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Tutorial 2: Customize Datasets

Customize datasets by reorganizing data

The simplest way is to convert your dataset to organize your data into folders.

An example of file structure is as followed.

├── data
│   ├── my_dataset
│   │   ├── img_dir
│   │   │   ├── train
│   │   │   │   ├── xxx{img_suffix}
│   │   │   │   ├── yyy{img_suffix}
│   │   │   │   ├── zzz{img_suffix}
│   │   │   ├── val
│   │   ├── ann_dir
│   │   │   ├── train
│   │   │   │   ├── xxx{seg_map_suffix}
│   │   │   │   ├── yyy{seg_map_suffix}
│   │   │   │   ├── zzz{seg_map_suffix}
│   │   │   ├── val

A training pair will consist of the files with same suffix in img_dir/ann_dir.

If split argument is given, only part of the files in img_dir/ann_dir will be loaded. We may specify the prefix of files we would like to be included in the split txt.

More specifically, for a split txt like following,

xxx
zzz

Only data/my_dataset/img_dir/train/xxx{img_suffix}, data/my_dataset/img_dir/train/zzz{img_suffix}, data/my_dataset/ann_dir/train/xxx{seg_map_suffix}, data/my_dataset/ann_dir/train/zzz{seg_map_suffix} will be loaded.

:::{note} The annotations are images of shape (H, W), the value pixel should fall in range [0, num_classes - 1]. You may use 'P' mode of pillow to create your annotation image with color. :::

Customize datasets by mixing dataset

MMSegmentation also supports to mix dataset for training. Currently it supports to concat, repeat and multi-image mix datasets.

Repeat dataset

We use RepeatDataset as wrapper to repeat the dataset. For example, suppose the original dataset is Dataset_A, to repeat it, the config looks like the following

dataset_A_train = dict(
        type='RepeatDataset',
        times=N,
        dataset=dict(  # This is the original config of Dataset_A
            type='Dataset_A',
            ...
            pipeline=train_pipeline
        )
    )

Concatenate dataset

There 2 ways to concatenate the dataset.

  1. If the datasets you want to concatenate are in the same type with different annotation files, you can concatenate the dataset configs like the following.

    1. You may concatenate two ann_dir.

      dataset_A_train = dict(
    type='Dataset_A',
    img_dir = 'img_dir',
    ann_dir = ['anno_dir_1', 'anno_dir_2'],
    pipeline=train_pipeline
)

    2. You may concatenate two split.

      dataset_A_train = dict(
    type='Dataset_A',
    img_dir = 'img_dir',
    ann_dir = 'anno_dir',
    split = ['split_1.txt', 'split_2.txt'],
    pipeline=train_pipeline
)

    3. You may concatenate two ann_dir and split simultaneously.

      dataset_A_train = dict(
    type='Dataset_A',
    img_dir = 'img_dir',
    ann_dir = ['anno_dir_1', 'anno_dir_2'],
    split = ['split_1.txt', 'split_2.txt'],
    pipeline=train_pipeline
)

      In this case, ann_dir_1 and ann_dir_2 are corresponding to split_1.txt and split_2.txt.

  2. In case the dataset you want to concatenate is different, you can concatenate the dataset configs like the following.

    dataset_A_train = dict()
dataset_B_train = dict()

data = dict(
    imgs_per_gpu=2,
    workers_per_gpu=2,
    train = [
        dataset_A_train,
        dataset_B_train
    ],
    val = dataset_A_val,
    test = dataset_A_test
    )

A more complex example that repeats Dataset_A and Dataset_B by N and M times, respectively, and then concatenates the repeated datasets is as the following.

dataset_A_train = dict(
    type='RepeatDataset',
    times=N,
    dataset=dict(
        type='Dataset_A',
        ...
        pipeline=train_pipeline
    )
)
dataset_A_val = dict(
    ...
    pipeline=test_pipeline
)
dataset_A_test = dict(
    ...
    pipeline=test_pipeline
)
dataset_B_train = dict(
    type='RepeatDataset',
    times=M,
    dataset=dict(
        type='Dataset_B',
        ...
        pipeline=train_pipeline
    )
)
data = dict(
    imgs_per_gpu=2,
    workers_per_gpu=2,
    train = [
        dataset_A_train,
        dataset_B_train
    ],
    val = dataset_A_val,
    test = dataset_A_test
)

Multi-image Mix Dataset

We use MultiImageMixDataset as a wrapper to mix images from multiple datasets. MultiImageMixDataset can be used by multiple images mixed data augmentation like mosaic and mixup.

An example of using MultiImageMixDataset with Mosaic data augmentation:

train_pipeline = [
    dict(type='RandomMosaic', prob=1),
    dict(type='Resize', img_scale=(1024, 512), keep_ratio=True),
    dict(type='RandomFlip', prob=0.5),
    dict(type='Normalize', **img_norm_cfg),
    dict(type='DefaultFormatBundle'),
    dict(type='Collect', keys=['img', 'gt_semantic_seg']),
]

train_dataset = dict(
    type='MultiImageMixDataset',
    dataset=dict(
        classes=classes,
        palette=palette,
        type=dataset_type,
        reduce_zero_label=False,
        img_dir=data_root + "images/train",
        ann_dir=data_root + "annotations/train",
        pipeline=[
            dict(type='LoadImageFromFile'),
            dict(type='LoadAnnotations'),
        ]
    ),
    pipeline=train_pipeline
)