vision-datasets/README.md

# Vision Datasets

## Introduction

This repo

- defines unified contract for dataset for purposes such as training, visualization, and exploration, via `DatasetManifest` and `ImageDataManifest`.
- provides many commonly used dataset operation, such as sample dataset by categories, sample few-shot sub-dataset, sample dataset by ratios, train-test split, merge dataset, etc. (See here [Link](vision_datasets/common/data_manifest.py) for available utilities)
- provides API for organizing and accessing datasets, via `DatasetHub`

Currently, six `basic` types of data are supported: 
- `classification_multiclass`: each image can is only with one label.
- `classification_multilabel`: each image can is with one or multiple labels (e.g., 'cat', 'animal', 'pet').
- `object_detection`: each image is labeled with bounding boxes surrounding the objects of interest.
- `image_caption`: each image is labeled with a few texts describing the images.
- `image_text_matching`: each image is associated with a collection of texts describing the image, and whether each text description matches the image or not.
- `image_matting`: each image has a pixel-wise annotation, where each pixel is labeled as 'foreground' or 'background'.

`multitask` type is a composition type, where one set of images has multiple sets of annotations available for different tasks, where each task can be of any basic type.


## Dataset Contracts

- `DatasetManifest` wraps the information about a dataset including labelmap, images (width, height, path to image), and annotations. `ImageDataManifest` encapsulates information about each image.
- `ImageDataManifest` encapsulates image-specific information, such as image id, path, labels, and width/height. One thing to note here is that the image path can be
    1. a local path (absolute `c:\images\1.jpg` or relative `images\1.jpg`)
    2. a local path in a **non-compressed** zip file (absolute `c:\images.zip@1.jpg` or relative `images.zip@1.jpg`) or
    3. an url
- `ManifestDataset` is an iterable dataset class that consumes the information from `DatasetManifest`.

`ManifestDataset` is able to load the data from all three kinds of paths. Both 1. and 2. are good for training, as they access data from local disk while the 3rd one is good for data exploration, if you have the data in azure storage.

For `multitask` dataset, the labels stored in the `ImageDataManifest` is a `dict` mapping from task name to that task's labels. The labelmap stored in `DatasetManifest` is also a `dict` mapping from task name to that task's labels.

### Creating DatasetManifest

In addition to loading a serialized `DatasetManifest` for instantiation, this repo currently supports two formats of data that can instantiates `DatasetManifest`,
using `DatasetManifest.create_dataset_manifest(dataset_info, usage, container_sas_or_root_dir)`: `COCO` and `IRIS` (legacy).

`DatasetInfo` as the first arg in the arg list wraps the metainfo about the dataset like the name of the dataset, locations of the images, annotation files, etc. See examples in the sections below
for different data formats.

Once a `DatasetManifest` is created, you can create a `ManifestDataset` for accessing the data in the dataset, especially the image data, for training, visualization, etc:

```{python}
dataset = ManifestDataset(dataset_info, dataset_manifest, coordinates='relative')
```

#### Coco format

Here is an example with explanation of what a `DatasetInfo` looks like for coco format, when it is serialized into json:

```{json}
    {
        "name": "sampled-ms-coco",
        "version": 1,
        "description": "A sampled ms-coco dataset.",
        "type": "object_detection",
        "format": "coco", // indicating the annotation data are stored in coco format
        "root_folder": "detection/coco2017_20200401", // a root folder for all files listed
        "train": {
            "index_path": "train.json", // coco json file for training, see next section for example
            "files_for_local_usage": [ // associated files including data such as images
                "images/train_images.zip"
            ]
        },
        "val": {
            "index_path": "val.json",
            "files_for_local_usage": [
                "images/val_images.zip"
            ]
        },
        "test": {
            "index_path": "test.json",
            "files_for_local_usage": [
                "images/test_images.zip"
            ]
        }
    }
```

Coco annotation format details w.r.t. `multiclass/label_classification`, `object_detection`, `image_caption`, `image_text_match` and `multitask`  can be found in `COCO_DATA_FORMAT.md`.

#### Iris format

Iris format is a legacy format which can be found in `IRIS_DATA_FORMAT.md`. Only `multiclass/label_classification`, `object_detection` and `multitask` are supported.

## Dataset management and access

Check [DATA_PREPARATION.md](DATA_PREPARATION.md) for complete guide on how to prepare datasets in steps.

Once you have multiple datasets, it is more convenient to have all the `DatasetInfo` in one place and instantiate `DatasetManifest` or even `ManifestDataset` by just using the dataset name, usage (
train, val ,test) and version.

This repo offers the class `DatasetHub` for this purpose. Once instantiated with a json including the `DatasetInfo` for all datasets, you can retrieve a `ManifestDataset` by

```{python}
import pathlib

dataset_infos_json_path = 'datasets.json'
dataset_hub = DatasetHub(pathlib.Path(dataset_infos_json_path).read_text())
stanford_cars = dataset_hub.create_manifest_dataset(blob_container_sas, local_dir, 'stanford-cars', version=1, usage='train')

# note that you can pass multiple datasets.json to DatasetHub, it can combine them all
# example: DatasetHub([ds_json1, ds_json2, ...])
# note that you can specify multiple usages in create_manifest_dataset call
# example dataset_hub.create_manifest_dataset(blob_container_sas, local_dir, 'stanford-cars', version=1, usage=['train', 'val'])

for img, targets, sample_idx_str in stanford_cars:
    img.show()
    img.close()
    print(targets)
```

Note that this hub class works with data saved in both Azure Blob container and on local disk.

If `local_dir`:

1. is provided, the hub will look for the resources locally and **download the data** (files included in "
   files_for_local_usage", the index files, metadata (if iris format), labelmap (if iris format))
   from `blob_container_sas` if not present locally
2. is NOT provided (i.e. `None`), the hub will create a manifest dataset that directly consumes data from the blob
   indicated by `blob_container_sas`. Note that this does not work, if data are stored in zipped files. You will have to
   unzip your data in the azure blob. (Index files requires no update, if image paths are for zip files: "a.zip@1.jpg").
   This kind of azure-based dataset is good for large dataset exploration, but can be slow for training.

When data exists on local disk, `blob_container_sas` can be `None`.

### Training with PyTorch

Training with PyTorch is easy. After instantiating a `ManifestDataset`, simply passing it in `vision_datasets.pytorch.torch_dataset.TorchDataset` together with the `transform`, then you are good to go with the PyTorch DataLoader for training.