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SRO: A primer on using HD images on large LED screens
By Randy Green   -      From: ,Staging Rental Operations
Editorial content partner



Related Articles

Staging Rental Operations: The art of projection


SOURCE: November/December 2003 issue · POSTED: 03/30/04

There is a lot of talk about high-definition video these days, especially in the high-end consumer and broadcast television industries. A great deal of time, energy and money are spent producing shows using HD equipment, and for good reason. When done right, HD images are significantly clearer, sharper and more enjoyable to watch than standard-definition images.

Although it seems that this is happening slowly, major sports and entertainment events are picking up the pace, producing and shooting shows in HD. Professional sports on all major networks routinely produce content in HD. Major awards shows, concert tours and other live television shows are also being produced in HD.

Ironically, many of the same events that are produced in HD are events that require large LED screens as part of the live production. In the near future, we will start seeing more requests for placing HD video images on LED screens — both for IMAG and special effects — due to the increased picture detail and clarity.

HD flavors

Large LED screens cannot automatically accommodate HD. Widescreen does not mean HD, and just because HD material is on a small screen does not necessarily mean it’s being seen in high definition. To further confuse the issue, all HD images are created and viewed at a 16:9 aspect ratio, but not all 16:9 images are HD.

Television resolution is measured by the number of horizontal scanning lines, and spacing of the picture elements (pixels) within each horizontal line that constitutes a complete television or monitor frame. As the number of scanning lines and picture elements increases, the detail, clarity and crispness of the picture improve. This is why HD images look so good.

What, then, is HD’s relevance to the LED world, and how do we incorporate it into live presentations? Basically, HDTV is a television system that provides picture detail, color purity and an aspect ratio greater than the standard NTSC system. Here’s a brief look at the two basic “flavors” of HD:

  • Analog HD — Analog is mainly used in high-end consumer, home theater and projection environments. YUV and RGBHV are the standard signals used for analog HD. Currently, analog HD comes in both interlaced (1080i) and progressive (720p) formats. Analog HD is being gradually phased out by consumer digital standards such as DVI and HDMI.
  • Digital HD — Digital HD exists in basically two environments: professional and consumer. The HD-SDI (serial digital interface) SMPTE 292M standard is mostly used for broadcast television and professional environments and consists mainly of two resolutions and scanning formats. One of the most common HD-SDI formats is based on the interlaced and progressive 1080 standard SMPTE 274M. The other common HD-SDI format is based on the progressive digital 720p SMPTE 296M standard.

DVI and HDMI are also digital HD formats, but are being adopted and used primarily for consumer and home theater applications as the HD input interface.

Here’s what HD is not: There is a common misconception that all widescreens are HD. This is not true — in fact, it is possible to have wide and ultrawide screens and not have an HD image.

Widescreens include screens that are 16:9, 1.85:1, 2:1 and the ultrawide 32:9 or 4:1 screens. In order for the image displayed to be true HD, the input source and display screen must be able to accept and display HD signals. In the case of LED screens, there must be enough pixels to display the entire HD image.

Screen requirements

To display true HD in either 1080 or 720, a very large screen is required. It’s true that when you increase the resolution with a tighter pixel pitch and increase the pixel density, you can reduce the screen size. But if you do that, you are increasing the cost per square foot either on a purchase or rental.

If you examine such a screen closely, it becomes clear that unless you have a pixel pitch of 16mm or less you will not even approach HD resolutions with the screen dimensions used for most productions (usually 35’x63’ required for 720p). In fact, pixel pitches around 10mm or less will likely end up being the indoor and outdoor standard for screens displaying HD signals because of their pixel density and more reasonable screen size.

Ultrawide screens (32:9) commonly used in stadiums and corporate presentations create another unique problem. Many times the horizontal number of pixels in the screen exceeds the number of pixels in the video signal displayed.

Few facilities have production equipment with the extra resolution in the input signal to fill such a screen without magnification. As a result, SDTV signals have to be scaled horizontally to fill the extra-wide format. This requires special processing.

Although it is possible to scale the image to fit the screen in these ultrawide formats, if the LED screen has more pixels than the input signal, the result is usually a fuzzy-looking image. A good rule of thumb is to always make sure your LED display has fewer than or as many pixels as your input signal. With HD as your input source, unless you have a very large display, this should not be a problem.

Processing

Processing is at the heart of all HD LED displays, and must not be taken lightly. Most LED displays operate in progressive or proprietary scanning formats, so it’s important for the input processor to accept all the SDTV, EDTV (480p), and HDTV standards and convert them into the right types of signals. This conversion must be high quality. If the input signal is digital, such as DVI, SDI or HD-SDI, it’s important for the digital signal to be processed and distributed to the display without being converted to analog. Since LED displays are digital, this all-digital approach is best and will result in the best image.

Input processing also must scale to lesser and greater than the original input resolution. Because LED screens are configured in varying sizes, the input processor must be able to scale the input image to match the number of pixels in the display. A quality scaling circuit is essential.

It is important to note one fundamental fact when comparing LED screens to projection for HD. LED resolution improves as the screen size increases. Because the pixel pitch is fixed and remains constant, more pixels are added as the screen size is increased, and thus the image will have a higher resolution. With projection, image resolution is fixed by the projector, so as you increase screen size, pixels grow larger, farther apart and resolution decreases.

There is much debate on the advantages and disadvantages of the two HD formats, but there is no debate about the fact that HD pictures have more information (three to eight times more) than standard-definition signals, and require larger, higher-resolution LED screens.

Therefore, HD is not your best bet for everyday productions. Rather, it’s most appropriate for those who want or need a truly unbelievable image that is clearer, more colorful and more detailed.


Disclaimer: This article originally appeared in a content partner publication. ICIA/InfoComm reserves the right to modify articles for concerns regarding grammar, style and format. 

· Table 1. Video formats and pixels per frame required
· Table 2a. Screen sizes required to display HD
· Table 2b. Screen sizes required to display SDTV and EDTV


   

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InfoComm - SRO: A primer on using HD images on large LED screens