New Year’s Resolutions
Feb 1, 2002 12:00 PM,
Josh Kairoff
THE NUMEROUS COMPUTER SIGNAL AND MONITOR resolutions may seem like nothing more than confusing letters and numbers. Adding to the confusion for those of us in the A/V industry are the cryptic names and other strange bits that seem to be part of the computer geek’s unrecognizable language, such as, “That Pentium III with the 4× AGP does UXGA at 75 Hz.”
For the uninitiated, it’s tough enough just figuring out why the computer display is sharp on the monitor but fuzzy on the projector.
But most display devices are categorized, specified, compared and selected in large part by their geek-speak letters and numbers. People in the computer display business have been known to take all this specification stuff very seriously. The humorous part of this, however, is that A/V professionals focus more on the issues of install and hook-up than on the actual specifications of the displays. We tend to think of them as being interchangeable like television monitors and we don’t dwell on it. But perhaps we should…at least for the next couple of pages. There are a few key concepts to be aware of when selecting or using display equipment.
There is an enormous amount of information available in books and online regarding the specifications and capabilities of various displays. Unfortunately, most of this information is organized and presented for people who speak Computer. Luckily, I speak both A/V and Computer, so I will take on the task of translation. (You can tear these pages from the magazine and put them above your desk for reference.)
KEY CONCEPTS
Resolution
When referring to electronic display equipment, resolution indicates the total amount of information (in pixels) that can be displayed. Resolution is expressed as the numeric value of the active horizontal and vertical pixels. This value can be either the actual number of pixels (as in a fixed-resolution display like an LCD, DLP or plasma) or the recommended maximum (as in a CRT). That’s what’s meant by specifications like 800 by 600 and 1280 by 768.
As you can see in the photo of me writing this article (page 26), increasing the resolution allows more picture information to be seen. With a VGA display, we would only be able to see the wooden wall. But going up to XGA we can see the lamp and my toes. At SXGA, the subject (that’s me) is now part of the image; and at UXGA you can see that I am not sitting on the floor.
Native Resolution
Native resolution refers to the actual resolution of a display. Simply, if a display generates 800 by 600 pixels, then that is its native resolution. This term should only be used in relation to fixed-resolution displays, although I have seen it incorrectly used to describe some variable-resolution CRT devices. The importance of this specification is that, in theory anyway, a fixed-resolution display will always look best when it is given a signal that matches its native resolution. It’s most often true that an 800×600 signal sent to an 800×600 display will look better than a 1280×768 signal sent to the same display. The idea is to match the native resolution.
Image Scalers
Most fixed-resolution displays use a kind of digital signal processor called an image scaler to convert many different input signal resolutions to its own native resolution. Let’s say a 640×480 (VGA) signal is sent into a 1024×768 (XGA) LCD projector. As the 640×480 signal contains approximately half the number of pixels as the 1024×768 display, the image would be very small on the screen. But when an image scaler is used, the original 640×480 signal is upconverted into a 1024×768 signal so that it fills the screen — and looks good.
Of course, there can be qualitative differences between various kinds of image scalers. Also, as a rule, the more drastic the converting an image scaler has to do, the worse the image may become. Furthermore, it’s better for a scaler to make pixels than remove them. For example, an 800×600 image will look better when upconverted and shown on a 1024×768 display than when it’s down-scaled for a 640×480 display. Going back to my photo, if we were to take the image (originally at 1600 by 1200) and compress it down to 640 by 480, it would lose a lot of display information and look like the inset photo.
Aspect Ratio
This is a fairly new issue for most of us, but it is simply the relationship of the horizontal resolution to the vertical resolution, expressed as a ratio. For instance, the resolution of 640 by 480 can be simplified to 4:3. For many years, everyone worked with displays having a 4:3 aspect ratio. With only one aspect ratio to consider, no one worried about compatibility; however, with the introduction of more powerful computers and HDTV, we now have to work with display aspect ratios of 16:9.
The Golden Rule of Aspect Ratios
Changing an aspect ratio necessarily requires that you stretch or crop the image. There is no magic box that can adjust aspect ratio without some sort of image stretching or cropping. If a 4:3 image is displayed as a full screen on a 16:9 display, the objects in the image will be slightly wider. If all of a 16:9 image is shown on a 4:3, the objects will be slightly taller. It’s always best to produce images that are formatted with the native aspect ratio of the display device.
While the idea of different aspect ratios may seem new, we’ve actually seen it for 100 years. You may not have noticed it, but the last time you watched a movie in a theater, the curtains around the screen moved back and forth just as the film began. Movie theaters’ curtains are moved to change a screen’s aspect ratio so that it matches each movie’s aspect ratio. The curtains crop the image as it’s projected without the audience noticing.
Curtains work great in a big theater but would look a little strange surrounding the display device on your desktop, or in your home theater or conference room. Display devices without curtains show black bars on the sides wherever the images are cropped. These are noticeable, of course, but sometimes cannot be helped. At least seeing the bars is less obtrusive than seeing images that look too fat or too skinny.
Some recent display devices are starting to feature switchable aspect ratio configurations as part of their image scaling functions. This technique usually works by stretching or squishing the edges of an image while keeping the center unmodified. While this is not a complete solution, it can accommodate an aspect ratio mismatch. There are also standalone scalers that will convert any signal for any display.
When installing, your main job is to make sure that the picture is going to look good. Whether you do this by specifying equipment with matching native resolutions or by including a scaler in the system will depend on budget, equipment availability, etc. But one way or another, you’ll need to deliver a good picture before your client gives you the standing ovation.
Josh Kairoff works for Pioneer New Media Technologies as a product planner. He can be reached via e-mail at jkairoff@pnmt.com.
