Overlay two same sized images in Python

Question

I've got two images that are exactly the same dimensions, all I'm trying to do is take one, make it 50% transparent and place it directly on top of the other, like so:

import Image

background = Image.open("bg.png")
overlay = Image.open("over.png")

background = background.convert("RGBA")
overlay = overlay.convert("RGBA")

background_pixels = background.load()
overlay_pixels = overlay.load()

for y in xrange(overlay.size[1]):
    for x in xrange(overlay.size[0]):
         background_pixels[x,y] = (background_pixels[x,y][0], background_pixels[x,y][1], background_pixels[x,y][2], 255)

for y in xrange(overlay.size[1]):
    for x in xrange(overlay.size[0]):
         overlay_pixels[x,y] = (overlay_pixels[x,y][0], overlay_pixels[x,y][1], overlay_pixels[x,y][2], 128)

background.paste(overlay)
background.save("new.png","PNG")

But all I get is the 50% transparent overlay (so half way there!).

Answer 1

Try using blend() instead of paste() - it seems paste() just replaces the original image with what you're pasting in.

try:
    from PIL import Image
except ImportError:
    import Image

background = Image.open("bg.png")
overlay = Image.open("ol.jpg")

background = background.convert("RGBA")
overlay = overlay.convert("RGBA")

new_img = Image.blend(background, overlay, 0.5)
new_img.save("new.png","PNG")

Answer 2

Maybe too old question, can be done with ease using opencv

cv2.addWeighted(img1, alpha, img2, beta, gamma)
#setting alpha=1, beta=1, gamma=0 gives direct overlay of two images

Documentation link