Add an option to start counter generator at index 0

[Eskapp]

This is a feature request.

As Python indexing starts at 0, it would be natural to have the option to start the pdf2image.generators.counter_generator starting at 0. Currently, it can only start at 1 (except if I missed something).
https://github.com/Belval/pdf2image/blob/master/pdf2image/generators.py#L43

Typically, a simple extra optional argument: index_start (or similar) could be added and default to the current behavior

Also (and this is where the request idea initially comes from), pymupdf / fitz starts page index at 0. Adding this option would allow to get the same indexing for the images generated with pdf2image and the page numbers generated by pymupdf / fitz.

[zachguo]

I suppose the interface allows the user to pass your own generator as output_file.

But it seems to be buggy.

from pdf2image.generators import counter_generator

outfn_gen = counter_generator("test")

convert_from_path(
    ...
    output_file=outfn_gen,
    ...
)

The file names would look like

test0001-1.jpg  test0001-3.jpg  test0001-5.jpg  test0001-7.jpg
test0001-2.jpg  test0001-4.jpg  test0001-6.jpg

The zero-padded index (0001) never increments.

pdf2image/pdf2image/generators.py

Lines 41 to 46 in 3bfb7f7

	def counter_generator(prefix="", suffix="", padding_goal=4):
	"""Returns a joined prefix, iteration number, and suffix"""
	i = 0
	while True:
	i += 1
	yield str(prefix) + str(i).zfill(padding_goal) + str(suffix)