18 mai 2020

Video walls need automatic calibration. Here’s why!

4 min de lecture

Automatic brightness and color calibration are featured in many Barco products, from video walls to medical displays. The reason is simple: to guarantee an optimal viewing experience at any time during the entire lifetime of the product. For medical displays, the importance of calibration is easy to understand: a suboptimal image quality can lead to a faulty diagnosis. But what about video walls? Is the image quality that crucial that small variations will interfere with the correct use? Probably not, but here we need to look at the bigger picture. Quite literally, that is.

Video walls consist of multiple display panels or projection units placed in a matrix structure. This poses a special kind of calibration challenge: the individual panels need to be perfectly calibrated amongst each other as the viewing experience is very sensitive to small relative differences. While the aging effects of an individual video wall display is only noticeable if you are really experienced in evaluating colors and brightness, only a slight variation with respect to the adjacent panels is clearly visible. You may already have noticed video walls that show these color variations. And if not, this post will probably haunt you forever and make you look for them (sorry for that). Let me share a story…

Decaying displays at airport terminals

Frequent travelers probably know the large video walls in airport terminals, used for digital signage and/or commercial purposes. These displays operate continuously (24hours/7days) and are therefore a perfect reference when it comes to aging effects on a complete video wall. Just like every A/V system, also video walls require maintenance and calibration. If not done properly, this can result in poor viewing experiences. As you might have guessed, it’s the last group that gives the most spectacular results. Here’s an example.

Though you might mistake this chessboard pattern in the LCD displays as an artistic attempt to create an attractive desktop background, it is actually the result of the different drifting and aging behavior of the adjacent panels. Yes, all panels receive the same kind of blue signal in their input modules but display it in a very different way. Here’s another image.

Would you have noticed the difference in color and brightness if these were standalone displays? Probably not. But the matrixed nature of tiled video walls just screams for a proper calibration procedure. The tricky part, however, is that you shouldn’t just calibrate the individual panels, but the complete wall with respect to each other. In other words, you need a way to calibrate all displays to the same objective values.

Calibration over complete LCD and rear-projection video walls

To do this, you can’t depend on the display’s internal settings (like color, white point, etc.). The shift in color and brightness are in no way related to a change in these settings, but a decay of the screen itself. You therefore need a measurement device (such as a color/brightness sensors or spectrometers) that can objectively measure the color and brightness values.

In Barco’s LCD video walls and rear-projection cubes, these sensors are built into the products themselves. They feed their results to Barco’s unique automatic calibration system, called Sense X, Sense5 or Sense6 (depending on the product), which originated more than 20 years ago when deploying the first Barco rear-projection video walls in 24/7 control rooms. This system then adjusts the display settings to obtain the same objective system over the complete video wall solution.

Calibration of LED displays

For direct-view LED video wall systems, the situation is quite different. Unlike LCD and projection, the LEDs hardly vary in color or brightness over time. So an accurate high-performance calibration process is especially needed during production of LED tiles.

Many companies do this in suboptimal conditions, with commercial grade cameras and on wall level, leading to results which are hard to reproduce. In other words, if you then swap a LED module, it will not have the exact same values and your wall won’t match anymore (see image).

That is why Barco calibrates LEDs on a tile level instead of on LED level. Keeping a fixed setup, under fixed conditions, the tiles can all be calibrated to the same exact settings.

Very important here, is the batch compliancy (binning) of LED modules. Every production batch has its own specification, which can differ quite heavily. Therefore, the batch compatible spare parts need to be stored to ensure the LED modules can be replaced with components of the same production batch. For our EssentialCare customers, Barco guarantees to store sufficient batch compatible spare parts for at least 7 years.