[Python] Removing Sourrounding black borders from image using python

Im using the below code to remove black borders left,right,top, bottom from an image. but the problem is its not removing borders left/right/top/bottom from some images. i checked the images it has some light white lines and dots. please help.

import cv2
import numpy as np
import os

def remove_black_border(image, pixel_thresh=40, black_ratio_thresh=0.10):
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
h, w = gray.shape

def is_row_black(y):
return np.mean(gray[y, :] <= pixel_thresh) >= black_ratio_thresh

def is_col_black(x):
return np.mean(gray[:, x] <= pixel_thresh) >= black_ratio_thresh

# Start from full image
top, bottom = 0, h - 1
left, right = 0, w - 1

# Remove top border
while top <= bottom and is_row_black(top):
top += 1

# Remove bottom border
while bottom >= top and is_row_black(bottom):
bottom -= 1

# Remove left border
while left <= right and is_col_black(left):
left += 1

# Remove right border
while right >= left and is_col_black(right):
right -= 1

# Return cropped image
return image[top:bottom+1, left:right+1]

# Set paths
input_folder = "input/RB Images"
output_folder = "output/RB Images"
os.makedirs(output_folder, exist_ok=True)

for filename in os.listdir(input_folder):
if filename.lower().endswith((".jpg", ".jpeg", ".png", ".tif", ".tiff")):
input_path = os.path.join(input_folder, filename)
image = cv2.imread(input_path)

if image is None:
print(f"❌ Failed to load: {filename}")
continue

cropped = remove_black_border(image)
output_path = os.path.join(output_folder, filename)
cv2.imwrite(output_path, cropped)
print(f"✅ Cropped and saved: {filename}")

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