add and expose `psf2otf` and `otf2psf`

[johnnychen94]

Add commonly used functions psf2otf and otf2psf

Note: The implementation mainly comes from the original MATLAB codes, e.g., edit psf2otf. The original code handles roundoff error, which in Julia there's no such need (I guess? ), so I skipped this part.

Reference: http://www.mathworks.com/help/images/ref/psf2otf.html http://www.mathworks.com/help/images/ref/otf2psf.html

[codecov[bot]]

Codecov Report

Merging #81 into master will increase coverage by 0.11%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #81      +/-   ##
==========================================
+ Coverage   94.94%   95.06%   +0.11%     
==========================================
  Files           8        9       +1     
  Lines         693      709      +16     
==========================================
+ Hits          658      674      +16     
  Misses         35       35

Impacted Files	Coverage Δ
src/ImageFiltering.jl	100% <ø> (ø)	:arrow_up:
src/fft.jl	100% <100%> (ø)

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[timholy]

I have some bad news for you: we can't merge this. Mathworks owns the copyright to their code, so merging this would be a copyright infringement. Since you looked at their code, even if you do a from-scratch implementation you are "contaminated." At this point we would need someone who hasn't referenced their source code to implement these functions.

Sorry about that. scikit-image has a BSD license, so their code is safe to copy unless specified otherwise in individual source files.

I'm going to have to close this, I'm afraid.

[johnnychen94]

Yeah, understood. I wasn’t aware of the license issue.

[timholy]

I'm sure you weren't, many people aren't. I know you put some effort into this, sorry not to be able to use it.