The Python Oracle

In scipy why doesn't idct(dct(a)) equal to a?

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Chapters
00:00 In Scipy Why Doesn'T Idct(Dct(A)) Equal To A?
01:00 Accepted Answer Score 13
01:17 Thank you

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Full question
https://stackoverflow.com/questions/3489...

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Tags
#python #scipy #dct

#avk47


ACCEPTED ANSWER

Score 13


You need to set scaling to ortho for both dct2 and idct2:

def dct2 (block):
  return dct(dct(block.T, norm = 'ortho').T, norm = 'ortho')

also, you cannot expect the values to be exactly the same, but almost the same within some margin of error:

np.allclose (a, idct2(dct2(a)))