MPEG Video Compression Standards Quiz
48 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the maximum number of motion vectors that can be sent from a B-frame's macroblock?

  • Three
  • One
  • Four
  • Two (correct)

    • In cases where a macroblock can be matched in only one reference frame, how many motion vectors will be used?

  • Only one motion vector (correct)
  • Only backward motion vector
  • No motion vectors
  • Two motion vectors from both frames

    • Which of the following is TRUE about MPEG-2 compared to MPEG-1?

  • MPEG-2 has only one defined profile.
  • MPEG-2 supports a higher bitrate than MPEG-1. (correct)
  • MPEG-2 is intended for lower quality video.
  • MPEG-1 was developed for digital broadcast TV.

    • What is one of the primary applications of MPEG-2?

    <p>Digital video broadcasting</p> Signup and view all the answers

    How many profiles are defined within the MPEG-2 standard?

    <p>Seven</p> Signup and view all the answers

    What is the maximum resolution allowed by the DVD video specification?

    <p>720 x 480</p> Signup and view all the answers

    What is a characteristic of the Simple Profile in MPEG-2?

    <p>It is optimized for low-delay videoconferencing.</p> Signup and view all the answers

    Which of the following is NOT one of the profiles defined in MPEG-2?

    <p>4:2:0 Profile</p> Signup and view all the answers

    What adjustment is made when the buffer within a rate control mechanism starts to empty?

    <p>The quantization step size is reduced.</p> Signup and view all the answers

    What is a primary benefit of using H.263 as a video coding standard?

    <p>It is designed for low bit-rate communications.</p> Signup and view all the answers

    Why are very high spatial frequency components less noticeable to humans in JPEG compression?

    <p>Psychophysical experiments show less perception of their loss.</p> Signup and view all the answers

    What is the primary reason for the loss of quality in JPEG compression?

    <p>The quantization step is the main source of loss.</p> Signup and view all the answers

    Which of the following describes the effect of increased scene activity on compression in video encoding?

    <p>Compression increases, reducing video quality.</p> Signup and view all the answers

    Which color space conversion is typically used in JPEG compression?

    <p>RGB to YIQ or YUV.</p> Signup and view all the answers

    What pixel precision does H.263 support compared to H.261?

    <p>Half-pixel precision.</p> Signup and view all the answers

    What is the effect of applying the DCT to 8x8 blocks in JPEG images?

    <p>It introduces blockiness to the image at high compression.</p> Signup and view all the answers

    What rate, at minimum, does H.263 aim to support for communications?

    <p>Below 64 kbps.</p> Signup and view all the answers

    How is the pixel value needed at half-pixel positions generated in H.263?

    <p>Through bilinear interpolation.</p> Signup and view all the answers

    How does changing the quantization matrix affect JPEG image quality?

    <p>It adjusts the amount of loss during compression.</p> Signup and view all the answers

    What is the purpose of run-length encoding in the JPEG compression process?

    <p>To encode repeated values more efficiently.</p> Signup and view all the answers

    Which network type was H.263 initially designed to utilize?

    <p>Circuit-switched networks.</p> Signup and view all the answers

    What does chroma subsampling in JPEG compression primarily address?

    <p>Minimizing the amount of color information retained.</p> Signup and view all the answers

    Which of the following best describes the compression and quality relationship in static versus active scenes?

    <p>Static scenes lead to low compression and high quality.</p> Signup and view all the answers

    What is the purpose of zig-zag ordering in JPEG image compression?

    <p>To prepare coefficients for entropy coding.</p> Signup and view all the answers

    What is the primary role of a Descriptor (D) in MPEG-7?

    <p>It represents a feature defined syntactically and semantically.</p> Signup and view all the answers

    Which tool in MPEG-7 is responsible for defining the structure and semantics of relationships between components?

    <p>Multimedia Description Schemes (DS)</p> Signup and view all the answers

    What foundational unit does MPEG-21 define for distribution and transaction purposes?

    <p>Digital Item</p> Signup and view all the answers

    Which concept relates to the interaction of users with Digital Items in the MPEG-21 framework?

    <p>User Interaction</p> Signup and view all the answers

    What is the main objective of MPEG-21 regarding Digital Items?

    <p>To support users in exchanging and consuming Digital Items efficiently.</p> Signup and view all the answers

    Which key element of MPEG-21 focuses on establishing a uniform declaration schema for Digital Items?

    <p>Digital item declaration</p> Signup and view all the answers

    In MPEG-7, which of the following tools handles aspects like binarization and transport of descriptors?

    <p>System tools</p> Signup and view all the answers

    What does the concept of Digital item identification in MPEG-21 aim to standardize?

    <p>Identification and description of digital items.</p> Signup and view all the answers

    What is the purpose of the base layer in spatial scalability?

    <p>to generate bitstream of reduced-resolution pictures</p> Signup and view all the answers

    Which of the following correctly describes temporal scalability?

    <p>It carries both base and enhancement layers at a reduced frame rate</p> Signup and view all the answers

    What is the significance of interlayer motion-compensation (MC) prediction in temporal scalability?

    <p>It helps refine predictions of matching macroblocks in the enhancement layer</p> Signup and view all the answers

    Which scalability type combines both spatial and rate-based elements?

    <p>Hybrid Scalability</p> Signup and view all the answers

    How does the enhancement layer in spatial scalability obtain higher resolution?

    <p>Through combining predicted macroblocks from both layers</p> Signup and view all the answers

    Which types of hybrid scalabilities can be formed?

    <p>Any combination of two of spatial, temporal, and SNR scalabilities</p> Signup and view all the answers

    Which process is performed by the base layer encoder in temporal scalability?

    <p>It executes normal single-layer coding procedures</p> Signup and view all the answers

    What is a characteristic of the base and enhancement layers in MPEG-2 spatial scalability?

    <p>They function independently without requiring synchronization</p> Signup and view all the answers

    What are the two main purposes of standardizing Profiles and Levels in MPEG-4?

    <p>Allowing testing for conformance and ensuring interoperability</p> Signup and view all the answers

    Which of the following profiles is NOT specified by MPEG-4?

    <p>Compression profiles</p> Signup and view all the answers

    What is the primary function of H.264 in video compression?

    <p>To offer better compression rates than MPEG-2 and H.263+</p> Signup and view all the answers

    Which standard primarily focuses on content-based retrieval of audiovisual objects?

    <p>MPEG-7</p> Signup and view all the answers

    What is a key feature of MPEG-7 regarding content description?

    <p>Description must be separate from the audiovisual content</p> Signup and view all the answers

    What technology does MPEG-7 use to store metadata?

    <p>XML</p> Signup and view all the answers

    Which of the following statements about H.264 is true?

    <p>It has two identical standards: ISO MPEG-4 Part10 and ITU-T H.264.</p> Signup and view all the answers

    Which characteristic does NOT apply to MPEG-4's object types?

    <p>They enhance the scalability of audio tracks.</p> Signup and view all the answers

    Study Notes

    2D Discrete Wavelet Transform (DWT)

    • Used for image input of size NxN
    • Convolve each row with h₀[n] and h₁[n], discard odd-numbered columns, concatenate
    • Convolve each column of the result with h₀[n] and h₁[n], discard odd-numbered rows, concatenate
    • One stage completes, resulting in four subbands (LL, HL, LH, HH)
    • LL subband can be further decomposed for more decomposition levels

    JPEG Standard

    • Developed by the Joint Photographic Experts Group (JPEG)
    • Formally accepted as an international standard in 1992
    • A lossy image compression method
    • Employs the Discrete Cosine Transform (DCT)
    • 2D DCT converts image from spatial domain (f(i, j)) to frequency domain (F(u, v))

    JPEG Observations

    • Observation 1: Image intensity changes slowly over small areas (spatial redundancy)
    • Observation 2: Humans are less sensitive to loss of high frequency components than low
    • Observation 3: Visual acuity is higher for grayscale than color (4:2:0 chroma subsampling used)

    JPEG Encoder Block Diagram

    • Input: YIQ or YUV image
    • DCT (8x8 blocks)
    • Quantization (Q(u,v) matrix)
    • Coding tables
    • Entropy coding
    • DPCM (DC coefficient)
    • Zig-zag ordering
    • Run-length encoding
    • AC coefficients
    • Header tables
    • Data

    DCT on Image Blocks

    • Divides images into 8x8 blocks
    • Appied 2D DCT to each block f(i, j)
    • Generates DCT coefficients F(u, v) for each block
    • Isolating each block from neighbouring context leads to "blocky" appearance at high compression

    Quantization

    • F(u, v) = round(F(u, v) / Q(u, v))
    • Represents quantized DCT coefficients for JPEG entropy coding
    • Main source of loss in JPEG compression
    • Compression ratio can be changed multiplicatively scaling Q(u, v) matrix
    • Quality factor in JPEG implementations is linearly tied to scaling factor

    Quantization Tables

    • Q(u, v) values tend to be larger towards lower right corner (higher loss at higher frequencies)
    • Psychophysical studies determine default Q(u,v) values to maximize compression ratio whilst minimizing perceptual losses

    Run-Length Coding (RLC) on AC Coefficients

    • Converts F(u,v) values into sets { #-zero-to-skip, next non-zero value }
    • Zig-zag scan turns 8x8 matrix into 64-vector to maximize zero runs

    DPCM on DC Coefficients

    • Differential Pulse Code Modulation (DPCM) for DC coefficients' coding
    • Different from AC coefficient coding
    • Computes differences between DC coefficients in successive image blocks

    JPEG Modes

    • Sequential Mode: Default mode, left-to-right, top-to-bottom scan
    • Progressive Mode
    • Hierarchical Mode
    • Lossless Mode: Discussed in Chapter 7, replaced by JPEG-LS

    JPEG 2000 Standard

    • More successful and popular image format than JPEG
    • Better rate-distortion tradeoff and improved subjective image quality
    • Additional functionalities lacking in current JPEG standard
    • Uses Embedded Block Coding with Optimized Truncation (EBCOT) algorithm
    • Partitions wavelet transform subbands into code blocks
    • Generates scalable bitstream for each code block, improving error resilience

    Layer Formation and Representation

    • JPEG 2000 offers resolution and quality scalability
    • Two-tiered coding strategy using layered bitstream organization
    • First tier produces embedded block bit-streams
    • Second tier encodes block contributions to each quality layer

    Region of Interest Coding in JPEG 2000

    • Images may contain important information in certain regions (ROI)
    • MAXSHIFT method scales ROI coefficients to higher bit-planes
    • ROI decoded and refined before rest of image at reduced bit-rate

    Problems with JPEG 2000

    • Higher computational demands
    • Higher memory demands

    H.261

    • Developed in 1990
    • Video compression standard (MC based)
    • Designed for videophone, video conferencing and audiovisual services over ISDN
    • Bit-rates of p x 64 kbps and delayed less than 150ms

    H.261 Frame Sequence

    • I-frames: Independent images using JPEG-style transform coding
    • P-frames: Dependent on previous P/I frame for prediction (forward predictive coding)
    • Temporal redundancy included in P-frame, spatial in I-frames

    Rate Control: Problem

    • H.261 encodes varying bit rates over constant bit rate channels (e.g 384 kbps)

    Rate Control: Solution

    • Buffered encoded bitstream
    • Increased quantization step size when buffer full
    • Reduced quantization step size when buffer empty

    H.263

    • Improved video coding standard (ITU-T)
    • Designed for low bit-rate communications (below 64 kbps)
    • For H.324, H.323, RTP/IP, RTSP solutions, streaming media and SIP

    Half-Pixel Precision

    • H.263 supports half-pixel precision for motion vectors, to reduce prediction error.
    • Uses bilinear interpolation to compute required half-pel pixel values

    Optional H.263 Coding Modes

    • Unrestricted motion vector mode: Motion vectors don't have to be within image boundary.
    • Syntax-based Arithmetic Coding Mode: Uses VLC/variable length coding for DCT coefficients
    • Advanced prediction mode: Four motion vectors from neighbouring blocks (left, right, above, below)
    • PB frames mode: Uses B-frames, similar to MPEG prediction, bidirectionally from previous and future frames

    MPEG Overview

    • Established in 1988 for digital video development
    • Defines only compressed bitstream to avoid proprietary interests
    • Compression algorithms are manufacturer's responsibility

    MPEG-1

    • Approved in 1991, for moving picture/audio storage
    • 1.5 Mbps bit-rates
    • Common storage media: CD, VCDs.
    • Uses specified CCIR601 digital TV format (SIF)
    • Non-interlaced coding, at 30/25fps, uses 4:2:0 chroma subsampling

    Motion Compensation in MPEG-1

    • Based on MC
    • Motion Estimation (ME) identifies best matching macroblock (MB) from previous I or P frame
    • Prediction error between current & matching MB sent for DCT
    • Uses forward prediction, previous frame as reference
    • Previous and next frames are potentially used for prediction

    Motion Compensation (MC) B-frame Coding

    • B-frames are predicted bi-directionally from previous and future frames, improving prediction accuracy
    • Weighted average of matches from forward and backward predictions are used as reference

    MPEG Frame Sequence

    • I/P/B frame arrangement (display vs coding order)

    MPEG-1 Video Bitstream

    • Layers of sequence header,GOP headers, picture headers, macroblocks and blocks
    • VLC encoding, run-length and Differential DC coefficient coding

    MPEG-2

    • Developed in 1994 & standard for higher quality video
    • Uses bitrates above 4 Mbps, initially for digital broadcast
    • Supports DVDs, digital video discs
    • Defines seven coding profiles for applications (low delay, scalable, HDTV)
    • Includes up to four levels per profile, defines display resolutions

    MPEG-2 Scalabilities

    • Provides flexibility via scalability in multiple domains:
    • SNR: Improves quality
    • Spatial: Higher resolution
    • Temporal: Higher frame rates
    • Hybrid: Combining features
    • Data Partitioning: Distributing DCT high/low frequencies

    SNR Scalability

    • Base layer has coarse quantization for fewer bits, low-quality video
    • Enhancement layer compares with original video and quantizes difference for coded refinement; bit-stream called Bits_enhance

    Spatial Scalability

    • Base layer produces lower resolution images; enhancement layer combines with base-layer predicted MB to get full resolution.

    Temporal Scalability

    • Input demultiplexed into two parts of reduced frame-rate, for encoding
    • Base layer uses normal single-layer procedures to generate Bits_base

    Hybrid Scalability

    • Combining any of above three types of scalabilities

    Data Partitioning

    • Base partition contains lower frequencies in DCT coefficients, and enhancement higher
    • Not considered layered coding; just breaks video data into separable partitions
    • Useful for noisy channels and progressive transmission

    Other Major Differences from MPEG-1

    • Better bit error resilience (Transport Stream)
    • 4:2:2 and 4:4:4 chroma for color quality
    • Non-linear quantization structure
    • More restricted slice structure
    • More flexible video formats

    MPEG-4 Overview

    • Focuses on user interactivity beyond basic compression
    • Uses object-based encoding
    • Allows for composition, manipulation, and retrieval of visual objects
    • Wide bit-rate range (5 kbps to 10 Mbps)

    MPEG-4 Object Types, Profiles, and Levels

    • Standardized profiles & levels ensure interoperability between implementations
    • Specifies visual, audio, graphics, scene description and object descriptor profiles

    MPEG-4 Part 10/H.264

    • New video compression standard (from JVT), which is also called H.264
    • Offers significant improvements (up to 30–50% better compression) vs. MPEG-2 or other standards
    • Designed for HDTV content

    MPEG-7

    • Facilitates audiovisual content retrieval using metadata
    • XML-based metadata is separate from actual encoding/storage

    MPEG-21

    • Defines a multimedia framework for multimedia distribution and consumption
    • Introduces a Digital Item as fundamental unit for distribution and transaction
    • Aims to provide technology for efficient item exchange/use

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    2D Discrete Wavelet Transform PDF

    Description

    Test your knowledge on MPEG video compression standards, focusing on MPEG-1 and MPEG-2, their profiles, and applications. This quiz covers motion vectors, resolutions, and the principles of video encoding and compression. Challenge yourself with advanced questions about video coding features and standards.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser