The 8-direction Sobel templates are convolution kernels used for edge detection in digital images.
3×3 convolution kernels for detecting edges in 8 different directions (0° to 315° at 45° intervals).
Top row: 0, 1, 2 direction
Middle row: 3, 4, 5 direction
Bottom row: 6, 7 direction
Right panel shows the corresponding edge direction numbering.