stanford_cars.py

import pathlib
from typing import Any, Callable, Optional, Tuple

from PIL import Image

from .utils import download_and_extract_archive, download_url, verify_str_arg
from .vision import VisionDataset


class StanfordCars(VisionDataset):
    """`Stanford Cars <https://ai.stanford.edu/~jkrause/cars/car_dataset.html>`_ Dataset

    The Cars dataset contains 16,185 images of 196 classes of cars. The data is
    split into 8,144 training images and 8,041 testing images, where each class
    has been split roughly in a 50-50 split

    .. note::

        This class needs `scipy <https://docs.scipy.org/doc/>`_ to load target files from `.mat` format.

    Args:
        root (string): Root directory of dataset
        split (string, optional): The dataset split, supports ``"train"`` (default) or ``"test"``.
        transform (callable, optional): A function/transform that takes in a PIL image
            and returns a transformed version. E.g, ``transforms.RandomCrop``
        target_transform (callable, optional): A function/transform that takes in the
            target and transforms it.
        download (bool, optional): If True, downloads the dataset from the internet and
            puts it in root directory. If dataset is already downloaded, it is not
            downloaded again."""

    def __init__(
        self,
        root: str,
        split: str = "train",
        transform: Optional[Callable] = None,
        target_transform: Optional[Callable] = None,
        download: bool = False,
    ) -> None:

        try:
            import scipy.io as sio
        except ImportError:
            raise RuntimeError("Scipy is not found. This dataset needs to have scipy installed: pip install scipy")

        super().__init__(root, transform=transform, target_transform=target_transform)

        self._split = verify_str_arg(split, "split", ("train", "test"))
        self._base_folder = pathlib.Path(root) / "stanford_cars"
        devkit = self._base_folder / "devkit"

        if self._split == "train":
            self._annotations_mat_path = devkit / "cars_train_annos.mat"
            self._images_base_path = self._base_folder / "cars_train"
        else:
            self._annotations_mat_path = self._base_folder / "cars_test_annos_withlabels.mat"
            self._images_base_path = self._base_folder / "cars_test"

        if download:
            self.download()

        if not self._check_exists():
            raise RuntimeError("Dataset not found. You can use download=True to download it")

        self._samples = [
            (
                str(self._images_base_path / annotation["fname"]),
                annotation["class"] - 1,  # Original target mapping  starts from 1, hence -1
            )
            for annotation in sio.loadmat(self._annotations_mat_path, squeeze_me=True)["annotations"]
        ]

        self.classes = sio.loadmat(str(devkit / "cars_meta.mat"), squeeze_me=True)["class_names"].tolist()
        self.class_to_idx = {cls: i for i, cls in enumerate(self.classes)}

    def __len__(self) -> int:
        return len(self._samples)

    def __getitem__(self, idx: int) -> Tuple[Any, Any]:
        """Returns pil_image and class_id for given index"""
        image_path, target = self._samples[idx]
        pil_image = Image.open(image_path).convert("RGB")

        if self.transform is not None:
            pil_image = self.transform(pil_image)
        if self.target_transform is not None:
            target = self.target_transform(target)
        return pil_image, target

    def download(self) -> None:
        if self._check_exists():
            return

        download_and_extract_archive(
            url="https://ai.stanford.edu/~jkrause/cars/car_devkit.tgz",
            download_root=str(self._base_folder),
            md5="c3b158d763b6e2245038c8ad08e45376",
        )
        if self._split == "train":
            download_and_extract_archive(
                url="https://ai.stanford.edu/~jkrause/car196/cars_train.tgz",
                download_root=str(self._base_folder),
                md5="065e5b463ae28d29e77c1b4b166cfe61",
            )
        else:
            download_and_extract_archive(
                url="https://ai.stanford.edu/~jkrause/car196/cars_test.tgz",
                download_root=str(self._base_folder),
                md5="4ce7ebf6a94d07f1952d94dd34c4d501",
            )
            download_url(
                url="https://ai.stanford.edu/~jkrause/car196/cars_test_annos_withlabels.mat",
                root=str(self._base_folder),
                md5="b0a2b23655a3edd16d84508592a98d10",
            )

    def _check_exists(self) -> bool:
        if not (self._base_folder / "devkit").is_dir():
            return False

        return self._annotations_mat_path.exists() and self._images_base_path.is_dir()