Padding of Image Error C++

Since your max is 5x5 pixels, you'll have to add a black border of 2 pixels wide, not just 1 pixel wide.

Part of your code already supports that, by looping from 0 to (Pin_t.Height+3), which gives you enough room for the image height itself, and two pixels before and two pixels after (for the border).
But you then proceed to add only one pixel border, with the image not properly centered in it.

To add a two pixel border, and center the image, you can do something like below.


Another thing I noticed, is that you use the width and height indexes in a non-standard manner. Normally, the first index of a 2D array is the row number (ie. along the height of the image), and the second is the column number (ie. along the width of the image).
As long as you do that consistently, there's no problem, but you should realize that it's non-standard, and thus potentially error prone, especially when other people work with the code too.

        //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++;
              }
         }
 
// etc. Remember that the real image goes from 2 to Pin_t.Height + 1 in the vertical direction and 2 to Pin_t.Width + 1 in the horizontal direction, so you'll have to adapt the masking code for that too ...

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Hi Infinity,

Thanks Infinity. Unfortunately, when I updated the code with the one you supplied, I still get the same error. The main loop (with the mask multiplication) doesn't even go one iteration through, still k=1, and j=1.

This is the error I am getting. which appears in the line:

+ Mask[3][1]*IMG_matrix[k+1][j-1] + Mask[3][4]*IMG_matrix[k+1][j+1]

Unhandled exception at 0x008b1e74 in Marr-Hildreth.exe: 0xC0000005: Access violation reading location 0xfdfdfe01.

To confirm the code:

#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 = 300;
            
		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=1; j <= Pin_t.Height; j++)
        {           
            for(int k=1; k <= Pin_t.Width; 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-1][j-1] = 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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Excellent. Thank you Infinity.