CODEWITHSUNDEEP
pythonnumpyopencv
Mihail
Mihail

Reputation: 81

How to correctly overlay two images with opencv

I am trying to overlay a transparent PNG over a JPG image, I somehow cannot get it to work, what I tried:

import cv2
import numpy as np

a = cv2.imread("a.jpeg")
b = cv2.imread("b.png", cv2.IMREAD_UNCHANGED)

# add alpha channel to jpeg
(h, w) = a.shape[:2]
a = np.dstack([a, np.ones((h, w), dtype="uint8") * 0])

c = cv2.add(b,a)
cv2.imwrite("out.jpeg", c)

The following code will combine the two images, but the PNG transparency is not correct, it's somehow more opaque than it should be. ( I read this could be a issue with opencv ? not reading alpha correctly from png )

What I am trying to do is simply stack two image over another, a background JPG and put over a PNG that has some transparent zones, both images are the same size.

Thanks!

Upvotes: 1

Views: 9108

Answers (1)

Mihail
Mihail

Reputation: 81

I found a example on github I modified a bit, works as expected:

import numpy as np
import cv2

img = cv2.imread('1_calib.jpeg')
overlay_t = cv2.imread('ol.png',-1) # -1 loads with transparency

def overlay_transparent(bg_img, img_to_overlay_t):
    # Extract the alpha mask of the RGBA image, convert to RGB 
    b,g,r,a = cv2.split(img_to_overlay_t)
    overlay_color = cv2.merge((b,g,r))

    mask = cv2.medianBlur(a,5)

    # Black-out the area behind the logo in our original ROI
    img1_bg = cv2.bitwise_and(bg_img.copy(),bg_img.copy(),mask = cv2.bitwise_not(mask))

    # Mask out the logo from the logo image.
    img2_fg = cv2.bitwise_and(overlay_color,overlay_color,mask = mask)

    # Update the original image with our new ROI
    bg_img = cv2.add(img1_bg, img2_fg)

    return bg_img

cv2.imshow('image',overlay_transparent(img, overlay_t))
cv2.waitKey(0)

Upvotes: 1

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