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yjunjung
yjunjung
Participating Frequently
July 18, 2020
Answered

Question about the preset document size for an iPad Pro (12.9in)

  • July 18, 2020
  • 4 replies
  • 4168 views

Hi, I would like to know how come the document size for an iPad Pro turns out to be 38 x 28 inch when it says 12.9 inch in inDesign? I know how the resolution is calculated (2732px / 72  x 2048px / 72 = 38 x 28) as the standard PPI is 72. But, I do not get why it says 12.9inch. Also, will everything show in the same way on all the iPads if I use this preset?

 

Thank you.

Correct answer Scott Falkner

InDesign has a unit it calls “pixels” but that unit is not pixels. Pixels have no fixed physical size. A 300 x 300 pixel image designed for print might have a resolution of 300 pixels per inch, or PPI. This means each pixel is a square 1/300 of an inch on each side. The same image designed for a screen would not need a PPI setting because it has no need for it. Each pixel of the image is a pixel on the display. Effectively it is one pixel per pixel. InDesign (and Illustrator) assume documetns designed using pixels as a unit are designed for the screen. Historically, screens have been assumed to be 72 pixels per inch.

 

 Now, remember I said InDesign’s pixel units is not pixels. That’s because InDesign always assumes one and only one fixed size of its “pixel” unit. That size is 72 ppi. A 12.9 inch iPad Pro display is 2732 × 2048 pixels. Since InDesign assumes pixels are always 1/72 inch the document size equals 37.94˝ × 28.44˝. When you export to pixels you end up with an image exactly the size of the iPad’s screen. If you are exporting to a meta format, like PDF or ePub then you don’t need to worry about pixels. But if you use this size and export at 72 ppi you will end up with a document exactly sized for an iPad Pro 12.9˝ screen.

4 replies

rayek.elfin
rayek.elfin
Legend
July 18, 2020

@rob_day That is the incorrect PPI setting for that image if the intent is to place your bitmaps at the correct size in an iPad Pro 12.9" document.

 

The correct setting would be 72PPI (and NOT 264PPI). When you place that file in a iPad Pro 12.9" document the placed relative size will be completely wrong: 745px by 558px, because InDesign assumes a base 72PPI for all device documents.

 

ALWAYS export your bitmaps at 72ppi, and they will be placed 1 on 1 pixel in a mobile device document. ALWAYS work with the actual pixels when preparing assets for screen work. NEVER rely on PPI for screen work. ALWAYS keep the multiplier in mind, if required (but that is another topic).

 

So, @Scott_Falkner 's answer is actually correct, and yours is incorrect.

 

In short: do NOT export your bitmap assets at 264PPI. Instead, work with the actual pixels of the screen, and set the PPI to 72, no matter the device template picked in InDesign. That is what InDesign expects for screen work.

    yjunjung
    yjunjungAuthor
    Participating Frequently
    July 19, 2020

    Wow, thank you for correcting as I unfortunately feel still a bit confused. I originally marked Rob's answer as a correct one because he explained the 12.9 inch was a diagonal size; not the width/height.

     

    But can we decrease the 264 PPI to 72 PPI? Will we notice when we import the bitmap asset into InDesign? I think in this case actual ppi will be 72 and the effective ppi will be 264? I know it is an extra work.

     

    EDIT: Okay, I finally got it. I just tested with a 264 PPI PNG file (745px by 558px). And It turns out that I had to INCREASE the size, thus the effective PPI became 72 from 264, which was supposed to be bigger than the actual PPI (264). Therefore, it is wrong and will end up as a low res png. God...it takes such a long time and trials to understand all these screen size things.

    rob day
    Community Expert
    rob dayCommunity Expert
    Community Expert
    July 19, 2020

    But can we decrease the 264 PPI to 72 PPI? Will we notice when we import the bitmap asset into InDesign? I think in this case actual ppi will be 72 and the effective ppi will be 264? I know it is an extra work.

     

    On Export, placed images will be upsampled if their Effective Resolution is less than the Export Resolution, and downsampled if the Effective Resolution is greater than the Export Resolution. Whether you setup the InDesign page as 2732 x 2048 pixels, or 10.348 x 7.758 inches you have to check the link’s Effective Resolution (the Actual Resolution doesn’t matter), and make sure it is equal to or higher than the final Export Resolution.

    yjunjung
    yjunjungAuthor
    Participating Frequently
    July 18, 2020

    Thank you, I finally understood how everything comes together. I think they should get rid of (12.9 inch) as it throws me off because it looks like either a width or a height measurement.

    rob day
    Community Expert
    rob dayCommunity Expert
    Community Expert
    July 18, 2020

    The 12.9 in the document preset name refers to the iPad Pro’s physical dimensions—10.35" x 7.76" (12.9" diagonal).

     

    The iPad’s display resolution is 264ppi, so if you wanted to set the document up in inches, you could use the physical inch dimensions, and export the page to an image format setting the export Resolution to 264, which would export a 2732px x 2048px JPEG or PNG.

     

     

    A PNG Export in Photoshop:

      Scott Falkner
      Community Expert
      Scott FalknerCommunity ExpertCorrect answer
      Community Expert
      July 18, 2020

      InDesign has a unit it calls “pixels” but that unit is not pixels. Pixels have no fixed physical size. A 300 x 300 pixel image designed for print might have a resolution of 300 pixels per inch, or PPI. This means each pixel is a square 1/300 of an inch on each side. The same image designed for a screen would not need a PPI setting because it has no need for it. Each pixel of the image is a pixel on the display. Effectively it is one pixel per pixel. InDesign (and Illustrator) assume documetns designed using pixels as a unit are designed for the screen. Historically, screens have been assumed to be 72 pixels per inch.

       

       Now, remember I said InDesign’s pixel units is not pixels. That’s because InDesign always assumes one and only one fixed size of its “pixel” unit. That size is 72 ppi. A 12.9 inch iPad Pro display is 2732 × 2048 pixels. Since InDesign assumes pixels are always 1/72 inch the document size equals 37.94˝ × 28.44˝. When you export to pixels you end up with an image exactly the size of the iPad’s screen. If you are exporting to a meta format, like PDF or ePub then you don’t need to worry about pixels. But if you use this size and export at 72 ppi you will end up with a document exactly sized for an iPad Pro 12.9˝ screen.

        yjunjung
        yjunjungAuthor
        Participating Frequently
        July 18, 2020

        Thank you for an indepth reply. I will always remember the 72 ppi that InDesign assumes.

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