AW: Question about NDPI

[Martin Weihrauch]

Thank you again for the great explanation!

Another issue for NDPI:
As the value/offset tags within the IFDs are only 4 bytes in Hamamatsu, I saw from OpenSlide that
- If it is not the 1st IFD, then it compares the offset of any tag with the offset to the tag from the 1st IFD. If the offset is the same --> take this 32bit offset, else combine the high bits of the 64bit offset of the IFD in the file with the tag 32 bit offset to 64bits. 

The question:
Isn't there the theoretical chance that the 32bit and the 64 bit offset could be the same though they are not?

E. g., let's assume, the label image is at the real offset of byte 17,000,000,123.
There is also another image at an offset of 123.
Isn't it possible that in the IFD, 123 is stored in the 32 bit and by looking at the first IFD, which also has an offset of 123, the software incorrectly assumes that this is the true offset instead of the one in the 17GB?

Best

Martin


-----Ursprüngliche Nachricht-----
Von: Benjamin Gilbert <bgilbert+openslide at cs.cmu.edu> 
Gesendet: Dienstag, 14. Mai 2024 06:00
An: openslide-users at lists.andrew.cmu.edu
Cc: Martin Weihrauch <m.weihrauch at smartinmedia.com>
Betreff: Re: Question about NDPI

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On Mon, May 13, 2024 at 10:30 PM Martin Weihrauch <m.weihrauch at smartinmedia.com> wrote:
> At Smart In Media, have a huge slide collection and our earliest ever NDPI slide dates back to Oct 2007 and the latest to this year. The models were S210, S360 and S20 and one from one, where I am not sure (2007).
> In all of them, I found the word "Hamamatsu" in a Hex Editor starting at byte #12 (in the oldest slide from 2007, it starts at #18). This would make it a lot easier at identifying Hamamatsu NDPI files from the content of the file, irrespective of the extension, by just searching the first e. g. 30 bytes for the string "Hamamatsu".
>
> Can you confirm this or do you have other findings?

That approach is probably okay, though personally I wouldn't rely on it.  That string "Hamamatsu" is referenced by the Make tag (271) of the first TIFF directory, and so its location within the file is probably not contractual.  For example, any other software that decided to generate NDPI-compatible files would not necessarily put the string in the same place, if it included the string at all.

Best,
--Benjamin Gilbert