This commit swaps out Wand (and its non-Python dependencies ImageMagick
and Ghostscript) for pypdfium2 for PageImage rendering. This has some
advantages:
- Less finicky: Wand often caused users problems, due to "MagickWand
shared library not found" and "PolicyError: not authorized `PDF'"
issues. By contrast, pypdfium2 seems (at least at first) to more
self-contained and not require any system-tweaking.
- Faster: pypdfium2 appears to render images more quickly than Wand (see
@cmdlineuser's tests in #899)
- More flexible: pypdfium2 appears to generate images with greater color
depth; by default, pdfplumber quantizes those images so that they
save/display compactly (in fact, with smaller file sizes than the
previous code), this commit also adds parameters to retain all/more of
the original, more detailed colors.
Thanks to @cmdlineuser in #899 for the suggestion.
See pdfminer.six's changelog for details:
https://github.com/pdfminer/pdfminer.six/blob/develop/CHANGELOG.md
... but a key difference is an improvement in how it assigns `line`,
`rect`, and `curve` objects. (Diagonal two-point lines, for instance,
are now `line` objects instead of `curve` objects.)
As a result, this commit also adjusts some of the tests, where the
pre-20211012 versions had been incorrectly assigning lines as `LTCurve`
objects.
Jeremy Singer-Vine