Can I randomly add a small image (13x12) to an array of pixels (random pixels of the same size of my small image)

Question

I have 20 small images (that I want to put in a target area of a background image (13x12). I have already marked my target area with a circle, I have the coordinates of the circle in two arrays of pixels. Now I want to know how I can randomly add my 20 small images in random area in my arrays of pixels which are basically the target area (the drawn circle).

In my code, I was trying for just one image, if it works, I'll pass the folder of my 20 small images.

# Depencies importation
import cv2
import numpy as np

# Saving directory
saving_dir = "../Saved_Images/"

# Read the background image
bgimg = cv2.imread("../Images/background.jpg")

# Resizing the bacground image
bgimg_resized = cv2.resize(bgimg, (2050,2050))

# Read the image that will be put in the background image (exemple of 1)
# I'm just trying with one, if it works, I'll pass the folder of the 20
small_img = cv2.imread("../Images/small.jpg")

# Convert the resized background image to gray
bgimg_gray = cv2.cvtColor(bgimg, cv2.COLOR_BGR2GRAY) 
# Convert the grayscale image to a binary image
ret, thresh = cv2.threshold(bgimg_gray,127,255,0)
# Determine the moments of the binary image
M = cv2.moments(thresh)
# calculate x,y coordinate of center
cX = int(M["m10"] / M["m00"])
cY = int(M["m01"] / M["m00"])

# Drawing the circle in the background image
circle = cv2.circle(bgimg, (cX, cY), 930, (0,0,255), 9)

print(circle) # This returns None

# Getting the coordinates of the circle
combined = bgimg[:,:,0] + bgimg[:,:,1] + bgimg[:,:,2]
rows, cols = np.where(combined >= 0)

# I have those pixels in rows and cols, but I don't know
# How to randomly put my small image in those pixel

# Saving the new image
cv2.imwrite(saving_dir+"bgimg"+".jpg", bgimg)

cv2.namedWindow('image', cv2.WINDOW_NORMAL)
cv2.resizeWindow("Test", 1000, 1200)
# Showing the images
cv2.imshow("image", bgimg)
# Waiting for any key to stop the program execution
cv2.waitKey(0)

In the expected results, the small images must be placed in the background image randomly.

Answer 1

If you have the center and the radius of your circle, you can easily generate random coordinates by randomly choosing an angle theta from [0, 2*pi] , calculating corresponding x and y values by cos(theta) and sin(theta) and scaling these by some random chosen scaling factors from [0, radius] . I prepared some code for you, see below.

I omitted a lot of code from yours (reading, preprocessing, saving) to focus on the relevant parts (see how to create a minimal, complete, and verifiable example ). Hopefully, you can integrate the main idea of my solution into your code on your own. If not, I will provide further explanations.

import cv2
import numpy as np

# (Artificial) Background image (instead of reading an actual image...)
bgimg = 128 * np.ones((401, 401, 3), np.uint8)

# Circle parameters (obtained somehow...)
center = (200, 200)
radius = 100

# Draw circle in background image
cv2.circle(bgimg, center, radius, (0, 0, 255), 3)

# Shape of small image (known before-hand...?)
(w, h) = (13, 12)

for k in range(200):

    # (Artificial) Small image (instead of reading an actual image...)
    smallimg = np.uint8(np.add(128 * np.random.rand(w, h, 3), (127, 127, 127)))

    # Select random angle theta from [0, 2*pi]
    theta = 2 * np.pi * np.random.rand()

    # Select random distance factors from center
    factX = (radius - w/2) * np.random.rand()
    factY = (radius - h/2) * np.random.rand()

    # Calculate random coordinates for small image from angle and distance factors
    (x, y) = np.uint16(np.add((np.cos(theta) * factX - w/2, np.sin(theta) * factY - h/2), center))

    # Replace (rather than "add") determined area in background image with small image
    bgimg[x:x+smallimg.shape[0], y:y+smallimg.shape[1]] = smallimg

cv2.imshow("bgimg", bgimg)
cv2.waitKey(0)

The exemplary output:

Caveat: I haven't paid attention, if the small images might violate the circle boundary. Therefore, some additional checks or limitations to the scaling factors must be added.

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EDIT: I edited my above code. To take the below comment into account, I shift the small image by (width/2, height/2) , and limit the radius scale factor accordingly, so that the circle boundary isn't violated, neither top/left nor bottom/right.

Before, it was possible, that the boundary is violated in the bottom/right part ( n = 200 ):

After the edit, this should be prevented ( n = 20000 ):

The touching of the red line in the image is due to the line's thickness. For "safety reasons", one could add another 1 pixel distance.