Python OpenCV轮廓.很难找到给定图像的所需轮廓

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这是我需要对其进行轮廓检测的图像.我需要勾画矩形内部和外部的字符轮廓，但不需要矩形本身.我附上的第二个图像是所需的输出.

这是我迄今为止try 过的方法:

import cv2

# Read the image
image = cv2.imread('fig1.jpg')

# Convert the image to grayscale
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

# Apply histogram equalization to enhance contrast
equalized = cv2.equalizeHist(gray)

# Apply Gaussian blur to the equalized image
blurred = cv2.GaussianBlur(equalized, (5, 5), 0)

# Apply Laplacian operator to detect edges
edges = cv2.Laplacian(blurred, cv2.CV_64F)

# Apply thresholding to create a binary image
_, edges_binary = cv2.threshold(edges, 20, 255, cv2.THRESH_BINARY)

# Convert edges_binary to the appropriate data type (CV_8UC1)
edges_binary = edges_binary.astype(np.uint8)

# Find contours of the edges
contours, _ = cv2.findContours(edges_binary, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

# Draw the sides of the rectangle (for visualization)
cv2.drawContours(image, contours, -1, (255, 255, 255), 2)

# Get the bounding box of the rectangle
x, y, w, h = cv2.boundingRect(contours[0])

# Omit the sides of the rectangle from the binary image
edges_binary[y:y+h, x:x+w] = 0
# Find contours in the modified binary image
contours, _ = cv2.findContours(edges_binary, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
# Draw contours on the original image
cv2.drawContours(image, contours, -1, (0, 255, 0), 2)

# Display the result
cv2.imshow('Contour Detection', image)
cv2.waitKey(0)
cv2.destroyAllWindows()

我觉得我已经很近了.我试过其他几种方法，但这一种方法最接近预期结果.我上周才学会了OpenCV，有谁能告诉我还有什么可以try 的吗？