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?
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Would placing a border around the image, then plotting the rotated image+border work for you?Derek O– Derek O2021-03-07 23:00:26 +00:00Commented Mar 7, 2021 at 23:00
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2 Answers
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:
1 Comment
JarneH
You helped me a lot with this, thank you!
You can use imshow to place the image at a given position. And add a transform to give the image the same rotation as the rectangle.
To steer away from possible copyright issues, the following code uses an image from wikipedia (author: Fernando Revilla):
import matplotlib.pyplot as plt
from matplotlib import transforms
from matplotlib.patches import Rectangle
file = 'https://upload.wikimedia.org/wikipedia/commons/thumb/8/82/Giant_Panda_Tai_Shan.JPG/1200px-Giant_Panda_Tai_Shan.JPG'
img = plt.imread(file, format='jpg')
fig, ax = plt.subplots()
# suppose a rectangle was drawn onto the plot
x, y = 20, 30
width, height = 12, 9
angle = 70
rect = Rectangle((x, y), width, height, angle=angle, ec='black', fc='none', lw=3)
ax.add_patch(rect)
# draw the image using the rectangles position and rotation
tr = transforms.Affine2D().translate(-x, -y).rotate_deg(angle).translate(x, y)
ax.imshow(img, extent=[x, x + width, y, y + height], transform=tr + ax.transData)
ax.set_aspect('equal') # keep right angles
ax.relim()
ax.autoscale()
plt.show()
