Diving Deeper on the Pixel 2 XL Display1 Recommended Answer
Three weeks ago we announced Pixel 2 and Pixel 2 XL, our new 5” and 6” smartphones with beautiful, high-resolution OLED displays; all-day battery that charges super fast; easy access to an even more capable Google Assistant; and, the world’s highest rated smartphone camera, along with free, unlimited storage of all of your photos and videos. We’ve been excited by the positive response from many of you and reviewers who have praised the new Pixel 2 phones.
Over the past few days, we've been investigating reports of suspected problems with the Pixel 2 XL display related to differential aging (also referred to as “burn-in”) as well as evaluating overall display vibrancy based on some user feedback. We take every report seriously because we want to ensure that the experience on our phones has not been compromised. Our investigation so far has given us confidence that our displays are as great as we hoped they would be, though we’re also taking steps to address the concerns we've heard.
In this post, we provide detail regarding the engineering of the Pixel 2 XL’s pOLED display, in tight coupling with Android 8.0 Oreo, for natural and accurate colors; we describe image retention artifacts in OLED technology; and we share our UI design efforts for optimizing user experience and performance of the display.
Android 8.0 Color Management
We’ve received some feedback about the Pixel 2 XL displays not appearing as saturated as other phones. We attribute this perception to our choice to calibrate the Pixel 2 XL for delivering natural, accurate colors, taking advantage of the new color management support in Android 8.0 Oreo.
Displays on mobile phones are often calibrated to the sRGB color profile, indicated by the black triangle in the diagram below. With the advent of OLED screens, things changed. An OLED display typically has a much wider gamut than sRGB. For example, the Pixel 2 XL has a Display P3 gamut (depicted by the larger yellow triangle).
Chromaticity diagram: You can think of x as the amount of red, and y as the amount of green. Blue is implied by the lack of red and green. The diagram represents colors independent of luminance (loosely, the amount of light). The colors in the chromaticity diagram have a tongue-like shape. The edge of the tongue represent pure wavelength light. The colors on the inside are made up of mixing the pure colors in different proportions. Colors outside of the tongue cannot be perceived by humans. Original source: Wikimedia
Before Android 8.0 Oreo, the Android OS was not aware of the color space of the content (e.g. image files) nor of the display. For JPEG or PNGs encoded in sRGB and with an LCD display typically calibrated to sRGB, color management wasn’t a pressing problem. For the most part, the “right” thing happened.
Now, Display P3 can render more colors than sRGB because it has a wider gamut. Without color management, the Android OS passes the decoded sRGB image through to the display, unaware that the display has a wider gamut than the content. As a result, the display reinterprets the color values in this wider gamut and effectively “stretches” the colors. This makes the reds more red, the greens more green, etc. To the user, the screen looks more saturated and colors “pop” more. But the stretching is imprecise; it’s not what the image designer intended. There’s no way for the designer to calculate the stretching effect, hence the rendered colors are not accurate. Most Android mobile phones with OLED displays look saturated for this reason.
With Android 8.0 on Pixel 2 XL, the phone now understands color spaces. It reads the color profile from JPEG, PNG, and WebP files so it’s aware of the color space used to author the content. And the OS is aware of the color space of the display. The Android graphics system uses more bit precision to represent a wider range of colors. As a result, the OS can make sure images are rendered with accurate colors, exactly as the author intended. We think it’s important that User Interface (UI) designers are in control of the rendered colors for their experience. In addition, Android 8.0 enables applications to opt-in to wide color support—an Android app developer can now make use of the wider Display P3 color gamut precisely for a wider range of colors. Google apps will take advantage of wide colors in the future.
Pixel 2 XL Display Tuning
The Pixel 2 XL has a wide Display P3 color gamut. The display is calibrated to a D67 white point. D67 refers to a color temperature of 6700 K. A D65 value (6500 K) corresponds to the color of the average midday light in Northern Europe, so the Pixel display errs ever so slightly on the blue side (users generally perceive the screen more “fresh” this way, probably because in the real world a yellow hue often indicates something has aged).
Out of the box, the Pixel 2 XL display defaults to sRGB + 10%. This is the sRGB gamut, expanded by 10% in all directions to make it slightly more vibrant. Humans perceive colors as less vibrant on smaller screens, such as on a smartphone, so we chose this for aesthetic reasons.
Color mode is really a user choice. Many users prefer accurate colors; others prefer more saturated colors. What we’ve found is that you can become acclimatized to either.
Based on the feedback we’ve received since announcing Pixel 2 and Pixel 2 XL, we learned that some users do want even more vibrant colors. So, through a software update to Pixel 2 and Pixel 2 XL, we will soon be adding a new “saturated” color mode. The saturated mode puts the display into an unmanaged configuration, similar to how the Pixel 1 operates. The colors will be more saturated and vibrant, but less accurate (similar to most other smartphones which display more vibrant colors): we give consumers the option to choose the color saturation.
OLED Differential Aging & UI Management
All OLED screens exhibit a degree of image retention (short-term) or burn-in (permanent) over their lifetime, starting the moment they are first powered on. This is also sometimes referred to as “differential aging” in the display industry. It appears as a faint outline of content on the screen from a previously displayed graphic.
We’ve received reports of Pixel 2 XL devices exhibiting image retention on the screen and have been actively investigating them. Extensive testing of the Pixel 2 XL display show that its decay characteristics are comparable to OLED panels used in other premium smartphones. The differential aging should not affect the user experience of the phone, as it’s not visible under normal use of your Pixel 2 XL. We understand, however, that it can be concerning to see evidence of aging when using a specialized display test app, so we've taken steps to reduce differential aging through software.
We designed the UI of the Pixel 2 and Pixel 2 XL to mitigate this phenomenon from being seen by the user over the lifetime of the phone. We are continuously updating our software to safeguard the user experience and to extend the life of the OLED display. This means finding ways to ensure consistent, predictably placed, high-contrast, efficient layouts without aging the display unnecessarily. For example, the always-on-display lock-screen moves the clock in a subtle zig-zag pattern on every minute boundary. It’s almost imperceptible yet it ensures that the same pixels do not stay lit persistently.
We’re currently testing a software update that further enhances protections against this issue by adding a new fade-out of the navigation bar buttons at the bottom of the Pixel screen after a short period of inactivity. In addition, we're working with more apps to use a light navigation bar to match their app's color scheme. The update will also reduce the maximum brightness of the Pixel 2 XL by a virtually imperceptible 50 cd/m2 (nits), thereby significantly reducing load on the screen with an almost undetectable change in the observed brightness.
The new saturated color mode mentioned above, the fade-out of icons on the navigation bar, more use of a white as a navigation bar color, and the max brightness curve change will be available as an update to Pixel 2 XL in the next few weeks.
We’re excited about seeing Pixel 2 and Pixel 2 XL in the hands of more and more users to experience the beautiful displays; the ever-smarter Google Assistant; the highest rated smartphone camera; peace-of-mind about storage, battery, security; the new two-year warranty; and much more. The new Pixel is the radically helpful smartphone that combines the best of Google AI, software and hardware. We hope you’ll love it as much as we do.
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