Detecting a specific color in a circular area and adding horizontal lines inside the circle-CodePudding

I was working to reproduce an optical illusion that you find

As you can see the values in the for loop are not proportional to the boundaries of the circle, so the lines are short(except the longest line). What am I missing here?

I tried the Hough transform but I had a similar problem.

For more clarity, I write a code to show what I wanted:

 for i in range(0, 360, 15):
        x = int(center[0]   radius * np.cos(np.deg2rad(i)))
        y = int(center[1]   radius * np.sin(np.deg2rad(i)))
        cv2.line(img, (x,y), (x, y), (0, 255, 255), 10)

I want to merge the yellow dots with horizontal lines. But my math is finished right here. Sorry, it's long, I was just trying to make things clear. Thank you for your time.

CodePudding user response：

As @fmw42 pointed out in the comment, splitting the RGB channels and applying a mask is very effective at being able to fill the inside of the circles with horizontal lines.

import numpy as np
import cv2

img = 255*np.ones((800, 800, 3), np.uint8)
height, width,_ = img.shape
for i in range(0, height, 15):
    cv2.line(img, (0, i 3), (width, i 3), (255, 0, 0), 4)
    cv2.line(img, (0, i 8), (width, i 8), (0, 255, 0), 4)
    cv2.line(img, (0, i 13), (width, i 13), (0, 0, 255), 4)
b, g, r = cv2.split(img)
mask_b = np.zeros((height, width), np.uint8)
mask_g = np.zeros((height, width), np.uint8)
mask_r = np.zeros((height, width), np.uint8)
for i in range(0, height, int(height/5)):
    cv2.circle(mask_b, (i, i), 75, 255, -1)
    cv2.circle(mask_g, (i, i), 75, 255, -1)
    cv2.circle(mask_r, (i, i), 75, 255, -1)

#apply the mask to the channels
b = cv2.bitwise_and(b, b, mask=mask_b)
g = cv2.bitwise_and(g, g, mask=mask_g)
r = cv2.bitwise_and(r, r, mask=mask_r)
#merge the channels
img = cv2.merge((b, g, r))

cv2.imshow('image', img)
cv2.waitKey(0)