Question about NDPI

[Martin Weihrauch]

Dear community,

my C-knowledge does not suffice to read the entire code of openslide-vendor-hamamatsu.c, but I am interested to better understand the Hamamatsu format.

If I see it correctly, it (ab)uses the Tiff format and stores a single JPEG in each zoom level, (ab)using the JPEG rules, e. g. by exceeding the 65,000 pixel limit, etc.

My question: how is it possible to quickly extract a tile from the large JPEG? Does it internally have multiple frames (the stripes) and if yes, how is it possible to locate the internal MCU/8x8 blocks without reading the entire stripe or does each stripe have to be "parsed" at least once completely? Is there something like a directory involved?

Thank you 

Martin