Graphics Hardware and Display Systems
Understanding the hardware used for computer graphics is essential because the capabilities and limitations of the display and input devices shape the algorithms we use. This chapter surveys the major categories of graphics hardware—display devices, input devices, frame buffers, and graphics processing units—while explaining how images are formed and refreshed on the screen.
Raster and Random-Scan Displays
Two fundamental display architectures are the random-scan (vector) display and the raster-scan (bitmap) display. A random-scan display directs the electron beam directly to the endpoints of lines to be drawn, producing smooth, flicker-free vector graphics suitable for engineering drawings. A raster-scan display, in contrast, sweeps the beam in a fixed pattern of horizontal scan lines from top to bottom, lighting up individual pixels to form an image. Almost all modern displays are raster based.
Cathode Ray Tube (CRT) Operation
Although largely obsolete, the CRT illustrates several concepts reused in modern displays. An electron gun emits a beam that is focused and deflected by magnetic or electrostatic fields toward a phosphor-coated screen. When the beam strikes the phosphor, it emits light whose colour depends on the phosphor type. In colour CRTs, three beams—one for each primary colour—pass through a shadow mask, hitting red, green, and blue phosphor dots. The image must be refreshed many times per second (typically 60 Hz or higher) to avoid flicker, a constraint that dictates the bandwidth of the video signal.
Flat-Panel Displays
Modern flat-panel technologies avoid the bulk and weight of CRTs. Liquid Crystal Displays modulate a backlight using voltage-controlled liquid crystals combined with colour filters. Light-Emitting Diodes provide the backlight in LED-backlit LCDs or act as the pixels themselves in OLED displays, where each pixel emits its own light. Micro-LED, quantum-dot enhanced LCD, and plasma screens represent further refinements. Key parameters include resolution, pixel pitch, contrast ratio, colour gamut, and refresh rate.
Frame Buffers and Video Controllers
A frame buffer is a block of memory in which the colour of every pixel on the screen is stored. For a 1920×1080 display with 24-bit colour, the frame buffer requires about 6 MB. The video controller reads the frame buffer at the refresh rate and sends the signal to the display. Double buffering uses two frame buffers—one being displayed and one being drawn—to eliminate tearing; the buffers are swapped during the vertical blanking interval.
Graphics Processing Units
The GPU is a specialized co-processor designed for the parallel computations common in graphics. A modern GPU contains thousands of small cores organized into streaming multiprocessors, dedicated memory, texture units, and fixed-function hardware for rasterization and tessellation. Programming APIs such as OpenGL, Vulkan, Direct3D, and Metal expose this hardware to application developers. Compute APIs such as CUDA and OpenCL allow the GPU to be used for general-purpose calculations beyond graphics.
Input Devices
Interactive graphics requires input devices. The mouse, keyboard, and touch screen are the most common. Trackballs, joysticks, data gloves, digital tablets, and 3D motion trackers serve specialized roles in gaming, CAD, and virtual reality. Scanners and cameras convert real-world images into digital form for processing.
Resolution, Aspect Ratio, and Colour Depth
Resolution is the number of pixels displayed horizontally and vertically. Aspect ratio is the ratio of horizontal to vertical extent of the display area; 16:9 is now standard for televisions and monitors. Colour depth is the number of bits used to represent each pixel's colour; 24 bits (true colour) allows 16.7 million distinct colours. Higher dynamic range (HDR) displays use 10 or 12 bits per channel to capture a wider range of brightness.
Printers and Plotters
Hardcopy output requires different hardware. Laser printers use electrostatic charge on a photosensitive drum to transfer toner to paper. Inkjet printers spray precisely timed droplets of ink. Plotters draw vectors directly with a pen and are used for large engineering drawings. 3D printers extend the idea to physical objects by depositing material layer by layer.
Summary
Graphics hardware spans a wide range of devices designed to transform digital data into visible output and to capture human input. Understanding the characteristics of these devices—refresh rate, resolution, colour depth, and bandwidth—is essential for designing efficient graphics software.