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I'm trying to understand how to calculate just how much bigger to make images for 'Retina' quality screens. I understand that the general answer is just 'x2' but it's never explained why this is.

For example, let's take a MacBook Air vs. the new MacBook Pro Retina.

Resolution

MacBook Air - 1440 x 900

MacBook Pro - 2560 x 1600 (this is not simply 'x2', it is x1.77 greater)

PPI

MacBook Air - 128

MacBook Pro - 227 (again this is not simply 'x2', it is x1.77 greater).

Can someone answer, is it simply just a general rule to make things 'x2' or whether that is actually the dimensions needed?

I'd really like this explained rather than just a simple Yes / No. Thanks

SparrwHawk
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1 Answers1

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The "×2" is simply a rough guideline.

On a "normal" computer monitor (96 dpi), a 200x200 pixel picture would be about 2" wide on the screen, while on a Macbook Pro it would be just under 1". So in order to get the same physical width, it would have to be approximately 2 times as large in terms of pixels.

Mr Lister
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  • Thanks for your answer. What I don't understand is what's referenced e.g. if I open Photoshop (PS) and set the canvas to 500px * 500px, does PS use my current screen resolution as a reference for what it's exporting (i.e. 128 ppi)? Or, because PS sets new documents to 72 ppi, does that mean I need to make my canvas about 3 times larger for retina screens? (227 / 72 is just over 3). – SparrwHawk Mar 03 '13 at 17:27
  • I'm not sure how Photoshop acts on such hi-dpi screens, sorry. (Haven't got PS running on my phone yet...) – Mr Lister Mar 03 '13 at 19:36