Extracting text with OpenCV

detect_letters.py

# A python port of http://stackoverflow.com/a/23565051/2416742

import cv2


def detect_letters(img, struct_elem_x=17, struct_elem_y=3, contour_size=100):
    img_gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    img_sobel = cv2.Sobel(img_gray, cv2.CV_8U, 1, 0, ksize=3, scale=1,
                          delta=0, borderType=cv2.BORDER_DEFAULT)
    ret, img_threshold = cv2.threshold(img_sobel, 0, 255,
                                       cv2.THRESH_OTSU + cv2.THRESH_BINARY)
    element = cv2.getStructuringElement(cv2.MORPH_RECT,
                                        (struct_elem_x, struct_elem_y))
    img_morphex = cv2.morphologyEx(img_threshold, cv2.MORPH_CLOSE, element)
    img_contours, contours, hierarchy = cv2.findContours(img_morphex, 0, 1)

    contours_poly = []
    for c in contours:
        if len(c) < contour_size:
            continue
        poly = cv2.approxPolyDP(c, epsilon=3, closed=True)
        x, y, w, h = cv2.boundingRect(poly)
        if w > h:
            contours_poly.append((x, y, w, h))
    return contours_poly


if __name__ == '__main__':
    # load image & find text
    img = cv2.imread('my_image.png', cv2.IMREAD_COLOR)
    res = detect_letters(img, struct_elem_x=30, struct_elem_y=30, contour_size=100)

    # draw results
    for r in res:
        x, y, w, h = r
        cv2.rectangle(img, (x, y), (x+w, y+h), (0, 255, 0), 2)
    cv2.imshow('image', img)
    cv2.waitKey(0)
    cv2.destroyAllWindows()