OnePlus 5T XDA Display Analysis (Review Part 2): A Coming of Age for OnePlus
When the OnePlus 3 was released in 2016, OnePlus received considerable backlash for shipping the phone with a wildly inaccurate “Optic AMOLED” display (with respect to the industry standard sRGB color gamut) and provided no option for a more accurate display calibration. Even though most consumers were satisfied with the phone’s default color profile, many photographers and designers wanted a display profile that was accurate to the sRGB color gamut, which is necessary for standardized color reproduction between displays. OnePlus was quick to address the issue, and released a software update which allowed users to enable an option that adjusted the display to target the sRGB color gamut. Although needing to toggle an option to apply the sRGB color profile defeats the purpose of color standardization, OnePlus did an impressive job calibrating the profile to the sRGB color gamut, as pointed out by Anandtech. We expect an even-superior calibration and display performance with the OnePlus 5T.
The 5T is OnePlus’ debut to the recent trend of smaller bezels and taller display aspect ratios with its 6.01-inch AMOLED display manufactured by Samsung. The screen holds a resolution of 2160×1080 PenTile Diamond Pixels (but losing a few due to its slightly-rounded corners), resulting in an 18:9 screen aspect ratio and a pixel density of approximately 401 pixels per inch.
The PenTile Diamond Pixel array provides intrinsic subpixel smoothing by its diamond pixel shape and lengthens panel longevity by including fewer blue subpixels, which deteriorate more quickly than red and green subpixels. Consequently, displays with the PenTile subpixel layout have one-third fewer total subpixels than displays with the conventional striped RGB pixel pattern found on most LCDs. However, the PenTile subpixel arrangement exploits the human eyes’ greater color sensitivity for green, which appears more luminous than red and blue, and greater sensitivity for luminance than for color, by maintaining a one-to-one green subpixel-to-pixel ratio. This results in the PenTile display having approximately the same luma resolution as the more commonly used striped RGB displays, but potentially introducing color fringe as a tradeoff.
While the 5T’s display has a lower pixel resolution than most other OLED PenTile displays in its generation, the screen appears mostly sharp at typical viewing distances (about one foot or 0.3 meters), but it could still definitely benefit from having a higher pixel density. We calculated that, for 20/20 vision, the achromatic image of the display is unresolvable past 8.6 inches, which is usually sharp enough for most people. However, color fringing may still be visible upon keen inspection (depending on the viewer’s visual acuity) due to fewer red and blue subpixels and their placement in the PenTile Diamond Pixel arrangement. For full color images, the pixels are completely unresolvable past 12.1 inches for 20/20 vision, which is within range of the typical viewing distance for most smartphone users. Note that 20/20 vision is considered just normal, and many users are likely to have even finer visual acuity.
Color Difference Metric
We will primarily be using the color difference measurement CIEDE2000 (shortened to ΔE), compensated for luminance error, as a metric for chromatic accuracy. CIEDE2000 is the industry standard color difference metric proposed by the International Commission on Illumination (CIE) that best describes perceptually uniform differences between color. Other color difference metrics exist as well, such as the color difference Δu′v′ on the CIE 1976 u′v′ chromaticity diagram—which we indeed will be using for our color accuracy plots—but these metrics are inferior in perceptual uniformity when assessing for visual noticeability, as the threshold for visual noticeability between measured colors and target colors can vary wildly. For example, a color difference Δu′v′ of 0.010 is not visually noticeable for blue, but the same measured color difference for yellow is noticeable at a glance.
CIEDE2000 normally considers luminance error in its computation, since luminance is a necessary component to completely describe color. Including luminance error in the ΔE is helpful for calibrating a display to a specific white level, but its aggregate value should not be used for assessing display performance; for that, chromaticity and luminance must be measured independently. This is because the human visual system interprets chromaticity and luminance separately.
In general, when the measured color difference ΔE is above 3.0, the color difference can be visually noticed at a glance. When the measured color difference ΔE is between 1.0 and 2.3, the difference in color can only be noticeable in diagnostic conditions (e.g. when the measured color and target color appear right next to the other on the display being measured), otherwise the color difference is not visually noticeable and appears accurate. A measured color difference ΔE of 1.0 or less is said to be imperceptible, and appears indistinguishable from the target color even when adjacent to it.
Our color space chart provides readers a brief way to observe a display’s target color gamuts. The colorful tongue-shaped figure below represents all the visible colors that the human eye can see. Note that the color gradient of the figure is not to scale, and is exaggerated due to our limitation of not being able to display the entire visible color spectrum with the current state of technology and its standards. The solid-colored triangles within the figure denote the region of colors that the display can output corresponding to its display profile. The black dashed triangles represent the different standard color gamuts for reference. The colored dots within the triangle represents the display profile’s white point, while the black dot represents the standard white point, labeled D65, for the sRGB and DCI-P3 color gamuts.
The OnePlus 5T comes with four display profiles: Default, DCI-P3, sRGB, and Adaptive mode.
The Default display profile of the OnePlus 5T is an intentionally oversaturated color profile that does not adhere to any of the standard color gamuts—not even to the outdated NTSC 1953 color gamut that others may have been led to believe. The Default calibration is the same color profile that OnePlus has used for their OnePlus 3, OnePlus 3T, and OnePlus 5, and it is based on the same color space that the Samsung Galaxy S7 targets in its Adaptive Display profile. The profile is very vibrant and cold, and it most closely matches a color space with NTSC red chromaticity, Adobe RGB green chromaticity, and Rec.2020 blue chromaticity.
The sRGB display profile is a great fit to the standard sRGB color gamut with an accurate D65 white point.
The DCI-P3 display profile is another intentionally oversaturated color profile that is a close fit to the DCI-P3 color gamut, but it falls short of red in the diagram. It correctly shares the same white point as the sRGB display profile.
The Adaptive mode display profile is also a great fit to the standard sRGB color gamut. Its green and blue chromaticities fit even closer to the sRGB color gamut than the respective values in the OnePlus 5T’s sRGB display profile, but slightly overshooting red. Furthermore, the white point for this display profile is noticeably colder, but not as cold as the white point of the Default profile. The calibration profile also provides a Sunlight Display that triggers in certain apps when the ambient light sensor notices harsh light. These apps include (but is not limited to) games, the stock OnePlus camera app, the stock OnePlus gallery app (does not work in Google Photos), and standalone images viewed in Chrome. This mode greatly reduces the contrast of the display for better visibility of shadows and midtones, and alters the white point to be slightly colder to offset sources of warm ambient light. We expected this mode to also increase the maximum brightness of the display, which it unfortunately does not even though the panel is capable of overdriving into high brightness mode (more on this later).
There also exists a Custom color display setting, which enables a slider that alters the color temperature/white point of the Default display profile, from Cold to Warm.
Note that at the time of this writing, our OnePlus 5T on Android Oreo does not support color management in any of its display modes, which is necessary for providing accurate color between color spaces. No matter how accurate the OnePlus 5T’s DCI-P3 display profile may be to the standard DCI-P3 color gamut, it will be inaccurate in use if it is not color managed since it will stretch out colors that are defined (or not defined) in sRGB out to DCI-P3. This also means that the OnePlus 5T’s sRGB display profile is not capable of displaying DCI-P3 or other wide color, even though color management was introduced in Android 8.0 Oreo.
When measuring the display performance of an OLED panel, it is important to understand how the technology differs from traditional LCD panels. Liquid-crystal displays, or LCDs, require a backlight to pass light through the liquid crystal layer to produce the colors that we see, while an OLED panel is capable of having each of its individual subpixels emit their own light. This means that the OLED panel must share a certain amount of power to every lit pixel from its maximum allotment. Thus, the more subpixels that need to be lit up, the more that the panel’s power needs to be divided, and the less power that each subpixel receives.
The APL (average pixel level or average picture level) of an image on a display is the average brightness percentage of each of the subpixels on the display, relative to the set display brightness. As an example, a completely red, green, or blue image has an APL of 33%, while the complete color mixtures cyan (green and blue), magenta (red and blue), or yellow (red and green) have an APL of 67%, and a full-white image has an APL of 100%. Finally, for OLED panels, the higher the display APL, the lower the brightness of each of the lit pixels. LCD panels do not exhibit this characteristic, and because of it, they tend to be much brighter at higher APLs than OLED panels.
At 100% APL, which is a full-screen white image, our OnePlus 5T at maximum brightness measures a white level of 448 cd/m². While a completely white screen may not seem like a practical scenario to be measuring for, many apps and websites tend to be designed with mostly-white components and a lot of white space that can bump the on-screen APL past the 80% range, so a 100% APL brightness reading is useful in speculating the worst case. At higher APLs, the OnePlus 5T should be legible in casual outdoor environments, but harsh direct sunlight may render the phone impractical for use, requiring the crafty use of the hand-shading maneuver.
At 50% APL, which is usually a reliable gauging of the pragmatic brightness level of an OLED panel, the OnePlus 5T gets about ~20% brighter at 537 cd/m². Empirically, displays just only start to become legible under the California summer sun at about 500 cd/m², and while the OnePlus 5T slightly surpasses that threshold at 50% APL, it would be helpful if the panel were able to draw just a bit more power to help brighten the image in sunny conditions.
Enter High Brightness Mode (HBM). High Brightness Mode is the internal name of the capability of most Samsung panels to draw additional power to the display to brighten the image, usually by a significant margin. Notice how the OnePlus 5T is listed twice in the reference display brightness charts above, additionally suffixed with “(HBM)”. The OnePlus 5T is not capable of toggling HBM on its own, but it can be enabled with root access by executing `echo 1 > /sys/devices/virtual/graphics/fb0/hbm` through ADB or a terminal, or by using a third-party app (still requiring root). With HBM, the OnePlus 5T becomes significantly brighter and pulls into Samsung’s territory, even surpassing our Note 8 unit in brightness at 100% APL. The OnePlus 5T is much more legible in the sunlight at these brightnesses, but unfortunately OnePlus did not natively incorporate the mode into their software.
The minimum brightness of the OnePlus 5T stoops to 2 cd/m², which is standard and about the same for most smartphones.
Gamma and Luminance
The gamma of a display determines the overall contrast of the colors on the screen. A higher display gamma will result in higher image contrast and darker color mixtures (in terms of color lightness, not necessarily in perceived brightness), assuming a non-sigmoidal (“S”-shaped) gamma transfer function. Note that gamma power does not affect colors with intensities of 0% (black) or 100% (pure red, pure green, pure blue, and 100% white), since 0 or 1 raised to any positive real number is itself. Gamma also affects the saturation of color mixtures, but factory calibration typically keeps the target gamma for colors consistent and a separate issue from the resulting luma (luminance of colors after gamma correction). This is how some panels can maintain accurate sRGB colors while having a non-standard measured display gamma. The standard gamma curve is described in the sRGB specification, which is approximately a power function of 2.2.
The OnePlus 5T’s gamma curve is similar between all display profiles, with the exception of the Sunlight Display triggered from the Adaptive mode display profile. The gamma curve appears mostly straight, but overall steeper than the sRGB reference gamma curve with an average overall gamma of 2.43, which means that the OnePlus 5T has a higher display contrast than what is standard. Colors below 10% intensity will have even more contrast and appear even darker, which is generally undesirable as it reduces the visibility of shadow detail.
If the OnePlus 5T display profile is set to Adaptive mode, the gamma of the display can change in certain apps when the ambient light sensor detects bright light. The overall contrast of the image is greatly reduced, significantly raising the shadows and midtones, and slightly lowering the highlights. This greatly reduces the fidelity of the image, but allows image details to be much more visible in sunlight.
Clipped or “crushed” blacks is a term for the incorrect rendering of darker shades on an image that makes all colors under a certain luminance appear black. This is usually a calibration issue, but it is also an inherent hardware limitation of current-generation OLED displays, as they have an absolute minimum non-black level that they can emit that is usually not dim enough to provide full 8-bit depth intensity at lower screen brightnesses. While the absolute darkest non-black shade that a display can theoretically show comes down to the quality of the OLED panel, in practice, faulty display calibration is what usually causes the bulk of black clipping, and it is still an issue most display calibrators will come across even with LCD panels.
Although the OnePlus 5T has a higher gamma than standard, it performs remarkably well in displaying darker colors. It performs better than the Note 8 in this regard, and significantly better than the Pixel 2 and Pixel 2 XL, as it correctly displays the darker colors of cinematic films. This is a sign of both an excellent quality display and an excellent screen calibration by OnePlus.
An accurate white point and grayscale are fundamental to producing accurate color. An error in grayscale will propagate the error throughout the entire color gamut (with the exception of the 100% primaries—red, blue, and green), so it is absolutely crucial to analyze a display’s grayscale to evaluate primary sources of error when measuring for total color accuracy.
In its Default display profile, the OnePlus 5T is exceptionally cold with a correlated color temperature of 7756K for white and an average correlated color temperature of 7742K for the entire grayscale. The white point temperature is similar to that of the OnePlus 3T, which is not a surprise since OnePlus intended them to share the same default display profile. The OnePlus 5T, however, does a much better job at keeping the color temperature consistent; its correlated color temperature curve is very smooth and keeps its average correlated color temperature close to that of the white point, unlike the 3T where the average (7342K) strays considerably from the white point (7738K). A colder, bluer white point is generally chosen for its vivid and artificial appearance, as it appears more sensational to the human eye. This was a cosmetic choice by OnePlus, and it diverges far from the D65 standard.
On the other hand, the grayscale on the sRGB and DCI-P3 display profiles is absolutely superb, with a correlated color temperature of 6467K for white and an average correlated color temperature of 6543K for the entire grayscale. It sets a record grayscale accuracy with an imperceptible white point color difference ΔE = 0.8 and an imperceptible average grayscale color difference ΔE = 0.4 for the entire grayscale. This is a significant improvement over the already-accurate grayscale on the OnePlus 3T, and OnePlus deserves praise on their grayscale calibration on the 5T.
The Adaptive mode display profile is very similar to the sRGB display profile, but the Adaptive profile is noticeably colder. It is about half as cold as the Default display profile relative to the sRGB display profile (average: 7162K) with a correlated color temperature of 7126K for white and an average correlated color temperature of 7274K for the entire grayscale. This is a great alternative for the sRGB display profile for those who want a colder profile. When Sunlight Display is triggered, the on-screen image becomes even colder, jumping up to 7595K and 7564K for the white point and grayscale correlated color temperatures, respectively.
Our color accuracy plots provides readers a rough assessment of the color performance of a display. Shown below is the base for the color accuracy targets, with the solid dots representing the target colors (borrowed from DisplayMate) and the dashed line representing the reference color gamut. The target colors on the perimeter of the color gamut include the primary and secondary colors along with colors in-between, which are spaced roughly even throughout the color gamut relative to the diagram. The inner dots represent the 75%, 50%, and 25% saturation levels for the respective color on the perimeter along with the white point. The target colors have a radius of 0.004, which—as an error—is considered a just-noticeable-difference. Measured colors (represented as solid-white dots) that touch its target color on the diagram appear accurate. If the measured color does not touch its target color, it can still appear accurate depending on its color difference ΔE—in that case, refer to the color difference charts below.
The Default display profile is intensely vivid, noticeably oversaturating almost all of its colors. If color accuracy is of any priority, then this display profile should be avoided. The colors in this display profile are quite arbitrary and its purpose is purely ornamental.
The sRGB display profile carries on its performance from its grayscale accuracy, and it is dead-on accurate. Like its grayscale, it sets a record sRGB color accuracy with an imperceptible average color difference ΔE = 0.7 with a very impressive, visually unnoticeable maximum color difference ΔE = 1.7 at 100% cyan. It is uncommon for displays that are not individually factory-calibrated to have a visually unnoticeable maximum color difference, and whether or not OnePlus individually calibrates their displays is unknown to us, but nevertheless, this feat by OnePlus is very impressive. OnePlus receives our commendation for their perceptually-perfect factory calibration.
The DCI-P3 display profile is very accurate to the DCI-P3 color gamut, but it is not color-managed. All colors in this mode will be stretched out from the image’s intended gamut to DCI-P3, which will lead to erroneous color reproduction for all images not meant to be displayed in the DCI-P3 color space. Nevertheless, when properly viewing DCI-P3 content, colors will appear mostly perfect with an imperceptible average color difference ΔE = 0.9 and a possibly noticeable maximum color difference ΔE = 2.9 at 100% cyan-blue.
The Adaptive display profile is essentially the sRGB profile shifted towards blue with slightly increased saturation for reds to compensate for the ambient light from the sun. Even with these deviations the profile appears mostly accurate with a visually unnoticeable average color difference ΔE = 1.8, with approximately 22% of its colors being at least possibly noticeable, and a maximum color difference ΔE = 4.9 at 50% yellow-red. In the Adaptive profile’s Sunlight Display, the colors shift even more towards blue, bumping its average color difference ΔE to 2.7, at which most colors will be possibly noticeable—under zero lighting, that is.
It is important to note that the perceived saturation and hue of the colors on a display can change under ambient light due to screen reflectance, depending on the brightness and color temperature of the illuminant. An illuminant will typically shift the perceived colors on a display towards the color of the illuminant, and the brightness of the illuminant affects the intensity of that shift. Thus, it makes sense for the OnePlus 5T’s sunlight mode to shift its colors towards blue under sunlight, a bright warm illuminant. However, OnePlus did not compensate for the loss of saturation (not to mention the varying color temperature of the sun) from the screen reflectance of a bright illuminant, so the perceived saturation of the display is still effectively diminished under sunlight. This entire notion is also the basis for Apple’s True Tone display on their newer iDevices, which takes into account the true color temperature and brightness of the illuminant, and adjusts the colors on the display accordingly.
Final Thoughts on the OnePlus 5T Display
It would be an understatement to say that OnePlus simply improved their display—their underlying calibration is absolutely stellar with improved display performance over its predecessors nearly all throughout. The display is adequately bright—with room for improvement, possibly by implementing High Brightness Mode—and ships with a vibrant display profile that aims to impress with its punchy colors and high image contrast. The grayscale of the screen is very consistent from black to white, and the brightness control contains a thousand steps, while Android only has 256 steps by default. The display provides for an appropriate cinematic experience with its higher display gamma and almost zero black clipping—score deducted for withholding the proper Widevine certification for HD films on Netflix. While the screen resolution may appear satisfactory to many, the OnePlus 5T’s pixel density does sit on the lower bound, having just-unresolvable pixels for 20/20 vision at about 12 inches, which is within typical viewing distances. It would still be favorable and more appreciated if OnePlus included a higher-resolution panel this time around.
Furthermore, the sRGB color reproduction on our OnePlus 5T is perceptually perfect with the sRGB display profile, and content optimized for DCI-P3—the standard color gamut for cinema—will appear very accurate with the DCI-P3 display profile. The sRGB and DCI-P3 profiles are among some of the most accurate we’ve seen. It is disappointing, however, to notice that the device does not include color management, which reduces the significance of its accurate DCI-P3 color reproduction.
Empirically, the panel exhibits very little color shift at small-to-moderate angles, but still falls victim to “rainbowing out” when the phone is being viewed at extreme angles, which is an issue that most Samsung-sourced OLED panels have that recent Samsung devices do not have with their own panels. “Black smear” at low brightnesses is also minimal on the OnePlus 5T. Both color shift and “black smear” are display characteristics that we wish to be able to quantize and measure with control and consistency in the future.
One last thing to note is OnePlus’ branding of their “Optic AMOLED” display, which was initially coined by OnePlus with their announcement of the OnePlus 3. According to their CEO, OnePlus “[took] Super AMOLED[,] and added [their] take on contrast and color temperature, to try and bring it more true to life.” OnePlus also “designed its performance profile to work well when outdoors in bright conditions”, which we can make sense of by the increased saturation, image contrast, and color temperature of the Default display calibration. OnePlus still uses the same branding for their display on the OnePlus 5T, but its purpose as a marketing ploy for their devices has mostly depreciated since then.
We would like OnePlus to continue in their pursuit of display performance. The display has many great aspects to consider, but we believe OnePlus still needs a few more advances to consolidate their progress. They have the correct ideas, but they run into some fundamental errors, such as not including color management in an Android version that expects it, not including native high brightness mode, and not including proper Widevine certification for a screen that can offer an otherwise-remarkable media experience (what a shame). It would also be impressive to see OnePlus expand on Adaptive mode, perhaps by implementing an automatic color temperature-changing solution like Apple’s True Tone display, which requires additional sensors on the device. All of this, however, is just additional polish on an already-impressive display; they are a list of “issues” which we hope shortens in our next OnePlus display write-up, but we won’t be completely disappointed if it doesn’t.
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