licenseplates/src/LicensePlate.py

from pylab import array, zeros, inv, dot, svd, shape, floor
from xml.dom.minidom import parse
from Error import Error
from Point import Point
from Character import Character
from GrayscaleImage import GrayscaleImage
from NormalizedCharacterImage import NormalizedCharacterImage

'''
    Creates a license plate object based on an XML file. The image should be
    placed in a folder 'images' the xml file in a folder 'xml'

    TODO: perhaps remove non required XML lookups
'''
class LicensePlate:

    def __init__(self, folder_nr, file_nr):
        filename = '%04d/00991_%04d%02d' % (folder_nr, folder_nr, file_nr)

        self.dom = parse('../images/Infos/%s.info' % filename)
        properties = self.get_properties()

        self.image = GrayscaleImage('../images/Images/%s.jpg' % filename)
        self.width = int(properties['width'])
        self.height = int(properties['height'])

        self.read_xml()

    # sets the entire license plate of an image
    def retrieve_data(self, corners):
        x0, y0 = corners[0].to_tuple()
        x1, y1 = corners[1].to_tuple()
        x2, y2 = corners[2].to_tuple()
        x3, y3 = corners[3].to_tuple()

        M = max(x0, x1, x2, x3) - min(x0, x1, x2, x3)
        N = max(y0, y1, y2, y3) - min(y0, y1, y2, y3)

        matrix = array([
          [x0, y0, 1,  0,  0, 0,    0,    0, 0],
          [ 0,  0, 0, x0, y0, 1,    0,    0, 0],
          [x1, y1, 1,  0,  0, 0, -M*x0, -M*y1, -M],
          [ 0,  0, 0, x1, y1, 1,    0,    0, 0],
          [x2, y2, 1,  0,  0, 0, -M*x2, -M*y2, -M],
          [ 0,  0, 0, x2, y2, 1, -N*x2, -N*y2, -N],
          [x3, y3, 1,  0,  0, 0,    0,    0, 0],
          [ 0,  0, 0, x3, y3, 1, -N*x3, -N*y3, -N]
        ])

        P = inv(self.get_transformation_matrix(matrix))
        data = array([zeros(M, float)] * N)

        for i in range(0, M):
            for j in range(0, N):
                or_coor   = dot(P, ([[i],[j],[1]]))
                or_coor_h = or_coor[1][0] / or_coor[2][0], or_coor[0][0] / or_coor[2][0]
                data[j][i] = self.pV(or_coor_h[0], or_coor_h[1])

        return data

    def get_transformation_matrix(self, matrix):
        # Get the vector p and the values that are in there by taking the SVD.
        # Since D is diagonal with the eigenvalues sorted from large to small on
        # the diagonal, the optimal q in min ||Dq|| is q = [[0]..[1]]. Therefore,
        # p = Vq means p is the last column in V.
        U, D, V = svd(matrix)
        p = V[8][:]

        return array([
            [ p[0], p[1], p[2] ],
            [ p[3], p[4], p[5] ],
            [ p[6], p[7], p[8] ]
        ])

    def pV(self, x, y):
        image = self.image

        '''Get the value of a point x,y in the given image, where x and y are not
        necessary integers, so the value is interpolated from its neighbouring
        pixels.'''
        if image.in_bounds(x, y):
            x_low  = floor(x)
            x_high = floor(x + 1)
            y_low  = floor(y)
            y_high = floor(y + 1)
            x_y    = (x_high - x_low) * (y_high - y_low)

            a = x_high - x
            b = y_high - y
            c = x - x_low
            d = y - y_low

            return image[x_low,  y_low] / x_y * a * b \
                + image[x_high,  y_low] / x_y * c * b \
                + image[x_low , y_high] / x_y * a * d \
                + image[x_high, y_high] / x_y * c * d

        return 0

    # Testing purposes
    def show(self):
        from pylab import imshow, show
        imshow(self.data, cmap="gray")
        show()

    def get_properties(self):
        children = self.get_children("properties")

        properties = {}

        for child in children:
            if child.nodeType == child.TEXT_NODE:
                properties[child.nodeName] = child.data
            elif child.nodeType == child.ELEMENT_NODE:
                properties[child.nodeName] = child.firstChild.data

        return properties

    # TODO : create function for location / characters as they do the same
    def read_xml(self):
        children = self.get_children("plate") # most recent version

        for child in children:
            if child.nodeName == "regnum":
              self.license_full = child.firstChild.data
            elif child.nodeName == "identification-letters":
              self.country = child.firstChild.data
            elif child.nodeName == "location":
                self.corners = self.get_corners(child)
            elif child.nodeName == "characters":
                nodes = child.childNodes

                self.characters = []

                for character in nodes:
                  if character.nodeName == "character":
                    value   = self.get_node("char", character).firstChild.data
                    corners = self.get_corners(character)
                    data    = self.retrieve_data(corners)
                    image   = NormalizedCharacterImage(data=data)

                    self.characters.append(Character(value, corners, image))
            else:
                pass

    def get_node(self, node, dom=None):
        if not dom:
            dom = self.dom

        return dom.getElementsByTagName(node)[0]

    def get_children(self, node, dom=None):
        return self.get_node(node, dom).childNodes

    def get_corners(self, child):
      nodes = self.get_children("quadrangle", child)

      corners = []

      for corner in nodes:
        if corner.nodeName == "point":
            corners.append(Point(corner))

      return corners