Image resolution for iPad publishing
What is the minimum image resolution required when designing for the iPad? The answer might surprise you: 72 ppi.
The pixel resolution of the screen of both the iPad 1 and 2 is 132 ppi. But, if you are designing a document at actual size for the iPad, with page dimensions of 1024 x 768 pixels (or points) or 768 x 1024 pixels, the minimum “effective” image resolution only needs to be 72 ppi. This is because InDesign considers a 1024 pixel wide screen to be about 14.22 inches wide, where the iPad screen is about 7.75″ wide when held horizontally.
In other words, lets say you create a page that is 1024 x 768 pixels in InDesign, and you place an image on the page and scale the image up. Look at the Info panel or the Links panel, and view the “Effective ppi”. As long as this is 72 ppi or above, your images will look their best on the iPad. If you go below 72 ppi, you will start to notice jagged edges and pixelization.
This rule applies whether you’re using Adobe Digital Publishing Suite, other iPad publishing InDesign plugins such as Twixl or WoodWing, or just creating a PDF specifically formatted for the iPad screen size. If the system that you are using will enable the user to pinch and zoom for more detail, you may want to include additional resolution for some images.
You can download templates for creating iPad pages with Adobe Digital Publishing Suite here. I just updated the templates to include a custom embedded iPad-specific preflight profile. This profile checks for a minimum effective image resolution of 72 ppi.
Put another way (I was explaining this in detail recently in another forum), InDesign considers a point and a pixel as synonymous, so to maintain the pixel dimensions of any image you’ve placed in a web- or device-destined document, you MUST ensure that 72 ppi is the output resolution. It’s the only way to maintain the as-designed dimensions of any pixel-based project.
InDesign is a little single-minded on the subject, and can be baffling if you don’t grasp the fixed idea planted in its noggin.
With the iPad 3 right around the corner, and a higher res Retina Display, will this change the way we plan our future publications? Or is it just too soon to know for sure.
@Steve: No, it won’t change the process, but it will probably change the dimensions. One of the important but not-entirely-intuitive things about publishing to screens (whether mobile device or monitor) vs. print is that in print the dimensions (mm, inches, picas) are fixed while the number of dots per inch can vary, but on screen the resolutions (“x” pixels by “y” pixels) are fixed. — Image sizes on screen, as measured by a ruler, will vary depending on the device and the zoom level chosen by the user.
For InDesign Magazine the PDFs are always created at 150 ppi. I think this is a good resolution for interactive PDF files, because it allows for zooming in. Because DPS doesn’t currently allow zooming, 72 is fine.
Another way to put this is the old photoshop adage that size doesn’t matter, only pixel dimensions matter. A 1024 x 768 image at 20ppi or 2000ppi is the same thing.
Hi Keith,
Let plugins worry about the screensize in InDesign for you (as well as Android if you need). On our planning tool it will create the right pages for you as well as allow you to add your own interactivity and display on an iPad for no fee directly from InDesign, see below press release and download.
We now have a 100% free version of our iPad and planning software which you can use for free to create versions of your magazine which can be published to the iPad.
See our website: http://www.gomobile.go-publish.co.uk/gomobilepro/
Here’s how we solve a problem with HTML imagery on our end here at mag+. Because the mag+ InDesign template is based on the resolution of 72dpi and the iPad’s resolution is 132dpi, the images in html elements are not converted by the plugin and need therefore to be at the exact size for the iPad before reviewing. The formula for this is to have the image being 1,83 times bigger (132/72 = 1,83) than what it is in the template. So if the image shown in the template is 558 px by 419 px than the image in the html element should be 1023 by 766px. Another good way to remember this is that the template is 560×420 while the resolution of the iPad is 1024×768 (1.83 times bigger)
Anyone out there playing with out tools yet?
Right! Only pixel counts at screen devices.
Unfortunately neither the iPad nor other devices like Adroid respect their own resulution.
Plus: you surely don’t want to create and publish different sizes = files for the same picture, being displayed at different devices, right?
=> They just display one pixel of an image to one pixel on the screen.
So there is no 10 cm (or 4 inch) wide picture on the ipAd, nor on Android, nor a web browser.
Even, if we are able to CSS encode fonts sor a certain pt size, like in print – the fonts will definately be displayed different at different screens and devices.
Think one step farther: even IF browsers would respect a screen resolution – imagine what would happen, if I have 2 screens connected to a computer – both being a 21” monitor, but one is an old one with a 72dpi resolution and the other with a 96dpi resolution…..
What would happen if I drag the browser window from one display onto the other?
Answer: nothing!
That is because a browser can not get a feedback on wich monitor it is displayed.
As long as both monitors run at the same screen resolution (i.e. full HD) really nothing would happen to the images and text.
What does that mean to the original question about the iPad devices?
=> Pixel is pixel. Not more not less.
Publish the same pictures to a pad than you would publish to the web.
So the author of this article is right: 72dpi is righ (and UNimportant as well).
Tilo Rust
Worldwide trainer and Top-Level Supporter for Adobe Master Collection and more…
tilorust.com
I’m creating a multi-page PDF that I want users to be able to read on their desktops (and print out) as well as on Ipad. I am doing a number of layouts in Photoshop first b/c I’m most comfortable using it – would I make this 1024×768 at 72 DPI or 11 x 8.5 at say 150-300 DPI. So confusing!
Elizabeth: Photoshop isn’t the ideal tool to use for this, since it creates bitmaps, and the resulting PDFs are going to be large. Ideally you’d have 8.5 x 11 inches at 300 ppi for print, and 1024 x 768 at 72 for the iPad. There isn’t any great way to create a single PDF that serves both purposes well.
we are in the process of converting our printed books to ebooks. all our layouts were done in InDesign. my problem right now is what will be the effective resolution for the images? i’m trained for print production so that all images were enhanced in photoshop at 300 dpi resolutions. my boss insists that we keep the same resolution for the ebooks. i told him that it isn’t the case as it would result to an ebook with a bigger file size. am i correct or not? please enlighten me on this matter.
Bottom line question:
If you are using InDesign and want to create a PDF with text and photos that can be viewed on a computer screen and an iPad, do you design for 8.5″x11″ and photos at 72 or 132 resolution? Or do you specify 768×1024px for size. If photos are 300 resolution, the file size would be huge I think, but you do want good screen (iPad and computer) clarity.
@Steve: If I were designing a PDF that is mainly going to be viewed on a computer screen and an iPad, I would design it at 768 x 1024, with the photos at 72 pixels per inch. It will look great on both the computer screen and the iPad.
Okay, I’m designing HD images for the iPad 3. After a lot of research I think I have a pretty good grasp on what the ideal size is. The Images need to be the exact size of the iPad 3 Screen and resolution as well as be able to zoom while still maintain TRUE HD format. Am I to understand that when looking at the full image without zooming, the image should export to a RASTOR (Bitmap) PDF at 150 ppi so it leaves room to zoom in? The top zoom would essentially display at 72 ppi?
All that considered, what are the precise “pixel dimensions” I should see in Photoshop? Or should I look at Document Size.
As I said I have a pretty good idea of how to execute this, but I am hoping to find someone to confirm these things –
Thanks!
We need to create the following deliverables for a client and I’m curious what approach you recommend.
/ PDF that is optimized for best quality for viewing on iPads versions 1, 2, and 3.
/ This InDesign file will be repurposed for the DPS workflow to create an iPad app that is optimized for iPads versions 1, 2 and 3.
For the iPad app, we were planning to create the InDesign file at 1024×768 and create a 2048×1536 folio and use renditions to have appropriate folio version distributed to the correct iPad version.
For the PDF file, should we keep that InDesign file at 1024×768, create it at 2048×1536 or should we have one for each iPad resolution version? Our hope is to have one PDF optimized for all iPads.
Thanks for any recommendations.
Josh