Hands-on IMAGE EDITING by Barbara Robertson
DIGITAL VIDEOTo display 16 colors takes four bits per pixel; to display 256, eight per pixel; to get enough onscreen colors to simulate a landscape takes 15 to 24 bits per pixel which buys you 32,000 to 16 million colors. When these numbers are tied to onscreen resolution, imaging gets expensive and processing intensive.CAPTURE AND DISPLAYThe amount of processing power needed for a digital image is determined by resolution -- the number of pixels used in the onscreen mosaic -- and by color. The "depth" of each pixel, that is, how many bits of data are assigned to it, determines the number of colors available (with a few tricky exceptions to the rule). The more pixels and the more bits per pixel, the closer a digital image comes to reality.WHEN disparate technologies converge, opportunities arise for pioneering souls with the vision and resources to take advantage of the new, emerging medium. Recently, three areas of technology have been merging -- video, computer graphics, and publishing. While many people are aware of the revolution in computer-aided publishing, few know of the connection between video and computer graphics, and only a handful are aware of the connections being crafted among all three.Today, multiple forces from at least four sectors -- engineering, image processing (medical, seismic, military), publishing/printing, and the video industry -- are driving down the price of frame grabbers and frame buffers.Strictly black-and-white images like those on a Macintosh require relatively little image-processing power since each pixel can be only black or white -- which helps keep hardware costs low and the programming task relatively simple. But when each pixel can be numerous colors, imaging begins to get sophisticated.AT&T'S WONDER BOARDAT&T also sells a painting package, TIPS, developed by Island Graphics specifically for this board. Although other software companies offer painting packages for the TARGA 16, TIPS, expensive at $1250, is still the lowest priced and the best value.The machines used by people to create the most spectactular effects cost millions -- a Cray for last year's sexy robot in the can commercial and this year's Mick Jagger "Hard Woman" music video, several Ridges for the long-running "Entertainment Tonight" logo. And the companies which produce these effects charge thousands for the service. (A flying, three-dimensional logo such as those used to introduce TV sports and movies can cost $5,000 a second, for example.) However, the price of the technology used to create these effects is being driven down by market pressure, and along the way, some interesting products for personal computers have evolved.Colors are important not just for "matching" reality, but also for "antialiasing." Antialiasing smooths the jagged lines that square/rectangular pixels are doomed to create by using color shades to blend the stair steps into the background. It thus tricks the eye into believing the lines are straight.The digital world of computers crashed headlong into the analog world of video in the early 1980s. The results, seen nightly on network television by millions of people, include a variety of special effects: flying beer cans, racing razors, and other animated objects that populate TV commercials; three-dimensional, rotating logos; bizarre distortions of reality like Max Headroom; the flights of fantasy on MTV; and the less startling graphics used for news, sports, and weather. Yet, amazingly, the million-dollar hardware, software, and service industry that creates these video-graphics is less than three years old.Since videotape runs at 30 frames per second, in order to capture a frame in "real time," computer hardware must convert the incoming video image into a digital picture in one-thirtieth of a second. Computer graphics, boards that do this are called "frame grabbers." ("Image digitizers" such as MacVision and Thunderscan (WER #47, p. 40) also convert analog signals into digital pictures, but not in "real time.") The result is a digital image made up of a mosaic of pixels -- tiny onscreen squares (or rectangles). Graphics boards that hold digital images are called "frame buffers."But until recently, image digitizers available for microcomputers merely translated video images into monochrome digital pictures, and then "pseudocolored" the image using mathematical algorithms to replace shades of grey with colors -- usually displaying no more than 256 colors onscreen. The result could be bizarre -- if the same shade of grey, for example, appeared in a tree leaf and on a person's face, the computer might put spots on green on someone's cheek, or flesh tones in leaves. What's more, the image digitizers captured pictures slowly -- many took one to two seconds to scan an image, so any movement would significantly blur the result.For high-quality, full-page printed images, pictures need a minimum of 2048 x 2048 pixel resolution which translates to approximately 200 printed lines per inch for an 8" x 10" picture. (The smaller the printed image, the higher the printed resolution appears since the pixels are compressed into a smaller space). Imagine the processing power and programming sophistication required to manage more than four million pixels, each with a long tail of bits following behind. The cost is reflected in the price of all the components -- from the board itself, to monitors that can display the image, to software that works with it.Videographics exist largely because computers can now capture and hold images in semiconductor memory in real time. Once a picture is in digital form, the image can be easily modified -- cut and pasted and painted on, color corrected, merged with other pictures. The result can be put back onto videotape or printed. Indeed, nearly everything you see on television has passed through a digital "still store" system, and very expensive computer graphics systems have been developed that allow easy editing of these digital, moving video images. With these systems, artists can easily change the appearance of a person in a videotape, add people to a crowd scene, and change day into night through simple cut and paste and painting functions. The alternations to the original videotape cannot be detected.Although the ability to quickly edit a video sequence is not available on microcomputers yet, it is now possible to transfer a video picture into a computer and edit that one frame. This ability to alter real-life images has some interesting applications in the none-video world.About two years ago a small group of engineers organized as an entrepreneurial group under AT&T's wing opened their offices in AT&T's former House of the Future in Indianapolis, Indiana. Last year, the EPICenter (Electronic Picture and Imaging Center) introduced a bombshell -- the TARGA 16, a combination frame grabber and frame buffer that works on household IBM PCs and compatibles.The board is pricey, $2995, but it's unique -- the first, and still the only, graphics board in its price range for a microcomputer that 1) captures and digitizes video images in real time; 2) displays images with enough colors to simulate a video picture (32,768 colors) in video resolution (512 x 480) 3;) generates a standard NTSC video signal (which means TARGA pictures can be transferred to videotape and broadcast on American television); 4) allows an incoming analog video signal to be mixed onscreen with the digital picture (genlock).
AT&T also sells a painting package, TIPS, developed by Island Graphics specifically for this board. Although other software companies offer painting packages for the TARGA 16, TIPS, expensive at $1250, is still the lowest priced and the best value.
Author: Barbara Robertson
