// Canny detects and returns edges from the given image.
// Each dst pixel is given one of three values:
// 0xff: an edge
// 0x80: possibly an edge
// 0x00: not an edge
func Canny(dst *image.Gray, src image.Image) error {
if dst == nil {
return errors.New("edge: dst is nil")
}
if src == nil {
return errors.New("edge: src is nil")
}
b := src.Bounds()
srcGray, ok := src.(*image.Gray)
if !ok {
srcGray = image.NewGray(b)
draw.Draw(srcGray, b, src, b.Min, draw.Src)
}
if err := graphics.Blur(srcGray, srcGray, nil); err != nil {
return err
}
mag, dir := image.NewGray(b), image.NewGray(b)
if err := Sobel(mag, dir, srcGray); err != nil {
return err
}
// Non-maximum supression.
for y := b.Min.Y; y < b.Max.Y; y++ {
for x := b.Min.X; x < b.Max.X; x++ {
d := dir.Pix[(y-b.Min.Y)*dir.Stride+(x-b.Min.X)*1]
var m0, m1 uint8
switch d {
case 0: // west and east
m0 = atOrZero(mag, x-1, y)
m1 = atOrZero(mag, x+1, y)
case 45: // north-east and south-west
m0 = atOrZero(mag, x+1, y-1)
m1 = atOrZero(mag, x-1, y+1)
case 90: // north and south
m0 = atOrZero(mag, x, y-1)
m1 = atOrZero(mag, x, y+1)
case 135: // north-west and south-east
m0 = atOrZero(mag, x-1, y-1)
m1 = atOrZero(mag, x+1, y+1)
default:
return fmt.Errorf("edge: bad direction (%d, %d): %d", x, y, d)
}
m := mag.Pix[(y-b.Min.Y)*mag.Stride+(x-b.Min.X)*1]
if m > m0 && m > m1 {
m = 0xff
} else if m > m0 || m > m1 {
m = 0x80
} else {
m = 0x00
}
dst.Pix[(y-b.Min.Y)*dst.Stride+(x-b.Min.X)*1] = m
}
}
return nil
}
// DifferenceOfGaussians produces the difference of Gaussians sd0 and sd1.
func DifferenceOfGaussians(dst *image.Gray, src image.Image, sd0, sd1 float64) {
b := src.Bounds()
srcg := image.NewGray(b)
m0 := image.NewGray(b)
m1 := image.NewGray(b)
draw.Draw(srcg, b, src, b.Min, draw.Src)
graphics.Blur(m0, srcg, &graphics.BlurOptions{StdDev: sd0})
graphics.Blur(m1, srcg, &graphics.BlurOptions{StdDev: sd1})
for y := b.Min.Y; y < b.Max.Y; y++ {
for x := b.Min.X; x < b.Max.X; x++ {
off := (y-m0.Rect.Min.Y)*m0.Stride + (x - m0.Rect.Min.X)
c := m0.Pix[off] - m1.Pix[off]
if c < 0 {
c = -c
}
doff := (y-dst.Rect.Min.Y)*dst.Stride + (x - dst.Rect.Min.X)
dst.Pix[doff] = c
}
}
}