make_border_map.py

# -*- coding:utf-8 -*- 
"""
This code is refer from:
https://github.com/WenmuZhou/DBNet.pytorch/blob/master/data_loader/modules/make_border_map.py
"""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals

import numpy as np
import cv2

np.seterr(divide='ignore', invalid='ignore')
import pyclipper
from shapely.geometry import Polygon
import sys
import warnings

warnings.simplefilter("ignore")

__all__ = ['MakeBorderMap']


class MakeBorderMap(object):
    def __init__(self,
                 shrink_ratio=0.4,
                 thresh_min=0.3,
                 thresh_max=0.7,
                 **kwargs):
        self.shrink_ratio = shrink_ratio
        self.thresh_min = thresh_min
        self.thresh_max = thresh_max

    def __call__(self, data):

        img = data['image']
        text_polys = data['polys']
        ignore_tags = data['ignore_tags']

        canvas = np.zeros(img.shape[:2], dtype=np.float32)
        mask = np.zeros(img.shape[:2], dtype=np.float32)

        for i in range(len(text_polys)):
            if ignore_tags[i]:
                continue
            self.draw_border_map(text_polys[i], canvas, mask=mask)
        canvas = canvas * (self.thresh_max - self.thresh_min) + self.thresh_min

        data['threshold_map'] = canvas
        data['threshold_mask'] = mask
        return data

    def draw_border_map(self, polygon, canvas, mask):
        polygon = np.array(polygon)
        assert polygon.ndim == 2
        assert polygon.shape[1] == 2

        polygon_shape = Polygon(polygon)
        if polygon_shape.area <= 0:
            return
        distance = polygon_shape.area * (
            1 - np.power(self.shrink_ratio, 2)) / polygon_shape.length
        subject = [tuple(l) for l in polygon]
        padding = pyclipper.PyclipperOffset()
        padding.AddPath(subject, pyclipper.JT_ROUND, pyclipper.ET_CLOSEDPOLYGON)

        padded_polygon = np.array(padding.Execute(distance)[0])
        cv2.fillPoly(mask, [padded_polygon.astype(np.int32)], 1.0)

        xmin = padded_polygon[:, 0].min()
        xmax = padded_polygon[:, 0].max()
        ymin = padded_polygon[:, 1].min()
        ymax = padded_polygon[:, 1].max()
        width = xmax - xmin + 1
        height = ymax - ymin + 1

        polygon[:, 0] = polygon[:, 0] - xmin
        polygon[:, 1] = polygon[:, 1] - ymin

        xs = np.broadcast_to(
            np.linspace(
                0, width - 1, num=width).reshape(1, width), (height, width))
        ys = np.broadcast_to(
            np.linspace(
                0, height - 1, num=height).reshape(height, 1), (height, width))

        distance_map = np.zeros(
            (polygon.shape[0], height, width), dtype=np.float32)
        for i in range(polygon.shape[0]):
            j = (i + 1) % polygon.shape[0]
            absolute_distance = self._distance(xs, ys, polygon[i], polygon[j])
            distance_map[i] = np.clip(absolute_distance / distance, 0, 1)
        distance_map = distance_map.min(axis=0)

        xmin_valid = min(max(0, xmin), canvas.shape[1] - 1)
        xmax_valid = min(max(0, xmax), canvas.shape[1] - 1)
        ymin_valid = min(max(0, ymin), canvas.shape[0] - 1)
        ymax_valid = min(max(0, ymax), canvas.shape[0] - 1)
        canvas[ymin_valid:ymax_valid + 1, xmin_valid:xmax_valid + 1] = np.fmax(
            1 - distance_map[ymin_valid - ymin:ymax_valid - ymax + height,
                             xmin_valid - xmin:xmax_valid - xmax + width],
            canvas[ymin_valid:ymax_valid + 1, xmin_valid:xmax_valid + 1])

    def _distance(self, xs, ys, point_1, point_2):
        '''
        compute the distance from point to a line
        ys: coordinates in the first axis
        xs: coordinates in the second axis
        point_1, point_2: (x, y), the end of the line
        '''
        height, width = xs.shape[:2]
        square_distance_1 = np.square(xs - point_1[0]) + np.square(ys - point_1[
            1])
        square_distance_2 = np.square(xs - point_2[0]) + np.square(ys - point_2[
            1])
        square_distance = np.square(point_1[0] - point_2[0]) + np.square(
            point_1[1] - point_2[1])

        cosin = (square_distance - square_distance_1 - square_distance_2) / (
            2 * np.sqrt(square_distance_1 * square_distance_2))
        square_sin = 1 - np.square(cosin)
        square_sin = np.nan_to_num(square_sin)
        result = np.sqrt(square_distance_1 * square_distance_2 * square_sin /
                         square_distance)

        result[cosin <
               0] = np.sqrt(np.fmin(square_distance_1, square_distance_2))[cosin
                                                                           < 0]
        # self.extend_line(point_1, point_2, result)
        return result

    def extend_line(self, point_1, point_2, result, shrink_ratio):
        ex_point_1 = (int(
            round(point_1[0] + (point_1[0] - point_2[0]) * (1 + shrink_ratio))),
                      int(
                          round(point_1[1] + (point_1[1] - point_2[1]) * (
                              1 + shrink_ratio))))
        cv2.line(
            result,
            tuple(ex_point_1),
            tuple(point_1),
            4096.0,
            1,
            lineType=cv2.LINE_AA,
            shift=0)
        ex_point_2 = (int(
            round(point_2[0] + (point_2[0] - point_1[0]) * (1 + shrink_ratio))),
                      int(
                          round(point_2[1] + (point_2[1] - point_1[1]) * (
                              1 + shrink_ratio))))
        cv2.line(
            result,
            tuple(ex_point_2),
            tuple(point_2),
            4096.0,
            1,
            lineType=cv2.LINE_AA,
            shift=0)
        return ex_point_1, ex_point_2