Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

TM355 > Block 2 Part 3 > Flashcards

Block 2 Part 3 Flashcards

1
Q

Perceptual redundancy

A
  • information contained in audio or visual signal that can be removed without affecting recipients experience of signal
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Compression level (coding efficiency

A
  • this is how far you can compress a file

- there is a trade off between how far you can compress a file and keeping enough of the original signal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Permissible distortion

A
  • once acquired a digital source representation, need to represent it using the smallest number of bits possible for permissible distortion
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Coding source into fewest possible number of bits

A
  • allows either lower bit rate (bandwidth) to be used for transmitting compressed data
  • or transmission to be completed faster
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Rate distortion (RD)

A
  • in all source coding algorithms, relationship between compression level achieved and resulting distortion formalised by RD
  • every source coding algorithm has RD
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Pulse code modulation (PCM)

A
  • digitising analogue signal normally done by PCM
  • analogue signal first subjected to sampling to create pulse amplitude modulation (PAM) signal
  • each sample assigned to one of finite number of possible discrete values in process called quantising
  • resulting bitstream goes through further lossless encoding to minimise final bit rate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Aliasing

A
  • means not enough samples taken so wave is just an alias of original
  • still has same shape but more spread out
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Analogue-to-digital converter (ADC)

A
  • combined process of sampling and quantising usually performed by ADC
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Quantisation noise (quantisation error)

A
  • difference between original and digital signals
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Differential pulse-code modulation (DPCM)

A
  • variant of PCM that also converts source analogue signal to digital representation
  • able to achieve lower bit rate by including sample prediction in its coding
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Advantages of DPCM over PCM

A
  • successive samples not very different from each other
  • encoder and decoder predict next sample will be same as current one
  • transmitted difference value is then error in prediction
  • difference values also known as prediction errors
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

MPEG-1

A
  • mainly used for efficient storage of moving pictures for multimedia on CD-ROM
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

MPEG-2

A
  • toolbox of optimised compression techniques for DTV systems to support both SD and HD picture resolutions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

MPEG-4

A
  • intended to provide high compression rates, allowing for transmission of moving pictures at bit rates below 64 kbit s-1
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

MPEG-7

A
  • specifies way multimedia can be indexed, and thus searched for in variety of ways relating to specific medium
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

MPEG-21

A
  • extends this notion further by including additional digital rights management (DRM) into MPEG systems
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Objective of JPEG and MPEG coding

A
  • removal of as much statistical and perceptual redundancy as possible, to achieve highest compression
  • this achieved in two stages
  • Spatial compression and Temporal compression
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Spatial compression

A

exploits fact that in many real pictures considerable similarity (correlation) exists between neighbouring areas of image

19
Q

Spatial compression - intra-frame compression

A
  • each individual picture able to be compressed

- basis of JPEG image compression standard

20
Q

Temporal compression

A
  • exploits fact that in most sequences, very little changes between consecutive frames
21
Q

Temporal compression - inter-frame compression

A
  • high correlation between frames offers further lossy compression opportunities, by removing detail without loss of quality
22
Q

JPEG coding

A
  • de facto lossy compression standard for colour and greyscale images
    though known as lossy it does have lossless mode
23
Q

JPEG limitations

A
  • no interactive functionality, cannot compress region of interest at different bit rate from remainder of image
  • not optimised for either natural images or synthetic computer generated images
  • poor compression of compound documents containing both images and text
  • degraded performance in noisy channel conditions
24
Q

JPEG2000

A
  • low-bit rate image compression standard
  • offers interactive, multi resolution and scalable functionality
  • superior coding performance with fewer visually perceptible artefacts
25
Q

JPEG2000 bitstream scalability

A
  • image can change its representation to satisfy requirements of application or receiver
26
Q

JPEG2000 discrete wavelet transform (DWT)

A
  • decomposes image into four sub images, each having different resolution corresponding to different frequency band
  • original image can be reconstructed by combining four images
27
Q

Region of interest

A
  • if in an image you are wanting to ensure a certain area has better quality than surrounding area then JPEG2000 can be used
  • Lossless compression is applied to this area to ensure the image is of high standard
  • the rest of the image can be coded at a much lower resolution
28
Q

Motion JPEG(M-JPEG)

A
  • allows moving images to be compressed

- uses only intra frame compression

29
Q

Motion vectors

A
  • means the difference in frame movement between two frames in a movie or video
30
Q

Motion prediction

A
  • idea is to predict current frame from previous frame by calculating set of MVs then determine motion prediction error
  • this prediction can then be compensated for at the decoder
31
Q

Three main picture types supported by MPEG

A
  • I-frames
  • P-frames
  • B-frames
32
Q

I-frames

A
  • (intra frame) are JPEG-coded and used as reference for random access in MPEG bitstreams
  • coded independently without reference to other picture types
  • don’t use motion vectors
  • achieve only low compression
  • used any time shot changes from one sequence to another
33
Q

P-frames

A
  • (prediction) use motion prediction and compensation to achieve higher compression than I-frames
  • used as reference for both future and past predictions
  • don’t offer random access capability within coded bitstream
34
Q

B-frames

A
  • (bidirectional prediction) interpolated frames between _ and P-frames in both forward and backward directions
  • not used as reference but fill in missing frames
  • provide highest compression and don’t propagate coding errors
35
Q

Correcting prediction

A
  • find best prediction using block-matching algorithm to determine set of motion vectors
  • calculate prediction error between estimated and actual object positions, transmit alongside motion vectors
36
Q

Group of pictures

A
  • used by MPEG to refer to particular combination of frames that represent sequence
  • always start with reference I-frame
  • defined by two parameter, total number of frames in GOP and number of adjacent B-frames plus one
37
Q

H.264/AVC

A
  • supports high quality delivery of audio and video
  • also low bit rate IP based streaming applications
  • offers range of profiles
38
Q

Switching P and I-frames (known as SP and SI)

A
  • incorporated into GOP format

- designed to support efficient switching between bitstreams

39
Q

Perceptual masking

A
  • composition of sound can alter ear’s ability to perceive specific frequencies at specific amplitudes
  • two types of masking; frequency masking and temporal masking
  • together referred to as noise masking
40
Q

Frequency masking

A
  • arises because of inherent property of ear

- relatively loud sound at particular frequency reduces sensitivity to neighbouring frequencies

41
Q

Temporal masking

A
  • refers to fact perceptual hearing sensitivity to sounds in narrow frequency range reduced for short period
42
Q

Speech coding methods

A
  • waveform encoding, process the source data using either time or frequency techniques
  • vocoder (voice encoder), formulate a mathematical model of voice production process that can be represented by small number of parameters
43
Q

Linear predictive coding (LPC)

A
  • estimates key speech production parameters relating to acoustics of vocal tract for both voiced and unvoiced signals
44
Q

Code-excited linear prediction(CELP)

A
  • not coding algorithm per se
  • grouping of low-bit rate speech-coding solutions that employ LPC as core compression model
  • constructs codebook of quantised excitation vectors, known as code words
  • all entered into codebook
  • transmits model coefficients and gain to decoder and sends index pointer to one codebook entry as best excitation

TM355 (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions