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实验环境: anaconda、jupyter notebook
实验用的包:numpy、matplotlib、opencv
实验的目的还是以熟悉图像的透视变换、轮廓特征提取为主要目的
关于如何判断答题卡被选项:通过几个覆盖备选项的掩膜与原二值图像想与,最终整个图像中白色像素点多的就是被选择的项
根据我的亲身体验cv2.bitwise_and(src1,src2)会把src1中与src2不同的点置为0!!!我排查了一下午,可恶啊!!!!
- import cv2
- import numpy as np
- import matplotlib.pyplot as plt
- answer_sheet = cv2.imread('answer_sheet.png')
- # 灰度图
- answer_sheet_gray = cv2.cvtColor(answer_sheet, cv2.COLOR_BGR2GRAY)
-
- # 二值图
- answer_sheet_bin = cv2.threshold(answer_sheet_gray, 127,255,cv2.THRESH_BINARY)[1]
- answer_sheet_bin_inv = cv2.threshold(answer_sheet_gray, 127,255,cv2.THRESH_BINARY_INV)[1]
-
- plt.imshow(answer_sheet_bin, 'gray')
- plt.show()
- # 获取轮廓
- binary, answer_sheet_contours, hierarchy = cv2.findContours(answer_sheet_bin, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)
-
- answer_sheet_contour = None
- answer_sheet_contour_length = 0
- for c in answer_sheet_contours:
- # 做近似
- epsilon = 0.1 * cv2.arcLength(c, True)
- approx = cv2.approxPolyDP(c, epsilon, True)
- # 求周长
- answer_sheet_contour_length_temp = cv2.arcLength(approx,True)
- # 找周长最大的轮廓
- if answer_sheet_contour_length_temp > answer_sheet_contour_length:
- answer_sheet_contour_length = answer_sheet_contour_length_temp
- answer_sheet_contour = approx
-
- # 展示轮廓
- answer_sheet_temp = answer_sheet.copy()
- res = cv2.drawContours(answer_sheet_temp, [answer_sheet_contour], -1, (0,0,255),3)
-
- plt.imshow(cv2.cvtColor(res, cv2.COLOR_BGR2RGB))
- plt.show()
- # 取到四个点
- answer_sheet_contour_deal = np.float32(answer_sheet_contour[:,0,:])
- A,B,C,D = answer_sheet_contour_deal
-
-
- # 在原始图像上画轮廓
- answer_sheet_temp = answer_sheet.copy()
- answer_sheet_contour_deal_temp = np.array([[np.int32(A)],[np.int32(B)],[np.int32(C)],[np.int32(D)]])
- cv2.drawContours(answer_sheet_temp, [answer_sheet_contour_deal_temp], -1, (0,255,0),10)
- plt.imshow(cv2.cvtColor(answer_sheet_temp, cv2.COLOR_BGR2RGB))
- plt.show()
-
- W1 = np.sqrt((A[0] - B[0]) ** 2 + (A[1] -B[1]) ** 2)
- W2 = np.sqrt((C[0] -D[0]) ** 2 + (C[1] -D[1]) ** 2)
- W = max(int(W1), int(W2))
-
- H1 = np.sqrt((A[0] - C[0]) ** 2 + (A[1] -C[1]) ** 2)
- H2 = np.sqrt((B[0] -D[0]) ** 2 + (B[1] -D[1]) ** 2)
- H = max(int(H1), int(H2))
-
- # 目标坐标
- dest = np.array([
- [0,0],
- [0,H],
- [W,H],
- [W,0]
- ], dtype=np.float32)
-
-
- # 在原始图像上画轮廓
- answer_sheet_temp = answer_sheet.copy()
- answer_sheet_contour_deal_temp = np.array([[np.int32(dest[0])],[np.int32(dest[1])],[np.int32(dest[2])],[np.int32(dest[3])]])
- cv2.drawContours(answer_sheet_temp, [answer_sheet_contour_deal_temp], -1, (0,255,0),10)
- plt.imshow(cv2.cvtColor(answer_sheet_temp, cv2.COLOR_BGR2RGB))
- plt.show()
- # 透视变换
- M = cv2.getPerspectiveTransform(answer_sheet_contour_deal, dest)
- answer_sheet_warped = cv2.warpPerspective(answer_sheet_gray, M, (int(W),int(H)))
-
- # 转为二值图
- answer_sheet_warped_bin = cv2.threshold(answer_sheet_warped, 0, 255, cv2.THRESH_BINARY_INV|cv2.THRESH_OTSU)[1]
-
- plt.imshow(answer_sheet_warped_bin, cmap='gray')
- plt.show()
- # 获取每个选项的外轮廓
- cnts = cv2.findContours(answer_sheet_warped_bin.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)[1]
-
- questionCnts = []
- for c in cnts:
- (x, y, w, h) = cv2.boundingRect(c)
- ar = w / float(h)
- # 筛选
- if w >= 20 and h >= 20 and ar >= 0.9 and ar <=1.1:
- yt = np.sum(c[:,:,1])
- xt = np.sum(c[:,:,0])
- questionCnts.append(c)
-
- # 行排序
- for i in range(len(questionCnts) - 1):
- for j in range(len(questionCnts) - 1 - i):
- if questionCnts[j][0][0][1] > questionCnts[j + 1][0][0][1]:
- questionCnts[j],questionCnts[j + 1] = questionCnts[j + 1],questionCnts[j]
- # 列排序
- for i in range(5):
- temp_array = questionCnts[i * 5 : (i + 1) * 5]
- for j in range(len(temp_array) - 1):
- for k in range(len(temp_array) - 1 - j):
- if temp_array[k][0][0][0] > temp_array[k + 1][0][0][0]:
- temp_array[k],temp_array[k + 1] = temp_array[k + 1],temp_array[k]
- questionCnts[i * 5 : (i + 1) * 5] = temp_array
-
- # 展示排序结果
- answer_sheet_warped_bin_temp = answer_sheet_warped_bin.copy()
- for c in questionCnts:
- cv2.drawContours(answer_sheet_warped_bin_temp, np.array([c]),-1,(0,255,0),3)
- plt.imshow(answer_sheet_warped_bin_temp, cmap='gray')
- plt.show()
可以看到排序后按从左到右,从上到下的顺序排列轮廓
- sum = 0
- for i in range(5):
- max_count = 0
- choose = 0
- temp_array = questionCnts[i * 5 : (i + 1) * 5]
- for (j,c) in enumerate(temp_array):
- #掩码图
- # 全黑
- mask = np.ones(answer_sheet_warped_bin.shape, dtype='uint8')
- # 在全黑图上画出白色圈
- cv2.drawContours(mask,[c], -1, 255, -1)
- # plt.imshow(mask, cmap='gray')
- # plt.show()
-
- t = cv2.bitwise_and(answer_sheet_warped_bin,mask)
- # 去除t里的杂色点
- for x in range(len(t)):
- for y in range(len(t[i])):
- if t[x][y] == 1:
- t[x][y] = 0
-
- # 非0像素点最多的就是所选项
- total = cv2.countNonZero(t)
- if total > max_count:
- max_count = total
- choose = j
- # 假定答案为全A
- if choose == 0:
- sum += 20
- answer_sheet_temp = answer_sheet_warped.copy()
- cv2.putText(answer_sheet_temp, "{}%".format(sum), (0, 25), cv2.FONT_HERSHEY_SIMPLEX, 0.65, (0,0,255),2)
- plt.imshow(answer_sheet_temp, 'gray')
- plt.show()
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