LED processors: Trust the process

LED screens provide instant impact, but it’s the LED processors behind the scenes doing a lot of the hard work. Paul Milligan finds out why they are so vital.

Products switchers and scalers, extenders, mounts and brackets are the unsung heroes in pro-AV. These are tools used in every installation which rarely get the glare of publicity. As LED has become the display technology of choice in pro-AV, the latest to join the list of unsung heroes are LED processors. With the growing influx of LED walls, it’s imperative that system integrators give them the best chance of producing an impressive result, and that is where LED processors come in. We thought it was about time to readdress the balance and showcase the vitality of LED processors.

Colour is clearly a crucial issue to producing the best LED wall possible, so how can LED processors ensure the best colour accuracy for your LED project? “What's really important is understanding the video signal coming in, and not only just trying to light up the pixels but lighting up the pixels in the best way possible, given their characteristics,” says Jeremy Hochman, co-founder and CEO of Megapixel.

To get to the right answer, you need to work through a series of questions he explains: “Has the content been mastered in Rec2020? (The Rec2020 gamut covers 75% of the visible light spectrum) Has it been mastered in DCI-P3? (The RGB colour space used in digital cinema) What is the colour container? What's the operating system that might be driving the signage system? These are all really important things that come with content, and knowing how to interpret that and do the right thing on the panel is hyper important.” 

Mexapixel works with manufacturers as a co-developer of new LED tiles. “I call it a hot-rodded tile, we help them understand how to get the best performance out of the tile, because we don't want to just be a black box in a rack somewhere. We want to contribute to the overall experience that people have with these things.” To do this Megapixel has undergone a review of the electronics inside, and gone down the full path of developing LED chemicals and making custom silicon to develop colours in LED packages that have never been seen before. NovaStar uses its own ‘Colour Manage’ technology to calibrate LED screens with a colourimeter to ensure accurate colour performance.

Jason Xiao, product director at NovaStar, describes how it works: “During Image Booster calibration the colourimeter will measure the original colour gamut of the LED screen, and with a NovaStar patented algorithm the LED screen will be able to show at a standard colour gamut, such as Rec709, DCI-P3, Rec2020, etc. Additionally, a report, which includes delta E value of various colours, can be generated as a proof of colour accuracy.” 

Samsung’s approach to the LED processor companies is slightly different because it can offer an end-to-end solution, as Paul Maloney, head of hardware tech consulting for Samsung Europe, explains. “We are not the processor company, we are not an LED company, we have an LED solution, so we have control of everything from the processing and the panel. A lot of the market is about having panel X connected to processor Y, therefore you are going to need much more manipulation in that processor to get the result you want because you're dealing with so many different variables every time. We have a controlled set of variables we deal with, and we can control our output.”

The way to deliver the best LED wall possible starts at the very beginning of the process he adds: “You have to start with the raw material, your colour is dependent on the diode you put in your panel, you need to have a standard that ensures that you are picking consistent diodes in a particular set of bandwidth to make your panel. We are very particular, we use a very narrow bandwidth of colour. You have to build the product well in the first place, that's fundamental.”

Deepsky is another doing things away from the pack as it uses a patented IC driver which can change with regards to the content. Antoine Doublet, general manager at Deepsky explains how it works: “Normally all IC drivers in the market are using constant current technology PWM (pulse width modulation), which means the LED are modulating in brightness by being turned on and off, but when they're on they're always at the same intensity. This leads to limits in grayscale. We have the ability to change the LED current to the size of one LED pulse. We can more finely control the amount of brightness emitted by an LED, especially at low brightness.”

Calibration is another key element for LED processors to produce the best results, but what are the different techniques you can employ to ensure the red you want is the one you see on your LED wall? “The panel is made, then it's calibrated, and calibration is going to set how the panel looks,” explains Cesar Caceres, product lead, Brompton Technology. There are two parts to calibration he says, the first is deciding what is the colour? And the second is making sure all the pixels can achieve that colour.

Lux Stage at Trilith Studios, powered by Megapixel processing. Photo credit: Lux Machina

To do this Brompton has something it calls ‘dynamic calibration’, Caceres details how it works: “We read the information from these pixels, and then we tell the processor, this is what the peak of the pixels can do. And the processor sets a maximum calibration for the panels we have connected, the panels communicate to the processor to say this is what we can do, and the processor says ok, this is more or less the maximum brightness that you can achieve, do you want to go a little bit higher than that?”

The second part is far trickier he explains, because how do you determine what colour is actually red or what makes up a blue colour? “Usually for 95% of people what they do is select the standard they want to choose, and then the panel will have to try to make that colour. We can read the information of the panel and the formation of the colour space and the formation of the image that they are trying to display and reassign that colour to the closest one, specifically for the colour of this pixel, at 60 times or 100 times per second for every single frame, for every single pixel in the whole world. That’s the trick, it’s having huge processing and reading and comparing colours to make sure that it’s as close as possible to the colour space.”

For calibration Megapixel has developed specialised software it gives to its partners producing LED tiles, so they are compatible with Megapixel processors. Hochman details the process, “We need to capture metadata for every single pixel to understand their capabilities. There's the chromaticity of red, green and blue sub-pixel of every LED package. Sometimes the pixels are RGB, sometimes they might be RGB W, RGB WW, or have other colours as well. We also characterise certain things about the panel, what does it do when you look at it off axis? Its characteristics are going to be different than when you're looking at it on axis. We record all this data as well, and once it has all been collected, scientific instrumentation takes all of these measurements. When we work with manufacturers, we make sure there's memory on every single LED module so all the metadata we collect gets stored in a memory chip on every module, so if that module gets removed or gets replaced, the data lives with the module.”

NovaStar has built its own scientific camera (the C3200) to work alongside the calibration algorithm and the company has a long history of innovation in this field as Xiao illustrates: “NovaStar developed the colour uniformity calibration algorithm and the chroma calibration for standard SMD LED cabinets, and we also developed the world's first calibration algorithm and calibration system for the CoB in 2018.”

The marketing message and general sales pitch for LED tiles in the last 10 years has been aimed squarely towards pixel pitch, the lower the number the better quality tile you’re buying for your dollars, has been the mantra. But with LED processors getting better and better, should we actually be focusing on these tools rather than obsessing over pixel pitch? We’ve seen this happen already in other product segments (consumer TVs, photographic cameras) says Doublet, “There is always a race for pixel pitch, but there’s also a point when people realise that because of the viewing distance it's probably the wrong feature they want to change to improve image quality.”

You need both says NovaStar’s Xiao: “Pixel pitch is important, because the physical display advantage of finer pixel pitch is irreplaceable. However, buyers should also consider both viewing distance and dimension of the LED screen. At the same time, buyers should pay more attention on LED processors and the receiving cards. The same LED panels will get different performance in different LED processors and different receiving cards. Because different LED processors and receiving cards have different levels of algorithms to help make the panel's performance better, especially on image quality.”

Achieving colour accuracy is obviously vital for LED, but has the battle to have the blackest blacks in the market now the biggest challenge for LED manufacturers and LED processor providers? “There are definitely a lot of companies spending a lot of money in new technologies to achieve deep blacks,” admits Caceres.

This question has come up more lately says Hochman because as pixel pitch gets smaller and smaller, it's harder and harder to achieve a really great black level, because you have less empty space around the pixels. “Especially with CoB technology and getting into 0.8 and 0.9mm resolutions, black level is harder and harder to achieve on those devices. Some of the manufacturers are struggling with packing so many LEDs and so many LED drivers into such a tight space, there's more heat and what happens when there's more heat? There’s more degradation to the LED. So now all of a sudden, instead of an LED tile being 2,000 nits, they only drive the tile at 800 nits right or 600 nits. If your dynamic range is only up to 600 nits you care a lot more about the black level.”

MGM Cotai, powered by Megapixel processing technology. Photo credit: MGM

To this end, it has recently developed a patented masking technology in which it paints carbon nanotubes around the LEDs which becomes a light absorbing material that Megapixel licences out to some manufacturers.  Another aspect of building a successful LED wall in which LED processors can help it is in managing frame rate and correcting jitter. But to do this you’ll need the appropriate muscle to fulfil the task you’re asking of them. “Processers need to be fundamentally fast enough with enough memory to process what's coming in and what's going out correctly,” says Maloney. “Often a lot of the problems will occur if there's a mismatch in the frame rates. Get the processor for the application, understand what it is you're going to be driving into it, and make sure the processor can handle it because it will affect what's going on further down the line.”

NovaStar’s LED controllers are able to remap frames from input to output, usually double or triple a low frame input to a higher frame rate output, like 24fps to 48fps or 72fps. “The jitter issue usually happens at low frame rate like 23.98 or 30Hz, with our Frame Adaptive technology we can ensure there is no jitter at all at frame rates from 23.98 to the max frame which the LED panel can achieve,” adds Xiao.

With the hype surrounding AI right now, you should resist the urge to let it do the LED processing for you warns Hochman, as you may end up with something that doesn’t look as indeed. “We've seen some manufacturers advertise things such as AI frame blending, where something can be made to look buttery smooth with a camera pan or something like that. But it's not actually what the artist intended with the content, because it's making things up from data that’s not there. We care about doing the best job representing what's in the original video content.”

Virtual production has grown exponentially since the pandemic and relies heavily on quality LED to make fake scenery look real. Can using a high-end LED processor help the Moon really look like the Moon, rather than some actors walking around a film set? If you want to ‘cheat’ the camera in virtual production, it’s a similar process to cheating the human eye says Doublet. “The critical thing to achieve is dynamics, both in terms of brightness and colour. If you look at the natural scene in a forest, like the light of an autumn day, you have natural dynamics that will range from below one nit to several 1000s, because that's how the natural world is made, and the human eye now is used to that level. If your LED screen is only capable of displaying from 2-1,500 nits you're very far still from a natural scene. This same applies to colours too, you need to be able to display a colour gamut as wide and accurate as possible because the human eye is used to seeing a leaf with the proper green colour, not the ‘wrong’ green either, so this is why processing is key.”

If this article has been able to establish the importance of using LED processors, is that message getting through to system integrators, or are they still fixated solely on the price of the LED tiles or the smallest pixel pitch achievable for their budget? “I think a lot of the square metres sold of LED screen are still purchased based on price and pixel pitch,” says Doublet. But it's not all doom and gloom he adds: “I do think, and it's especially driven from the emergence of new, more advanced applications, such as VP, eSports, and broadcast, in those extremely demanding environments, system integrators have been requiring an advanced processing solution.”

The decision to invest in a decent LED processor is directly related to the type of project says Maloney. “We're not going to typically get that kind of question if we're installing a screen in a boardroom or going into a shop, but if we're doing a design studio, or command and control, or broadcast, most definitely those are conversations that you have.” To meet this need, Samsung offers two ‘flavours’ of processors, one for everyday jobs and one which can be operated by the user live in a virtual production setup. The last word goes to Hochman, with a dose of realism on this whole issue, while also pointing the way forward for these products; “At some point LED is going to become a commodity, there's only so many factories for the frames and chassis in China, they're making all of it for everybody. It's then a case of who is bolting it together with the right ingredients and making a good recipe. Processing is one of the most critical pieces of that recipe."

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