datasets/ImbalanceCIFAR.py

"""
Adopted from https://github.com/Megvii-Nanjing/BBN
Customized by Kaihua Tang
"""

import torchvision
import numpy as np
from PIL import Image

# CIFAR10: 
# many: 0,1,2
# median: 3,4,5,6
# few: 7,8,9

class IMBALANCECIFAR10(torchvision.datasets.CIFAR10):
    cls_num = 10

    def __init__(self, train, transform, imbalance_ratio=0.01, root='/ssd1/haotao/datasets', imb_type='exp'):
        super(IMBALANCECIFAR10, self).__init__(root, train, transform=transform, target_transform=None, download=True)
        self.train = train
        if self.train:
            img_num_list = self.get_img_num_per_cls(self.cls_num, imb_type, imbalance_ratio)
            self.gen_imbalanced_data(img_num_list)

        self.labels = self.targets

        # print("{} Mode: Contain {} images".format("train" if train else "test", len(self.data)))

    def _get_class_dict(self):
        class_dict = dict()
        for i, anno in enumerate(self.get_annotations()):
            cat_id = anno["category_id"]
            if not cat_id in class_dict:
                class_dict[cat_id] = []
            class_dict[cat_id].append(i)
        return class_dict


    def get_img_num_per_cls(self, cls_num, imb_type, imb_factor):
        img_max = len(self.data) / cls_num
        img_num_per_cls = []
        if imb_type == 'exp':
            for cls_idx in range(cls_num):
                num = img_max * (imb_factor**(cls_idx / (cls_num - 1.0)))
                img_num_per_cls.append(int(num))
        elif imb_type == 'step':
            for cls_idx in range(cls_num // 2):
                img_num_per_cls.append(int(img_max))
            for cls_idx in range(cls_num // 2):
                img_num_per_cls.append(int(img_max * imb_factor))
        else:
            img_num_per_cls.extend([int(img_max)] * cls_num)
        self.img_num_per_cls = img_num_per_cls
        return img_num_per_cls

    def gen_imbalanced_data(self, img_num_per_cls):
        new_data = []
        new_targets = []
        targets_np = np.array(self.targets, dtype=np.int64)
        classes = np.unique(targets_np)

        self.num_per_cls_dict = dict()
        for the_class, the_img_num in zip(classes, img_num_per_cls):
            self.num_per_cls_dict[the_class] = the_img_num
            idx = np.where(targets_np == the_class)[0]
            # np.random.shuffle(idx) # This is very problametic. Different runs are using different training samples! So I removed this line.
            selec_idx = idx[:the_img_num]
            new_data.append(self.data[selec_idx, ...])
            new_targets.extend([the_class, ] * the_img_num)
        new_data = np.vstack(new_data)
        self.data = new_data
        self.targets = new_targets

    def __getitem__(self, index):
        img, label = self.data[index], self.labels[index]

        # doing this so that it is consistent with all other datasets
        # to return a PIL Image
        img = Image.fromarray(img)

        if self.transform is not None:
            img = self.transform(img)

        if self.target_transform is not None:
            label = self.target_transform(label)

        return img, label
    
    def __len__(self):
        return len(self.labels)

    def get_num_classes(self):
        return self.cls_num

    def get_annotations(self):
        annos = []
        for label in self.labels:
            annos.append({'category_id': int(label)})
        return annos
        
    def get_cls_num_list(self):
        cls_num_list = []
        for i in range(self.cls_num):
            cls_num_list.append(self.num_per_cls_dict[i])
        return cls_num_list

class IMBALANCECIFAR100(IMBALANCECIFAR10):
    """`CIFAR100 <https://www.cs.toronto.edu/~kriz/cifar.html>`_ Dataset.
    This is a subclass of the `CIFAR10` Dataset.
    """
    cls_num = 100
    base_folder = 'cifar-100-python'
    url = "https://www.cs.toronto.edu/~kriz/cifar-100-python.tar.gz"
    filename = "cifar-100-python.tar.gz"
    tgz_md5 = 'eb9058c3a382ffc7106e4002c42a8d85'
    train_list = [
        ['train', '16019d7e3df5f24257cddd939b257f8d'],
    ]

    test_list = [
        ['test', 'f0ef6b0ae62326f3e7ffdfab6717acfc'],
    ]
    meta = {
        'filename': 'meta',
        'key': 'fine_label_names',
        'md5': '7973b15100ade9c7d40fb424638fde48',
    }