OpenCV python copy polygon from one image to another

Question

I have two images. I want to grab a region (polygon, not rectangle) from one image and copy that region onto the other image. How can I accomplish this? Here is what I have so far.

import cv2
import numpy as np

#load two images
srcfilename = 'foo.jpg'
src1 = cv2.imread(srcfilename)
srcfilename = 'bar.jpg'
src2 = cv2.imread(srcfilename)


src1_mask = np.zeros(src1.shape[:-1])
#create a polygon for region of interest
poly = np.array([ [150,150], [200,100], [350,150], [350,200], [300,220], [200,200], [190,180] ], np.int32)
cv2.fillPoly(src1_mask, [poly], 255)

at this point I have my two images loaded and I have a polygon and mask for the region. Now I don't know how to use this mask/polygon to copy that part of src1 onto src2.

#I can also create a mask that has the same number of channels (3)
src1_mask = np.zeros(src1.shape)
#create a polygon for region of interest
poly = np.array([ [150,150], [200,100], [350,150], [350,200], [300,220], [200,200], [190,180] ], np.int32)
cv2.fillPoly(src1_mask, [poly], (255,255,255))

FINAL EDIT

Using bitwise operations I have been able to achieve what I wanted. Here is example code.

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

#load two images
srcfilename = 'foo.jpg'
src1 = cv2.imread(srcfilename)
srcfilename = 'bar.jpg'
src2 = cv2.imread(srcfilename)

#create mask template
src1_mask = src1.copy()
src1_mask = cv2.cvtColor(src1_mask,cv2.COLOR_BGR2GRAY)
src1_mask.fill(0)

#define polygon around region
poly = np.array([ [0,0], [20,0], [65,40], [150,40], [225,5], [225,170],[120,200], [10,190] ], np.int32)

#fill polygon in mask
_ = cv2.fillPoly(src1_mask, [poly], 255)

#create region of interest
roi = src2[np.min(poly[:,1]):np.max(poly[:,1]),np.min(poly[:,0]):np.max(poly[:,0])]
mask = src1_mask[np.min(poly[:,1]):np.max(poly[:,1]),np.min(poly[:,0]):np.max(poly[:,0])]

mask_inv = cv2.bitwise_not(mask)
img1_bg = cv2.bitwise_and(roi,roi,mask = mask_inv)
src1_cut = src1[np.min(poly[:,1]):np.max(poly[:,1]),np.min(poly[:,0]):np.max(poly[:,0])]

img2_fg = cv2.bitwise_and(src1_cut,src1_cut,mask = mask)

# Put logo in ROI and modify the main image
dst = cv2.add(img1_bg,img2_fg)
src2_final = src2.copy()
src2_final[np.min(poly[:,1]):np.max(poly[:,1]),np.min(poly[:,0]):np.max(poly[:,0])] = dst

plt.imshow(cv2.cvtColor(src2_final, cv2.COLOR_BGR2RGB))

Great answer, i searched for this for soooo long and i even tried the answer below, but I'm probably too stupid to use it, TYSFM — NoBlockhit
– NoBlockhit, Commented Jan 24, 2023 at 19:33

Saransh Kejriwal · Accepted Answer · 2016-03-04 02:30:39Z

5

Assuming that src1 is your image and src1_mask is your binary mask:

    src1_mask=cv2.cvtColor(src1_mask,cv2.COLOR_GRAY2BGR)#change mask to a 3 channel image 
    mask_out=cv2.subtract(src1_mask,src1)
    mask_out=cv2.subtract(src1_mask,mask_out)

Now mask_out contains the part of the image src1 located inside the polygon you defined.

answered Mar 4, 2016 at 2:30

Saransh Kejriwal

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mdilip · Accepted Answer · 2018-04-24 13:56:26Z

2

Assuming src1 is source image poly is your polygon, src2 is destination image onto which you want to copy poly.

Copy poly to mask:

mask = np.zeros(src1.shape)
cv2.fillPoly(mask,[poly],1)
poly_copied = np.multiply(mask,src1)

Maskout poly in src2:

mask = np.ones(src2)
#assuming src1 and src2 are of same size
cv2.fillPoly(mask,[poly],0)
src2 = np.multiply(mask,src2)

Copy poly to src2:

src2 = np.add(poly_copied,src2)

answered Apr 24, 2018 at 13:56

mdilip

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