deepzoom_tile.py creates tiles with inconsistent width or height  #111

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1. ToshitakaK commented on Jan 21, 2021

   

   ToshitakaK

   on Jan 21, 2021

   Author

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   Update:

   I found DeepZoomGenerator.get_tile() returns tiles which have incorrect shape.
   https://github.com/openslide/openslide-python/blob/v1.1.2/openslide/deepzoom.py#L141-L160

   It seems that PIL.Image.thumbnail() is the cause. This function is used to resize the image while keeping the aspect ratio, but sometimes it becomes smaller than z_size.

       def get_tile(self, level, address):
           """Return an RGB PIL.Image for a tile.
           level:     the Deep Zoom level.
           address:   the address of the tile within the level as a (col, row)
                      tuple."""
   
           # Read tile
           args, z_size = self._get_tile_info(level, address)  # z_size=(212, 8) 
           tile = self._osr.read_region(*args)  # tile.size=(423, 14)
   
           # Apply on solid background
           bg = Image.new('RGB', tile.size, self._bg_color)
           tile = Image.composite(tile, bg, tile)
   
           # Scale to the correct size
           if tile.size != z_size:
               tile.thumbnail(z_size, Image.ANTIALIAS)  # tile.size=(212, 7), it's smaller than z_size
           
           return tile

   DeepZoom users would expect tiles in the same row to have the same height, and tiles in the same column to have the same width.
   I think we need to do something like using PIL.ImageOps.fit(), which is a function that "generates the exact tile size while maintaining the aspect ratio", seems like a good idea.
2. lambda-science commented on Mar 25, 2021

   

   lambda-science

   on Mar 25, 2021

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   Update:

   I found DeepZoomGenerator.get_tile() returns tiles which have incorrect shape.
   https://github.com/openslide/openslide-python/blob/v1.1.2/openslide/deepzoom.py#L141-L160

   It seems that PIL.Image.thumbnail() is the cause. This function is used to resize the image while keeping the aspect ratio, but sometimes it becomes smaller than z_size.

       def get_tile(self, level, address):
           """Return an RGB PIL.Image for a tile.
           level:     the Deep Zoom level.
           address:   the address of the tile within the level as a (col, row)
                      tuple."""
   
           # Read tile
           args, z_size = self._get_tile_info(level, address)  # z_size=(212, 8) 
           tile = self._osr.read_region(*args)  # tile.size=(423, 14)
   
           # Apply on solid background
           bg = Image.new('RGB', tile.size, self._bg_color)
           tile = Image.composite(tile, bg, tile)
   
           # Scale to the correct size
           if tile.size != z_size:
               tile.thumbnail(z_size, Image.ANTIALIAS)  # tile.size=(212, 7), it's smaller than z_size
           
           return tile

   DeepZoom users would expect tiles in the same row to have the same height, and tiles in the same column to have the same width.
   I think we need to do something like using PIL.ImageOps.fit(), which is a function that "generates the exact tile size while maintaining the aspect ratio", seems like a good idea.

   Is there any update or fix for this ?
   Some tiles that are generated doesn't make sens and are almost blank. It's weird
   
   Some other slide are just weirdly-sized rectangle (and not 255x255).
   Some tiles are generated while not existing in original image
   
3. bkf15 commented on Jun 20, 2021

   

   bkf15

   on Jun 20, 2021

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   I am having the same issue with viewing tiff files. Some generated tiles are white with checker lines across it, like shown above. Weirdly, this only seems to happen on certain 'levels' of the image, while others are unaffected.
4. Brysch commented on Nov 9, 2022

   

   Brysch

   on Nov 9, 2022

   More actions

   I solved it (for my needs) by modifying /Lib/site-packages/openslide/deepzoom.py

       def get_tile(self, level, address, method="fill"):
           """Return an RGB PIL.Image for a tile.
   
           level:     the Deep Zoom level.
           address:   the address of the tile within the level as a (col, row)
                      tuple.
           method:    "fill" - fills the space of partial images and the target image size
                      "rescale" - scales partial images to the target size
           """
           # Read tile
           args, z_size = self._get_tile_info(level, address)
           tile = self._osr.read_region(*args)
   
           # Apply on solid background
           bg = Image.new(mode='RGBA', size=(self._z_t_downsample, self._z_t_downsample), color=self._bg_color)
   
           if method=="fill":
               tile = Image.composite(tile, bg, tile)
               # Scale to the correct size
               if tile.size != z_size:
                   # Image.Resampling added in Pillow 9.1.0
                   # Image.LANCZOS removed in Pillow 10
                   # tile.thumbnail(z_size, getattr(Image, 'Resampling', Image).LANCZOS)            
                   tile.thumbnail(tile.size, getattr(Image, 'Resampling', Image).LANCZOS) # fill
                   
           if method=="rescale":           
               tile_new = Image.composite(tile, bg, tile)
               # Scale to the correct size
               if tile_new.size != z_size:
                   tile = tile.resize(tile_new.size, Image.ANTIALIAS) # scale
   
           return tile

   now one can choose to fill the space or to rescale the partial image by

   image_tiles = DeepZoomGenerator(image_slides, tile_size=tile_size, overlap=0, limit_bounds=False)
   image_tiles .get_tile(level, (col, row), method="fill")

   or

   image_tiles = DeepZoomGenerator(image_slides, tile_size=tile_size, overlap=0, limit_bounds=False)
   image_tiles .get_tile(level, (col, row), method="rescale")