August 9, 2016

How The LED Virtual Pixel Really Works:

How the LED Virtual Pixel Really Works 1PR1PG1PB vs 2R1G1B

How The LED Virtual Pixel Really Works:
Why do LED screens use the virtual pixel technology, and what exactly is it?

The virtual pixel is a video-management feature that allows a 400% increase in image quality. LED screen manufacturers use it to show better quality, realistic-looking images.

But why do LED screens need to increase the image quality through a video-management feature in first place? It’s pretty simple: despite its huge size, an LED screen usually has many less pixels than the common computer screen you are looking at right now. How is that possible? Because on an LED display, the distance between two pixels can be up to 30mm or even more. As a result, on a normal computer screen, you have 1024×768 physical pixels or more while on a 4×3 meters LED wall you have 192×144 physical pixels. Big difference!

So how can we actually see anything on an LED screen with a resolution of only 192×144 (27.648 physical pixels total)? Easy! Thanks to the virtual pixel technology, we can double the number of pixels in length and in height. Therefore we can increase the number of pixels perceived by the human eye by four times. So the same screen with virtual pixel technology will have a perceived resolution of 384×288 pixels (or 110.592 pixels). Isn’t that beautiful?

Now you are probably asking, how is that possible? Well, there are two different types of virtual pixels: geometrical/squared and interpolated. In Part 1 of this article we will discuss the geometrical/squared virtual pixel technology.

Geometrical/Squared Virtual Pixel—2R1G1B

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This technology is based on pretty simple geometrical concepts. If you have two identical shapes placed next to each other, by taking half of each shape you can create other two identical shapes. For example, if you have two identical pixels lying next to each other, by taking half of each pixel, you can create two more pixels identical to the first two, doubling the number of pixels from two to four. Now imagine to double the number of pixels you have in length, and with the same technique double the number of pixels you have in height: to increase the number of pixels (and therefore the image quality) by 400%.

Geometrical Pixel and formation of Virtual Pixel

There are some limitations and side effects of this technology, especially when compared with the interpolated technology. The geometrical/squared virtual pixel technique uses half of two adjacent pixels to create other two. It is pretty easy and straightforward once you understand the mechanism, but there is one limitation.

We just saw how two adjacent pixels can create another two by “switching” the side LEDs of each pixel. In this case everything worked fine because the distance between the LEDs is the same distance between the pixels. But let’s say for example that I have an LED screen with a bigger pixel pitch for higher viewing distances. What happens if the distance between LEDs and pixels is not the same anymore? In this case the virtual pixel is not identical to the real pixel anymore. The virtual pixels are more stretched than the real ones and therefore the overall image quality will be affected.

Over the past 15 years some manufacturers developed a technology that allows going beyond these limitations and guaranteeing a superior image quality with any resolution. Does it mean that the geometrical/squared virtual pixel is not a good technology? Well, let’s just say that it is definitely not the most recent one. Some LED wall manufacturers still use it, so when considering your LED screen supplier, make you check how their virtual pixel technology works.

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How the LED Virtual Pixel Really Works: Part 2 of 2

How can you increase the image quality on your LED screen without using squared pixel technology and its related side effects? In Part 2 of this essay we will look at the other method used for increasing the image quality on LED screens known as Interpolated Technology.

Interpolated Technology is very similar to MP3 technology used in the music industry. MP3 is an audio-specific compression format based on the acoustic perception of the human ear. It provides a representation of pulse-code modulation-encoded audio in much less space than straightforward methods, by using psychoacoustic models to discard components less audible to human hearing and recording the remaining information in an efficient manner (similar principles are used by JPEG, an image compression format).

In the same way, the Interpolated Pixel is a compression based on the visual perception of the human eye: by compressing a big image to fit the small resolution available on the screen, the interpolated pixel proprietary algorithm compresses the images the way MP3 compresses sounds. This compression (together with the image persistence on the retina) allows us to control the visual perception by showing details, in our case one pixel, where there is nothing: that’s why it is called “virtual.”

With this state-of-the-art technology it doesn’t matter how far away the pixels are because the image quality does not rely on a geometrical distribution of the LEDs on the screen surface.

Formation of Virtual Pixel on Interpolated Technology

It also has other key advantages. As we discussed in Part 1, “geometrical pixel” is a relatively old technology and it only works properly when LEDs are equidistant to

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each other. The problem is that even in this case, there can be some side effects. The main side effects are related to the minimum viewing distance, chromatic fidelity, and contrast ratio.

With minimum viewing distance if LEDs are spread all over, what actually happens is that the pixels get bigger. As the pixels get bigger, the image must be looked from a greater distance or it will appear pixilated, so the minimum viewing distance must increase. This is something to consider, especially if you are installing an LED screen indoors.

Chromatic fidelity is the distance between the LEDs and has other side effects. The closer the LEDs are to each other, the better their single colors will mix, and the sooner your eye will perceive the entire pixel color (the sum of the three basic colors: red + blue + green).). On the flip side, the more distance you put between LEDs, the more distance there must be in order to perceive the right color mix. Which means that not only can images at short distances look pixilated, but they might also have a poorer chromatic fidelity (for example, the color yellow might appear as a dot half red and half green).

Last but not least, if you have LEDs spread on the LED screen, the surface might not be as black as you would like it to be to ensure the best contrast ratio. Each LED has a white (or clear) background that is much lighter than the black surface of the screen. If you spread these white LEDs on the black surface you get a grey area. Since the contrast level is a ratio between the light emitted by the LEDs and the environmental light reflected by the screen, you can very well understand that your surface should be as dark as possible.

1R1G1B per Pixel

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Screen with 1R-1G-1B Pixels

How can Interpolated Technology avoid all these problems? Because it allows LEDs to be closer together to form a clear pixel unit. Meaning,

1. A smaller minimum viewing distance because the pixel has a smaller surface;
2. Getting a higher chromatic fidelity because LEDs are closer and therefore colors mix faster;

and 3. Increasing the contrast ratio because the more space there is between LEDs the more black the surface will look.

Each manufacturer will of course highlight the strong point of its technology, but bear in mind this information and make your own conclusions. I tried to clarify a fairly complicated topic that often creates confusion. I hope I provided you with useful information that will help you to make a more conscious consideration when you have to decide which kind of LED screen better suits your needs.

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