YOLOv8-16bit/ultralytics/yolo/utils/anchors.py

# YOLOv5 🚀 by Ultralytics, GPL-3.0 license
"""
AutoAnchor utils
"""

import random

import numpy as np
import torch
import yaml
from tqdm import tqdm

from ultralytics.yolo.data import BaseDataset
from ultralytics.yolo.utils import LOGGER, TryExcept

from .loggers import colorstr

PREFIX = colorstr('AutoAnchor: ')


def check_anchor_order(m):
    # Check anchor order against stride order for YOLOv5 Detect() module m, and correct if necessary
    a = m.anchors.prod(-1).mean(-1).view(-1)  # mean anchor area per output layer
    da = a[-1] - a[0]  # delta a
    ds = m.stride[-1] - m.stride[0]  # delta s
    if da and (da.sign() != ds.sign()):  # same order
        LOGGER.info(f'{PREFIX}Reversing anchor order')
        m.anchors[:] = m.anchors.flip(0)


@TryExcept(f'{PREFIX}ERROR: ')
def check_anchors(dataset, model, thr=4.0, imgsz=640):
    # Check anchor fit to data, recompute if necessary
    m = model.module.model[-1] if hasattr(model, 'module') else model.model[-1]  # Detect()
    shapes = imgsz * dataset.shapes / dataset.shapes.max(1, keepdims=True)
    scale = np.random.uniform(0.9, 1.1, size=(shapes.shape[0], 1))  # augment scale
    wh = torch.tensor(np.concatenate([l[:, 3:5] * s for s, l in zip(shapes * scale, dataset.labels)])).float()  # wh

    def metric(k):  # compute metric
        r = wh[:, None] / k[None]
        x = torch.min(r, 1 / r).min(2)[0]  # ratio metric
        best = x.max(1)[0]  # best_x
        aat = (x > 1 / thr).float().sum(1).mean()  # anchors above threshold
        bpr = (best > 1 / thr).float().mean()  # best possible recall
        return bpr, aat

    stride = m.stride.to(m.anchors.device).view(-1, 1, 1)  # model strides
    anchors = m.anchors.clone() * stride  # current anchors
    bpr, aat = metric(anchors.cpu().view(-1, 2))
    s = f'\n{PREFIX}{aat:.2f} anchors/target, {bpr:.3f} Best Possible Recall (BPR). '
    if bpr > 0.98:  # threshold to recompute
        LOGGER.info(f'{s}Current anchors are a good fit to dataset ✅')
    else:
        LOGGER.info(f'{s}Anchors are a poor fit to dataset ⚠️, attempting to improve...')
        na = m.anchors.numel() // 2  # number of anchors
        anchors = kmean_anchors(dataset, n=na, img_size=imgsz, thr=thr, gen=1000, verbose=False)
        new_bpr = metric(anchors)[0]
        if new_bpr > bpr:  # replace anchors
            anchors = torch.tensor(anchors, device=m.anchors.device).type_as(m.anchors)
            m.anchors[:] = anchors.clone().view_as(m.anchors)
            check_anchor_order(m)  # must be in pixel-space (not grid-space)
            m.anchors /= stride
            s = f'{PREFIX}Done ✅ (optional: update model *.yaml to use these anchors in the future)'
        else:
            s = f'{PREFIX}Done ⚠️ (original anchors better than new anchors, proceeding with original anchors)'
        LOGGER.info(s)


def kmean_anchors(dataset='./data/coco128.yaml', n=9, img_size=640, thr=4.0, gen=1000, verbose=True):
    """ Creates kmeans-evolved anchors from training dataset

        Arguments:
            dataset: path to data.yaml, or a loaded dataset
            n: number of anchors
            img_size: image size used for training
            thr: anchor-label wh ratio threshold hyperparameter hyp['anchor_t'] used for training, default=4.0
            gen: generations to evolve anchors using genetic algorithm
            verbose: print all results

        Return:
            k: kmeans evolved anchors

        Usage:
            from utils.autoanchor import *; _ = kmean_anchors()
    """
    from scipy.cluster.vq import kmeans

    npr = np.random
    thr = 1 / thr

    def metric(k, wh):  # compute metrics
        r = wh[:, None] / k[None]
        x = torch.min(r, 1 / r).min(2)[0]  # ratio metric
        # x = wh_iou(wh, torch.tensor(k))  # iou metric
        return x, x.max(1)[0]  # x, best_x

    def anchor_fitness(k):  # mutation fitness
        _, best = metric(torch.tensor(k, dtype=torch.float32), wh)
        return (best * (best > thr).float()).mean()  # fitness

    def print_results(k, verbose=True):
        k = k[np.argsort(k.prod(1))]  # sort small to large
        x, best = metric(k, wh0)
        bpr, aat = (best > thr).float().mean(), (x > thr).float().mean() * n  # best possible recall, anch > thr
        s = f'{PREFIX}thr={thr:.2f}: {bpr:.4f} best possible recall, {aat:.2f} anchors past thr\n' \
            f'{PREFIX}n={n}, img_size={img_size}, metric_all={x.mean():.3f}/{best.mean():.3f}-mean/best, ' \
            f'past_thr={x[x > thr].mean():.3f}-mean: '
        for x in k:
            s += '%i,%i, ' % (round(x[0]), round(x[1]))
        if verbose:
            LOGGER.info(s[:-2])
        return k

    if isinstance(dataset, str):  # *.yaml file
        with open(dataset, errors='ignore') as f:
            data_dict = yaml.safe_load(f)  # model dict

        dataset = BaseDataset(data_dict['train'], augment=True, rect=True)

    # Get label wh
    shapes = img_size * dataset.shapes / dataset.shapes.max(1, keepdims=True)
    wh0 = np.concatenate([l[:, 3:5] * s for s, l in zip(shapes, dataset.labels)])  # wh

    # Filter
    i = (wh0 < 3.0).any(1).sum()
    if i:
        LOGGER.info(f'{PREFIX}WARNING ⚠️ Extremely small objects found: {i} of {len(wh0)} labels are <3 pixels in size')
    wh = wh0[(wh0 >= 2.0).any(1)].astype(np.float32)  # filter > 2 pixels
    # wh = wh * (npr.rand(wh.shape[0], 1) * 0.9 + 0.1)  # multiply by random scale 0-1

    # Kmeans init
    try:
        LOGGER.info(f'{PREFIX}Running kmeans for {n} anchors on {len(wh)} points...')
        assert n <= len(wh)  # apply overdetermined constraint
        s = wh.std(0)  # sigmas for whitening
        k = kmeans(wh / s, n, iter=30)[0] * s  # points
        assert n == len(k)  # kmeans may return fewer points than requested if wh is insufficient or too similar
    except Exception:
        LOGGER.warning(f'{PREFIX}WARNING ⚠️ switching strategies from kmeans to random init')
        k = np.sort(npr.rand(n * 2)).reshape(n, 2) * img_size  # random init
    wh, wh0 = (torch.tensor(x, dtype=torch.float32) for x in (wh, wh0))
    k = print_results(k, verbose=False)

    # Plot
    # k, d = [None] * 20, [None] * 20
    # for i in tqdm(range(1, 21)):
    #     k[i-1], d[i-1] = kmeans(wh / s, i)  # points, mean distance
    # fig, ax = plt.subplots(1, 2, figsize=(14, 7), tight_layout=True)
    # ax = ax.ravel()
    # ax[0].plot(np.arange(1, 21), np.array(d) ** 2, marker='.')
    # fig, ax = plt.subplots(1, 2, figsize=(14, 7))  # plot wh
    # ax[0].hist(wh[wh[:, 0]<100, 0],400)
    # ax[1].hist(wh[wh[:, 1]<100, 1],400)
    # fig.savefig('wh.png', dpi=200)

    # Evolve
    f, sh, mp, s = anchor_fitness(k), k.shape, 0.9, 0.1  # fitness, generations, mutation prob, sigma
    pbar = tqdm(range(gen), bar_format='{l_bar}{bar:10}{r_bar}{bar:-10b}')  # progress bar
    for _ in pbar:
        v = np.ones(sh)
        while (v == 1).all():  # mutate until a change occurs (prevent duplicates)
            v = ((npr.random(sh) < mp) * random.random() * npr.randn(*sh) * s + 1).clip(0.3, 3.0)
        kg = (k.copy() * v).clip(min=2.0)
        fg = anchor_fitness(kg)
        if fg > f:
            f, k = fg, kg.copy()
            pbar.desc = f'{PREFIX}Evolving anchors with Genetic Algorithm: fitness = {f:.4f}'
            if verbose:
                print_results(k, verbose)

    return print_results(k).astype(np.float32)