Computer Graphics Primer
T. C. O'Haver, University of Maryland, revised Spring 1996.
The language of chemistry has always involved graphical representations of structures, data and concepts. Early computers, however, were largely text-oriented, and it has only been since the mid 1980s that personal computer and software with standardized and convenient graphics capabilities has been available. The appearance of specialized graphics programs for scientific work, such a chemical structure drawing tools, scientific data plotting programs, and mathematical equation editors, has greatly enhanced the utility of the personal computer as an everyday tool of chemists and chemical educators. It is now commonplace for instructors to use computers as tools for the preparation of graphic images for incorporation into printed papers, exams, handouts, etc., or for class presentation by slide or overhead projection.
Working with graphics on a computer has been greatly simplified in recent years by graphical user environments such as Microsoft Windows and the Macintosh. Rather than having separate text and graphics screens and modes like earlier systems, these modern user environments dispense with the text screen altogether and display everything in "graphics mode", thereby allowing all of the typographic conventions and embedded graphical structures of chemical writing to be expressed freely on the computer screen and on the print-out.
Vector vs. raster graphics
In dealing with computer graphics it is important to understand that there are basically two fundamentally different kinds of computer graphics: vector and raster. A vector graphic is a symbolic table listing the positions, sizes, and colors of lines, squares, circles, and other graphical objects; it is basically a list of instructions for re-creating the image. A raster graphic, on the other hand, is simply a rectangular "bit map": a grid of dots (pixels or "picture elements"), each one with a specified color (black, white, or a color). These represent two different metaphors for computer drawing. In vector-based drawing the metaphor is that of the collage of graphic objects (lines, shapes, text, etc) that are created, changed, moved, and deleted individually. In raster-based drawing the metaphor is that of the tile mosaic, where each tile (pixel) can be manipulated individually. A somewhat different set of drawing tools are used in vector drawing and in raster drawing: raster programs are provided with tools that can manipulate individual pixels, whereas in a vector program, entire objects can be edited, moved and deleted as a unit, but individual pixels can not be edited individually because the pixels exist only on the screen or on the printout, not in the graphic file itself. It is not a matter of one drawing metaphor being "better" than the other; both types coexist because they each have their place.
In general, the graphics programs most widely used by chemists produce vector graphics; examples include chemistry structure drawing programs (e.g., ChemDraw, ChemWindow), molecular modeling programs (e.g., Chem3D, HyperChem), equation formaters (e.g., MathType), data plotters (e.g., Cricket Graph, SigmaPlot, and many others), spreadsheets (e.g., Lotus, Excel, Quattro, Wingz), general-purpose math programs and equation solvers (e.g., Mathematica, Maple, MatLab, MathCAD, TK Solver) and CAD programs (e.g., AutoCAD). On the other hand, scanners, video digitizers, "paint" programs (e.g. MacPaint, the Paintbrush program in Windows, and the drawing tools in HyperCard), and data visualization programs (e.g. NIH Image) produce raster graphics. Some drawing programs have both vector and raster layers (e.g. Canvas, CorelDraw).
An image of real-world objects, such as a digitized photograph or a digital video, can only be represented as a raster image, but a line drawing could be represented either as a vector or as a raster graphic. Consider, for example, a graphic consisting of a single black open circle on a white background. This could be represented in vector form as a list of numbers specifying the type of object (circle), the coordinates of its center, the radius, and the color and thickness of the line forming the circle. In a raster file, this graphic would simply be a circular arrangement of black pixels on a background of white pixels. Modern computer screens are raster devices. Therefore when a vector graphic is displayed on the computer's screen, it is displayed as a raster image at the resolution of the screen. If we were to compare our vector circle to a same-sized raster circle, they would look identical on the screen. So what's the difference?
1. The two graphics would look different on a hard-copy printout. All commonly used computer printers (e.g. dot matrix, inkjet, and laser printers) are raster devices (in contrast to a plotter, for example, which is a vector device). Printers usually have much higher resolution that computer screens; for example, common laser printers have a resolution of 300 dots per inch, whereas a PC in 16-color VGA mode or a Macintosh has a screen resolution of about 75 dots per inch. When a vector graphic is printed out, it is printed as a raster image the same overall size as the screen display, but at the resolution of the printer. The resulting image looks much smoother than the screen display. On the other hand, when a raster graphic is printed out on a 300 dot per inch laser printer, it has the same number of dots (pixels) as the screen image. In order to preserve the physical size of the graphic, each pixel is printed out as a block of several laser printer dots. As a result, it looks crude and blocky compared to the printout of the vector circle.
2. The file size of the two graphics are likely to be different. The raw data size of an uncompressed raster graphic file is directly proportional to its area but independent of its complexity, whereas the size of a vector graphic file is independent of its physical size on the printed page but related to the complexity of the graphic. Thus simple graphics are usually smaller in vector form than in raster form. On the other hand, a vector graphic must be re-drawn from scratch each time it is displayed, so that a complex graphic, e.g. a large three dimensional shaded molecular model, may take a long time to display, whereas complex raster images can be displayed more quickly.
3. Vector and raster graphics behave differently when they are enlarged or contracted. Using the example of the circle graphic, if we were to enlarge the graphic by selecting it and dragging its selection handle to stretch it out, we would see the raster image become crude and blocky as the pixels grow proportionally into large black square blocks. The vector image on the other hand would show a larger circle with more pixels along its circumference.
4. Text labels are handled differently. In a vector graphic, text is stored symbolically, so you can go back at any time and insert and delete parts, change the font, size and style, much like a word processor. In a raster graphic, the text is "degraded" into a bit-map, so to change it you have to erase it and type it over again.
Graphic file types
There are so many different file types used in computer graphics work that books have been published on the subject of converting graphic formats. Some file types are used only for raster (bit-map) graphics, such as the PCX, BMP, TIFF and the PAINT formats; some are used for vector graphics and text (Postscript, HPGL), and some formats can incorporate both vector and raster elements (e.g. PICT). Many formats are associated strongly with one particular hardware platform or operating system (e.g., PCX with DOS, BMP with Windows, PICT with Macintosh), but others are more platform-independent (TIFF, GIF, JPG, Postscript). Graphics programs can often read and save in more than one format. There are even some graphic file-exchange programs available whose purpose is simply to read and write many different graphic formats.
A widely used format for the the cross-platform porting of raster graphics is the GIF (Graphics Interchange Format), which was originally developed by Compuserve, a commercial on-line information service that serves users with many different computer platforms. GIF is a raster format that can handle black-and-white and color images, including digitized photographs, with up to 256 colors per image. Freeware and low cost GIF viewers and GIF converter programs (that can convert many other graphic formats into GIF) are available for every computer platform in common use.
Compression schemes: lossless vs lossy compression
Graphics files tend to be much larger than text files. For example, a full page of text takes up about 3,000 bytes (3 KBytes) of storage, but a full-page 6" X 8" graphic at 75 dots/inch (450 X 600 pixels) could take anywhere from 34 KBytes for a black-and-white drawing to 270 KBytes for a 256-color image. At 300 dots/inch, such a graphic would require 540 KBytes for a black-and-white drawing and 4.3 MBytes for a 256-color image! Clearly some method of compressing such large files is desirable. In fact, most computer file formats include some form of built-in file compression. There are basically two types of compression schemes: lossless and lossy. A lossless compression does not produce any degradation in the quality of the graphic, whereas a lossy scheme actually degrades the information content of the graphic, but in a way that is cleverly engineered so as to be minimally noticeable. As you might expect, lossy compression can be more efficient. GIF uses a lossless compression (based on the Lempel-Ziv method) that reduces the size of the file by an amount that depends on the complexity of the image: the simpler the image the greater the compression. This compression method depends upon the fact that in most drawings there are many rows of pixels that have exactly the same color, such as in the white background in a black-on-white line drawing. In practice, compression factors of 2 (for a 256-color digitized photograph) to 10 or more (for a simple line drawing) are achieved. Thus a simple line drawing (the most common type of graphic used in chemical publication) can be reduced to little more that the size of the same area of text. Digitized photographs and complex shaded color images remain a problem; the size of such graphics can be controlled by reducing their dimensions. A 2" X 3" 256-color digitized photograph, about the size of a small color picture in a newsmagazine article, would typically occupy about 20 KBytes as a GIF file.
Lossy compression schemes can reduce the sizes of digitized photographic images even more, yielding overall compression factors of 50 or 100 in some cases, depending on the amount of quality loss that is tolerable. JPEG (Joint Photographic Experts Group) is the most common lossy compression scheme for still photographic images. JPEG compression is based on a 2 dimensional discrete cosine Fourier transform. Essentially the idea is that the images is converted into a 2-dimensional Fourier transform and the higher harmonic frequency components (sharp fine structure) are represented with fewer bits, that is, at lower data resolution than the lower harmonics. The resulting truncation of data creates a quantization error, but mainly in those regions of the image that contain lots of fine structure, so it's not so noticeable.
Some but not all graphics viewers support JPEG. Macintosh's with the QuickTime system extension support JPEG compression and viewing of photographic images at the operating system level, which means that compressed images can be viewed within any conventional program that supports PICT graphics, such as word processors, database programs, multimedia presentation programs, or spreadsheets, even if they don't w support JPEG compression.
It is often necessary to import graphics produced by many different graphic-generating programs into one document for distribution or presentation. For example, a chemistry instructor might want to illustrate a word processor document or to embellish a hypertext tutorial with graphics from a chemistry structure drawing or molecular modeling program, equation formatter, data plotter, or spreadsheet. There are basically two ways to accomplish this: through a disk file or via the clipboard. Presentation programs, page layout (i.e. "desktop publishing") programs and some word processors have a command to "open" graphic disk files in one or more common file formats. The generating program must be able to save in one of those formats, or you must use a file format conversion program. Graphical user environments have introduced an alternative and sometimes more convenient way to accomplish this task, by using the "clipboard copy and paste" operations. The clipboard is temporary multiple-format storage area that exists on a plane above individual programs and can interpret and translate data between them. The clipboard allows various kinds of data, including text, graphics, and even digitized sound and video, to be transferred between different programs, even if the programs do not have have the ability to save and open graphic files directly. The generating program must have the ability to select the desired graphic and to transfer it to the clipboard (in either Microsoft Windows or on the Macintosh, this is done with the "Copy" command in the "Edit" menu), and the receiving program must have the ability to transfer the clipboard to the document at a specified location (this is done with the "Paste" command in the Edit menu). The advantages of the clipboard are that it avoids the necessity of creating and naming a separate graphic file and that it performs appropriate format conversions automatically. The clipboard and the copy and paste commands are almost universally implemented in all Microsoft Windows and Macintosh programs.
If the generating program has neither the ability to save a graphic as a file nor the ability to select and copy a graphic to the clipboard, it is still possible to use a "screen capture" program to capture an image of the displayed graphic. The disadvantage is that you get only a raster image at the resolution of the screen, and you can capture only what is shown on the screen. Screen capture programs operate as background tasks (TSR or RAM-resident programs in MS-DOS; "inits" on the Macintosh) that can be called up while running any program by pressing a special combination of keys. Screen capture programs are also useful for generating an exact image of the entire computer screen - complete with menu bar, pulled-down menus, dialog boxes, and the mouse pointer - for use in illustrating instruction manuals for software.
Page layout programs and word processors have the capability of changing the size of a graphic after it is pasted or placed into the document, by shrinking or stretching the image in the horizontal and vertical directions. This is done either by means of a command or by directly dragging the "selection handles" that appear on the border of the graphic when it is selected (clicked on). A raster graphic, e.g., from a paint program or a screen capture program, will look much better on the printout of a high-resolution (e.g. laser or inkjet) printer if it is reduced after importing. This is because the pixels of the image will be printed as smaller blocks of printer dots, resulting is an image that looks less "blocky" to the eye (although it still contains the same number of pixels as the original). If you are drawing a picture in a raster ("paint") program for later importing and printing, you should draw it as large as possible so you be able to reduce it after importing. (The best results are obtained when the reduction factor is integral multiple of the screen/printer resolution ratio - often 0.25 for 300 dpi laser printers). Avoid reducing a raster image in the generating program or enlarging it after importing; it makes the blockiness even more obvious. On the other hand, a vector graphic can be enlarged or reduced either in the generating program or after importing. However, it is still best to prepare a vector graphic at the desired final size in the generating program and not to re-size it after importing into the receiving program; this is because the alignment of text and graphics may be slightly effected by re-sizing, especially if your computer uses bit-map screen fonts rather than a scalable font technology.
The most common printers for graphics work are black-and-white dot matrix, ink jet, and laser printers. Ink jet and laser printers most commonly have a resolution of 300 or 600 dots/inch. These printers can also print continuous-tone black-and-white photographs and shaded images by using the "halftone" technique familiar in newspaper photographs. A halftone is a grid of variable-size black dots that makes it possible for a black-ink printer to approximate various shades of gray. On a computer printer, the variable-size black dots are formed from blocks of variable numbers of printer pixels. The problem is that the resolution of the image is degraded in the process. For example, on a 300 dot/inch printer, if you make the halftone dots from 5x5 blocks of printer pixels , you would get only 52 = 25 levels of gray and a halftone dot resolution of only 300/5 = 60 halftone dots/inch. This is a rather crude "newspaper quality" halftone. Substantially better halftone images can be obtained from 600 dot/inch laser printers, which now cost as little as $450.
Color printers are getting better and less expensive. In 1996 you can buy an ink jet color printer for $200-$600, a color thermal transfer printer for around $1000), and a color laser or dye sublimation printer for $3000 and up. Color printers use either three colors of ink or toner (the three primary colors) or four colors (the primary colors plus black). Intermediate colors are formed by blending the colors in a "dither" or halftone pattern, at the expense of reduced spacial resolution. Software drivers for color printers have many adjustments that determine the trade-off between output quality and printing speed. The printout quality of inkjet printers is particularly dependent on the type of paper used, because of the way the liquid ink behaves on the paper. For regular paper hardcopy, the best results are obtained with coated paper; for overheads, the best results are obtained with transparency material that is especially designed for inkjet printer; it is slightly roughened on the print side to hold the ink better. Inkjet and thermal printers can produce excellent color line drawings on paper or on transparency material, and with the proper printer driver settings and paper type, can do a good job on smoothly shaded graphics and continuous-tone digitized color photographs by utilizing dithering to simulate a wide range of colors colors. Dye sublimation printers are capable of really high-quality reproduction of color photographs, because the primary color dyes are smoothly blended together without visible dithering.
Photographic image capture
Hand-held or flat-bed scanners with a resolution of 300 dots/inch or better are now available at reasonable cost. Many are "8-bit" models that can register 256 shades of grey, good for scanning photographs. Color models are available but are more expensive and often much slower in operation. Scanners produce raster output only, and the software supplied with them can usually save images in a variety of raster file formats. Scanner software varies considerably in ease of use; Ofoto is one of the easiest, especially for beginners; it does automatic location, cropping, rotating, and exposure adjustment, making the process of obtaining a good scan almost completely automatic. Note that converting scanned text into an editable text or word processor file requires optical character recognition (OCR) software, which is available separately; OmniPage is one of the popular OCR programs.
An inexpensive way to capture color images is to use a video digitizer card ($300 - $1500) that plugs into you computer's bus and hooks up to an ordinary home video camera, camcorder, or VCR. The resolution is not so good as a flat-bed color scanner, but it is faster and cheaper if you already have a video camera. Popular low-cost video digitizer cards are the VideoSpigot (for Macintosh) and VideoBlaster and Snappy (for IBM-PC).
Kodak's PhotoCD system allows you to have your 35 mm still photographs processed digitally and returned to you on a compact disk (CD-ROM) that can be viewed on your TV with a special CD-ROM player or via your computer's CD-ROM drive. Special software allows the images to be saved as files in various formats and pasted into documents just like any other color raster graphic.
Digital cameras are also available that record still images in their built-in memory or on miniature disks for later transfer to a computer. Most are black and white only. Unfortunately, the cheap ones are not very good and the good ones are not cheap.
Making slides and transparencies from computer output
Usually the easiest way to make a high-quality black-and-white projectable still graphic from a computer output is to print an 8" X 10" overhead transparency on a laser printer. This way you get the finished product immediately. You need to use the right kind of transparency material; see your printer instructions. Not all color printers do a good job on transparency material; the quality of projection depends on the ability of the printed colored areas to transmit light without excessive diffusion or scattering. This depends on the surface smoothness of the printed areas of the transparency, which varies substantially with the type of printer and transparency material used.
A slide maker (film recorder) is a special peripheral that is used to prepare high-quality color slides of computer output; it is essentially a camera with a built-in color screen that has a resolution much higher than that of the computer's own monitor. These are relatively expensive devices, but they can produce slides of superb quality.
The cheapest way to make a moderate-quality 35 mm color slide of computer output is to photograph the computer's screen with ordinary color slide film (e.g. Kodachrome or Ektachrome). This obviously works only if the graphic fits on the screen. Put the camera on a tripod, set the shutter speed to 1 second or slower, set the exposure to manual, turn off the room lights, and adjust the exposure on a gray test graphic. You may have to bracket the exposure to get the best results. Ideally the results will look exactly like the computer screen display.
Dynamic animated and interactive graphics
In the case where it is possible for the audience to view or to interact with a live computer display, it is possible to go beyond the limitations of the printed page and to make use of the dynamic animation and interactive graphics capabilities of computers.
Most commercially available chemistry instructional software makes extensive use of animation and interactive graphics. Diatomic: Molecular Mechanics and Motion, by Brian P. Reid of Allegheny College (distributed by Trinity Software) shows a fascinating animation of the combined translational, rotational, and vibrational motions of a user-selected diatomic molecule as it flies around the screen "bouncing" off the edges of the screen. Inorganic Qualitative Analysis, by Joseph Crook of Western Washington University (distributed by Trinity Software) is an interactive simulation of a portion of the inorganic qualitative analysis scheme. Students are presented with an unknown (or "known" unknown), select from a list of standard reagents and unit operations (heat, centrifuge, decant, etc.), and observe the resulting reactions. The result of each step is displayed as an excellent quality 256-color digitized still photograph of the test tube and its contents. Teddy, an animated simulation of monoatomic gas kinetics developed at the Physics Department of the Technical University of Budapest (Hungary), effectively illustrates velocity distribution with and without mutual collisions, mixing of two types of particles, two peaked velocity distribution, entropy as the function of time at free expansion, simulation of a Maxwell demon, barometric distribution in a gravitational field, and barometric distribution for two types of particles. Interactive capabilities play an important role in molecular modeling programs such as Chem 3D and HyperChem. Models are constructed, rotated, and viewed by interactive direct manipulation of on-screen graphics.
It is now easier that ever for the individual instructor to create software with interactive graphics capabilities, without tedious programming. The introduction of "hypermedia" development systems such as HyperCard and ToolBook has been an empowering influence for many chemical educators. Some fine commercial software has been developed in this way. In SpectraDeck/SpectraBook, Paul Schatz of the University of Wisconsin makes extremely effective use of hypertext authoring tools (HyperCard for Macintosh and ToolBook for Windows) for teaching proton and carbon NMR, IR, and MS structure-spectra correlations. Richard A. Paseik of Humbolt State University used HyperCard to develop Atomic Orbitals (distributed by Falcon Software), an interactive hypermedia visualization of the shapes of atomic orbitals utilizing computer-generated 3D orbital shapes that the student can rotate, slice, and plot. Andrew F. Montana of the California State University at Fullerton used MicroMind's Director to develop Organic Reaction Mechanisms, which won the 1992 EDUCOM/CRYSTAL award for Best Chemistry program. This software allows students to interact with over forty animated sequences of important organic chemical reactions, observing changes in geometry, charge distribution and solvation in the reaction process. Graphs of potential energy vs. progress of reaction illustrate the changes in potential energy as the reaction animation proceeds.
Many examples of non-commercial courseware and tutorials written by individual chemistry instructors for their own use have been made available by the authors. Copies of these can be downloaded (transferred to your computer) from commercial information services and from several Internet archives. Some fine examples can be found on truth.chem.sfu.ca (in pub/chemcai and pub/chem1) and on archive.umich.edu (in mac/misc/chemistry).
Instructors should not overlook the possibility of using popular business, math and engineering productivity packages as instructional development tools. Spreadsheets, and math programs like Mathematica, MathCAD, and MatLab have considerable interactive graphical capabilities. Spreadsheets are not usually thought of as development tools, but the latest versions feature much easier scripting (macro) creation, hugely expanded graphical capabilities and many options for advanced end-user interaction. Wingz, for example, allows complete control of screen design and provides a full set of user-interface objects, such as pull-down and pop-up menus, scrolling text fields and list boxes, windows, buttons, number wheels, calibrated sliders, radio buttons, and check boxes. These objects can be placed directly on the worksheet or in dialog boxes that are called up by pull-down menu selection of from other dialog boxes. These capabilities allow the instructor to construct spreadsheet templates with an attractive interactive user interface that accepts and displays information, while the full power of the spreadsheet is performing calculations in the background.
One of the most interesting computer graphics developments in the early 1990's was the introduction of digital video. It has long been possible to display analog video from a tape deck or laser disk under computer control, either on a separate TV screen or in a window of the computer's regular color monitor. Many interesting educational applications have been made of this possibility: some excellent and well-known examples are Stan Smith and Loretta Jones' series of general chemistry tutorials and laboratory simulations that use video disk. However, this approach requires the addition of a video disk player, controller, and special video board to each computer, a substantial investment in an educational setting. Moreover, the production of a video disk can not be done casually; it requires the use of a professional service bureau. Both of these limitations are reduced by the use of digital video. In digital video, the video images and their sound tracks are digitized and stored on a disk just like any other data file. With the appropriate software, the digital video files can be played back in a window on the computer's color monitor, without any special hardware. This development greatly widens the market for video-based software because it lowers the entry barrier for consumers. Moreover, the production of original digital video material can be done with a conventional camcorder and a relatively low-cost video digitizer add-in board to interface the camera to the computer. Digital video is becoming another standard data type, joining the more familiar text, vector and raster graphics, and digitized sound. With the appropriate software, digital video can be edited, processed, archived, transferred over networks, cut-and-pasted, and integrated into all kinds of software and electronic documents. With currently available low-end computers, the frame rate and size of the movie are limited compared to analog video, but it is still adequate for many instructional purposes. At the current rapid rate of development of computer hardware, it will not be long before machines capable of displaying video at full screen and 30 frames per second are available at affordable prices. Sophisticated compression techniques are used to reduce the file size; nevertheless digital video files tend to be quite large. CD-ROM is the preferred distribution medium because of its large capacity and low media cost. Because digital video is stored on disk as ordinary binary files, it is in principle possible to distribute video-based materials over a high-speed network from a large, fast hard disk "video server", further reducing the cost per station.
At the present time, there are three competing digital video systems for microcomputers: Apple's QuickTime and QuickTime for Windows, IBM's PhotoMotion, and Microsoft's Video for Windows. An excellent example of the application of digital video to chemistry instruction is the Smith and Jones' Exploring Chemistry, distributed on CD-ROM by Falcon Software, which is available in both PC and Macintosh form. The only requirement for playback is a low-end PC clone with a hard disk and a VGA screen.
On the Macintosh platform, digital video is well integrated into the rest of the system and is well suited for production of original material as well as the play-back of material produced by others. (In fact, some IBM-PC multimedia developers produce their materials on the Macintosh first and then port it to the PC platform for distribution). The newest versions of some programs (e.g. Mathematica 2.0) can save animations as QuickTime movies. MacMolecule, a public domain molecular visualization program, can produce movies of rotating molecules that can be converted to QuickTime format. Movie clips can be copied and pasted just like any other data type. With either a Macintosh "AV" model, which has a built-in video digitizer, or an add-in third-party card (e,g, a SuperMac VideoSpigot card, about $300), live video and sound can be recorded from home video camera or VCR. You can tape images in the field with your camcorder and then capture them later by playing the tape back into the video digitizer. QuickTime movies can be displayed from within HyperCard, a popular medium for multimedia presentations and tutorials, and from the latest versions of presentation programs and word processors (WordPerfect, Microsoft Word 5.1), or over the Internet using Mosaic or Netscape. To see some chemistry animations done in this way, use Netscape to open http://www.ch.ic.ac.uk/chemical_mime.html (Hyperactive molecules using chemical MIME).
Where to find graphics software
Graphics software for microcomputers need not be expensive. There is a substantial selection of low-cost commercial packages, and many simple but useful graphics programs can be downloaded from the commercial online information services and from the major public network software archives. The following table lists some Web pages that contain some useful graphics-related files:
Graphics and electronic mail
One area where graphics has been slow to penetrate is telecommunications and wide-area networking. In recent years, some commercial online information services have provided graphically-oriented front-end software for their customers to make interaction with their services more convenient and attractive. For academic users, however, email systems are highly variable and mostly text-oriented. If you want to send a graphic file to another person via e-mail, you have to convert the graphic into text. Fortunately, there is a standard way to do this, using "UUencode/UUdecode" programs that are available for all common computer platforms. You use the UUencode program to encode the graphic into text and then send the resulting text via e-mail just like any other message. Then the receiving party must capture the text message and use the UUdecode program to decode the message back into a graphic file that can be opened up and viewed by means of a graphics program. If you use a platform independent graphic format such as GIF, you will be able to exchange graphics via e-mail between different computer platforms. In principle, it is possible to transfer digital data of any type in this way, including formatted word-processor documents, chemical structures, spreadsheets, executable binaries, stackware, etc. The exchange of non-text data by e-mail is greatly simplified by the development of "Multi-Media Mail" (MIME for short), an electronic mail specification that allows formatted text, graphics, sound, and even digital video to be included in mail messages.