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I don't know if this belongs in StackOverflow or some other SE site, but here goes.

I have a PSD design I have an iOS development team turning into a Retina iPad app. However, this design is made in the default 72 dpi.

The development team is now saying the design should be 264 dpi (same as a Retina iPad) -- as well as a 132 dpi version for the non-Retina edition.

This confuses me, as I was under the impression that dpi just represents how many pixels go into an inch of output, and therefore would only matter in printing. The dpi of an iPad just represents the number of pixels for each inch of screen, and therefore doesn't according to my brain have anything to do with the dpi of the PSD. Especially since it already is in the 2048×1536 size required for Retina.

I told them this, but they insist, which has made me doubt my own infallibility.

Who's in the right here? Does the dpi of the design file have anything to do with the dpi of the device? What would make an otherwise smart dev team think this?

Emphram Stavanger
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    Great question; I can't guarantee an answer, but all the designers I have worked with do as you have done - 72 dpi PSD but naturally double size in terms of pixels to cover the retina devices. I have not had any issues or noticed any pixel/display issues when using these graphics and testing on retina displays. – Luke Aug 09 '12 at 09:30

6 Answers6

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The DPI of your Photoshop file does not matter. You can go into Photoshop and change the DPI to whatever you want. Going from non-Retina to Retina is "sort of" like doubling your DPI, however.

If you've already created a design assuming a 1024x768 resolution for the iPad, you will need to recreate the design to at 2048x1536. Where the concept of dpi comes into play is that the density of data should remain consistent at both retina and non-retina resolutions. You'll just need to recreate each bitmap-based element in your file at 4 times the resolution you originally had if you start with a non-retina file. It is sort of like going from 72 dpi to 144 dpi.

Adam B
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  • I perhaps should've specified this in the question, but the file is already in the 2048x1536 resolution required for Retina. The only hassle with the dev team is about the dpi listed in the psd, which I thought not to matter. – Emphram Stavanger Aug 09 '12 at 09:33
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    Thats good from your perspective. One thing to know is the dev team will need to create "normal" (original iPad) resource images as well as "@2x" (retina iPad) resource images. If your design does not scale down to the original size (some places are too detailed, for example), you might want to provide both resolutions of the design, with minor tweaks for things that don't look good if you scale it down just by halving the resolution. – Adam B Aug 09 '12 at 09:40
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    The DPI in the PSD does not matter. What matters is that you have the appropriate pixel dimensions in the produced image. – Jesper Aug 09 '12 at 09:43
  • Yeah, sounds like maybe the dev team was trying to say they wanted two design files - one for non-retina and one for retina. – Adam B Aug 09 '12 at 09:47
  • I did consider that, seeing as this is an outsourced team. But no, they actually sent me a screenshot of the iPad comparison page on Apple's site, with the PPI values highlighted, and explained that it's not possible to have 72 dpi in both the Retina and non-Retina design files, as the Retina psd should have exactly double the dpi, even if not the same one as in the iPad. That's what confused me. – Emphram Stavanger Aug 09 '12 at 09:55
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    You may want to take this as a red flag regarding the remainder of the development process. – Adam B Aug 09 '12 at 09:57
  • Did they notice the Retina image has 4x pixels, didn't they? :) – Teejay Aug 09 '12 at 10:07
  • Thanks for clearing this up; I had the opposite experience where I got two PSDs, one with 300dpi and one 72dpi but same physical size. I just asked the designers to provide one *physically* at 300dpi and they were able to do that. This confused me too as I thought the DPI mattered as well. – kamranicus Oct 09 '12 at 21:17
4

You are right.

In a PSD, the DPI is not significant as it only serves to the system to determine how to print the file.

You can always change your PSD's DPI setting to make them happy :) That's definitely not significant.

If set to 264 DPI, a 2048*1536 printed image will be exactly iPad-sized.

And similarly a SD 1024*768 image set to 132 DPI will be same size.

Teejay
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DPI/PPI makes no difference when you're working for a screen, it's the amount of pixels on the screen that matter. If you design for iPad at 2048x1536px at 264ppi or 72ppi, it's still 2048x1536px in both cases. The only difference is if you full size the preview in photoshop.

PPI = Pixels Per Inch. If you're dealing with inches, PPI matters because its the density of that size. If you're measuring the document/canvas size by pixels, then the density would be "Pixels per Pixel" and that's just ridiculous.

Just make sure you're designing at accurate or higher pixels so they can be shrunken if needed for older iOS devices, low res Androids, desktop web, etc.

user3340876
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Don't forget that an image, with a higher resolution than can be displayed at normal size, can improve the look of the graphic when it is zoomed into. Zooming happens all the time in iOS, especially on the iPhone, because the screen is too small to be really useful and it's just so easy to do.

Shaun
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DPI matters greatly. You can't just jack up dpi properly, you must develop at the highest dpi or even better, the proper dpi. For an example why, imagine you're creating a smooth, rounded edge using algorithms from an effect. The level of detail, as it fills in every change in the curve and selects each color gradient will be finer when the dpi is higher. A;though yu can pop in and change the dpi from 72 to 132 or 264 afterward, it doesn't apply the intelligence of each effect, yourself, etc, it simply fills based on what's there. That means you are defeating the entire purpose of the clearer high dpi screen and bringing it down to the quality of 72 dpi.

gfinale
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Even if you think your right the "dev" team wont listen to just do what they said, up the DPI to 144 and give them the images.

Why make a big deal out of it when you can do this in 5 minutes. They are obviously wrong but why waste your time.

deleted_user
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  • Because I like making them sweat :) Long story short, the later they are with the app, the sweeter the contract is for me, and delays like this are definitely their fault. – Emphram Stavanger Aug 09 '12 at 10:37
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    Yeha thats funny except you are posting up here not knowing the answer and wasting my time too. This stuff is all in apple docs and you had no reason to even post this. So go waste your own developers time some more – deleted_user Aug 09 '12 at 10:40
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    I'm sorry I've wasted your time with answers as deep and constructive as "just do it anyway to avoid confrontation". And I was under the impression the point of Q&A sites was to ask questions you don't know the answers to. But I apologize for failing to live up to these standards of such a decorated veteran as yourself. I hope I can make it up to you by reciprocating - I'll vote your answer down too. – Emphram Stavanger Aug 09 '12 at 12:34