The Curious Case of iPhone 6+ 1080p Display

Internally, application sees 1242px by 2208px as its native resolution. It’s downsampled into a 1080p display as its physical representation. Question: 1. Why did Apple choose 1080p panel instead of 1242px by 2208px panel? 2. If Apple had to go with 1080p panel, why didn’t Apple simply set 1080px by 1920px as its native resolution instead of going through the hassle of downsampling?

Update: As of now, with the release of iPhone 7+, Apple is still using the same 1080p panel without any indication that this is going to change. I guess it will take a lot of courage to go to its supplier and demand a non-compromised display panel for its latest greatest audio jack-less iPhone.

For its iPhone 6+ screen panel, Apple had to make a compromise this time and to be honest Apple pulled a smart move.

Apple has decided to run its biggest iPhone ever at a native resolution of 1242px by 2208px. It’s enough screen estate to show a lot more content than iPhone 5S and iPhone 6. Unfortunately, it is only virtually written on the software side. On the hardware, Apple has to use lower resolution 1080p panel as its physical display representation. Through the downsampling magic, 1242px by 2208px content on iPhone 6+ will be rendered into 1920px by 1080px display at the same 5.5" physical size.

Here goes the story. We are going to explore the philosophy behind Apple’s decision. Instead of merely giving out the fact that downsampling is happening on latest iPhone 6+, we will try to understand what are those restrictions behind it. It’s interesting to see how Apple was so adamant about pixel-perfect scaling for all its devices in the past but decided to take a compromise at last for its latest iPhone 6+. Of course in the perfect world scenario, Apple would have chosen 1242px by 2208px panel and this article wouldn’t even exist.

When I have more time, I will write less. I promise.

Update: The fascinating story and explanation of pixel density and User Interface are getting way too long. I set it aside as its own story here: The Story of Pixel Density and Touch Interface. And, I’ve reduced this article from 14-min reading into less than 6-min reading. My target was 3-min reading.

iPhone 6+ resolution

On 9th September 2014, armed with a motto “bigger than bigger”, Apple released not only iPhone 6 but also a bigger iPhone 6+. As usual, Apple issued all their specifications and prices during the announcement of the products. I was researching on the resolutions for Apple’s new devices. It was odd to me to see that iPhone 6+ has 401ppi. It was based on issued specifications on Apple’s website. I wasn’t aware yet that this wasn’t the real device resolution. So I thought it was wrongly stated. I did a quick math calculation. Take the resolution of 1080px by 1920px, divide the diagonal pixel by its physical diagonal. I arrived at 400.52ppi. Yes 401ppi, it couldn’t be a mistake.

I imagined a few scenarios based on the hard fact:

1. Apple could choose scaling factor of 2x, the effective resolution will be 540pt by 960pt, a reasonable dimension for a phablet sized phone. But unfortunately its density will then be 200dpi. UI elements will be shrunk down beyond usable. Not really a good choice.

2. Try 3x scaling now. The effective resolution is now 360pt by 640pt. This resolution is smaller than the iPhone 6 effective resolution of 375pt by 667pt. It’s clearly unacceptable when Apple was saying during the keynote that iPhone 6+ will be able to display more contents as compared to iPhone 6.

3. Both 2x and 3x scalings don’t come without significant compromise. Some suggested that Apple will use 2.5x scaling which is completely foreign to me.

While poking around the scenarios above, I did a little further digging across the web. It turns out that Apple is going to use a theoretical virtual resolution of 1242px by 2208px (at 3x scaling, it is effectively 414pt by 736pt). And there will be downsampling on hardware level to fit all those pixel into its existing 1080p panel.

It’s a 5.5" panel

And it’s not 5.2" panel. Normally, at 1080p the diagonal display of similar device will be around 4.9" — 5.2". Take Google Nexus 5 for example. It has 5.0" screen with 1080p display resolution. Apple chose to use 1080p display and make a larger 5.5" 1080p display. Hence the drop from 462ppi to 401ppi in terms of pixel density. Despite the compromise on 1080p resolution, Apple maintained the same physical size as it was originally intended. In near future when Apple has finally switched to 1242px by 2208px resolution, user will not notice any difference.

What’s lost in translation was not physical size, but fidelity of the image rendered

Let’s talk about fidelity lost

We now understand that downsampling magic is currently working its ass off to fit those overcrowded pixels into a smaller living screen area. There are pixels being sub-rendered. Downsampling introduce antialiased artifacts. Those artifacts are what we commonly described as blurry edges, non pixel-perfect rendering. Obviously downsampling introduces different rendered result from its original image, we call it fidelity lost.

Now imagine that I am trying to draw 1pt black line to a non retina screen at coordinate x=0, y=0.25. This line will occupy 2 pixel grid with each grid filled with fraction amount of the color intensity. Meanwhile, if I draw this on 2x retina display, it will probably occupy 1/2 full pixels and 2 half pixels. Taking it further away upscale at 3x retina HD display, it will probably occupy 2/3 full pixels and 2 half pixels. But in the case of xx-hidpi screen 1px grid on the display is probably less than 0.0025" in physical size. I squint my eyes when I think of that. Will you be able to see that with your naked eyes?

For illustration purpose, in actuality there is no significant border gap in between pixels

With downsampling at such a high density display, fidelity lost is not so much an issue when your eyes can barely notice any artifact.

Update: I’ve got my hands on an iPhone 6+ unit, and I can’t see any pixel artifact. Great news for those who are concerned with pixel perfection.

Get it right from the start?

Why didn’t Apple just get it right instead of a compromise. A few valid reasons were exchanged among my circle of friends.

1. Apple is probably trying to cut cost. It uses commonly available 1080p panel that we have seen on many competitors’ devices. Apple has to keep a certain profit margin and it is not like iPhone 6+ price differs a lot from iPhone 6. It’s only $100 more expensive. Bigger screen, bigger battery, better camera. And potentially iPhone 6+ cutting into iPad sales. Where do we cover the lost to begin with?

2. Supply of panels. If Apple has to come out with its own customized display, will iPhone 6+ be delayed?

3. Battery life and processing power come into equation. With higher resolution comes higher demand in both of these aspects.

Well, this is not like it’s going to be resolution-gate case but I can say Apple pulled a smart move. A move that:
1. In the future, let’s imagine the next hypothetical iPhone 7+. Apple can return to original 1242px by 2208px without much changes and clashes with app developers.
2. It fits nicely to satisfy the DPI requirement and effective device resolution. Physically 1080p, but way more than 1080p.
3. Cost wise helps the profit margin. Surely 1080p panel is cheaper to produce.
4. Tapping on available supply helps Apple quickly produce iPhone 6+ to meet the demands if indeed it was about production shortage.

And yes it hurts to see that Apple is willing to compromise.

TLDR; In the landscape of touch devices, PPI is getting higher and higher. An exercise of choosing the right scaling factor has to be carried out to get the touch devices fit into acceptable range of DPIs. At the heart of the implementation, Apple chose precise 3x scaling for its iPhone 6+ at 1242px by 2208px effective resolution. But it is downsampled to fit its physical 1080p panel. Native resolution of 1242px by 2208px has been officially sealed, at least inside the OS. It is just waiting for the hardware to catch up.

TLDR of TLDR; On hardware, Apple screwed up. Not only we won’t get rumoured Sapphire glass screen, it is lower resolution screen than intended. On software, kudos to Apple for keeping its original native resolution.

p.s. Don’t use 1920 x 1080 for iPhone 6+ design, instead use 2208 x 1242

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