CHEM 498C
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.
Importing graphics
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.
Printers
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.
Authoring systems
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.
Digital video
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:
http://www.public.iastate.edu/~stark/gutil_sv.html
http://www.mps.org/~ebennett/
http://www.cs.bgsu.edu/~jburns/gifs.html
http://www.yahoo.com/Computers/Multimedia/Pictures/
http://www.phoenix.net/~castlman/
http://photo2.si.edu/
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.