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HFR Displays Not Necessarily Better Than Low Frame Rate Displays
May 10, 2020
90Hz and 120Hz panels are the latest trend in the smartphone world but not every 120Hz phone offers the same display quality, features, and certainly not the same battery life. Phones by Google and Samsung with high refresh displays hamper their implementation for the sake of battery life. While 90Hz and 120Hz displays make the motion from certain apps and elements of the user interface (UI) appear smoother, color accuracy, gamma correction, and white balance, which are independent of the refresh rate, have a much larger impact on the look of most content. Lower end displays are more likely to have noticeable issues and poor color calibration. Affordable phones boasting high refresh rate panels could be a distraction from other issues. Flagship tier phone displays can go above and beyond the factory color calibration, as OnePlus showcased with the 8 Pro, so it’s worth paying attention to traditional display quality metrics and not just the refresh rate.
Display quality varies from device to device and the availability of high refresh rate content can vary too. The frame rate of an app or game depends not just on the underlying hardware, but also the way that the application is coded to render and the way the OS works. Google has published insights into how high refresh rate displays work with content on Android. The frame rates are limited by rendering times, controlled by the Android Choreographer. 120Hz displays have just 8.3ms in-between frames in which the GPU has to draw the frame. Some apps and games render at the display’s v-sync refresh rate, so they can operate at the full frame rate. However, others simply take too long to render or have custom rendering pipelines with slower update speeds, so they simply can’t hit 120Hz. Instead, games may stick to 90, 60, 45, or even 30fps. Android 11 improves handling of mixed refresh rate content, providing apps make use of the new API. The situation is further complicated by using multiple apps and UI elements at once. Google notes that 120Hz displays are good for viewing 24, 30, 45, and 60fps content without judder, as these rates as easily divisible by 120. Playing back a 24fps video on a 120Hz display avoids the 3:2 pulldown algorithm required by a 60Hz display, for example. However, conflicts can occur between software, such as a low frame rate video and high frame rate UI. At which point Android has to step in and pick a frame rate, which can result in judder and/or a fallback to the standard 60Hz. There’s a new set FrameRate API in Android 11 that helps to find the optimal frame rate for multiple apps running at once. However, current devices have to make do with a preference setting that can lead to conflicts. Ultimately, applications and games can influence the refresh rate, but the final decision is made by the platform. Expect next year’s Android 11 phones to handle mixed refresh rate content better than current models.
Overall, hitting very high frame rates for every app is highly unlikely. Instead, Android dynamically switches frames rates to best match the app you’re currently using. But even this may depend on the manufacturer’s implementation.
Individual smartphone OEMs can also add in their own display processing layer to upscale or remove judder outside of the standard Android framework. Processing power is important here, as some effects can be energy-intensive. Dedicated display processors (DPU) can run these tasks more efficiently. Qualcomm’s Snapdragon processors include display and visual processors as part of its Adreno GPU pipeline. These handle video decoding as well as graphics rendering, and the application processor can also run additional display processing software. For example, Pixelworksleverages the Snapdragon 865 to run its Soft Iris calibration and features like tone-mapping and SDR to HDR on the OnePlus 8 series. Other SoCs have their own display processing units as well, but mid-range and lower-end chips don’t have the hardware to run higher-end features efficiently. For example, the Snapdragon 765G only supports 120Hz up to FHD+, while the 865 can manage 144Hz at QHD+ resolutions. To date Apple has not implemented refresh rates beyond 60 Hz.
May 10, 2020
90Hz and 120Hz panels are the latest trend in the smartphone world but not every 120Hz phone offers the same display quality, features, and certainly not the same battery life. Phones by Google and Samsung with high refresh displays hamper their implementation for the sake of battery life. While 90Hz and 120Hz displays make the motion from certain apps and elements of the user interface (UI) appear smoother, color accuracy, gamma correction, and white balance, which are independent of the refresh rate, have a much larger impact on the look of most content. Lower end displays are more likely to have noticeable issues and poor color calibration. Affordable phones boasting high refresh rate panels could be a distraction from other issues. Flagship tier phone displays can go above and beyond the factory color calibration, as OnePlus showcased with the 8 Pro, so it’s worth paying attention to traditional display quality metrics and not just the refresh rate.
Display quality varies from device to device and the availability of high refresh rate content can vary too. The frame rate of an app or game depends not just on the underlying hardware, but also the way that the application is coded to render and the way the OS works. Google has published insights into how high refresh rate displays work with content on Android. The frame rates are limited by rendering times, controlled by the Android Choreographer. 120Hz displays have just 8.3ms in-between frames in which the GPU has to draw the frame. Some apps and games render at the display’s v-sync refresh rate, so they can operate at the full frame rate. However, others simply take too long to render or have custom rendering pipelines with slower update speeds, so they simply can’t hit 120Hz. Instead, games may stick to 90, 60, 45, or even 30fps. Android 11 improves handling of mixed refresh rate content, providing apps make use of the new API. The situation is further complicated by using multiple apps and UI elements at once. Google notes that 120Hz displays are good for viewing 24, 30, 45, and 60fps content without judder, as these rates as easily divisible by 120. Playing back a 24fps video on a 120Hz display avoids the 3:2 pulldown algorithm required by a 60Hz display, for example. However, conflicts can occur between software, such as a low frame rate video and high frame rate UI. At which point Android has to step in and pick a frame rate, which can result in judder and/or a fallback to the standard 60Hz. There’s a new set FrameRate API in Android 11 that helps to find the optimal frame rate for multiple apps running at once. However, current devices have to make do with a preference setting that can lead to conflicts. Ultimately, applications and games can influence the refresh rate, but the final decision is made by the platform. Expect next year’s Android 11 phones to handle mixed refresh rate content better than current models.
Overall, hitting very high frame rates for every app is highly unlikely. Instead, Android dynamically switches frames rates to best match the app you’re currently using. But even this may depend on the manufacturer’s implementation.
Individual smartphone OEMs can also add in their own display processing layer to upscale or remove judder outside of the standard Android framework. Processing power is important here, as some effects can be energy-intensive. Dedicated display processors (DPU) can run these tasks more efficiently. Qualcomm’s Snapdragon processors include display and visual processors as part of its Adreno GPU pipeline. These handle video decoding as well as graphics rendering, and the application processor can also run additional display processing software. For example, Pixelworksleverages the Snapdragon 865 to run its Soft Iris calibration and features like tone-mapping and SDR to HDR on the OnePlus 8 series. Other SoCs have their own display processing units as well, but mid-range and lower-end chips don’t have the hardware to run higher-end features efficiently. For example, the Snapdragon 765G only supports 120Hz up to FHD+, while the 865 can manage 144Hz at QHD+ resolutions. To date Apple has not implemented refresh rates beyond 60 Hz.
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