// examineArea looks in the area surrounding x,y.
// if n points are above or n points are below, return keypoint=true.
func (d *Detector) isKeypoint(x int, y int) (keypoint bool) {
// if within 3 of one of the edges, don't do anything (yet)
if d.img.Bounds().Max.X-r < x {
return false
}
if d.img.Bounds().Min.Y+r > y {
return false
}
if d.img.Bounds().Min.X+r > x {
return false
}
if d.img.Bounds().Max.Y-r < y {
return false
}
abv := uint(0)
bel := uint(0)
for i := 0; i < 16; i++ {
dx, dy := mask.DiamondOffset(i, r)
// check if above or below threshold
if d.Value(x+dx, y+dy, d) > (d.Value(x, y, d) + d.threshold) {
abv++
} else if d.Value(x+dx, y+dy, d) < (d.Value(x, y, d) - d.threshold) {
bel++
}
}
if abv > n {
return true
} else if bel > n {
return true
}
return false
}
// pointVal returns 1 if the index in question is greater than point and
// 0 if it is less or equal to
func pointVal(i int, point image.Point, img image.Image, f PxVal) (val int) {
dx, dy := mask.DiamondOffset(i, r)
if f(point.X, point.Y, img) <= f(point.X+dx, point.Y+dy, img) {
return 0
} else {
return 1 * pow(2, i)
}
}
