What Pixel Pitch Do We Need for a Smooth Image?

How fine should the dots on your display be to make it look good to the audience? Let's find out

By Morgan MacArthur

Pixel pitch and pixel density are inversely related. Pixel pitch is the distance between the center of adjacent pixels, and pixel density is the number of pixels in a given area. So the smaller the value of pixel pitch the finer the picture; but the higher the value of pixel density, the better.

Resolution, on the other hand, is simply the number of pixels across by the number of pixels vertically on a display. For example, the resolution of Sony's first Jumbotron was 240x192 pixels, about what early phones recorded for video. Today's displays can be literally 100 times finer.

For large displays, pixel pitch is a key decision factor. The required pixel pitch to give a smooth display is driven by the distance the audience is from the screen. And buying only as fine as display as necessary will moderate costs.

A simple rule of thumb is to divide the nearest audience distance in feet by ten. That number, in millimeters, will generally yield a high-quality result. So if the nearest audience will be 20 feet away, divided by 10 means a 2.0mm pixel pitch (or something close) will give a smooth non-pixelated display to the audience.

Most large displays do not give values for pixel density for the finished product, it is more often used to describe a particular technology than a particular board.

The term pixel is actually short for picture-element. These little dots are what make up the images on LED displays. Every pixel in screen is usually comprised of three diodes: one red, one green, and one blue. Each picture-element is an actual discrete dot in an image. The more points, the better the image quality.

There is a need for LED manufacturers to develop ever larger screens at lower costs, and manufacturers are constantly searching for new ways to do so. Inevitably, this leads to cutting some corners, and the consumer should be aware of that this is happening.

Be aware of the difference between pixels and "virtual pixels". Usage of virtual pixels (sometimes called pixel-sharing) were conceived as a cost cutting measure. The logic is simple-- diodes are the most expensive component of an LED display, so if you can make a display with fewer diodes, the display costs less to make.

There are two ways to reduce the number of required diodes. First, make a smaller or less-dense display, or, modify the diode configuration and allow diodes to be shared by multiple pixels.

In essence, a pixel can borrow green from a neighboring pixel to its left, and borrow red from another pixel to its right. This does cut down on the number of actual pixels needed to create an image-- but it results in poorer image quality.

Some manufacturers are using marketing terms that describe their product that uses a virtual pixel pattern as optimized, enhanced or other things like HD15 (implying a 15mm pixel pitch). This is an attempt to describe a pixel pattern — but this product does not physically have that many actual pixels. The term HD15, for example leads the customer to believe that there are 15 pixels per millimeter in the display.

It’s important to note that true pixel density is a critical factor in image quality of an LED display. And it is important to compare apples to apples when making such a high-stakes purchasing decision. Real pixels are actual physical points of light, and the more there are, the higher the resolution and therefore a better quality of picture. To return to our example, HD15 is simply not the same as 15mm pixel pitch.

The advantage may be lower sale prices, but in the end the picture quality is not as good as the specification would suggest. All the advancements in electronic display quality have come from adding smaller, but real, physical pixels. Software optimization can provide some minor improvements, but it does not actually increase the resolution of the screen.

In summary, it is important that the buyer understand the pixel pitch, pixel density and resolution of the product they are considering, and compare it to other like products. While the price may be lower with a virtual pixel product, the cost will be quite evident in loss of picture quality.


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