Pixel pitch has been the industry standard at the time of defining the resolution for an LED sign. The lower the pitch, the higher the resolution. Or so we have been made believe.
True Pixel Matrix
Traditionally, pixel pitch measured the distance from the center of an LED cluster (or pixel) to the center of the next LED cluster/pixel in millimeters. However, many LED display manufacturers now offer a new pixel configuration and quote the resolution in “Virtual Pixels”; claiming that “Virtual Pixels” double the actual resolution of the screen, i.e a 20mm pixel pitch LED screen would have a 10mm virtual pixel pitch.
In the traditional true pixel configuration, each pixel consists of one red, one blue, and one green LED diode. However, a virtual pixel LED screen uses two lower output red LED lights per pixel to work as one; in a virtual pixel LED panel, each pixel consists of two red, one blue and one green LED diode ordered in a square matrix. This, in our experience, is more of a fail-safe design decision than a higher pitch resolution commitment on behalf of these LED panel manufacturers; since red lights tend to age quicker and a double red diode allows this fabricators to use lower quality materials.
Since red LED lights are more likely to fail, in a virtual pixel configuration they are set to display at fifty percent of the power, that means that over time, red LED diodes fade at a slower rate than the blue or green LED diodes, which more often than not gives the LED sign a pinkish tinge after it has been on for as little as six months.
Virtual Pixel Matrix
However, the virtual pixel LED board manufacturers claim that this configuration allows each LED diode to be “shared” by the contiguous four pixels. Therefore, when counting pixels, the first four diodes grouped together are counted as the first pixel. Then the third, fourth, fifth and sixth form the second pixel. After that, the fifth and sixth diodes are combined with seventh and eighth and grouped as a third pixel, and so on. In a traditional true pixel matrix each LED diode gets counted as part of one pixel, in a virtual pixel matrix it gets counted as part of four virtual pixels. And it stands to reason that each LED diode can produce one level of brightness, not four.
In a “virtual pixel” screen one red diode contains the information of four pixels of the initial image. The image projected on a screen has double the resolution in each dimension compared to a “physical” resolution of a video screen. This usually leads people to conclude that screen resolution also doubles. Which is not exactly true. In fact, a diode can’t hold and display all the information for four pixels, part of the information will get lost.
In reality, at very close distance, a virtual pixel sign might look crispier but at farther distances, the lack of black space between pixels does not allow for enough contrast and the image gets blurrier. Considering that most people purchase LED signs to attract attention at a significant distance, it is not close proximity viewability that they have in mind when they are looking for a LED message center or digital billboard.
Furthermore, to avoid distortions that were not corrected by the designers during the image adaptation, “virtual pixel” LED boards frequently operate on standard “true pixel” mode with one of the red LED lights turned off.
Nevertheless, when determining pixel pitch virtual configuration LED sign manufacturers take advantage of the way they count each pixel to measure the pixel pitch by calculating the distance between one LED diode and the next -instead of between the center of two RGB true pixels- that way, a 20mm pixel pitch becomes a 10mm virtual pixel pitch, making this approach more about sales and marketing than providing a quality product.
In the end, one has to wonder why all the higher end brands steered away from this configuration and only manufacture true pixel LED boards.
ABOUT THE AUTHOR
Guadalupe Tofalo has over eight years of experience in the technology field. She works in the Marketing Department at Cirrus Systems LED, the revolutionary LED sign manufacturer behind N2, BLADE and SOLO Systems. Cirrus Systems strives to deliver the newest and most advanced display technologies available by creating hardware and software intelligently designed for ease of deployment and use.
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