为了用红色着色遮罩，我们不必找到轮廓，我们可以简单地将thresh设置为BGR图像的红色通道（绿色和蓝色通道为零）：

import cv2
import numpy as np

input_image = cv2.imread('input_image.png', cv2.IMREAD_GRAYSCALE)  # Read input image as grayscale.
_retval, thresh = cv2.threshold(input_image, 125, 255, cv2.THRESH_BINARY)
output = np.zeros((input_image.shape[0], input_image.shape[1], 3), dtype=np.uint8)

output[:, :, 2] = thresh  # Set thresh as the red color channel of the output image (blue and green channels are zeros).

cv2.imwrite('output.png', output)

输出：

如果期望的输出是较粗的线，我们可以在彩色输出上绘制轮廓：

import cv2
import numpy as np

input_image = cv2.imread('input_image.png', cv2.IMREAD_GRAYSCALE)  # Read input image as grayscale.
_retval, thresh = cv2.threshold(input_image, 125, 255, cv2.THRESH_BINARY)
output = np.zeros((input_image.shape[0], input_image.shape[1], 3), dtype=np.uint8)

output[:, :, 2] = thresh  # Set thresh as the red color channel of the output image (blue and green channels are zeros).

contours, hierarchy = cv2.findContours(image=thresh, mode=cv2.RETR_EXTERNAL, method=cv2.CHAIN_APPROX_NONE)
#output = np.zeros((input_image.shape[0], input_image.shape[1], 3), dtype=np.uint8)
for i, contour in enumerate(contours):
    cv2.drawContours(output, contours, i, (0,0,255), thickness=3)

cv2.imwrite('output.png', output)

输出：