How do I find an image on screen ignoring transparent pixels

Question

I have a png of an asset, say:

and I'm trying to find it on my screen which looks something like:

Normally, I would use pyautoGUI as such:

pyautogui.locateCenterOnScreen('banana.png', grayscale=True, confidence=0.9)

but it currently isn't working. It seems that the problem might be with the transparent pixels of my banana asset, which obviously aren't matched. Is there a way to do this by ignoring the transparent pixels of the banana asset and treating them as wildcards? Or another way of accomplishing this?

So far in my search, I've found this Git issue with the same issue unresolved since 2014.

Thanks!

Answer 1

In OpenCV, matchTemplate() has a masked mode. So you basically read the transparent template image as is and then extract its base image and the alpha channel. The alpha channel is used as the mask in matchTemplate(). See https://docs.opencv.org/4.1.1/df/dfb/group__imgproc__object.html#ga586ebfb0a7fb604b35a23d85391329be

Input:

Template:

import cv2
import numpy as np

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

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

# extract bananas 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
threshhold = 0.95
loc = np.where(correlation >= threshhold)

# draw matches 
result = img.copy()
for pt in zip(*loc[::-1]):
    cv2.rectangle(result, pt, (pt[0]+ww, pt[1]+hh), (0,0,255), 1)
    print(pt)

# save results
cv2.imwrite('bananas_base.png', base)
cv2.imwrite('bananas_alpha.png', alpha)
cv2.imwrite('game_bananas_matches.jpg', result)  

cv2.imshow('base',base)
cv2.imshow('alpha',alpha)
cv2.imshow('result',result)
cv2.waitKey(0)
cv2.destroyAllWindows()

Result: