Suddenly the world is full of “scalers.” They are sold as standalone models and combined with switchers in one box. Some are seamless and every display we buy these days seems to have one built-in. But what are they, what do they do and why do you need one?
Scalers are devices that take in one resolution video signal and output another. They can take in standard NTSC video and output a 1024 x 768 XGA resolution signal. Or they can take in a 1600 x 1200 UXGA resolution signal and output an 800 x 600 SVGA signal. Don’t confuse them with a scan converter. A scan converter always takes in a computer graphics video signal, such as XGA or SVGA and outputs standard NTSC video.
We need scalers because 10 years ago the world of large screen displays changed from being based on CRT technology to being based on fixed resolution technologies such as LCD and Plasma monitors and LCD, DLP and LCOS projections. Fixed resolution displays have a “native” or “panel” resolution and all other incoming resolutions must be changed to meet that native resolution before they can be displayed.
The number one thing a scaler does, is “Simplify Connectivity.” Let’s look at the example of a simple system with a projector mounted in the ceiling as the main display along with three sources, a VCR, a DVD player, and a computer. In this example, three wires would have to be run from the sources, up to the projector, one for each source. Then, we would have to switch the inputs on the projector to switch between the sources. That’s a lot of wires. If we added a scaler/switcher to this system, we could run one cable from the scaler up to the projector.
In this example, we have done three important things. First, we cut down on the number of cables we have to snake up to the projector because we only have to run one cable to the projector. This saves money and time.
Second, we relieved the projector of having to do the switching. Projectors are not designed to be switchers by the manufactures. In fact, they tend to muck that process up when they are required to perform that task. When projectors do switching, there is always a “glitch.” Something unpleasing or distracting will happen on the screen. Perhaps you have seen this when an image suddenly looses sync and all kinds of wavy things happen on the screen, or a message comes up that says something like “perfecting the image – please wait.” Scaler/switchers will provide you with a transition effect such as a fade through black to eliminate this problem. More advanced seamless switchers can actually cut from one frame to the other seamlessly.
Finally, we have used our scaler to “match” the native resolution of the projector, and accordingly, we have “by-passed” the scaler built into the projector. If you send a fixed resolution display an image that matches their native resolution precisely, you will achieve a higher quality image because you will by-pass the relatively inexpensive scaler that the manufacturer incorporated into their display. In the world of fixed resolution displays we live in today, margins are virtually non-existent. Manufacturers, in order to compete, can not put high priced scalers in their products. They put in scalers that get the job done. With an outboard scaler we can do the work outside the display and achieve higher picture quality.
There are four kinds of scalers. There are video scalers, RGB scalers, single chip scalers/switchers and dual chip seamless scalers.
Video scalers just take in standard NTSC video and up convert it to a computer graphics video resolution such as XGA or SXGA. If you had a system with 4 computers in, and you were employing a computer graphics video switcher, and suddenly you needed to add a DVD player to the system, you could use a video scaler to convert that DVD output to a computer graphics video signal and feed it into the system.
RGB scalers take in computer graphics video signals and convert from one output resolution to another. They can take in UXGA and output SVGA. Or they can take in XGA and output SXGA as an example. This “moving around” within graphics standards is called “full graphics scaling.”
Single chip seamless switchers, or rather scaler/switchers as they should appropriately be referred to, incorporate switching and scaling in one box. A single chip scaler/switcher is not really seamless at all. Only scalers with dual chips can perform seamless switching. Single chip scaler/switchers allow for multiple input sources while outputting a single scaled output to the display. Whatever goes in, regardless of resolution (XGA, SVGA, etc.) or format type (composite video, s-Video, RGBHV), comes out as RGBHV at a resolution you specify that matches your display’s native resolution. This simplifies connectivity. As for the switching, these units usually employ a fade through black. Typically, the image from the active input is frozen and faded down to black. The newly selected input image is then brought back up out of black. This transition happens so quickly, it just looks like the sources have been switched. For the viewer it is not at all distracting. Meanwhile, it eliminates the loss of sync that drives displays crazy which is indeed very distracting.
Finally, there are true seamless switchers with dual scaler chips in them. Because these units have two scalers inside, they cost more, but they deliver the ability to truly switch seamlessly from one image to another and they provide a “preview” and “program” output that is very important in live event production. Seamless switchers usually also have “universal inputs” so each input can accept multiple format types, making them more flexible in that regard over their single chip counterparts that usually have predefined connector/input types. Seamless switchers usually also provide multiple “transition effects” for switching, such as a corner wipe or circle out to enhance the visual experience.
All scalers need to be seen to be properly evaluated. You can not judge one from another from a specification sheet or product description. They all perform to different levels of quality. Scalers do three important things. They de-interlace, decode and provide motion compensation. How well a scaler does these three things will determine its quality. De-Interlacing is the process of converting interlaced standard NTSC video to a progressively scanned video signal. Decoding is the process of converting one kind of video signal format such as composite video or component video to another, in the case of scalers, that output format will always be an RGBHV signal. Motion compensation is probably the most important of these three functions and it is the easiest to measure. When all the calculations are done in the scaler to convert the signal, if the image being converted has a lot of motion in the frame, there will be some degree of degradation in the output image.
The better the scaler is, the better the final product will be. Get a copy of the movie Twister or some other movie with a lot of motion in it. This will tell you a lot about the motion compensation of your scaler. Always use the same DVD player to test scalers. Each DVD player will bring its own set of performance issues to the table, especially if they are outputting a progressive scan image. In fact, it is best not to send a progressive scanned image to a scaler because that means you are using the DVD player to do the de-interlacing. Let the scaler do the de-interlacing. It will do a better job.
Scalers are absolutely necessary in this age of fixed resolution displays with their native resolutions. For applications such as those in houses of worship, a scaler/switcher or seamless switcher is a very important part of any system because it simplifies the connectivity, allows for distraction-free switching of sources, and delivers the highest quality image possible. This last point varies from scaler to scaler, so you will need to see for yourself before buying.