OpenGL

Computer graphics is a process of generating images using a computer. Images can be realistic imitations to piecharts and everything in between, including graphical user interfaces.

It is a subfield of visual computing. Visual computing, aka image informatics, is a field that deals with both image analysis and image synthesis.

In perspective projection, what is visible to the camera(or eye) can be modeled as frustum (apex chopped off a rectangular pyramid).

Perspective View

In this diagram, the invisible apex of the pyramid represents the camera (or viewer).

The smaller area (chopped top of the pyramid) is called near clipping plane (or near plane). The objects lying between the camera and near plane is not visible.

The larger rectangular surface at rear (or the base of the pyramid) is called far clipping plane (or far plane). The objects behind this surface is invisible to the camera.

The objects outside the other four boundries is also not visible.

The process of determining which objects (or parts of the objects) are inside this frustum shown in the diagram is called 3D clipping. It is very important in CG because it helps to avoid the unneeded computations and speeds up the rendering of the scene. If a object is inside the frustum does not mean that it is visible; it could be obscured by other objects.

The process of determining which parts of the objects is invisible to the viewer is called hidden face culling.

Clipping and culling together determines the visibility of the objects in the scene.

The process of generating two dimensional image from a 3D dimensional scene is called rendering.