Kapitel 10

Question 1

Two distinct steps of the creation of an image using 3D-graphics

Answer 1

One step is the creation, encoding, storage and manipulation of the scene to be photographed. The other is the process of producing the image. The former is a creative artistic process, the latter is a computationally intense process.

Question 2

Bump mapping

Answer 2

a way of generating small variations in the apparent orientation of a surface so that the surface appears to be rough. Also adds a degree of randomness to the interpolation process applied by traditional shading algorithms so tha the overall surface appears to have texture.

Question 3

Perspective projection versus parallel projection

Answer 3

In perspective projection all objects are projected along straight lines called projectors that extend from a common point called the center of projection, or the view-point. Parallel projection means that the projectors are parallel. A perspective projection produces a projection similar to that seen by the human eye, whereas parallel projection produces a “true” profile of an object which is often useful in context of engineer drawings.

Question 4

Texture mapping

Answer 4

a process in which certain color patterns can be associated with an objects surface. It associatesa predefined image with the surface of an object. This image might be a digital photograph, an artists rendering or perhaps a computer generated image.

Question 5

The process of creating and displaying images: 1. Modeling

Answer 5

analogous to designing and constructing a set in the traditional motion picture industry, except that the 3D graphics scene is contructed from digitally encoded data and algorithms.

Question 6

Gouraud shading and Phong shading

Answer 6

Both uses the information about the surface orientation at a patchs vetices to approximate the surface orientation along the boundaries of the patch. Gouraud shading then applies that information to determine the appearance of the surface along the patch boundaries and, finally, interpolates that boundary appearance to estimate ethe appearance of the surface at points in the interior of the patch. In contrast, phongs shading interpolates the orientation of the surface along the patchs boundaries to estimate the surface orientation at points within the patchs interior and only then considers questions of appearance. (in short, Gouraud shading converts orientation information into color information and then interpolates the color information. Phong shading interpolates orientation until the orientation of the point in question is estimated, and then converts that orientation information into color information.

Question 7

Bezier curves

Answer 7

a concept which allows a curved line segment in three dimensional space to be defined by only a few points called control points.

Question 8

Ray tracing

Answer 8

essentially the process of following a ray of light backwatd to find its source.

Question 9

Particle systems

Answer 9

a system that simulate the underlying structure of an object as a large collection of particles.

Question 10

Standard software interfaces

Answer 10

consists of software routines that convert standardized commands into the specific instructions required by a particular graphics hardware-system. Examples are OpenGL, Direct3D.

Question 11

The process of creating and displaying images (3 steps)

Answer 11

Modeling, rendering and displaying

Question 12

Normal vectors

Answer 12

A polygonal mesh with arrows used to estimate the surface orientation at the vertices of the polygonal mesh.

Question 13

Specular light

Answer 13

If a surface is smooth, parallel light rays (such as those arriving from the same light source) that strike the surface in the same area will be reflected in essentially the same direction and travel away from the object as parallel rays. Such reflected light is called specilar light.

Question 14

Local and global lighting model

Answer 14

The rendering pipeline has disadvantages and one is that it only implements a local lighting model, meaning that the pipeline renders each objecti in relation to the light sources as though it were the only object in the scene. Light interactions between objects are therefore not captured. In a global lighting model those sort of interactions are considered.

Question 15

Rendering pipeline

Answer 15

A well established paradigm used for the process of producing an image from a scene graph.

Question 16

Planar patches

Answer 16

the shape of an object in 3D graphics is usually described as a collection of flat surfaces, these are called planar patches. These polygons form a polygonal mesh that approximates the shape of the object being described.

Question 17

Anisotropic and isotropic surfaces

Answer 17

Isotropic surfaces have refletion patterns which are symmetric. Anisotropic surfaces are not and can be found in fabric such as satin, where the nap of the cloth alters the materials appearance depending on its orientation. A grassy surface is another example.

Question 18

Image window

Answer 18

The restricted portion of the projection plane that defines the boundaries of the final image.

Question 19

Digitizing

Answer 19

the process to build a physical model of an object and then record the location of points on the surface of the model by touching the surface with a pen device that records its position in three-dimensional space.

Question 20

2d graphics

Answer 20

focuses on the task of converting two-dimensional shapes into patterns of pixels to produce an image.

Question 21

Diffuse light

Answer 21

When many light rays strike a surface at points whose orientations differ from that of the prefailing surface or also penetrate the immediate boundary of a surface and ricochet among the surface particles before finally departing as reflected light. The result is that many rays will be scattered in different directions. This is called diffuse light.

Question 22

The process of creating and displaying images: 2. Rendering

Answer 22

producing a two-dimensional image of the scene by computing how the objects in the scene would appear in a photograph made by a camera at a specified position. Applies the mathematics of analytic geometry to compute the projection of the objects in the scene onto a flat surface known as the projection plane in a manner analogous to a camera projecting a scene onto film.

Question 23

Radiosity

Answer 23

radiosity takes a more regional approach by considering the total light energy radiated between pairs of planar patches. This radiated light energy is essentially diffuse light. The light energy that is radiated from an object is either generated by the object (as in the case of a light source) or reflected off the object. The appearance of each object is then determined by considering the light energy it receives from other objects.

Question 24

Rasterization

Answer 24

The process of associating pixel compositions with points in the scene is called scan conversion or rasterization (because an array of pixels is known as a raster).

Question 25

Frame buffer

Answer 25

a storage area where each pixel, as the appearance of it is determined, are stored. May be an area of main memory, or, in the case of hardware designe specifically for graphics applications it may be a block of special purpose memory circuitry.

Question 26

Refraction

Answer 26

Light striking an object that is transparent rather than opaque. In this case light rays pass through the object rather than bounce off its surface. As the rays penetrate the surface their direction is altered. This phenomenon is called refraction.

Question 27

Procedural models

Answer 27

a program unit that applies an algorithm to generate a desired structure.

Question 28

Incidence angle

Answer 28

the angle at which a ray of light is reflected.

Question 29

Scene graph

Answer 29

the collective information of each objects location, size and orientation within a scene.

Question 30

Ambient light

Answer 30

“Stray” or scattered light that is not associated with any particular source or direction.

Question 31

Image processing

Answer 31

focuses on analyzing the pixels in an image in order to identify patterns that can be used to enhance or perhaps “understand” the image.

Question 32

Distributed ray tracing

Answer 32

rather than tracing a single ray backward from a point of reflection, distributed ray tracing traces multiple rays from that point, each extending in a slightly different direction.

Question 33

Flat shading

Answer 33

the use of the orientation of a planar patch as the orientation of each point on the patch. The result is that the final image will appear faceted rather than rounded. In a sense, flat shading produces an image of the polygonal mesh itself rather than the object being modeled by the mesh.