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always fftshift+iffshift for Fraunhofer propagation #658

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always fftshift+iffshift for Fraunhofer propagation #658

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0429db8
always (i)fftshift for fft2
kvangorkom Jan 28, 2025
029d69e
Merge branch 'develop' into fftshift
kvangorkom Jan 28, 2025
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4 changes: 2 additions & 2 deletions poppy/accel_math.py
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Original file line number Diff line number Diff line change
Expand Up @@ -221,7 +221,7 @@ def fft_2d(wavefront, forward=True, normalization=None, fftshift=True):
_log.debug("using {2} FFT of {0} array, FFT_direction={1}".format(
str(wavefront.shape), 'forward' if forward else 'backward', method))

if (forward) and fftshift: # shift before backwards propagations (using forward FFT)
if fftshift: # shift before backwards propagations (using forward FFT)
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Very very minor: It would be nice to also update the comment text here to "shift before all propagations" instead of "shift before backwards propagations"

# This needs to be an ifftshift, for machine-precision equivalence to MFT
# as tested by test_MFT_FFT_equivalence_in_OpticalSystem; ifftshift and fftshift are
# precisely equivalent for even-sized arrays but differ by 1 pixel offset for odd-sized
Expand Down Expand Up @@ -287,7 +287,7 @@ def fft_2d(wavefront, forward=True, normalization=None, fftshift=True):
wavefront = do_fft(wavefront)
t2 = time.time()

if (not forward) and fftshift: # shift after forwards propagations (using inverse FFT)
if fftshift: # shift after forwards propagations (using inverse FFT)
# This needs to be a fftshift here, since we use ifftshift above
# See comment above in this function.
wavefront = _fftshift(wavefront)
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5 changes: 5 additions & 0 deletions poppy/tests/test_matrixDFT.py
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Expand Up @@ -695,5 +695,10 @@ def test_MFT_FFT_equivalence_in_OpticalSystem(tmpdir, display=False, source_offs
poppy.display_psf_difference(fftpsf, mftpsf, title='Diff FFT-MFT')


# difference of intensities
absdiff = np.abs(np.asarray(mftpsf[0].data - fftpsf[0].data)) # Extra asarray helps with optional GPU support
assert(np.all(absdiff < 1e-10))

# absolute value of difference of complex fields
absdiff_c = np.abs(np.asarray(mftplanes[-1].wavefront - fftplanes[-1].wavefront))
assert(np.all(absdiff_c < 1e-10))