Draw image in rectangle python

Question

I have plotted a rectangle using matplotlib and would like to place an image in it as shown in the image below. Does anyone have an idea how I can achieve this in python?

Answer 1

Here is one way using Python/OpenCV/Numpy. Do a perspective warp of the panda image using its 4 corners and the 4 corners of the rectangle. Then make a mask of the excess regions, which are black in the warped image. Finally, blend the warped image and background image using the mask.

Input:

Graph Image:

import numpy as np
import cv2
import math

# read image to be processed
img = cv2.imread("panda.png")
hh, ww = img.shape[:2]

# read background image
bck = cv2.imread("rectangle_graph.png")
hhh, www = bck.shape[:2]

# specify coordinates for corners of img in order TL, TR, BR, BL as x,y pairs
img_pts = np.float32([[0,0], [ww-1,0], [ww-1,hh-1], [0,hh-1]])

# manually pick coordinates of corners of rectangle in background image
bck_pts = np.float32([[221,245], [333,26], [503,111], [390,331]])

# compute perspective matrix
matrix = cv2.getPerspectiveTransform(img_pts,bck_pts)
#print(matrix)

# change black and near-black to graylevel 1 in each channel so that no values 
# inside panda image will be black in the subsequent mask
img[np.where((img<=[5,5,5]).all(axis=2))] = [1,1,1]

# do perspective transformation setting area outside input to black
img_warped = cv2.warpPerspective(img, matrix, (www,hhh), cv2.INTER_LINEAR, borderMode=cv2.BORDER_CONSTANT, borderValue=(0,0,0))

# make mask for area outside the warped region
# (black in image stays black and rest becomes white)
mask = cv2.cvtColor(img_warped, cv2.COLOR_BGR2GRAY)
mask = cv2.threshold(mask, 0, 255, cv2.THRESH_BINARY)[1]
mask = cv2.merge([mask,mask,mask])
mask_inv = 255 - mask

# use mask to blend between img_warped and bck
result = ( 255 * (bck * mask_inv + img_warped * mask) ).clip(0, 255).astype(np.uint8)

# save images
cv2.imwrite("panda_warped.png", img_warped)
cv2.imwrite("panda_warped_mask.png", mask)
cv2.imwrite("panda_in_graph.png", result)

# show the result
cv2.imshow("warped", img_warped)
cv2.imshow("mask", mask)
cv2.imshow("result", result)
cv2.waitKey(0)
cv2.destroyAllWindows()

Warped Input:

Mask:

Result: