// compute angle in most accurate manner that handles 360 degrees using 32-bit floats
// compute the number of wraps that would make us closeset to the last value
float FindAngle(float x, float y)
{
int wraps;
float theta;
if (fast_fabsf(x) < fast_fabsf(y))
theta = atan2f(y,x);
else
theta = PI_2F-atan2f(x,y);
// Diff between expected position and position with no wraps
// Diff nearest zero, offset by 1024 wraps to avoid requiring floor()
wraps = (int)(((LastAngle-theta)+(1024.0f*TWO_PI_F+PI_F))*(1.0f/TWO_PI_F))-1024;
// factor in wraparounds
LastAngle=theta + wraps*TWO_PI_F;
return LastAngle;
}
void imlib_edge_canny(image_t *src, rectangle_t *roi, int low_thresh, int high_thresh)
{
int w = src->w;
gvec_t *gm = fb_alloc0(roi->w*roi->h*sizeof*gm);
//1. Noise Reduction with a Gaussian filter
imlib_sepconv3(src, kernel_gauss_3, 1.0f/16.0f, 0.0f);
//2. Finding Image Gradients
for (int gy=1, y=roi->y+1; y<roi->y+roi->h-1; y++, gy++) {
for (int gx=1, x=roi->x+1; x<roi->x+roi->w-1; x++, gx++) {
int vx=0, vy=0;
// sobel kernel in the horizontal direction
vx = src->data [(y-1)*w+x-1]
- src->data [(y-1)*w+x+1]
+ (src->data[(y+0)*w+x-1]<<1)
- (src->data[(y+0)*w+x+1]<<1)
+ src->data [(y+1)*w+x-1]
- src->data [(y+1)*w+x+1];
// sobel kernel in the vertical direction
vy = src->data [(y-1)*w+x-1]
+ (src->data[(y-1)*w+x+0]<<1)
+ src->data [(y-1)*w+x+1]
- src->data [(y+1)*w+x-1]
- (src->data[(y+1)*w+x+0]<<1)
- src->data [(y+1)*w+x+1];
// Find magnitude
int g = (int) fast_sqrtf(vx*vx + vy*vy);
// Find the direction and round angle to 0, 45, 90 or 135
int t = (int) fast_fabsf((atan2f(vy, vx)*180.0f/M_PI));
if (t < 22) {
t = 0;
} else if (t < 67) {
t = 45;
} else if (t < 112) {
t = 90;
} else if (t < 160) {
t = 135;
} else if (t <= 180) {
t = 0;
}
gm[gy*roi->w+gx].t = t;
gm[gy*roi->w+gx].g = g;
}
}
// 3. Hysteresis Thresholding
// 4. Non-maximum Suppression and output
for (int gy=0, y=roi->y; y<roi->y+roi->h; y++, gy++) {
for (int gx=0, x=roi->x; x<roi->x+roi->w; x++, gx++) {
int i = y*w+x;
gvec_t *va=NULL, *vb=NULL, *vc = &gm[gy*roi->w+gx];
// Clear the borders
if (y == (roi->y) || y == (roi->y+roi->h-1) ||
x == (roi->x) || x == (roi->x+roi->w-1)) {
src->data[i] = 0;
continue;
}
if (vc->g < low_thresh) {
// Not an edge
src->data[i] = 0;
continue;
// Check if strong or weak edge
} else if (vc->g >= high_thresh ||
gm[(gy-1)*roi->w+(gx-1)].g >= high_thresh ||
gm[(gy-1)*roi->w+(gx+0)].g >= high_thresh ||
gm[(gy-1)*roi->w+(gx+1)].g >= high_thresh ||
gm[(gy+0)*roi->w+(gx-1)].g >= high_thresh ||
gm[(gy+0)*roi->w+(gx+1)].g >= high_thresh ||
gm[(gy+1)*roi->w+(gx-1)].g >= high_thresh ||
gm[(gy+1)*roi->w+(gx+0)].g >= high_thresh ||
gm[(gy+1)*roi->w+(gx+1)].g >= high_thresh) {
vc->g = vc->g;
} else { // Not an edge
src->data[i] = 0;
continue;
}
switch (vc->t) {
case 0: {
va = &gm[(gy+0)*roi->w+(gx-1)];
vb = &gm[(gy+0)*roi->w+(gx+1)];
break;
}
case 45: {
va = &gm[(gy+1)*roi->w+(gx-1)];
vb = &gm[(gy-1)*roi->w+(gx+1)];
break;
}
case 90: {
va = &gm[(gy+1)*roi->w+(gx+0)];
vb = &gm[(gy-1)*roi->w+(gx+0)];
break;
}
case 135: {
va = &gm[(gy+1)*roi->w+(gx+1)];
vb = &gm[(gy-1)*roi->w+(gx-1)];
break;
}
}
if (!(vc->g > va->g && vc->g > vb->g)) {
src->data[i] = 0;
} else {
src->data[i] = 255;
}
}
}
fb_free();
}
