OpenCV Python透明模板匹配遇大量黑屏像素时失效问题咨询

我使用OpenCV Python的模板匹配功能识别游戏中的各类UI元素区域。这些UI元素包含多变的图形、文本和图标，因此无法直接使用通用模板匹配。我制作了带透明通道的模板，将UI的非静态部分设为透明，使其在匹配时被忽略。脚本在多数场景下正常工作，但当屏幕存在大量黑色像素时会失效。

参考过两篇Stack Overflow文章：

• 《How do I find an image on screen ignoring transparent pixels》
• 《How to template match a simple 2D shape in OpenCV?》

示例截图 #

游戏画面 #

透明模板 #

测试脚本 #

''' mostly based on: https://stackoverflow.com/questions/71302061/how-do-i-find-an-image-on-screen-ignoring-transparent-pixels/71302306#71302306'''

import cv2
import time
import math

# read game image
img = cv2.imread('base.png')

# read image template
template = cv2.imread('minimap.png', cv2.IMREAD_UNCHANGED)
hh, ww = template.shape[:2]

# extract base image and alpha channel and make alpha 3 channels
base = template[:,:,0:3]
alpha = template[:,:,3]
alpha = cv2.merge([alpha,alpha,alpha])

# do masked template matching and save correlation image
correlation = cv2.matchTemplate(img, base, cv2.TM_CCORR_NORMED, mask=alpha)

# set threshold and get all matches
threshold = 0.90

''' from:  https://stackoverflow.com/questions/61779288/how-to-template-match-a-simple-2d-shape-in-opencv/61780200#61780200 '''
# search for max score
result = img.copy()
max_val = 1
rad = int(math.sqrt(hh*hh+ww*ww)/4)

# find max value of correlation image
min_val, max_val, min_loc, max_loc = cv2.minMaxLoc(correlation)
print(max_val, max_loc)

if max_val > threshold:
    # draw match on copy of input
    cv2.rectangle(result, max_loc, (max_loc[0]+ww, max_loc[1]+hh), (0,0,255), 1)

    # save results
    cv2.imwrite('match.jpg', result)
    cv2.imshow('result', result)
    cv2.waitKey(0)
else:
    print("No match found")

匹配结果 #

大量黑色像素场景（错误匹配） #

黑色像素较少场景（正确匹配） #

我不太理解模板匹配算法对alpha通道的处理逻辑，因此不清楚黑色像素为何会干扰匹配，能否解释其中原因？

内容的提问来源于stack exchange，提问作者ktom