Digital Signage: Why pixel pitch matters

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Photos courtesy Nanolumens

By Brett Farley
Terms like high-resolution, high-definition (HD), ‘4K’ ultra-high-definition (UHD), Widescreen Ultra Extended Graphics Array (WUXGA), pixel density and pixel pitch get tossed around a great deal these days with regard to digital signage. It is important to demystify and place these terms into the proper context when investigating display technology for a particular application or project.

Audiovisual (AV) professionals frequently ask questions that are essentially misdirected—such as “Is the display HD?”—when trying to determine whether or not a light-
emitting diode (LED) display of particular dimensions will deliver the content clarity and sharpness they require for a given application. Their miscues are largely a result of their comfort in using terminology inherited from liquid crystal display (LCD) technology. It is time to help clarify the world of LED screen pixel pitch and density, so sign customers can obtain the real value of the technology’s features and benefits.

Resolution vs. definition
HD is a relative and often catch-all term for high-resolution when describing the clarity and sharpness needed for the viewing of specific content, as it does measure resolution, i.e. the fineness of detail that can be distinguished in an image. For high-resolution content to be considered HD, however, it must meet three specific criteria:

  1. 
Widescreen format incorporating the 16:9 aspect ratio.
  2. 
Resolution of 1,920 x 1,080 pixels.
  3. 
Frame rate between 24 and 30 frames-per-second (FPS).

Such constraints were created as units of standardization for the AV industry, but they are not necessarily optimal for every situation, in terms of the display used and the content presented.

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LED screens are sometimes unfairly judged using terminology inherited from LCD technology.

By way of example, for a 4-mm (0.16-in.) pixel-pitch LED display to be truly HD, it would have to be at least 9.4 m (30 ft) wide. And if the pixel pitch were increased to 6 mm (0.24 in.), the same display would have to be at least 12.4 m (40 ft) wide.

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As for ‘4K’ ultra-high-definition (UHD), which is four times the resolution of true HD, what previously would have been impractically huge is beginning to become practical through the use of displays with less than 2-mm (0.08-in.) pixel pitch. A 1.8-mm (0.07-in.) pixel-
pitch 4K/UHD display, for example, would be 6.9 m (22.6 ft) across, which could be accommodated in many of today’s sports bars.

‘High-resolution,’ on the other hand, is specific, as it can refer to any display with sharp, clear and finely detailed resolution, whether or not it is true HD. It is also a more appropriate term for LED displays which, unlike traditional LCDs, are not bounded by the forced form factor of an HD 16:9 aspect ratio or 1,920 x 1,080 pixels.

It is more realistic to show high-resolution content on an LED display based on the number of pixels (i.e. the pixel matrix) and the quality of the LED lamps. High-resolution content can certainly be scaled for effective display on such an array.

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