VLOG & Articles

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 an overgeneralization 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 halation or flare. Most consumer displays and many professional displays have only one algorithm mode 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 to prioritize different viewing needs.

Peak

The Peak optimized modulation mode ensures the peak highlight code values are represented accurately on screen even if this results in some 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. 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 important small bright object highlight detail with no way to switch to a mode like Peak to see highlight code values represented accurately. Peak is the mode we find most colorists use for grading any given scene. Because Peak Modulation mode prioritizes accurate code value representation above all else it is also the mode that should be used for calibration verification.

Motion

This mode balances peaks and contrast and puts specific emphasis on LED/LCD sync and halation reduction. Motion Optimized Modulation employs faster backlight response speed than Peak Modulation mode making it particularly well suited to dealing with rapid large area luminance changes, especially those you may experience during abrupt scene cuts where full screen luminance mapping can change dramatically from one frame to the next. Left unchecked this ultra-fast backlight response speed would cause severe strobing as bright objects move from one LED zone to the next within a given scene. To help reduce the potential of perceived small bright object strobing and halation the Motion Mode may limit peak highlights somewhat and this is the primary tradeoff of this mode compared to the Peak Modulation Mode. Motion is the mode many facilities use for completed content review or client viewing.

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 useful by colorists when grading a high contrast static frame.

Modulation modes are assignable to Function buttons. Facility preferences can vary, but generally speaking the way most operators utilize the XM310K is to have the monitor in PEAK by default with MOTION assigned to a function button for client playback / review.

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. A significant update to the Peak Modulation mode algorithms was released with firmware version 1.1.84 based on such feedback and research, but even with such updates we strongly believe that having variable modes is of great value in professional environments.

We hope this overview provides some helpful background on the reasoning and advised use cases for these modes.