functional_tensor.py

import torch
from torch import Tensor
from torch.jit.annotations import List, BroadcastingList2


def _is_tensor_a_torch_image(x: Tensor) -> bool:
    return x.ndim >= 2


def _get_image_size(img: Tensor) -> List[int]:
    if _is_tensor_a_torch_image(img):
        return [img.shape[-1], img.shape[-2]]
    raise TypeError("Unexpected type {}".format(type(img)))


def vflip(img: Tensor) -> Tensor:
    """Vertically flip the given the Image Tensor.

    Args:
        img (Tensor): Image Tensor to be flipped in the form [C, H, W].

    Returns:
        Tensor:  Vertically flipped image Tensor.
    """
    if not _is_tensor_a_torch_image(img):
        raise TypeError('tensor is not a torch image.')

    return img.flip(-2)


def hflip(img: Tensor) -> Tensor:
    """Horizontally flip the given the Image Tensor.

    Args:
        img (Tensor): Image Tensor to be flipped in the form [C, H, W].

    Returns:
        Tensor:  Horizontally flipped image Tensor.
    """
    if not _is_tensor_a_torch_image(img):
        raise TypeError('tensor is not a torch image.')

    return img.flip(-1)


def crop(img: Tensor, top: int, left: int, height: int, width: int) -> Tensor:
    """Crop the given Image Tensor.

    Args:
        img (Tensor): Image to be cropped in the form [..., H, W]. (0,0) denotes the top left corner of the image.
        top (int): Vertical component of the top left corner of the crop box.
        left (int): Horizontal component of the top left corner of the crop box.
        height (int): Height of the crop box.
        width (int): Width of the crop box.

    Returns:
        Tensor: Cropped image.
    """
    if not _is_tensor_a_torch_image(img):
        raise TypeError("tensor is not a torch image.")

    return img[..., top:top + height, left:left + width]


def rgb_to_grayscale(img: Tensor) -> Tensor:
    """Convert the given RGB Image Tensor to Grayscale.
    For RGB to Grayscale conversion, ITU-R 601-2 luma transform is performed which
    is L = R * 0.2989 + G * 0.5870 + B * 0.1140

    Args:
        img (Tensor): Image to be converted to Grayscale in the form [C, H, W].

    Returns:
        Tensor: Grayscale image.

    """
    if img.shape[0] != 3:
        raise TypeError('Input Image does not contain 3 Channels')

    return (0.2989 * img[0] + 0.5870 * img[1] + 0.1140 * img[2]).to(img.dtype)


def adjust_brightness(img: Tensor, brightness_factor: float) -> Tensor:
    """Adjust brightness of an RGB image.

    Args:
        img (Tensor): Image to be adjusted.
        brightness_factor (float):  How much to adjust the brightness. Can be
            any non negative number. 0 gives a black image, 1 gives the
            original image while 2 increases the brightness by a factor of 2.

    Returns:
        Tensor: Brightness adjusted image.
    """
    if brightness_factor < 0:
        raise ValueError('brightness_factor ({}) is not non-negative.'.format(brightness_factor))

    if not _is_tensor_a_torch_image(img):
        raise TypeError('tensor is not a torch image.')

    return _blend(img, torch.zeros_like(img), brightness_factor)


def adjust_contrast(img: Tensor, contrast_factor: float) -> Tensor:
    """Adjust contrast of an RGB image.

    Args:
        img (Tensor): Image to be adjusted.
        contrast_factor (float): How much to adjust the contrast. Can be any
            non negative number. 0 gives a solid gray image, 1 gives the
            original image while 2 increases the contrast by a factor of 2.

    Returns:
        Tensor: Contrast adjusted image.
    """
    if contrast_factor < 0:
        raise ValueError('contrast_factor ({}) is not non-negative.'.format(contrast_factor))

    if not _is_tensor_a_torch_image(img):
        raise TypeError('tensor is not a torch image.')

    mean = torch.mean(rgb_to_grayscale(img).to(torch.float))

    return _blend(img, mean, contrast_factor)


def adjust_hue(img, hue_factor):
    """Adjust hue of an image.

    The image hue is adjusted by converting the image to HSV and
    cyclically shifting the intensities in the hue channel (H).
    The image is then converted back to original image mode.

    `hue_factor` is the amount of shift in H channel and must be in the
    interval `[-0.5, 0.5]`.

    See `Hue`_ for more details.

    .. _Hue: https://en.wikipedia.org/wiki/Hue

    Args:
        img (Tensor): Image to be adjusted. Image type is either uint8 or float.
        hue_factor (float):  How much to shift the hue channel. Should be in
            [-0.5, 0.5]. 0.5 and -0.5 give complete reversal of hue channel in
            HSV space in positive and negative direction respectively.
            0 means no shift. Therefore, both -0.5 and 0.5 will give an image
            with complementary colors while 0 gives the original image.

    Returns:
         Tensor: Hue adjusted image.
    """
    if not (-0.5 <= hue_factor <= 0.5):
        raise ValueError('hue_factor ({}) is not in [-0.5, 0.5].'.format(hue_factor))

    if not _is_tensor_a_torch_image(img):
        raise TypeError('tensor is not a torch image.')

    orig_dtype = img.dtype
    if img.dtype == torch.uint8:
        img = img.to(dtype=torch.float32) / 255.0

    img = _rgb2hsv(img)
    h, s, v = img.unbind(0)
    h += hue_factor
    h = h % 1.0
    img = torch.stack((h, s, v))
    img_hue_adj = _hsv2rgb(img)

    if orig_dtype == torch.uint8:
        img_hue_adj = (img_hue_adj * 255.0).to(dtype=orig_dtype)

    return img_hue_adj


def adjust_saturation(img: Tensor, saturation_factor: float) -> Tensor:
    """Adjust color saturation of an RGB image.

    Args:
        img (Tensor): Image to be adjusted.
        saturation_factor (float):  How much to adjust the saturation. Can be any
            non negative number. 0 gives a black and white image, 1 gives the
            original image while 2 enhances the saturation by a factor of 2.

    Returns:
        Tensor: Saturation adjusted image.
    """
    if saturation_factor < 0:
        raise ValueError('saturation_factor ({}) is not non-negative.'.format(saturation_factor))

    if not _is_tensor_a_torch_image(img):
        raise TypeError('tensor is not a torch image.')

    return _blend(img, rgb_to_grayscale(img), saturation_factor)


def center_crop(img: Tensor, output_size: BroadcastingList2[int]) -> Tensor:
    """Crop the Image Tensor and resize it to desired size.

    Args:
        img (Tensor): Image to be cropped.
        output_size (sequence or int): (height, width) of the crop box. If int,
                it is used for both directions

    Returns:
            Tensor: Cropped image.
    """
    if not _is_tensor_a_torch_image(img):
        raise TypeError('tensor is not a torch image.')

    _, image_width, image_height = img.size()
    crop_height, crop_width = output_size
    # crop_top = int(round((image_height - crop_height) / 2.))
    # Result can be different between python func and scripted func
    # Temporary workaround:
    crop_top = int((image_height - crop_height + 1) * 0.5)
    # crop_left = int(round((image_width - crop_width) / 2.))
    # Result can be different between python func and scripted func
    # Temporary workaround:
    crop_left = int((image_width - crop_width + 1) * 0.5)

    return crop(img, crop_top, crop_left, crop_height, crop_width)


def five_crop(img: Tensor, size: BroadcastingList2[int]) -> List[Tensor]:
    """Crop the given Image Tensor into four corners and the central crop.
    .. Note::
        This transform returns a List of Tensors and there may be a
        mismatch in the number of inputs and targets your ``Dataset`` returns.

    Args:
        img (Tensor): Image to be cropped.
        size (sequence or int): Desired output size of the crop. If size is an
            int instead of sequence like (h, w), a square crop (size, size) is
            made.

    Returns:
       List: List (tl, tr, bl, br, center)
                Corresponding top left, top right, bottom left, bottom right and center crop.
    """
    if not _is_tensor_a_torch_image(img):
        raise TypeError('tensor is not a torch image.')

    assert len(size) == 2, "Please provide only two dimensions (h, w) for size."

    _, image_width, image_height = img.size()
    crop_height, crop_width = size
    if crop_width > image_width or crop_height > image_height:
        msg = "Requested crop size {} is bigger than input size {}"
        raise ValueError(msg.format(size, (image_height, image_width)))

    tl = crop(img, 0, 0, crop_width, crop_height)
    tr = crop(img, image_width - crop_width, 0, image_width, crop_height)
    bl = crop(img, 0, image_height - crop_height, crop_width, image_height)
    br = crop(img, image_width - crop_width, image_height - crop_height, image_width, image_height)
    center = center_crop(img, (crop_height, crop_width))

    return [tl, tr, bl, br, center]


def ten_crop(img: Tensor, size: BroadcastingList2[int], vertical_flip: bool = False) -> List[Tensor]:
    """Crop the given Image Tensor into four corners and the central crop plus the
        flipped version of these (horizontal flipping is used by default).

    .. Note::
        This transform returns a List of images and there may be a
        mismatch in the number of inputs and targets your ``Dataset`` returns.

    Args:
        img (Tensor): Image to be cropped.
        size (sequence or int): Desired output size of the crop. If size is an
            int instead of sequence like (h, w), a square crop (size, size) is
            made.
        vertical_flip (bool): Use vertical flipping instead of horizontal

    Returns:
       List: List (tl, tr, bl, br, center, tl_flip, tr_flip, bl_flip, br_flip, center_flip)
                Corresponding top left, top right, bottom left, bottom right and center crop
                and same for the flipped image's tensor.
    """
    if not _is_tensor_a_torch_image(img):
        raise TypeError('tensor is not a torch image.')

    assert len(size) == 2, "Please provide only two dimensions (h, w) for size."
    first_five = five_crop(img, size)

    if vertical_flip:
        img = vflip(img)
    else:
        img = hflip(img)

    second_five = five_crop(img, size)

    return first_five + second_five


def _blend(img1: Tensor, img2: Tensor, ratio: float) -> Tensor:
    bound = 1 if img1.dtype in [torch.half, torch.float32, torch.float64] else 255
    return (ratio * img1 + (1 - ratio) * img2).clamp(0, bound).to(img1.dtype)


def _rgb2hsv(img):
    r, g, b = img.unbind(0)

    maxc = torch.max(img, dim=0).values
    minc = torch.min(img, dim=0).values

    # The algorithm erases S and H channel where `maxc = minc`. This avoids NaN
    # from happening in the results, because
    #   + S channel has division by `maxc`, which is zero only if `maxc = minc`
    #   + H channel has division by `(maxc - minc)`.
    #
    # Instead of overwriting NaN afterwards, we just prevent it from occuring so
    # we don't need to deal with it in case we save the NaN in a buffer in
    # backprop, if it is ever supported, but it doesn't hurt to do so.
    eqc = maxc == minc

    cr = maxc - minc
    # Since `eqc => cr = 0`, replacing denominator with 1 when `eqc` is fine.
    s = cr / torch.where(eqc, maxc.new_ones(()), maxc)
    # Note that `eqc => maxc = minc = r = g = b`. So the following calculation
    # of `h` would reduce to `bc - gc + 2 + rc - bc + 4 + rc - bc = 6` so it
    # would not matter what values `rc`, `gc`, and `bc` have here, and thus
    # replacing denominator with 1 when `eqc` is fine.
    cr_divisor = torch.where(eqc, maxc.new_ones(()), cr)
    rc = (maxc - r) / cr_divisor
    gc = (maxc - g) / cr_divisor
    bc = (maxc - b) / cr_divisor

    hr = (maxc == r) * (bc - gc)
    hg = ((maxc == g) & (maxc != r)) * (2.0 + rc - bc)
    hb = ((maxc != g) & (maxc != r)) * (4.0 + gc - rc)
    h = (hr + hg + hb)
    h = torch.fmod((h / 6.0 + 1.0), 1.0)
    return torch.stack((h, s, maxc))


def _hsv2rgb(img):
    h, s, v = img.unbind(0)
    i = torch.floor(h * 6.0)
    f = (h * 6.0) - i
    i = i.to(dtype=torch.int32)

    p = torch.clamp((v * (1.0 - s)), 0.0, 1.0)
    q = torch.clamp((v * (1.0 - s * f)), 0.0, 1.0)
    t = torch.clamp((v * (1.0 - s * (1.0 - f))), 0.0, 1.0)
    i = i % 6

    mask = i == torch.arange(6)[:, None, None]

    a1 = torch.stack((v, q, p, p, t, v))
    a2 = torch.stack((t, v, v, q, p, p))
    a3 = torch.stack((p, p, t, v, v, q))
    a4 = torch.stack((a1, a2, a3))

    return torch.einsum("ijk, xijk -> xjk", mask.to(dtype=img.dtype), a4)


def _pad_symmetric(img: Tensor, padding: List[int]) -> Tensor:
    # padding is left, right, top, bottom
    in_sizes = img.size()

    x_indices = [i for i in range(in_sizes[-1])]  # [0, 1, 2, 3, ...]
    left_indices = [i for i in range(padding[0] - 1, -1, -1)]  # e.g. [3, 2, 1, 0]
    right_indices = [-(i + 1) for i in range(padding[1])]  # e.g. [-1, -2, -3]
    x_indices = torch.tensor(left_indices + x_indices + right_indices)

    y_indices = [i for i in range(in_sizes[-2])]
    top_indices = [i for i in range(padding[2] - 1, -1, -1)]
    bottom_indices = [-(i + 1) for i in range(padding[3])]
    y_indices = torch.tensor(top_indices + y_indices + bottom_indices)

    ndim = img.ndim
    if ndim == 3:
        return img[:, y_indices[:, None], x_indices[None, :]]
    elif ndim == 4:
        return img[:, :, y_indices[:, None], x_indices[None, :]]
    else:
        raise RuntimeError("Symmetric padding of N-D tensors are not supported yet")


def pad(img: Tensor, padding: List[int], fill: int = 0, padding_mode: str = "constant") -> Tensor:
    r"""Pad the given Tensor Image on all sides with specified padding mode and fill value.

    Args:
        img (Tensor): Image to be padded.
        padding (int or tuple or list): Padding on each border. If a single int is provided this
            is used to pad all borders. If a tuple or list of length 2 is provided this is the padding
            on left/right and top/bottom respectively. If a tuple or list of length 4 is provided
            this is the padding for the left, top, right and bottom borders
            respectively. In torchscript mode padding as single int is not supported, use a tuple or
            list of length 1: ``[padding, ]``.
        fill (int): Pixel fill value for constant fill. Default is 0.
            This value is only used when the padding_mode is constant
        padding_mode (str): Type of padding. Should be: constant, edge or reflect. Default is constant.
            Mode symmetric is not yet supported for Tensor inputs.

            - constant: pads with a constant value, this value is specified with fill

            - edge: pads with the last value on the edge of the image

            - reflect: pads with reflection of image (without repeating the last value on the edge)

                       padding [1, 2, 3, 4] with 2 elements on both sides in reflect mode
                       will result in [3, 2, 1, 2, 3, 4, 3, 2]

            - symmetric: pads with reflection of image (repeating the last value on the edge)

                         padding [1, 2, 3, 4] with 2 elements on both sides in symmetric mode
                         will result in [2, 1, 1, 2, 3, 4, 4, 3]

    Returns:
        Tensor: Padded image.
    """
    if not _is_tensor_a_torch_image(img):
        raise TypeError("tensor is not a torch image.")

    if not isinstance(padding, (int, tuple, list)):
        raise TypeError("Got inappropriate padding arg")
    if not isinstance(fill, (int, float)):
        raise TypeError("Got inappropriate fill arg")
    if not isinstance(padding_mode, str):
        raise TypeError("Got inappropriate padding_mode arg")

    if isinstance(padding, tuple):
        padding = list(padding)

    if isinstance(padding, list) and len(padding) not in [1, 2, 4]:
        raise ValueError("Padding must be an int or a 1, 2, or 4 element tuple, not a " +
                         "{} element tuple".format(len(padding)))

    if padding_mode not in ["constant", "edge", "reflect", "symmetric"]:
        raise ValueError("Padding mode should be either constant, edge, reflect or symmetric")

    if isinstance(padding, int):
        if torch.jit.is_scripting():
            raise ValueError("padding can't be an int while torchscripting, set it as a list [value, ]")
        pad_left = pad_right = pad_top = pad_bottom = padding
    elif len(padding) == 1:
        pad_left = pad_right = pad_top = pad_bottom = padding[0]
    elif len(padding) == 2:
        pad_left = pad_right = padding[0]
        pad_top = pad_bottom = padding[1]
    else:
        pad_left = padding[0]
        pad_top = padding[1]
        pad_right = padding[2]
        pad_bottom = padding[3]

    p = [pad_left, pad_right, pad_top, pad_bottom]

    if padding_mode == "edge":
        # remap padding_mode str
        padding_mode = "replicate"
    elif padding_mode == "symmetric":
        # route to another implementation
        if p[0] < 0 or p[1] < 0 or p[2] < 0 or p[3] < 0:  # no any support for torch script
            raise ValueError("Padding can not be negative for symmetric padding_mode")
        return _pad_symmetric(img, p)

    need_squeeze = False
    if img.ndim < 4:
        img = img.unsqueeze(dim=0)
        need_squeeze = True

    out_dtype = img.dtype
    need_cast = False
    if (padding_mode != "constant") and img.dtype not in (torch.float32, torch.float64):
        # Here we temporary cast input tensor to float
        # until pytorch issue is resolved :
        # https://github.com/pytorch/pytorch/issues/40763
        need_cast = True
        img = img.to(torch.float32)

    img = torch.nn.functional.pad(img, p, mode=padding_mode, value=float(fill))

    if need_squeeze:
        img = img.squeeze(dim=0)

    if need_cast:
        img = img.to(out_dtype)

    return img