The following is a basic discussion about computer graphics as it relates to video and specifically as an introduction to the capabilities and requirements for Truevision products. What is the difference between my computer monitor and my television? There is a somewhat complex distinction between what appear to be similar technologies. In fact, about the only thing in common between a television and a computer monitor is the use of an electron beam used to excite the phosphors on the inside surface of a cathode ray tube. For the sake of simplicity, I have broken down this question into several related areas. VIDEO: A history of video begins with the advent of television. In the United States, the National Television System Committee (NTSC) set the standard for video transmission in the black and white past and we are still using the same narrow signal bandwidth to carry all video information. When color television was developed in the fifties, the industry wanted to maintain backwards compatibility so that the older black and white sets would still be able to read the signal. This resulted in an additional color channel modulated over the black and white original. Other countries have other standards, such as PAL and SECAM, but essentially all broadcast video in the world today consists of a medium resolution black and white image combined with minimal color information. It is our perceptions that fill in the missing information as to how things are supposed to look. A video signal contains color, brightness and timing information which is interpreted by the receiver to create an image. This strict standard is needed to ensure compatibility between the broadcasting source and the television receiver. A television signal is analog, meaning that it consists of a continuous, varying voltage to produce a theoretically infinite number of shades. Actually, due to the low resolution nature of video signals and technology, you never get to see any subtle hues or shading. The television industry has become very sophisticated in using the medium to look as good as possible. The composition, lighting and color choices are made with the limitations of video in mind and only when someone shows up on the Tonight Show wearing a herringbone jacket, which appears to vibrate, do the weaknesses of video become glaringly apparent. This is due to a trait shared among all video standards that describes how the electron beam "paints" the image on the screen called interlacing. That means that the beam scans down the screen hitting only every other line and then returns back to the top of the screen and fills in the missing lines. Thin horizontal lines will appear to jump as the beam hits and misses them as it scans the image. Each scan down the image is called a field, with the combined two fields making up one frame of video. When you hit the pause button on a 2-head VCR and the image is jumping around, it's because the play head of the VCR is stuck between fields. Video, like film, is actually made out of still frames passing by so fast that our eyes are fooled into thinking the motion is continuous. NTSC video displays 60 fields, or 30 frames, every second. An important consideration in the video market is the relative low cost required to build an interlaced monitor like your home television set. What is the difference between analog RGB and composite video? Consumer grade video cameras have a single tube or chip that receives and must separate all the colors presented to it. Industrial and professional cameras have separate elements for each shade of red, green and blue. This results in more information available for each color component and therefore a higher quality signal. Computer displays also have separate red, green, blue and sync wires contained in their cables. While RGB is the preferred method of creating and viewing images, because the separate components remain distinct resulting in a cleaner look, most video equipment works only with composite. Composite video, called RS170A by the NTSC, is a combined signal that holds luminance (brightness), chrominance (color) and timing (synchronization or sync) all in one signal. When all these components are combined, through a process called encoding, into a single signal, it is composite video. Remember, if you are working with computer video, the work you are creating that looks so good on your RGB display may look completely different once the signals have been encoded into composite. Another difference between most computer displays and NTSC video is the subject of aspect ratios that will be discussed later. One improvement in video standards is the relatively new standard S-VHS. It provides separate signals for color and brightness, and so provides a better quality than RS170A composite, which rolls everything into one. COMPUTER DISPLAYS: Since computer displays are not tied to any 50 year old specification as to how fast and frequently they refresh the screen, they can exceed the video standard of 60 fields per second (60Hz) and 525 lines for the sharp presentation of text and graphics. The only standards in the PC industry are those that have been traditionally passed down from IBM and Apple. Most importantly, computer displays are non-interlaced, meaning that each pass down the cathode ray tube in the monitor, they hit every line and start the process again from the top. The faster the scanning, the more stable the image appears, and the more lines to be scanned, the sharper the image. Non-interlaced displays are more expensive to produce but have a much sharper appearance. The increased screen resolution of new standards means different screen descriptions and pushed monitor technology to accept higher and higher frequencies. The state of evolving computer display technology makes buying a multiscanning monitor a necessity to keep up with the latest video cards. When the IBM PC was first introduced, it was a monochrome system, and a low resolution one at that. It was a digital display, meaning that each picture element, or pixel, was either on or off. Strictly speaking, monochrome systems are only capable of displaying text. The display card manufacturer Hercules was the first to introduce a black and white graphics adapter. In 1984, IBM introduced their first color display called CGA (Color Graphics Adapter). Like the monochrome display it was digital and non-interlaced, but it was capable of 320 vertical lines by 200 horizontal resolution with 4 colors. When on, the pixels could be several different colors meaning that the video card's memory had to be large enough to "remember" and display the additional information. As we will see later, more colors and higher resolutions means that much more data the card's memory must contain and process. EGA (Extended Graphics Adapter), their next color standard ran at 640 x 350 with 16 possible colors. The next step up, VGA (Video Graphics Array), originally meant 16 colors at 640 x 480, although now with SuperVGA cards from a variety of manufacturers and IBM's own 8514/A, VGA now usually means at least 256 colors. The VGA resolution of 640 x 480 has also been pushed to 1024 x 768 and beyond, territory in the past that was reserved for high resolution CAD work stations. As the amount of on-screen information increases the display board must run at a faster speed to paint all the rows quickly enough to maintain stability. Many of the fastest boards available have an accelerator or graphics co-processing chip on board to keep this refresh level up and free the computer's CPU (Central Processing Unit) from performing such a mundane task. TRUEVISION: Truevision, formerly known as EPIC (Electronic Photography and Imaging Center), started producing graphics adapters for the young PC market in 1984. They began as an entrepreneurial subsidy of AT&T and, although they became a privately owned company in 1987, they still have access to AT&T technological resources. Their first two products were the ICB (Image Capture Board) and the VDA (Video Display Adapter), introduced when CGA and EGA were the only available color boards for the PC. The VDA was capable of displaying 256 colors at a resolution of 256 x 240. The ICB went further because, as it's name implies, it could do a real time capture of a video signal at the same low resolution, but with a palette of more than 30,000 colors. Here was an exciting product that allowed an interlaced signal to pass though the computer for capture or overlay of computer images. Since they were not compatible with any of the digital standards such as CGA or EGA, or existing software, Truevision stations took on their now familiar two monitor configuration. One display is the standard DOS system monitor, whether monochrome or color, and the other monitor was usually a NTSC frequency RGB (Red, Green, Blue) display cabled to the Truevision board. As you might imagine, although there wasn't even any specific software available yet for these products, the sight of thousands of colors on a PC display when 16 was the maximum was pretty impressive. The real problem was one of resolution and that would be addressed by their future products that will be discussed shortly. So even now we have a fixed, interlaced standard for video and an ever changing game of one upmanship among the manufacturers of displays cards that involve higher and higher non-interlaced frequencies to accommodate better resolution and image quality. The worldwide video community is still trying to decide upon a high definition video standard, but this will require a larger bandwidth to pass the additional information and specialized televisions to receive the new signal. Each country and company has what it thinks should be the new standard, while still providing backwards compatibility with the millions of existing television sets. Chances are that the adopted high definition standard will require some form of image compression to move the images. VGA/NTSC SIDEBAR: The term "multimedia" is defined in a thousand different ways. In my opinion, Apple's advertising people created a future market for something that didn't even exist at the time. On the PC side we have seen two converging technologies: VGA to NTSC devices and "high color" VGA cards. Ever since the dawn of computer displays, people wanted the ability to take what they saw on their monitor and dump it somehow to video. The proliferation of many animation programs available for the PC, such as Paul Mace's GRASP and Autodesk's Animator, has made this seemingly simple process even more attractive. In a simple sense, this technology has been with us for some time and the only device required was called a scan converter. This is the type of technology required to convert a European PAL video, which has more lines (625) and a slower refresh (50Hz) than NTSC. The drawback to scan converters is their price. A typical professional unit, capable of producing broadcast quality video, costs well in excess of $ 10,000, more than the price of most entire PC systems. Several hardware developers, such as Willow, USVideo and Jovian, produced VGA boards, add-in boards or external devices that would take the non-interlaced computer signal, slow it down and turn it into a RS170A compatible signal. Now, there are literally dozens of products like this on the market, providing different features and capabilities. Some offer a genlock ability, meaning that it can sync to an external video source for a more stable image and perhaps even combining some form of live video pass through or overlay features. Some can even do frame grabbing and digitizing although, unlike the Targa technology, they must do their capturing in a VGA compatible format, meaning a variable resolution, usually 320 x 200, with a maximum of 256 colors per "grab". I have seen several of these devices in action and have been underwhelmed. They may have some limited appeal, but the quality of the affordable units will not give most people the quality they expect. One thing to consider when attempting to convert computer graphics to video are the different aspect ratios of the different formats that I touched on before. Computer displays work in an underscan mode, meaning that they will show all the available information on your monitor. Television standard video works in overscan, in that it is designed to "bleed" off the edges of the television set, filling the entire screen edge to edge. More exciting for the VGA artist, in my opinion, is the new generation of "high color" VGA display boards. These sophisticated VGA cards have special circuitry, called RAMDAC, that greatly expands the number of displayable color from 256 to more than 60,000. This allows the computer to display nearly photorealistic images on a standard VGA monitor. Since VGA is an analog signal, like video, the monitor can display an infinite spectrum of colors, it is the card that determines the number of shades displayed. Since they do not yet effectively allow the images created to be sent out directly to video, I will return to the development of Truevision's product line: TRUEVISION TODAY: In 1985, only one year after introducing the ICB and VDA, Truevision came out with their Targa series of video graphics adapters. With four times the displayable resolution and up to 512 more available colors than the earlier boards, the Targa boards were the state of the art in color boards for the PC. The first Targa boards came in both underscan (512 x 400 displayable resolution) and overscan (512 x 482) versions. Since then, all new Truevision boards come with built in overscan capabilities. Two years later they followed with their ATVista series for true broadcast quality video. The company still aggressively develops new products that add more features, at lower prices, for all levels of PC computer artists. They have set the standard for others to follow with their NuVista Plus boards for the Apple Macintosh and the new family of Targa, the Plus series, which can operate at different resolutions and offers VGA pass through for a potential one monitor solution. They also have recently introduced their own VGA to NTSC board, the VideoVGA, and the 1024/32 color board for high end 32-bit desktop graphics. The Targa Plus and NuVista Plus boards produce RGB, composite and S-VHS signals internally. The ATVista series only outputs RGB and so requires an encoder. A quick course on color depth: I will be referring to color by describing the amount of color information that the particular Truevision frame buffer can contain and process. The terminology is to describe a file as either 16 or 32 bits deep. Actually, some of the bits are used for video imaging purposes only, so let me start by describing 15 and 24 bit color before addressing 16 and 32. A 15-bit image contains 5 bits of information for red, green and blue. A bit is either on or off, meaning that there are 2 to the fifth power of information possible for each color component. In other words, you can define 32 shades of red, green and blue for each individual pixel in your 15-bit image. More math will tell us that means a total of 32,768 possible combinations (32 x 32 x 32) or shades available, from a value of 0 red, 0 blue and 0 green, which is displayed as pure white, to 32 red, 32 green and 32 blue, which is completely black. Interestingly, 15-bit color can describe only 32 shades of gray. Since gray is composed of equal amounts of red, green and blue, there are only 32 available combinations with that ratio. 32,000 colors sounds like more than enough, but it's not: The human eye is capable of distinguishing more than 40,000 shades and so a 15-bit image appears slightly blotchy upon close inspection. When you have subtle shading, the colors tend to band or dither from one to the next. For low resolution video output this may be acceptable, usually it is not. This brings me to 24-bit color: With this expanded file type, we can now have 8 bits of information, or 256 possible shades, each for red, green and blue. That means each pixel could be any one of 16,777,216 distinct colors (256 x 256 x 256). Now we have a file that can be called "truecolor", meaning photographic quality. What about those additional bits that make a file 16 or 32-bits? Those are called alpha channel information and are only used with video. The alpha channel tells each pixel if it is on or off, meaning can live video pass through the frame buffer transparently or opaquely. The 16-bit image has 15 color bits and a 1-bit alpha channel, meaning that either that bit is on or off, live or not. The 8-bit alpha channel of the 32-bit image has 256 "shades" of on and off, giving the live video pass through many potential levels of transparency. Resolution: All the Truevision video boards can work in different resolutions, both interlaced and non-interlaced, but all are limited by the amount of VRAM they have on board. As a general rule, with a fixed video memory, it becomes a trade off between the amount of color information and physical resolution that the board can support. Obviously a 32-bit image carries more information per pixel than does a 16-bit image. Similarly, an entire image at high resolution contains more video information than a low resolution image. Time for more math: The equation for figuring out the file size at a specific resolution is the following: (Hs x Vs x Bp)/8 = file size, where Hs is horizontal size, Vs is vertical size and Bp is bits per pixel. We divide by eight to turn bits into bytes. Using that formula, we can see that a Targa 16 image at 512 x 486 NTSC resolution is ((512 x 486 x 16)/8) 497,664 bytes, or almost a half megabyte, in size. This fits neatly in the half meg of video memory on the Targa Plus 16. At the high end of the spectrum, a Vista board will go as high as 1024 x 768 x 32-bits for an image size of greater than three meg. The only board capable of displaying a file that large would be the 4Mb Vista. Of course a scanner can create a Targa file much larger than 3Mb, but the entire image wouldn't be viewable without specialized software. Before investing in a Truevision system, you should have a good idea of both your input and final output options. For the most part, inputing images into the Targa environment ranges in quality from scanning to video grabbing. With high resolution color scanners dropping in price, you could create images many megabytes in size, much larger than the frame buffer size of most Truevision boards. When grabbing from a video source, you are at the mercy of both the input quality from either tape or live camera and the capture resolution of your Truevision board. There are professional quality video cameras that will output a relatively high quality RGB signal for the frame buffer. This results in a better source input than sending in a composite signal that must be decoded (the opposite of encoding, decoding turns RS170A composite video back into RGB and sync information) for the frame buffer to accept. When outputing your images you can either create high resolution slides, variable resolution color or black and white prints or relatively low resolution video. Since we are used to the poor quality of television (most of the better TV sets are only capable of displaying 350 to 400 lines of resolution), people are not bothered by the low quality of video so long as it moves and looks good. Obviously a 512 or 756 line video image can't compete in quality with a 4,000 or 8,000 line 35mm slide for still images. Once you have decided upon your output requirements you can look at the software available for the Truevision file format. Since Truevision pioneered it in the early eighties, the Truevision .TGA Targa file format has become an industry standard, supported by hundreds of software titles for a variety of purposes, and compatible with almost any possible output device. The most common program would be "Paint" software, that would allow you to touch up acquired images or create your own artwork. These packages range in price and power from less than $ 500.00 to more than $ 2,000.00. TRUEVISION BOARDS: Targa Plus series: All share some features such as VGA pass through, RGB and composite output and input. Note that, while the 16/32 and 64 boards can display higher resolutions, they have an upper NTSC limit of 512 x 486 at 32-bits. They must be ordered as NTSC or PAL and offer a MCA (Microchannel) bus model. Targa Plus 16: has a .5Mb frame buffer of high speed video memory, or VRAM. Capable of grabbing and displaying a 16-bit image up to 512 x 486 NTSC resolution. This is a fairly limited board that replaces the original Targa 16 at a lower price. Targa Plus 16/32: With 1Mb VRAM, it can go up to 32-bits at 512 x 486. Targa Plus 64: 2Mb VRAM, capable again of 512 x 486 at 32-bits for video display. The 64 board allows for dual buffering, meaning that you can fade from two images that are in the board's memory at one time for some excellent video effects. This would be the premium Targa Plus board if you are planning to work extensively in video production. ATVista series also differ in the amount of on board video memory, either 1, 2 or 4Mb versions are available. The ATVista series differ from their Targa counterparts in that they do not have composite input or output. They also do not offer VGA pass through and are available only in ISA or Mac bus versions. They do not share the 512 line limit of the Targa series, meaning that, if their memory allows, they can go as high as 756 x 486 broadcast video resolution or even to 1024 x 768 if you aren't going out to video. The Vista is a programmable board with an on board video processor. Vista software tends to be higher priced than their Targa based counterparts and Vista systems are typically more hardware intensive as well. The NuVista Plus boards share the same programmability as their AT bus counterparts, except they have built-in encoding and decoding, like the Targas, so that they can directly accept composite video in and out. The VidI/O box is Truevision's standalone encoder/decoder box. It provides for RGB input, output, looping, composite and S-VHS in and out. Decoding, the reverse of encoding, turns a composite video source into separate RGB and Sync components to run into an ATVista for image grabbing. VideoVGA: A VGA to NTSC board that allows for overlaying VGA images or animations over a live video pass through. It can simultaneously output non-interlaced VGA and interlaced composite NTSC signals. 1024/32 board is an advanced, co-processed board for Windows and CAD applications. It works at 32-bits at resolutions up to 1024 x 768 at up to 76Hz for a stable, high resolution display. It also has on-board VGA and can run in standard NTSC and PAL modes. If you are looking to do true broadcast quality, the Vista is the board for you. Keep in mind that what separates true broadcast quality isn't always apparent to the untrained eye; sometimes the signals must be analyzed by an engineer through a scope to determine their true quality. Naturally, an encoder built into the Targa board can't hope to match the stringent specifications as to what constitutes broadcast quality like an external $ 5,000 professional encoder can do. The Targa, however, is well suited to all forms of industrial video applications. Generic Truevision configuration (s), excluding board and software: Computer: Minimum Recommended 386SX 20MHz 386/33 or better 4Mb RAM 8Mb RAM 80Mb fast hard drive 200Mb drive monochrome card VGA card monochrome monitor VGA monitor (**) mouse digitizing tablet 13" Long Persistence 19" Long Persistence Phosphor monitor (*) Phosphor monitor (**) Due to the potentially large image files, especially if you have access to a scanner, some form of removable mass storage is highly recommended. * The Targa Plus sends out both RGB and, due to the on board encoder, composite video signals. Therefore it would be possible to hook the Targa directly to a VCR or NTSC monitor that accepts composite. While this would provide you with a good idea of how your images will look if they are going out to video as your primary output medium, it will not give you a high quality interface to work from. Also, if you don't use a multiscan monitor, you will be limited to working at a fixed NTSC resolution. A quality display will greatly reduce eye fatigue and make you more happy and productive in the long run. ** The Targa Plus series can run what is called VGA pass through, meaning that you could have a one monitor solution if you already have a VGA card. Some software, however, requires a two monitor configuration and the only cost savings is that of the additional VGA display. To run the Targa Plus in an interlaced (video) mode, the Long Persistence monitor is required to reduce the amount of flicker. Also, be warned if you want to try running a single monitor with the VGA pass through: Truevision obviously can't test compatibility between the Targa and every VGA card to hit the market. There are some VGA adapters that will not function properly in this configuration. We have noted this problem with the higher end cards, especially those using the Tseng chip set. Some application notes: Video pass through: This technique of combining video with computer graphics can be accomplished in two ways: Overlay and Chroma Key. Overlay takes advantage of the alpha channel and allows live video to literally pass through the frame buffer. Chromakeying is the process that puts the television weatherman in front of the map. It involves a screen behind the subject that is a consistent color, usually blue or green so it won't interfere with flesh tones. When the image passes through the frame buffer, the key color is stripped out electronically and is replaced by the computer generated graphic. Sometimes you may have noticed, if he is wearing a blue tie, you can see the map through the weatherman. A word about 3-D animation. Some people are convinced that 3-D is the ultimate combination of computer imaging and video. While this may be true, they may not have a full understanding of how complex it is to lay down rendered images to tape so that they appear in continuous motion. As we have calculated, a broadcast quality Vista frame at 756 x 486 x 32-bits can yield a file 1.469664Mb in size. Obviously, unless you have an enormous RAM drive, your hard drive won't be capable of displaying files that large at 30 images per second for video output. Additionally, depending on your choice of 3-D animation software and the complexity of the scene, each image may take many minutes to fully render, especially if the PC calculates shadows, texture maps, reflections and the like. Therefore you will need an animation controller that will interface between the PC and your frame by frame editing VCR. Essentially, the controller holds the video tape at a specific frame until the PC is done rendering an image, it then tells the deck to record that image and then wait for the next one. This can be a time consuming process, as well as an expensive one: an animation controller costs a few thousand and a broadcast quality deck many times more. Additionally, you may require one or more of the following pieces of video equipment: A Time Base Corrector, a Sync Generator and encoder. Some of the more expensive pieces may be rented until they can be cost justified. Kevin Freeman