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OCR of Hand-written Digits

我們的目標是構建一個可以讀取手寫數字的應用程序, 為此，我們需要一些train_data和test_data. OpenCV附帶一個images digits.png（在文件夾opencv\sources\samples\data\中），它有5000個手寫數字（每個數字500個,每個數字是20x20圖像）.所以首先要將圖片切割成5000個不同圖片,每個數字變成一個單行400像素.前面的250個數字作為訓練數據，后250個作為測試數據.

									import numpy as np

									import cv2

									import matplotlib.pyplot as plt

									img = cv2.imread('digits.png')

									gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)

									# Now we split the image to 5000 cells, each 20x20 size

									cells = [np.hsplit(row,100) for row in np.vsplit(gray,50)]

									# Make it into a Numpy array. It size will be (50,100,20,20)

									x = np.array(cells)

									# Now we prepare train_data and test_data.

									train = x[:,:50].reshape(-1,400).astype(np.float32) # Size = (2500,400)

									test = x[:,50:100].reshape(-1,400).astype(np.float32) # Size = (2500,400)

									# Create labels for train and test data

									k = np.arange(10)

									train_labels = np.repeat(k,250)[:,np.newaxis]

									test_labels = train_labels.copy()

									# Initiate kNN, train the data, then test it with test data for k=1

									knn = cv2.ml.KNearest_create()

									knn.train(train, cv2.ml.ROW_SAMPLE, train_labels)

									ret,result,neighbours,dist = knn.findNearest(test,k=5)

									# Now we check the accuracy of classification

									# For that, compare the result with test_labels and check which are wrong

									matches = result==test_labels

									correct = np.count_nonzero(matches)

									accuracy = correct*100.0/result.size

									print( accuracy )

輸出：91.76

進一步提高準確率的方法是增加訓練數據,特別是錯誤的數據.每次訓練時最好是保存訓練數據,以便下次使用.

									# save the data

									np.savez('knn_data.npz',train=train, train_labels=train_labels)

									# Now load the data

									with np.load('knn_data.npz') as data:

									  print( data.files )

									  train = data['train']

									  train_labels = data['train_labels']

OCR of English Alphabets

在opencv / samples / data /文件夾中附帶一個數據文件letter-recognition.data.在每一行中,第一列是一個字母表,它是我們的標簽. 接下來的16個數字是它的不同特征.

									import numpy as np

									import cv2

									import matplotlib.pyplot as plt

									# Load the data, converters convert the letter to a number

									data= np.loadtxt('letter-recognition.data', dtype= 'float32', delimiter = ',',

									          converters= {0: lambda ch: ord(ch)-ord('A')})

									# split the data to two, 10000 each for train and test

									train, test = np.vsplit(data,2)

									# split trainData and testData to features and responses

									responses, trainData = np.hsplit(train,[1])

									labels, testData = np.hsplit(test,[1])

									# Initiate the kNN, classify, measure accuracy.

									knn = cv2.ml.KNearest_create()

									knn.train(trainData, cv2.ml.ROW_SAMPLE, responses)

									ret, result, neighbours, dist = knn.findNearest(testData, k=5)

									correct = np.count_nonzero(result == labels)

									accuracy = correct*100.0/10000

									print( accuracy )