I haven't checked this - so Pillow never ever writes out tiles ATM, even when using libtiff?

LGTM otherwise

I ask because the alternative could be: if you detect (existing?) tile-based tags, one could force libtiff writing and remove the stripe-based ones instead, so you can potentially keep the original data arrangement?

When saving, whether using libtiff or not, strip tags are always set.

In encoding TIFF using libtiff, you can see a call to TIFFWriteScanline ("It is not possible to write scanlines to a file that uses a tiled organization").

And for another opinion, #672 (comment)

Pillow appears to support reading tiled tiff but not writing.

Indeed, so this PR is a "must have" then. 👍

Thanks!