class_docstr: Control the contrast of the image. A magnitude=0 gives a gray image,
  whereas magnitude=1 gives the original imageThe bboxes, masks and
  segmentations are not modified.
  
  Required Keys:
  
  - img
  
  Modified Keys:
  
  - img
  
  Args:
      prob (float): The probability for performing Contrast transformation.
          Defaults to 1.0.
      level (int, optional): Should be in range [0,_MAX_LEVEL].
          If level is None, it will generate from [0, _MAX_LEVEL] randomly.
          Defaults to None.
      min_mag (float): The minimum magnitude for Contrast transformation.
          Defaults to 0.1.
      max_mag (float): The maximum magnitude for Contrast transformation.
          Defaults to 1.9.
docstr: Adjust the image contrast.
docstr_tok: ["Adjust","the","image","contrast","."]
code: def _transform_img(self, results: dict, mag: float) -> None:
      """Adjust the image contrast."""
      img = results["img"]
      results["img"] = mmcv.adjust_contrast(img, mag).astype(img.dtype)
  
imports: import math
  from typing import Optional
  import mmcv
  import numpy
  from mmcv.transforms import BaseTransform
  from mmcv.transforms.utils import cache_randomness
  from mmdet.registry import TRANSFORMS
  from .augment_wrappers import _MAX_LEVEL, level_to_mag
label_desc: Use image node_id 2 for calling the Contrast obj's underlying member method code with example usage: obj._transform_img(results, mag) without return types