Source code for akida_models.detection.generate_anchors

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# Copyright (c) 2017 Ngoc Anh Huynh
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"""
This module provides a method to generate YOLO anchors from dataset annotations.
"""

import random
import numpy as np


def _iou(ann, centroids):
    w, h = ann
    similarities = []

    for centroid in centroids:
        c_w, c_h = centroid

        if c_w >= w and c_h >= h:
            similarity = w * h / (c_w * c_h)
        elif c_w >= w and c_h <= h:
            similarity = w * c_h / (w * h + (c_w - w) * c_h)
        elif c_w <= w and c_h >= h:
            similarity = c_w * h / (w * h + c_w * (c_h - h))
        else:  #means both w,h are bigger than c_w and c_h respectively
            similarity = (c_w * c_h) / (w * h)
        similarities.append(similarity)  # will become (k,) shape

    return np.array(similarities)


def _avg_iou(anns, centroids):
    n, _ = anns.shape
    s = 0.

    for i in range(anns.shape[0]):
        s += max(_iou(anns[i], centroids))

    return s / n


def _run_kmeans(ann_dims, anchor_num):
    ann_num = ann_dims.shape[0]
    prev_assignments = np.ones(ann_num) * (-1)
    iteration = 0

    indices = [random.randrange(ann_dims.shape[0]) for _ in range(anchor_num)]
    centroids = ann_dims[indices]
    anchor_dim = ann_dims.shape[1]

    while True:
        distances = []
        iteration += 1
        for i in range(ann_num):
            d = 1 - _iou(ann_dims[i], centroids)
            distances.append(d)
        distances = np.array(distances)

        # assign samples to centroids
        assignments = np.argmin(distances, axis=1)

        if (assignments == prev_assignments).all():
            return centroids

        #calculate new centroids
        centroid_sums = np.zeros((anchor_num, anchor_dim), np.float)
        for i in range(ann_num):
            centroid_sums[assignments[i]] += ann_dims[i]
        for j in range(anchor_num):
            centroids[j] = centroid_sums[j] / (np.sum(assignments == j) + 1e-6)

        prev_assignments = assignments.copy()


[docs]def generate_anchors(annotations_data, num_anchors=5, grid_size=(7, 7)): """ Creates anchors by clustering dimensions of the ground truth boxes from the training dataset. Args: annotations_data (dict): dictionnary of preprocessed VOC data num_anchors (int, optional): number of anchors grid_size (tuple, optional): size of the YOLO grid Returns: list: the computed anchors """ annotation_dims = [] # run k_mean to find the anchors for item in annotations_data: cell_w = item['image_shape'][0] / grid_size[0] cell_h = item['image_shape'][1] / grid_size[1] for box in item['boxes']: relative_w = float(box['x2'] - box['x1']) / cell_w relative_h = float(box['y2'] - box['y1']) / cell_h annotation_dims.append(tuple(map(float, (relative_w, relative_h)))) annotation_dims = np.array(annotation_dims) centroids = _run_kmeans(annotation_dims, num_anchors) print('\nAverage IOU for', num_anchors, 'anchors:', '%0.2f' % _avg_iou(annotation_dims, centroids)) anchors = np.sort(np.round(centroids, 5), 0).tolist() print('Anchors: ', anchors) return anchors