Hamamatsu NDPI missing some levels

[ap--]

ts_slide = TiffSlide('OS-3.ndpi'), os_slide = OpenSlide('OS-3.ndpi')

    def test_level_count(ts_slide, os_slide):
>       assert ts_slide.level_count == os_slide.level_count
E       assert 10 == 13
E         +10
E         -13

[ap--]

This is really minor. TiffSlide levels are a strict subset of the OpenSlide levels.

[stergioc]

Hi :)

I am coming back to this after some years just to mention that in case you want to process a WSI on a specific level that is not available through tiffslide then you will have to perform on the fly downsampling and that can affect the throughput performance.

From the snippet at #49 you can quickly see the differences.