Frequently Asked Questions

This part of the documentation answers some common questions. To add questions, please open an issue here.

Does Camelot work with image-based PDFs?

No, Camelot only works with text-based PDFs and not scanned documents. (As Tabula explains, “If you can click and drag to select text in your table in a PDF viewer, then your PDF is text-based”.)

How to reduce memory usage for long PDFs?

During table extraction from long PDF documents, RAM usage can grow significantly.

A simple workaround is to divide the extraction into chunks, and save extracted data to disk at the end of every chunk.

For more details, check out this code snippet from @anakin87:

import camelot


def chunks(l, n):
    """Yield successive n-sized chunks from l."""
    for i in range(0, len(l), n):
        yield l[i : i + n]


def extract_tables(filepath, pages, chunks=50, export_path=".", params={}):
    """
    Divide the extraction work into n chunks. At the end of every chunk,
    save data on disk and free RAM.

    filepath : str
        Filepath or URL of the PDF file.
    pages : str, optional (default: '1')
        Comma-separated page numbers.
        Example: '1,3,4' or '1,4-end' or 'all'.
    """

    # get list of pages from camelot.handlers.PDFHandler
    handler = camelot.handlers.PDFHandler(filepath)
    page_list = handler._get_pages(filepath, pages=pages)

    # chunk pages list
    page_chunks = list(chunks(page_list, chunks))

    # extraction and export
    for chunk in page_chunks:
        pages_string = str(chunk).replace("[", "").replace("]", "")
        tables = camelot.read_pdf(filepath, pages=pages_string, **params)
        tables.export(f"{export_path}/tables.csv")

How can I supply my own image conversion backend to Lattice?

When using the Lattice flavor, you can supply your own image conversion backend by creating a class with a convert method as follows:

>>> class ConversionBackend(object):
>>>     def convert(pdf_path, png_path):
>>>         # read pdf page from pdf_path
>>>         # convert pdf page to image
>>>         # write image to png_path
>>>         pass
>>>
>>> tables = camelot.read_pdf(filename, backend=ConversionBackend())