Basics of a Computer Graphics System

Introduction to Computer Graphics CSE 470/598

Arizona State University

Dianne Hansford

Elements

Input Devices

ProcessorMemory

Frame Buffer

Output Devices

keyboard, mouse

CRT (cathode-ray tube)

pixels live here,VRAM, DRAM memory

rasterization:geometry to pixels

Frame Buffer (FB)

A picture is produced by an n x m array of pixels (picture elements)

Also known as raster

Pixels live in memory called the frame buffer.

Fast re-display of FB implemented with special memory: DRAM, VRAM

Frame Buffer Depth

Depth: number of bits for each pixel number of colors represented

1 bit = 2 colors (black and white)

8 bit = 2^8 = 256 colors

16 bit = “high color”

24 bit = 16M colors “full color” or “true color”

32 bit = a lot!RGB color

Color index mode Color map

RGB Color

Primary colors: red, green, blue

In each pixel, individual bits assigned to each color

24 bit 8 bits R, 8 bits G, 8 bits B

RGB Color Scheme

Frame Buffer Resolution

Resolution: number of pixels

640 x 480 ≈ 300K pixels

1024 x 768 ≈ 780K pixels

1600 x 1200 ≈ 2M pixels

color bufferdepth buffer

buffer data stored uniformlyfor each pixel

fragments = pre-FB rasterization info, correspond to pixels, color and depth

Output Device: Raster System

Pixels from FB displayed as points on CRT

CRT: electrons strike phosphor and light is emitted and directed toward screen 3 phosphors: RGB

Light emitted a short time (milliseconds) must refresh

Common: refresh at 60-80 Hz (times per second)

Other rasters: LCD, plasma, digital projection, …