132 ppi? 72 dpi? 144? 264 ppi? What image resolution should you use for the new iPad with Retina display?

There was an interesting question on the Quark Forum: http://forums.quark.com/t/27985.aspx

Bottom line, what resolution is ideal for the iPad and what to do now for the NEW iPad (with Retina display)? And I am sure, like the original poster, most of us heard the rule to use “72 dpi” (which should be ppi of course) when designing for screen. The 72 dpi you hear a lot results from 1) the misunderstanding about dpi and ppi (dots and pixels) and 2) monitors historically having a resolution of 72 ppi. By the way, modern monitors have much more — the Retina display of the new iPad uses 264 ppi.

So what’s the best resolution for designing for tablets?

If you are interested in the background and exhaustive explanation, then please read this excellent blog post, which my colleague Sarbjit referenced: The Myth of DPI

If you just want to hear the bottom line, my advice is:
Forget resolution. Use pixels.

That means if you want to use a picture fullscreen on the iPad 2, make sure it has 1024 x 768 pixels. For the new iPad? Twice as many pixels in both directions (2048 x 1536 pixels). Resolution? It doesn’t matter: use any. (For Print of course that’s a completely different story.)

Have a look at the following example, where I used the same photo just using a different resolution each time — the last one even having only 1 ppi (yes, ONE ppi, no typo). Do you see a difference?

Screenshot of an iPad2 showing the same motive with different ppi values

Screenshot from an iPad 2 showing the same photo using different resolutions but always the same pixel count (click to see full image)

And don’t let anyone tell you that ppi has an influence on file size when you keep the same amount of pixel. So as I kept the number of pixels exactly the same for all four examples, they all even have the same file size. Try in Photoshop yourself (deselect “Resample” obviously), when you change the ppi value and the pixel count stays constant, only the output size changes.

Feel free to download the issue (.zave) to see for yourself on an iPad using Quark AVE Publishing using the Quark AVE Issue Previewer:

Click to download iPad issue

If you want to have the original QuarkXPress document, please send me an email.


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