I agree Yleb, higher resolution only has real significance if printing the images - the more dots.points/pixels per inch - makes an enlaged image sharper.
To explain, after long to'ing and fro'ing replies with the iBook Support team, and not really getting anything more positive that " Apples requires images NOT to exceeed 2 million pixels" I applied whe the English call....Irish logic!
The retina display "sharper" the the iPad / iPad 2 i.e. greater resolution because its physically the same size.
Support will advice to teh effect " images of :-
1024 x 767 or 1024 x 748
2048 x 1496 or 2048 x 1536 these are landscale swith around for Portrait.
The first size caters for none retina, the second caters for all iPads.
The next consideration for me came about after a ticket stated images were to small and when expanded became blurred. So to cater for Retina and expanded images - I simply made the reolution greater to maintain a sharper image when enlarged.
As I only make photo books, I will attract other photographers who wil be critical of image quality.
The thing to take acoount is deal with your audience first. If you are displaying only 1024 x 748 at 72ppi - expanded on Retina they look blurred.
This is from the Retina iPad page, Apple store:-
- Retina display
- 9.7-inch (diagonal) LED-backlit Multi-Touch display with IPS technology
- 2048-by-1536 resolution at 264 pixels per inch (ppi)
- Fingerprint-resistant oleophobic coating
That seems to answer all questions about image sizes to use..and contradics all those who say that 1024 x 768 at 72ppi OK for all iPads.
Finally, Apples mantra is no images greater than 2 million pixels - BUT 2048 multiplied by 1536 = 3,145,738 pixels!