Unlike televisions and related video equipment that always use the same display resolution, computer monitors generate a wide range of display resolutions with varying refresh rates “Resolution” refers to the number of pixels, or dots, that comprise the image. “Refresh rate” is the speed at which the image is painted on the screen, in one-pixel-high horizontal lines drawn from left to right, top to bottom. The video card inside your computer determines the resolution and refresh rate displayed on your monitor, and often you can choose between a number of different settings. Common computer resolutions are 640 x 480, 800 x 600 and 1024 x 768, but they may go as high as 1600 x 1280 and beyond. Common vertical refresh rates are 60 Hz (an entire screen is drawn from top to bottom 60 times per second), 70, 72 and 75 Hz, although there are many others.

The most basic, low-end scan converters usually provide support only for computer resolutions of 640 x 480 with a vertical refresh rate of 60 Hz. This is because this combination of resolution and refresh rate is mathematically easy to convert to a standard TV resolution. The number of pixels on both the computer and TV monitors are almost the same, and the TV refresh rate is just about half of the computer refresh rate. As of a few years ago, most PCs and Macs operated in 640 x 480 as a default setting. However, as computer applications have become more graphic intensive, including applications such as web-surfing, many people prefer to set their computers to higher display resolutions. In these cases, a scan converter that only supports resolutions of 640 x 480 will not suffice.

Mid-range scan converters often support resolutions as high as 1024 x 768. However, be careful to also check the vertical refresh rates the scan converter supports. Many scan converters only support lower refresh rates at higher resolutions. For example, if you generally operate your computer in 1024 x 768 with a 72 Hz refresh rate, and the scan converter only supports 1024 x 768 at 60 Hz, the scan converter will not be compatible with your computer. Also, make sure that if a scan converter supports resolutions such as 1024 x 768, the entire converted image will be viewable on the TV monitor at one time. Some scan converters “support” 1024 x 768, but only allow you to see 640 x 480 pixels at any one time, forcing you to scroll across and down the screen.

High-end scan converters support the even higher resolutions used by workstation computers, such as 1280 x 1024 and 1600 x 1280. Sometimes, the refresh rates these high-end scan converters support are defined by the horizontal, rather than vertical, refresh rate. The vertical refresh rate is the speed at which the entire screen is drawn from top to bottom, whereas the horizontal refresh rate is the speed at which one line of pixels is drawn from left to right. Because in high resolutions there can be more than 1000 horizontal lines on the screen at one time, the horizontal refresh rate is much faster than the vertical refresh rate and is measured in kilohertz, or 1000’s of times per second.

In summary, before you go shopping for a scan converter, make sure you know the resolution and refresh rate you use on your computer. Then, be certain that the scan converter you buy supports both.

The NTSC standard is the very precise definition of television signals as they are used in North America and Japan. Created by the National Television Systems Committee in the early 1950’s, the NTSC standard specifies the format of the transmission signal used to create a television picture, including information defining the picture’s resolution, color and brightness. The reason you can buy any camcorder or VCR and know that they’ll both work with your TV is because each piece of equipment is required to adhere to the NTSC standard. In other parts of the world, PAL is the accepted video standard.

You might assume that the TV output generated by a scan converter would, by definition, adhere to the NTSC (and/or PAL) standard. However, this is a false assumption. The output should adhere to the standard. Should and do are two very different things!

While it’s pretty safe to assume that any mid-priced or high-performance scan converter will generate a true NTSC signal, many low-end models take shortcuts in the conversion process, therefore failing to meet all the rigid NTSC specifications. Most consumer-grade televisions are lenient in accepting sub-standard NTSC signals, so the “cheating” of the scan converter may not be evident to the user. However, problems will inevitably arise when attempting to use the scan converter with other, less-accommodating types of professional video equipment. One of the most common ways a scan converter might violate the NTSC standard is by not locking the colors in sync with the brightness portion of the TV image. This is called unlocking the color subcarrier and will make the colors on the TV appear to wave or “swim,” even on a consumer TV.

Once you are assured that a scan converter outputs a true, NTSC (or PAL) standard, you need to evaluate the formats in which it provides this output. There are actually many different types of NTSC output. The most basic is called composite video. All scan converters provide this output as a standard feature. In composite video, all the information defining the picture is combined into a single, “composite” signal. This is the format that you are most accustomed to viewing. It is also the poorest quality.

S-video is a better quality NTSC format because it separates the color and brightness information into two separate signals before going into the TV or video monitor. This separation results in a crisper picture with less distortion. Many higher-end consumer TVs and projectors as well as all professional video equipment offer an S-video jack. By purchasing a scan converter that offers an S-video output, you will be able to make use of this input option on your TV or video equipment and benefit from a far superior picture.

The best quality NTSC display format is RGB at 15 kHz. Like a computer picture, NTSC in an RGB format keeps the red, green and blue information as separate signals. (“Sync”, or information regarding the synchronization of the picture, is carried in a separate fourth signal.) Certain professional types of equipment, such as video projectors with separate red, green and blue “guns,” accept NTSC in this format. While still not as good as a computer picture, NTSC displayed in RGB offers a vast improvement over the quality of NTSC in standard composite format.

“Component video” is another variation of NTSC, similar to RGB in picture quality, that was developed exclusively for use in professional video production and recording There are multiple variations of component video, including Betacam and MII. Some scan converters in the mid-price range and almost all high-end scan converters offer component video output.

Finally, certain high-end scan converters offer a digital version of NTSC output. Serial digital output, or D-1, enables the scan converter output to be used in conjunction with other digitally-based equipment in a broadcast environment.

Although the above discussion has referred only to the various formats of NTSC, the same format options also apply to the PAL video standard – composite, S-video, RGB and component. Some scan converters offer both NTSC and PAL outputs in the same unit. Others support only one or the other. Depending on where you plan on using your scan converter, you can determine your specific needs.

The maximum number of colors that can be displayed on a computer monitor is a function of the graphics card in the computer and the number of “bits” it uses for color processing. What does this mean? Before a computer can tell a monitor what colors to display, it processes the color by breaking it into individual “bits” of information, each containing an “on” or “off” message. The maximum number of colors that the computer can describe to the monitor is a function of how many bits are dedicated to this process. The more bits, the more colors. The following chart shows the maximum number of colors a computer monitor can display based upon the number of bits used in color processing, ranging from 6 to 24-bit color. 24-bit color means that 8 bits of information are dedicated to describing the color red, 8 different bits describe the level of green, and 8 more bits describe blue.

By contrast, televisions use an analog, rather than digital, means to process color.To visualize an analog signal, think of a wavy horizontal line. Information describing the color of the television picture is carried along that wavy line. There are no discreet “bits” of information. Instead, the level of color can fall anywhere on the continuum of the wave, from a peak (maximum color) to a valley (no color). Of course this is a very simplified explanation, but you can imagine how the continuous nature of an analog signal would allow the color processing within a television to describe a huge range of color, without the limitations that digital processing (containing a low number of bits) might impose.

So, if a computer monitor running in 24-bit color and a TV monitor can both display millions of colors, shouldn’t a scan converter connecting the two also be able to output this number of colors? Not necessarily.

Today, most scan converters use digital processing for at least part of the scan conversion process. So, just as a computer graphics card operates in settings ranging from 6 to 24-bit color, scan converters can differ in the number of bits they dedicate to color processing. Some scan converters offer 24-bit processing; others provide only 16-bit or less. If the incoming computer image contains 24-bit color but the scan converter doesn’t offer 24-bit processing, the maximum number of colors displayed in the converted image will be limited to the level of processing offered by the scan converter.

When evaluating scan converters for their ability to convert and output 24-bit color, be wary of advertising claims. Some manufacturers promote their products as having the ability to “support” 24-bit color, but this may simply mean the scan converter can accept a 24-bit color input without crashing. The unit may not necessarily provide a 24-bit color output. If full and accurate color representation is important to you, shop for a scan converter that provides 24-bit sampling and processing.

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.