OpenCV error in cvtColor

[alanbernstein]

Camelot failed with some OpenCV error on a personal document of mine. I tried again with this file https://arxiv.org/pdf/1706.05137.pdf, and saw the same error. This is just after having resolved ModuleNotFoundError: No module named 'cv2' with pip install opencv-python. I've used OpenCV on this machine without trouble before, but I'm not too familiar with the installation process/dependencies for OpenCV. Apologies if this is just a goofy problem with my setup.

Running this:

import camelot
tables = camelot.read_pdf("whatever.pdf")
tables[0]
tables[0].parsing_report
tables[0].df

I get this traceback:

Traceback (most recent call last):
  File "test.py", line 6, in <module>
    tables = camelot.read_pdf(fname)
  File "/usr/local/lib/python3.7/site-packages/camelot/io.py", line 91, in read_pdf
    tables = p.parse(flavor=flavor, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/camelot/handlers.py", line 146, in parse
    t = parser.extract_tables(p)
  File "/usr/local/lib/python3.7/site-packages/camelot/parsers/lattice.py", line 339, in extract_tables
    self._generate_table_bbox()
  File "/usr/local/lib/python3.7/site-packages/camelot/parsers/lattice.py", line 212, in _generate_table_bbox
    blocksize=self.threshold_blocksize, c=self.threshold_constant)
  File "/usr/local/lib/python3.7/site-packages/camelot/image_processing.py", line 38, in adaptive_threshold
    gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
cv2.error: OpenCV(3.4.3) /Users/travis/build/skvark/opencv-python/opencv/modules/imgproc/src/color.cpp:181: error: (-215:Assertion failed) !_src.empty() in function 'cvtColor'

Note /Users/travis/ does not exist on my machine.

>>> import platform; print(platform.platform())
Darwin-16.7.0-x86_64-i386-64bit
>>> import sys; print('Python', sys.version)
Python 3.7.0 (default, Jul 23 2018, 20:24:19)
[Clang 9.0.0 (clang-900.0.39.2)]
>>> import numpy; print('NumPy', numpy.__version__)
NumPy 1.15.2
>>> import cv2; print('OpenCV', cv2.__version__)
OpenCV 3.4.3
>>> import camelot; print('Camelot', camelot.__version__)
Camelot 0.2.3

[vinayak-mehta]

This is just after having resolved ModuleNotFoundError: No module named 'cv2' with pip install opencv-python.

@alanbernstein To install Camelot, you need to do pip install camelot-py[all] as given in the README.

A traceback with /Users/travis is weird, could be that opencv-python is built on Travis-CI before being uploaded to PyPI and you installed a broken build. Let me look into this.

[vinayak-mehta]

@alanbernstein I was not able to reproduce this. Can you check if you face the same error with the most recent release? If yes, please open a new issue.