Computer Graphics_Lec2

1-4 Computer Animation

Each of the photos in Fig. 1-30 represents one frame of an animation sequence. The glider in Fig. 1-30 (a) is moved slightly from one frame to the next to simulate motion about the room. Similarly, the compass in Fig. 1-30 (b) is displayed at a different position in each frame to simulate drawing of the curved line. Such frame techniques are used also in creating cartoons and science-fiction movies.

Each frame is drawn with a graphics system and recorded on film, with only slight changes in the positions of objects from one frame to the next. When the frames are displayed in rapid succession, we have an animated movie sequence. Figure 1-32 shows artists creating a cartoon frame, and Fig. 1-33 shows some scenes that were generated for the movie Star Trek—The Wrath of Khan.
Animation methods are also used in education, training, and research applications. Figure 1-34, for example, is an animated simulation for the Voyager space probe. Such simulations can be used to study the behavior of physical systems or as an aid to instruction. For some training applications, special systems are designed. Examples of such specialized systems are the simulators for training ship captains and aircraft
pilots. One type of aircraft simulator is shown in Fig. 1-35. Figures 1-36 through
1-38 show some scenes that can be presented to a pilot operating a flight simulator.
An output from an automobile-driving simulator is given in Fig. 1-39. This simulator is used to investigate the behavior of drivers in critical situations. The drivers reactions are then used as a basis for optimizing vehicle design to maximize traffic safety.

1-5 Graphical User Interfaces

Input options to many computer programs are designed as a set of icons, which are
graphic symbols that look like the processing option they are meant to represent. Users of such programs select processing options by pointing to the appropriate icon. The advantage of such systems is that the icons can take up less screen space than the corresponding textual description of the functions, and they can be understood more quickly if well designed.
Figure 1—40 illustrates typical icons used in word processing programs. In
these programs, the process for adding an item to a file is represented by a picture of a filing cabinet, a file drawer, or a file folder. Deleting a file can be represented by a wastebasket icon. A stop sign can stand for an exit operation, and a picture of a ruler can be used to adjust text margins. Icons can be useful in many applications.

1-6 Image Processing

The graphics technique used for producing visual displays from photographs or TV
scans is called image processing. Although computers are used with these displays,
image processing methods differ from conventional computer graphics methods. In
traditional computer graphics, a computer is used to create the picture. Image processing techniques, on the other hand, use a computer to digitize the shading
and color patterns from an already existing picture. This digitized information is
then transferred to the screen of a video monitor. Such methods are useful for viewing many systems or objects that we cannot see directly, such as TV scans from
spacecraft or views from the eye of an industrial robot. Figure 1—42 displays an
image-processed picture of one of the moons of the planet Jupiter.
Once a picture has been digitized, additional processing techniques can be applied to rearrange picture parts, to enhance color separations, or to improve the quality of shading. An example of the application of image processing methods to the enhancement of picture quality is shown in Fig. 1—43.
Image processing is used extensively in commercial art applications involving the retouching and rearranging of sections of photographs and other artwork. An image processing workstation for setting up advertising layouts is shown in Fig.
1-44. Medical applications make use of image processing techniques both for picture enhancements and in tomography. Figure 1-45 shows a cancer cell enhanced through image processing. Tomography is a technique of X-ray photography that allows cross-sectional views of physiological systems to be displayed. Both computed X-ray tomography (CT) and position emission tomography (PET) use projection methods to reconstruct cross sections from digital data.


An example of a CT scan is given in Fig. 1-46, while Figs. 1-47 and 1-48 show PET scans. These techniques are also used to monitor internal functions and show cross sections during surgery. Other medical imaging techniques include ultrasonics and nuclear medicine scanners. With ultrasonics, high-frequency sound waves, instead of X- rays, are used to generate digital data. Nuclear medicine scanners collect digital
data from radiation emitted from ingested radionuclides and plot color-coded images. Conventional graphics methods are also used in medical applications to model and study physical functions and in the design of artificial limbs.


Numerous other fields make use of imaging techniques to generate pictures and analyze collected data. Figure 1—49 shows satellite photos used to analyze terrain features, The display of Fig. 1-50 was used to discover an oil field in the North Sea.