augments.py

# Copyright (c) OpenMMLab. All rights reserved.
import random

import numpy as np

from .builder import build_augment


class Augments(object):
    """Data augments.

    We implement some data augmentation methods, such as mixup, cutmix.

    Args:
        augments_cfg (list[`mmcv.ConfigDict`] | obj:`mmcv.ConfigDict`):
            Config dict of augments

    Example:
        >>> augments_cfg = [
                dict(type='BatchCutMix', alpha=1., num_classes=10, prob=0.5),
                dict(type='BatchMixup', alpha=1., num_classes=10, prob=0.3)
            ]
        >>> augments = Augments(augments_cfg)
        >>> imgs = torch.randn(16, 3, 32, 32)
        >>> label = torch.randint(0, 10, (16, ))
        >>> imgs, label = augments(imgs, label)

    To decide which augmentation within Augments block is used
    the following rule is applied.
    We pick augmentation based on the probabilities. In the example above,
    we decide if we should use BatchCutMix with probability 0.5,
    BatchMixup 0.3. As Identity is not in augments_cfg, we use Identity with
    probability 1 - 0.5 - 0.3 = 0.2.
    """

    def __init__(self, augments_cfg):
        super(Augments, self).__init__()

        if isinstance(augments_cfg, dict):
            augments_cfg = [augments_cfg]

        assert len(augments_cfg) > 0, \
            'The length of augments_cfg should be positive.'
        self.augments = [build_augment(cfg) for cfg in augments_cfg]
        self.augment_probs = [aug.prob for aug in self.augments]

        has_identity = any([cfg['type'] == 'Identity' for cfg in augments_cfg])
        if has_identity:
            assert sum(self.augment_probs) == 1.0,\
                'The sum of augmentation probabilities should equal to 1,' \
                ' but got {:.2f}'.format(sum(self.augment_probs))
        else:
            assert sum(self.augment_probs) <= 1.0,\
                'The sum of augmentation probabilities should less than or ' \
                'equal to 1, but got {:.2f}'.format(sum(self.augment_probs))
            identity_prob = 1 - sum(self.augment_probs)
            if identity_prob > 0:
                num_classes = self.augments[0].num_classes
                self.augments += [
                    build_augment(
                        dict(
                            type='Identity',
                            num_classes=num_classes,
                            prob=identity_prob))
                ]
                self.augment_probs += [identity_prob]

    def __call__(self, img, gt_label):
        if self.augments:
            random_state = np.random.RandomState(random.randint(0, 2**32 - 1))
            aug = random_state.choice(self.augments, p=self.augment_probs)
            return aug(img, gt_label)
        return img, gt_label