象棋图像只能圈出一个棋子但我想圈出所有棋子该怎么改

这个象棋为什么只能圈出来一个

import cv2

import numpy as np
import matplotlib.pyplot as plt

gray = cv2.imread('666.jpg', cv2.IMREAD_GRAYSCALE)
gray = cv2.medianBlur(gray, 5)
circles = cv2.HoughCircles(gray, cv2.HOUGH_GRADIENT, 1, 300,
param1=50, param2=30,
minRadius=15,maxRadius=25)

img = cv2.imread('666.jpg')
o = cv2.cvtColor(img,cv2.COLOR_BGR2RGB)
circles = np.uint16(np.around(circles))
for i in circles[0,:55]:
cv2.circle(o, (i[0],i[1],), i[2], (255,0,0), 1)

plt.imshow(o)
plt.axis('off')
plt.show()

是要把全部棋子圈出来但我这只能圈出来一个