class_docstr: Extension of `MaskFile` for VOC masks.
  Removes the color pallete and optionally drops void pixels.
  
  # Arguments
      drop_void (bool): drops the void pixels, which should have the value 255.
      filepath: Path to the mask image file.
code: def __init__(
      self, filepath: Union[str, Path], drop_void: bool = True
  ):
      super().__init__(filepath=filepath)
      self.drop_void = drop_void
  
imports: from icevision.imports import *
  from icevision.utils import *
  from PIL import Image
label_desc: Use image node_id 1 to create a new VocMaskFile object from inherited base classes: MaskFile with example: obj = VocMaskFile(filepath, drop_void)