Paint a PDF file to hide parts of words

pdf_paint.py

#!/usr/bin/env python3
import os

import argparse
import random

import fitz

class Config:
    def get_mark_range(self, y, mark):
        rel_pos = (self.bottom - y) / (self.bottom - self.top)
        if mark:
            alpha = rel_pos + 2.0 * (1 - rel_pos)
            mark_range = (0.5 * alpha, 1.0 * alpha)
        else:
            alpha = rel_pos + 1.0 * (1 - rel_pos)
            mark_range = (1.0 * alpha, 1.5 * alpha)
        return mark_range

    def __init__(self, debug):
        if debug:
            # https://htmlcolorcodes.com/color-chart/material-design-color-chart/
            self.color = (255, 87, 51)

            def get_width(top, bottom, mark):
                mark_range = self.get_mark_range(top, mark)
                height = bottom - top
                return height * 0.5 * sum(mark_range)
            self.get_width = get_width

        else:
            # https://htmlcolorcodes.com/color-chart/material-design-color-chart/
            self.color = (255, 249, 196)

            def get_width(top, bottom, mark):
                mark_range = self.get_mark_range(top, mark)
                height = bottom - top
                return height * random.uniform(*mark_range)
            self.get_width = get_width

class Paint:
    def __init__(self):
        self.__mark = True
        self.__next_w = None
        self.__offset = 0

    def generate(self, rect, cfg):
        if self.__next_w is None:
            self.__next_w = cfg.get_width(rect.y0, rect.y1, self.__mark)

        extra_width = rect.width + self.__offset
        while True:
            if self.__mark:
                mark_left = rect.x1 - extra_width
                r = fitz.Rect(mark_left, rect.y0,
                              mark_left + self.__next_w, rect.y1)
                yield r & rect

            if extra_width < self.__next_w:
                break

            extra_width -= self.__next_w
            self.__mark = not self.__mark
            self.__next_w = cfg.get_width(rect.y0, rect.y1, self.__mark)

        extra_width += rect.width
        self.__offset = extra_width - rect.width

def page_paint(page, cfg):
    rect = page.rect
    cfg.top = rect.y0
    cfg.bottom = rect.y1

    paint = Paint()

    page_dict = page.getText('dict')
    for block in page_dict['blocks']:
        if block['type'] != 0:
            continue

        for line in block['lines']:
            for r in paint.generate(fitz.Rect(line['bbox']), cfg):
                # create a pixmap with RGB as colorspace and bounded by irect
                pm = fitz.Pixmap(fitz.Colorspace(fitz.CS_RGB), r.round())
                pm.clearWith(0xff)
                pm.tintWith(*cfg.color)
                page.insertImage(r, pixmap=pm, overlay=True)

def pdf_paint(pdf, pages, cfg):
    doc = fitz.open(pdf)
    # Restrict pages to those presented in document
    pages = pages & set(range(doc.pageCount))

    page_count = len(pages)
    for count, page_num in enumerate(sorted(pages)):
        page = doc[page_num]
        print('Processing page {} / {}...'.format(count + 1, page_count),
              end='\r')
        page_paint(page, cfg)
    print()

    basename, ext = os.path.splitext(pdf)
    doc.save(basename + '_paint' + ext)
    doc.close()

if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('pdf', type=str, help='PDF file')
    parser.add_argument('-p', '--pages', required=True, type=int, nargs='+',
                        help='Pages to paint')
    parser.add_argument('-d', '--debug', action='store_true',
                        help='Debug the script')
    args = parser.parse_args()

    # Pass zero-based pages to function
    pages = set(map(lambda n: n - 1, args.pages))
    pdf_paint(args.pdf, pages, Config(args.debug))

requirements.txt

PyMuPDF>=1.14,<=1.14.10

Ok, I see that the problem is that Debian 9 doesn't have Python 3.6. I will rewrite the script and throw away dataclasses.

Now it should work. I prefer to use virtualenv to manage Python environments:

vonavi@desktop ~> mkdir -p ~/.virtualenvs                              
vonavi@desktop ~> virtualenv -p /usr/bin/python3.5 ~/.virtualenvs/mupdf
Running virtualenv with interpreter /usr/bin/python3.5
Using base prefix '/usr'
New python executable in /home/vonavi/.virtualenvs/mupdf/bin/python3.5
Also creating executable in /home/vonavi/.virtualenvs/mupdf/bin/python
Installing setuptools, pip, wheel...done.
vonavi@desktop ~> source ~/.virtualenvs/mupdf/bin/activate             
(mupdf) vonavi@desktop ~> git clone https://gist.github.com/1368605a4700008ba38278b0f6bc2fde.git       
Cloning into '1368605a4700008ba38278b0f6bc2fde'...
remote: Enumerating objects: 18, done.
remote: Counting objects: 100% (18/18), done.
remote: Compressing objects: 100% (13/13), done.
remote: Total 18 (delta 3), reused 11 (delta 1), pack-reused 0
Unpacking objects: 100% (18/18), done.
(mupdf) vonavi@desktop ~> cd 1368605a4700008ba38278b0f6bc2fde 
(mupdf) vonavi@desktop ~/1368605a4700008ba38278b0f6bc2fde> pip install -r requirements.txt                                                     master
Collecting PyMuPDF==1.14.12 (from -r requirements.txt (line 1))
  Using cached https://files.pythonhosted.org/packages/11/2d/80deffcca33da2321ef28d32f4dd401e8fcac8cb0fef0cf6d6f2f2b46600/PyMuPDF-1.14.12-cp35-cp35m-manylinux1_x86_64.whl
Installing collected packages: PyMuPDF
Successfully installed PyMuPDF-1.14.12
(mupdf) vonavi@desktop ~/1368605a4700008ba38278b0f6bc2fde> ./pdf_paint.py ~/sample.pdf -p $(seq 1 10)                                          master
Processing page 2 / 2...
(mupdf) vonavi@desktop ~/1368605a4700008ba38278b0f6bc2fde> xdg-open ~/sample_paint.pdf

I fixed PyMuPDF versions which work correctly.

I followed your virtualenv guide and script worked fine.
Thank you!

Tried to launch script today.

1. Needed to upgrade dependency from "PyMuPDF>=1.14,<=1.14.10" to "PyMuPDF>=1.14,<=1.14.20".

2. Also tried to replace line 13 with "mark_range = (0.3 * alpha, 0.2 * alpha)" - easier for new person, less shock :)
   Can "difficulty" be passed in script on launch time?

Sorry for a delay. I will check item 1 soon and fix the script in accordance. As for item 2, I agree to add such a parameter as "difficulty". The problem is how to formulate the difficulty itself when we need to control four parameters. Do you have a hint?

No worries. This script depends on the library, so issue with version will happen again and again I guess.

The problem is how to formulate the difficulty itself when we need to control four parameters. Do you have a hint?

I couldn't wrap my head around those parameters. I just tweaked them till result was acceptable. Image below generated by parameters - "mark_range = (1.0 * alpha, 0.3 * alpha)" - if I remember correctly, code was lost.
I think by experimenting one could come up to 3-4 configurations corresponding to easy-...-hard difficulty. I can do that later (by later I mean "don't know when"). No need for you to make any changes for now.

I'm not suggesting for you to make actual git repo, but it will allow making pull requests.