UPDATE 2012-03-24 18:00 — I can hear my Apple friends shaking their heads in unison, “oh Joseph, why are you trying to figure this out… just let iTunes scale the images for you and it’ll all be fine!”. You know what… they’d be right. Read on; updates today are in red.

There has been quite a bit of discussion in the last week on how to best scale your photographs to sync to the new iPad to take advantage of the retina display.

(If you’re looking for the article on displaying images on a web page for viewing on the iPad, go here: How Do You Make Web Graphics & Photos Look Great On The New iPad?)

I’ve been doing a ton of research and testing, and here are my findings. If you just want the “what to do”, skip to the end. To understand why, start reading here.

Facts and figures

1. The native resolution of the new iPad is 2,048 x 1,526, so you can export a photo to have a max dimension of 2,048 by making a preset “fit within: 2048 x 2048” and that will display at 1:1 and look amazing—but if you pinch in you’ll be past 100% view (obviously) so if you want to zoom in, you need more pixels. If you don’t care about that, then just make a preset to fit within 2,048 wide and be done with it.
2. If you copy any photo to your iPad using iTunes that is over 3,072 pixels on the short side it will be scaled down to 3,072. For a normal aspect-ratio photo (2:3, 5:4, etc.) that equates to roughly 14 Megapixels (MP).
3. Even though the photo will be 14 MP in size, the Photos app on the iPad will not display that image at full size; i.e. at 1:1. I have not been able to determine what it does show, but it’s not the full size. [UPDATE: Photos app appears to zoom in to 3x the photo size when you double-tap on it, regardless of the original size. It will not go farther, however iPhoto will. But I no longer am confident that even iPhoto is showing images at 1:1 pixels, because I can zoom in more than 3x (by measuring with a ruler on the screen) in iPhoto, yet if I zoomed into a 2048 image 3x that’d be 6,144 wide, which is beyond even a 21MP image. Maybe we are seeing 1 photo pixel per four retina pixels? I really don’t know…] This is easy to test; just copy over a 14 MP image and open it in Photos, then open it in iPhoto for iOS ($4.99), and zoom in as far as you can. You will see that you can zoom in farther in iPhoto.
4. If you use the Camera Connection Kit, you can import any resolution photo (well, maybe not Hasselblad photos, but maybe!) however iPhoto will only display it at 100% if it’s under 19MP. That does appear to be a hard line; I had a test with a 19.1 MP image and it was not presented at full size. If you go over 19 MP, then iPhoto will show you a version is scaled down by a factor of four. This is a huge difference; suddenly your 12 MP camera photos look better in iPhoto than your 21 MP camera photos. (Consider shooting RAW+smaller JPG if this is a critical part of your workflow).
5. If you actually edit the image in iPhoto, there is a maximum export size of 4,000 pixels per side. For an un-cropped photo that means about 12 MP; for a square photo that’s 4k² = 16 MP
6. You can use an app like PhotoSync ($1.99 and a cool way to quickly get photos onto the iPad without having to sync—especially handy if you are traveling and away from your primary sync computer) to push higher resolution photos to the iPad, which is essentially the same as using the Camera Connection Kit. You will have a full rez image on the iPad, but be limited in how you can view them as described above.

What does that mean?

For the average user who is editing in Aperture and just wants their synced photos to rock on their new iPad, what does this mean?

If you’re syncing the iPad through iTunes connected to your Aperture library, and you want the max quality possible, you need to ensure your Previews are set bigger than 3,072 on the short side. That’s a lot!

• For example my 12 MP Fuji X100 makes a 4288 x 2848 (12.2 MP) file, so if I have previews set to render at half-size (the default), then I’m only giving iTunes a 2144 x 1424 image to send to the iPad, well below its maximum. Yes it’s still bigger than the 2048 screen, but I can’t pinch in much. And if I don’t limit preview size, then iTunes will send the entire preview over since the shorter side is less than 3072.
• On the other hand, my 21 MP Canon photos 5616 x 3744 (21.0 MP) at half size would be 2808 x 1872, giving me some pinching room, but if I leave them at full size then they will be scaled to 4608 x 3072 (that’s the 3072 max we’re talking about here). That’s a 14.15 MP file, yet remember, Photos app won’t show it at full size! So unless you plan on looking at them in iPhoto, then what’s the point?

OK that doesn’t answer your question, does it. The Preview sizes you can choose from in Aperture are “don’t limit” (full size), “half”, then “fit within” and you will see your screen resolution, plus 1680, 1440 and 1280. “Don’t limit” is the easiest option, since iTunes will handle scaling down to 3,072 for you. But that will take up more room on your hard drive if all your images are rendering full-size previews. You might be able to set it to half, but that really depends on your camera resolution.

I don’t have iTunes sync from my Aperture library—I have multiple libraries and find it easier to maintain a folder of photos that I sync to my iPad. So that gives me more control over the image that’s exported, but here’s the rub… the max size on the iPad through iTunes is 3,072… on the short side. That means you can’t make a preset in Aperture that exports to a maximum of 3,072 on the short side without making two presets; one for horizontal and one for vertical photos. Why not? Because which side do you put 3072 in, the width or the height? So you would need two presets:

• For portrait photos: width 3,072 x height 20,000 (or some ridiculous massive number so no matter how you’ve cropped it it still gets the 3072 on the short side)
• For landscape photos: width 20,000 x height 3,072
• OR, just set your export preset to 3,072 x 3,072 and accept that your files will be less than maximum size (but still look awesome). Most cameras shoot at a 3:2 aspect ration. 3072 x 2 ÷ 3 = 2048. Did you get that? The 3072 max isn’t a random number. If most cameras shoot at 3:2 ratio, then your output set to fit within 3072 on both sides will make a file that is 3072 x 2048. So if you have a landscape photo, but view it in portrait mode and pinch to fit (top to bottom, cutting off the sides), you’ll be at 1:1. If you’re viewing it in landscape mode on the iPad, your 3,072 width is exactly 50% larger than the 2,048 pixels, which will render nicely and give you a reasonable amount to pinch in. And guess what… if you double-tap, it actually zooms in farther than that, so you’re technically seeing it beyond 1:1, and hey, it look awesome. That’s the joy and beauty of the retina display, isn’t it.
• I no longer like this previous statement. I realized today looking at some images that I was zoomed too far in. I now know that when you double-tap on a photo, regardless of the original resolution, the iPad zooms in 3x. So if you load a image that is too small, it will look soft when you zoom in. The 3,072 max I proposed before means that the long side (on a horizontal 2:3 photo) will be 3,072, which is only 50% more than 2048, the width of the iPad screen. Therefore double-tapping, zooming into 3x, means you’re looking at a photo at 200%.
• If you actually export an image at 3,072 on the short side, that makes the long side 4,608 which is still less than 3x the width of the iPad (3x2048=6144). Doubling the width of the iPad is 2x2048=4096, so you’re between double and triple the resolution. So the fact that when you double-tap and zoom 3x in means you’re zoomed beyond 100%. But you can’t really tell, because the pixels are so small. And you can’t put an image on there that’s 3x the screen resolution; that’d be 3x2048=6144, so a 2:3 image would be 6144 x 9216 = 56.6 MP image. So, um, forget about the true 1:1 viewing. There’s just too many pixels.
• So unless you want dual presets, I’m concluding that you just export at full size and let iTunes scale appropriately. Really. After all that… just let iTunes scale it to 3,072 on the short side and don’t worry about it.

So… make it easy. What do I do?

If you sync from Aperture “the easy way”, meaning you just have previews turned on, pick the albums you want synced in iTunes, and hit go, either set your Previews to don’t limit (full size) if you have a 14 MP camera or lower, or set to half size if you have a 20 MP camera or higher. If you have somewhere in-between, I think personally I’d choose full size previews to get that bigger photo. But try it. Can you see the difference? If not, set it to half. Unless your camera is shooting over 6144 on the short side, (and it isn’t, because even the new Nikon D800 36.3 MP shoots 6144 x 4912), then setting your previews to half size will limit what iTunes syncs to your iPad. Aperture has no 75% preview size, so you’ll want to leave it at full. 

If you sync from a collection of photos in a folder, create a preset in Aperture for 3072 x 3072 and call it “new iPad export”, and use that one. That’s what I’m doing and it looks great. just export at full/original size to your iTunes sync folder. Really. Why? Sure you could take the time to export at 3072 on the short side, but let’s make this easy. If you did that, you’d have to be sure you weren’t exporting any smaller photos using that preset, or they’d be scaled UP from Aperture.

So…

Set previews to DON’T LIMIT, or export photos at ORIGINAL SIZE

What’s that web thing you mentioned earlier?

Right… if your head isn’t hurting yet (I know mine is), head over to this article “How Do You Make Web Graphics & Photos Look Great On The New iPad?” and read up on the other half of this research, where we hopefully have resolved how to make web graphics look awesome no matter what device you view them on.

It’s a brave new world. If you disagree, see something different, or just want to share your experience, let’s hear it in the comments below!