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前言
使用opencv对图像进行操作,要求:(1)定位银行票据的四条边,然后旋正。(2)根据版面分析,分割出小写金额区域。
图像校正
首先是对图像的校正
- 读取图片
- 对图片二值化
- 进行边缘检测
- 对边缘的进行霍夫曼变换
- 将变换结果从极坐标空间投影到笛卡尔坐标得到倾斜角
- 根据倾斜角对主体校正
- import os
- import cv2
- import math
- import numpy as np
- from scipy import ndimage
- filepath = './task1-misc/'
- filename = 'bank-bill.bmp'
- filename_correct = 'bank-bill-correct.png'
- def image_correction(input_path: str, output_path: str) -> bool:
- # 读取图像
- img = cv2.imread(input_path)
- # 二值化
- gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
- # 边缘检测
- edges = cv2.Canny(gray,50,150,apertureSize = 3)
- #霍夫变换
- lines = cv2.HoughLines(edges,1,np.pi/180,0)
- for rho,theta in lines[0]:
- a = np.cos(theta) # 将极坐标转换为直角坐标
- b = np.sin(theta)
- x0 = a*rho
- y0 = b*rho
- x1 = int(x0 + 1000*(-b)) # 保证端点够远能够覆盖整个图像
- y1 = int(y0 + 1000 * a)
- x2 = int(x0 - 1000*(-b))
- y2 = int(y0 - 1000 * a)
- if x1 == x2 or y1 == y2:
- continue
- t = float(y2-y1)/(x2-x1)
- # 得到角度后将角度范围调整至-45至45度之间
- rotate_angle = math.degrees(math.atan(t))
- if rotate_angle > 45:
- rotate_angle = -90 + rotate_angle
- elif rotate_angle < -45:
- rotate_angle = 90 + rotate_angle
- # 图像根据角度进行校正
- rotate_img = ndimage.rotate(img, rotate_angle)
- # 在图中画出线
- cv2.line(img, (x1, y1), (x2, y2), (0, 0, 255), 2)
- cv2.imwrite(filepath + 'marked-'+filename_correct, img)
- # 输出图像
- cv2.imwrite(output_path, rotate_img)
- return True
-
- input_path = filepath + filename
- output_path = filepath + filename_correct
- if image_correction(input_path, output_path):
- print("角度校正成功")
复制代码 图(左)中的红线斜率和偏置是经过霍夫变换并进行极坐标转换后得到,后续将根据这条线进行角度的校正,校正后的结果如图(右)所示。
为了便于后续操作,我们选择将背景去掉,保存为.png图片。- filename_clear = 'bank-bill-clear.png'
- # 去除背景
- def remove_background(input_path: str, output_path: str) -> bool:
- # 读取图像
- img = cv2.imread(input_path, cv2.IMREAD_UNCHANGED)
- # 检查是否已经具有 alpha 通道,如果没有则创建一个
- if img.shape[2] == 3:
- alpha_channel = np.ones_like(img[:, :, 0], dtype=img.dtype) * 255
- img = np.dstack((img, alpha_channel))
- # 提取图像的 alpha 通道(透明度)
- alpha_channel = img[:, :, 3]
- # 将白色或黑色(背景)的像素设置为透明
- alpha_channel[(img[:, :, :3] == [255, 255, 255]).all(axis=2)] = 0
- alpha_channel[(img[:, :, :3] == [0, 0, 0]).all(axis=2)] = 0
- # 保存为带有透明通道的 PNG 图像
- cv2.imwrite(output_path, img)
- return True
- input_path = filepath + filename_correct
- output_path = filepath + filename_clear
- if remove_background(input_path, output_path):
- print("去除背景成功")
复制代码 版面分析与分割金额区域
使用opencv对图像进行版面分析得到表格线的投影。- def detectTable(img, save_path):
- gray_img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
-
- thresh_img = cv2.adaptiveThreshold(~gray_img,255,cv2.ADAPTIVE_THRESH_MEAN_C,cv2.THRESH_BINARY,15,-2)
-
- h_img = thresh_img.copy()
- v_img = thresh_img.copy()
- scale = 20
- h_size = int(h_img.shape[1]/scale)
- h_structure = cv2.getStructuringElement(cv2.MORPH_RECT,(h_size,1)) # 形态学因子
- h_erode_img = cv2.erode(h_img,h_structure,1)
- h_dilate_img = cv2.dilate(h_erode_img,h_structure,1)
- # cv2.imshow("h_erode",h_dilate_img)
- v_size = int(v_img.shape[0] / scale)
- v_structure = cv2.getStructuringElement(cv2.MORPH_RECT, (1, v_size)) # 形态学因子
- v_erode_img = cv2.erode(v_img, v_structure, 1)
- v_dilate_img = cv2.dilate(v_erode_img, v_structure, 1)
- mask_img = h_dilate_img+v_dilate_img
- joints_img = cv2.bitwise_and(h_dilate_img,v_dilate_img)
- joints_img = cv2.dilate(joints_img,None,iterations=3)
- cv2.imwrite(os.path.join(save_path, "joints.png"),joints_img)
- cv2.imwrite(os.path.join(save_path, "mask.png"), mask_img)
- return joints_img, mask_img
- img = cv2.imread(os.path.join(filepath, filename_clear))
- _, mask_img = detectTable(img, save_path=filepath)
复制代码 投影得到两张图,一张表示交叉点的投影,另一张表示表格线的投影,如下图所示,后续的边缘检测我们将用到右侧的图。
[code]def find_bound(img): # 查找图像中的轮廓 contours, _ = cv2.findContours(img, cv2.RETR_CCOMP, cv2.CHAIN_APPROX_TC89_L1) # 遍历所有轮廓 site = [] for contour in contours: # 计算边界矩形 x, y, w, h = cv2.boundingRect(contour) if 20 < w < 35 and 20 |
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