What is image capture?

ImageAdvantage Drawing as a design tool was explored in the July/August issue of Landscape Architecture. Superb renderings conveyed the power of the hand-drawn sketch and drew attention to the skills of a successful sketch artist. Computer graphics were shown to be less demanding of hand skills, but they required more of the viewer for inte1pretation. The following article presents a middle ground that combines artistry and technology to create realistic, full-color scenes of proposed developments. blend of video technology and computer graphics has created a new technique that allows the designer to work directly with a realistic image "captured" from video tape . Powerful computer software edits the image , adding new items or removing unwanted ones . While traditional artwork and photographs are easily used in small group presentations, reproduction and distribution costs reduce their usefulness for broader public viewing . "Image editing" offers a major advantage to those simulating future developments , large or small , for presentation to public audiences. Images in video format are in a medium familiar to most American television viewers and can be broadcast through cable TV networks , enabling more people to become involved in the decision-making process. Beyond producing good quality , realistic simulations, the format offers extensive possibilities: Simply videotaping the output images and incorporating them into site analysis video footage will be a powerful tool. " Slide-show " programs can display images from the microcomputer memory , dissolving from one image to the next in various dramatic ways. Complete images can be transmitted by modem or telephone line to remote sites almost instantaneously . In the early sketch stage of a project as well as in the production of presentation-quality imagery , the speed and ease of this technique will make it possible to readily test different designs and assess their visual impact. Traditional rendering and photomontage techniques are time-consuming and depend on highly skilled illustrators to achieve a realistic level of detail . Video is a more "forgiving" medium : Although TV images are inherently less sharply detailed than artwork or photos , people tend to accept that deficiency. The lack of sharpness (resolution) in the captured image allows the editing to proceed faster in the knowledge that small errors in the final image will be less visible. Although the alternatives seem bewildering at first , one may set up a useful system for a relatively small capital investment. An office environment that uses computer-aided drafting (CAD) and has access to a good home video camera and video cassette recorder can choose from several alternatives in the $1500-5000

A

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price range. The more sophisticated editing systems are capable of almost overwhelming image manipulations .

What is image capture? Many practitioners are familiar with the business computer graphics of office managem ent software , and with computeraided drafting , in which a geometric database produces construction document ation. In video image capture, the signal from a video camera or video recorder is processed to create a photographlike image on the computer display screen. Unlike business or drafting graphics, in which the screen image represents information within a computer database , the database of the captured image is merely a record of which color to assign to each picture element (pixel). Parts of the screen image can be " painted " over or " pasted " over, but the image cannot be adjusted to give the view from a new position. Once an image is captured , " paint " computer programs offer a wide range of editing capabilities. Programs such as Macpaintrn or PC-paint allow the designer to draw on the computer screen with different brush widths in a broad range of tones or colors; parts of an image may be moved from one part of the screen to another . More sophisticated programs have more extensive editing function s. Images can be stored in files and retrieved for insertion into the screen images; for example , images of trees might be selected from a file, changed in size and moved around the screen until a suitable place is found for " pasting " them down . Other functions then blend these tree images into the background screen image . Many output formats are available for the resulting images . Hard copy of the screen image can be obtained through a dot matrix or ink jet printer . Presentation video tapes can be made from some image capture systems that allow the audience to see the same image that the designer worked on . Color photographs can be made from the computer screen , although this approach requires a high-quality image capture system. The technique described here does not replace the traditional visualization skills of the landscape designer , but rather uses many of the same skills through a powerful simulation tool that provides highly realistic images in a medium more familiar to the public . The potential interface with optical disk technology gives a taste for the future of image capture and manipulation for environmental simulation. With the ability to store more than 50,000 images on a single disk , it will be possible to allow viewers to " walk through " simulations of new environments. The power of this technique to improve communication and its potential for reducing the costs involved in making presentation

ComputerVisualSimulations

Fanciful bean.field shows how paint functions can be used for simple sketching (wire frame building) or sophisticated modellin g (drums), using perspective and shading functions. All images in this article were captured from projected color slides, using a Canon VC-30 home video camera. Author Brian Orland and Gary Clay made the illustrations with an IBM PC-AT computer, AT&T Truevision"' image capture board and processing software. For magazine reproduction, color slides were taken of the actual computer screen, beautifully illustrating that video is, indeed, the best method of output.

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Images and elements are stored, retrieved and remixed to suit the needs of depiction. Left , Epcot comes to Blenheim in a triplet of images: (]) original image of the China Pavillion at Florida 's Epcot Center; (2) John limbrugh 's bridge at Blenheim Palace; and (3) the unlikely but easily simulated merge,: simulations ensures that this technique will soon be part of many professional practices.

A cautionary note Although a fairly recent development in the microcomputing area , image editing is an extension of the commercial and industrial computer graphics used in popular movies or in modelling new automobiles. With this background , capture and editing systems vary widely in ease of operation, speed of operation , quality of output and output media supported. They also vary in their usefulness for landscape architects. It is not easy to buy a complete system "off the shelf." Assembling a hybrid system of video and computer technologies is complicated, and few suppliers will be able to give you the full story. The following guidelines are intended to help you ask the right questions along the way.

Components The image source for most users will be either live video from a camera or the output from a video recorder ; other source s might include telephone line transmissions of images from users at distant locations or the output from video disc players. The first system component is a converter/digitizer, which takes the composite video input from a home video source and processes the signal to create a digital image for display by the computer. The next system component is the paint /edit computer program. Editing functions are analogous to the familiar cut-and-paste process : Portions of an image can be selected by the program and then moved to new positions . Other " part-images 'c__portions of other captured images or artwork produced by a paint program-can be retrieved from memory and overlaid on the screen image . Paint functions match the techniques of graphic art , but also have many special effects that are peculiar to the computer art environment. All of these techniques are used to directly alter the screen image . The final part of the system is an encoder and digital-to-analog converter, if domestic-quality video or video tape is the desired output. The options for hard copy at this time include a screen "dump ," which prints the screen image throu gh a dot matri x printer. Color slides can be photographed from the computer screen , but most users will find video tape the easiest and most logical output format.

Choosing a system Many of the available systems were not designed for the goals of the landscape architect, so there are critical decisions to be made to ensure system compatibility and utility . There are two major

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OUTPUT

Image Editing System- Main Components INPUT

Video

~~~~~~~~Rec~·or~cler~

Video Camera

Converter

Digitizer

-

Comput er Display

TV rvlonitor

Video Recorder

or Disc Player

Editing and Paint

Progn1111s

differences between the electronics of home video and those of the computer: the form of signal that creates the display, and the way color signals are handled. Television signals are analog in form; i.e. while a stream of electrons scans back and forth across the screen, the intensity of the beam is changed up and down to create a picture of many horizontal lines with dark and light patches of various lengths. In contrast , the computer displays a digital image. Instead of scanning lines, the computer divides the picture into many tiny rectangular pixels. Each pixel has an assigned color according to a numeric (digital) code and is addressed individually in creating a complete picture. The computer cannot process analog signals, so it is essential to have the digitizing process, which changes the analog video signal to a digital signal. The second major consideration is the type of color signal available. Color is produced on the TV or computer screen by mixing together red , green and blue images. The three images are produced by electron guns energizing three types of sensitive phosphors. Black images occur when all guns are off, white when all are fully on. Studio-quality video cameras produce separate red, green and blue (RGB) signals, which can be digitized to give digital information for each of the three color guns in the computer display. However, home video equipment uses a composite of red, green, blue and synchronization signals for its operation . Before digitizing can take place, this composite video signal must be "converted ," breaking out the individual red, green and blue signals. After image editing, the digital RGB must be converted and encoded back to an analog composite video signal for display on a television. Each of these processes entails a small but distinct loss in image quality.

The image source The quality of the output image inevitably depends on the quality of the input. Acceptable results can be obtained with a good home video camera and/or video recorder, but better cameras and recorders improve image quality substantially. Home color video cameras have a rather low resolution : They scan a full picture in only 200-250 horizontal lines, so a lot of detail and sharpness are lost. Higher resolution cameras are available (600- 800 lines) at a much higher price . Better quality color signals are obtained from broadcast-specification cameras that provide separate RGB and synchroniz ation channels. The preferred broadcast specification signal is NTSC RS1170A. Home video cameras are mostly Beta format , VHS or, more recently, 8mm. While appropriate to their original purpose , they are not ideal for image capture. Capture systems that require

more than ~o of a second to load an image into the computer need a stable, stationary video source . Home video recorders do not have adequate freeze-frame facility. Only large-format (% or 1 inch) video tape equipment can achieve a still frame free of interference . For important contracts, then, it might be worthwhile to subcontract for broadcast-quality, large-format taping of chosen images. Beyond this, sophisticated film-chain and laser scanning devices can produce extremely high-quality imagesfor an equally high price. High-resolution black and white cameras cost much less than their color counterparts. Under some circumstances, color images can be obtained with a black and white camera . With the use of a flat-field lens, other potentially useful functions (e.g. document capture) might be achieved , with the resolution of the computer's graphics display card determining final image quality.

Color/converter digitizer This is the most complex stage in the capture and editing process . Although complete "turn-key" systems are available, there are many combinations of pieces that can achieve similar ends : 1. Color converter: It may be a stand-alone piece of hardware with color controls built in, or may be an integral part of an image-capture board, which uses software controls for color balance, brightness and contrast. For work with home video color cameras, this item is essential. 2. Graphics controller board: The heart of any computer graphics system, it determines the resolution and color palette available on the screen display. Those already using drafting software will have made a sizeable investment in sophisticated graphic controller boards , so it will probably be more economical for them to design a capture system that uses the same board . However, greater versatility may be gained by using a package in which the graphics controller is an integral part of the image capture board. 3. Digitizer-image capture board: Again , there are many options available, ranging from inexpensive " 1-bit" devices that give two colors or levels of intensity (e.g. black and white) , to "24-bit " boards that give 250,000 color displays. The digitizing process breaks the scene into numerous pixels and assigns each one a digital code that describes its color and brightness . These codes are interpreted by the computer to create a screen image. Editing involves changing the digital descriptions of groups of pixels, which will then be displayed as view colors . Speed of capture, storage-in -memory requirements and realism of color display should be evaluated. A digitized video image represents a tremendous amount of information. Each pixel is

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Central Park is "cleaned up and improved" by removing the New York skyline and introducing the Column of Victory from Blenheim Palace.

described in terms of the individual intensities of red , green and blue that make its final color. Since display resolution (set by the choice of graphics controller board) will be from 256x256 pixels to 1024x l024 pixels or more; and since each pixel may be defined by as many as 24 bits of information, processing may take a long time. Some image capture devices take several seconds to " load" the image onto the board , but other designs take }'30 of a second or less. If the intention is to capture live or video-taped images, this instant "snap " ability is desirable. If the intended application is to use video of hard copy (e.g. photos), then a long scanning time is acceptable. For relatively inexpensive but high-resolution capture of color photo images , a good quality black and white camera can be used with red , green and blue photographic-quality filters to load three separate color images , which are recombined on the graphics controller board. A second consequence of the high information content of captured images is the amount of computer storage required if images must be saved to memory . For example, a 672 pixel x480 pixel x 8 bit (256 colors) image will occupy more than 300,000 bytes of memory. A double-density 5 'A-inch floppy disk will hold just one image. Even a IO-megabyte hard disk has space for fewer than 30 images. Many boards can "compress " the memory size for storage purposes , but the restoration to display size inevitably loses some quality . Most boards have composite video outputs that allow storage of completed images to video tape, but the higher the quality of image, the fewer working images can be held in the microcomputer memory . High-quality black and white images are relatively easy to achieve and are smaller to handle in memory. An image with 64 levels of gray (6-bit) achieves a high level of realism within the limitations of black and white. Realistic color is harder to attain . Although 256 colors displayable at one time (8-bit) seems to be a working minimum , there are microcomputer-based systems that display over one million colors simultaneously . 4. Genlock: This feature locks the synchronization of an image capture device to that of a live video input (i.e. camera or VCR). It is standard for " instantaneou s" systems. If video output to a VCR or into a broadcast environment is anticipated, genlock is needed to synchronize the image capture device to the output signal.

Edit and paint programs Most computer graphics users are familiar with paint programs and their capabilities. Many are available as free or nearly free add-ons with the purchase of color graphics controller boards . I. Color palette and color mapping: As already noted , the realism of a color image is related to the number of colors that

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can be displayed at any one time: As a rule , 256 is a workable minimum. A 256 color range is available with eight bits per pixel; typically three red , three green and two blue . An advanced microcomputer-based color graphics system may be able to display as many as 32,768 colors simultaneously-a 15-bit image. Most color graphics controllers used with computer-aided drafting tools can display 256 colors , but there may be serious limitations for image capture and editing. If the 256 available colors were "spread " to cover the range of hues, saturation and brightness levels available in nature-the "steps" between colorswould be noticeable . A displayed image using a relatively small part of the 256-color range would have a posterlike appearance . To approach realism, images are generally "color-mapped" ; i.e. the input image is mapped to 256 colors from a much larger palette. These 256 colors are then the colors of the image itself and the "steps" between colors can be much smaller . A scene in bright greens and blues will have few reds , few low-saturation colors, and few low-brightness colors in the palette. The problem is that additions , whether " pasted-in" or "printed-in ," cannot use colors outside the image palette . A garish circus tent , for example , could not be added to a subtle , moody forest scene. An image capture system based on a separate graphics controller board may suffer from this limitation , but systems with integral controllers and systems sold as stand-alone units will not generally be so limited. 2. Overlay/underlay: For editing flexibility, it is desirable to combine a partial image with a "context" image. A system may store partial images that can be overlaid onto the screen image, or a newly edited partial image might be underlaid by a context image from memory. In both cases the range of manipulations available should include changes in size, angle, mirroring and color adjustments . However, the critical consideration will be background transparency. If a potential insertion is cut from a scene it is usually as a rectangular block . When the required subject matter is not rectangular, there will be some excess background. This background can easily be erased , but in overlay operations it will require laborious color matching and filling-in. It is best to have a transparent overlay capability. 3. Blending and anti-aliasing: These are desirable features in a paint/editing system. Blending is analogous to smudging charcoal with the thumb. Given the jagged edges between an insertion and its background, blending averages the pixel colors across a narrow path to improve the appearance of one image fitting into the other . Anti-aliasing , a related function , reduces the stairstep effect seen on diagonal and curved lines by means of antialiasing algorithms, which smooth the lines by averaging with background colors.

Output devices Again , there are marked contrasts between the requirements of CAD systems and image capture systems. These devices must be chosen with regard to the previously discussed components. I. Monitors: If the large capture system uses a high-resolution color graphics controller that is already part of a CAD system, the output will usually be to an RGB digital monitor. Some controller /monitor combinations have limited color palettes (i.e . 16 colors) and are unsuitable for realistic color display. The output from most image editing systems requires the use of good quality composite video or RGB analog monitors, which can display an infinite range of colors. Several CV and RGB monitors with suitable inputs are sold to the domestic TV market. RGB monitors give much better color rendition and image sharpness , but it is necessary to check the compatibility of synchronization signal polarity with the image capture board. Most computer manufacturers in the United States use a positive-polarity sychronization signal, but at least one major importer uses a negative-polarity signal, which requries an expensive connector. Domestic color TV sets will work if an RF modulator is used between capture board output and TV. RGB digital monitors , i.e. IBM Graphics Monitor, cannot be used unless the graphics controller is enhanced to support digital displays. Compatibility and performance should be tested before settling on a final configuration. 2. Video tape: Most image capture devices will also encode the digital display image into an analog signal that is displayed on an analog monitor. This signal can also be recorded with a video recorder, which will require a composite video input. In some cases it is possible to overlay titles and other graphics over live video for recording to video tape . Some devices can provide a broadcast-quality output. The requirements for this include the

ability to genlock to a studio synchronization signal and a signal quality of NTSC RSI 170A specification. 3. Permanent copy: In some instances a simple screen "dump" can provide an image by a dot matrix or inkjet printer. Color slides can be photographed directly from the monitor; attachments are available to shield out reflections on the monitor screen and to reduce the distortions of screen curvature. Several companies make cameras driven by the RGB output from the computer that are capable of achieving publication-quality hard copy. While new equipment is continually becoming available, here are some broad recommendations: I. The highest resolution color controller board is worth the expense. Anything less than a 512 X512 pixel display will probably soon seem a disappointingly low-quality image. 2. Aim for the widest range of colors that can be afforded, and be sure that they can be displayed simultaneously . A display image mapped to 256 colors chosen from the whole range will not allow enough flexibility in editing. 3. Try to buy an image capture device that will allow separate RGB inputs. High-quality portable video cameras can provide an RGB output and the increase in captured image quality that it allows. If our experience at the University of Illinois is typical , designing an image capture and editing system is alternately frustrating, bewildering and intensely annoying. However, the final product is very gratifying and seductive-it's hard to drag yourself away once you start editing. D

This project is supported in part by the Research Board and the Department of Landscape Architecture , University of Illinois. Special thanks to Gary Clay and Doug Youngs for their assistance .

A Partial List of Equipment and Suppliers Apple Macintosh

IBM-PC & Compatibles . . . . Chorus Data Systems P.O. Box 370 Me rrima ck, NH 03054

PC Eye'" & Imigit'"

AT&TTruevisionT"'. Image Capture Boa rd and Processing Software

. . . . . . . . . . . . . . . . . . . . . . . AT&T Consumer Produ cts 2002 Wellesley Blvd. Indianapolis, IN 46219

PC Vision® Fram e Grabber, Image Action'" Software and Image Process ing Boards Lumena T"Paint Software

....

Imaging Technology, Inc. 600 West Cummings Park Woburn , MA 01801

Macpainf )I.

. . . . . Apple Computer , Inc . 20525 Mariani Avenue Cupertino, CA 95014

Thunderscanrn, digitizing scanner

MacVisionn,

.

....

. ......

Thund erware, Inc. 2 1 Orinda Way Orinda , CA 94563 Koala Technologies 3100 Pmrick Henr y Drive Santa Clara, CA 95052

... Time Arts, Inc. 3436 Mendoc ino Avenue Santa Rosa, CA 95401

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