Extracting embedded PNG byte streams from PDF - pdf

Question

I am programming in Python, but if some tool/library exists in another language that would help me considerably, I am open to suggestions.
I have a large collection of pdf pages that live in a database, and I am trying to automate the collection of those pages to build some image recognition models with them.
These "pdfs" are actually just PNG images encased with a PDF wrapper (presumably so they can be read by PDF readers like Adobe Acrobat). I need the pdfs in image format to feed into the image recognition model pipeline. I am assuming they are PNG images, because when I save the images from the browser (i.e., right click and save image as), the resulting file is a PNG file.
After reading this question from 2010, and checking out this blog post from 2007, I've concluded that there must be a way to just extract the PNG byte array from the PDF instead of re-converting the PDF into a new image. Oddly though, I couldn't find the PNG file header with
#Python 3.6
header = bytes([137, 80, 78, 71, 13, 10, 26, 10])
#the resulting header looks like this: b'\x89PNG\r\n\x1a\n'
file.find(header)
Does that mean that the embedded image is not in fact a PNG image?
If there is no easy way to extract the embedded image byte array, what tool might I use to automate the conversion of each PDF file to some image format (preferably JPEG, PNG, or TIFF)?
Edit: I know tools like ImageMagick exist for format conversions, but I'd really rather do the extraction method for the sake of learning more about these file formats.

Answer 1

pip install pdf2image
pip install pillow
pip install numpy
pip install opencv-python
Then,
import numpy as np
from pdf2image import convert_from_path as read
import PIL
import cv2
#pdf in the form of numpy array to play around with in OpenCV or PIL
img = np.asarray(read('path to the pdf file')[0])#first page of pdf
cv2.imwrite('path to save the image with the file extension',img)