Not really. But today we are using TV and computer monitors for increasingly similar purposes, and so many of us are unaware that these two types of equipment are technically quite different. In fact, each generates its picture in a unique way. Some new products on the market, such as those that allow you to browse the internet on a TV, make the differences in technology invisible to the user. However, whenever a computer picture is displayed on a TV, you can be sure that a sophisticated conversion process is taking place, whether it's being performed by a free-standing scan converter or by components hidden within another type of equipment. And as the quality of this scan conversion process can vary greatly, so can the quality of your final, converted image.

Computer and TV monitors differ technically in two important ways. First of all, the rate at which an image is "painted" onto a computer monitor can be more than twice as fast as the rate at which it is "painted" onto a TV monitor. This is called the scan rate. A computer paints an image onto a computer monitor going from left to right at a horizontal scan rate of 24,000 to over 65,000 times a second (also referred to as 24 to 65 kilohertz [kHz]), and from top to bottom at a vertical scan rate or refresh rate of up to 75 times a second or more (75 Hz). By contrast, a TV scans much more slowly, going from left to right approximately 15,000 times a second and from top to bottom 60 times a second. The role of a scan converter is to change or convert the faster scan rate of the computer image to the slower scan rate that is compatible with TV technology. This basic process is called scan rate conversion.

The second fundamental difference between computer and TV monitors is the form of the video signal received by the monitor. When a computer sends an image to the computer monitor, the video signal is divided into separate red, green, blue and sync components. A TV monitor, on the other hand, is designed to receive a single electrical signal, called composite video, that combines all the necessary visual information together. A scan converter changes the multiple video signals coming from the computer to the single composite video signal that the TV can receive. This process is called encoding.

So, in order to connect a TV to a computer, the computer output must first undergo both scan rate conversion and encoding.

As for the mechanics of physically connecting a computer to a TV monitor, today's scan converters make this an easy process. Most TVs feature a video input (RCA jack) on the back that allows you to hook up a scan converter with a simple cable. Older TV sets, that do not have a video input, require you to purchase a small device called an RF modulator that permits the attachment of a scan converter through the antenna jack. When using an RF modulator, your incoming computer signal will "ride" on a TV channel, such as Channel 3.

Only if you have a really bad computer monitor and a really super TV!

In fact, the very reason that separate computer monitor technology was invented was that TV's were insufficient for displaying certain high-resolution images, such as small text, spreadsheets and still photography. For example, have you ever tried to read the small disclaimer text at the end of car commercials?

Why is TV technology so inferior? TVs are based on a video standard developed 45 years ago, called NTSC (or PAL outside the US and Japan). Computer monitors, by comparison, were developed using today's improved technology, allowing us to create affordable displays with more information content (bandwidth) and higher resolutions.

So what are the primary differences between NTSC and the technology used in today's computer monitors?

First of all, computer monitors receive their video signal in a more basic, pristine form than TVs do. As discussed earlier, the video signal sent by a computer to its monitor is broken into multiple electrical components (red, green, blue and sync) while a TV signal has all necessary information combined into a single composite signal. In order to process this composite signal, a TV must break it up into its original components, inevitably degrading the picture quality and creating distortions.

A second factor contributing to the inferior quality of images displayed on TV monitors is interlacing, a technique by which a complete TV picture is drawn in two passes from top to bottom on the picture tube. In interlacing, the first pass paints all the "odd" lines and the second pass paints the "even" lines. Noticeable flicker occurs when the images in the odd lines are very different from the images in the even lines. As the odd and even lines are alternately displayed, the eye perceives the quick appearing and disappearing of visual information. Flicker is especially noticeable when viewing thin horizontal lines that only take up a single odd or even row. If, for example, the line happens to be on an odd row, it totally disappears every time the even rows are displayed.

Unlike TV monitors, computer monitors paint an entire image in one pass from top to bottom, in a display format called non-interlaced. Images displayed in a non-interlaced format do not suffer from the same flicker problems.

One day in the not-too-distant future, high-definition TV, or HDTV, will replace our current NTSC standard. Like computer monitors, the new HDTV standard will be non-interlaced, eliminating the flicker problem. Also,the new standard will possess more than twice the number of lines of resolution that the current NTSC picture. So, when HDTV becomes a reality, you will at last be able to enjoy the same quality of picture on your TV as on your computer monitor.

Maybe. On a good day. And with a lot of luck in adjusting your TV controls.

Even without using a scan converter, the colors on your TV monitor will tend to look less vivid and less pure than the colors on your computer monitor. This is because of inherent differences in the way computer monitors and TV monitors process color, and also differences in the construction of their picture tubes. Computer monitors have an advantage over TV monitors in that the colors defined by the computer are sent to the monitor using the three primary colors: red, green and blue (RGB). The computer monitor has to perform almost no processing in order to display them. TV monitors, on the other hand, receive a composite signal that they must separate and process into meaningful color components (red, green and blue) before displaying them on the picture tube. As discussed previously, the additional processing performed by TV monitors degrades both picture quality and color reproduction.

A scan converter, then, cannot be held totally responsible if the colors on your TV display do not exactly match the colors on your computer monitor. (Video professionals often joke that NTSC stands for "never the same color.") However, all scan converters will add further distortions and small amounts of color impurities when converting from computer RGB to composite video. These distortions are more evident with certain colors. For example, red on a green background looks fine on a computer monitor but looks terrible on a TV monitor. Fully saturated (bright, intense) colors also look noticeably poorer on TV monitors than they do on computer monitors.

This is not to say that all scan converters perform equally in color reproduction, or offer the same level of control in adjusting color output. For example, some scan converters actually provide features such as test pattern generators and output processing controls to help you make as close a match as possible between the colors on your TV and computer monitor. To learn more about the specifics of how scan converters differ in their ability to generate colors, refer to Question #3 in Ten Questions You Should Ask Before Purchasing a Computer Video Scan Converter.

Not necessarily. It depends on what level of scan converter you are purchasing.

From high-end scan converters, priced above $4000, it is reasonable to expect a virtually flicker-free image without significant blurring or softening of the converted image. However, even at this level, you will find dramatic variation in the quality and control offered by different models, so be sure to do some comparisons. When testing a flicker-filter, look at a variety of images, ranging from graphics to text, as different types of images respond differently to the anti-flicker processing.

Among mid-priced scan converters ($800 to $3000), eliminating most of the flicker is generally a better solution than eliminating all of it. Here's why: Anti-flicker filters work by altering the information in the odd and even lines of a TV picture so that the alternating lines are more similar to each other. This way, when they appear and disappear in the interlacing process, the flicker is less noticeable. The more similar the lines are made to appear, the less flicker is visible. However, the obvious trade-off is that as flicker is reduced, more and more information is being altered or lost from the original picture. Vertical resolution is therefore sacrificed. The reason more expensive, high-end scan converters can eliminate more flicker with less loss of resolution is because, among other reasons, they are able to selectively apply flicker reduction only to those portions of an image where the effect will be beneficial. Mid-range scan converters tend to apply the anti-flicker filtering process to the entire screen.

Low end scan converters, priced in the low to mid-$100s, generally eliminate all flicker. These low-end models eliminate flicker by completely discarding every other line of the image, and displaying two successive passes of the remaining lines. Because the interlaced lines are now identical, no flicker is visible. Obviously, this method of removing flicker has serious drawbacks, as half the visual information from your original image has been lost. Small text becomes unreadable. Thin, horizontal lines may disappear. Plus, this method of flicker reduction compromises the actual NTSC standard - the very signal the scan converter was designed to create. (Remember, adherence to the NTSC standard is essential in professional video applications.)

So, don't be too quick to judge the quality of a scan converter based simply on the amount of flicker in its output. Effective flicker reduction (and not necessarily removal) must always be evaluated in conjunction with the scan converter's ability to generate a consistently crisp and readable image

While images generated by scan converters won't look exactly the same as the original computer image, there are many things you can do to get the best picture possible. First, if your TV monitor has an S-video input and your scan converter has an S-video output, use them! This is the one thing that will have the most impact on the quality of your picture.

Next, adjust the brightness, contrast, color, and tint (or hue) controls on the TV monitor. In order to correctly adjust for brightness, turn down the brightness level until the black on your screen appears as true black - not as dark gray. To correctly adjust for contrast, look at the border between a light and dark object displayed on your screen. When contrast is set too high, blooming may occur, in which the light area bleeds or blooms into the dark. To properly adjust the color and tint, you really should use test color bars, but if this is impossible and you're using a scan converter, you can use the colors generated by your computer for reference. (As discussed earlier, you won't be able to obtain an exact match.)

Finally, when creating images on your computer for display on a TV monitor, keep in mind the limitations of television technology. To avoid excessive flicker, refrain from using thin horizontal lines whenever possible. Try to avoid using saturated colors next to each other, such as intense reds and greens. Grays, on the other hand, tend to display quite well in NTSC. Also, avoid small text, as it will always be difficult to read.

And here's one last pointer. If you intend to record your computer generated image on a VCR, record it in the two-hour mode using a professional quality tape.

And a Geo Metro and a Mercedes are both cars - one just has power windows.

Scan converters vary widely in price but not simply because some have more features than others. The price differences are mainly due to the differences in circuitry used to accomplish the basic scan converter functions. Low-end, mid-range and high-performance scan converters vary greatly in the way they process images.

Let's start with low-end scan converters, priced in the low to mid-$100s. These scan converters are sometimes "software-aided." This means that the can conversion process is not performed entirely by external hardware, but that the computer itself is aiding in the conversion process. The use of a software driver may conflict with the graphics processing of your computer and/or some of the applications you intend to use. Also, these low-end scan converters offer a very poor-quality anti-flicker filter (if they offer one at all). The low price of the units prohibit the inclusion of processing components necessary to do anything but the most rudimentary flicker reduction - that is, eliminating every other line of the image. And, low-end scan converters are limited in the resolutions they support. Generally, they support only 640 x 480, with some newer models also supporting 800 x 600 at low refresh rates. However, often if they support 800 x 600, they only allow you to see 640 x 480 pixels at a time, clipping off the remainder of the image.

Mid-range scan converters offer software-free performance and a much improved level of flicker reduction. In addition, mid-range scan converters are able support higher resolutions (generally up to 1024 x 768). They also offer 24-bit color processing, meaning that the converted image will features the same depth of color as the original computer picture. Low-end scan converters may be able to accomodate16.8 million colors in the incoming computer signal, but the converted image rarely maintains this level of color depth.

Finally, high-end scan converters offer an even greater level of image processing. These models are able to support resolutions as high as 1600 x 1280, and therefore require the expense of much more memory than scan converters that only support lower resolutions. These models also have superior anti-flicker algorithms and are often more flexible in accepting non-standard incoming computer signals.

So, separate from the many features that differentiate scan converters in different price ranges, there are also real differences in the quality and complexity of the scan conversion process. Price/quality trade-offs exist throughout the scan converter design. As with most things in life, you get what you pay for.