ADVANCED IMAGE STICKING MEASUREMENTS

Application Note – Advanced sticking image measurements

This page shows a summary of the application note. Topic of the document is the measurement of sticking image on displays and the most important aspects that have to be considered during a measurement. These concepts are general and thus independent on any specific evaluation method.

Luminance images of the evaluation period that show the vanishing image sticking phenomenon

Measurement of image sticking and its measurement aspects

Image sticking measurements, or rather a measurement series, consist of three steps:

1. Warm-up period to recover the display from possible initial image sticking and to ensure a steady-state condition
2. Burn-in period pattern is displayed to induce a worst-case scenario for image sticking (different patterns and grey levels are used depending on the method)
3. Relaxation period to measure the time-resolved image sticking relaxation (different patterns and grey levels are used depending on the method)

Sticking image measurements can be very time-consuming and, depending on the display, may not be repeated, for example, with OLED displays. In this context, three main aspects of an image sticking measurement should be considered before and during the measurement. These are the temporal alignment, the grey levels used, and the type of display non-uniformity correction.

Top: General setup of an image sticking measurement using an Imaging Luminance Measurement Device (ILMD) as for instance the LMK6 Bottom: General schedule of an image sticking measurement series with exemplarily test patterns

Top: User-Interface to select the trigger position

Bottom: Working principle of the trigger during an image sticking measurement

Impact of timing

The measurement start of the first relaxation image needs to be well-aligned with the pattern switching from the burn-in to the relaxation image to correctly asses the initial level of image sticking. If the measurement starts too late, the image sticking will already begin to vanish. If the measurement starts too early, and parts of the burn-in pattern are evaluated by accident, then the value will be too high. All this gets more complex in the context of setup and display-depended input lags between sending the pattern switching signal and the actual pattern switching.

To overcome complex temporal alignment strategies, TechnoTeam developed an image content-based trigger for the LMK6. The camera will observe a freely adjustable part of the burn-in pattern with a very high frequency and optically detect the pattern switching. From this well-defined reference point, any delay can define the measurement start in a simple and highly reproducible way. The images on the right visualize the working principle of TechnoTeams image content-based trigger during an image sticking measurement.

Grey-level dependency and uniformity correction

In sticking image measurements, it is key to separate static display non-uniformity from non-uniformity caused by image sticking. There are two different ways to do this separation: The temporal and the local approach. Furthermore, static non-uniformity and the induced image sticking can strongly depend on the grey level, as shown in the measurement data on the right.

TechnoTeams software solutions offer total flexibility regarding the applied grey levels and the type of non-uniformity corrections with all their advantages and disadvantages — even in post-processing. That way, we can ensure that the sticking image measurement can be tailored to the specific project.

Example for the impact of the grey levels: For this liquid crystal test display, different burn-in and relaxation grey levels lead to significantly different image sticking results