opencvc识别A4纸完整代码

OpenCV可以使用霍夫变换检测A4纸，以下是完整代码：

import cv2
import numpy as np

# 定义图片路径
img_path = "a4_paper.jpg"

# 读取图片
img = cv2.imread(img_path)

# 灰度化处理
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

# 边缘检测
edges = cv2.Canny(gray, 50, 150, apertureSize=3)

# 使用霍夫变换检测直线
lines = cv2.HoughLines(edges, 1, np.pi / 180, 200)

# 定义变量保存检测到的四个角点坐标
pts1 = np.zeros((4, 2), dtype=np.float32)

for line in lines:
    rho, theta = line

    if (theta < (np.pi / 4.)) or (theta > (3. * np.pi / 4.0)):
        # 水平直线
        pt1 = (int(rho / np.cos(theta)), 0)
        pt2 = (int((rho - edges.shape * np.sin(theta)) / np.cos(theta)), edges.shape)

        # 计算交点
        pts1 = np.vstack((pts1, [pt1, pt1]))
        pts1 = np.vstack((pts1, [pt2, pt2]))
    else:
        # 垂直直线
        pt1 = (0, int(rho / np.sin(theta)))
        pt2 = (edges.shape, int((rho - edges.shape * np.cos(theta)) / np.sin(theta)))

        # 计算交点
        pts1 = np.vstack((pts1, [pt1, pt1]))
        pts1 = np.vstack((pts1, [pt2, pt2]))

# 执行透视变换，提取A4纸区域
pts1 = pts1[4:]
pts2 = np.array([[0, 0], [0, 595], [842, 595], [842, 0]], dtype=np.float32)
M = cv2.getPerspectiveTransform(pts1, pts2)
dst = cv2.warpPerspective(img, M, (842, 595))

# 显示原图和处理后的图片
cv2.imshow("img", img)
cv2.imshow("dst", dst)
cv2.waitKey(0)