Designing LED Screens For Virtual Production
Given the scope of technology required for virtual production, getting down to the technical details of how each technology performs and what specifications actually mean requires a combination of experts from the respective worlds at play. This brings us to the true purpose of this article, to write from the perspective of an industry leading direct view LED manufacturer on what goes into designing an LED screen for virtual production.
LED Screen Configuration
The configuration and curvature of an LED volume largely depends on how the virtual backdrop will be captured and how the cameras will be moving while filming. Will the volume be used for broadcast and live stream? If so, will the camera shoot from stationary angles or will it pan around the focus point? Or otherwise will the virtual set be used for full motion video? If so, how will the live action personnel and materials be captured in the volume? These types of considerations allow LED volume designers to determine the appropriate dimensions of the LED screen, whether the screen should be flat or curved and at what angles, ceiling and/or floor requirements. Key factors to manage include providing a large enough canvas to allow for complete viewing frustums and minimizing colour shift, which results from the viewing angles of the LED panels that make up the screen.
Pixel Pitch and Moire Patterns
Moire patterns can be a big issue when filming LED screens. Selecting the correct pixel pitch is the best combatant against moire patterns. If you’re unfamiliar with pixel pitch you can learn more about it here. Moire patterns are caused by the camera picking up high frequency interference patterns caused by the individual pixels of the LED screen. The relationship between pixel pitch and viewing distance for virtual production is not only with respect to where the camera is but the closest focal point for all scenes. If the focal point is within the optimal viewing distance for a respective pixel pitch, moire effect will occur. Depth of field adjustment can further reduce moire effect by shooting the background slightly softer. As a rule of thumb, multiply the pixel pitch by ten in order to get the optimal viewing distance in feet.
Refresh Rate and Flicker
The flicker seen when filming monitors or for our case LED screens, is caused by a mismatch in refresh rate of the display and frame rate of the camera. LED screens require a high refresh rate of 3840hz as it helps to eliminate screen flicker and is absolutely necessary for virtual production application. Ensuring the LED screen has a high refresh rate is step one to avoiding screen flicker while filming, aligning camera shutter speed with refresh rate completes the fix.
For LED screens serving off-camera applications, brighter is generally taken as better. However, for virtual production, the brightness of an LED screen is often overpowering and brightness is turned down significantly. When an LED screen’s brightness is reduced, colour performance is sacrificed. The grayscale gets reduced due to there being less intensity levels available per colour. Ensuring the LED screens maximum brightness is aligned with the maximum light output required for sufficient lighting within the LED volume minimizes the amount the LED screen brightness needs to be turned down and minimizes loss of colour performance.
Colour Space, Grayscale, and Contrast Ratio
Colour performance for LED screens is made up of three main components; colour space, grayscale, and contrast ratio. Colour space and grayscale play important roles in virtual production applications, whereas contrast ratio is less critical.
Colour space refers to the specific organization of colours achievable by the screen. Producers should consider the colour space that will be required ahead of time as an LED volume can be designed with different colour spaces if desired.
Grayscale is measured in bits and indicates how many intensity levels are available per colour. Generally speaking, the higher the bits, the more colour available which results in smoother colour transitions and eliminates banding. For virtual production LED screens, grayscale of 12 bits or high is recommended.
Contrast ratio is the difference between the brightest white, and the darkest black. In theory it allows viewers to distinguish content of an image regardless of the brightness of the image. However, the specification is often misrepresented. LED screens capable of higher brightness, by extension have higher contrast ratios. At the other extreme rests fill factor, where using smaller (typically cheaper) LEDs increase the black of the displays leading to higher contrast ratios. Contrast is important, but it’s important to understand the factors in determining the contrast ratio.
Effectively designing an LED volume for the space and productions it will be built for is the first step to successful implementation of LED technology for virtual production. Given the custom nature of LED screens, virtually building an LED volume in a 3D world is the most effective way to plan the dimensions, curves, mounting, and viewing distances of the LED screen. This allows producers and engineers to visualize the volume and discuss requirements ahead of time while making informed decisions along the way.
Last but not least, throughout the design process, as teams design and discuss the LED volume important site specific topics will be considered including but not limited to structural, power, data, and ventilation requirements. All of these factors will need to be appropriately considered and made available for proper implementation of the designed LED screen.
For more information on LED screens for virtual production, or to start your project with LIGHTVU, click here.