Display An Image Over Another Image At A Particular Co-ordinates In OpenCV

I am trying to display an image over another image at a particular co-ordinates. I have detected the aruco markers using the webcam and I want to display another image over the aru

Solution 1:

To replace a part of image

import cv2
import numpy as np

img1 = cv2.imread('Desert.jpg')
img2 = cv2.imread('Penguins.jpg')

img3 = img1.copy()
# replace values at coordinates (100, 100) to (399, 399) of img3 with region of img2
img3[100:400,100:400,:] = img2[100:400,100:400,:]
cv2.imshow('Result1', img3)

To alpha blend two images

alpha = 0.5
img3 = np.uint8(img1*alpha + img2*(1-alpha))
cv2.imshow('Result2', img3)

Solution 2:

Actually, I found that image homography can be used to do it. Here is the updated code.

import numpy as np
import cv2
import cv2.aruco as aruco

cap = cv2.VideoCapture(0)

while(True):
    ret, frame = cap.read()

    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    aruco_dict = aruco.Dictionary_get(aruco.DICT_6X6_250)
    arucoParameters =  aruco.DetectorParameters_create()

    corners, ids, rejectedImgPoints = aruco.detectMarkers(gray, aruco_dict, parameters=arucoParameters)
    if np.all(ids != None):
        display = aruco.drawDetectedMarkers(frame, corners)
        x1 = (corners[0][0][0][0], corners[0][0][0][1]) 
        x2 = (corners[0][0][1][0], corners[0][0][1][1]) 
        x3 = (corners[0][0][2][0], corners[0][0][2][1]) 
        x4 = (corners[0][0][3][0], corners[0][0][3][1])  

        im_dst = frame 
        im_src = cv2.imread("mask.jpg")
        size = im_src.shape
        pts_dst = np.array([x1,x2,x3,x4])
        pts_src = np.array(
                       [
                        [0,0],
                        [size[1] - 1, 0],
                        [size[1] - 1, size[0] -1],
                        [0, size[0] - 1 ]
                        ],dtype=float
                       );


        h, status = cv2.findHomography(pts_src, pts_dst)
        temp = cv2.warpPerspective(im_src, h, (im_dst.shape[1],im_dst.shape[0])) 
        cv2.fillConvexPoly(im_dst, pts_dst.astype(int), 0, 16);
        im_dst = im_dst + temp  
        cv2.imshow('Display',im_dst) 
    else:
        display = frame
        cv2.imshow('Display',display)
    if cv2.waitKey(1) & 0xFF == ord('q'):
            break

cap.release()
cv2.destroyAllWindows()

Solution 3:

@user8190410's answer works fine. Just to give a complete answer, in order to alpha blend two images with different size at a particular position, you can do the following:

alpha= 0.7
img1_mod = img1.copy()
img1_mod[:pos_x,:pos_y,:] = img1[:pos_x,:pos_y,:]*alpha + img2*(1-alpha)
cv2.imshow('Image1Mod', img1_mod)