mmsegmentation/mmseg/datasets/pipelines/transforms.py

# Copyright (c) OpenMMLab. All rights reserved.
import mmcv
import numpy as np
from mmcv.utils import deprecated_api_warning, is_tuple_of
from numpy import random

from ..builder import PIPELINES


@PIPELINES.register_module()
class ResizeToMultiple(object):
    """Resize images & seg to multiple of divisor.

    Args:
        size_divisor (int): images and gt seg maps need to resize to multiple
            of size_divisor. Default: 32.
        interpolation (str, optional): The interpolation mode of image resize.
            Default: None
    """

    def __init__(self, size_divisor=32, interpolation=None):
        self.size_divisor = size_divisor
        self.interpolation = interpolation

    def __call__(self, results):
        """Call function to resize images, semantic segmentation map to
        multiple of size divisor.

        Args:
            results (dict): Result dict from loading pipeline.

        Returns:
            dict: Resized results, 'img_shape', 'pad_shape' keys are updated.
        """
        # Align image to multiple of size divisor.
        img = results['img']
        img = mmcv.imresize_to_multiple(
            img,
            self.size_divisor,
            scale_factor=1,
            interpolation=self.interpolation
            if self.interpolation else 'bilinear')

        results['img'] = img
        results['img_shape'] = img.shape
        results['pad_shape'] = img.shape

        # Align segmentation map to multiple of size divisor.
        for key in results.get('seg_fields', []):
            gt_seg = results[key]
            gt_seg = mmcv.imresize_to_multiple(
                gt_seg,
                self.size_divisor,
                scale_factor=1,
                interpolation='nearest')
            results[key] = gt_seg

        return results

    def __repr__(self):
        repr_str = self.__class__.__name__
        repr_str += (f'(size_divisor={self.size_divisor}, '
                     f'interpolation={self.interpolation})')
        return repr_str


@PIPELINES.register_module()
class Resize(object):
    """Resize images & seg.

    This transform resizes the input image to some scale. If the input dict
    contains the key "scale", then the scale in the input dict is used,
    otherwise the specified scale in the init method is used.

    ``img_scale`` can be None, a tuple (single-scale) or a list of tuple
    (multi-scale). There are 4 multiscale modes:

    - ``ratio_range is not None``:
    1. When img_scale is None, img_scale is the shape of image in results
        (img_scale = results['img'].shape[:2]) and the image is resized based
        on the original size. (mode 1)
    2. When img_scale is a tuple (single-scale), randomly sample a ratio from
        the ratio range and multiply it with the image scale. (mode 2)

    - ``ratio_range is None and multiscale_mode == "range"``: randomly sample a
    scale from the a range. (mode 3)

    - ``ratio_range is None and multiscale_mode == "value"``: randomly sample a
    scale from multiple scales. (mode 4)

    Args:
        img_scale (tuple or list[tuple]): Images scales for resizing.
            Default:None.
        multiscale_mode (str): Either "range" or "value".
            Default: 'range'
        ratio_range (tuple[float]): (min_ratio, max_ratio).
            Default: None
        keep_ratio (bool): Whether to keep the aspect ratio when resizing the
            image. Default: True
    """

    def __init__(self,
                 img_scale=None,
                 multiscale_mode='range',
                 ratio_range=None,
                 keep_ratio=True):
        if img_scale is None:
            self.img_scale = None
        else:
            if isinstance(img_scale, list):
                self.img_scale = img_scale
            else:
                self.img_scale = [img_scale]
            assert mmcv.is_list_of(self.img_scale, tuple)

        if ratio_range is not None:
            # mode 1: given img_scale=None and a range of image ratio
            # mode 2: given a scale and a range of image ratio
            assert self.img_scale is None or len(self.img_scale) == 1
        else:
            # mode 3 and 4: given multiple scales or a range of scales
            assert multiscale_mode in ['value', 'range']

        self.multiscale_mode = multiscale_mode
        self.ratio_range = ratio_range
        self.keep_ratio = keep_ratio

    @staticmethod
    def random_select(img_scales):
        """Randomly select an img_scale from given candidates.

        Args:
            img_scales (list[tuple]): Images scales for selection.

        Returns:
            (tuple, int): Returns a tuple ``(img_scale, scale_dix)``,
                where ``img_scale`` is the selected image scale and
                ``scale_idx`` is the selected index in the given candidates.
        """

        assert mmcv.is_list_of(img_scales, tuple)
        scale_idx = np.random.randint(len(img_scales))
        img_scale = img_scales[scale_idx]
        return img_scale, scale_idx

    @staticmethod
    def random_sample(img_scales):
        """Randomly sample an img_scale when ``multiscale_mode=='range'``.

        Args:
            img_scales (list[tuple]): Images scale range for sampling.
                There must be two tuples in img_scales, which specify the lower
                and upper bound of image scales.

        Returns:
            (tuple, None): Returns a tuple ``(img_scale, None)``, where
                ``img_scale`` is sampled scale and None is just a placeholder
                to be consistent with :func:`random_select`.
        """

        assert mmcv.is_list_of(img_scales, tuple) and len(img_scales) == 2
        img_scale_long = [max(s) for s in img_scales]
        img_scale_short = [min(s) for s in img_scales]
        long_edge = np.random.randint(
            min(img_scale_long),
            max(img_scale_long) + 1)
        short_edge = np.random.randint(
            min(img_scale_short),
            max(img_scale_short) + 1)
        img_scale = (long_edge, short_edge)
        return img_scale, None

    @staticmethod
    def random_sample_ratio(img_scale, ratio_range):
        """Randomly sample an img_scale when ``ratio_range`` is specified.

        A ratio will be randomly sampled from the range specified by
        ``ratio_range``. Then it would be multiplied with ``img_scale`` to
        generate sampled scale.

        Args:
            img_scale (tuple): Images scale base to multiply with ratio.
            ratio_range (tuple[float]): The minimum and maximum ratio to scale
                the ``img_scale``.

        Returns:
            (tuple, None): Returns a tuple ``(scale, None)``, where
                ``scale`` is sampled ratio multiplied with ``img_scale`` and
                None is just a placeholder to be consistent with
                :func:`random_select`.
        """

        assert isinstance(img_scale, tuple) and len(img_scale) == 2
        min_ratio, max_ratio = ratio_range
        assert min_ratio <= max_ratio
        ratio = np.random.random_sample() * (max_ratio - min_ratio) + min_ratio
        scale = int(img_scale[0] * ratio), int(img_scale[1] * ratio)
        return scale, None

    def _random_scale(self, results):
        """Randomly sample an img_scale according to ``ratio_range`` and
        ``multiscale_mode``.

        If ``ratio_range`` is specified, a ratio will be sampled and be
        multiplied with ``img_scale``.
        If multiple scales are specified by ``img_scale``, a scale will be
        sampled according to ``multiscale_mode``.
        Otherwise, single scale will be used.

        Args:
            results (dict): Result dict from :obj:`dataset`.

        Returns:
            dict: Two new keys 'scale` and 'scale_idx` are added into
                ``results``, which would be used by subsequent pipelines.
        """

        if self.ratio_range is not None:
            if self.img_scale is None:
                h, w = results['img'].shape[:2]
                scale, scale_idx = self.random_sample_ratio((w, h),
                                                            self.ratio_range)
            else:
                scale, scale_idx = self.random_sample_ratio(
                    self.img_scale[0], self.ratio_range)
        elif len(self.img_scale) == 1:
            scale, scale_idx = self.img_scale[0], 0
        elif self.multiscale_mode == 'range':
            scale, scale_idx = self.random_sample(self.img_scale)
        elif self.multiscale_mode == 'value':
            scale, scale_idx = self.random_select(self.img_scale)
        else:
            raise NotImplementedError

        results['scale'] = scale
        results['scale_idx'] = scale_idx

    def _resize_img(self, results):
        """Resize images with ``results['scale']``."""
        if self.keep_ratio:
            img, scale_factor = mmcv.imrescale(
                results['img'], results['scale'], return_scale=True)
            # the w_scale and h_scale has minor difference
            # a real fix should be done in the mmcv.imrescale in the future
            new_h, new_w = img.shape[:2]
            h, w = results['img'].shape[:2]
            w_scale = new_w / w
            h_scale = new_h / h
        else:
            img, w_scale, h_scale = mmcv.imresize(
                results['img'], results['scale'], return_scale=True)
        scale_factor = np.array([w_scale, h_scale, w_scale, h_scale],
                                dtype=np.float32)
        results['img'] = img
        results['img_shape'] = img.shape
        results['pad_shape'] = img.shape  # in case that there is no padding
        results['scale_factor'] = scale_factor
        results['keep_ratio'] = self.keep_ratio

    def _resize_seg(self, results):
        """Resize semantic segmentation map with ``results['scale']``."""
        for key in results.get('seg_fields', []):
            if self.keep_ratio:
                gt_seg = mmcv.imrescale(
                    results[key], results['scale'], interpolation='nearest')
            else:
                gt_seg = mmcv.imresize(
                    results[key], results['scale'], interpolation='nearest')
            results[key] = gt_seg

    def __call__(self, results):
        """Call function to resize images, bounding boxes, masks, semantic
        segmentation map.

        Args:
            results (dict): Result dict from loading pipeline.

        Returns:
            dict: Resized results, 'img_shape', 'pad_shape', 'scale_factor',
                'keep_ratio' keys are added into result dict.
        """

        if 'scale' not in results:
            self._random_scale(results)
        self._resize_img(results)
        self._resize_seg(results)
        return results

    def __repr__(self):
        repr_str = self.__class__.__name__
        repr_str += (f'(img_scale={self.img_scale}, '
                     f'multiscale_mode={self.multiscale_mode}, '
                     f'ratio_range={self.ratio_range}, '
                     f'keep_ratio={self.keep_ratio})')
        return repr_str


@PIPELINES.register_module()
class RandomFlip(object):
    """Flip the image & seg.

    If the input dict contains the key "flip", then the flag will be used,
    otherwise it will be randomly decided by a ratio specified in the init
    method.

    Args:
        prob (float, optional): The flipping probability. Default: None.
        direction(str, optional): The flipping direction. Options are
            'horizontal' and 'vertical'. Default: 'horizontal'.
    """

    @deprecated_api_warning({'flip_ratio': 'prob'}, cls_name='RandomFlip')
    def __init__(self, prob=None, direction='horizontal'):
        self.prob = prob
        self.direction = direction
        if prob is not None:
            assert prob >= 0 and prob <= 1
        assert direction in ['horizontal', 'vertical']

    def __call__(self, results):
        """Call function to flip bounding boxes, masks, semantic segmentation
        maps.

        Args:
            results (dict): Result dict from loading pipeline.

        Returns:
            dict: Flipped results, 'flip', 'flip_direction' keys are added into
                result dict.
        """

        if 'flip' not in results:
            flip = True if np.random.rand() < self.prob else False
            results['flip'] = flip
        if 'flip_direction' not in results:
            results['flip_direction'] = self.direction
        if results['flip']:
            # flip image
            results['img'] = mmcv.imflip(
                results['img'], direction=results['flip_direction'])

            # flip segs
            for key in results.get('seg_fields', []):
                # use copy() to make numpy stride positive
                results[key] = mmcv.imflip(
                    results[key], direction=results['flip_direction']).copy()
        return results

    def __repr__(self):
        return self.__class__.__name__ + f'(prob={self.prob})'


@PIPELINES.register_module()
class Pad(object):
    """Pad the image & mask.

    There are two padding modes: (1) pad to a fixed size and (2) pad to the
    minimum size that is divisible by some number.
    Added keys are "pad_shape", "pad_fixed_size", "pad_size_divisor",

    Args:
        size (tuple, optional): Fixed padding size.
        size_divisor (int, optional): The divisor of padded size.
        pad_val (float, optional): Padding value. Default: 0.
        seg_pad_val (float, optional): Padding value of segmentation map.
            Default: 255.
    """

    def __init__(self,
                 size=None,
                 size_divisor=None,
                 pad_val=0,
                 seg_pad_val=255):
        self.size = size
        self.size_divisor = size_divisor
        self.pad_val = pad_val
        self.seg_pad_val = seg_pad_val
        # only one of size and size_divisor should be valid
        assert size is not None or size_divisor is not None
        assert size is None or size_divisor is None

    def _pad_img(self, results):
        """Pad images according to ``self.size``."""
        if self.size is not None:
            padded_img = mmcv.impad(
                results['img'], shape=self.size, pad_val=self.pad_val)
        elif self.size_divisor is not None:
            padded_img = mmcv.impad_to_multiple(
                results['img'], self.size_divisor, pad_val=self.pad_val)
        results['img'] = padded_img
        results['pad_shape'] = padded_img.shape
        results['pad_fixed_size'] = self.size
        results['pad_size_divisor'] = self.size_divisor

    def _pad_seg(self, results):
        """Pad masks according to ``results['pad_shape']``."""
        for key in results.get('seg_fields', []):
            results[key] = mmcv.impad(
                results[key],
                shape=results['pad_shape'][:2],
                pad_val=self.seg_pad_val)

    def __call__(self, results):
        """Call function to pad images, masks, semantic segmentation maps.

        Args:
            results (dict): Result dict from loading pipeline.

        Returns:
            dict: Updated result dict.
        """

        self._pad_img(results)
        self._pad_seg(results)
        return results

    def __repr__(self):
        repr_str = self.__class__.__name__
        repr_str += f'(size={self.size}, size_divisor={self.size_divisor}, ' \
                    f'pad_val={self.pad_val})'
        return repr_str


@PIPELINES.register_module()
class Normalize(object):
    """Normalize the image.

    Added key is "img_norm_cfg".

    Args:
        mean (sequence): Mean values of 3 channels.
        std (sequence): Std values of 3 channels.
        to_rgb (bool): Whether to convert the image from BGR to RGB,
            default is true.
    """

    def __init__(self, mean, std, to_rgb=True):
        self.mean = np.array(mean, dtype=np.float32)
        self.std = np.array(std, dtype=np.float32)
        self.to_rgb = to_rgb

    def __call__(self, results):
        """Call function to normalize images.

        Args:
            results (dict): Result dict from loading pipeline.

        Returns:
            dict: Normalized results, 'img_norm_cfg' key is added into
                result dict.
        """

        results['img'] = mmcv.imnormalize(results['img'], self.mean, self.std,
                                          self.to_rgb)
        results['img_norm_cfg'] = dict(
            mean=self.mean, std=self.std, to_rgb=self.to_rgb)
        return results

    def __repr__(self):
        repr_str = self.__class__.__name__
        repr_str += f'(mean={self.mean}, std={self.std}, to_rgb=' \
                    f'{self.to_rgb})'
        return repr_str


@PIPELINES.register_module()
class Rerange(object):
    """Rerange the image pixel value.

    Args:
        min_value (float or int): Minimum value of the reranged image.
            Default: 0.
        max_value (float or int): Maximum value of the reranged image.
            Default: 255.
    """

    def __init__(self, min_value=0, max_value=255):
        assert isinstance(min_value, float) or isinstance(min_value, int)
        assert isinstance(max_value, float) or isinstance(max_value, int)
        assert min_value < max_value
        self.min_value = min_value
        self.max_value = max_value

    def __call__(self, results):
        """Call function to rerange images.

        Args:
            results (dict): Result dict from loading pipeline.
        Returns:
            dict: Reranged results.
        """

        img = results['img']
        img_min_value = np.min(img)
        img_max_value = np.max(img)

        assert img_min_value < img_max_value
        # rerange to [0, 1]
        img = (img - img_min_value) / (img_max_value - img_min_value)
        # rerange to [min_value, max_value]
        img = img * (self.max_value - self.min_value) + self.min_value
        results['img'] = img

        return results

    def __repr__(self):
        repr_str = self.__class__.__name__
        repr_str += f'(min_value={self.min_value}, max_value={self.max_value})'
        return repr_str


@PIPELINES.register_module()
class CLAHE(object):
    """Use CLAHE method to process the image.

    See `ZUIDERVELD,K. Contrast Limited Adaptive Histogram Equalization[J].
    Graphics Gems, 1994:474-485.` for more information.

    Args:
        clip_limit (float): Threshold for contrast limiting. Default: 40.0.
        tile_grid_size (tuple[int]): Size of grid for histogram equalization.
            Input image will be divided into equally sized rectangular tiles.
            It defines the number of tiles in row and column. Default: (8, 8).
    """

    def __init__(self, clip_limit=40.0, tile_grid_size=(8, 8)):
        assert isinstance(clip_limit, (float, int))
        self.clip_limit = clip_limit
        assert is_tuple_of(tile_grid_size, int)
        assert len(tile_grid_size) == 2
        self.tile_grid_size = tile_grid_size

    def __call__(self, results):
        """Call function to Use CLAHE method process images.

        Args:
            results (dict): Result dict from loading pipeline.

        Returns:
            dict: Processed results.
        """

        for i in range(results['img'].shape[2]):
            results['img'][:, :, i] = mmcv.clahe(
                np.array(results['img'][:, :, i], dtype=np.uint8),
                self.clip_limit, self.tile_grid_size)

        return results

    def __repr__(self):
        repr_str = self.__class__.__name__
        repr_str += f'(clip_limit={self.clip_limit}, '\
                    f'tile_grid_size={self.tile_grid_size})'
        return repr_str


@PIPELINES.register_module()
class RandomCrop(object):
    """Random crop the image & seg.

    Args:
        crop_size (tuple): Expected size after cropping, (h, w).
        cat_max_ratio (float): The maximum ratio that single category could
            occupy.
    """

    def __init__(self, crop_size, cat_max_ratio=1., ignore_index=255):
        assert crop_size[0] > 0 and crop_size[1] > 0
        self.crop_size = crop_size
        self.cat_max_ratio = cat_max_ratio
        self.ignore_index = ignore_index

    def get_crop_bbox(self, img):
        """Randomly get a crop bounding box."""
        margin_h = max(img.shape[0] - self.crop_size[0], 0)
        margin_w = max(img.shape[1] - self.crop_size[1], 0)
        offset_h = np.random.randint(0, margin_h + 1)
        offset_w = np.random.randint(0, margin_w + 1)
        crop_y1, crop_y2 = offset_h, offset_h + self.crop_size[0]
        crop_x1, crop_x2 = offset_w, offset_w + self.crop_size[1]

        return crop_y1, crop_y2, crop_x1, crop_x2

    def crop(self, img, crop_bbox):
        """Crop from ``img``"""
        crop_y1, crop_y2, crop_x1, crop_x2 = crop_bbox
        img = img[crop_y1:crop_y2, crop_x1:crop_x2, ...]
        return img

    def __call__(self, results):
        """Call function to randomly crop images, semantic segmentation maps.

        Args:
            results (dict): Result dict from loading pipeline.

        Returns:
            dict: Randomly cropped results, 'img_shape' key in result dict is
                updated according to crop size.
        """

        img = results['img']
        crop_bbox = self.get_crop_bbox(img)
        if self.cat_max_ratio < 1.:
            # Repeat 10 times
            for _ in range(10):
                seg_temp = self.crop(results['gt_semantic_seg'], crop_bbox)
                labels, cnt = np.unique(seg_temp, return_counts=True)
                cnt = cnt[labels != self.ignore_index]
                if len(cnt) > 1 and np.max(cnt) / np.sum(
                        cnt) < self.cat_max_ratio:
                    break
                crop_bbox = self.get_crop_bbox(img)

        # crop the image
        img = self.crop(img, crop_bbox)
        img_shape = img.shape
        results['img'] = img
        results['img_shape'] = img_shape

        # crop semantic seg
        for key in results.get('seg_fields', []):
            results[key] = self.crop(results[key], crop_bbox)

        return results

    def __repr__(self):
        return self.__class__.__name__ + f'(crop_size={self.crop_size})'


@PIPELINES.register_module()
class RandomRotate(object):
    """Rotate the image & seg.

    Args:
        prob (float): The rotation probability.
        degree (float, tuple[float]): Range of degrees to select from. If
            degree is a number instead of tuple like (min, max),
            the range of degree will be (``-degree``, ``+degree``)
        pad_val (float, optional): Padding value of image. Default: 0.
        seg_pad_val (float, optional): Padding value of segmentation map.
            Default: 255.
        center (tuple[float], optional): Center point (w, h) of the rotation in
            the source image. If not specified, the center of the image will be
            used. Default: None.
        auto_bound (bool): Whether to adjust the image size to cover the whole
            rotated image. Default: False
    """

    def __init__(self,
                 prob,
                 degree,
                 pad_val=0,
                 seg_pad_val=255,
                 center=None,
                 auto_bound=False):
        self.prob = prob
        assert prob >= 0 and prob <= 1
        if isinstance(degree, (float, int)):
            assert degree > 0, f'degree {degree} should be positive'
            self.degree = (-degree, degree)
        else:
            self.degree = degree
        assert len(self.degree) == 2, f'degree {self.degree} should be a ' \
                                      f'tuple of (min, max)'
        self.pal_val = pad_val
        self.seg_pad_val = seg_pad_val
        self.center = center
        self.auto_bound = auto_bound

    def __call__(self, results):
        """Call function to rotate image, semantic segmentation maps.

        Args:
            results (dict): Result dict from loading pipeline.

        Returns:
            dict: Rotated results.
        """

        rotate = True if np.random.rand() < self.prob else False
        degree = np.random.uniform(min(*self.degree), max(*self.degree))
        if rotate:
            # rotate image
            results['img'] = mmcv.imrotate(
                results['img'],
                angle=degree,
                border_value=self.pal_val,
                center=self.center,
                auto_bound=self.auto_bound)

            # rotate segs
            for key in results.get('seg_fields', []):
                results[key] = mmcv.imrotate(
                    results[key],
                    angle=degree,
                    border_value=self.seg_pad_val,
                    center=self.center,
                    auto_bound=self.auto_bound,
                    interpolation='nearest')
        return results

    def __repr__(self):
        repr_str = self.__class__.__name__
        repr_str += f'(prob={self.prob}, ' \
                    f'degree={self.degree}, ' \
                    f'pad_val={self.pal_val}, ' \
                    f'seg_pad_val={self.seg_pad_val}, ' \
                    f'center={self.center}, ' \
                    f'auto_bound={self.auto_bound})'
        return repr_str


@PIPELINES.register_module()
class RGB2Gray(object):
    """Convert RGB image to grayscale image.

    This transform calculate the weighted mean of input image channels with
    ``weights`` and then expand the channels to ``out_channels``. When
    ``out_channels`` is None, the number of output channels is the same as
    input channels.

    Args:
        out_channels (int): Expected number of output channels after
            transforming. Default: None.
        weights (tuple[float]): The weights to calculate the weighted mean.
            Default: (0.299, 0.587, 0.114).
    """

    def __init__(self, out_channels=None, weights=(0.299, 0.587, 0.114)):
        assert out_channels is None or out_channels > 0
        self.out_channels = out_channels
        assert isinstance(weights, tuple)
        for item in weights:
            assert isinstance(item, (float, int))
        self.weights = weights

    def __call__(self, results):
        """Call function to convert RGB image to grayscale image.

        Args:
            results (dict): Result dict from loading pipeline.

        Returns:
            dict: Result dict with grayscale image.
        """
        img = results['img']
        assert len(img.shape) == 3
        assert img.shape[2] == len(self.weights)
        weights = np.array(self.weights).reshape((1, 1, -1))
        img = (img * weights).sum(2, keepdims=True)
        if self.out_channels is None:
            img = img.repeat(weights.shape[2], axis=2)
        else:
            img = img.repeat(self.out_channels, axis=2)

        results['img'] = img
        results['img_shape'] = img.shape

        return results

    def __repr__(self):
        repr_str = self.__class__.__name__
        repr_str += f'(out_channels={self.out_channels}, ' \
                    f'weights={self.weights})'
        return repr_str


@PIPELINES.register_module()
class AdjustGamma(object):
    """Using gamma correction to process the image.

    Args:
        gamma (float or int): Gamma value used in gamma correction.
            Default: 1.0.
    """

    def __init__(self, gamma=1.0):
        assert isinstance(gamma, float) or isinstance(gamma, int)
        assert gamma > 0
        self.gamma = gamma
        inv_gamma = 1.0 / gamma
        self.table = np.array([(i / 255.0)**inv_gamma * 255
                               for i in np.arange(256)]).astype('uint8')

    def __call__(self, results):
        """Call function to process the image with gamma correction.

        Args:
            results (dict): Result dict from loading pipeline.

        Returns:
            dict: Processed results.
        """

        results['img'] = mmcv.lut_transform(
            np.array(results['img'], dtype=np.uint8), self.table)

        return results

    def __repr__(self):
        return self.__class__.__name__ + f'(gamma={self.gamma})'


@PIPELINES.register_module()
class SegRescale(object):
    """Rescale semantic segmentation maps.

    Args:
        scale_factor (float): The scale factor of the final output.
    """

    def __init__(self, scale_factor=1):
        self.scale_factor = scale_factor

    def __call__(self, results):
        """Call function to scale the semantic segmentation map.

        Args:
            results (dict): Result dict from loading pipeline.

        Returns:
            dict: Result dict with semantic segmentation map scaled.
        """
        for key in results.get('seg_fields', []):
            if self.scale_factor != 1:
                results[key] = mmcv.imrescale(
                    results[key], self.scale_factor, interpolation='nearest')
        return results

    def __repr__(self):
        return self.__class__.__name__ + f'(scale_factor={self.scale_factor})'


@PIPELINES.register_module()
class PhotoMetricDistortion(object):
    """Apply photometric distortion to image sequentially, every transformation
    is applied with a probability of 0.5. The position of random contrast is in
    second or second to last.

    1. random brightness
    2. random contrast (mode 0)
    3. convert color from BGR to HSV
    4. random saturation
    5. random hue
    6. convert color from HSV to BGR
    7. random contrast (mode 1)

    Args:
        brightness_delta (int): delta of brightness.
        contrast_range (tuple): range of contrast.
        saturation_range (tuple): range of saturation.
        hue_delta (int): delta of hue.
    """

    def __init__(self,
                 brightness_delta=32,
                 contrast_range=(0.5, 1.5),
                 saturation_range=(0.5, 1.5),
                 hue_delta=18):
        self.brightness_delta = brightness_delta
        self.contrast_lower, self.contrast_upper = contrast_range
        self.saturation_lower, self.saturation_upper = saturation_range
        self.hue_delta = hue_delta

    def convert(self, img, alpha=1, beta=0):
        """Multiple with alpha and add beat with clip."""
        img = img.astype(np.float32) * alpha + beta
        img = np.clip(img, 0, 255)
        return img.astype(np.uint8)

    def brightness(self, img):
        """Brightness distortion."""
        if random.randint(2):
            return self.convert(
                img,
                beta=random.uniform(-self.brightness_delta,
                                    self.brightness_delta))
        return img

    def contrast(self, img):
        """Contrast distortion."""
        if random.randint(2):
            return self.convert(
                img,
                alpha=random.uniform(self.contrast_lower, self.contrast_upper))
        return img

    def saturation(self, img):
        """Saturation distortion."""
        if random.randint(2):
            img = mmcv.bgr2hsv(img)
            img[:, :, 1] = self.convert(
                img[:, :, 1],
                alpha=random.uniform(self.saturation_lower,
                                     self.saturation_upper))
            img = mmcv.hsv2bgr(img)
        return img

    def hue(self, img):
        """Hue distortion."""
        if random.randint(2):
            img = mmcv.bgr2hsv(img)
            img[:, :,
                0] = (img[:, :, 0].astype(int) +
                      random.randint(-self.hue_delta, self.hue_delta)) % 180
            img = mmcv.hsv2bgr(img)
        return img

    def __call__(self, results):
        """Call function to perform photometric distortion on images.

        Args:
            results (dict): Result dict from loading pipeline.

        Returns:
            dict: Result dict with images distorted.
        """

        img = results['img']
        # random brightness
        img = self.brightness(img)

        # mode == 0 --> do random contrast first
        # mode == 1 --> do random contrast last
        mode = random.randint(2)
        if mode == 1:
            img = self.contrast(img)

        # random saturation
        img = self.saturation(img)

        # random hue
        img = self.hue(img)

        # random contrast
        if mode == 0:
            img = self.contrast(img)

        results['img'] = img
        return results

    def __repr__(self):
        repr_str = self.__class__.__name__
        repr_str += (f'(brightness_delta={self.brightness_delta}, '
                     f'contrast_range=({self.contrast_lower}, '
                     f'{self.contrast_upper}), '
                     f'saturation_range=({self.saturation_lower}, '
                     f'{self.saturation_upper}), '
                     f'hue_delta={self.hue_delta})')
        return repr_str


@PIPELINES.register_module()
class RandomCutOut(object):
    """CutOut operation.

    Randomly drop some regions of image used in
    `Cutout <https://arxiv.org/abs/1708.04552>`_.
    Args:
        prob (float): cutout probability.
        n_holes (int | tuple[int, int]): Number of regions to be dropped.
            If it is given as a list, number of holes will be randomly
            selected from the closed interval [`n_holes[0]`, `n_holes[1]`].
        cutout_shape (tuple[int, int] | list[tuple[int, int]]): The candidate
            shape of dropped regions. It can be `tuple[int, int]` to use a
            fixed cutout shape, or `list[tuple[int, int]]` to randomly choose
            shape from the list.
        cutout_ratio (tuple[float, float] | list[tuple[float, float]]): The
            candidate ratio of dropped regions. It can be `tuple[float, float]`
            to use a fixed ratio or `list[tuple[float, float]]` to randomly
            choose ratio from the list. Please note that `cutout_shape`
            and `cutout_ratio` cannot be both given at the same time.
        fill_in (tuple[float, float, float] | tuple[int, int, int]): The value
            of pixel to fill in the dropped regions. Default: (0, 0, 0).
        seg_fill_in (int): The labels of pixel to fill in the dropped regions.
            If seg_fill_in is None, skip. Default: None.
    """

    def __init__(self,
                 prob,
                 n_holes,
                 cutout_shape=None,
                 cutout_ratio=None,
                 fill_in=(0, 0, 0),
                 seg_fill_in=None):

        assert 0 <= prob and prob <= 1
        assert (cutout_shape is None) ^ (cutout_ratio is None), \
            'Either cutout_shape or cutout_ratio should be specified.'
        assert (isinstance(cutout_shape, (list, tuple))
                or isinstance(cutout_ratio, (list, tuple)))
        if isinstance(n_holes, tuple):
            assert len(n_holes) == 2 and 0 <= n_holes[0] < n_holes[1]
        else:
            n_holes = (n_holes, n_holes)
        if seg_fill_in is not None:
            assert (isinstance(seg_fill_in, int) and 0 <= seg_fill_in
                    and seg_fill_in <= 255)
        self.prob = prob
        self.n_holes = n_holes
        self.fill_in = fill_in
        self.seg_fill_in = seg_fill_in
        self.with_ratio = cutout_ratio is not None
        self.candidates = cutout_ratio if self.with_ratio else cutout_shape
        if not isinstance(self.candidates, list):
            self.candidates = [self.candidates]

    def __call__(self, results):
        """Call function to drop some regions of image."""
        cutout = True if np.random.rand() < self.prob else False
        if cutout:
            h, w, c = results['img'].shape
            n_holes = np.random.randint(self.n_holes[0], self.n_holes[1] + 1)
            for _ in range(n_holes):
                x1 = np.random.randint(0, w)
                y1 = np.random.randint(0, h)
                index = np.random.randint(0, len(self.candidates))
                if not self.with_ratio:
                    cutout_w, cutout_h = self.candidates[index]
                else:
                    cutout_w = int(self.candidates[index][0] * w)
                    cutout_h = int(self.candidates[index][1] * h)

                x2 = np.clip(x1 + cutout_w, 0, w)
                y2 = np.clip(y1 + cutout_h, 0, h)
                results['img'][y1:y2, x1:x2, :] = self.fill_in

                if self.seg_fill_in is not None:
                    for key in results.get('seg_fields', []):
                        results[key][y1:y2, x1:x2] = self.seg_fill_in

        return results

    def __repr__(self):
        repr_str = self.__class__.__name__
        repr_str += f'(prob={self.prob}, '
        repr_str += f'n_holes={self.n_holes}, '
        repr_str += (f'cutout_ratio={self.candidates}, ' if self.with_ratio
                     else f'cutout_shape={self.candidates}, ')
        repr_str += f'fill_in={self.fill_in}, '
        repr_str += f'seg_fill_in={self.seg_fill_in})'
        return repr_str