What makes the iPhone 6's display striking is that Apple has improved the application for bonding the glass to the display from the last generation iPhone 5s. The latest report examines the iPhone 5s and the iPhone 6 displays under a microscope and finds that the iPhone 6 looks more pleasing because the display is closer to the glass. In turn, this results in a screen that's more vibrant with deeper blacks and better contrast.
According to retinal neuroscientist Bryan Jones:
So, why does this display look so good? It turns out that what is different, like the iPhone 5 vs. the iPhone 4 is the proximity of the pixels to the glass in the iPhone 6 compared with the iPhone 5. With the iPhone 6, the pixels appear to be almost one with the glass. When the iPhone 5 came out, Apple bonded the display to the glass in an effort to get the pixels closer to the surface and Apple has appeared to make the pixels in the 6 even closer still.
Because of this change, the iPhone 6's display produces a better visual experience. Of note is that contrast is higher, colors are more vibrant, and blacks are deeper:
Some of what we are seeing with the iPhone 6 may be a polarizing filter underneath the glass, but even so, the glass appears thinner and required less focus distance adjustment to get from the surface of the glass to the pixel on another microscope. I don't know what that precise distance is in microns between the surface of the glass and the pixels, but it was a shorter distance as judged by rotation of the focus knob in the iPhone 6 vs. the iPhone 5. What this accomplishes is making the display appear to be higher resolution. The blacks are blacker, contrast is higher and colors are more vibrant, even with the same OS.
Jones noted that Apple had changed the subpixel geometry in the iPhone 6 display as well, something that we had previously recognized in our review on iMore. Here is what we wrote:
With the iPhone 6, Apple is using dual-domain (DD-IPS) panels. DD-IPS skews the pixels, essentially slanting one column down and next on up. This helps compensate for uneven lighting and color distortion, providing for even wider viewing angles and a better contrast ratio, typically 1400:1. That's compared to 800:1 on the iPhone 5s.
Source: Bryan Jones