Q5Computer Graphics and Multimedia

JPEG (ISO/IEC 10918) is the dominant standard for photographic image compression. It is a lossy compression method (baseline JPEG mode) with the following processing steps:

• Step 1 — Color Space Conversion: Convert RGB to YCbCr (Y=luminance, Cb/Cr=chrominance). Human eyes are more sensitive to luminance than chrominance.
• Step 2 — Downsampling: Chrominance channels (Cb, Cr) are downsampled (typically 4:2:0 — halved in both dimensions) since humans perceive less color detail.
• Step 3 — Block Division: Each channel is divided into 8×8 pixel blocks.
• Step 4 — DCT (Discrete Cosine Transform): Applied to each 8×8 block, converting spatial information to frequency domain. Low-frequency components (top-left of DCT matrix) contain most of the visual information.
• Step 5 — Quantization (Lossy): Each DCT coefficient is divided by a quantization value and rounded. High-frequency coefficients are quantized more aggressively (less visible to human eye). Quality factor controls quantization aggressiveness.
• Step 6 — Entropy Coding: Quantized coefficients are ordered in zigzag scan, run-length encoded (exploiting zero runs), then Huffman coded.
• Achieves 10:1 to 20:1 compression; baseline JPEG widely supported; JPEG2000 uses wavelets.

MPEG (ISO/IEC 11172, 13818, 14496) standards define audio-video compression for different applications. MPEG exploits both intra-frame (spatial) and inter-frame (temporal) redundancy.

• I-Frames (Intra-coded): Self-contained frames compressed like JPEG using DCT. Serve as random-access points.
• P-Frames (Predictive): Encoded as difference (residual) from previous I or P frame using Motion Compensation — only changed blocks are encoded.
• B-Frames (Bidirectional): Predicted from both previous and future reference frames — highest compression, lowest quality, requires reordering.
• Motion Estimation: Video is divided into macroblocks; motion vectors indicate how each block moved between frames.
• GOP (Group of Pictures): Sequence pattern like IBBPBBPBBI defining frame arrangement.
• MPEG-1: VCD quality (~1.5 Mbps, 352×240); MPEG-2: DVD and HDTV (2-80 Mbps); MPEG-4: Internet video (H.264/AVC, H.265/HEVC — most efficient modern codecs).
• MPEG Audio: MP3 (MPEG-1 Layer 3), AAC (MPEG-4 Audio) — uses psychoacoustic masking.

Virtual Reality (VR) is a computer-generated, three-dimensional interactive environment that immerses users in a simulated world, replacing or augmenting their real-world environment. VR systems use specialized hardware and software to create convincing sensory experiences.

• Head-Mounted Display (HMD): Stereoscopic displays (one per eye) with head tracking, creating 3D depth perception. Examples: Oculus Quest, HTC Vive, PlayStation VR.
• Motion Controllers: Track hand/controller position and orientation; provide haptic feedback.
• Positional Tracking: Inside-out (cameras on HMD) or outside-in (external sensors) track body position in 3D space.
• High-Performance Rendering: Must render at 90+ fps at high resolution for both eyes (2× for stereo) to prevent motion sickness.
• Spatial Audio: 3D positional audio matching the virtual environment to enhance immersion.

• Immersive VR: Full immersion with HMD (Oculus, Vive).
• Non-Immersive VR: Desktop-based virtual environments (e.g., 3D simulations on a monitor).
• Semi-Immersive VR: Large-screen displays, CAVE (Cave Automatic Virtual Environment) systems.
• Augmented Reality (AR): Overlays digital elements on the real world (HoloLens, smartphone AR).
• Mixed Reality (MR): Digital objects interact with the real world.

• Medical Training & Surgery Simulation: Surgeons practice complex procedures risk-free (e.g., laparoscopic surgery training).
• Military & Defense: Flight simulators, combat training, PTSD therapy.
• Education: Virtual field trips, molecular visualization, historical reconstructions.
• Architecture & Real Estate: Virtual walkthroughs of unbuilt structures.
• Gaming & Entertainment: Fully immersive gaming experiences (Beat Saber, Half-Life: Alyx).
• Industrial Training: Safe simulation of dangerous procedures (mining, chemical plants, power stations).
• Rehabilitation & Therapy: Physical therapy, phobia treatment (acrophobia, arachnophobia), pain management.
• Automotive Design: Virtual prototyping and ergonomics testing without physical models.
• Space Exploration Training: NASA uses VR for astronaut training and spacewalk simulation.

• Motion Sickness (Cybersickness): Caused by mismatch between visual and vestibular systems — mitigated by high refresh rates (90+ Hz) and accurate tracking.
• High Computational Cost: Requires powerful GPUs to render stereo images at high frame rates.
• Latency: Motion-to-photon latency must be below 20ms to prevent discomfort.
• Content Creation: Creating high-quality VR content is more complex than traditional 3D content.
• Cost and Accessibility: High-end VR hardware remains expensive for mass adoption.