Help Gaussian filter application

Question

PPM filtroDeGaus(PPM img){
int l,c,a,b,s=0;
int mask[5][5] = {{ 2,  4,  5,  4, 2 },
                 { 4,  9, 12,  9, 4 },
                 { 5, 12, 15, 12, 5 },
                 { 4,  9, 12,  9, 4 },
                 { 2,  4,  5,  4, 2 }};

for( l= 2; l < img.l-2; l++){
    for(c = 2; c < img.c-2; c++){
        for(a = -2; a < 2; a++){
            for(b = -2; b < 2; b++){
                s+=(img.pixel[l+a][c+b].r * mask[a+2][b+2]);
            }
        }
                img.pixel[l][c].r = s/159;
                img.pixel[l][c].g = s/159;
                img.pixel[l][c].b = s/159;
                s=0;

    }
}
 return img;
}

estruct you receive as a parameter.

typedef struct {
    int r, g, b;
}PIXELS;

typedef struct {
int c;
int l;
char tipo[2];
unsigned int corMax;
PIXELS **pixel;
}PPM;  

This function is to apply Gaussian filter, only that the output is being this:

http://s000.tinyupload.com/? file_id=043004874145399340