iPhone resolutions (image 002)

With the iPhone 6 Plus, Apple took the unusual route of rendering apps at 3× scale into a backing store of 1,242-by-2,208 “logical” pixels which the GPU then scales down to the device’s native full HD screen resolution of 1,920-by-1,080 pixels.

This is different from every other iOS device to date and required to simplify app development as developers must simply create two times crisper graphics assets for standard Retina screens and three times denser images to account for the new “Retina HD” screens of the iPhone 6 and iPhone 6 Plus.

On the downside, the system down samples everything by approximately 13 percent to the native resolution so some unwanted artifacts do appear which degrade image quality slightly in certain situations.

Berlin-based iPhone and Mac developer Ole Begemann did an awesome job explaining the unwanted artifacts by taking highly detailed photographs of the iPhone 6 Plus screen using a closeup camera rig consisting of an Olympus E-M1 and a Panasonic GH3 using an Olympus M 60 mm f/2.8 lens.

The first test involves rendering a grid of vertical green hairlines with varying spacing on a black background using CoreGraphics, at the logical resolution of 1,242-by-2,208 pixels.

The lines are perfectly crisp when rendered into a backing store of 1,242-by-2,208 logical pixels. But after the iPhone 6 Plus does its downsampling magic for display on the 1,080-by-1,920 pixel screen, the crisp lines lose the black 1-pixel-wide gaps between each green line and a very subtle Moiré pattern is introduced.

iPhone 6 Plus (downsampling artifacts, Ole Begemann 001)

The good news is, apps (mostly games) which tap OpenGL or Apple’s Metal for rendering can opt out of the downsampling routine and draw directly into an image buffer which matches the native device resolution, so no blurring or artifacts occur.

“Rendering the test pattern using OpenGL at the native hardware resolution yields a perfect result,” said Begemann. “The lines are very bright and there’s no bleeding into neighboring pixels.”

However, as UI elements are introduced into the OpenGL view, some blurring occurs. You can observe the effect on your iPhone 6 Plus yourself: simply launch a game and then change the volume or pull down Notification Center.

The same thing happens when watching a video on the device. Here’s a video by Hendrik Kueck which demonstrates the effect using a test pattern image on an iPhone 6 Plus.

Because your iPhone 6 Plus uses hardware-accelerated decoding of iOS-friendly video formats, videos played using the stock Video app are rendered directly at the native screen resolution, skipping the scaling stage.

But the moment you bring up playback controls, the system must blend the blurred toolbars with the video. It does so by — you guessed right — upsampling the video view to the logical 3× scale in order to compute the blur before downsampling everything to the hardware resolution.

As a result, temporary degradation in image quality occurs when the video controls are overlaid over the video. “Pixel-perfect rendering is a thing of the past on the iPhone platform,” Begemann concludes.

The automatic downsampling mostly is not an issue in practice, he says, and developers should ignore the image degradation rather than waster resources accounting for unwanted image artifacts.

“Just do what Apple recommends and treat the iPhone 6 Plus as a 414×736@3× device and you’re gonna be fine in all but the most extreme corner cases,” he summed up.

With the iPhone 6 and iPhone 6 Plus, Apple has inevitably increased fragmentation of the platform in terms device resolution. In turn, developers now must account for non-Retina and Retina screens by providing normal, 2x and 3x assets in their apps, which makes downloads bigger and puts a strain on device storage when installing apps.

iPhone resolutions

Developers behind the PaintCode app have put together this webpage which does an excellent job explaining all the various screen sizes and pixel configurations on Apple’s mobile devices. The image above is part of the larger infographic so check out the webpage to inform yourself on the topic.

Bottom line: the vast majority of iPhone 6 Plus users won’t notice any blurring with naked eye, but those that look closer will notice some artifacts in certain situations, induced by the downscaling.

If Begemann’s findings have piqued your interest, he’s published the code on GitHub that you can download and build the same two demo apps he used to run them on your iPhone 6 Plus and observe image degradation yourself.

By the way, screenshots taken on the iPhone 6 Plus are always saved in the logical 3× size at 1,242-by-2,208 pixels.

[Ole Begemann via The Loop]

  • mav3rick

    Subpar and cheaper it goes: iOS buggy and sluggish UI, critical bugs, TLC memory, downsampling, etc

    • Umut Bilgiç

      This must be the most ignorant comment of the year. Buggy and sluggish ui? My iphone works perfectly fine with ios 8 and even with a jb. Critical bugs wtf are you talking about. Why dont you name a few of these critical bugs if you have this amazing wisdom. Downsampling is not an issue, it is a concept used in many areas of graphics for decades. You probably had no idea about what downsampling is before reading to this article if you can say such a thing. Downsampling is used at powerful grqphics cards, so that it can render out scene in a higher resolution (greater detail), and downsample it to regular hd to get better anti aliasing results, crisper detail. You can also record at 4k and than downsample it to 1080p which will result in a much better quality if you had recorded it with native 1080p. As in iphone, it is a convenience factor so that it makes devs lifes easier. Devs can use opengl to push the exact res they want to frame buffer. So ehatever i dont what you are talking about when you say critical bugs, sluggish experience, tlc memory or stating downsampling concept as a downer. Also i think you dont know much about what you are talking about either.

      • Guest

        TL;DR
        But I am sure it’s just another fanboy defending Apple.

      • Umut Bilgiç

        Not defeding apple by any means. What he said is basically not true.

      • Alberto Espinal

        That ignorant troll must be talking about Android

      • Umut Bilgiç

        Haha lol indeed

    • Alberto Espinal

      You are talking about Android, right?

  • powermixx

    Is it snapier?

  • Yunsar

    Are the @2x and @3x assets all present in all device versions of the app? For example, would the @3x assets still exist on an iPhone 5 app?

    • BoardDWorld

      yes, if the app has been designed with @3x assets. iCleaner Pro cleans all that out if you’re jailbroken though…