When I want to compress PDF，I got an bigger PDF

[Syntamin]

Description of the bug

I want to compress a PDF. I extracted images from the PDF file and then used pngquant to compress them. Their size was reduced by more than 70%. However, when I used the replace_image function to replace the images, the size of the new PDF became bigger. I want to know why this happens, and if I used the save function incorrectly.

How to reproduce the bug

def compress_pdf(input_path, output_path=""):
doc = pymupdf.open(input_path)

doc_name_with_extension = os.path.basename(input_path)
doc_name = os.path.splitext(doc_name_with_extension)[0]

for page_index in range(10):
    page = doc[page_index]
    image_list = page.get_images()

    for image_index, img in enumerate(image_list, start=1):
        xref = img[0]
        pix = pymupdf.Pixmap(doc, xref)

        if pix.n - pix.alpha > 3:
            pix = pymupdf.Pixmap(pymupdf.csRGB, pix)

        origin_png_path = "./origin/%s_page_%s-image_%s.png" % (
            doc_name,
            page_index,
            image_index,
        )

        pix.save(origin_png_path)  # 存储提取出的图片
        pix = None

        pngquant.compress_png(origin_png_path)

        compressed_png_path = "./origin/%s_page_%s-image_%s-fs8.png" % (
            doc_name,
            page_index,
            image_index,
        )

        # print(os.path.getsize(compressed_png_path), compressed_png_path)

        # 1. replace to file
        # page.replace_image(xref, filename=compressed_png_path)

        with open(compressed_png_path, "rb") as compressed_png:
            compressed_png_bytes = compressed_png.read()
            print(len(compressed_png_bytes), "111")
            page.replace_image(xref, stream=compressed_png_bytes)

doc.save(output_path, garbage=3, clean=True)
doc.close()

PyMuPDF version

1.24.6

Operating system

MacOS

Python version

3.9