I'm writing a canny edge detector for my intro to robotic vision class. There are output samples to check if we have it right, and my magnitude image is coming out exact but my peak finder is not complete. The peaks I have found appear to be in the correct output but I am missing a significant amount. I have looked through the peaks part of the code many times and still cannot find where the problem is. I was hoping that maybe someone with more experience with the canny algorithm could help me out. I've looked around the web for examples of canny algorithms but can't find the difference that is causing the problem. Any help or info would be appreciated. Thank you.

Code:#include <stdio.h> #include <math.h> #define PICSIZE 256 #define MAXMASK 100 int pic[PICSIZE][PICSIZE]; double outpicx[PICSIZE][PICSIZE]; double outpicy[PICSIZE][PICSIZE]; double ival[PICSIZE][PICSIZE]; double maskx[MAXMASK][MAXMASK]; double masky[MAXMASK][MAXMASK]; double peaks[PICSIZE][PICSIZE]; main() { int i,j,p,q,mr,centx,centy, sig; double maskval,sum1, sum2, maxival, dir; FILE *fo1, *fo2,*fp1, *fo3; char str [80]; fp1=fopen("garb34.pgm","rb"); fscanf(fp1, "%s", str); fscanf(fp1, "%s", str); fscanf(fp1, "%s", str); //the 3 output files fo1=fopen("garb34mag.pgm","wb"); fo2=fopen("garb34peaks.pgm","wb"); fo3=fopen("garb34dblthrsh.pgm","wb"); printf("Enter the value for sigma.\n"); scanf("%d", &sig); mr = (int)(sig * 3); centx = (MAXMASK / 2); centy = (MAXMASK / 2); for (i=0;i<256;i++) { for (j=0;j<256;j++) { pic[i][j] = getc (fp1); } } for (p=-mr;p<=mr;p++) { for (q=-mr;q<=mr;q++) { maskval = ((-q)*(exp(-1*(((p*p)+(q*q))/(2*(sig*sig)))))); (maskx[p+centy][q+centx]) = maskval; maskval = ((-p)*(exp(-1*(((p*p)+(q*q))/(2*(sig*sig)))))); (masky[p+centy][q+centx]) = maskval; } } for (i=mr;i<=255-mr;i++) { for (j=mr;j<=255-mr;j++) { sum1 = 0; sum2 = 0; for (p=-mr;p<=mr;p++) { for (q=-mr;q<=mr;q++) { sum1 += pic[i+p][j+q] * maskx[p+centy][q+centx]; sum2 += pic[i+p][j+q] * masky[p+centy][q+centx]; } } outpicx[i][j] = sum1; outpicy[i][j] = sum2; } } maxival = 0; for (i=mr;i<256-mr;i++) { for (j=mr;j<256-mr;j++) { ival[i][j]=sqrt((double)((outpicx[i][j]*outpicx[i][j]) + (outpicy[i][j]*outpicy[i][j]))); if (ival[i][j] > maxival) maxival = ival[i][j]; } } //print the headers for all of the files. fprintf(fo1,"P5\n"); fprintf(fo1,"%d %d\n", PICSIZE, PICSIZE); fprintf(fo1,"255\n"); fprintf(fo2,"P5\n"); fprintf(fo2,"%d %d\n", PICSIZE, PICSIZE); fprintf(fo2,"255\n"); fprintf(fo3,"P5\n"); fprintf(fo3,"%d %d\n", PICSIZE, PICSIZE); fprintf(fo3,"255\n"); //loop through each pixel and output its according value for each //of the 3 images. for (i=0;i<256;i++) { for (j=0;j<256;j++) { //gradient magnitude. ival[i][j] = (ival[i][j] / maxival) * 255; fprintf(fo1,"%c",(char)((int)(ival[i][j]))); if (outpicx[i][j] == 0) { //printf("here\n"); outpicx[i][j] = 10^-15; } dir = (atan2(outpicy[i][j],outpicx[i][j]))/3.14159 * 180.0; // Calculate actual direction of edge peaks[i][j] = 0; /* Convert actual edge direction to approximate value */ if (((dir < 22.5) && (dir > -22.5) ) || (dir > 157.5) || (dir < -157.5) ) { if((ival[i][j] > ival[i][j-1]) && (ival[i][j] > ival[i][j+1])) peaks[i][j] = 255; } else if(((dir > 22.5) && (dir < 67.5)) || ((dir < -112.5) && (dir > -157.5))) { if((ival[i][j] > ival[i+1][j+1]) && (ival[i][j] > ival[i-1][j-1])) peaks[i][j] = 255; } else if (((dir > 112.5) && (dir < 157.5)) || ((dir < -22.5) && (dir > -67.5))) { if((ival[i][j] > ival[i-1][j+1]) && (ival[i][j] > ival[i+1][j-1])) peaks[i][j] = 255; } else { if((ival[i][j] > ival[i+1][j]) && (ival[i][j] > ival[i-1][j])) peaks[i][j] = 255; } //low threshold of 40 /*if(ival[i][j] > 40) fprintf(fo2,"%c",(char)((int)(255))); else fprintf(fo2,"%c",(char)((int)(0))); */ //high threshold of 100 if(ival[i][j] > 100) fprintf(fo3,"%c",(char)((int)(255))); else fprintf(fo3,"%c",(char)((int)(0))); } } for (i=0;i<PICSIZE;i++) { for (j=0;j<PICSIZE;j++) { if (peaks[i][j] == 255) fprintf(fo2,"%c",(char)((int)(255))); else fprintf(fo2,"%c",(char)((int)(0))); } } //close all of the files. fclose(fp1); fclose(fo1); fclose(fo2); fclose(fo3); system("PAUSE"); }

Can't attach the pgm files but

here the input file can be found:

http://www.cs.ucf.edu/courses/cap4453/inputpics/ under garb34.pgm

here the correct output can be found:

http://www.cs.ucf.edu/courses/cap4453/outputpics/ under cannypeaks.pgm

Run my code to see what i am getting which is a partial output of the correct one it seems. (i.e. what outputs is correct its just missing parts)