Python - OpenCV - detect red line

# Code for answer to question on Stackoverflow:
# "opencv - find a red line in image by python cv2 - Stack Overflow"
# https://stackoverflow.com/questions/77037396/find-a-red-line-in-image-by-python-cv2


import cv2


class RedLineDetector:

    def __init__(self):
        self.image = None

    def load_image(self, image_path):
        self.image = cv2.imread(image_path)

    def detect_line(self):
        if self.image is None:
            raise ValueError("No image loaded. Please load an image using 'load_image' method.")

        height, width, _ = self.image.shape
        print(height, width)

        min_width = 300  # Minimum width of the red line
        min_height = 10  # Minimum height of the red line
        max_height = 50  # Maximum height of the red line

        ### I reduce size to see full image on screen ###
        preview_image = cv2.resize(self.image, (width//4, height//4))
        cv2.imshow('image', preview_image)
        #cv2.waitKey(0)

        # find red pixels in some range
        thresh = cv2.inRange(self.image, (50,50,160), (120, 120, 200))
        #print(thresh)

        ### I reduce size to see full image on screen ###
        preview_thresh = cv2.resize(thresh, (width//4, height//4))
        cv2.imshow('thresh', preview_thresh)
        #cv2.waitKey(0)

        # find contours with red pixels
        contours = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
        contours = contours[0] if len(contours) == 2 else contours[1]
        print('len(contours)', len(contours))
        #print(contours)

        result = self.image.copy()
        bounding_box = None

        for c in contours:
            #area = cv2.contourArea(c)
            x, y, w, h = cv2.boundingRect(c)

            if  min_width < w and min_height < h < max_height:
                bounding_box = x, y, w, h
                cv2.drawContours(result, [c], -1, (0, 255, 0), 2)
                print('w, h:', w, h)
                break

        ### I reduce size to see full image on screen ###
        preview_result = cv2.resize(result, (width//4, height//4))
        cv2.imshow('result', preview_result)
        cv2.waitKey(0)

        return bounding_box

# Example usage
detector = RedLineDetector()
detector.load_image('frame3.jpg')
bounding_box = detector.detect_line()
if bounding_box is not None:
    print("Bounding Box Coordinates:", bounding_box)
else:
    print("No red line detected.")