Chromatic aberration on iPad

Kasper Pyndt
Kasper Pyndt Posts: 36
in Font Technology
Hi people,

I'm usually proofing my typefaces on iPad in addition to printing, but I've always had some chromatic aberration related issues when viewing the fonts in Acrobat Reader or Notability (the latter of which is my preferred proofing-software due to its much better rendering of handwritten notes).

There's a small red-ish and blue-ish lines showing along the edges of the letters. A rather distracting issue when trying to assess the qualities of a font. 

Do you know if it's possible to improve the display performance on iPad and get rid of the colored lines around the letters? 

If at all relevant: I'm using an iPad Pro from 2020 if memory serves me well (i believe the generation JUST before the M1 ipads).

Thanks! 
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Comments

  • John Hudson
    John Hudson Posts: 3,186
    Do you see the same thing in e.g. a browser on your iPad? Are the fonts CFF or TTF?

    If this is not an issue in browsers or other software, then it may be the result of Acrobat’s rendering engine (and whatever Notability is using). I am not very familiar with Acrobat on iPad, but on desktop it actually uses three different rasterisers, depending on the size of the text and the format of the font, so depending on zoom level and content a single page in a PDF might be using more than one rasteriser.
  • Kasper Pyndt
    Kasper Pyndt Posts: 36
    John Hudson said:
    Do you see the same thing in e.g. a browser on your iPad? Are the fonts CFF or TTF?

    If this is not an issue in browsers or other software, then it may be the result of Acrobat’s rendering engine (and whatever Notability is using). I am not very familiar with Acrobat on iPad, but on desktop it actually uses three different rasterisers, depending on the size of the text and the format of the font, so depending on zoom level and content a single page in a PDF might be using more than one rasteriser.
    The fonts are CFF and yes, I see the same thing on a browser. So I'm probably leaning to it being a firmware related issue. 
  • Russell McGorman
    Russell McGorman Posts: 262
    This a stab in the dark, but can this be due to sub pixel rendering?? I believe that's just a PC thing. 
  • John Hudson
    John Hudson Posts: 3,186
    Yes, colour fringing is a characteristic subpixel rendering artifact, but to my knowledge Apple are not currently using subpixel rendering in iOS (and it is off by default in Mac OS).
  • John Butler
    John Butler Posts: 290
    Very dumb question: do you wear eyeglasses? When I wear mine, the chromatic aberration on my iPad is intolerably distracting. I just take mine off and hold it up about 20cm from my face instead. Perhaps it‘s the lightweight high-index lenses.
  • Thomas Phinney
    Thomas Phinney Posts: 2,883
    Note that Adobe Acrobat and Acrobat Reader uses Adobe’s own imaging and text rendering, which is cross-platform and independent of the OS. It indeed has the option to do subpixel rendering which can be seen as color fringing.

    Here is where the preference is in the full Acrobat. 

    Smooth text “for Laptop/LCD screens” is what can cause color fringing. “For monitor” is the grayscale subpixel rendering, more similar to what Apple uses, and the most recent Windows approach. You can also turn it off.
  • Mark Simonson
    Mark Simonson Posts: 1,734
    edited March 2023
    Is it possible for iPad apps to use anything other than the iPadOS text rendering engine? In any case, I don't see a "Smooth Text" setting on the iPad version of Acrobat.
  • Mark Simonson
    Mark Simonson Posts: 1,734
    To answer my own question, I think perhaps they can. I just opened a PDF in Acrobat on the iPad and it used the Adobe substitute roman font.
  • Kasper Pyndt
    Kasper Pyndt Posts: 36
    John Butler said:
    Very dumb question: do you wear eyeglasses? When I wear mine, the chromatic aberration on my iPad is intolerably distracting. I just take mine off and hold it up about 20cm from my face instead. Perhaps it‘s the lightweight high-index lenses.

    I don't :-)

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