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Computer Graphics (COMP136) Quiz 7


This is a standard multiple choice test.  Each question has only one correct answer.  Please mark that one answer clearly on the answer sheet provided.  If any question ahs more than one answer filled in, it will be marked wrong.  There are 20 questions.  You will have 20 minutes.


1)      The following drawing illustrates which of the following?

A)    Interpolating curve

B)     Approximating curve

C)    Extrapolating curve

Use the following set of curves to match with the questions below.







                       (A)                                        (B)                                         (C)

2)      Which is an example of degree elevation? A

3)      Which is an example of deCasteljau subdivision? B

4)      Which is an example of a degree 2 curve? B

5)      Which of the following properties of rational Bezier curves fails if the weight assigned to a control point is negative? (P.S. The property missing below is Linear Independence of the control functions… FYI)

a)      Coordinate System Independence

b)      Convex-Hull

c)      Symmetry

d)      Variation Diminishing

e)      End-point interpolation

6)      Which of the following properties of Bezier curves guarantees that a line passes through the control polygon as many times or more times than the line passes through the Bezier curve itself?

a)      Coordinate System Independence

b)      Convex-Hull

c)      Symmetry

d)      Variation Diminishing

e)      End-point interpolation

7)      Which of the following properties of Bezier curves guarantees that any affine transform performed on the control points also directly applies to the curve itself?

a)      Coordinate System Independence

b)      Convex-Hull

c)      Symmetry

d)      Variation Diminishing

e)      End-point interpolation

8)      True or false.  The Bernstein polynomials as defined in class work for 2D Curves as well as 3D Curves.

a)      true

b)      false

9)      Which of the following parts of our Bezier curve discussion was compared to 3D projections onto a 2D plane?

a)      End point tangency

b)      deCasteljau subdivision

c)      Degree elevation

d)      Swept surfaces

e)      Rational Beziers (i.e. weights)

10)  When extracting surface locations of 3D Bezier surfaces, two techniques were presented: evaluation of the Bernstein polynomials and deCasteljau subdivision.  Which of those two allowed for easy and accurate solutions to the surface normal?

a)      Evaluation of the Bernstein polynomials

b)      deCasteljau subdivision

11)  Which of the following is a good use of Bezier volumes?

a)      Design of airplane wings

b)      Global Illumination rendering

c)      Free-form deformation

d)      Surface normal extraction

12)  If two Bezier curves meet at the same point as shown in the control polygons shown below, what is the MAXIMUM continuity they can have?  (NOTE the two edges that meet are not of the same length, but do have the same direction)

a)      C0

b)      C1

c)      C2

d)      G0

e)      G1


13)  True or false.  B-Splines are a way of creating sets of Bezier curves with a guaranteed continuity at their join points.

a)      true

b)      false

14)  Which of the following is considered the Father of Fractals?

a)      Lyle Ramshaw

b)      Benoit Mandelbrot

c)      Bernard Julia

d)      Ivan Sutherland

15)  In class, we discussed 3 forms of Fractals.  Which one required some randomness and several thousand loop executions to give a result?

a)      Non-linear fractals

b)      Iterated Function Systems

c)      L-Systems

16)  In class, we discussed 3 forms of Fractals.  Which one could be represented by strings with recursion rules?

a)      Non-linear fractals

b)      Iterated Function Systems

c)      L-Systems

17)  Which of the following fractals could have a fractal of degree 2.7?

a)      Koch Snowflake

b)      A sponge with infinite holes

c)      Serpinsky Gadget

d)      A fern with very high branching factor

18)  In class, two examples were shown of how to use sets of affine transforms to create complex seeming animations.  Which required glPushMatrix and glPopMatrix?

a)      the cars with wheels spinning around a globe

b)      the links of a chain swinging back and forth

19)  True or false.  When creating an animation of a person walking using sets of affine transforms the animator should set the cycle of the legs to a different control variable than the cycle for the arms.

a)      true

b)      false

20)  In class, we discussed physically-based simulation.  In order to maintain a simulation, a set of variables must be maintained called “state variables”.  State variables are those variables which must be maintained from one time-step to the next in a simulation to maintain correct simulation.  Of all of the following variables, only one is NOT a state variable.  Which is it?

a)      mass

b)      position

c)      velocity

d)      acceleration


What is the concept of positive and negative angles?


Angles are positive angles if the terminal ray rotates counterclockwise around the vertex from the initial ray . Angles are negative angles if the terminal ray rotates clockwise around the vertex from the initial ray


Give the concept for line at right angle?


The lines are said to be at right angles if the rotating half line (or ray) from starting from initial position to the final position describes one quarter of a circle.


What is Quadrant?


Let X'OX and Y'OY perpendicular coplanar lines intersecting each other at O. We refer X'OX as x-axis and Y'OY as y-axis. It is clear from the adjoining figure, that these two lines divide the plane into four equal parts, each part is called a Quadrant. The four Quadrants are: XOY - first Quadrant YOX' - second Quadrant X'OY' - third Quadrant Y'OX - fourth Quadrant


What Software packages are used to design "Room Layout Design and Architectural Simulations" as in e-handouts?


Following are some famous known applications used for this purpose: CAD system -> Designing and building then simulating layouts used mostly by builders, engineers etc 3D Studio Max -> Designing of 3D objects Maya -> Designing of 3D objects


I tried to run code given in Lecture 13 using DevC for Table drawing but both codes are not compiled?


This code is made using Borland Turbo C which will not run using other compilers or coding languages, but actual purpose of this code for you is to learn it by looking at how it works and map it into your own coding by what ever you are using as compiler. Or try to use turbo C to compile this code. Use this code as a learning tool pseudocode.


Explain Virtual Reality Systems?


Virtual Reality Systems present a computer-generated visual and auditory experience that allows a user to be immersed within a computer generated “ world ” for various purposes. Used in conjunction with traditional computer input systems this can be used, for example, as a powerful design tool allowing a user to see objects that he or she is designing. The application to entertainment or training simulation systems is equally useful as it allows for the creation of an infinite number of immersive environments to suit any need. The addition of haptic systems to virtual reality will greatly increase its effectiveness at simulating real-world situations. One example can potentially include a medical training system using a simulator and virtual reality where a haptic system provides doctors with the “feel” of virtual patients. Figure 1 shows the schematic of such a medical simulation system, the visual display and the haptic gloves are combined to simulate, in this example, an abdominal aortic aneurysm surgery.


What are the Working principles of Virtual Reality Systems?


The working principle of dielectric polymers can be summarized as follows: an elastomeric polymer film that acts as a capacitor is sandwiched between two compliant electrodes. Two effects occur simultaneously when an electric field is applied between the two electrodes. The polymer is stretched in surface and compressed in thickness during actuation. The change in thickness can be used for mechanical output. However, there is a need to stack many layers of dielectric films and electrodes to obtain large displacements. On the other hand, the area expansion can be used as another method for actuation. The reported strains obtained by pre-stretching the film are much larger than in thickness but a restoring force is required to ensure the desired boundary conditions on the film. This can be achieved either by using an antagonistic pair of actuators or return springs. The following section describes the design of some compliant frames used as a spring back force to generate a two-way actuator.


What is meant by stencil buffer?


A stencil buffer is an extra buffer, in addition to the color buffer (pixel buffer) and depth buffer (z-buffering) found on modern computer graphics hardware. The buffer is per pixel, and works on integer values, usually with a depth of one byte per pixel. The depth buffer and stencil buffer often share the same area in the RAM of the graphics hardware.


What is the logic behind fractal geometry using in computer science? If fractal is modern geometry than why we use euclidean geometry technique?


A fractal is generally "a rough or fragmented geometric shape that can be split into parts, each of which is (at least approximately) a reduced-size copy of the whole a property called self-similarity. The term was coined in 1975 and was derived from the Latin fractus meaning "broken" or "fractured." Fractal is modern geometry and uses of fractal often has the following features: • It has a fine structure at arbitrarily small scales. • It is too irregular to be easily described in traditional language. • It is self-similar (at least approximately or stochastically). • It has a Hausdorff dimension which is greater than its topological dimension (although this requirement is not met by space-filling curves such as the Hilbert curve). • It has a simple and recursive definition. Because they appear similar at all levels of magnification, fractals are often considered to be infinitely complex (in informal terms). Natural objects that approximate fractals to a degree include clouds, mountain ranges, lightning bolts, coastlines, and snow flakes. However, not all self-similar objects are fractal for example, the real line is formally self-similar but fails to have other fractal characteristics.


What is difference between quadratic and cubic parametric curves?


Quadratic parametric curves require three control point; whereas cubic curves requires four control points. 2. Obviously three control points can create less complex curves; therefore quadratic curves can have only one curvature because two control points represent the starting and ending point; whereas; third control point in between control the curvature of the curve


What is the main difference between Forward Scattering and Back Scattering?


Forward scattering is the normal scattering of light after interacting with any surface but back scattering results only when the surface is very rough and irregular so the light is reflected back in the direction it comes.


What is meant by Blending?


Blending means how much the background and foreground colors are mixed, for example if we set alpha value equal 100% than only front color is visible. What is perspective matrix? The perspective matrix is used to represent the actual point according to our monitor screen settings how we want to project that point on screen(perspective projection ).


What is Fudge Factor?


By fudge factor we mean the value that will solve our problem and will help us in avoiding calculations so the term of ambient light we use is fudge factor.


Please explain Radio-city Method?


Radio city method calculates the ambient light that will be emitted from different materials, using scientific calculations.


Explain about Attenuation Factor?


Attenuation factor mean's how much light is attenuated after covering a certain distance d, and it is given by the relation light intensity is directly proportional to 1/d2 meaning light decreases as distance increases.


Is Ambient in features are not prominent due to solid color?


Ambient light is due to atmosphere and we assume in most cases that certain value of ambient light is present in the scene because for every point its calculation consumes a lot of time and computational cost.


Please explain the Impressive and Interactive 3D Environment?


By 3D we mean actual real time environment around us as you know our monitor screen is 2D (Without Depth) but we have to draw on it pictures that are real word (3D) So we have to use different techniques to create pictures that look like 3D in 2D monitor screen.


If all value of rgb is maximum in positive then we get White in other hand if we get rgb values in negative maximum then we get Black Color. Please guide.


The basic idea is that white color reflects all rays on the other hand black color absorb all rays, now it once again depend on graphics package used as some packages treat white as maximum rgb value and some treat black as maximum rgb value. Maximum negative value is taken as minimum Maximum positive value is taken as maximum


If we get the r value in negative then only r gets the dark impact on the object others values g and b in positive and these values are not getting the dark impact on the object. Explain


Maximum negative value has lower value as compared to lesser negative value, also Red color is more prominent than Blue and Green.


Is 4 color Mode use in Printing and 3 color Mode use for Monitors or digital display?


No, infact it is based on our graphics rendering engine we are using for example open gl supports 4 color mode but there are other engines that don't support 4 color mode, it doesn't depend on the monitor or printer.


What exactly do we mean by pipeline clipping approach?


The basic concept here is that if we want to first check and than draw a polygon after clipping than the steps we take are: Check all the vertices of the polygon if they are inside of our clipping rectangle or not if they are out side than the intersection point in the path of that vertex is saved after all this we draw the polygon


What is the rastering and what is different b/w raster and rastering line?


Rasterization mean translating an image into pixels or raster lines. A Raster line is horizontal scan line which is used in filling algorithms. Triangle rasterization is related to scan line. And we fill the triangle using the scan lines (Raster line).


Why is the Bresenham's line drawing algorithm more efficient than the DDA line drawing algorithm?


Bresenham’s algorithm uses integer arithmetic whereas the DDA uses floating point arithmetic; and as you know floating point arithmetic is much slower than integer arithmetic that is why Bresenham’s algorithm is more efficient than DDA algorithm.


What is the difference between bitmap graphics & vector graphics?


In vector graphics we use lines ( In fact vectors) to represent and store images so they have smaller size, on the other hand in bitmap graphics we use pixels store and represent the image data.


What is meant by Resolution?


Resolution (In bits ) is No. of Horizontal pixels * No of Vertical pixels * No of bits used to represent per pixel.


What is the basic difference b/w Flat shading and Phong shading?


Flat shading produce shading in a flat manner (It produces constant shading everywhere on the object). In Phong shading we keep in mind the viewer position so in it the shading output produced is more natural and can represent shiny spots that are viewable from certain angles on reflecting object's surfaces.


How many colors are used in the image if N bits are required to store a pixel?


2n colors will be stored per pixel.


What is the difference between bitmap graphics & colored graphics?


Bitmaps graphics store per pixel information. How much is the per pixel image information depends upon the image type for example the black and white need only one bit per pixel while colored image need 8, 16,24 bits per pixel.


What are Evaluators?


Evaluators are used to compute points on a curve or surface. Using them we can draw curves or surfaces. One dimensional evaluators are used to draw Curves for example Bezier curve. Tow dimensional evaluators are used to draw Surfaces for example Bezier surface


Explain what are "FRACTALS" & also their use in computer graphics?


Fractals Fractal are geometric patterns that is repeated at ever smaller scales to produce irregular shapes and surfaces that can not be represented by classical geometry. Fractals are used in computer modeling of irregular patterns and structure in nature. Use of Fractals: Fractals are used to represent that kind of complex natural objects that can not be represented by ordinary classical geometry.


what is antialiasing?


Antialiasing is a technique for removing the non continuous irregular effects produced at the boundary (edges) of different shapes due to smaller resolutions (Big Pixel size) . In this technique we change the color of some pixels surrounding the shape boundary so that the image look more natural and real.


What is the opacity of the color?


Opacity Opaque objects does not allow the light to pass through them. For example Walls, Metals, Wood, and their this property is called opacity. Opacity and Transparency are converse to each other. Transparency is the measure of how much light that is passed through an object.


What is hue?


Hue is the measure of pureness of any color, and saturation is the measure (amount) of hue.


What is local and global co-ordinate system?


Every thing in the real world is represented by x, y, z Coordinates these are the global valus of these three variables. And within this world there are different objects that have their own dimensions along x, y, z these values are for that particular object and represent only that object are called local coordinates of that particular object.


How to improve performance of Bresenham line algorithms?


Several techniques can be used to improve the performance of line-drawing procedures. These are important because line drawing is one of the fundamental primitives used by most of the other rendering applications. An improvement in the speed of line-drawing will result in an overall improvement of most graphical applications. Removing procedure calls using macros or inline code can produce improvements. Unrolling loops also may produce longer pieces of code, but these may run faster. The use of separate x and y coordinates can be discarded in favour of direct frame buffer addressing.


What is the concept behind clipping?


It is desirable to restrict the effect of graphics primitives to a sub-region of the canvas, to protect other portions of the canvas. All primitives are clipped to the boundaries of this clipping rectangle; that is, primitives lying outside the clip rectangle are not drawn.


What do you know about clipping individual points?


If the x coordinate boundaries of the clipping rectangle are Xmin and Xmax, and the y coordinate boundaries are Ymin and Ymax, then the following inequalities must be satisfied for a point at (X,Y) to be inside the clipping rectangle: Xmin < X < Xmax and Ymin < Y < Ymax If any of the four inequalities does not hold, the point is outside the clipping rectangle.


What is clipping?


In rendering, clipping refers to an optimization where the computer only draws things that might be visible to the viewer.


What is the importance of Clipping in Games?


Good clipping strategy is important in the development of video games in order to maximize the game's frame rate and visual quality. Despite GPU chips that are faster every year, it remains computationally expensive to transform, texture, and shade polygons, especially with the multiple texture and shading passes common today. Hence, game developers must live within a certain "budget" of polygons that can be drawn each video frame.


How can Lights be understood in Computer Graphics?


In order to understand how an object's color is determined, you'll need to understand the parts that come into play to create the final color. First, you need a source of illumination, typically in the form of a light source in your scene. A light has the properties of color (an rgb value) and intensity. Typically, these are multiplied to give scaled rgb values. Lights can also have attenuation, which means that their intensity is a function of the distance from the light to the surface. Lights can additionally be given other properties such as a shape (e.g., spotlights) and position (local or directional), but that's more in the implementation rather than the math of lighting effects.


Why shaders have importance in 3D Computer Graphics?


One of the nice things about shaders is that you can create your own for whatever special effects you are looking for In fact, one of the reasons that shaders have finally made it into mainstream 3D computer graphics is the flexibility that they provide, which can finally be realized in real time on consumer grade hardware. Unfortunately, with power comes responsibility the responsibility to understand how lighting and shading in computer graphics is traditionally done and how you can do it yourself (or do it differently) in a shader. But first, you'll need an understanding of the mathematics behind lighting and shading.


What can be done using Shaders?


With shaders you can * Perform basic geometry transformations * Warp the geometry * Blend or skin geometry * Generate color information (specular and diffuse) * Tween vertices between transformation matrices * Generate texture coordinates * Transform texture coordinates * Size point sprites * Use a custom illumination model * Perform nonphotorealistic rendering * Perform bump, environment, and specular mapping * Perform your own texture-blending operations * Clip pixels In fact, your options are limited only by your ingenuity and the size of the shader buffer (which limits how complicated your shader can be).


What the term reflections on reflections represent?


The term reflection actually encompasses three entirely different types of optical phenomena. These three kinds of reflection are specular reflection (like a mirror), diffuse reflection (often called Lambertian) and reflexive reflection (or retro-reflection).


How can rendering be elaborated in 3D Computer Graphics?


Rendering is all about simulating the real world as much as possible. If you are rendering something sitting on your table, think about everything that is going on in the room. What is around the object? Where is the light coming from? Is there light coming from different places around the room? How bright is it? What color is the light? What do the shadows look like? What is reflecting in the object? What kinds of highlights are on the object? All of these things are the result of lighting and the environment. Novice users often don't take the time to consider these things and then try to replicate them. It's no wonder most beginners' renderings don't look very good.


What is Diffuse Reflection?


The ideal diffuse reflector (or Lambertian reflector): Incident light is reflected with equal intensity in all directions, regardless of viewing position. How much light is reflected depends on the “reflectiveness” of the surface. A highly reflective surface reflects most of the light.


What is Specular Reflection?


Specular reflection is for shiny objects In contrast to diffuse reflection, specular reflection is not constant at all angles from the surface.


What is Attenuation?


Attenuate means “to weaken”. Light loses energy as it travels further.


What is point?


Points are most often considered within the framework of Euclidean geometry, where they are one of the fundamental objects. Euclid originally defined the point vaguely, as "that which has no part". In two dimensional Euclidean space, a point is represented by an ordered pair (x,y) coordinates.


What is Circle?


A circle is a simple shape of Euclidean geometry consisting of those points in a plane which are the same distance from a given point called the centre. The common distance of the points of a circle from its center is called its radius.


What is Transformation?


In mathematics, a transformation could be any function mapping a set X on to another set or on to itself. However, often the set X has some additional algebraic or geometric structure and the term "transformation" refers to a function from X to itself which preserves this structure. Examples include linear transformations and affine transformations such as rotations, reflections and translations. These can be carried out in Euclidean space, particularly in dimensions 2 and 3. They are also operations that can be performed using linear algebra, and described explicitly using matrices.


What is 3D Computer Graphics?


3D computer graphics (in contrast to 2D computer graphics) are graphics that use a three-dimensional representation of geometric data (often Cartesian) that is stored in the computer for the purposes of performing calculations and rendering 2D images. Such images may be for later display or for real-time viewing.


What is curve?


In mathematics, a curve consists of the points through which a continuously moving point passes. This notion captures the intuitive idea of a geometrical one-dimensional object, which furthermore is connected in the sense of having no discontinuities or gaps. Simple examples include the sine wave as the basic curve underlying simple harmonic motion, and the parabola.


What is vector?


In elementary mathematics, physics, and engineering, a vector (sometimes called a geometric or spatial vector) is a geometric object that has both a magnitude (or length) and direction. A vector is frequently represented by a line segment with a definite direction, or graphically as an arrow, connecting an initial point A with a terminal point B.


What is OpenGL?


OpenGL(R) is the software interface for graphics hardware that allows graphics programmers to produce high-quality color images of 3D objects. OpenGL is a rendering only, vendor neutral API providing 2D and 3D graphics functions, including modelling, transformations, color, lighting, smooth shading, as well as advanced features like texture mapping, NURBS, fog, alpha blending and motion blur. OpenGL works in both immediate and retained (display list) graphics modes. OpenGL is window system and operating system independent. OpenGL has been integrated with Windows NT and with the X Window System under UNIX. Also, OpenGL is network transparent. A defined common extension to the X Window System allows an OpenGL client on one vendor's platform to run across a network to another vendor's OpenGL server.


What does the .gl or .GL file format have to do with OpenGL?


.gl files have nothing to do with OpenGL, but are sometimes confused with it. .gl is a file format for images, which has no relationship to IRIS GL or OpenGL.


What is the GLUT toolkit?


GLUT is a portable toolkit which performs window and event operations to support OpenGL rendering. GLUT version 2.0 has: o window functions, including multiple windows for OpenGL rendering o callback driven event processing o sophisticated input devices, including dials and buttons box, tablet, Spaceball(TM) o idle routines and timers o a simple cascading pop-up menu facility o routines to generate wire and solid objects o bitmap and stroke fonts o request and queries for multisample and stereo windows o OpenGL extension query support


What is GLUT?


GLUT is the OpenGL Utility Toolkit, a window system independent toolkit for writing OpenGL programs. It implements a simple windowing application programming interface (API) for OpenGL. GLUT makes it considerably easier to learn about and explore OpenGL Programming. Libraries that are modeled on the functionality of GLUT providing support for things like: windowing and events, user input, menuing, full screen rendering, performance timing


What is GLU?


GLU is the OpenGL Utility Library. This is a set of functions to create texture mipmaps from a base image, map coordinates between screen and object space, and draw quadric surfaces and NURBS.


What do I need to compile and run OpenGL programs?


The following applies specifically to C/C++ usage. To compile and link OpenGL programs, you'll need OpenGL header files and libraries. To run OpenGL programs you may need shared or dynamically loaded OpenGL libraries, or a vendor-specific OpenGL Installable Client Driver (ICD) specific to your device. Also, you may need include files and libraries for the GLU and GLUT libraries. Where you get these files and libraries will depend on which OpenGL system platform you're using. OpenG.org maintains a list of links to OpenGL Utility libraries. You can download most of what you need from there. Under Microsoft Windows 9x, NT, and 2000: If you're using Visual C++, your compiler comes with include files for OpenGL and GLU, as well as .lib files to link with. For GLUT, download these files. Install glut.h in your compiler's include directory, glut32.lib in your compiler's lib directory, and glut32.dll in your Windows system directory (c:\windows\system for Windows 9x, or c:\winnt\system32 for Windows NT/2000). In summary, a fully installed Windows OpenGL development environment will look like this: File Location [compiler]\include\gl gl.h glut.h glu.h [compiler]\lib Opengl32.lib glut32.lib glu32.lib [system] Opengl32.dll glut32.dll glu32.dll where [compiler] is your compiler directory (such as c:\Program Files\Microsoft Visual Studio\VC98) and [system] is your Windows 9x/NT/2000 system directory (such as c:\winnt\system32 or c:\windows\system).


What is GLUT? How is it different from OpenGL?


Because OpenGL doesn't provide routines for interfacing with a windowing system or input devices, an application must use a variety of other platform-specific routines for this purpose. The result is nonportable code. Furthermore, these platform-specific routines tend to be full-featured, which complicates construction of small programs and simple demos. GLUT is a library that addresses these issues by providing a platform-independent interface to window management, menus, and input devices in a simple and elegant manner. Using GLUT comes at the price of some flexibility.


What is GLU? How is it different from OpenGL?


If you think of OpenGL as a low-level 3D graphics library, think of GLU as adding some higher-level functionality not provided by OpenGL. Some of GLU's features include: o Scaling of 2D images and creation of mipmap pyramids o Transformation of object coordinates into device coordinates and vice versa o Support for NURBS surfaces o Support for tessellation of concave or bow tie polygonal primitives o Specialty transformation matrices for creating perspective and orthographic projections, positioning a camera, and selection/picking o Rendering of disk, cylinder, and sphere primitives o Interpreting OpenGL error values as ASCII text The best source of information on GLU is the OpenGL red and blue books and the GLU specification, which you can obtain from the OpenGL org Web page.


How does the camera work in OpenGL?


As far as OpenGL is concerned, there is no camera. More specifically, the camera is always located at the eye space coordinate (0., 0., 0.). To give the appearance of moving the camera, your OpenGL application must move the scene with the inverse of the camera transformation.


How can I move my eye, or camera, in my scene?


OpenGL doesn't provide an interface to do this using a camera model. However, the GLU library provides the gluLookAt() function, which takes an eye position, a position to look at, and an up vector, all in object space coordinates. This function computes the inverse camera transform according to its parameters and multiplies it onto the current matrix stack.


Where should my camera go, the ModelView or Projection matrix?


The GL_PROJECTION matrix should contain only the projection transformation calls it needs to transform eye space coordinates into clip coordinates. The GL_MODELVIEW matrix, as its name implies, should contain modeling and viewing transformations, which transform object space coordinates into eye space coordinates. Remember to place the camera transformations on the GL_MODELVIEW matrix and never on the GL_PROJECTION matrix. Think of the projection matrix as describing the attributes of your camera, such as field of view, focal length, fish eye lens, etc. Think of the ModelView matrix as where you stand with the camera and the direction you point it.


Given the current ModelView matrix, how can I determine the object-space location of the camera?


The "camera" or viewpoint is at (0., 0., 0.) in eye space. When you turn this into a vector [0 0 0 1] and multiply it by the inverse of the ModelView matrix, the resulting vector is the object-space location of the camera. OpenGL doesn't let you inquire (through a glGet* routine) the inverse of the ModelView matrix. You'll need to compute the inverse with your own code.


How do I get a specified point (XYZ) to appear at the center of the scene?


gluLookAt() is the easiest way to do this. Simply set the X, Y, and Z values of your point as the fourth, fifth, and sixth parameters to gluLookAt().


How do I draw 3D objects on a 2D screen?


There are many ways to do this. Some approaches map the viewing rectangle onto the scene, by shooting rays through each pixel center and assigning color according to the object hit by the ray. Other approaches map the scene onto the viewing rectangle, by drawing each object into the region, keeping track of which object is in front of which. The mapping mentioned above is also referred to as "projection", and the two most popular projections are perspective projection and parallel projection. For example, to do a parallel projection of a scene onto a viewing rectangle, you can just discard the Z coordinate (divide by depth), and "clip" the objects to the viewing rectangle (discard portions that lie outside the region).


How do I draw a circle as a Bezier (or B-Spline) curve?


The short answer is, "You can't." Unless you use a rational spline you can only approximate a circle. The approximation may look acceptable, but it is sensitive to scale. Magnify the scale and the error of approximation magnifies. Deviations from circularity that were not visible in the small can become glaring in the large.


What is color?


Color is the perceptual result of light in the visible region of the spectrum, having wavelengths in the region of 400 nm to 700 nm, incident upon the retina. Physical power (or radiance) is expressed in a spectral power distribution (SPD), often in 31 components each representing a 10 nm band.


What is Intensity?


Intensity is a measure over some interval of the electromagnetic spectrum of the flow of power that is radiated from, or incident on, a surface. Intensity is what I call a linear-light measure, expressed in units such as watts per square meter. The voltages presented to a CRT monitor control the intensities of the color components, but in a nonlinear manner. CRT voltages are not proportional to intensity.


What is CIE color model?


A color model based on human perception developed by the CIE (Commission Internationale de l'Eclairage) committee. While widely regarded as the most accurate color model, CIE is unsuitable for many technologies, including color printing and color monitors. Consequently, these systems need to use other color models, such as CMYK and RGB.


What is CMYK?


Short for Cyan-Magenta-Yellow-Black, and pronounced as separate letters. CMYK is a color model in which all colors are described as a mixture of these four process colors. CMYK is the standard color model used in offset printing for full-color documents. Because such printing uses inks of these four basic colors, it is often called four-color printing.


What is color monitor?


A display monitor capable of displaying many colors. In contrast, a monochrome monitor can display only two colors -- one for the background and one for the foreground. Color monitors implement the RGB color model by using three different phosphors that appear red, green, and blue when activated. By placing the phosphors directly next to each other, and activating them with different intensities, color monitors can create an unlimited number of colors. In practice, however, the real number of colors that any monitor can display is controlled by the video adapter. Color monitors based on CRT technology employ three different techniques to merge phosphor triplets into pixels: Dot-trio shadow masks place a thin sheet of perforated metal in front of the screen. Since electrons can pass only through the holes in the sheet, each hole represents a single pixel. Aperture-grille CRTs place a grid of wires between the screen and the electron guns. Slot-mask CRTs uses a shadow mask but the holes are long and thin. It's sort of a cross between the dot-trio shadow mask and aperture-grill techniques.


What is monochrome?


One color. Monitors, for example, can be monochrome, grayscale or color. Monochrome monitors actually use two colors, one for the display image (the foreground) and one for the background. Graphic images can also be monochrome, grayscale, or color.


What is CRT?


Abbreviation of cathode-ray tube, the technology used in most televisions and computer display screens. A CRT works by moving an electron beam back and forth across the back of the screen. Each time the beam makes a pass across the screen, it lights up phosphor dots on the inside of the glass tube, thereby illuminating the active portions of the screen. By drawing many such lines from the top to the bottom of the screen, it creates an entire screenful of images.


What is Pixel?


Short for Picture Element, a pixel is a single point in a graphic image. Graphics monitors display pictures by dividing the display screen into thousands (or millions) of pixels, arranged in rows and columns. The pixels are so close together that they appear connected.


How many colors or shades can be displayed on a system?


The number of bits used to represent each pixel determines how many colors or shades of gray can be displayed. For example, in 8-bit color mode, the color monitor uses 8 bits for each pixel, making it possible to display 2 to the 8th power (256) different colors or shades of gray.


How can quality of display system be determined?


The quality of a display system largely depends on its resolution, how many pixels it can display, and how many bits are used to represent each pixel. VGA systems display 640 by 480, or about 300,000 pixels. In contrast, SVGA systems display 800 by 600, or 480,000 pixels. True Color systems use 24 bits per pixel, allowing them to display more than 16 million different colors.


What is convergence?


In graphics, convergence refers to how sharply an individual color pixel on a monitor appears. Each pixel is composed of three dots -- a red, blue, and green one. If the dots are badly misconverged, the pixel will appear blurry. All monitors have some convergence errors, but they differ in degree.


What is VGA?


Abbreviation of video graphics array, a graphics display system for PCs developed by IBM. VGA has become one of the de facto standards for PCs. In text mode, VGA systems provide a resolution of 720 by 400 pixels. In graphics mode, the resolution is either 640 by 480 (with 16 colors) or 320 by 200 (with 256 colors). The total palette of colors is 262,144.


What is graphics mode?


Many video adapters support several different modes of resolution, all of which are divided into two general categories: character mode and graphics mode. Of the two modes, graphics mode is the more sophisticated. Programs that run in graphics mode can display an unlimited variety of shapes and fonts, whereas programs running in character mode are severely limited. Programs that run entirely in graphics mode are called graphics-based programs. In character mode, the display screen is treated as an array of blocks, each of which can hold one ASCII character. In graphics mode, the display screen is treated as an array of pixels. Characters and other shapes are formed by turning on combinations of pixels.


What is text mode?


A video mode in which a display screen is divided into rows and columns of boxes. Each box can contain one character. Text mode is also called character mode. All video standards for the PC, including VGA, support a text mode that divides the screen into 25 rows and 80 columns. In addition to text mode, most video adapters support a graphics mode, in which the display screen is divided into an array of pixels. Whereas character-based programs run in text mode, all graphics-based programs run in graphics mode.


What is animation?


A simulation of movement created by displaying a series of pictures, or frames. Cartoons on television is one example of animation. Animation on computers is one of the chief ingredients of multimedia presentations. There are many software applications that enable you to create animations that you can display on a computer monitor. Note the difference between animation and video. Whereas video takes continuous motion and breaks it up into discrete frames, animation starts with independent pictures and puts them together to form the illusion of continuous motion.


What is CAD?


Acronym for computer-aided design. A CAD system is a combination of hardware and software that enables engineers and architects to design everything from furniture to airplanes. In addition to the software, CAD systems require a high-quality graphics monitor; a mouse, light pen, or digitizing tablet for drawing; and a special printer or plotter for printing design specifications.


What is SVGA?


Short for Super VGA, a set of graphics standards designed to offer greater resolution than VGA. SVGA supports 800 x 600 resolution, or 480,000 pixels. The SVGA standard supports a palette of 16 million colors, but the number of colors that can be displayed simultaneously is limited by the amount of video memory installed in a system. One SVGA system might display only 256 simultaneous colors while another displays the entire palette of 16 million colors. The SVGA standards are developed by a consortium of monitor and graphics manufacturers called VESA.




Brightness is defined by the CIE as the attribute of a visual sensation according to which an area appears to emit more or less light. Because brightness perception is very complex, the CIE defined a more tractable quantity luminance which is radiant power weighted by a spectral sensitivity function that is characteristic of vision.


What is Lightness?


Human vision has a nonlinear perceptual response to brightness: a source having a luminance only 18% of a reference luminance appears about half as bright. The perceptual response to luminance is called Lightness.


What is Hue?


According to the CIE, hue is the attribute of a visual sensation according to which an area appears to be similar to one of the perceived colors, red, yellow, green and bue, or a combination of two of them. Roughly speaking, if the dominant wavelength of an SPD shifts, the hue of the associated color will shift.


What is satuation?


From the CIE, saturation is the colorfulness of an area judged in proportion to its brightness. Saturation runs from neutral gray through pastel to saturated colors. Roughly speaking, the more an SPD is concentrated at one wavelength, the more saturated will be the associated color. You can desaturate a color by adding light that contains power at all wavelengths.


Can blue be assigned fewer bits than red or green?


Blue has a small contribution to the brightness sensation. However, human vision has extraordinarily good color discrimination capability in blue colors. So if you give blue fewer bits than red or green, you will introduce noticeable contouring in blue areas of your pictures.


What is True color?


True color is the provision of three separate components for additive red, green and blue reproduction. True color systems often provide eight bits for each of the three components, so true color is sometimes referred to as 24-bit color.


What is gamma?


The intensity of light generated by a physical device is not usually a linear function of the applied signal. A conventional CRT has a power-law response to voltage: intensity produced at the face of the display is approximately the applied voltage, raised to the 2.5 power. The numerical value of the exponent of this power function is colloquially known as gamma. This nonlinearity must be compensated in order to achieve correct reproduction of intensity.


What is contrast ratio?


Contrast ratio is the ratio of intensity between the brightest white and the darkest black of a particular device or a particular environment. Projected cinema film - or a photographic reflection print - has a contrast ratio of about 80:1. Television assumes a contrast ratio - in your living room - of about 30:1. Typical office viewing conditions restrict contrast ratio of CRT display to about 5:1.


What is motion capture?


Motion capture is a technique by which a performer's movements can be recorded digitally, and reproduced by a CG character either in real-time or after the data has been processed (depending on how the data is sampled). This allows for more realistic and natural motion in character animation. A variation of this technique uses an armature instead of a performer, and movements are made and keyframed the same way that stop-motion animators have been doing it for many years.


How do I do a hidden surface test (backface culling) with 2D points?


c = (x1-x2)*(y3-y2)-(y1-y2)*(x3-x2) x1,y1, x2,y2, x3,y3 = the first three points of the polygon. If c is positive the polygon is visible. If c is negative the polygon is invisible (or the other way).


What are the Applications for Computer Graphics?


Computer graphics applications are found in almost all areas. Some of the important areas are: User Interfaces Layout and Design Scientific Visualization and Analysis Art Design Medicine and Virtual Surgery Layout Design Architectural Simulations History and cultural heritage Entertainment Simulations Games


How do I rotate a 2D point?


In 2D, you make (X,Y) from (x,y) with a rotation by angle t so: X = x cos t - y sin t Y = x sin t + y cos t As a 2x2 matrix this is very simple. If you want to rotate a column vector v by t degrees using matrix M, use M = [cos t -sin t] [sin t cos t] in the product M v. If you have a row vector, use the transpose of M (turn rows into columns and vice versa). If you want to combine rotations, in 2D you can just add their angles, but in higher dimensions you must multiply their matrices.


What is meant by Computer Graphics?


Computer Graphics involves technology to accept, process, transform and present information in a visual form that also concerns with producing images (or animations) using a computer.


what are Computer Graphics Applications?


Computer graphics applications are found in almost all areas.

Some of the important areas are:

  1. User Interfaces
  2. Layout and Design
  3. Scientific Visualization and Analysis
  4. Art and Design
  5. Medicine and Virtual Surgery
  6. Layout Design & Architectural Simulations
  7. History and cultural heritage
  8. Entertainment
  9. Simulations
  10. Games



What is the difference between pixel and resolution?


A pixel is the smallest unit in a computer image or display. Resolution is mapping between the monitor screen size and the pixels.With higher resolution, more pixels can be displayed and therefore the image is more discrete and detailed, however, pixels are smaller at high resolution and detail can be hard to visualize on smaller screens.

Three Dimension Pipeline (3D Pipeline) :

The process of 3D graphics can be divided into three-stages: tessellation, geometry, and rendering. In the tessellation stage, a described model of an object is created, and the object is then converted to a set of polygons. The geometry stage includes transformation, lighting, and setup. The rendering stage, which is critical for 3D image quality, creates a two dimensional display from the polygons created in the geometry stage.

Alpha Blending :

The real world is composed of transparent, translucent, and opaque objects. Alpha blending is a technique for adding transparency information for translucent objects. It is implemented by rendering polygons through a stipple mask whose on-off density is proportional to the transparency of the object. The resultant color of a pixel is a combination of the foreground and background color. Typically, alpha has a normalized value of 0 to 1 for each color pixel. new pixel = (alpha)(pixel A color) + (1 - alpha)(pixel B color)

Alpha Buffer :

An extra Color channel to hold transparency information; pixels become quad values (RGBA). In a 32-bit frame buffer there are 24 bits of color, 8 each for red, green, and blue, along with an 8-bit alpha channel.

Anti-aliasing :

Anti-aliasing is sub pixel interpolation, a technique that makes edges appear to have better resolution.

Atmospheric Effect :

Effects, such as fog and depth cueing that improve the rendering of real-world environments.

Bitmap :

A Bitmap is a pixel by pixel image.

Bilinear Filtering :

Bilinear filtering is a method of anti-aliasing texture maps. A texture-aliening artifact occurs due to sampling on a finite pixel grid. Point-sampled telexes jump from one pixel to another at random times. This aliening is very noticeable on slowly rotating or moving polygons. The texture image jumps and shears along pixel boundaries. To eliminate this problem, bilinear filtering takes a weighted average of four adjacent texture pixels to create a single telex.

BitBLTs :

The BitBLT is the single most important acceleration function for windowed GUI environments. A BitBLT is simply the movement of a block of data from one place to another, taking into account the special requirements and arrangements of the graphics memory. For example, this function is utilized every time a window is moved; in which case, the BitBLT is a simple Pixel Block Transfer. More complicated cases may occur where some transformation of the source data is to occur, such as in a Color Expanded Block Transfer, where each monochromatic bit in the source is expanded to the color in the foreground or background register before being written to the display.

Blending :

Blending is the combining of two or more objects by adding them on a pixel-by-pixel basis.

Bus Mastering :

A feature of PCI buses that allows a card with this feature to retrieve data directly from system memory without any interaction with the host CPU

Chroma Keying :

Chroma Keying or texture transparency is the ability to recognize a key color within a texture map and make it transparent during the texture mapping process. Since not all objects are easily modeled with polygons, chroma keying is used to include complex objects in a scene as texture maps.

Depth Cueing :

Depth cueing is the lowering of intensity as objects move away from the viewpoint.

Dithering :

Dithering is a technique for archiving 24-bit quality in 8 or 16-bit frame buffers. Dithering uses two colors to create the appearance of a third, giving a smooth appearance to an otherwise abrupt transition.

Double Buffering :

A method of using two buffers, one for display and the other for rendering. While one of the buffers is being displayed, the other buffer is operated on by a rendering engine. When the new frame is rendered, the two buffers are switched. The viewer sees a perfect image all the time.


Dynamic Random Access Memory is the memory at any location in a computer that can be accessed immediately for reading and writing operations.

Hexadecimal :

16 digits, 0-9 and A-F used to define color values in HTML.

Hue :

A specific color, such as red or green.


Icon. Standard format for icon files.


Interchange File Format. The Amiga Interchange File Format is used for working with Video Toaster and transferring files to and from the Commodore Amiga system. It supports RGB, indexed-color, grayscale and Bitmap color modes. It does not support alpha channels.

Illustration :

A diagram, drawing, photograph, etc. which further explains or clarify the information contained in the surrounding body of text.


Joint Photographic Experts Group. A commonly used graphics file format that uses lossy compression. It supports up to 24 bit color. Its small size makes it ideal for web graphics.

L*a*b* color model :

Based on the model proposed by the Commission Internationale d'Eclairage (CIE) in 1931 as an international standard for color measurement. It's designed to be device independent; creating consistent color whatever the device (such as monitor, printer, computer, or scanner) used to create or output an image. L*a*b color consists of a luminance or lightness component (L) and two chromatic components: the a component (from green to red) and the b component (from blue to yellow). In 1976, this model was refined and named CIE L*a*b.


Lemple-Zif-Welch. A lossless compression technique supported by TIFF, PDF, GIF and Postscript file formats. It's most useful in compressing images that contain large areas of single color, such as screenshots or simple paint images.

Line art :

Art that contains no graded tones. Usually black on white (as in comic manga) or solid color on white. In either case there are no middle tones.

lossy :

Image compression techniques that remove detail as they reduce file size.

pixel :

picture element. The smallest element that can be independently assigned color.

saturation :

The amount of color.


Targa. Graphic file format that supports any bit depth, and includes features such as alpha channels, gamma settings and built in thumbnails.

Computer Vision :

Computer vision, sometimes called image understanding, describes the automatic deduction of the structure and the properties of a possibly dynamic three-dimensional world from either a single or multiple two-dimensional images of the world.

lossless :

Image compression techniques that don't remove detail as they reduce file size

Macromedia :

A family of programs used for graphics and web development. They produce programs such as Dreamweaver and Flash. Macromedia purchased eHelp, makers of RoboHelp, in 2003.

moire' :

A shimmering 'interference' pattern produced when two geometrically regular patterns are superimposed.

multimedia :

An application or presentation that uses any combination of animation, audio, images, text, and video to deliver information to an audience.

OpenOffice.org (OOo) :

A suite of freeware productivity applications offered by OpenOffice.org that includes Writer (for word processing and document layout), Calc (for spreadsheets), Draw (for graphics and illustrations), and Impress (for presentations). The software is as robust as for-profit suites, such as Microsoft Office.


Commonly used by IBM PC-compatible computers. It supports RGB, indexed-color, grayscale and Bitmap color modes. It does not support alpha channels. PCX supports the RLE compression method


Portable Document Format. Computer file format that contains vector and bitmap graphics, and can contain electronic document search/navigation features. The format allows for easy sharing of files between platforms.


Apple graphic file format. It can include bitmapped or vector images, and can use different compression schemes. It's available only for Apple.


Portable Network Graphics. Developed as a patent-free alternative to GIF, it's used for losslessly compressing and displaying images on the Internet. It supports 24-bit images and produces background transparency without jagged edges. It supports grayscale and RGB color modes with a single alpha channel, and Bitmap and indexed-color modes without alpha channels.


Photoshop native file format. It contains layer and transparency information.

primitive :

A point, a line, a polygon, a bitmap or an image.

RGB (red, green, blue) color model :

A color model. A large percentage of the visible spectrum can be represented by mixing red, green and blue (RGB) in various proportions and intensities. Where the colors overlap, they create cyan, magenta, and yellow. RGB colors are known as addative colors because they combine to form white. RGB colors are used for lighting, video and monitors.


Run Length Encoding. A lossless compression technique supported by Photoshop and TIFF file formats as well as some common Windows file formats.

rasterize :

The process of converting a projected point, line, polygon, or the pixels of a bitmap or image to fragments, each corresponding to a pixel in the framebuffer.

register :

The correct alignment of colors during printing.

register mark :

A symbol defining the correct alignment of overlay copy and color during printing.

resolution :

For a CRT, the maximum number of displayable pixels in the horizontal and vertical directions. For a printer or plotter, the number of pixels per inch.

rotation :

A geometric transformation that causes points to be re-oriented about an axis.


Scalable Vector Graphics. Graphic file format developed for the web that uses vector graphics. The format produces higher resolution graphics with smaller file sizes.


Draw document. Draw is the graphics application in the OpenOffice.org suite.

subtractive colors :

Cyan (C), magenta (M), and yellow (Y). These colors combine to absorb all color and produce a muddy brown color. Black is added to produce pure black. Also known as CMYK.


Tagged Image File Format. Graphics file format used to store images from scanners and video devices. It's the most common file format used in printing.

true color system :

A 24-plane graphics subsystem which produces the complete range of 16.7 million available colors.

vector graphics :

Images determined by mathematical functions utilizing besier curves. Vector graphics provide more flexibility for scaling than raster graphics.

Unit Vector :

The vector having Unit Magnitude.


Windows metaFile. Standard Windows graphics format supported by most Windows software.


Extensible Style Language

Y2K :

Year 2000


The acronym for Moving Pictures Expert Group, MPEG is an international standard for video compression and desktop movie presentation. A special viewing application is needed to run MPEG files on your computer.

Hypermedia :

The hypertext concept extended to include linked multiple media.

Image Processing :

The enhancement or other manipulation of an image--the result of which is usually another image.


Extensible HyperText Markup Language


Quicken Import File/Interchange Format (file name extension)

2D Graphics :

Displayed representation of a scene or an object along two axes of reference: height and width (x and y).

Two Dimension Graphics (2D Graphics) :

Displayed representation of a scene or an object along two axes of reference: height and width (x and y).

Three Dimension Graphics (3D Graphics) :

Displayed representation of a scene or an object that appears to have three axes of reference: height, width, and depth (x, y, and z).


A type of DRAM that has enhanced readability in the Extended-Data-Out mode.

Flat Shading :

The flat shading method is also called constant shading. For rendering, it assigns a uniform color throughout an entire polygon. This shading results in the lowest quality, an object surface with a faceted appearance and a visible underlying geometry that looks 'blocky'.

Fog :

Fog is the blending of an object with a fixed color as its pixels become farther away from the viewpoint.

Gamma :

The characteristics of displays using phosphors (as well as some cameras) are nonlinear. A small change in voltage when the voltage level is low produces a change in the output display brightness level; but this same small change in voltage at a high voltage level will not produce the same magnitude of change in the brightness output. This effect, or actually the difference between what you should have and what you actually measured, is known as gamma.

Gamma Correction :

Before being displayed, linear RGB data must be processed (gamma corrected) to compensate for the gamma (nonlinear characteristics) of the display.

Gouraud Shading :

Gouraud shading, one of the most popular smooth shading algorithms, is named after its French originator, Henri Gouraud. Gouraud shading, or color interpolation, is a process by which color information is interpolated across the face of the polygon to determine the colors at each pixel. It assigns color to every pixel within each polygon based on linear interpolation from the polygon's vertices. This method improves the 'blocky' (see Flat Shading) look and provides an appearance of plastic or metallic surfaces.

Hidden Surface Removal :

Hidden Surface Removal or visible surface determination entails displaying only those surfaces that are visible to a viewer because objects are a collection of surfaces or solids.

Interpolation :

Interpolation is a mathematical way of regenerating missing or needed information. For example, an image needs to be scaled up by a factor of two, from 100 pixels to 200 pixels. The missing pixels are generated by interpolating between the two pixels that are on either side of the pixel that needs to be generated. After all of the 'missing' pixels have been interpolated, 200 pixels exist where only 100 existed before, and the image is twice as big as it used to be.


Lighting :

There are many techniques for creating realistic graphical effects to simulate a real-life 3-D object on a 2-D display. One technique is lighting. Lighting creates a real-world environment by means of rendering the different grades of darkness and brightness of an object's appearance to make the object look solid.



Line Buffer :

A line buffer is a memory buffer used to hold one line of video. If the horizontal resolution of the screen is 640 pixels and RGB is used as the color space, the line buffer would have to be 640 locations long by 3 bytes wide. This amounts to one location for each pixel and each color plane. Line buffers are typically used in filtering algorithms.



MIP Mapping :

Multum in Parvum (Latin) means 'many in one'. A method of increasing the quality of a texture map by applying different-resolution texture maps for different objects in the same image, depending on their size and depth. If a texture-mapped polygon is smaller than the texture image itself, the texture map will be undersampled during rasterization. As a result, the texture mapping will be noisy and 'sparkly'. The purpose of MIP mapping is to remove this effect.



Occlusion :

The effect of one object in 3-D space blocking another object from view.



Palletized Texture :

Palletized Texture means compressed texture formats, such as 1-, 2-, 4-, and 8-bit instead of 24-bit; this allows more textures to be stored in less memory.



Perspective Correction :

A particular way to do texture mapping; it is extremely important for creating a realistic image. It takes into account the effect of the Z value in a scene while mapping texels onto the surface of polygons. As a 3D object moves away from the viewer, the length and height of the object become compressed, making it appear shorter. Without perspective correction, objects will appear to shift and 'tear' in an unrealistic way. True perspective correction is that the rate of change per pixel of texture is proportional to the depth. Since it requires a division per pixel, perspective correction is very computing intensive.



Phong Shading :

Phong shading is a sophisticated smooth shading method, originated by Phong Bui-tuong. The Phong shading algorithm is best known for its ability to render precise, realistic specula highlights. During rendering, Phong shading achieves excellent realism by calculating the amount of light on the object at tiny points across the entire surface instead of at the vertices of the polygons. Each pixel representing the image is given its own color based on the lighting model applied at that point. Phong shading requires much more computation for the hardware than Gouraud shading.



Projection :

The process of reducing three dimensions to two dimensions for display is called Projection. It is the mapping of the visible part of a three dimensional object onto a two dimension screen.



Rasterization :

Translating an image into pixels.



Rendering :

The process of creating life-like images on a screen using mathematical models and formulas to add shading, color, and lamination to a 2D or 3D wireframe.



Rendering Engine :

"Rendering Engine" generically applies to the part of the graphics engine that draws 3D primitives, usually triangles or other simple polygons. In most implementations, the rendering engine is responsible for interpolation of edges and "filling in" the triangle.



Scissors Clip :

Test pixel coordinates against clip rectangles and reject them if outside.



Set-up Engine :

A set-up engine allows drivers to pass polygons to the rendering engine in the form of raw vertex information, subpixel polygon addresses. Whereas, most common designs force the host CPU to pre-process polygons for the rendering engine in terms of delta values for edges, color, and texture. Thus, a set-up engine moves processing from the host CPU to the graphics chip, reducing bus bandwidth requirements by 30% for small, randomly placed triangles and by proportionately more for larger polygons.




Synchronous DRAM is a type of DRAM to which reads or writes can be performed synchronously with the memory clock and at much higher speeds than with Fast-Page or EDO DRAM.




Synchronous Graphics Random Access memory (SGRAM) is a type of memory that is optimized for graphics use. SGRAM is capable of running at much higher speeds than fast page or EDO DRAM. SGRAM is able to execute a small number of frequently executed operations, such as buffer clears, specific to graphics applications independently of the controller.



Span :

In raster graphics architecture a primitive is formed by scan conversion where each scan line intersects the primitive at two ends, P left and P right. A contiguous sequence of pixels on the scan line between P left and P right is called a Span. Each pixel within the span contains the z, R, G, and B data values.



Tessellation :

Processing 3D graphics can be pipelined into three-stages: tessellation, geometry, and rendering. Tessellation is the process of subdividing a surface into smaller shapes. To describe object surface patterns, tessellation breaks down the surface of an object into manageable polygons. Triangles or quadrilaterals are two usually used polygons in drawing graphical objects because computer hardware can easy manipulate and calculate these two simple polygons. An object divided into quads and subdivided into triangles for convenient calculation.



Texture Anti-aliasing :

An interpolation technique used to remove texture distortion, staircasing or jagged edges, at the edges of an object.



Texture Filtering :

Removing the undesirable distortion of a raster image, also called aliasing artifacts, such as sparkles and blockiness, through interpolation of stored texture images.



Texture Mapping :

Texture mapping is based on a stored bitmap consisting of texture pixels, or texels. It consists of wrapping a texture image onto an object to create a realistic representation of the object in 3D space. The object is represented by a set of polygons, usually triangles. The advantage is complexity reduction and rendering speed, because only one texel read is required for each pixel being written to the frame buffer. The disadvantage is the blocky image that results when the object moves.



Transformation :

Change of coordinates; a series of mathematical operations that act on output primitives and geometric attributes to convert them from modeling coordinates to device coordinates.



Tri-linear Filtering :

Based on bilinear filtering, trilinear filtering takes the weighted average of two levels of bilinear filtering results to create a single telex. The resultant graphics image is smoother and less flashy.



Tri-linear MIP Mapping :

A method of reducing aliasing artifacts within texture maps by applying a bilinear filter to four texels from the two nearest MIP maps and then interpolating between the two.



Z-buffer :

A part of off-screen memory that holds the distance from the viewpoint for each pixel, the Z-value. When objects are rendered into a 2D frame buffer, the rendering engine must remove hidden surfaces.



Z-buffering :

A process of removing hidden surfaces using the depth value stored in the Z-buffer. Before bringing in a new frame, the rendering engine clears the buffer, setting all Z-values to 'infinity'. When rendering objects, the engine assigns a Z-value to each pixel: the closer the pixel to the viewer, the smaller the Z value. When a new pixel is rendered, its depth is compared with the stored depth in the Z-buffer. The new pixel is written into the frame buffer only if its depth value is less than the stored one.



Z-sorting :

A process of removing hidden surfaces by sorting polygons in back-to-front order prior to rendering. Thus, when the polygons are rendered, the forward-most surfaces are rendered last. The rendering results are correct unless objects are close to or intersect each other. The advantage is not requiring memory for storing depth values. The disadvantage is the cost in more CPU cycles and limitations when objects penetrate each other.



AI :

Adobe Illustrator. Adobe Illustrator native file format.




Architecture Review Board. An independent consortium that governs OpenGL specifications, defines conformance tests and approves OpenGL enhancements. The board includes representatives from companies such as 3Dlabs, Compaq, Evans & Sutherland, Hewlett Packard, IBM, Intel, Intergraph, NVIDIA, Microsoft, and SGI.



additive colors :

The additive colors are red, green, and blue. Adding these colors together creates white (all light reflects back to the eye).



Adobe :

A family of programs used for electronic, web, and print publishing. Adobe produces great programs such as Photoshop, GoLive, and FrameMaker.



aliasing :

Visual artifacts produced in graphics images that use pixels for display. One example of aliasing is jagged edges on curved lines.



alpha :

A fourth color component in the RGB color model representing opacity. Alpha values can range from completely transparent to completely opaque.



animated GIF :

Solid-color motion graphic file format that doesn't include audio. It's best suited for small frame sizes, and ideal for use on the web.



bleed :

Printing that extends to the edge of a sheet or page of paper after it has been trimmed.



butt :

When two or more art or color elements meet edge to edge.




A family of lossless compression techniques for black-and-white images. It's supported by PDF and Postscript file formats. (CCITT is an abbreviation for the French spelling of International Telegraph and Telekeyed Consultive Committee.)




Cyan, Magenta, Yellow, black. The subtractive colors. Cyan (C), magenta (M), and yellow (Y) combine to absorb all color and produce a muddy brown. Black (K) ink is added to produce a true black. (K is used instead of B to avoid confusion with blue.) Combining these inks to reproduce color is called four-color process printing.



color index :

A single value that represents a color by name, rather than by value.



color map :

A table showing index-to-RGB mapping that's accessed by display hardware. Each color index is read from a color buffer, converted to an RGB triple by lookup in the color map then sent to the monitor.



color model :

Models used to describe and reproduce color.



compression :

Hardware and software techniques that reduce the storage space required by bitmap image data. There are two common techniques. The first, lossless, compresses image data without removing detail. The second, lossy, compresses images by removing detail.




Desktop Color Separations. A version of the standard EPS format developed by Quark. The DCS 1.0 format supports CMYK files without alpha channels and clipping paths. The DCS 2.0 format supports multi-channel and CMYK files with a single alpha channel, clipping paths and multiple spot channels.



dpi :

dots per inch. The display resolution of devices such as monitors or printers.




AutoCAD Drawing. Standard file format for saving vector graphics created in AutoCAD.




Enhanced metaFile. Graphic file format available for Windows and WinNT. It saves both vector and pixel information




Encapsulated Postscript. Computer file containing Postscript commands with images.



extrusion :

Extending a 2D object into 3D space by adding a z plane.




Flash Movie. Standard format for Flash movies.



UC2 :

Compressed File (file name extension) [UltraCompressor]



X2D :

Hexadecimal to Decimal [REXX]




Bitmap. A standard Windows uncompressed image format. It supports RGB, indexed-color, grayscale, and Bitmap color modes. It doesn't support alpha channels.




Graphics Interchange Format. A common file format used to display indexed-color graphics and images for HTML documents. It can display interlaced lines of an image as it downloads. It can also store multiple bitmaps in one file, producing animated GIFs. GIF 89a supports transparency.



GZ :

GIMP image file



graphics engine :

Software that generates interactive 2D and 3D graphics. Examples of graphics engines are Direct3D and OpenGL.



graphics library :

A tool set for application programmers. It usually includes a defined set of primitives and function calls that enable the programmer to bypass many low-level programming tasks.



graphics pipeline :

A sequence of operations that creates an image from user defined settings to final output. The pipeline determines how color information and geometric coordinates are processed in the hardware and software.




hue, saturation, brightness. Based on the human perception of color, the HSB model describes three fundamental characteristics of color. Hue is the color reflected from or transmitted through an object, such as red, green or blue. It's measured as a location on the color wheel and is expressed as a degree between 0 and 360 on that wheel. Saturation, also called chroma, is the strength or purity of the color. Saturation represents the amount of gray in proportion to the hue and is measured as a percentage from 0% (gray) to 100% (fully saturated). Brightness is the relative lightness or darkness of the color, usually measured as a percentage from 0% (black) to 100% (white).



Image :

A digitally sampled picture.



Scene :

The "reality" from which an image was taken.



Transfer Function :

The Fourier transform of an imaging system



Modulation Transfer Function :

The magnitude part of a Transfer Function



Phase Transfer Function :

The phase part of the Transfer Function



Scale Space :

An image (or function of an image) as measured at multiple scales.



Laplacian :

Second spatial derivative.



Binary Image :

A strictly black and white image (0s and 1s). One bit of information per pixel.



Grayscale Image :

An image consisting of scalar values representing intensity. These are usually stored as one byte per pixel (256 levels) or two bytes per pixel (65,536 levels).



Range Image :

An image whose values represent distance from the imaging device


Sampling :

The process of recording the value of some function only at discrete points in the domain.



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