Extract all images from a pdf file and enhance text in those images.

combine_images.py

import sys
from pathlib import Path
import numpy as np
from skimage.io import imread, imsave
from skimage.color import gray2rgb

def to_rgba(img_):
	if 3 == img_.ndim:
		if 4 == img_.shape[2]:
			return img_
		out = np.ones((*img_.shape[:2], 4), dtype=np.float64)
		out[:, :, :3] = img_
		return out
	if 2 == img_.ndim:
		return gray2rgb(i, alpha=True)


if '__main__' == __name__:
	assert len(sys.argv) >= 3
	dir_names = [Path(d) for d in sys.argv[1:]]

	all_file_names = zip(*[d.glob('*.png') for d in dir_names])

	for file_names in all_file_names:
		images = [imread(fname=fn) for fn in file_names]
		# combine
		img_out = sum(to_rgba(i) for i in images) / len(images)
		img_out /= np.amax(img_out)
		img_out[:, :, 3] = 1  # reset alpha channel to no transparency
		path_out = file_names[0].parent.parent.joinpath('out', file_names[0].name)
		imsave(fname=path_out, arr=img_out)  # save to png
		# imsave(fname=(str(path_out)[:-3] + 'jpg'), arr=img_out[..., :-1])  # save to jpg
	print(f'images saved at out/')

pdf_to_images.sh

!#/bin/bash

mkdir denoised_img
mkdir cleaned_denoised_img
mkdir enhanced_denoised_img
mkdir out


# convert my_file.pdf images.png


# http://www.fmwconcepts.com/imagemagick/denoise/index.php

for file in img/*.png; do
 ./denoise -f 1 -s "20x20+203+152" $file "denoised_${file%.png}.png"
done


# http://www.fmwconcepts.com/imagemagick/textcleaner/index.php

for file in denoised_img/*.png; do
# ./textcleaner -g -e none -f 15 -o 20 $file "cleaned_${file%.png}.png"
 ./textcleaner -e normalize -f 15 -o 5 -S 200 $file "cleaned_${file%.png}.png"
done


for file in denoised_img/*.png; do
# convert -enhance -equalize -contrast $file "enhanced_${file%.png}.png"
 convert -auto-gamma -auto-level -normalize $file "enhanced_${file%.png}.png"
done


python combine_images.py cleaned_denoised_img enhanced_denoised_img


for file in out/*.png; do
 convert $file -quality 99 "${file%.png}.jpg"
done