Merge bounding boxes together.

merge_bboxes.py

import copy
import cv2
import os


def merge_bboxes(bboxes, delta_x=0.1, delta_y=0.1):
    """
    Arguments:
        bboxes {list} -- list of bounding boxes with each bounding box is a list [xmin, ymin, xmax, ymax]
        delta_x {float} -- margin taken in width to merge
        detlta_y {float} -- margin taken in height to merge
    Returns:
        {list} -- list of bounding boxes merged
    """

    def is_in_bbox(point, bbox):
        """
        Arguments:
            point {list} -- list of float values (x,y)
            bbox {list} -- bounding box of float_values [xmin, ymin, xmax, ymax]
        Returns:
            {boolean} -- true if the point is inside the bbox
        """
        return point[0] >= bbox[0] and point[0] <= bbox[2] and point[1] >= bbox[1] and point[1] <= bbox[3]

    def intersect(bbox, bbox_):
        """
        Arguments:
            bbox {list} -- bounding box of float_values [xmin, ymin, xmax, ymax]
            bbox_ {list} -- bounding box of float_values [xmin, ymin, xmax, ymax]
        Returns:
            {boolean} -- true if the bboxes intersect
        """
        for i in range(int(len(bbox) / 2)):
            for j in range(int(len(bbox) / 2)):
                # Check if one of the corner of bbox inside bbox_
                if is_in_bbox([bbox[2 * i], bbox[2 * j + 1]], bbox_):
                    return True
        return False
    
    def good_intersect(bbox, bbox_):
        return (bbox[0] < bbox_[2] and bbox[2] > bbox_[0] and
                bbox[1] < bbox_[3] and bbox[3] > bbox_[1])

    # Sort bboxes by ymin
    bboxes = sorted(bboxes, key=lambda x: x[1])

    tmp_bbox = None
    while True:
        nb_merge = 0
        used = []
        new_bboxes = []
        # Loop over bboxes
        for i, b in enumerate(bboxes):
            for j, b_ in enumerate(bboxes):
                # If the bbox has already been used just continue
                if i in used or j <= i:
                    continue
                # Compute the bboxes with a margin
                bmargin = [
                    b[0] - (b[2] - b[0]) * delta_x, b[1] - (b[3] - b[1]) * delta_y,
                    b[2] + (b[2] - b[0]) * delta_x, b[3] + (b[3] - b[1]) * delta_y
                ]
                b_margin = [
                    b_[0] - (b_[2] - b_[0]) * delta_x, b_[1] - (b[3] - b[1]) * delta_y,
                    b_[2] + (b_[2] - b_[0]) * delta_x, b_[3] + (b_[3] - b_[1]) * delta_y
                ]
                # Merge bboxes if bboxes with margin have an intersection
                # Check if one of the corner is in the other bbox
                # We must verify the other side away in case one bounding box is inside the other
                if intersect(bmargin, b_margin) or intersect(b_margin, bmargin):
                    tmp_bbox = [min(b[0], b_[0]), min(b[1], b_[1]), max(b_[2], b[2]), max(b[3], b_[3])]
                    used.append(j)
                    # print(bmargin, b_margin, 'done')
                    nb_merge += 1
                if tmp_bbox:
                    b = tmp_bbox
            if tmp_bbox:
                new_bboxes.append(tmp_bbox)
            elif i not in used:
                new_bboxes.append(b)
            used.append(i)
            tmp_bbox = None
        # If no merge were done, that means all bboxes were already merged
        if nb_merge == 0:
            break
        bboxes = copy.deepcopy(new_bboxes)

    return new_bboxes