'Opencv Masking via grayscale img does not work

I am a newbe in Opencv. When I use inverse of gray scale image for masking it works but gray scale does not work. What do I miss ? What does mask actually do? I want to use gray img to mask real img.

img1 = cv2.imread('cv_python/DATA/watermark_no_copy.png')
img1 = cv2.cvtColor(img1, cv2.COLOR_BGR2RGB)
plt.imshow(img1)

img1_gray = cv2.cvtColor(img1, cv2.COLOR_RGB2GRAY)
plt.imshow(img1_gray, cmap = 'gray')

img1_g_inv = 255 - img1_gray
my_background = np.full(img1.shape, (255, 255, 255), dtype = np.uint8)
plt.imshow(my_background)

my_mask = cv2.bitwise_and(my_background, my_background, mask = img1_gray)
plt.imshow(my_mask)

my_mask2 = cv2.bitwise_and(my_background, my_background, mask = img1_g_inv)
plt.imshow(my_mask2)

Solution 1:^[1]

Can you change my_background and my_mask like

before

my_background = np.full(img1.shape, (255, 255, 255), dtype = np.uint8)
my_mask = cv2.bitwise_and(my_background, my_background, mask = img1_gray)

after

my_background = np.full(img1_gray.shape, 255, dtype = np.uint8)
my_mask = cv2.bitwise_and(img1_gray, img1_gray, mask = my_background)

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'Opencv Masking via grayscale img does not work

Solution 1:[1]

Sources

Related Questions

Solution 1:^[1]