Remove background from images of black text

background_killer.py

# %%
import glob
import sys

import cv2
import numpy as np


# %%
def remove_background(frame):
    # convert the BGR color space of image to HSV color space
    hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)

    # Threshold of black-ish in HSV space
    lower_blue = np.array([0, 0, 0])
    upper_blue = np.array([360, 150, 150])

    # mask contains the text, but not the background
    mask = cv2.inRange(hsv, lower_blue, upper_blue)
    # smooth the edges a little bit
    mask = cv2.GaussianBlur(mask, (7, 7), sigmaX=0.2)

    # invert colors, mask to cut out the background, inverse again
    n_frame = cv2.bitwise_not(frame)  # white text, black bg
    result = cv2.bitwise_or(n_frame, n_frame, mask=mask)
    result = cv2.bitwise_not(result)  # text is black again
    return result


# %% convert all files in a directory
folder = "./doc/word/media"
for p in glob.glob(f"{folder}/*.png"):
    frame = cv2.imread(p)
    res = remove_background(frame)
    cv2.imwrite(p, res)