A video mixer/scalar is able to analyze and convert signals in any format into one standard output format.
The benefits of mixers/scalars should be obvious: any source of video can be called up on the fly and mixed into a live production.
Of all the tools available to those who design large-screen electronic presentations, video/computer mixer/scalars may be the most unique. These devices allow the seamless blending of interlaced and progressive-scan images from virtually any source, regardless of its signal format and scan rate.
Thinking about using big electronic images in your next production? Perhaps you've been put off by the idea of trying to blend signals from such disparate sources as a personal computer, DVD player, or hard-drive video recorder. Based on outward appearances, none of these sources of “video” appear to have anything in common.
The connectors couldn't be more different — what we think of as a traditional “video” connector is often a piece of coaxial cable with a small RCA or BNC plug on it. How does that have anything in common with the 15-pin, knuckle-busting “HD”-style plug on a computer monitor?
The fact is, “video” can come in many flavors. All that's required to produce an electronic image is some sort of luminance signal (how bright the image should be), signals that determine the levels of red, green, and blue in the image, and signals that synchronize each frame of the image.
In a broadcast video signal, all of this information travels on one wire. The same thing applies to a consumer video camera or VCR — the luminance, chrominance (color), and synch information is carried on that black cable with the yellow RCA plugs on either end. This is known as a composite video system — the separation of all signals is done in the TV set or monitor.
We can get more sophisticated with video signals. To improve picture quality, the luminance/synchh signals (Y) and chrominance (C) can travel on two separate wires. This component signal format is known as S-video, or S-VHS. If you've purchased a DVD player, you may notice three RCA jacks on its rear panel colored green, blue, and red. This component signal format goes S-video one better by dividing the chrominance information into two channels (R-Y and B-Y).
So we can deliver “video” in three different formats — a single wire, two-wire, or three-wire. Computer video displays aren't all that different, except that they only use component signal formats. Depending on the format, three color channels (red, green, and blue) travel on their own wires, while horizontal and vertical picture synch are carried together (composite synch) or separately (component synch). These two formats are known as RGBS and RGBHV, respectively.
A video mixer/scalar is able to analyze and convert signals in any of these formats to one standard output format. While the luminance and chrominance information may arrive in very different ways, the mixer/scalar is able to translate rapidly between formats and convert everything to one output format that you choose. Typically, it will be RGBHV, which is the same format used by computer monitors and flat-matrix front projectors.
By converting everything to the same format, a mixer lets us dissolve, cut, and wipe between each of these disparate video sources as easily as we can with a conventional broadcast video mixer/switcher. In addition, the mixer converts interlaced scan video sources (composite, S-video, and component video) to progressive scan, matching the progressive-scan format used by computer monitors. But there's another important part to the process.
Each incoming signal has a specific image resolution, which can be measured as either the total number of electronic scanning lines, or the number of horizontal and vertical pixels. You've probably guessed that video images will have less resolution than images from a graphics workstation computer, or even a notebook computer. How can two images of different sizes and resolutions possibly blend together?
The answer is in the video scalar. This is a series of custom-integrated circuits that performs some pretty sophisticated mathematical calculations on all incoming signals, and re-sizes them to match the output resolution you've chosen previously. If your mixer/scalar is set up to output a RGBHV signal with a specified resolution of 1,024 × 768 pixels (known as XGA), then all signals connected to the mixer/scalar will be converted to that resolution.
This means that lower-resolution video signals may not appear as crisp when enlarged (that's because the pixels are blown up in size). A better approach is to have the mixer/scalar create additional duplicate pixels from the original material, interpolating what these pixels should look like based on the original signal. That takes a ton of microprocessing power, and isn't easy to pull off.
Higher-resolution signals require a similar juggling act. They will have more pixels than the specified output resolution, so the scalar must throw away data, a process known as “decimation,” to shrink the image down to the desired size. This process can work quite well if implemented correctly.
To the end-user — you — the process is largely transparent. Setting up a mixer/scalar will require you to specify an output resolution, typically one that matches common computer display resolutions. These can include VGA (640 × 480 pixels), SVGA (800 × 600 pixels), XGA (1,024 × 768 pixels), and SXGA (either 1,365 × 1,024 pixels or 1,280 × 1,024 pixels).
Most mixer/scalars are intelligent enough to detect the incoming signal sources and automatically perform the conversions. You'll have to connect the cables from your video sources to specific input jacks, but that's about it. Onboard menus will show you what sources you have connected and how you've set up the output signal.
What's in It for Me?
Why use a mixer/scalar? Because flat-matrix displays (LCD, DLP, LCoS, plasma) all have a specific pixel resolution, also known as their “native” resolution. For your mixed images to look as sharp and crisp as possible, you'll want to match that “native” resolution exactly. The number of times each frame of video is refreshed each second is also important — for flat-matrix projectors, you may want to use 60Hz, 70Hz, 72Hz, or some other refresh rate. The mixer/scalar lets you do just that.
The human interfaces on scalars are very similar to those of broadcast switchers — large, backlit buttons that can contain custom labels for inputs and outputs. There are generally two banks of buttons to allow dissolves, cuts, and wipes, plus a joystick or T-bar to execute the effect. Mixer/scalars also have a second output channel for previewing the signal you are going to “take,” in addition to the “main” program output channel.
The benefits of mixer/scalars should be immediately obvious: any source of video can be called up on the fly and mixed into a live production. Those sources could include image magnification (IMAG), computer graphics (.JPEG, .TIF, and Powerpoint images), clips from hard-drive servers or DVD, video rolls from broadcast formats like Betacam SP and DV/DVCAM/DVCPRO, and even video clips from Internet sources.
In short, you are not constrained by the source material. As long as you can interface your source to a mixer/scalar (and the source picture scan rates are supported), you're in business. These products will work with different aspect ratios, too — most computer display resolutions work out to a 4 × 3 or 5 × 4 aspect ratio. But at least one manufacturer is now supporting widescreen (16 × 9) aspect ratios.
Who Makes Them
Video mixer/scalars are comparatively new products, but several manufacturers have jumped on the mixing/scaling bandwagon in the past few years.
Folsom Research of Rancho Cordova, CA, was the first manufacturer to successfully market a video mixer/scalar to the rental and staging markets. Their Variable Format Converter (VFC-2200) was able to seamlessly scale and blend a variety of component video signal sources at resolutions up to 1,280 × 1,024 pixels. A preview output and custom video switcher interface rounded out the package.
Folsom's ScreenPro product takes the concept to a new level, adding support for composite and S-video sources and providing auto-setup of all inputs. A new interface that included a built-in matrix of input and output pushbuttons as well as pushbuttons for executing cuts, dissolves, and wipes was added. A small LCD display provides all setup and operating information to the user.
The ScreenPro can also “key” one image on top of another, which is useful for superimposing text. It features eight separate inputs for component and composite video sources, up to a maximum resolution of 1,600 × 1,200 pixels (UXGA). The ScreenPro outputs standard computer display rates and is capable of storing up to 64 pre-programmed transitions in memory.
While Folsom's VFC-2200 mixer/scalar was the first such product to be widely adopted, a French company — Analog Way of Paris — has the distinction of rolling out the first full-integrated mixer/scalar with a built-in switcher. The company's newest version, the Graphic Switcher II, has large backlit buttons for each input and output, “preview” and “program” outputs, and individual pushbuttons for taking each selected effect.
Early models could only support progressive-scan video, requiring an external line doubler. The GSW II supports both interlaced and progressive-scan signals in any form — composite or component. Depending on configuration, it has eight RGB inputs (including component DTV signals), eight composite video, or four S-video inputs. The GSW II will also mix and output signals at HDTV rates, such as 480p, 720p, and 1,080p.
FSR, Inc. of West Paterson, NJ, also offers a fully integrated, eight-input, dual-output mixer/scalar. The Omni Navigator presents the usual video switcher interface for selecting inputs and outputs, plus auto-configuration on any input signal. Three pushbuttons select programmable wipes, cuts, or dissolves between sources, and an external video switcher can be interfaced for studio-type operation. Input sources to 1,600 × 1,200 are supported, and output signals are fed as standard computer resolutions to 1,280 × 1,024.
Extron Electronics of Anaheim, CA (best known for its broad line of video/computer interface products), has a full-featured mixer/scalar. Their SGS 408 product has eight high-resolution inputs that will take anything from composite video to 1,600 × 1,200 workstation images and blend them at standard computer resolutions. Both “preview” and “program” outputs are standard. Accessory control panels include a pushbutton panel (RCP 1000) and production switcher (ECP 1000) with T-bar.
RGB Spectrum of Alameda, CA, has a simpler configuration in its SynchroMaster 450. It's not as fully featured as the preceding models, but it allows seamless scaling and blending of four RGB signals or two RGB and two video signals (depending on configuration). The SynchroMaster 450 accepts input signals up to 1,280 × 1,024 resolution, and there's also an option to output serial digital video (DVI) to projectors and monitors so equipped.
Odds and Ends
Each of the products mentioned is a fully featured mixer/scalar. This means you have total control over all signal adjustment parameters (provided you know how to tweak them; otherwise, let the scalar do the calculating), and each product can also be controlled remotely, via an RS-232C interface.
Video effects (cuts, fades, and dissolves) can be remotely triggered independently or in conjunction with other lighting and stage effects. As IP-type control protocols are adopted by the professional AV industry, you can expect mixer/scalars to adopt IP addressing for placement on custom LANs. Expect direct digital signal connections to follow shortly.
Want to check them out? There are several trade shows that provide excellent opportunities to see mixer/scalars in operation, such as NAB 2001 in late April, and InfoComm 2001 in June. Some manufacturers will periodically take their mixer/scalars on the road for demonstrations and training — check with your local staging/rental house or professional AV dealer to see if such a demo is headed your way.