Bit Depth and Brightness for Film, TV & Broadcast

When specifying an LED screen, bit depth and brightness are key considerations, but brighter isn’t always better, especially for studio applications.

The LEDs making up the screen are digitally dimmed using pulse width modulation (PWM). This means there are a fixed number of brightness levels at which each LED can be illuminated, depending on the PWM bit depth. For example, a screen using 16 bit PWM will have 216 = 65536 levels. The more brightness levels, the smoother the image looks, especially in dark areas of video content. If the bit depth is too low then artefacts such as banding can appear. (Processing features such as Dark Magic can help reduce or eliminate this banding, but it’s desirable to start with as high a bit depth as possible to minimise this issue in the first place.)

Running a screen at its full design brightness ensures the full range of levels are available for displaying video content. If the screen is run at reduced brightness, a correspondingly smaller number of levels can be used to display the video content. Every time the screen brightness is halved, only half the number of brightness levels remain available for displaying video content. This effectively reduces the PWM bit depth that the screen is operating at by one bit each time the brightness is halved.

Let’s say the requirement is to run a screen at 250 Nits, and a choice of two different panel types is available: 500 Nits panels or 2000 Nits panels. If all other things are equal the 500 Nits panels would likely perform better at 250 Nits as the brightness only needs to be halved (thus losing a single bit of PWM bit depth). In contrast, the 2000 Nits panels would need to be run at an eighth of their brightness, which is equivalent to halving their brightness three times and so results in losing three bits of PWM bit depth.

This often means that specifying a needlessly bright screen may end up compromising the video quality if the screen will only ever be operated at a much lower brightness.

Some panel types with Brompton processing support ‘Studio Mode’ which enables the panels to switch to a lower brightness mode without reducing the PWM bit depth, thus maintaining the best possible image quality when operating at low brightness, but also retaining the ability to switch back to the higher brightness when required.

For screens where HDR content will be displayed, sufficient brightness should still be available to ensure the highlights have enough ‘punch’, even if much of the video content is much lower brightness.