autoaugment.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import math
from enum import Enum
from typing import Dict, List, Optional, Tuple

import torch
from torch import Tensor
from torchvision.transforms import InterpolationMode
from torchvision.transforms import functional as F

__all__ = ["AutoAugmentPolicy", "AutoAugment", "RandAugment", "TrivialAugmentWide", "AugMix"]


def _apply_op(
    img: Tensor, op_name: str, magnitude: float, interpolation: InterpolationMode, fill: Optional[List[float]]
):
    if op_name == "ShearX":
        # magnitude should be arctan(magnitude)
        # official autoaug: (1, level, 0, 0, 1, 0)
        # https://github.com/tensorflow/models/blob/dd02069717128186b88afa8d857ce57d17957f03/research/autoaugment/augmentation_transforms.py#L290
        # compared to
        # torchvision:      (1, tan(level), 0, 0, 1, 0)
        # https://github.com/pytorch/vision/blob/0c2373d0bba3499e95776e7936e207d8a1676e65/torchvision/transforms/functional.py#L976
        img = F.affine(
            img,
            angle=0.0,
            translate=[0, 0],
            scale=1.0,
            shear=[math.degrees(math.atan(magnitude)), 0.0],
            interpolation=interpolation,
            fill=fill,
            center=[0, 0],
        )
    elif op_name == "ShearY":
        # magnitude should be arctan(magnitude)
        # See above
        img = F.affine(
            img,
            angle=0.0,
            translate=[0, 0],
            scale=1.0,
            shear=[0.0, math.degrees(math.atan(magnitude))],
            interpolation=interpolation,
            fill=fill,
            center=[0, 0],
        )
    elif op_name == "TranslateX":
        img = F.affine(
            img,
            angle=0.0,
            translate=[int(magnitude), 0],
            scale=1.0,
            interpolation=interpolation,
            shear=[0.0, 0.0],
            fill=fill,
        )
    elif op_name == "TranslateY":
        img = F.affine(
            img,
            angle=0.0,
            translate=[0, int(magnitude)],
            scale=1.0,
            interpolation=interpolation,
            shear=[0.0, 0.0],
            fill=fill,
        )
    elif op_name == "Rotate":
        img = F.rotate(img, magnitude, interpolation=interpolation, fill=fill)
    elif op_name == "Brightness":
        img = F.adjust_brightness(img, 1.0 + magnitude)
    elif op_name == "Color":
        img = F.adjust_saturation(img, 1.0 + magnitude)
    elif op_name == "Contrast":
        img = F.adjust_contrast(img, 1.0 + magnitude)
    elif op_name == "Sharpness":
        img = F.adjust_sharpness(img, 1.0 + magnitude)
    elif op_name == "Posterize":
        img = F.posterize(img, int(magnitude))
    elif op_name == "Solarize":
        img = F.solarize(img, magnitude)
    elif op_name == "AutoContrast":
        img = F.autocontrast(img)
    elif op_name == "Equalize":
        img = F.equalize(img)
    elif op_name == "Invert":
        img = F.invert(img)
    elif op_name == "Identity":
        pass
    else:
        raise ValueError(f"The provided operator {op_name} is not recognized.")
    return img


class AutoAugmentPolicy(Enum):
    """AutoAugment policies learned on different datasets.
    Available policies are IMAGENET, CIFAR10 and SVHN.
    """

    IMAGENET = "imagenet"
    CIFAR10 = "cifar10"
    SVHN = "svhn"


# FIXME: Eliminate copy-pasted code for fill standardization and _augmentation_space() by moving stuff on a base class
class AutoAugment(torch.nn.Module):
    r"""AutoAugment data augmentation method based on
    `"AutoAugment: Learning Augmentation Strategies from Data" <https://arxiv.org/pdf/1805.09501.pdf>`_.
    If the image is torch Tensor, it should be of type torch.uint8, and it is expected
    to have [..., 1 or 3, H, W] shape, where ... means an arbitrary number of leading dimensions.
    If img is PIL Image, it is expected to be in mode "L" or "RGB".

    Args:
        policy (AutoAugmentPolicy): Desired policy enum defined by
            :class:`torchvision.transforms.autoaugment.AutoAugmentPolicy`. Default is ``AutoAugmentPolicy.IMAGENET``.
        interpolation (InterpolationMode): Desired interpolation enum defined by
            :class:`torchvision.transforms.InterpolationMode`. Default is ``InterpolationMode.NEAREST``.
            If input is Tensor, only ``InterpolationMode.NEAREST``, ``InterpolationMode.BILINEAR`` are supported.
        fill (sequence or number, optional): Pixel fill value for the area outside the transformed
            image. If given a number, the value is used for all bands respectively.
    """

    def __init__(
        self,
        policy: AutoAugmentPolicy = AutoAugmentPolicy.IMAGENET,
        interpolation: InterpolationMode = InterpolationMode.NEAREST,
        fill: Optional[List[float]] = None,
    ) -> None:
        super().__init__()
        self.policy = policy
        self.interpolation = interpolation
        self.fill = fill
        self.policies = self._get_policies(policy)

    def _get_policies(
        self, policy: AutoAugmentPolicy
    ) -> List[Tuple[Tuple[str, float, Optional[int]], Tuple[str, float, Optional[int]]]]:
        if policy == AutoAugmentPolicy.IMAGENET:
            return [
                (("Posterize", 0.4, 8), ("Rotate", 0.6, 9)),
                (("Solarize", 0.6, 5), ("AutoContrast", 0.6, None)),
                (("Equalize", 0.8, None), ("Equalize", 0.6, None)),
                (("Posterize", 0.6, 7), ("Posterize", 0.6, 6)),
                (("Equalize", 0.4, None), ("Solarize", 0.2, 4)),
                (("Equalize", 0.4, None), ("Rotate", 0.8, 8)),
                (("Solarize", 0.6, 3), ("Equalize", 0.6, None)),
                (("Posterize", 0.8, 5), ("Equalize", 1.0, None)),
                (("Rotate", 0.2, 3), ("Solarize", 0.6, 8)),
                (("Equalize", 0.6, None), ("Posterize", 0.4, 6)),
                (("Rotate", 0.8, 8), ("Color", 0.4, 0)),
                (("Rotate", 0.4, 9), ("Equalize", 0.6, None)),
                (("Equalize", 0.0, None), ("Equalize", 0.8, None)),
                (("Invert", 0.6, None), ("Equalize", 1.0, None)),
                (("Color", 0.6, 4), ("Contrast", 1.0, 8)),
                (("Rotate", 0.8, 8), ("Color", 1.0, 2)),
                (("Color", 0.8, 8), ("Solarize", 0.8, 7)),
                (("Sharpness", 0.4, 7), ("Invert", 0.6, None)),
                (("ShearX", 0.6, 5), ("Equalize", 1.0, None)),
                (("Color", 0.4, 0), ("Equalize", 0.6, None)),
                (("Equalize", 0.4, None), ("Solarize", 0.2, 4)),
                (("Solarize", 0.6, 5), ("AutoContrast", 0.6, None)),
                (("Invert", 0.6, None), ("Equalize", 1.0, None)),
                (("Color", 0.6, 4), ("Contrast", 1.0, 8)),
                (("Equalize", 0.8, None), ("Equalize", 0.6, None)),
            ]
        elif policy == AutoAugmentPolicy.CIFAR10:
            return [
                (("Invert", 0.1, None), ("Contrast", 0.2, 6)),
                (("Rotate", 0.7, 2), ("TranslateX", 0.3, 9)),
                (("Sharpness", 0.8, 1), ("Sharpness", 0.9, 3)),
                (("ShearY", 0.5, 8), ("TranslateY", 0.7, 9)),
                (("AutoContrast", 0.5, None), ("Equalize", 0.9, None)),
                (("ShearY", 0.2, 7), ("Posterize", 0.3, 7)),
                (("Color", 0.4, 3), ("Brightness", 0.6, 7)),
                (("Sharpness", 0.3, 9), ("Brightness", 0.7, 9)),
                (("Equalize", 0.6, None), ("Equalize", 0.5, None)),
                (("Contrast", 0.6, 7), ("Sharpness", 0.6, 5)),
                (("Color", 0.7, 7), ("TranslateX", 0.5, 8)),
                (("Equalize", 0.3, None), ("AutoContrast", 0.4, None)),
                (("TranslateY", 0.4, 3), ("Sharpness", 0.2, 6)),
                (("Brightness", 0.9, 6), ("Color", 0.2, 8)),
                (("Solarize", 0.5, 2), ("Invert", 0.0, None)),
                (("Equalize", 0.2, None), ("AutoContrast", 0.6, None)),
                (("Equalize", 0.2, None), ("Equalize", 0.6, None)),
                (("Color", 0.9, 9), ("Equalize", 0.6, None)),
                (("AutoContrast", 0.8, None), ("Solarize", 0.2, 8)),
                (("Brightness", 0.1, 3), ("Color", 0.7, 0)),
                (("Solarize", 0.4, 5), ("AutoContrast", 0.9, None)),
                (("TranslateY", 0.9, 9), ("TranslateY", 0.7, 9)),
                (("AutoContrast", 0.9, None), ("Solarize", 0.8, 3)),
                (("Equalize", 0.8, None), ("Invert", 0.1, None)),
                (("TranslateY", 0.7, 9), ("AutoContrast", 0.9, None)),
            ]
        elif policy == AutoAugmentPolicy.SVHN:
            return [
                (("ShearX", 0.9, 4), ("Invert", 0.2, None)),
                (("ShearY", 0.9, 8), ("Invert", 0.7, None)),
                (("Equalize", 0.6, None), ("Solarize", 0.6, 6)),
                (("Invert", 0.9, None), ("Equalize", 0.6, None)),
                (("Equalize", 0.6, None), ("Rotate", 0.9, 3)),
                (("ShearX", 0.9, 4), ("AutoContrast", 0.8, None)),
                (("ShearY", 0.9, 8), ("Invert", 0.4, None)),
                (("ShearY", 0.9, 5), ("Solarize", 0.2, 6)),
                (("Invert", 0.9, None), ("AutoContrast", 0.8, None)),
                (("Equalize", 0.6, None), ("Rotate", 0.9, 3)),
                (("ShearX", 0.9, 4), ("Solarize", 0.3, 3)),
                (("ShearY", 0.8, 8), ("Invert", 0.7, None)),
                (("Equalize", 0.9, None), ("TranslateY", 0.6, 6)),
                (("Invert", 0.9, None), ("Equalize", 0.6, None)),
                (("Contrast", 0.3, 3), ("Rotate", 0.8, 4)),
                (("Invert", 0.8, None), ("TranslateY", 0.0, 2)),
                (("ShearY", 0.7, 6), ("Solarize", 0.4, 8)),
                (("Invert", 0.6, None), ("Rotate", 0.8, 4)),
                (("ShearY", 0.3, 7), ("TranslateX", 0.9, 3)),
                (("ShearX", 0.1, 6), ("Invert", 0.6, None)),
                (("Solarize", 0.7, 2), ("TranslateY", 0.6, 7)),
                (("ShearY", 0.8, 4), ("Invert", 0.8, None)),
                (("ShearX", 0.7, 9), ("TranslateY", 0.8, 3)),
                (("ShearY", 0.8, 5), ("AutoContrast", 0.7, None)),
                (("ShearX", 0.7, 2), ("Invert", 0.1, None)),
            ]
        else:
            raise ValueError(f"The provided policy {policy} is not recognized.")

    def _augmentation_space(self, num_bins: int, image_size: Tuple[int, int]) -> Dict[str, Tuple[Tensor, bool]]:
        return {
            # op_name: (magnitudes, signed)
            "ShearX": (torch.linspace(0.0, 0.3, num_bins), True),
            "ShearY": (torch.linspace(0.0, 0.3, num_bins), True),
            "TranslateX": (torch.linspace(0.0, 150.0 / 331.0 * image_size[1], num_bins), True),
            "TranslateY": (torch.linspace(0.0, 150.0 / 331.0 * image_size[0], num_bins), True),
            "Rotate": (torch.linspace(0.0, 30.0, num_bins), True),
            "Brightness": (torch.linspace(0.0, 0.9, num_bins), True),
            "Color": (torch.linspace(0.0, 0.9, num_bins), True),
            "Contrast": (torch.linspace(0.0, 0.9, num_bins), True),
            "Sharpness": (torch.linspace(0.0, 0.9, num_bins), True),
            "Posterize": (8 - (torch.arange(num_bins) / ((num_bins - 1) / 4)).round().int(), False),
            "Solarize": (torch.linspace(255.0, 0.0, num_bins), False),
            "AutoContrast": (torch.tensor(0.0), False),
            "Equalize": (torch.tensor(0.0), False),
            "Invert": (torch.tensor(0.0), False),
        }

    @staticmethod
    def get_params(transform_num: int) -> Tuple[int, Tensor, Tensor]:
        """Get parameters for autoaugment transformation

        Returns:
            params required by the autoaugment transformation
        """
        policy_id = int(torch.randint(transform_num, (1,)).item())
        probs = torch.rand((2,))
        signs = torch.randint(2, (2,))

        return policy_id, probs, signs

    def forward(self, img: Tensor) -> Tensor:
        """
            img (PIL Image or Tensor): Image to be transformed.

        Returns:
            PIL Image or Tensor: AutoAugmented image.
        """
        fill = self.fill
        channels, height, width = F.get_dimensions(img)
        if isinstance(img, Tensor):
            if isinstance(fill, (int, float)):
                fill = [float(fill)] * channels
            elif fill is not None:
                fill = [float(f) for f in fill]

        transform_id, probs, signs = self.get_params(len(self.policies))

        op_meta = self._augmentation_space(10, (height, width))
        for i, (op_name, p, magnitude_id) in enumerate(self.policies[transform_id]):
            if probs[i] <= p:
                magnitudes, signed = op_meta[op_name]
                magnitude = float(magnitudes[magnitude_id].item()) if magnitude_id is not None else 0.0
                if signed and signs[i] == 0:
                    magnitude *= -1.0
                img = _apply_op(img, op_name, magnitude, interpolation=self.interpolation, fill=fill)

        return img

    def __repr__(self) -> str:
        return f"{self.__class__.__name__}(policy={self.policy}, fill={self.fill})"


class RandAugment(torch.nn.Module):
    r"""RandAugment data augmentation method based on
    `"RandAugment: Practical automated data augmentation with a reduced search space"
    <https://arxiv.org/abs/1909.13719>`_.
    If the image is torch Tensor, it should be of type torch.uint8, and it is expected
    to have [..., 1 or 3, H, W] shape, where ... means an arbitrary number of leading dimensions.
    If img is PIL Image, it is expected to be in mode "L" or "RGB".

    Args:
        num_ops (int): Number of augmentation transformations to apply sequentially.
        magnitude (int): Magnitude for all the transformations.
        num_magnitude_bins (int): The number of different magnitude values.
        interpolation (InterpolationMode): Desired interpolation enum defined by
            :class:`torchvision.transforms.InterpolationMode`. Default is ``InterpolationMode.NEAREST``.
            If input is Tensor, only ``InterpolationMode.NEAREST``, ``InterpolationMode.BILINEAR`` are supported.
        fill (sequence or number, optional): Pixel fill value for the area outside the transformed
            image. If given a number, the value is used for all bands respectively.
    """

    def __init__(
        self,
        num_ops: int = 2,
        magnitude: int = 9,
        num_magnitude_bins: int = 31,
        interpolation: InterpolationMode = InterpolationMode.NEAREST,
        fill: Optional[List[float]] = None,
    ) -> None:
        super().__init__()
        self.num_ops = num_ops
        self.magnitude = magnitude
        self.num_magnitude_bins = num_magnitude_bins
        self.interpolation = interpolation
        self.fill = fill

    def _augmentation_space(self, num_bins: int, image_size: Tuple[int, int]) -> Dict[str, Tuple[Tensor, bool]]:
        return {
            # op_name: (magnitudes, signed)
            "Identity": (torch.tensor(0.0), False),
            "ShearX": (torch.linspace(0.0, 0.3, num_bins), True),
            "ShearY": (torch.linspace(0.0, 0.3, num_bins), True),
            "TranslateX": (torch.linspace(0.0, 150.0 / 331.0 * image_size[1], num_bins), True),
            "TranslateY": (torch.linspace(0.0, 150.0 / 331.0 * image_size[0], num_bins), True),
            "Rotate": (torch.linspace(0.0, 30.0, num_bins), True),
            "Brightness": (torch.linspace(0.0, 0.9, num_bins), True),
            "Color": (torch.linspace(0.0, 0.9, num_bins), True),
            "Contrast": (torch.linspace(0.0, 0.9, num_bins), True),
            "Sharpness": (torch.linspace(0.0, 0.9, num_bins), True),
            "Posterize": (8 - (torch.arange(num_bins) / ((num_bins - 1) / 4)).round().int(), False),
            "Solarize": (torch.linspace(255.0, 0.0, num_bins), False),
            "AutoContrast": (torch.tensor(0.0), False),
            "Equalize": (torch.tensor(0.0), False),
        }

    def forward(self, img: Tensor) -> Tensor:
        """
            img (PIL Image or Tensor): Image to be transformed.

        Returns:
            PIL Image or Tensor: Transformed image.
        """
        fill = self.fill
        channels, height, width = F.get_dimensions(img)
        if isinstance(img, Tensor):
            if isinstance(fill, (int, float)):
                fill = [float(fill)] * channels
            elif fill is not None:
                fill = [float(f) for f in fill]

        op_meta = self._augmentation_space(self.num_magnitude_bins, (height, width))
        for _ in range(self.num_ops):
            op_index = int(torch.randint(len(op_meta), (1,)).item())
            op_name = list(op_meta.keys())[op_index]
            magnitudes, signed = op_meta[op_name]
            magnitude = float(magnitudes[self.magnitude].item()) if magnitudes.ndim > 0 else 0.0
            if signed and torch.randint(2, (1,)):
                magnitude *= -1.0
            img = _apply_op(img, op_name, magnitude, interpolation=self.interpolation, fill=fill)

        return img

    def __repr__(self) -> str:
        s = (
            f"{self.__class__.__name__}("
            f"num_ops={self.num_ops}"
            f", magnitude={self.magnitude}"
            f", num_magnitude_bins={self.num_magnitude_bins}"
            f", interpolation={self.interpolation}"
            f", fill={self.fill}"
            f")"
        )
        return s



class TrivialAugmentWide(torch.nn.Module):
    r"""Dataset-independent data-augmentation with TrivialAugment Wide, as described in
    `"TrivialAugment: Tuning-free Yet State-of-the-Art Data Augmentation" <https://arxiv.org/abs/2103.10158>`_.
    If the image is torch Tensor, it should be of type torch.uint8, and it is expected
    to have [..., 1 or 3, H, W] shape, where ... means an arbitrary number of leading dimensions.
    If img is PIL Image, it is expected to be in mode "L" or "RGB".

    Args:
        num_magnitude_bins (int): The number of different magnitude values.
        interpolation (InterpolationMode): Desired interpolation enum defined by
            :class:`torchvision.transforms.InterpolationMode`. Default is ``InterpolationMode.NEAREST``.
            If input is Tensor, only ``InterpolationMode.NEAREST``, ``InterpolationMode.BILINEAR`` are supported.
        fill (sequence or number, optional): Pixel fill value for the area outside the transformed
            image. If given a number, the value is used for all bands respectively.
    """

    def __init__(
        self,
        num_magnitude_bins: int = 31,
        interpolation: InterpolationMode = InterpolationMode.NEAREST,
        fill: Optional[List[float]] = None,
    ) -> None:
        super().__init__()
        self.num_magnitude_bins = num_magnitude_bins
        self.interpolation = interpolation
        self.fill = fill

    def _augmentation_space(self, num_bins: int) -> Dict[str, Tuple[Tensor, bool]]:
        return {
            # op_name: (magnitudes, signed)
            "Identity": (torch.tensor(0.0), False),
            #"ShearX": (torch.linspace(0.0, 0.99, num_bins), True),
            #"ShearY": (torch.linspace(0.0, 0.99, num_bins), True),
            #"TranslateX": (torch.linspace(0.0, 32.0, num_bins), True),
            #"TranslateY": (torch.linspace(0.0, 32.0, num_bins), True),
            #"Rotate": (torch.linspace(0.0, 135.0, num_bins), True),
            "Brightness": (torch.linspace(0.0, 0.99, num_bins), True),
            "Color": (torch.linspace(0.0, 0.99, num_bins), True),
            "Contrast": (torch.linspace(0.0, 0.99, num_bins), True),
            "Sharpness": (torch.linspace(0.0, 0.99, num_bins), True),
            "Posterize": (8 - (torch.arange(num_bins) / ((num_bins - 1) / 6)).round().int(), False),
            "Solarize": (torch.linspace(255.0, 0.0, num_bins), False),
            "AutoContrast": (torch.tensor(0.0), False),
            "Equalize": (torch.tensor(0.0), False),
        }


    def forward(self, img: Tensor) -> Tensor:
        """
            img (PIL Image or Tensor): Image to be transformed.

        Returns:
            PIL Image or Tensor: Transformed image.
        """
        fill = self.fill
        channels, height, width = F.get_dimensions(img)
        if isinstance(img, Tensor):
            if isinstance(fill, (int, float)):
                fill = [float(fill)] * channels
            elif fill is not None:
                fill = [float(f) for f in fill]

        op_meta = self._augmentation_space(self.num_magnitude_bins)
        op_index = int(torch.randint(len(op_meta), (1,)).item())
        op_name = list(op_meta.keys())[op_index]
        magnitudes, signed = op_meta[op_name]
        magnitude = (
            float(magnitudes[torch.randint(len(magnitudes), (1,), dtype=torch.long)].item())
            if magnitudes.ndim > 0
            else 0.0
        )
        if signed and torch.randint(2, (1,)):
            magnitude *= -1.0

        return _apply_op(img, op_name, magnitude, interpolation=self.interpolation, fill=fill)


    def __repr__(self) -> str:
        s = (
            f"{self.__class__.__name__}("
            f"num_magnitude_bins={self.num_magnitude_bins}"
            f", interpolation={self.interpolation}"
            f", fill={self.fill}"
            f")"
        )
        return s



class AugMix(torch.nn.Module):
    r"""AugMix data augmentation method based on
    `"AugMix: A Simple Data Processing Method to Improve Robustness and Uncertainty" <https://arxiv.org/abs/1912.02781>`_.
    If the image is torch Tensor, it should be of type torch.uint8, and it is expected
    to have [..., 1 or 3, H, W] shape, where ... means an arbitrary number of leading dimensions.
    If img is PIL Image, it is expected to be in mode "L" or "RGB".

    Args:
        severity (int): The severity of base augmentation operators. Default is ``3``.
        mixture_width (int): The number of augmentation chains. Default is ``3``.
        chain_depth (int): The depth of augmentation chains. A negative value denotes stochastic depth sampled from the interval [1, 3].
            Default is ``-1``.
        alpha (float): The hyperparameter for the probability distributions. Default is ``1.0``.
        all_ops (bool): Use all operations (including brightness, contrast, color and sharpness). Default is ``True``.
        interpolation (InterpolationMode): Desired interpolation enum defined by
            :class:`torchvision.transforms.InterpolationMode`. Default is ``InterpolationMode.NEAREST``.
            If input is Tensor, only ``InterpolationMode.NEAREST``, ``InterpolationMode.BILINEAR`` are supported.
        fill (sequence or number, optional): Pixel fill value for the area outside the transformed
            image. If given a number, the value is used for all bands respectively.
    """

    def __init__(
        self,
        severity: int = 3,
        mixture_width: int = 3,
        chain_depth: int = -1,
        alpha: float = 1.0,
        all_ops: bool = True,
        interpolation: InterpolationMode = InterpolationMode.BILINEAR,
        fill: Optional[List[float]] = None,
    ) -> None:
        super().__init__()
        self._PARAMETER_MAX = 10
        if not (1 <= severity <= self._PARAMETER_MAX):
            raise ValueError(f"The severity must be between [1, {self._PARAMETER_MAX}]. Got {severity} instead.")
        self.severity = severity
        self.mixture_width = mixture_width
        self.chain_depth = chain_depth
        self.alpha = alpha
        self.all_ops = all_ops
        self.interpolation = interpolation
        self.fill = fill

    def _augmentation_space(self, num_bins: int, image_size: Tuple[int, int]) -> Dict[str, Tuple[Tensor, bool]]:
        s = {
            # op_name: (magnitudes, signed)
            "ShearX": (torch.linspace(0.0, 0.3, num_bins), True),
            "ShearY": (torch.linspace(0.0, 0.3, num_bins), True),
            "TranslateX": (torch.linspace(0.0, image_size[1] / 3.0, num_bins), True),
            "TranslateY": (torch.linspace(0.0, image_size[0] / 3.0, num_bins), True),
            "Rotate": (torch.linspace(0.0, 30.0, num_bins), True),
            "Posterize": (4 - (torch.arange(num_bins) / ((num_bins - 1) / 4)).round().int(), False),
            "Solarize": (torch.linspace(255.0, 0.0, num_bins), False),
            "AutoContrast": (torch.tensor(0.0), False),
            "Equalize": (torch.tensor(0.0), False),
        }
        if self.all_ops:
            s.update(
                {
                    "Brightness": (torch.linspace(0.0, 0.9, num_bins), True),
                    "Color": (torch.linspace(0.0, 0.9, num_bins), True),
                    "Contrast": (torch.linspace(0.0, 0.9, num_bins), True),
                    "Sharpness": (torch.linspace(0.0, 0.9, num_bins), True),
                }
            )
        return s

    @torch.jit.unused
    def _pil_to_tensor(self, img) -> Tensor:
        return F.pil_to_tensor(img)

    @torch.jit.unused
    def _tensor_to_pil(self, img: Tensor):
        return F.to_pil_image(img)

    def _sample_dirichlet(self, params: Tensor) -> Tensor:
        # Must be on a separate method so that we can overwrite it in tests.
        return torch._sample_dirichlet(params)

    def forward(self, orig_img: Tensor) -> Tensor:
        """
            img (PIL Image or Tensor): Image to be transformed.

        Returns:
            PIL Image or Tensor: Transformed image.
        """
        fill = self.fill
        channels, height, width = F.get_dimensions(orig_img)
        if isinstance(orig_img, Tensor):
            img = orig_img
            if isinstance(fill, (int, float)):
                fill = [float(fill)] * channels
            elif fill is not None:
                fill = [float(f) for f in fill]
        else:
            img = self._pil_to_tensor(orig_img)

        op_meta = self._augmentation_space(self._PARAMETER_MAX, (height, width))

        orig_dims = list(img.shape)
        batch = img.view([1] * max(4 - img.ndim, 0) + orig_dims)
        batch_dims = [batch.size(0)] + [1] * (batch.ndim - 1)

        # Sample the beta weights for combining the original and augmented image. To get Beta, we use a Dirichlet
        # with 2 parameters. The 1st column stores the weights of the original and the 2nd the ones of augmented image.
        m = self._sample_dirichlet(
            torch.tensor([self.alpha, self.alpha], device=batch.device).expand(batch_dims[0], -1)
        )

        # Sample the mixing weights and combine them with the ones sampled from Beta for the augmented images.
        combined_weights = self._sample_dirichlet(
            torch.tensor([self.alpha] * self.mixture_width, device=batch.device).expand(batch_dims[0], -1)
        ) * m[:, 1].view([batch_dims[0], -1])

        mix = m[:, 0].view(batch_dims) * batch
        for i in range(self.mixture_width):
            aug = batch
            depth = self.chain_depth if self.chain_depth > 0 else int(torch.randint(low=1, high=4, size=(1,)).item())
            for _ in range(depth):
                op_index = int(torch.randint(len(op_meta), (1,)).item())
                op_name = list(op_meta.keys())[op_index]
                magnitudes, signed = op_meta[op_name]
                magnitude = (
                    float(magnitudes[torch.randint(self.severity, (1,), dtype=torch.long)].item())
                    if magnitudes.ndim > 0
                    else 0.0
                )
                if signed and torch.randint(2, (1,)):
                    magnitude *= -1.0
                aug = _apply_op(aug, op_name, magnitude, interpolation=self.interpolation, fill=fill)
            mix.add_(combined_weights[:, i].view(batch_dims) * aug)
        mix = mix.view(orig_dims).to(dtype=img.dtype)

        if not isinstance(orig_img, Tensor):
            return self._tensor_to_pil(mix)
        return mix

    def __repr__(self) -> str:
        s = (
            f"{self.__class__.__name__}("
            f"severity={self.severity}"
            f", mixture_width={self.mixture_width}"
            f", chain_depth={self.chain_depth}"
            f", alpha={self.alpha}"
            f", all_ops={self.all_ops}"
            f", interpolation={self.interpolation}"
            f", fill={self.fill}"
            f")"
        )
        return s