make_shrink_map.py

# -*- coding:utf-8 -*- 

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
from shapely.geometry import Polygon
import pyclipper

__all__ = ['MakeShrinkMap']


class MakeShrinkMap(object):
    r'''
    Making binary mask from detection data with ICDAR format.
    Typically following the process of class `MakeICDARData`.
    '''

    def __init__(self, min_text_size=8, shrink_ratio=0.4, **kwargs):
        self.min_text_size = min_text_size
        self.shrink_ratio = shrink_ratio

    def __call__(self, data):
        image = data['image']
        text_polys = data['polys']
        ignore_tags = data['ignore_tags']

        h, w = image.shape[:2]
        text_polys, ignore_tags = self.validate_polygons(text_polys,
                                                         ignore_tags, h, w)
        gt = np.zeros((h, w), dtype=np.float32)
        # gt = np.zeros((1, h, w), dtype=np.float32)
        mask = np.ones((h, w), dtype=np.float32)
        for i in range(len(text_polys)):
            polygon = text_polys[i]
            height = max(polygon[:, 1]) - min(polygon[:, 1])
            width = max(polygon[:, 0]) - min(polygon[:, 0])
            if ignore_tags[i] or min(height, width) < self.min_text_size:
                cv2.fillPoly(mask,
                             polygon.astype(np.int32)[np.newaxis, :, :], 0)
                ignore_tags[i] = True
            else:
                polygon_shape = Polygon(polygon)
                distance = polygon_shape.area * (
                    1 - np.power(self.shrink_ratio, 2)) / polygon_shape.length
                subject = [tuple(l) for l in text_polys[i]]
                padding = pyclipper.PyclipperOffset()
                padding.AddPath(subject, pyclipper.JT_ROUND,
                                pyclipper.ET_CLOSEDPOLYGON)
                shrinked = padding.Execute(-distance)
                if shrinked == []:
                    cv2.fillPoly(mask,
                                 polygon.astype(np.int32)[np.newaxis, :, :], 0)
                    ignore_tags[i] = True
                    continue
                shrinked = np.array(shrinked[0]).reshape(-1, 2)
                cv2.fillPoly(gt, [shrinked.astype(np.int32)], 1)
                # cv2.fillPoly(gt[0], [shrinked.astype(np.int32)], 1)

        data['shrink_map'] = gt
        data['shrink_mask'] = mask
        return data

    def validate_polygons(self, polygons, ignore_tags, h, w):
        '''
        polygons (numpy.array, required): of shape (num_instances, num_points, 2)
        '''
        if len(polygons) == 0:
            return polygons, ignore_tags
        assert len(polygons) == len(ignore_tags)
        for polygon in polygons:
            polygon[:, 0] = np.clip(polygon[:, 0], 0, w - 1)
            polygon[:, 1] = np.clip(polygon[:, 1], 0, h - 1)

        for i in range(len(polygons)):
            area = self.polygon_area(polygons[i])
            if abs(area) < 1:
                ignore_tags[i] = True
            if area > 0:
                polygons[i] = polygons[i][::-1, :]
        return polygons, ignore_tags

    def polygon_area(self, polygon):
        """
        compute polygon area
        """
        area = 0
        q = polygon[-1]
        for p in polygon:
            area += p[0] * q[1] - p[1] * q[0]
            q = p
        return area / 2.0