix[k+1][j+1]
									 + Mask[1][1]*IMG_matrix[k-1][j-1] + Mask[1][4]*IMG_matrix[k-1][j+1];
 
                                     
                 if(LoGValue < threshVal) LoGValue = 0;
                 else if(LoGValue < threshVal) LoGValue = 255;
 
                 IMG_temp_matrix[k-2][j-2] = LoGValue;
            } 
        }
        
        //output the calculated 2D matrix to original 1D
        pixelCnt = 0;
        for(int j = 0; j < Pin_t.Height; j++)
        {
              for(int k = 0; k < Pin_t.Width; k++)
              {
                    Pin_t.img[pixelCnt] = (unsigned char) (IMG_temp_matrix[k][j]);
                    pixelCnt++;
              }
         }
 
        WritePGM(outfile_Pout, Pin_t);
 }
 
 
int main()
{  
    
	ifstream infile_Pin1;                /* input file */
    char inFileName_Pin1[128]="Lena.pgm";            /* input file name */
    PIC Pin1;            //source image
    
    /* open input/output file */
    infile_Pin1.open(inFileName_Pin1, ios::binary);
 
	/* check input file */
    if(!infile_Pin1)
    {
        cout<<"Cannot open input file "<< inFileName_Pin1 <<endl;
        return 1;
    }
 
 
   int LaplacianOfGaussian[5][5] = {{0, 0, 1, 0, 0},
                                 {0, 1, 2, 1, 0},
                                 {1, 2, -16, 2, 1},
								 {0, 1, 2, 1, 0},
                                 {0, 0, 1, 0, 0}};
 
 
 
    if (LoadP5Header(infile_Pin1, Pin1)) // load pgm (Pin) image header information
    {
        // allocate the memory for the input image
        //the dimensions of the original
 
        Pin1.img = new BYTE[Pin1.Width*Pin1.Height];
 
        LoadImage(infile_Pin1, Pin1);
   
       MaskFiltering(Pin1,LaplacianOfGaussian, "Lena_Hildreth_1.pgm");   
 
   }
   
}

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