[ITK] Question about BigTIFF

[Gib Bogle]

I observe that an ITK-created tiff that is bigger than 2^31 but smaller than 2^32 is a BigTIFF - it has Version number = 43 in the header.  I am suddenly wondering why such a file is a BigTIFF.  On this site:
http://www.awaresystems.be/imaging/tiff/bigtiff.html
it says:
"The TIFF file format uses 32bit offsets and, as such, is limited to 4 gigabytes. This has been quite sufficient for many years. Today however, there is a need for a good multi-purpose open image file format that can handle huge images, or very large collections of images, breaking the 4 gig boundary. There is currently an ongoing attempt to launch a new variant of TIFF, called BigTIFF, that closely resembles TIFF, but uses 64bit offsets instead...."

In other words, BigTIFF is needed for files bigger than 2^32 bytes, or 4 GB.

Can somebody explain this?

Cheers
Gib
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