Added documentation for ImageMorph module

[johnnygitgud]

This pull request adds documentation for the ImageMorph module
For issue #713 ("Todo: Docs for ImageMorph").

The updated documentation has:

• Overview of morphological operations in Pillow
• Explanation of structuring element patterns and ASCII masks
• Usage examples for LutBuilder and MorphOp
• Examples demonstrating pattern matching and apply()
• Information about LUT loading, saving, and reuse
• Guidance on required image modes

[radarhere]

I'm interested, why did you feel the need to mention _imagingmorph? _imagingft and _imagingmath aren't mentioned in our docs, for precisely the reason you mention here - we don't want users to deal with them directly. How do you think users would discover _imagingmorph in the first place?

[hugovk]

Thank you for filling this gap in the docs!

---

Please can you check the Sphinx warnings?

https://app.readthedocs.org/projects/pillow/builds/30336202/?utm_source=pillow&utm_content=notification#294395027--277

ImageMorph.rst:13: WARNING: py:class reference target not found: LutBuilder [ref.class]
ImageMorph.rst:13: WARNING: py:class reference target not found: MorphOp [ref.class]
ImageMorph.rst:54: WARNING: py:class reference target not found: LutBuilder [ref.class]
ImageMorph.rst:59: WARNING: py:class reference target not found: LutBuilder [ref.class]
ImageMorph.rst:62: WARNING: py:class reference target not found: LutBuilder [ref.class]
ImageMorph.rst:83: WARNING: py:meth reference target not found: LutBuilder.get_lut [ref.meth]
ImageMorph.rst:83: WARNING: py:meth reference target not found: LutBuilder.load_lut [ref.meth]
ImageMorph.rst:83: WARNING: py:meth reference target not found: LutBuilder.save_lut [ref.meth]
ImageMorph.rst:87: WARNING: py:class reference target not found: MorphOp [ref.class]
ImageMorph.rst:90: WARNING: py:class reference target not found: MorphOp [ref.class]
ImageMorph.rst:90: WARNING: py:meth reference target not found: MorphOp.apply [ref.meth]
ImageMorph.rst:109: WARNING: py:meth reference target not found: MorphOp.match [ref.meth]
ImageMorph.rst:109: WARNING: py:meth reference target not found: MorphOp.get_on_pixels [ref.meth]
ImageMorph.rst:125: WARNING: py:class reference target not found: LutBuilder [ref.class]
ImageMorph.rst:145: WARNING: py:mod reference target not found: _imagingmorph [ref.mod]
ImageMorph.rst:145: WARNING: py:class reference target not found: LutBuilder [ref.class]
ImageMorph.rst:145: WARNING: py:class reference target not found: MorphOp [ref.class]

[hugovk]

Suggested change

	Example: creating a LUT for a 2×2 corner detector::
	For example, creating a LUT for a 2×2 corner detector::

[hugovk]

Yep, let's remove mention of internal details.

Suggested change

	Relationship to `_imagingmorph`
	-------------------------------
	The :mod:`PIL.ImageMorph` module provides a Python interface, while the
	low-level implementation of morphological lookup table evaluation is handled
	by the C extension module :mod:`_imagingmorph`. Users should interact
	with :class:`LutBuilder` and :class:`MorphOp`, not with the C extension
	directly.

[radarhere]

Suggested change

	im = Image.open("input.png").convert("L")
	# Built-in 8-connected dilation
	op = ImageMorph.MorphOp(op_name="dilation8")
	count, out = op.apply(im)
	with Image.open("input.png") as im:
	im = im.convert("L")
	# Built-in 8-connected dilation
	op = ImageMorph.MorphOp(op_name="dilation8")
	count, out = op.apply(im)