Computer Graphics, Multimedia & Mobile Computing
DSSSB TGT CS — Section B P2 (Rank ~7). Exam style: definitions, comparisons, format/compression traps.
1. Pixels, Resolution, Aspect Ratio
| Term | Meaning |
|---|---|
| Pixel | Smallest addressable picture element (picture element) |
| Resolution | Number of pixels (e.g. 1920×1080) — higher → sharper image |
| DPI / PPI | Dots/pixels per inch — print/screen density |
| Aspect ratio | Width : Height (e.g. 16:9, 4:3, 1:1) |
- Trap: Resolution is count of pixels, not file size. Compression changes size, not native resolution.
- Screen resolution ≠ print DPI (different contexts).
2. Raster vs Vector
| Raster (bitmap) | Vector | |
|---|---|---|
| Made of | Grid of pixels | Math curves/lines (paths) |
| Scale | Pixelates when enlarged | Scales cleanly |
| Best for | Photos, scanned images | Logos, icons, fonts, CAD |
| Formats | BMP, JPEG, PNG, GIF | SVG, AI, CDR, EPS (often) |
| Edit | Pixel-level | Object/path-level |
- Trap: JPEG is raster; SVG is vector.
3. Color Models
| Model | Type | Use |
|---|---|---|
| RGB | Additive (light) | Screens, cameras |
| CMYK | Subtractive (ink) | Printing |
| HSV / HSB | Hue, Saturation, Value/Brightness | Design / selection UI |
| Grayscale | Intensity only | B/W images |
- Primary additive: Red, Green, Blue → white when combined.
- Primary subtractive: Cyan, Magenta, Yellow (+ Black K) → darker when combined.
- Trap: Monitors use RGB; professional print workflows convert to CMYK.
4. Graphics Primitives
Basic drawing building blocks:
- Point, line, circle/ellipse, arc, polyline, polygon, rectangle, character/text
- Fill styles: solid, pattern, hatch
- Attributes: color, thickness, style (solid/dashed)
5. Line Algorithms (idea only)
| Algorithm | Idea |
|---|---|
| DDA | Digital Differential Analyzer — uses floating increments along slope |
| Bresenham | Integer arithmetic decision parameter — faster, preferred in exams |
- Both rasterize a continuous line onto discrete pixels.
- Trap: Bresenham avoids floating-point ops (exam favorite).
6. 2D Transformations
| Transform | Effect | Homogeneous idea |
|---|---|---|
| Translation | Move by (tx, ty) | Add offsets |
| Scaling | Enlarge/shrink by (sx, sy) | Multiply coords |
| Rotation | Rotate by θ about origin/point | Use sin/cos matrix |
| Reflection | Mirror across axis | Flip sign of coord |
| Shear | Skew shape | Off-diagonal factors |
- Order matters: rotate-then-translate ≠ translate-then-rotate.
- Composite transforms = multiply matrices (right-to-left apply order depends on convention).
7. Multimedia Components
| Component | Examples |
|---|---|
| Text | Plain, rich, hypertext |
| Audio | Speech, music, WAV/MP3 |
| Images | Still graphics/photos |
| Video | Sequence of frames + audio |
| Animation | Frame-by-frame or tweened motion |
| Hypermedia | Linked multimedia (web) |
- Multimedia = integrated use of multiple media types.
- Interactive multimedia: user controls flow (games, CBT).
8. Compression
| Type | Idea | Examples |
|---|---|---|
| Lossless | Exact rebuild | PNG, GIF (palette), ZIP, FLAC |
| Lossy | Discard “less noticed” data | JPEG, MP3, MPEG video |
| Format | Typical |
|---|---|
| JPEG | Lossy still images (photos) |
| PNG | Lossless images + transparency |
| GIF | Limited colors, simple animation |
| MP3 | Lossy audio |
| MPEG | Lossy video (family: MPEG-1/2/4) |
| WAV | Often uncompressed / lightly compressed audio |
- Trap: JPEG is lossy; PNG is lossless. MP3 is lossy audio.
9. Common File Formats (quick)
| Kind | Formats |
|---|---|
| Image | BMP, JPEG/JPG, PNG, GIF, TIFF, SVG |
| Audio | WAV, MP3, AAC, MIDI (instructions, not waveform) |
| Video | AVI, MP4, MKV, MPEG, MOV |
| Doc/vector | PDF, SVG |
- MIDI stores note events, not sampled sound (exam trap).
10. Mobile Computing — Networks
| Tech | Idea |
|---|---|
| GSM | Global System for Mobile — TDMA-based 2G family; SIM-centric |
| CDMA | Code Division Multiple Access — codes separate users on shared spectrum |
| GPRS / EDGE | Packet data on GSM path |
| 3G / 4G / 5G | Higher data rates generations |
- Cellular idea: geographic cells, frequency reuse, handoff/handover when moving.
11. Mobile OS
| OS | Notes |
|---|---|
| Android | Google; Linux-based kernel; open ecosystem; APK |
| iOS | Apple; closed ecosystem; App Store |
| Others (legacy/exam) | Windows Mobile/Phone, Symbian, BlackBerry OS |
- Apps: native vs web vs hybrid.
- Sensors: GPS, accelerometer, gyroscope, camera — enable location/AR apps.
12. Wireless Short-Range
| Tech | Typical range / use |
|---|---|
| Bluetooth | Short range PAN — headsets, file transfer, IoT |
| Wi-Fi (IEEE 802.11) | LAN/WLAN internet access |
| NFC | Very short range — payments, pairing |
| Infrared (IR) | Line-of-sight (older mobiles) |
- Trap: Bluetooth ≠ Wi-Fi; different range, power, and primary use.
13. VR / AR Keywords
| Term | Meaning |
|---|---|
| VR (Virtual Reality) | Fully immersive computer-generated environment |
| AR (Augmented Reality) | Digital overlays on real world (camera/glasses) |
| MR / XR | Mixed / umbrella extended reality terms |
| HMD | Head-mounted display |
| Degrees of freedom | 3DoF / 6DoF tracking |
- VR replaces view; AR adds to real view.
- Exam: Pokémon GO-style → AR; full headset game world → VR.
Quick Revision Traps
- Bresenham = integer decisions; DDA = floating increments.
- RGB = screens; CMYK = print.
- Raster scales poorly; vector scales well.
- JPEG/MP3/MPEG → lossy; PNG/ZIP → lossless.
- MIDI is not recorded audio samples.
- GSM vs CDMA = different multiple-access families.
- AR overlays reality; VR immerses in virtual world.