Thread: Edge Detection Of A PPM Image In C?

So far this is what I've got:

What I'm trying to do is read in a PPM, store it in an array (done), then prompt the user to enter a threshold. Then detect the edges in an image and output to a new internal array image where pixels that are part of an edgeare white, other pixels are black.

I've been given this formula:
grad = abs(im(x+1, y) - im(x-1, y)) + abs(im(x, y+1) - im(x, y-1))
and am told to compare it to a threshold then sum grad over the colour channels. Any pointers would be welcome. Thanks.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>


#define maxheight 1080
#define maxwidth 1920
#define RGB_COMPONENT_COLOUR 255
#define pgmtype "P2"
#define ppmtype "P3"


typedef struct
{
    int red, green, blue;
} PPMPixel;


typedef struct
{
    int x, y;
    //PPMPixel *data;
} PPMImage;


typedef struct 
{
    int rgb_comp_colour;
    char filetype[3];
    int height;
    int width;
} PPMHead;


PPMHead head[3];


PPMPixel r;


PPMPixel data; //Defines pointer to PPMPixel
PPMPixel **EdgeArray;

void edge_detection()
{
    int i, j;
    FILE *fed;
    char fnameed[100];
    printf("\tEnter first file's name: \n");
    scanf("%s", fnameed);
    fseek(stdin,0,SEEK_END);
    fed = fopen(fnameed, "r");
    if (fed == NULL)
    {   
        printf("\tError while opening the file\n");
    }
    else    
    {
        printf("\tWriting in %s\n", fnameed);
    }


    fscanf(fed, "%s %d %d %d", head[3].filetype, &head[3].width, &head[3].height, &head[3].rgb_comp_colour);
    printf("%s %d %d %d", head[3].filetype, head[3].width, head[3].height, head[3].rgb_comp_colour);


    EdgeArray = (PPMPixel **)malloc(head[3].height*sizeof(PPMPixel*)); //Points to malloc
    if((EdgeArray == NULL))
    {
        printf("\tError allocating memory to the array\n");
    }
    else
    {
        printf("\tMemory allocated to the PPM array sucessfully\n");
    }
    for (i=0;i<head[3].height;i++)
    {
        EdgeArray[i] = (PPMPixel *)malloc(head[3].width*sizeof(PPMPixel));
    }
    
    //Initialising each element
    for (j=0;j<head[3].height;j++)
    {
        for (i=0;i<head[3].width;i++)
        {
            fscanf(fed, "%d %d %d ", &r.red, &r.green, &r.blue);
            PPMPixel* data = &EdgeArray[j][i];
            data->red = r.red;
            data->green = r.green;
            data->blue = r.blue;
        }
    }
}