How to optimize images for display on iPhone or iPad?

[Gellman]

I have been asked to provide images for a client's iPhone and iPad apps, which include a photo gallery. My client's app is like a mini website that runs on the iPhone and iPad. Does anyone know of any articles or other resources that discuss how to best prepare photos for display on an iPhone or an iPad? To be clear, I am not looking for a photo processing app that runs on these devices.

I assume JPEGs @72 dpi, sRGB, but don't know what the size should be. Normally, I like to sharpen for exact output size. Since the displays of each device are different sizes, should everything be done twice or is there a single happy medium? Unfortunately, I do not have an iPhone or iPad, so I can't experiment with my own stuff. What have you all found that works best, short of purchasing an iPhone and iPad and viewing the results?  (I have 2 kids in college at the same time, so there are limits to my purchasing power.)

Thanks in advance for any advice.

-John

[jeremypayne]

http://spyder.datacolor.com/product-ms-spydergallery.php

[Gellman]

Thanks, Jeremy, but I already work in a color calibrated environment.

[Slobodan Blagojevic]

... I assume JPEGs @72 dpi, sRGB, but don't know what the size should be. Normally, I like to sharpen for exact output size. Since the displays of each device are different sizes, should everything be done twice or is there a single happy medium?...

I am sure there are better experts on iPhone/iPad image preparation than me, but just wanted to point out one thing: images on those devices are usually not "static", in the sense that they stay at their original size, but they can be enlarged for a number of reasons: user desire, slideshow transitions, etc. Hence it is a bit risky to supply only the size that fits the respective screen. Ipad screen is 1024x768, so I would usually go for something around 1500-2000 px on the longer side, and sharpen for that.

[AFairley]

http://spyder.datacolor.com/product-ms-spydergallery.php

Just want to point out that AFAIK, the Spyder app only color-manages within its own photo browser, so it is irrelevant to preparing images for general distribution. 

[Wayne Fox]

I am sure there are better experts on iPhone/iPad image preparation than me, but just wanted to point out one thing: images on those devices are usually not "static", in the sense that they stay at their original size, but they can be enlarged for a number of reasons: user desire, slideshow transitions, etc. Hence it is a bit risky to supply only the size that fits the respective screen. Ipad screen is 1024x768, so I would usually go for something around 1500-2000 px on the longer side, and sharpen for that.

I export all of my images for display on my iPhone and iPad at exactly twice the resolution of the iPad, so I know it will be an exact 50% reduction. For iPhones etc the extra size doesn't seem to slow them down ...  seems to work well  This also gives me the ability to enlarge it.

Another reason is I assume future iPads will have much higher resolution displays.