Velox EMD Complex dtype issue

[bryandesser]

Applied fix to Velox EMD fft_dtype to allow for FFT selection with odd numbers of pixels. Small 128x128 HAADF examples are provided, one with an FFT selection with odd number of pixels, one with an even number of pixels. The even selection works, the odd cannot be imported with hyperspy.

Description of the change

There remains a small bug in reading Velox EMD files with FFTs. In _read_image(): fft_dtype = [('realFloatHalfEven', '<f4'), ('imagFloatHalfEven', '<f4')]; however, this is not always the case. If, for example, an FFT is taken of a region with odd number of pixels, then Velox saves the data as fft_dtype = [('realFloatHalfOdd', '<f4'), ('imagFloatHalfOdd', '<f4')]

This issue causes hs.load() to fail in the presence of an FFT with odd number of pixels.

In emd.py:

• Expand fft_dtype to accomodate odd pixel dimensions (line 1101):
  fft_dtype = [[('realFloatHalfEven', '<f4'),('imagFloatHalfEven', '<f4')],[('realFloatHalfOdd', '<f4'), ('imagFloatHalfOdd', '<f4')]]
• Change dtype check statement accordingly (line 1105):
  if h5data.dtype in fft_dtype or h5data.dtype == dpc_dtype:

Progress of the PR

• Change implemented (can be split into several points),
• update docstring (if appropriate),
• update user guide (if appropriate),
• add an changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• Check formatting changelog entry in the readthedocs doc build of this PR (link in github checks)
• add tests,
• ready for review.

hyperspyComplexOddEven.zip

Minimal example of the bug fix or the new feature

import hyperspy.api as hs

dataEven = hs.load("hyperspyComplexEven.emd")
dataEven
[<ComplexSignal2D, title: Half FFT, dimensions: (|36, 70)>,
 <Signal2D, title: HAADF, dimensions: (|128, 128)>]

dataOdd = hs.load("hyperspyComplexOdd.emd")
# ERROR:hyperspy.io:If this file format is supported, please report this error to the HyperSpy developers.

[codecov]

Codecov Report

Base: 81.42% // Head: 81.42% // No change to project coverage 👍

Coverage data is based on head (7376a42) compared to base (19f62eb).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@                 Coverage Diff                  @@
##           RELEASE_next_patch    #3040    +/-   ##
====================================================
  Coverage               81.42%   81.42%            
====================================================
  Files                     200      200            
  Lines                   27042    27042            
  Branches                 5996     5811   -185     
====================================================
  Hits                    22018    22018            
  Misses                   3574     3574            
  Partials                 1450     1450            

Impacted Files	Coverage Δ
hyperspy/io_plugins/emd.py	66.84% <100.00%> (ø)

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[ericpre]

Thank you @bryandesser, this looks good.

For information, I have rebased on RELEASE_next_patch and added a changelog entry and pushed these changes to your branch.