Read about kernel correlation and implemented cv2 filter2D but for an example test input and kernel, the output produced does not match output from cv2.filter2D(). What am I missing here?

```
# input two tensors, images is 3d, kernel 2d
def my_filter2D(image, kernel):
kx, ky = kernel.shape
x_n = kx//2
y_n = kx//2
padded_image = torch.nn.functional.pad(image, (0, 0, ky//2, ky//2, kx//2, kx//2))
filtimg = torch.Tensor(image)
px, py, nc = padded_image.shape
for x in range(px):
for y in range(py):
for c in range(nc):
if x - x_n < 0:
continue
if x + x_n >= px:
continue
if y - y_n < 0:
continue
if y + y_n >= py:
continue
total = 0.0
image_n = padded_image[x-x_n:x+x_n+1, y-y_n:y+y_n+1,c]
for x_i in range(kx):
for y_i in range(ky):
total += image_n[x_i,y_i]*kernel[x_i,y_i]
filtx = x-x_n
filty = y-y_n
filtimg[filtx,filty,c] = total
return filtimg
```

Here’s sample input and kernel from a stackoverflow response:

```
import numpy as np
import cv2
a = np.array([[0.0,0.0,0.0,0.0,0.0],
[0.0,0.0,0.0,0.0,0.0],
[10.0,0.0,0.0,0.0,0.0],
[20.0,20.0,20.0,0.0,0.0],
[30.0,30.0,30.0,30.0,30.0]], dtype=np.float32)
kernel = np.ones((3,3), dtype=np.float32)
filtered_a = cv2.filter2D(a, -1, kernel)
```

The output of the above cv2.filter2D() call produces:

```
array([[ 0., 0., 0., 0., 0.],
[ 10., 10., 0., 0., 0.],
[ 70., 70., 40., 20., 0.],
[160., 160., 130., 110., 90.],
[210., 210., 170., 130., 90.]], dtype=float32)
```

But the output from my filter2D implementation does not match the above from cv2.filter2D() - how to fix the code above?

```
a = np.array([[0.0,0.0,0.0,0.0,0.0],
[0.0,0.0,0.0,0.0,0.0],
[10.0,0.0,0.0,0.0,0.0],
[20.0,20.0,20.0,0.0,0.0],
[30.0,30.0,30.0,30.0,30.0]], dtype=np.float32)
testkernel = np.ones((3,3), dtype=np.float32)
a3d = a.reshape(5,5,1)
my_filter2d_a = my_filter2D(torch.from_numpy(a3d), torch.from_numpy(testkernel))
and output:
tensor([[ 0., 0., 0., 0., 0.],
[ 10., 10., 0., 0., 0.],
[ 50., 70., 40., 20., 0.],
[110., 160., 130., 110., 60.],
[100., 150., 130., 110., 60.]])
```

Please redirect me the correct algorithm for to implement cv2 filter2D().