Source code for mmocr.utils.bbox_utils

# Copyright (c) OpenMMLab. All rights reserved.
from typing import List, Tuple

import numpy as np
from shapely.geometry import LineString, Point

from mmocr.utils.check_argument import is_type_list
from mmocr.utils.point_utils import point_distance, points_center
from mmocr.utils.typing_utils import ArrayLike


def rescale_bbox(bbox: np.ndarray,
                 scale_factor: Tuple[int, int],
                 mode: str = 'mul') -> np.ndarray:
    """Rescale a bounding box according to scale_factor.

    The behavior is different depending on the mode. When mode is 'mul', the
    coordinates will be multiplied by scale_factor, which is usually used in
    preprocessing transforms such as :func:`Resize`.
    The coordinates will be divided by scale_factor if mode is 'div'. It can be
    used in postprocessors to recover the bbox in the original image size.

    Args:
        bbox (ndarray): A bounding box [x1, y1, x2, y2].
        scale_factor (tuple(int, int)): (w_scale, h_scale).
        model (str): Rescale mode. Can be 'mul' or 'div'. Defaults to 'mul'.

    Returns:
        np.ndarray: Rescaled bbox.
    """
    assert mode in ['mul', 'div']
    bbox = np.array(bbox, dtype=np.float32)
    bbox_shape = bbox.shape
    reshape_bbox = bbox.reshape(-1, 2)
    scale_factor = np.array(scale_factor, dtype=float)
    if mode == 'div':
        scale_factor = 1 / scale_factor
    bbox = (reshape_bbox * scale_factor[None]).reshape(bbox_shape)
    return bbox


def rescale_bboxes(bboxes: np.ndarray,
                   scale_factor: Tuple[int, int],
                   mode: str = 'mul') -> np.ndarray:
    """Rescale bboxes according to scale_factor.

    The behavior is different depending on the mode. When mode is 'mul', the
    coordinates will be multiplied by scale_factor, which is usually used in
    preprocessing transforms such as :func:`Resize`.
    The coordinates will be divided by scale_factor if mode is 'div'. It can be
    used in postprocessors to recover the bboxes in the original
    image size.

    Args:
        bboxes (np.ndarray]): Bounding bboxes in shape (N, 4)
        scale_factor (tuple(int, int)): (w_scale, h_scale).
        model (str): Rescale mode. Can be 'mul' or 'div'. Defaults to 'mul'.

    Returns:
        list[np.ndarray]: Rescaled bboxes.
    """
    bboxes = rescale_bbox(bboxes, scale_factor, mode)
    return bboxes


def bbox2poly(bbox: ArrayLike, mode: str = 'xyxy') -> np.array:
    """Converting a bounding box to a polygon.

    Args:
        bbox (ArrayLike): A bbox. In any form can be accessed by 1-D indices.
         E.g. list[float], np.ndarray, or torch.Tensor. bbox is written in
            [x1, y1, x2, y2].
        mode (str): Specify the format of bbox. Can be 'xyxy' or 'xywh'.
            Defaults to 'xyxy'.

    Returns:
        np.array: The converted polygon [x1, y1, x2, y1, x2, y2, x1, y2].
    """
    assert len(bbox) == 4
    if mode == 'xyxy':
        x1, y1, x2, y2 = bbox
        poly = np.array([x1, y1, x2, y1, x2, y2, x1, y2])
    elif mode == 'xywh':
        x, y, w, h = bbox
        poly = np.array([x, y, x + w, y, x + w, y + h, x, y + h])
    else:
        raise NotImplementedError('Not supported mode.')

    return poly


def is_on_same_line(box_a, box_b, min_y_overlap_ratio=0.8):
    # TODO Check if it should be deleted after ocr.py refactored
    """Check if two boxes are on the same line by their y-axis coordinates.

    Two boxes are on the same line if they overlap vertically, and the length
    of the overlapping line segment is greater than min_y_overlap_ratio * the
    height of either of the boxes.

    Args:
        box_a (list), box_b (list): Two bounding boxes to be checked
        min_y_overlap_ratio (float): The minimum vertical overlapping ratio
                                    allowed for boxes in the same line

    Returns:
        The bool flag indicating if they are on the same line
    """
    a_y_min = np.min(box_a[1::2])
    b_y_min = np.min(box_b[1::2])
    a_y_max = np.max(box_a[1::2])
    b_y_max = np.max(box_b[1::2])

    # Make sure that box a is always the box above another
    if a_y_min > b_y_min:
        a_y_min, b_y_min = b_y_min, a_y_min
        a_y_max, b_y_max = b_y_max, a_y_max

    if b_y_min <= a_y_max:
        if min_y_overlap_ratio is not None:
            sorted_y = sorted([b_y_min, b_y_max, a_y_max])
            overlap = sorted_y[1] - sorted_y[0]
            min_a_overlap = (a_y_max - a_y_min) * min_y_overlap_ratio
            min_b_overlap = (b_y_max - b_y_min) * min_y_overlap_ratio
            return overlap >= min_a_overlap or \
                overlap >= min_b_overlap
        else:
            return True
    return False


def stitch_boxes_into_lines(boxes, max_x_dist=10, min_y_overlap_ratio=0.8):
    # TODO Check if it should be deleted after ocr.py refactored
    """Stitch fragmented boxes of words into lines.

    Note: part of its logic is inspired by @Johndirr
    (https://github.com/faustomorales/keras-ocr/issues/22)

    Args:
        boxes (list): List of ocr results to be stitched
        max_x_dist (int): The maximum horizontal distance between the closest
                    edges of neighboring boxes in the same line
        min_y_overlap_ratio (float): The minimum vertical overlapping ratio
                    allowed for any pairs of neighboring boxes in the same line

    Returns:
        merged_boxes(list[dict]): List of merged boxes and texts
    """

    if len(boxes) <= 1:
        return boxes

    merged_boxes = []

    # sort groups based on the x_min coordinate of boxes
    x_sorted_boxes = sorted(boxes, key=lambda x: np.min(x['box'][::2]))
    # store indexes of boxes which are already parts of other lines
    skip_idxs = set()

    i = 0
    # locate lines of boxes starting from the leftmost one
    for i in range(len(x_sorted_boxes)):
        if i in skip_idxs:
            continue
        # the rightmost box in the current line
        rightmost_box_idx = i
        line = [rightmost_box_idx]
        for j in range(i + 1, len(x_sorted_boxes)):
            if j in skip_idxs:
                continue
            if is_on_same_line(x_sorted_boxes[rightmost_box_idx]['box'],
                               x_sorted_boxes[j]['box'], min_y_overlap_ratio):
                line.append(j)
                skip_idxs.add(j)
                rightmost_box_idx = j

        # split line into lines if the distance between two neighboring
        # sub-lines' is greater than max_x_dist
        lines = []
        line_idx = 0
        lines.append([line[0]])
        rightmost = np.max(x_sorted_boxes[line[0]]['box'][::2])
        for k in range(1, len(line)):
            curr_box = x_sorted_boxes[line[k]]
            dist = np.min(curr_box['box'][::2]) - rightmost
            if dist > max_x_dist:
                line_idx += 1
                lines.append([])
            lines[line_idx].append(line[k])
            rightmost = max(rightmost, np.max(curr_box['box'][::2]))

        # Get merged boxes
        for box_group in lines:
            merged_box = {}
            merged_box['text'] = ' '.join(
                [x_sorted_boxes[idx]['text'] for idx in box_group])
            x_min, y_min = float('inf'), float('inf')
            x_max, y_max = float('-inf'), float('-inf')
            for idx in box_group:
                x_max = max(np.max(x_sorted_boxes[idx]['box'][::2]), x_max)
                x_min = min(np.min(x_sorted_boxes[idx]['box'][::2]), x_min)
                y_max = max(np.max(x_sorted_boxes[idx]['box'][1::2]), y_max)
                y_min = min(np.min(x_sorted_boxes[idx]['box'][1::2]), y_min)
            merged_box['box'] = [
                x_min, y_min, x_max, y_min, x_max, y_max, x_min, y_max
            ]
            merged_boxes.append(merged_box)

    return merged_boxes


def bezier2polygon(bezier_points: np.ndarray,
                   num_sample: int = 20) -> List[np.ndarray]:
    # TODO check test later
    """Sample points from the boundary of a polygon enclosed by two Bezier
    curves, which are controlled by ``bezier_points``.

    Args:
        bezier_points (ndarray): A :math:`(2, 4, 2)` array of 8 Bezeir points
            or its equalivance. The first 4 points control the curve at one
            side and the last four control the other side.
        num_sample (int): The number of sample points at each Bezeir curve.
            Defaults to 20.

    Returns:
        list[ndarray]: A list of 2*num_sample points representing the polygon
        extracted from Bezier curves.

    Warning:
        The points are not guaranteed to be ordered. Please use
        :func:`mmocr.utils.sort_points` to sort points if necessary.
    """
    assert num_sample > 0, 'The sampling number should greater than 0'

    bezier_points = np.asarray(bezier_points)
    assert np.prod(
        bezier_points.shape) == 16, 'Need 8 Bezier control points to continue!'

    bezier = bezier_points.reshape(2, 4, 2).transpose(0, 2, 1).reshape(4, 4)
    u = np.linspace(0, 1, num_sample)

    points = np.outer((1 - u) ** 3, bezier[:, 0]) \
        + np.outer(3 * u * ((1 - u) ** 2), bezier[:, 1]) \
        + np.outer(3 * (u ** 2) * (1 - u), bezier[:, 2]) \
        + np.outer(u ** 3, bezier[:, 3])

    # Convert points to polygon
    points = np.concatenate((points[:, :2], points[:, 2:]), axis=0)
    return points.tolist()


def sort_vertex(points_x, points_y):
    # TODO Add typehints & docstring & test
    """Sort box vertices in clockwise order from left-top first.

    Args:
        points_x (list[float]): x of four vertices.
        points_y (list[float]): y of four vertices.
    Returns:
        sorted_points_x (list[float]): x of sorted four vertices.
        sorted_points_y (list[float]): y of sorted four vertices.
    """
    assert is_type_list(points_x, (float, int))
    assert is_type_list(points_y, (float, int))
    assert len(points_x) == 4
    assert len(points_y) == 4
    vertices = np.stack((points_x, points_y), axis=-1).astype(np.float32)
    vertices = _sort_vertex(vertices)
    sorted_points_x = list(vertices[:, 0])
    sorted_points_y = list(vertices[:, 1])
    return sorted_points_x, sorted_points_y


def _sort_vertex(vertices):
    # TODO Add typehints & docstring & test
    assert vertices.ndim == 2
    assert vertices.shape[-1] == 2
    N = vertices.shape[0]
    if N == 0:
        return vertices

    center = np.mean(vertices, axis=0)
    directions = vertices - center
    angles = np.arctan2(directions[:, 1], directions[:, 0])
    sort_idx = np.argsort(angles)
    vertices = vertices[sort_idx]

    left_top = np.min(vertices, axis=0)
    dists = np.linalg.norm(left_top - vertices, axis=-1, ord=2)
    lefttop_idx = np.argmin(dists)
    indexes = (np.arange(N, dtype=np.int_) + lefttop_idx) % N
    return vertices[indexes]


def sort_vertex8(points):
    # TODO Add typehints & docstring & test
    """Sort vertex with 8 points [x1 y1 x2 y2 x3 y3 x4 y4]"""
    assert len(points) == 8
    vertices = _sort_vertex(np.array(points, dtype=np.float32).reshape(-1, 2))
    sorted_box = list(vertices.flatten())
    return sorted_box


def bbox_center_distance(box1: ArrayLike, box2: ArrayLike) -> float:
    """Calculate the distance between the center points of two bounding boxes.

    Args:
        box1 (ArrayLike): The first bounding box
            represented in [x1, y1, x2, y2].
        box2 (ArrayLike): The second bounding box
            represented in [x1, y1, x2, y2].

    Returns:
        float: The distance between the center points of two bounding boxes.
    """
    return point_distance(points_center(box1), points_center(box2))


def bbox_diag_distance(box: ArrayLike) -> float:
    """Calculate the diagonal length of a bounding box (distance between the
    top-left and bottom-right).

    Args:
        box (ArrayLike): The bounding box represented in
        [x1, y1, x2, y2, x3, y3, x4, y4] or [x1, y1, x2, y2].

    Returns:
        float: The diagonal length of the bounding box.
    """
    box = np.array(box, dtype=np.float32)
    assert (box.size == 8 or box.size == 4)

    if box.size == 8:
        diag = point_distance(box[0:2], box[4:6])
    elif box.size == 4:
        diag = point_distance(box[0:2], box[2:4])

    return diag


def bbox_jitter(points_x, points_y, jitter_ratio_x=0.5, jitter_ratio_y=0.1):
    """Jitter on the coordinates of bounding box.

    Args:
        points_x (list[float | int]): List of y for four vertices.
        points_y (list[float | int]): List of x for four vertices.
        jitter_ratio_x (float): Horizontal jitter ratio relative to the height.
        jitter_ratio_y (float): Vertical jitter ratio relative to the height.
    """
    assert len(points_x) == 4
    assert len(points_y) == 4
    assert isinstance(jitter_ratio_x, float)
    assert isinstance(jitter_ratio_y, float)
    assert 0 <= jitter_ratio_x < 1
    assert 0 <= jitter_ratio_y < 1

    points = [Point(points_x[i], points_y[i]) for i in range(4)]
    line_list = [
        LineString([points[i], points[i + 1 if i < 3 else 0]])
        for i in range(4)
    ]

    tmp_h = max(line_list[1].length, line_list[3].length)

    for i in range(4):
        jitter_pixel_x = (np.random.rand() - 0.5) * 2 * jitter_ratio_x * tmp_h
        jitter_pixel_y = (np.random.rand() - 0.5) * 2 * jitter_ratio_y * tmp_h
        points_x[i] += jitter_pixel_x
        points_y[i] += jitter_pixel_y