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Is there any update on this issue as I am having the same problem?

I have had exactly the same problem with MPSImageLaplacianPyramid and believe it is a flaw with the way Apple are applying the EXPAND. The headers refer to the upsampling with 'zero-stuffing' then applying the interpolation. But this will reduce the energy in the upsampled image, the interpolation needs to have values that are x2 for both vertical and horizontal convolution. However, you cannot specify a 1x5 matrix for this kernel, only a center weight (which doesn't address the issue) or the full 5x5 matrix kernel. I have tried this with a 5x5 matrix with the x4 weights and now get the correct pyramid. The 5x5 matrix is created by multipling the 5x1 and 1x5 matrices of the form:{1/4 - a/2, 1/4, a, 1/4, 1/4 - a/2} and ensure each element in this matrix is x2.