def canny(F, s):
Fx = gD(F, s, 1, 0)
Fy = gD(F, s, 0, 1)
Fxy = gD(F, s, 1, 1)
Fxx = gD(F, s, 2, 0)
Fyy = gD(F, s, 0, 2)
Fw = np.sqrt(Fx**2 + Fy**2)
Fww = (Fx**2 * Fxx) + (2 * Fx * Fy * Fxy) + (Fy**2 * Fyy)
canny = np.zeros_like(Fw)
height, width = F.shape
# For all pixels check if the second derivative of that pixel has changed
# sign. If so, draw a pixel.
for y in range(width - 2):
for x in range(height - 2):
if ((Fww[y-1][x-1] > 0 and Fww[y+1][x-1] < 0) or
(Fww[y-1][x] > 0 and Fww[y+1][x] < 0) or
(Fww[y-1][x+1] > 0 and Fww[y+1][x+1] < 0) or
(Fww[y-1][x-1] < 0 and Fww[y+1][x-1] > 0) or
(Fww[y-1][x] < 0 and Fww[y+1][x] > 0) or
(Fww[y-1][x+1] < 0 and Fww[y+1][x+1] > 0) or
(Fww[y-1][x-1] > 0 and Fww[y-1][x+1] < 0) or
(Fww[y][x-1] > 0 and Fww[y][x+1] < 0) or
(Fww[y+1][x-1] > 0 and Fww[y+1][x+1] < 0) or
(Fww[y-1][x-1] < 0 and Fww[y-1][x+1] > 0) or
(Fww[y][x-1] < 0 and Fww[y][x+1] > 0) or
(Fww[y-1][x-1] < 0 and Fww[y+1][x+1] > 0)):
canny[y][x] = 1
return canny
def comparison():
F = plt.imread('../images/cameraman.png')
# Values and meshgrid used below.
x = np.arange(-128, 128)
y = np.arange(-128, 128)
Y, X = np.meshgrid(x, y)
A = 1
V = 6*np.pi/201
# Fx
Fx = A*V*np.cos(V*X)
# dFx
dFx = gD(F, 1, 1, 0)
plt.subplot(131)
plt.title("Fx")
plt.imshow(Fx, cmap=plt.cm.gray)
plt.subplot(132)
plt.title("dFx")
plt.imshow(dFx, cmap=plt.cm.gray)
plt.subplot(133)
plt.title("Fx/dFx")
plt.imshow(Fx/dFx, cmap=plt.cm.gray)
plt.show()