Reshape 5-dimensional tiled image to 3-dimensional normal image

I’m creating a program that takes use of an RGB image that is tiled of the shape (n, n, 3, l, l). n is the number of each tile on each side of the image, and l is the length of each tile in pixels. I am trying to reshape this into a (3, l * n, l * n) shape. An example would be shape (7, 7, 3, 224, 224) to (3, 224, 224).

I want to keep the positions of the pixels in the new matrix, so I can visualise this image later. If I start with an image of a checkerboard pattern (every other tile has all pixel values set to 1, see example below), and use .reshape((3, 224, 224)) the result is the following:

Checkerboard (wanted result)

Wrong way of reshaping

I have made this for loop method of merging the tiles, which works, but is quite slow:

# l: the pixel length of each tile
img_reshaped = torch.zeros((3, 224, 224))
for i in range(len(img)):
    for j in range(len(img[i])):
        img_reshaped[:, i * l:(i + 1) * l, j * 32:(j + 1) * l] = noise[i, j]

I’ve also tried using .fold(), but this only works with 3D matrices, and not 5D.

Any tips on how to solve this? I feel it should be relatively simple, but just can’t wrap my head around it just now.

PS: The code I used to generate the checkerboard:

noise = torch.zeros((7, 7, 3, 32, 32))

for i in range(len(noise)):
    for j in range(len(noise[i])):
        if (i % 2 == 0 and j % 2 != 0) or (i % 2 != 0 and j % 2 == 0):
            noise[i][j] = torch.ones((3, 32, 32))

Answer

I think you need to transpose before reshape:

n,l=2,3
arr=np.zeros((n,n,3,l,l))

for i in range(n):
    for j in range(n):
        arr[i,j] = (i+j)%2

out= arr.transpose(2,0,3,1,4).reshape(3,n*l,-1)

Output:

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Answer