Also Photoshop has an upper file size to what can be reduced. Not trivial?
Note the question mark. It was put there to designate it as a question. Also in the remaining part of the post there are two other question marks. The whole post,as a post, was designated as a question. This I see this as nit picking. The members can make up their own mind. BTW I think in this instance copy & pasting the whole post to see the context would have been appropriate?
For versions of Photoshop prior to Photoshop CS, Photoshop had a 2GB file size limit, as well as a 30,000 pixel limit in each dimension. Therefore, even in older versions of Photoshop the file size limitation is far in excess of what the D800 is capable of producing.
In the current version of Photoshop CS 5.5, that limit still holds for the Photoshop (PSD) file format, however, you can actually work with images far larger than that. In Photoshop CS 5.5 the maximum pixel dimensions are 300,000 x 300,000 pixels, or 90,000 MP,