Chapter I: Basics
Although computer graphics is a vast field that encompasses almost any graphical aspect, we are mainly
interested in the generation of images of 3-dimensional scenes. Computer imagery has applications for film
special effects, simulation and training, games, medical imagery, flying logos, etc.
Computer graphics relies on an internal
of the scene, that is, a mathematical representation
suitable for graphical computations (see Chapter II).
The model describes the 3D shapes, layout and
materials of the scene.
This 3D representation then has to be projected to compute a 2D image from a given viewpoint, this is
step (see Chapter III). Rendering involves projecting the objects (perspective), handling
visibility (which parts of objects are hidden) and computing their appearance and lighting interactions.
Finally, for animated sequence, the motion of objects has to be specified. We will not discuss animation
in this document.
A computer image is usually represented as a discrete grid of picture elements a.k.a.
. The number
of pixels determines the
of the image. Typical resolutions range from 320*200 to 2000*1500.
For a black and white image, a number describes the intensity of each pixel. It can be expressed between
0.0 (black) and 1.0 (white). However, for internal binary representation reasons, it is usually stored as an
integer between 0 (black) and 255 (white)
A low-resolution digital image. Left: Black and white. Right: Color.
(Image © Pixar).
For a color image, each pixel is described by a triple of numbers representing the intensity of red, green and
blue. For example, pure red is (255, 0, 0) and purple is (255, 0, 255).
Because the image is represented by a discrete array of pixels,
problems may occur. The most
classical form of aliasing is the jaggy aspect of lines (see figure below).
techniques are thus
required. In the case of the line, it consists in using intermediate gray levels to “smooth” the appearance of
the line. Another form of aliasing can be observed on television when people wear shirts with a fine