The display will play a central role in the marketing, appearance and performance of the iPhone 5, which will be announced in a couple of days. The iPhone 4 display is no longer state of the art. While I don't have any inside information about the iPhone 5 display, below are a series of Sherlock Holmes deductions based on existing information and trends from the iPhone 4 and the latest competing smartphone displays.
The iPhone 5 will need to meet most of these goals in order to retain its top ranking. These same display goals apply to any smartphone that wants to be a first-tier smartphone.
Dr Raymond Soneira of DisplayMate Technologies has made it his mission to suss out the best smartphone, tablet, HDTV and multimedia displays from the worst with his Display Technology Shoot-Out series. Now, he cooks up a few predictions on what the iPhone 5 display might be like.
The aspect ratio (screen width divided by its height) for the iPhone 4 is 3:2. For the iPhone 5, the rumour mill has settled on 16:9, the same as HDTVs and most video content. This looks like an excellent bet, so we'll work with that... First-tier smartphone goal and iPhone 5 best guess: 16:9 aspect ratio.
The current iPhone 4 screen resolution is 960x640 pixels. In order to maintain compatibility with existing apps, the iPhone 5 can't stray too far from this. Since the aspect ratio is increasing from 3:2 to 16:9, the best guess is that the iPhone 5 will keep the same 640 pixels and just increase the 960 pixel value based on the new aspect ratio. In that case, the screen resolution will be 1136x640 pixels. That's 176 more vertical pixels, so existing apps expecting 960x640 will simply be letterboxed with 88-pixel black borders on the top and bottom. But since we are already letterboxing, why not raise the 640 pixel base up to 720 pixels and add 40-pixel black borders there as well? Even better... 720 pixels is true high definition — that is not only a major marketing advantage but there is much less processor overhead (and battery power) from rescaling content from 1080p to 720p than to 640p (rescaling by 3/2=1.50 rather than by 1.69). While the Samsung Galaxy S III and Galaxy Nexus have 1280x720 pixels, they are PenTile displays that are not as sharp as true RGB 1280x720 displays. First-tier smartphone goal and iPhone 5 best guess: 1136x640 pixels — but 1280x720 pixels (true HD) would be much better.
Pixels Per Inch (PPI)
The higher the pixel density the sharper the image on the screen. But what really matters is the sharpness perceived by your eyes, which depends on the viewing distance from the screen (and also how good your vision is compared to 20/20 vision). So pixel density must be used in conjunction with the viewing distance in order to draw any conclusions about visual sharpness and whether or not it qualifies as a retina display. Apple's retina display criterion is based on 20/20 vision. The iPhone 4 has 326ppi and appears perfectly sharp for 20/20 vision down to a viewing distance of 10.5 inches. The new iPad has a lower 264ppi, but it is still a retina display because it appears perfectly sharp for 20/20 vision down to a viewing distance of 13 inches, which is less than its typical viewing distance. To be a retina display down to a viewing distance of 12 inches the display needs to be 286ppi or more. First-tier smartphone goal and iPhone 5 best guess: 326ppi, but it can go down to 286ppi and still be a smartphone retina display.
The Screen Size will depend on the screen resolution and pixels per inch. If the iPhone 5 keeps the same 326ppi as the iPhone 4 and has 1136x640 resolution, then the screen size will be 3.96 inches, an 18.5 per cent increase in the area of the screen (the diagonal size increases by 13 per cent). But with Steve Jobs's 300ppi value, the screen would be 4.35 inches. Using 286ppi, the screen would be 4.56 inches and remain a retina display down to a viewing distance of 12 inches. Finally, with a resolution of 1280x720 and 326ppi the screen would be 4.5 inches. So there is lots of room for a smartphone retina display up to 4.5 inches. First-tier smartphone goal and iPhone 5 best guess: 4 inches, but could go as large as 4.5 inches and still be a retina display.
Most smartphones are used in reasonably bright ambient lighting. Reflections from the screen not only decreases picture quality, but it makes the screen harder to read and causes eye strain. We measured the iPhone 4 reflectance at 7 per cent, but many mobile displays now have reflectance values much lower than that. The current record holder is the Nokia Lumia 900, with a screen reflectance of 4.4 per cent — so the iPhone 4 reflects 59 per cent more light than the Lumia 900. The iPhone 5 needs to do a lot better... First-tier smartphone goal and iPhone 5 best guess: reflectance under 5 per cent.
Contrast Rating for High Ambient Light
The screen reflectance together with the screen brightness determine how easy it is to see the screen under high ambient lighting conditions. We have defined a DisplayMate contrast rating for high ambient light (CRHAL) that is an excellent visual indicator of how screens look under high ambient light. This article has screen shots of nine displays from zero lux up to 40,000 lux ambient lighting — watch how they each degrade as the ambient lighting increases. The iPhone 4 has a CRHAL of 77. The current record holder is the Nokia Lumia 900 with a CRHAL of 90. First-tier smartphone goal and iPhone 5 best guess: contrast rating for high ambient light over 90.
The colour gamut is the range of colours that a display can produce. If you want to see accurate colours in photos, videos and all standard consumer content, the display needs to match the standard colour gamut that was used to produce the content, which is called sRGB / Rec.709. Most mobile LCD displays produce around 60 per cent of the standard colour gamut in order to maximise screen brightness and battery running time. The iPhone 4 has a colour gamut of 64 per cent of the standard, which produces somewhat subdued colours. The new iPad 3 has a virtually perfect 99 per cent of the standard, so we expect the iPhone 5 to do the same. This figure shows the colour gamuts for the iPhone 4, iPad 2, new iPad 3 and sRGB / Rec.709 standard. A widely held and exploited misconception is that the bigger the colour gamut the better; a display with a larger than 100 per cent colour gamut cannot show colours that are not in the original content — it just exaggerates and distorts the colours. First-tier smartphone goal and iPhone 5 best guess: 100 per cent of the sRGB / Rec.709 colour gamut standard — not larger!