1.2 - What is 3D Computer Graphics?

Basic Definitions

Computer graphics are pictures and movies created using computers. (1)

There are two basic ways to describe a picture using a computer:

  • Raster graphics, which describes a picture using many small dots of color. The dots are typically arranged in a rectangular grid. Each dot is called a pixel, which is an abbreviation for “picture element”. If the dots are small enough and close enough together, a person does not sees the individual dots, but rather sees a “picture” (or “image”).
  • Vector graphics, which describes objects as geometric shapes using mathematical equations. A picture is created from the mathematical descriptions through a process called rendering. The results of a rendering is a 2-dimensional raster image.

Computer tools have been developed to create and manipulate both types of computer graphics. For example, Adobe PhotoShop is the premier tool for working with raster images. (An open-source equivalent to PhotoShop is gimp.) Creating new images by manipulating many small dots of color is not advantageous for animations where objects are changing over time. PhotoShop is great for creating single images or “touching up” an existing image, but it is an inadequate tool for creating movies.

Computer-generated imagery (CGI) is the application of computer graphics tools to create or manipulate images in art, printed media, video games, films, television programs, commercials, videos, and simulators. (2) The average person has probably only heard the term CGI in relationship to video games and movies, but it has wide applications to many fields.

3D computer graphics are graphics that use three-dimensional representations of geometric data for the purposes of performing calculations and the rendering of 2D images. (3) This textbook teaches you how to use 3D computer graphic techniques to create CGI. Or, said more technically, these tutorials teach you how to create vector graphic representations of 3-dimensional objects and then render them into a raster image.

If you can create data and algorithms that render raster images in less than 1/30th of a second, you can create real-time video. Most video games are based on real-time rendering. If it takes longer than 1/30th of a second to create each image, you can always store the images to a file and play them back in real-time. Most movie CGI is not rendered in real-time. In fact, it is not uncommon for the CGI processing for a single image (frame) of a movie to take from 1 to 10 hours!

Summary

The field of computer graphics uses computational devices to create images from geometric descriptions of 3D objects or from algorithmically created data.

Note

Don’t confuse computer graphics with image processing. Computuer Graphics applications create raster images as their output. Image Processing takes a raster image as input and manipulates it or tries to interpret what the image means. Image enhancement and face recognition are sub-fields of image processing.

Note

Raster images are also sometimes called bitmaps. In general, a bitmap is a mapping from information to binary numbers, or bits. Since a raster image is a set of pixel color values stored as binary numbers, it is indeed a bitmap. The term bitmap is more generic, while raster image is specifically a computer graphics term. Some people use bitmap to refer to a black and white image where each pixel is a single bit, and they use the term pixmap for images that have multiple bits per pixel.

Jobs in Computer Graphics

The field of computer graphics is very broad and includes many different types of jobs, ranging from artists to technicians. Here are just a few recent job openings related to computer graphics:

  • Character Artist - design and create models of animated characters (e.g., Kermit the Frog).
  • FX Artists - design and create models of special effects, such as explosions.
  • Senior Concept Artist - design storyboards for animations or movies.
  • 3D Animator - design the motion of animated characters.
  • Systems Engineer (GPU Architecture Modeling) - drive the next generation of GPU architecture and rendering APIs through rigorous top-down modeling process.
  • Graphics Performance Engineer - Analyze graphics application performance.
  • Software Engineer, Graphics - pioneer, develop and build out our stunning visual experiences.
  • Computer Graphics Research Scientist - develop new algorithms from foundational theory.

Most, if not all, computer graphics projects are a team effort because of the large range of skills needed. Just take a look at the credits of any movie that contains CGI content to understand the number of people involved!

This textbook teaches the technical side of computer graphics and its intended audience is computer scientists who want to build computer applications that contain 3D graphical content, especially in a web browser.

Glossary

computer graphics
pictures and movies created using computers.
raster graphics
a picture defined by many small dots of color.
vector graphics
a picture defined by geometric data and/or algorithms.
bitmap
a picture where each pixel is a single binary digit (0/1 for black/white)
pixmap
a picture where each pixel is represented by more than one bit.
computer-generated imagery (CGI)
using computers to create or modify raster images.
3D computer graphics
using computers to create raster images from vector graphics data.
render
the specific process that creates a raster image (picture) from vector graphics data.

Assessments

    Q-5: A raster graphics image is composed of what?
  • A rectangular grid of pixels, where each pixel has a specific color.
  • Yes. Each pixel is a *picture element*.
  • A description of a scene, including the types of objects in a scene (e.g., a dog eating a bone.)
  • No. But this might be the output of an *image processing* detection algorithm.
  • A set of geometric primitives, such as lines, arcs, polygons, etc.
  • No. This is a *vector graphics* image description.
  • A group of spline curves that form an interesting pattern.
  • No. This is a *vector graphics* image description.
    Q-6: How do you define a scene for a 3D computer graphics rendering?
  • A rectangular grid of pixels, where each pixel has a specific color.
  • No. This is a *raster image*.
  • A description of the types of objects in a scene (e.g., a boy walking a dog.)
  • No. The computer does not understand such high level descriptions.
  • A set of geometric primitives, such as points, lines, and/or triangles.
  • Yes. A *3D computer graphics* rendering creates a picture from the geometric primitives.
  • A group of colors.
  • No. Color information is important, but insufficient to create a rendering.
    Q-7: Which answer below best describes the input and the output of 3D computer graphics?
  • Input: geometric primitives; Output: raster image
  • Correct.
  • Input: raster image; Output: modified raster image
  • No, this is image processing.
  • Input: pixels; Output: geometric primitives
  • No, this is converting an raster image into a "higher level" description, which is image processing.
  • Input: small dots of color Output: a scene description in English
  • No, this is image processing.
    Q-8: Real-time 3D computer graphics means …?
  • the rendering of a scene can be produced in less than 1/30th of a second.
  • Correct. Displaying 30 frames per second allows most people to perceive motion without flicker.
  • the resulting image contains the current time.
  • No, that's silly!
  • the rendering of a scene happens right now.
  • Maybe, but the important issue is whether 30 or more images per second can be created.
  • the rendering is really fast.
  • No, fast rendering does not guarantee motion without flicker, the number of frames per second does.
Q-10: Q-9: Perform a web search using the search term "computer graphics jobs" and examine the details of some of the jobs you find. Now describe the type of job you would enjoy being qualified to apply for.

Next Section - 1.3 - The 3D Graphics Pipeline