overlay image on another image with opencv and numpy-CodePudding

i have two images, i need to use numpy and opencv to overlay foreground on top of background using numpy masks.

import numpy as np
import cv2
import matplotlib.pyplot as plt

background = cv2.imread("background.jpg")
foreground = cv2.imread("foreground.png")
foreground = cv2.cvtColor(foreground ,cv2.COLOR_BGR2GRAY)
background = cv2.cvtColor(background ,cv2.COLOR_BGR2GRAY)

arr = []
for i in range(foreground.shape[1]): #parse forground pixels
    temp_row = []
    for j in range(foreground.shape[0]):
        if((foreground [i][j] == 0)):#if pixel transperant draw background
            temp_row.append(background[i][j])
        else: # draw forground
            temp_row.append(foreground[i][j])
    arr.append(temp_row)

res_im = np.array(arr)
plt.figure()
plt.imshow(res_im, cmap='gray', vmin=0, vmax=255)
plt.show()

i used this solution but was told i needed to use masks.. help?

CodePudding user response：

Here is one way to do that in Python/Opencv.

Read the transparent foreground image
Read the background image
Extract the alpha channel from the foreground image
Extract the BGR channels from the foreground image
Composite them together using np.where conditional
Save the result

Front:

Back:

import cv2
import numpy as np

# read foreground image
img = cv2.imread('front.png', cv2.IMREAD_UNCHANGED)

# read background image
back = cv2.imread('back.png')

# extract alpha channel from foreground image as mask and make 3 channels
alpha = img[:,:,3]
alpha = cv2.merge([alpha,alpha,alpha])

# extract bgr channels from foreground image
front = img[:,:,0:3]

# blend the two images using the alpha channel as controlling mask
result = np.where(alpha==(0,0,0), back, front)

# save result
cv2.imwrite("front_back.png", result)

# show result
cv2.imshow("RESULT", result)
cv2.waitKey(0)

Result: