Secrets of Barco’s automatic calibration technology revealed

Upon installation, just about all video walls look good. Often they are manually calibrated so that all individual panels show the same brightness and color values. So no wall will have the ‘checkerboard pattern’ we often see in older video walls that are not maintained properly (see image on the right). In this blog post, we already explained the concept of inter-tile uniformity and the difference in brightness levels when video walls age. This issue is solved automatically with Barco’s intelligent Sense X algorithm, which brings all panels to the same level.

Upholding uniformity within every display

However, there is also the issue of intra-tile uniformity (so within the same panel). Especially in LCD video walls, we see a difference in color from the center towards the edges. The reason is in fact the very nature of an LCD video wall, and has nothing to do with quality or production mistakes. It will be only slightly visible when displaying videos or images, but when the complete video wall has the same color, it will become quite disturbing. On a complete video wall, this will again create an unbalanced image that makes the canvas look sloppy. 

Intra-tile uniformity is generally measured like this: the brightness of different points on the canvas are measured, and compared to each other. The result is the percentage of equality between these points. This can be done by comparing 9, 13 or 21 points on the display. The image on the right is a picture of a 3x3 Barco UniSee video wall that comes out of production, put on a black background for some increased contrast. If you look closely, you will see the image become a bit darker towards the edges. Nothing too bad on this small image, but if you see it on a full-size video wall it is very noticeable. 

For a Barco UniSee panel that comes out of production, this is:

• 9 points: 95%
• 13 points: 92%
• 21 points: 83%

Already very good compared to industry benchmarks. But not good enough for Barco standards. That is why we looked for a way to further improve these specifications. The result is Sense X.

To measure is to know

Instead of limiting ourselves to only 21 points, we actually use the data of more than 30,000 reference positions on the display. Using a high-quality camera and reference luminance and color meters, we can create a detailed distribution pattern of color and brightness. This pattern is unique for every individual display.

Using this information, we can steer the brightness and color information on the display in such a way that it creates a more uniform canvas. In this way, we succeed in creating a uniformity of:

• 9 points: 98%
• 13 points: 98%
• 21 points: 91%

This not only affects the balance within one display, but also improves the uniformity of the complete video wall. If you look closely to the image on the right (again a Barco UniSee 3x3 set on a black background, but with Sense X calibration), you will barely notice the dark lines in between the panels.

Improving uniformity for all colors

To make matters even more challenging, the distribution pattern is not the same for every greyscale and color. So dark grey will have a different color and brightness distribution pattern than white. That is why the values of multiple grey levels are measured and combined into a so-called 3D look-up table. This table is then used to provide the data for the color and brightness corrections. There is correction data for 64 RGB reference levels, with 10 bit precision. A Barco proprietary algorithm applies the corrections that lead to the smooth images on the Barco LCD displays.

One more thing to mention is that Barco Sense X works continuously in real-time. It is not a matter of calibrating the wall every year or so: our automatic calibration system makes sure that your video wall is calibrated at every moment!