Computer Graphics - Introduction

Computer Graphics

Lecture 01 – Introduction

Edirlei Soares de Lima

<edirlei.lima@universidadeeuropeia.pt>

What is Computer Graphics?

•

The term computer graphics describes

any use of computers to create and

manipulate images [Marschner, S., et

al., 2015].

Computer graphics is the science and

art of communicating visually via a

computer’s display and its interaction

devices. [Hughes, J. F., et al., 2013]

What is Computer Graphics?

•

Computer graphics is a cross-disciplinary field:

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Physics (e.g.: model light behavior);

Mathematics (e.g.: describe shapes);

Human Perception (e.g.: only render things that will be

noticed);

–

Human-Computer Interaction (e.g.: interaction devices);

Engineering (e.g.: optimize allocation of memory, and

processor time);

–

Graphic Design and Art (e.g.: make the computer-to-

human communication more effective);

What is Computer Graphics?

Geometric Modeling

Data

Rendering and

Computer Vision

Animation

Image

Image Processing

Computer Graphics Areas

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Modeling: Deals with the mathematical specification of shape

and appearance.

–

Definition of surface, interpolation rules, reflection models.

Computer Graphics Areas

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Rendering: Term inherited from art – create shaded images

from 3D computer models.

–

Many techniques and styles of rendering.

Computer Graphics Areas

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Animation: technique to create an illusion of motion through

sequences of images.

–

Time is a key issue, not usually dealt with in basic modeling and

rendering.

Computer Graphics Areas

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Image processing: deals with the manipulation of 2D images

and is used in both the fields of graphics and vision.

Computer Graphics Areas

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Virtual reality: attempts to immerse the user into a 3D virtual

world.

–

Typically requires at least stereo graphics and response to head

motion.

Computer Graphics Areas

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3D scanning: uses range-finding technology to create

measured 3D models.

Computer Graphics Areas

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Computational photography: explores the use of computer

graphics, computer vision, and image processing methods to

enable new ways of photographically capturing objects,

scenes, and environments.

Applications – Video Games

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Video games increasingly use sophisticated 3D models and

rendering algorithms.

Applications – Cartoons

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Cartoons are often rendered directly from 3D models.

–

Many traditional 2D cartoons use backgrounds rendered from 3D

models.

Applications – Visual Effects

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Visual effects use almost all types of computer graphics

technology.

–

Superimpose backgrounds with separately filmed foregrounds.

–

Synthetic environments, objects, and even characters.

Applications – Animated Films

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Animated films use many of the same techniques that are

used for visual effects, but without necessarily aiming for

images that look real.

Applications – CAD/CAM

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Computer-Aided Design and Computer-Aided Manufacturing

use computer technology to design parts and products on the

computer to guide the manufacturing process.

Applications – Simulation

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Simulation can be thought of as accurate video gaming.

Applications – Medical Imaging

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Medical imaging creates meaningful images of scanned

patient data.

Applications – Information Visualization

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Information visualization creates images of data that do not

necessarily have a “natural” visual representation.

Graphics APIs

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A graphics API (Application Program Interface) is a set of

functions that perform basic operations such as drawing

images and 3D surfaces into windows on the screen.

–

Graphics APIs vs User-Interface APIs.

Dominant Graphics APIs: Direct3D and OpenGL.

Graphics Hardware

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Computer hardware and software (graphics card and device

driver) that generates computer graphics and allows them to

be shown on a display.

The processors on GPUs are highly parallel and support

thousands of concurrent threads.

–

The hardware is designed to process larger numbers of pixels and

vertices in short amounts of time.

Graphics Pipeline

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The Graphics Pipeline is a special software/hardware

subsystem that efficiently draws 3D primitives on screen.

–

Is optimized for processing 3D triangles with shared vertices.

The basic operations in the pipeline map the 3D vertex

locations to 2D screen positions and shade the triangles so

that they both look realistic and appear in proper back-to-

front order.

–

Geometric manipulation using matrices and vectors.

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The speed at which images can be generated depends

strongly on the number of triangles being drawn.

Raster Images

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Most computer graphics images are

presented to the user on some kind of raster

display.

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Raster displays show images as rectangular arrays

of pixels.

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Different colors are achieved by mixing varying

intensities of red, green, and blue light.

A raster image is simply a 2D array that stores

the pixel value for each pixel—usually a color

stored as three numbers, for red, green, and

blue (RGB model).

Raster Devices

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Displays:

–

Current displays (televisions, computer displays, digital cinematic

projectors) are nearly universally based on fixed arrays of pixels.

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Emissive displays directly emit controllable amounts of light (e.g. LED).

Transmissive displays require a light source to illuminate the pixels,

which vary the amount of light that they allow to pass (e.g. LCD).

Input Devices:

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Digital cameras are 2D array input devices. The image sensor is a

semiconductor device with a grid of light-sensitive pixels.

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The camera’s lens projects an image of the scene to be photographed

onto the sensor, and then each pixel measures the light energy falling

on it, ultimately resulting in a number that goes into the output image.

Graphics Coding Tips

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Class Design: vector2, vector3, vector4, matrix4x4, transform, ...

Float vs. Double: tradeoff between performance and precision.

Optimizations are important, but unnecessary "optimizations"

make the code harder to read without speeding things up.

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Debugging Graphics Programs:

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Images as coded debugging output;

Traditional debugger;

Data visualization for debugging;