Digital Displays: A Little More About High Definition

When it comes to HD, it's not one size fits all.

Last week, I made a simple point in this space, namely that just because a display device, such as a plasma or LCD panel, is flat doesn't mean that it's capable of displaying high definition content as part of digital signage messaging.

By way of review of last week's column, a display panel can be SD, or standard definition, ED, or enhanced definition, or HD, high definition. Displays are made up of individual picture elements, called pixels. Basically, the idea is the more pixels, the higher the resolution of an image. Thus, an SD display with a pixel count of 704 (horizontal) x 480 (vertical) has less resolution than an ED display with 852 x 480 pixels. HD displays, which have even more pixels and are at the top of the resolution food chain for displays, come in three flavors: 720p, 1080i and 1080p. (More on the "i" and the "p" in a moment.)

A 720p HD display has 1280 pixels (horizontal) by 720 (vertical); 1080i and 1080p displays have 1920 pixels by 1080 pixels, or more than 2 million individual picture elements. The letters "i" and "p" stand for interlaced and progressive, respectively. Interlaced displays, like ordinary TV sets and 1080i HDTVs, paint individual lines of pixels back and forth top to bottom across the display on the odd numbered lines (in HDTVs those are 1, 3, 5...1079) first and then the evens (2, 4, 6...1080) before beginning the process over and over. Taken together the odd numbered line "field" and the even numbered line field create one "frame," or complete still image. There are 30 such frames displayed per second.

Progressive displays, like computer monitors and 1080p HDTVs, display lines sequentially (1, 2, 3... 1080) before beginning the process again. These 1080p HD displays paint 60 new still images on the screen every second. With twice the frame rate (60 versus 30), 1080p demands twice the amount of data as 1080i.

That difference in frame rates means different things to different parties interested in high definition. To marketers using an HD as the display technology in a digital signage network, 1080p is the top-of-the-line image quality they can expect to achieve for the foreseeable future. If the message they are communicating requires the utmost resolution, 1080p may be the right choice. However, 1080p displays are more expensive and there will be a price to pay in terms of content storage required to drive that messaging.

To broadcasters who must work within the law administered by the FCC for transmission of HD, 1080p is too much. Simply given what they must work with, 1080p is beyond their capacity to deliver. Thus, 1080i and 720p are the broadcast HD formats.

To movie studios wishing to distribute their films in the highest display format available in the home, 1080p is the answer. Much of the buzz over Blu-ray and HD-DVD optical discs is in part about the ability of the competing formats to deliver superb image quality. Those formats -and their use of a blue frequency laser with a shorter wavelength that can write more data per area of storage- were designed to be able to write the all of the 1080p data to disk that's needed to playback a full-length movie plus bonus material.

But here's the most important party in the 1080p HD resolution equation: the audience. Whether you're a digital signage marketer, a broadcaster or a movie studio, you are faced with same question: How do I affordably deliver the level of quality to my audience that satisfies my desired communications goal? In other words, how much resolution is enough for the communications task at hand?

Only you can answer that question. To illustrate how subjective the answer is, consider this: ABC, ESPN, Fox and My Network TV rely on 720p, or 720 progressive lines, for HD service while NBC, CBS and PBS rely on 1080i. Perhaps before you decide which level of HD resolution is most appropriate for your high definition digital signage network, you should flip between ESPN's "Sportscenter HD" (720p), "The Tonight Show with Jay Leno" (1080i) and "March of the Penguins" (1080p) playing back from an HD-DVD player or "Mr. & Mrs. Smith" (1080p) from a Blu-ray player on your 1080p display. You may be surprised by what you observe.

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