Unit 7: Graphics and Multimedia

Computer graphics is the creation, storage, and manipulation of images as digital data, while multimedia combines several media types (text, graphics, sound, video, animation) into a single interactive presentation. This unit builds on one core distinction — how an image is represented in memory — because that choice drives file size, editing behaviour, hardware needs, and every software decision downstream.

I. Foundations: How Computers Represent Images

Every digital image is ultimately numbers, but there are two rival schemes for turning a picture into numbers. Almost everything in this unit refers back to this split.

• Raster (bitmap) images: a grid of pixels, each holding a colour value. Resolution-dependent — scaling up causes blocky "pixelation." Used for photographs.
• Vector images: mathematical descriptions of shapes (lines, curves, fills). Resolution-independent — scale to any size with no quality loss. Used for logos and diagrams.
• Pixel: the smallest addressable point in a raster image; "picture element."
• Resolution: pixel dimensions (e.g. 1920 × 1080) or density in dots per inch (dpi) / pixels per inch (ppi).
• Colour depth (bit depth): bits used per pixel, fixing how many colours are possible.
  • 1-bit: 2 colours (black/white).
  • 8-bit: 256 colours (indexed palette).
  • 24-bit "true colour": ~16.7 million colours (8 bits each for Red, Green, Blue).
• Colour models: RGB (additive, for screens), CMYK (subtractive: Cyan, Magenta, Yellow, blacK, for print), HSB (Hue, Saturation, Brightness).

A rough uncompressed raster file size:

size (bytes) = width_px × height_px × (bit_depth / 8)
example: 800 × 600 × 3 = 1,440,000 bytes ≈ 1.4 MB

II. Understanding Graphics File Formats

A file format defines how image data is encoded, whether it is compressed, and what extra information it carries. Format choice trades quality against file size and against which features (transparency, animation, layers) survive saving.

A. Compression: the underlying decision

Compression shrinks files, and its type is the single most important property of any raster format.

• Lossless: discards no data; the image reopens identical to the original. Used where every pixel matters. Formats: PNG, GIF, BMP (uncompressed), TIFF.
• Lossy: discards detail the eye is unlikely to notice, achieving far smaller files at the cost of permanent quality loss. Repeated saving degrades the image ("generation loss"). Format: JPEG.

B. Raster file formats

Each format suits a different job.

• JPEG / JPG: lossy, 24-bit colour, adjustable quality. Best for photographs; no transparency, no animation. Small files for web use.
• GIF: lossless but limited to 256 colours (8-bit). Supports simple transparency and animation. Best for flat graphics and short animated clips.
• PNG: lossless, supports 24-bit colour plus an alpha channel for smooth partial transparency. The modern web standard for logos and screenshots.
• BMP: Windows bitmap, usually uncompressed and therefore very large. Simple, but rarely used online.
• TIFF: lossless, high quality, supports layers and CMYK. Favoured in publishing and archiving.

C. Vector and metafile formats

These store shapes, so they scale freely.

• SVG: Scalable Vector Graphics, an XML text format that browsers render natively.
• AI / EPS / CDR: native or exchange formats for Illustrator, PostScript, and CorelDRAW.
• Metafile / composite: formats such as PDF can hold both vector and raster content together.

D. Choosing a format

• Photograph for web: JPEG (small size).
• Logo with transparent background: PNG or SVG.
• Line art that must resize: vector (SVG).
• Print-ready master: TIFF or EPS with CMYK.

III. Getting Images into Your Computer

Before an image can be edited it must be captured or transferred into digital form. The main routes differ in whether the source is already digital or must be converted.

A. Scanners

A scanner converts a physical document or photo into a raster image by measuring reflected light.

• Mechanism: a moving light source illuminates the page; a CCD (Charge-Coupled Device) sensor reads reflected light row by row and converts it to pixel values.
• Types: flatbed (glass plate, general purpose), sheet-fed (documents pulled through), drum (high-end, professional).
• Key setting: scan resolution in dpi. Higher dpi means more detail and larger files; scan text at ~300 dpi, photos higher.
• OCR: paired Optical Character Recognition software turns a scanned page of text back into editable characters rather than a picture.

B. Digital cameras and smartphones

These capture images directly as digital files, skipping any physical print.

• Mechanism: light passes through a lens onto a CCD or CMOS sensor; the image processor stores it as a raster file, usually JPEG or a lossless RAW file.
• Megapixels: total pixel count (millions); a 12 MP sensor yields roughly 4000 × 3000 pixels.
• Transfer: via USB cable, memory card (SD), or wireless (Wi-Fi / Bluetooth / cloud sync).

C. Screen capture

Grabbing what is currently displayed.

• Method: the operating system copies the framebuffer — Windows Print Screen key or Snipping Tool — saving a raster image (commonly PNG).

D. Downloading and clip art

Acquiring images already in digital form.

• Sources: web downloads, clip art libraries, and stock photo sites.
• Caution: respect copyright and licensing; use public-domain or licensed material rather than copying arbitrary web images.

IV. Graphics Software

Graphics software provides the tools to create and edit images, and each program is built around either the raster or vector model from Section I.

A. Paint (raster) programs

These edit images pixel by pixel.

• Purpose: retouch photographs and paint free-form images by changing pixel colour values.
• Typical tools: brush, eraser, fill/bucket, selection (lasso, marquee), clone stamp.
• Layers: stack independent transparent sheets so elements are edited without disturbing others.
• Examples: Adobe Photoshop, GIMP (free), Microsoft Paint (basic), Corel Painter.
• Limitation: output is resolution-dependent and loses quality when enlarged.

B. Draw (vector) programs

These build images from editable shapes.

• Purpose: create logos, illustrations, and technical diagrams as scalable objects.
• Typical tools: pen/Bézier curves, shape primitives, node editing, path operations.
• Advantage: infinitely scalable and small file sizes; each object stays independently editable.
• Examples: Adobe Illustrator, CorelDRAW, Inkscape (free).

C. Specialist categories

Beyond the two core types, software targets specific tasks.

• 3-D modelling and animation: build and render objects in three dimensions — Blender, 3ds Max, Maya.
• CAD: precise engineering and architectural drawing — AutoCAD.
• Image viewers / organisers: catalogue and quickly display files without heavy editing.
• Common capabilities: format conversion (save-as between JPEG, PNG, etc.), cropping, resizing, colour adjustment, filters and special effects.

V. Multimedia Basics

Multimedia is the integrated use of multiple content types in a computer-controlled presentation, usually with interactivity that lets the user steer the experience.

A. The elements of multimedia

Multimedia is defined by the media it combines.

• Text: the base element; fonts, sizes, and hyperlinks convey information.
• Graphics: still images (raster or vector) that illustrate and decorate.
• Audio: speech, music, sound effects. Formats: MP3 (lossy), WAV (uncompressed), AAC.
• Video: moving images with sound, measured in frames per second (fps). Formats: MP4, AVI, MOV.
• Animation: computer-generated movement of graphics; frame-by-frame or tweened (software fills frames between keyframes).

B. Interactivity and hypermedia

The feature that separates multimedia from a passive film.

• Interactivity: the user controls navigation and pacing through buttons, menus, and links.
• Hypermedia: hyperlinks that jump between media elements non-linearly — the model behind web pages.

C. Analog vs digital, and key concepts

Media must be digitised before a computer can handle it.

1. Analog: continuous signals (traditional tape, film) — not directly usable by a computer.
2. Digital: discrete numeric samples — required for storage and editing.

• Sampling: measuring an analog audio wave many times per second. Sample rate in Hz (e.g. CD quality 44,100 Hz) sets fidelity.
• Streaming vs downloading: streaming plays media as it arrives; downloading stores the whole file first.

D. Applications and delivery

Where multimedia is used and how it reaches the user.

• Applications: education and e-learning, gaming, advertising, business presentations, virtual tours, and entertainment.
• Delivery media: optical disc (CD/DVD), the web, and mobile apps.
• Authoring tools: software that assembles the elements into a finished title — Adobe Animate, Adobe Director (historic), and presentation tools such as PowerPoint for simple work.
• Hardware demands: multimedia is resource-heavy, needing adequate RAM, storage, a sound card, a graphics card (GPU), and speakers or headphones.

E. Compression in multimedia

Because audio and video files are huge, compression is essential to their delivery.

• Codec: short for coder–decoder; software that compresses on save and decompresses on play (e.g. H.264 for video, MP3 for audio).
• Trade-off: as with images, stronger lossy compression means smaller files but reduced quality — the same principle established in Section II now applied to sound and motion.