How to test the touch screen latency?
Previously, touch gestures' importance and which tests are needed to check whether they would work properly on a touch-enabled device were explained.
Now, let's talk about how the performance is determined from the end user's perspective.
User Interface Related Performance Tests
Performance tests are accomplished with robot-assisted platforms that mimic human interaction with touch-enabled systems. These platforms run on XY stages that use linear guides and encoders to position the DUT (device under test) accurately. The system is equipped with fingertips that accomplish the touch activity to perform the gestures and tests. The system is also equipped with cameras and other sensors to test the user interface's stability and reliability.
Some examples of performance tests
Determining the quality of performance from the end user's perspective requires closely monitoring the user interface (UI) content's visual and non-visual changes. Hence, high-speed cameras and machine vision algorithms are needed.
UI Latency Test
This test is used to measure the lag of a touch-enabled system. As part of this test, response times and latencies of user interfaces are measured. For example, it can define the starting, loading, and closing time of an application or an event by measuring the time from tapping the icon to when the application initiates, loads, and closes on the display. The system automatically detects visual, audio, and haptic events from the user interface during the test and report the events with accurate timestamps. By analyzing the speed, latency, and response time of a user interface, the test reports what happens after a user interacts with a touch-enabled system.
Scroll Performance Analysis (SPA) Test
This test detects a display content update rate from a stream of images captured with a high-speed camera. This test's typical use case is for example to scroll content on the DUT display. The update rate is measured to determine if there are unexpected glitches and pauses during scrolling.
Pen to Ink (P2I) Tests
This test measures the drawn ink line's latency on the DUT screen with respect to the robotic finger. The latency is measured with a high-speed camera by detecting fingertip and ink line tips from each image with an associated timestamp. During the measurement, a machine vision algorithm is used to calculate the latency between finger movement and the end of the drawn line.
In the below video from Google's Chrome OS team, similar tests are performed to measure Android and Chrome OS devices' end-to-end latencies.
Summary
Smooth user experience relies on accurate and repeatable touch gestures, which are only possible when the touch user interface (UI) is functional, responsive, and fast over the entire surface area. In this article, a few performance tests are mentioned to test delays and latency times. These tests are used to warrant the user interface's performance from the end user's perspective. The manufacturers of touch-enabled devices need to perform various tests on the system, device, and individual component level to fulfill the end user's expectations.
Next week, I will write about which functional tests are used to determine the performance of a user interface on touch-enabled devices.
With Regards,
All images are courtesy of OptoFidelity.