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Understanding Modulation Modes on the XM310K

The XM310K is a zoned backlight monitor featuring a full array local dimming (FALD) backlight with over 2000 LED zones. The advantages of FALD backlights are that they remain one of the most efficient, practical, and cost effective ways to achieve very high peak luminance as well as very good black levels. The behavior and visual quality of any zoned backlight system are regulated both by the number of zones and the performance of the display’s backlight/LCD driving algorithms.

Generally speaking, displays with a higher number of individually controllable zones will outperform displays with a lower number of individually controllable zones. A display like the XM310K with over 2000 zones can therefore be expected to outperform displays that may only have 500 zones. This comes down to simple physics as more zones means finer tuned control over regions of the display. However, it is also important to consider the behavior of the human visual system as there is a point of diminishing returns as backlight density increases. Bright objects do result in a degree of veiling glare in the human eye so our ability to discern local contrast (sometimes called point spread function), especially in HDR, is not necessarily the same as the resolution of the display. This is ultimately very content and adaption state dependent so it would be unwise to suggest that one particular zone count is the perfect solution for all scenarios. Displays with near perfect pixel level luminance control are of course the ideal target and there are in fact displays that essentially achieve this (OLED and LMCL for example), but typically at the cost of other performance benchmarks like peak luminance to name just one potential limitation.

The backlight algorithms that drive a FALD display will necessarily need to compromise between different aspects of display performance. To minimize the appearance of halation for example the backlight algorithms may dim highlights or globally lift black levels. Or conversely the algorithms may maximize peak luminance response of even small bright objects at the cost of significant halation or flare. Most consumer displays and many professional displays have only one algorithm behavior in place. This is not to say that the algorithm behavior doesn’t adjust based on content, but ultimately there is often no way to force specific behaviors that might be incredibly important in a professional mastering context. The XM310K is built for use in a professional mastering environment and as such has three manually selectable backlight modulation modes accessible to the operator.

Motion

The default dynamic backlight mode on the XM310K is the Motion optimized modulation mode. This mode balances peaks and contrast and as the name implies prioritizes motion handling to minimize potential artifacts. This mode puts specific emphasis on LED/LCD sync and halation reduction making it very well suited to viewing realtime playback of the majority of material. The Motion optimized modulation mode is the one we suggest for the bulk of day to day viewing on the XM310K and is also the mode that is typically used for client viewing and playback of mastered HDR content.

Peak

The Peak optimized modulation mode ensures the peak highlight code values are represented accurately on screen even if this results in significant halation or flare. To put this in context if you have a black background with just a few bright pixels present with code values representing 3000nits they will be shown at 3000nit nits in Peak mode with the side effect of a halo around those bright pixels. This can also lead to less desirable motion handling as a small bright object traveling from one zone to another causes rapid activation / deactivation of backlight zones. This coarse backlight behavior is more visible to users than the Motion optimized behavior. The value of the Peak optimized modulation mode comes in QC applications where operators want to ensure that highlight details contain the information they expect. The backlight algorithm behavior of many other FALD display devices may hide small bright object highlight detail with no way to switch to a mode like Peak for quality control purposes. So while not typically suggested for video playback this mode can be an invaluable QC tool.

Contrast

The Contrast optimized modulation mode can provide an improved black level to peak highlight behavior compared to the Motion optimized mode, but at the sacrifice of more robust motion handling. While not generally suggested for client playback this mode is sometimes found very useful by colorists when grading a high contrast static frame.

A great deal of time and effort have been put into selectable backlight driving modes on the XM310K. These continue to be refined as we receive more feedback from users and conduct more research, but we do strongly believe that having variable modes is of great value in professional environments and we hope this overview provides some helpful background on the reasoning and advised use cases for these modes.