Describe the bug
I have binary mask .tiff files.

1. Attribute .show() shows a black image, but taking the .resampled_array() * 255 shows the correct mask.
2. Tile extraction on these .tiff binary mask doesnt work (but works with OpenSlide .read_region())

To Reproduce
Steps to reproduce the Issue 1:

1. from histolab.slide import Slide
2. annotation_mask = Slide(annotation_path, processed_annotation_path)
3. annotation_mask.show() # shows a black image
4. (annotation_mask.resampled_array() * 255) shows the correct mask

Steps to reproduce the Issue 2:

1. from histolab.slide import Slide
   from histolab.tiler import RandomTiler
2. annotation_mask = Slide(annotation_path, processed_annotation_path)
3. random_tiles_extractor = RandomTiler(tile_size=(256, 256),
   n_tiles=30,
   level=3,
   seed=42,
   check_tissue=True,
   tissue_percent=80.0,
   prefix=prefix + '_',
   suffix=".png"
   )
4. random_tiles_extractor.extract(annotation_mask )
5. ValueError: n should be smaller than the number of regions [0], got 1

Expected behavior issue 2
import openslide as ops
reader = ops.OpenSlide(test_annotation_path)
patch = reader.read_region(location=(47800, 12901), level=3, size=(256, 256))
reader.close()

Screenshots

Software (please complete the following information):

• OS: Ubuntu
• Python Version: 3.8
• histolab version: 0.5.1

Additional context
Data can be downloaded here
images: WSI_part_02/ID-29_HE_active.ndpi
mask: TIFF-annotations/ID-29_HE_active.tiff