Beyond HD
Nov 1, 2008 12:00 PM, By Craig Birkmaier
Will 1080p improve the quality of HDTV?
Commercial TV became possible thanks to the round tube TV, like this one from Zenith.
Does anyone out there still have a dot matrix printer? It seems they have gone the way of the horse-and-buggy and round tube TVs, a term that the consumer electronics industry is using to put the last nail in the shipping crates for CRT-based displays.
In 1984, I bought my first computer and first printer, a dot matrix machine that could print at 72 dots per inch (DPI), which also happened to be the resolution of the Mac Classic display. The term what you see is what you get (WYSIWYG) was coined to describe the benefits of a graphical user interface and printer that could reproduce what you saw on the computer screen. Unfortunately, the results had more in common with the mechanical TV demonstrated by John Logie Baird in 1926 than a modern ink jet or laser printer.
Much the same can be said about the evolution of TV from the early experimental days through the worldwide deployment of 525-line (NTSC) and 625-line (PAL/SECAM) systems to today's SDTV and HDTV systems with 480, 576, 720 and 1080 lines. We are only a decade into the era of HDTV, yet some folks are already talking about moving beyond HDTV. In fact, the consumer electronics industry is now promoting 1080p displays, despite the fact that nobody is broadcasting 1080 at 50p or 60p, or is planning to in the near future.
The trouble with dot matrix printers, and legacy TV systems, is that they did not offer enough resolution to deliver high-quality, alias-free images. Despite this shortcoming, however, TV has prospered, based primarily upon the content that is delivered, rather than the quality of the pictures. While digital television can deliver outstanding quality pictures, the unfortunate reality is that what we watch today is often compromised by the decision of program distributors to focus on quantity rather than quality.
So what gives with the seeming disconnect between the quality of the images that go into the transmitter and the push for displays that offer far more resolution than a broadcast can deliver? And why are people talking about even higher resolutions for TV image acquisition?
Decoupling and oversampling
Baird's television system used a camera with a rotating disk to sample the image. The display had a rotating disk that recreated those samples. The major advancement that made commercial TVs a practical reality was the development of the round tube TV, aka, a scanning CRT display. The camera electronically scanned the image on a pickup tube from top to bottom, and the display scanned this image onto the surface of the round tube display. We could delve deeper into interlaced vs. progressive scanning, but for the purpose of this discussion, the important takeaway is that everything was tightly coupled. The camera and the receiver/display all operated synchronously using the same scanning parameters.
John Logie Baird first demonstrated his mechanical TV system in 1926.
With digital television, all that has changed. Image acquisition (the camera), image processing (production, master control and transmission) and reception/display are completely decoupled. Today, a TV program may be displayed on a 65in HDTV display, a notebook computer, an iPod or a cell phone. Low-quality images can be viewed on high-quality displays, and high-quality images can easily be encoded for delivery at multiple resolutions.
In most cases, the limiting factor in delivered image quality is not the camera or the TV. It is the bandwidth of the channel that is being used to deliver the compressed bits to the receiver, which in turn must decode these bits and present them on a display — any display, no matter the resolution.
A modern digital TV receiver must deal with video formats at multiple resolutions, converting them to the resolution of the local display for presentation to the viewer. And that DTV display may be connected to additional sources of bits, which have different characteristics from a video signal, like video game consoles and multimedia PCs. Some TVs are even shipping with integrated Web browsers that bring the world of Internet content to the big screen in the family room.
There is one golden rule when it comes to the creation and delivery of high-quality imagery, whether it is video, digital photography or computer-generated images. It is desirable to start with higher quality than you plan to deliver. The term for this is oversampling. In laymen's terms, it is the difference between a dot matrix printer that creates characters and images at 72DPI versus a laser printer that produces characters and images at 300DPI. More samples allow the digital imaging system to reproduce higher frequencies without aliasing artifacts.
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