cutout.py

import numpy as np

class Cutout:

    def __init__(self, size=16) -> None:
        self.size = size

    def _create_cutout_mask(self, img_height, img_width, num_channels, size):
        """Creates a zero mask used for cutout of shape `img_height` x `img_width`.
        Args:
          img_height: Height of image cutout mask will be applied to.
          img_width: Width of image cutout mask will be applied to.
          num_channels: Number of channels in the image.
          size: Size of the zeros mask.
        Returns:
          A mask of shape `img_height` x `img_width` with all ones except for a
          square of zeros of shape `size` x `size`. This mask is meant to be
          elementwise multiplied with the original image. Additionally returns
          the `upper_coord` and `lower_coord` which specify where the cutout mask
          will be applied.
        """
        # assert img_height == img_width

        # Sample center where cutout mask will be applied
        height_loc = np.random.randint(low=0, high=img_height)
        width_loc = np.random.randint(low=0, high=img_width)

        size = int(size)
        # Determine upper right and lower left corners of patch
        upper_coord = (max(0, height_loc - size // 2), max(0, width_loc - size // 2))
        lower_coord = (
            min(img_height, height_loc + size // 2),
            min(img_width, width_loc + size // 2),
        )
        mask_height = lower_coord[0] - upper_coord[0]
        mask_width = lower_coord[1] - upper_coord[1]
        assert mask_height > 0
        assert mask_width > 0

        mask = np.ones((img_height, img_width, num_channels))
        zeros = np.zeros((mask_height, mask_width, num_channels))
        mask[upper_coord[0]: lower_coord[0], upper_coord[1]: lower_coord[1], :] = zeros
        return mask, upper_coord, lower_coord

    def __call__(self, pil_img):
        pil_img = pil_img.copy()
        img_height, img_width, num_channels = (*pil_img.size, 3)
        _, upper_coord, lower_coord = self._create_cutout_mask(
            img_height, img_width, num_channels, self.size
        )
        pixels = pil_img.load()  # create the pixel map
        for i in range(upper_coord[0], lower_coord[0]):  # for every col:
            for j in range(upper_coord[1], lower_coord[1]):  # For every row
                pixels[i, j] = (125, 122, 113, 0)  # set the colour accordingly
        return pil_img