基于python与opencv的车牌识别

车牌识别是计算机视觉领域的一个重要应用，基于Python和OpenCV实现车牌识别是比较常见的方法。下面是一个简单的车牌识别程序的示例：

首先，需要导入OpenCV库和其他必要的库：

import cv2
import numpy as np
import pytesseract

然后，读取需要识别的图像文件：

img = cv2.imread('car_plate.jpg')

接下来，对图像进行预处理，包括灰度化、二值化和形态学操作：

gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
gray = cv2.GaussianBlur(gray, (5, 5), 0)
thresh = cv2.adaptiveThreshold(gray, 255, cv2.ADAPTIVE_THRESH_GAUSSIAN_C, cv2.THRESH_BINARY_INV, 11, 2)
kernel = cv2.getStructuringElement(cv2.MORPH_RECT, (3, 3))
thresh = cv2.morphologyEx(thresh, cv2.MORPH_OPEN, kernel, iterations=1)

然后，使用轮廓检测技术来定位车牌：

contours, hierarchy = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
for cnt in contours:
    area = cv2.contourArea(cnt)
    if area > 500:
        rect = cv2.minAreaRect(cnt)
        box = cv2.boxPoints(rect)
        box = np.int0(box)
        cv2.drawContours(img, [box], 0, (0, 0, 255), 2)

最后，使用Tesseract OCR引擎来识别车牌号码：

plate_roi = cv2.boundingRect(cnt)
x, y, w, h = plate_roi
plate_img = thresh[y:y+h, x:x+w]
plate_text = pytesseract.image_to_string(plate_img, lang='eng', config='--psm 11')
print("车牌号码：", plate_text)

完整代码如下：

import cv2
import numpy as np
import pytesseract

img = cv2.imread('car_plate.jpg')

gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
gray = cv2.GaussianBlur(gray, (5, 5), 0)
thresh = cv2.adaptiveThreshold(gray, 255, cv2.ADAPTIVE_THRESH_GAUSSIAN_C, cv2.THRESH_BINARY_INV, 11, 2)
kernel = cv2.getStructuringElement(cv2.MORPH_RECT, (3, 3))
thresh = cv2.morphologyEx(thresh, cv2.MORPH_OPEN, kernel, iterations=1)

contours, hierarchy = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
for cnt in contours:
    area = cv2.contourArea(cnt)
    if area > 500:
        rect = cv2.minAreaRect(cnt)
        box = cv2.boxPoints(rect)
        box = np.int0(box)
        cv2.drawContours(img, [box], 0, (0, 0, 255), 2)
        plate_roi = cv2.boundingRect(cnt)
        x, y, w, h = plate_roi
        plate_img = thresh[y:y+h, x:x+w]
        plate_text = pytesseract.image_to_string(plate_img, lang='eng', config='--psm 11')
        print("车牌号码：", plate_text)

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

需要注意的是，上述程序只是一个简单的示例，实际应用中可能需要更复杂的算法和优化。