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COLOUR CHOICE In discussion with Megapixel, we go into detail about the benefits of sub-pixel colour metadata on the LED module Part 2
then, in real time, able to read back the metadata from the tile and process it in a way that is accurate and helps the user understand what is represented by the LED screen.” The integrity of metadata is always honoured to ensure that colour gamut, greyscale performance and tone mapping look right the first time. Or, if desired, can be tweaked and managed within the colour grading page of HELIOS. “It’s opened in a browser, so there’s no special software to download – which allows for live colour grading of the LED screen at 24-bit per colour accuracy, providing more precision than you’d traditionally expect from doing it in a render engine,” says Hochman. THE GRADING PAGE The purpose of real-time colour grading isn’t necessarily to style the scene, but to calibrate for how the camera is interpreting it. Out of the box, tiles are right at D65 and produce the colours they are meant to. But elements in the scene can sometimes affect what they look like. Hochman explains: “Imagine you’re doing a process shot and there’s a bright green sports car on stage with a lot of light shining on it. That bounces back onto the LED wall, creating a green wash across the screens themselves. You need the
LAST TIME, WE got into the nitty-gritty of what makes HELIOS production-friendly for ICVFX and why. In part two of a three-part series exploring Megapixel’s HELIOS LED Processing platform, we break down its cinema-grade colour accuracy by delving into the inner workings. Mini PX1 processors that fit into each LED tile deviate from the archetypal method of having a rack unit as a choke point. Instead, these allow for proper metadata management, to remove the all-too-common interference problem that occurs when pointing a camera at an LED screen. HELIOS acts as a traffic cop, taking in all the incoming data and dispatching it from tile to tile. In-tile processing is unique to HELIOS, and it’s a technique that extends to the platform’s handling of colour metadata. Having also built cameras and lenses (and won an Emmy Award for the former), Megapixel’s engineering team understand the importance of colour accuracy and the process in which it goes from video ingest through to display output. “A big thing we pride ourselves on is that, with every single LED tile, we develop a process with the manufacturer to capture the raw metadata of not just what the tile is doing, but each pixel,” explains Jeremy Hochman, CEO at Megapixel. “HELIOS is
MAKE THE GRADE Real-time colour grading lets you tune to the camera’s performance as you work
opportunity to remove it, because you don’t want that coloured tint to affect what the camera is capturing for the volume. HELIOS allows for this correction.” He continues: “Likewise, various camera models process colour differently. Rather than trying to tune an 8- or 10-bit video signal to make them match, you can tune the native output of the LED screen because the tech touches every single sub- pixel – it’s not in the upstream equipment.” The grading interface also has a report button, which gives users a tristimulus colour coordinate value of every single tile – and, because it’s in real time, you can see exactly what the wall and each of the pixels are doing in the entire system. From this, the x and y values of RGB may be obtained, and used for an ACEScg workflow. In regards to colour accuracy, HELIOS provides dynamic colour gamut retargeting; you can configure the screen to process Rec. 709, Rec. 2020, DCI-P3 or custom gamuts. For more accurate shadow detail – along with separation in highlights – this results in greater greyscale performance, for spectacular images. “We understand that, creatively, a colourist might decide they want to crush the scene and have the shadow details be incredibly black. That’s absolutely fine, but the technology should never force you into creative intent,” concludes Hochman. “We’re giving users a choice with HELIOS.”
HELIOS
TRADITIONAL PROCESSING
A LIGHT IN THE DARKNESS The HELIOS LED Processing Platform offers improved greyscale performance – and thus more accurate shadow details – compared to your traditional processing tool, as seen above
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