Image blending results as a noise

edit

I'm trying to blend 3 images.

1. First i overlay photo.png over base.png with some positioning. And it works.

1. Second i'm trying to overlay effect.png

over resulting image from previous step.

The result looks like this

I'm using opencv blending described here. I've tried to use cv2.addWeighted but the result was the same

# blending function
def img_overlay(background, overlay, x_offset, y_offset):
    y1, y2 = y_offset, y_offset + overlay.shape[0]
    x1, x2 = x_offset, x_offset + overlay.shape[1]

    alpha_s = overlay[:, :, 3] / 255.0
    alpha_l = 1.0 - alpha_s

    for c in range(0, 3):
        background[y1:y2, x1:x2, c] = (alpha_s * overlay[:, :, c] +
                                   alpha_l * background[y1:y2, x1:x2, c])

    return background

# First step
background = cv2.imread('base.png')
overlay = cv2.imread('photo.png', -1)
x_offset = 386
y_offset = 70
base_photo = img_overlay(background, overlay, x_offset, y_offset)

# Second step
overlay = cv2.imread('effect.png', -1)
final_photo = img_overlay(base_photo, overlay, 0, 0)

cv2.imwrite(result, final_photo)

How i can fix img_overlay function so it will overlay effect.png correctly?