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    Brompton Technology
    Brompton Technology Ltd
    272 Gunnersbury Avenue
    Chiswick, London W4 5QB

    Recreating Reality: Synchronisation Artefacts

    3rd April, 2023
    Synchronisation Artefacts

    An important part of recreating reality is ensuring that there are no artefacts in the image, as these could potentially disengage the audience from the visual experience. Achieving synchronisation of systems, with the use of genlock, is the first step to achieving this uninterrupted experience and is the foundation on which we offer two other powerful Tessera features: Phase Offset and ShutterSync®.

    Genlock

    Traditionally, synchronisation was applied when using multiple video sources. This ensured the machines’ refresh rates matched, and in this way avoiding artefacts being introduced when switching between machines.

    With the evolution of video systems, this technology was adopted by many other systems, including LED walls. When the LED processors controlling different sections of the same LED wall are not correctly synchronised, one of the main artefacts that can appear is tearing.

    Synchronisation is achieved with the use of genlock. Genlock keeps cameras, servers, trackers, processors and other devices‘ refresh rates following a reference clock. Typically, this is done by distributing a single, external reference to each machine. However, to increase users’ options, Brompton’s Tessera processors can also be genlocked to one of its video inputs, whether it is the active input or not.

    Phase Offset

    As a further level of precision, and to maintain the best quality content when using LED for ICVFX, you need to ensure that the camera shutter and the LED are not only genlocked, but also in the right phase. When the phase is correct, the LED displays a single full frame for the time that the camera shutter is open to expose the sensor.

    This phase synchronisation avoids frame blending – the effect seen when the LED has finished displaying one frame and begins displaying the next frame before the camera has finished capturing.

    Phase Offset can fix blending by allowing the user to manually match the phase of the LED with the camera shutter.

    ShutterSync®

    When a camera is looking at an LED display, a common issue that can occur is horizontal banding: bright or dark horizontal lines that are visible through the camera feed. This artefact is the result of a difference between the timing of the camera’s shutter and the LED wall refresh rate.

    To overcome this issue, the camera settings could be adjusted to an appropriate combination of shutter angle, phase and refresh rate to match the LED wall. However, to provide maximum creative flexibility for camera configurations, Tessera processors come equipped with ShutterSync®. This feature offers a straightforward interface for tackling the problem by synchronising the precise LED wall refresh rate to the camera’s shutter timing, putting full control back in the hands of the creative team.