Remove dependency on distro specific packages

[vinayak-mehta]

Something to think about for the future:

• OpenCV: maybe implement morph transform within the library itself/vendorize the code (not sure about dependency on C extensions)?
• tk: Required for matplotlib.
• ghostscript: maybe use some Python library to convert PDF to image (same quality as ghostscript).

[vinayak-mehta]

Some questions:
[1] Can pdftoppm be an alternative to ghostscript?
[2] Are poppler-utils more widely available (pre-installed) than ghostscript?

[tkelman]

Could the matplotlib dependency be made optional? The plotting features here look like not a lot of code, and it's a pretty complicated dependency to pull in.

Similarly might pillow be a viable smaller alternative to the use of opencv here?

[vinayak-mehta]

Hello @tkelman! I think making matplotlib optional makes sense. Let me look into it as I go on to adding more tests for the plotting code #127.

Camelot uses adaptive threshold and morphological transformations from opencv. I haven't worked with pillow in the past but a quick google search got me this morph transform equivalent in pillow. I think removing opencv as a dependency would mean replacing the current image processing code with a combination of pillow + adaptive threshold / morph transform implementations. Let me explore this a bit further. Meanwhile if you have any other alternatives or suggestions on how we could do this, would love if you could share them on this thread!

[vinayak-mehta]

matplotlib is now an optional requirement!

[sweco-sekrsv]

I'm not exaclty sure what you are using Ghostscript for but I switched to pdftoppm for rasterizing pdf to images. I'm using the CLI tool and calling it from python.
For my scenarios, it's stable and generate images quicker than Ghostscript. I have had better success with fonts using pdftoppm as well.

I'm on windows and are using the latest binaries from here:
http://blog.alivate.com.au/poppler-windows

On a side note it can also fix "broken" PDF' files. As the ones in this ticket:
#306
Resaving them with pdftocairo in the poppler tools makes the file load ok with pdf-miner

On another side note I tried making Ghostscript run using multiprocessing (to speed things up) but that did not seem to work very good. Not sure Ghostscript is designed to run using several threads.

[vinayak-mehta]

Moved to #13.