Change contrast of pdf using python

pdf_contrast.py

"""
# pdf_contrast.py
Modify contrast of pdf

## Install
```
pip install Pillow pdf2image img2pdf tqdm
```
> Save this file as pdf_contrast.py

## USAGE
```
$ python pdf_contrast.py 2.3 -i in.pdf -o out.pdf
Loading pdf in.pdf
Pages: 48
Contrast x2.3: 100%|███████████████████████| 48/48 [00:02<00:00, 18.42pages/s]
Saving pdf to out.pdf
```
"""
from argparse import ArgumentParser
import io

from PIL import ImageEnhance
import img2pdf
import pdf2image
from tqdm import tqdm


def pdf_contrast(input_file: str, contrast: float, output_file: str):
    """
    Create a new pdf corresponding to the contrast multiplier

    `input_file`: name the of the input_file
    `contrast`: contrast multiplier. 1 corresponds to no change
    `output_file`: name of the file to be saved
    """

    print(f'Loading pdf {input_file}')
    input_images = pdf2image.convert_from_path(input_file)
    print(f'Pages: {len(input_images)}')

    output_images: list[bytes] = []
    for img in tqdm(input_images,
                    desc=f"Contrast x{contrast}",
                    unit="pages"
                    ):
        enhancer = ImageEnhance.Contrast(img)
        out_im = enhancer.enhance(contrast)
        out_img_bytes = io.BytesIO()
        out_im.save(out_img_bytes, format="JPEG")
        output_images.append(out_img_bytes.getvalue())

    print(f'Saving pdf to {output_file}')
    with open(output_file, "wb") as outf:
        img2pdf.convert(*output_images, outputstream=outf)


if __name__ == "__main__":
    input_file = "in.pdf"
    contrast = 1.2
    output_file = f"out_contrast{contrast}.pdf"
    parser = ArgumentParser(description="Modify contrast of pdfs")
    parser.add_argument('-i', '--input',
                        help="Input filename",
                        dest="input_file")
    parser.add_argument('-o', '--output',
                        help="Output file name",
                        dest="output_file")
    parser.add_argument('contrast', type=float,
                        help="""
                             Contrast multipler, must be a float.
                             1 corresponds to no change (1x).
                             2 corresponds to double (2x).
                             0.5 corresponds to half (0.5x).
                             """)
    args = parser.parse_args()
    pdf_contrast(args.input_file, args.contrast, args.output_file)