[Python] Find contrast between two colours

I would like to write a function in Python that compares two colours. Let's say I have a background colour and a font colour. And I want wo check if the font has enough contrast to be visible on the background. I receive the colours in RGB format like 16777215 (white). How can I do that?

What does the difference between two colour values, e.g. 16777215 - 12788622 mean? Does the difference say anything about the contrast?

Edit: A solution based on the comments of @VC.One that loops through a pdf document to find text with low contrast on a white background:

import streamlit as st
import pymupdf

def main():
# File Uploader
uploaded_file = st.file_uploader("Select PDF file: ", type='pdf')

# Search document
if uploaded_file is not None:
find_low_contrast_font(uploaded_file)

def find_low_contrast_font(uploaded_file):
# Open document
doc = pymupdf.open("pdf", uploaded_file.read())

# Loop through the pages
for page_num in range(doc.page_count):
page = doc[page_num]
for text in page.get_text("dict")["blocks"]:
for line in text["lines"]:
for span in line["spans"]:
if contrast_is_low(span["color"]):
st.write(f"Low contrast font on page {page_num + 1}: {span['text']}")

# Close document
doc.close()

def contrast_is_low(font_color):
background_color = 16777215 # White
minimum_distance = 40 # (DF,DF,DF) / (223,223,223) / 14671839 / light grey: distance to white is 32
low_contrast = False

background_color_rgb_dict = get_rgb_values_from_integer(background_color)
background_color_luminance = calculate_luminance(background_color_rgb_dict)

font_color_rgb_dict = get_rgb_values_from_integer(font_color)
font_color_luminance = calculate_luminance(font_color_rgb_dict)

distance = calculate_distance(background_color_luminance, font_color_luminance)

if distance <= minimum_distance:
low_contrast = True

return low_contrast

def get_rgb_values_from_integer(rgb_int):
blue = rgb_int & 255
green = (rgb_int >> 8) & 255
red = (rgb_int >> 16) & 255
rgb_dict = {
"r": red,
"g": green,
"b": blue
}
return rgb_dict

def calculate_luminance(rgb_dict):
return 0.299 * rgb_dict["r"] + 0.587 * rgb_dict["g"] + 0.114 * rgb_dict["b"]

def calculate_distance(background_color_luminance, font_color_luminance):
return abs(background_color_luminance - font_color_luminance)

if __name__ == "__main__":
main()

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