Add image data structure classes

[nfahlgren]

Describe your changes This PR contains prototype features for the purpose of discussion and development.

Adds Python classes for image data structures, subclassed from NumPy n-dimensional arrays. In the current PR, a generic class Image is subclassed from the np.ndarray class and has one additional attribute, filename. All other classes are subclassed from Image.

Image BGR: OpenCV-type color image - currently behaves exactly like Image RGB: scikit-image-type color image - currently behaves exactly like Image GRAY: grayscale image - currently behaves exactly like Image HSI: hyperspectral image - has additional attributes/methods

HSI would replace Spectral_data. It currently contains attributes in addition to Image: wavelengths - a list of wavelengths, default_wavelengths - a list of default wavelengths for visualizing the data cube, and wavelength_units. When an instance is built it automatically adds attributes for min and max wavelengths, can automatically pick default wavelengths if needed, and automatically creates a "thumbnail" for visualizing the data cube (what we have been calling "pseudo_rgb". The thumb attribute is itself either a BGR or GRAY image.

As these classes are based on np.ndarray, properties like height, width, etc. can be accessed using .shape and other standard ndarray class methods/attributes, or NumPy functions.

Some (but not all) to-do items:

• Other classes, e.g. THERMAL, MASK?
• Automatic conversion between classes? - For example, if a BGR/RGB is subsetted to a single channel that new image should be GRAY
• Built-in converters in some cases? - For example, would it be convenient to have BGR.torgb and RGB.tobgr methods?

Type of update Is this a: Work in progress

Associated issues Related: #775 #896

For the reviewer See this page for instructions on how to review the pull request.

• [ ] PR functionality reviewed in a Jupyter Notebook
• [ ] All tests pass
• [ ] Test coverage remains 100%
• [ ] Documentation tested
• [ ] New documentation pages added to plantcv/mkdocs.yml
• [ ] Changes to function input/output signatures added to updating.md
• [ ] Code reviewed
• [ ] PR approved

[codecov[bot]]

Codecov Report

Merging #909 (9a4aca0) into 4.x (696704c) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               4.x      #909   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          160       161    +1     
  Lines         6827      6880   +53     
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+ Hits          6827      6880   +53     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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Impacted Files	Coverage Δ
plantcv/plantcv/__init__.py	100.00% <ø> (ø)
plantcv/plantcv/classes.py	100.00% <100.00%> (ø)
plantcv/plantcv/images.py	100.00% <100.00%> (ø)
plantcv/__init__.py	100.00% <0.00%> (ø)

[nfahlgren]

Moved to a separate repository: https://github.com/danforthcenter/eidc