Digital Image Processing Chapter 8: Image Compression 11 August 2006
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Transcript of Digital Image Processing Chapter 8: Image Compression 11 August 2006
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Digital Image ProcessingChapter 8:
Image Compression
11 August 2006
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Data vs Information Data vs Information
Information = Matter (สาระ)
Data = The means by which information is conveyed
Reducing the amount of data required to represent a digital image while keeping information as much aspossible
Image Compression Image Compression
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Relative Data Redundancy and Compression Ratio Relative Data Redundancy and Compression Ratio
RD C
R 11
Relative Data Redundancy
Compression Ratio
2
1
nnCR
Types of data redundancy1. Coding redundancy2. Interpixel redundancy3. Psychovisual redundancy
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Coding Redundancy Coding Redundancy
Different coding methods yield different amount of data needed to represent the same information.
Example of Coding Redundancy : Example of Coding Redundancy : Variable Length Coding vs. Fixed Length CodingVariable Length Coding vs. Fixed Length Coding
Lavg 3 bits/symbol Lavg 2.7 bits/symbol(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Variable Length Coding Variable Length Coding
Concept: assign the longest code word to the symbol with the least probability of occurrence.
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Interpixel Redundancy Interpixel Redundancy
Interpixel redundancy:Parts of an image arehighly correlated.
In other words,we canpredict a given pixelfrom its neighbor.
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Run Length CodingRun Length Coding
The gray scale imageof size 343x1024 pixels
Binary image= 343x1024x1 = 351232 bits
Line No. 100
Run length coding
Line 100: (1,63) (0,87) (1,37) (0,5) (1,4) (0,556) (1,62) (0,210)
Total 12166 runs, each run use 11 bits Total = 133826 Bits(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Psychovisual Redundancy Psychovisual Redundancy
The eye does not response with equal sensitivity to all visual information.
8-bit gray scale image
4-bit gray scale image
4-bit IGS image
False contours
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Improved Gray Scale Quantization Improved Gray Scale Quantization
Pixeli-1i
i+1i+2i+3
Gray levelN/A0110 1100
1000 10111000 01111111 0100
Sum0000 0000
0110 11001001 01111000 11101111 0100
IGS CodeN/A0110
100110001111
+
Algorithm1. Add the least significant 4 bits of the previous value of Sum to the 8-bit current pixel. If the most significant 4 bit of the pixel is 1111 then add 0000 instead. Keep the result in Sum
2. Keep only the most significant 4 bits of Sum for IGS code.
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Fidelity Criteria: Fidelity Criteria: how good is the compression algorithm how good is the compression algorithm
-Objective Fidelity Criterion- RMSE, PSNR
-Subjective Fidelity Criterion:-Human Rating
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Image Compression Models Image Compression Models
Source encoder Channel encoder
Source decoder Channel decoder
Channel
),(ˆ yxf
),( yxf
Reduce data redundancy
Increase noiseimmunity
Noise
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Source Encoder and Decoder Models Source Encoder and Decoder Models
Mapper Quantizer Symbol encoder),( yxfSource encoder
Inverse mapper Symbol decoder
Source decoder
),(ˆ yxf
Reduceinterpixel
redundancy
Reducepsychovisual redundancy
Reducecoding
redundancy
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Channel Encoder and Decoder Channel Encoder and Decoder
- Hamming code, Turbo code, …
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Information Theory Information Theory
Measuring information
)(log)(
1log)( EPEP
EI
Entropy or Uncertainty: Average information per symbol
j
jj aPaPH ))(log()(
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Simple Information System Simple Information System
Binary Symmetric Channel Binary Symmetric Channel
A = {a1, a2} ={0, 1}z = [P(a1), P(a2)]
B = {b1,b2} ={0, 1}v = [P(b1), P(b2)]
Source Destination
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
0
1
(1-Pe)
Pe
0
1Pe
(1-Pe)
Source Destination
Pe= probability of error
P(a1)
1-P(a1)
P(a1)(1-Pe)+(1-P(a1))Pe
(1-P(a1))(1-Pe)+P(a1)Pe
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Binary Symmetric Channel Binary Symmetric Channel
A = {a1, a2} ={0, 1}z = [P(a1), P(a2)]
B = {b1,b2} ={0, 1}v = [P(b1), P(b2)]
H(z) = - P(a1)log2P(a1) - P(a2)log2P(a2)
Source Destination
H(z|b1) = - P(a1|b1)log2P(a1|b1) - P(a2|b1)log2P(a2|b1)
H(z|b2) = - P(a1|b2)log2P(a1|b2) - P(a2|b2)log2P(a2|b2)
H(z|v) = H(z|b1) + H(z|b2)
Mutual information I(z,v)=H(z) - H(z|v)
Capacity ),(max vzz
IC
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Binary Symmetric Channel Binary Symmetric Channel Let pe = probability of error
bs
bs
ee
ee
pp
pppp
11
v
bs
bs
pp
apap
)(1)(
1
1z
)1(log)1()(log)( 22 bsbsbsbs ppppH z
)(log))1)(1((log)1)(1( ))1((log)1())1((log)1()|(
22
22
ebsebsebsebs
ebsebsebsebs
ppppppppppppppppH
vz
)()(),( ebsebsebsbs pHppppHvzI
)(1 ebs pHC
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Binary Symmetric Channel Binary Symmetric Channel
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Communication System ModelCommunication System Model
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
2 Cases to be considered: Noiseless and noisy
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Noiseless Coding TheoremNoiseless Coding Theorem
Problem: How to code data as compact as possible?
Shannon’s first theorem: defines the minimum average code word length per source that can be achieved.
Let source be {A, z} which is zero memory source with J symbols. (zero memory = each outcome is independent from other outcomes)
then a set of source output of n element be
},...,,{ 321 nJA
}111,110,101,100,011,010,001,000{A
Example:
}1,0{A
for n = 3,
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Noiseless Coding Theorem (cont.)Noiseless Coding Theorem (cont.)
Probability of each j is
)()()()( 21 jnjjj aPaPaPP
Entropy of source :
)())(log()()(1
zz nHPPHnj
iii
Each code word length l(i) can be
1)(
1log)()(
1log i
ii P
lP
Then average code word length can be
1)(
1log)()()()(
1log)(111
i
J
iii
J
ii
i
J
ii P
PlPP
Pnnn
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Noiseless Coding Theorem (cont.)Noiseless Coding Theorem (cont.)
nH
nL
H avg 1)()(
zz
or
)(lim zHn
Lavg
n
The minimum average code word length per source symbol cannotlower than the entropy.
Coding efficiency
avgLzHn
)(
We get 1)()( zz HLH avg
from )()( zz nHH
then
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Extension Coding Example Extension Coding Example
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
H = 1.83Lavg = 1.89
H = 0.918Lavg = 1
918.01918.011 97.0
89.183.1
2
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Noisy Coding TheoremNoisy Coding Theorem
Problem: How to code data as reliable as possible?
Example: Repeat each code 3 times:
Source data = {1,0,0,1,1}
Data to be sent = {111,000,000,111,111}
Shannon’s second theorem: the maximum rate of coded information is
rR log
r = Block length = code size
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Rate Distortion Function for BSC Rate Distortion Function for BSC
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Error-Free Compression: Huffman Coding Error-Free Compression: Huffman Coding
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Step 1: Source reduction
Huffman coding: give the smallest possible number of code symbols per source symbols.
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Error-Free Compression: Huffman Coding Error-Free Compression: Huffman Coding
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Step 2: Code assignment procedure
The code is instantaneous uniquely decodable without referencing succeeding symbols.
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Near Optimal Variable Length Codes Near Optimal Variable Length Codes
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Arithmetic Coding Arithmetic Coding
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Nonblock code: one-to-one correspondence between source symbolsAnd code words does not exist.Concept: The entire sequences of source symbols is assigned a singlearithmetic code word in the form of a number in an interval of real number between 0 and 1.
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Arithmetic Coding Example Arithmetic Coding Example
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
0.2x0.4 0.04+0.8x0.04 0.056+0.8x0.016
0.2x0.2 0.04+0.4x0.04 0.056+0.4x0.016
The number between 0.0688and 0.06752can be used torepresent thesequence a1 a2 a3 a3 a4
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LZW Coding LZW Coding
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Lempel-Ziv-Welch coding : assign fixed length code words to variable length sequences of source symbols.
24 Bits
9 Bits
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LZW Coding Algorithm LZW Coding Algorithm 0. Initialize a dictionary by all possible gray values (0-255)1. Input current pixel2. If the current pixel combined with previous pixels form one of existing dictionary entries Then 2.1 Move to the next pixel and repeat Step 1 Else
2.2 Output the dictionary location of the currently recognized sequence (which is not include the current pixel)
2.3 Create a new dictionary entry by appending the currently recognized sequence in 2.2 with the current pixel
2.4 Move to the next pixel and repeat Step 1
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LZW Coding Example LZW Coding Example
Input pixel
3939
1261263939
1261263939
126126
Dictionary Location Entry 0 0 1 1 … … 255 255 256 39-39 257 39-126 258 126-126 259 126-39 260 39-39-126 261 126-126-39 262 39-39-126-126
EncodedOutput (9 bits)
3939126126
256
258
260
CurrentlyrecognizedSequences
393912612639
39-39126
126-12639
39-3939-39-126
126
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Bit-Plane Coding Bit-Plane Coding
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Original imageBit 7
Bit 6
Bit 0
…
Bit planeimages
Binary image compression
Binary image compression
Binary image compression
Example of binary image compression: Run length coding
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Bit Planes Bit Planes
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Original grayscale image
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
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Gray-coded Bit Planes Gray-coded Bit Planes
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
a7
a6
a5
a4
g7
g6
g5
g4
Gray code:
60for 1
iaag iii
77 ag
and
ai= Original bit planes
= XOR
Originalbit planes
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Gray-coded Bit Planes (cont.) Gray-coded Bit Planes (cont.)
a3
a2
a1
a0
g3
g2
g1
g0
There are less 0-1 and 1-0 transitions in grayed codebit planes. Hence gray coded bit planes are more efficient for coding.
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Relative Address Coding (RAC) Relative Address Coding (RAC)
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Concept: Tracking binary transitions that begin and end eack black and white run
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Contour tracing and CodingContour tracing and Coding
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Represent each contour by a set of boundary points and directionals.
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Error-Free Bit-Plane Coding Error-Free Bit-Plane Coding
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Lossless VS Lossy Coding Lossless VS Lossy Coding
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Mapper Quantizer Symbol encoder),( yxfSource encoder
Reduceinterpixel
redundancy
Reducepsychovisual redundancy
Reducecoding
redundancy
Mapper Symbol encoder),( yxfSource encoder
Reduceinterpixel
redundancy
Reducecoding
redundancy
Lossless coding
Lossy coding
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Transform Coding (for fixed resolution transforms) Transform Coding (for fixed resolution transforms)
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Construct nxn
subimages
Forward transform Quantizer Symbol
encoderInput image
(NxN)
Compressedimage
Construct nxn
subimages
Inverse transform
Symboldecoder
Decompressedimage
Decoder
Encoder
Examples of transformations used for image compression: DFT and DCT
Quantization process causesThe transform coding “lossy”
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Transform Coding (for fixed resolution transforms) Transform Coding (for fixed resolution transforms)
3 Parameters that effect transform coding performance:
1. Type of transformation
2. Size of subimage
3. Quantization algorithm
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2D Discrete Transformation 2D Discrete Transformation
1
0
1
0
),,,(),(),(N
x
N
y
vuyxgyxfvuT
Forward transform:
1
0
1
0
),,,(),(),(N
u
N
v
vuyxhvuTyxf
Inverse transform:
where g(x,y,u,v) = forward transformation kernel or basis function
where h(x,y,u,v) = inverse transformation kernel or inverse basis function
T(u,v) is called the transform coefficient image.
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Transform Example: Transform Example: Walsh-Hadamard Basis Functions Walsh-Hadamard Basis Functions
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
1
0
)()()()(
)1(1),,,(),,,(
m
iiiii vpybupxb
Nyxvuhvuyxg
N = 4
N = 2m
bk(z) = the kth bit of z
)()()(
)()()()()()(
)()(
011
322
211
10
ububup
ububupububup
ubup
m
mm
mm
m
Advantage: simple, easy to implementDisadvantage: not good packing ability
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Transform Example: Transform Example: Discrete Cosine Basis Functions Discrete Cosine Basis Functions
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
DCT is one of the most frequently used transform for image compression.For example, DCT is used in JPG files.
N = 4
N
vyN
uxvuyxvuhvuyxg2
)12(cos2
)12(cos)()(),,,(),,,(
1,,1for 2
0for 1
)(Nu
N
uNu
N = 4Advantage: good packing ability,modulate computational complexity
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Transform Coding Examples Transform Coding Examples
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Original image512x512 pixels
Fourier
Hadamard
DCT
Error
Subimage size:8x8 pixels = 64 pixels
Quatization by truncating 50% of coefficients (only32 max cofficients are kept.)
RMS Error = 1.28
RMS Error = 0.86
RMS Error = 0.68
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DCT vs DFT Coding DCT vs DFT Coding
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Advantage of DCT over DFT is that the DCT coefficients aremore continuous at boundaries of blocks.
DFT coefficientshave abruptchanges atboundariesof blocks
1 Block
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Subimage Size and Transform Coding PerformanceSubimage Size and Transform Coding Performance
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
This experiment:Quatization is made bytruncating 75% of transform coefficients
DCT is the best
Size 8x8 is enough
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(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Subimage Size and Transform Coding PerformanceSubimage Size and Transform Coding Performance
Zoomed detailOriginal
Reconstructedby using 25%of coefficients(CR = 4:1)with 8x8 sub-images
DCT Coefficients
Zoomed detailSubimage size:
8x8 pixels
Zoomed detailSubimage size:
2x2 pixels
Zoomed detailSubimage size:
4x4 pixels
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Quantization Process: Bit Allocation Quantization Process: Bit Allocation
To assign different numbers of bits to represent transform coefficients based on importance of each coefficient:
- More importance coefficeitns assign a large number of bits
- Less importance coefficients assign a small number of bits or not assign at all
2 Popular bit allocation methods1. Zonal coding : allocate bits based on the basis of
maximum variance, using fixed mask for all subimages
2. Threshold coding : allocate bits based on maximum magnitudes of coefficients
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Example: Example: Results with Different Bit Allocation MethodsResults with Different Bit Allocation Methods
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Reconstructedby using 12.5%of coefficients(8 coefficientswith largestmagnitude areused)
Threshold codingError
Zoom details
Reconstructedby using 12.5%of coefficients(8 coefficients with largest variance are used)
Zonal codingError
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Zonal Coding Example Zonal Coding Example
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Zonal mask Zonal bit allocation
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Threshold Coding Example Threshold Coding Example
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Threshold mask Thresholded coefficientordering
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Thresholding Coding Quantization Thresholding Coding Quantization
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
3 Popular Thresholding MethodsMethod 1: Global thresholding : Use a single global threshold
value for all subimagesMethod 2: N-largest coding: Keep only N largest coefficientsMethod 3: Normalized thresholding: each subimage is normalized by a
normalization matrix before rounding
Example of Normalization Matrix Z(u,v)
),(),(),(ˆ
vuZvuTroundvuT
),(),(ˆ),(~ vuZvuTvuT
Bit allocation
Restoration before decompressing
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DCT Coding Example DCT Coding Example
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
(CR = 38:1) (CR = 67:1)
Zoom details
Method: - Normalized Thresholding,- Subimage size: 8x8 pixels
BlockingArtifact at Subimageboundaries
Error imageRMS Error = 3.42
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Wavelet Transform Coding: Multiresolution approachWavelet Transform Coding: Multiresolution approach
Wavelet transform Quantizer Symbol
encoderInput image
(NxN)
Compressedimage
Inverse wavelet
transform
Symboldecoder
Decompressedimage
Decoder
Encoder
Unlike DFT and DCT, Wavelet transform is a multiresolution transform.
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What is a Wavelet TransformWhat is a Wavelet TransformOne up on a time, human uses a line to represent a number. For example
= 25With this numerical system, we need a lot of space to representa number 1,000,000.Then, after an Arabic number system is invented, life is much easier.We can represent a number by a “digit number”:
X,XXX,XXX
The 1st digit = 1xThe 2nd digit = 10xThe 3rd digit = 100x
…
An Arabic number is onekind of multiresolutionRepresentation.
Like a number, any signal can also be represented by a multiresolutiondata structure, the wavelet transform.
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What is a Wavelet TransformWhat is a Wavelet Transform
Wavelet transform has its background from multiresolutionanalysis and subband coding.
- Nyquist theorem: The minimun sampling rate needed for samplinga signal without loss of information is twice the maximum frequencyof the signal.
-We can perform frequency shift by multiplying a complex sinusiodalsignal in time domain.
Other important background:
),(),( 00)(2 00 vvuuFeyxf yvxuj
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Wavelet History: Image PyramidWavelet History: Image Pyramid
Pyramidal structured image
Coarser, decrease resolution
Finer, increase resolution
If we smooth and then down sample an image repeatedly, we willget a pyramidal image:
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Image Pyramid and Multiscale DecompositionImage Pyramid and Multiscale Decomposition
ImageNxN Smooth
DownSampling
By 2
ImageN/2xN/2
Question: What Information is loss after downSampling?
Answer: Loss Information isA prediction error image:
UpSampling
By 2
Interpolate
PredictedImageNxN
Prediction Error
(loss details)NxN
-
+
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Image Pyramid and Multiscale Decomposition (cont.)Image Pyramid and Multiscale Decomposition (cont.)Hence we can decompose an image using the following process
ImageNxN
Smooth and down sampling
by 2
Approxi--mationImage
N/2xN/2
Upsamplingby 2 and
interpolate
Prediction ErrorNxN
Smooth and down sampling
by 2
Approxi--mationImage
N/4xN/4
Upsamplingby 2 and
interpolate
Prediction Error
N/2xN/2
+-
+-
….
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Image Pyramid and Multiscale Decomposition (cont.)Image Pyramid and Multiscale Decomposition (cont.)
Original ImageNxN
Prediction error(residue)
NxN
Predictionerror
N/2xN2
Prediction error N/4xN/4
Approximation image N/8xN/8
=
Multiresolution Representation
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Multiresolution Decomposition Process Multiresolution Decomposition Process
Note that this process is not a wavelet decomposition process !
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Example of Pyramid Images Example of Pyramid Images
ApproximationImages (usingGaussian Smoothing)
Predictionresidues
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Subband Coding Subband Coding
x(n)N points
LPF
HPF
DownSampling
by 2
Freq.shift by
N/2
DownSampling
by 2
Subband decomposition process
h1(n)
h0(n)
a(n)N/2 points
d(n)N/2 points
All information of x(n) is completely preserved in a(n) and d(n).
Approximation
Detail
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Subband Coding (cont.) Subband Coding (cont.)
x(n)N points
UpSampling
by 2
UpSampling
by 2
Subband reconstruction process
Interpolation
g0(n)
a(n)N/2 points
d(n)N/2 points Interpolation
Freq.shift by
N/2
g1(n)
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Subband Coding (cont.) Subband Coding (cont.)
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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2D Subband Coding 2D Subband Coding
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Example of 2D Subband CodingExample of 2D Subband Coding
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Diagonal detail:filtering in bothx and y directionsusing h1(n)
Horizontal detail:filtering in x-direction using h1(n) and in y-direction usingh0(n)
Approximation:filtering in bothx and y directionsusing h0(n)
Vertical detail: filtering in x-direction using h0(n) and in y-direction using h1(n)
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1D Discrete Wavelet Transformation 1D Discrete Wavelet Transformation
x(n)N points
h(n)
h(n) 2
2
h (n)
h (n) 2
2
h (n)
h (n) 2
2
d1(n) N/2 points
d2(n) N/4 points
d3(n) N/8 points
a3(n) N/8 points
Wavelet coefficients(N points)
Note that the numberof points of x(n) andwavelet coefficients are equal.
(n) = a wavelet function(n) = a scaling function
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1D Discrete Wavelet Transformation 1D Discrete Wavelet Transformation
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2D Discrete Wavelet Transformation 2D Discrete Wavelet Transformation
d2 h2
v2 a2
a1
h1d1
v1
Original imageNxN
a3d3 h3v3
Level 1
Level 2
Level 3
d = diagonal detailh = horizontal detailv = vertical detaila = approximation
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2D Discrete Wavelet Transformation (cont.) 2D Discrete Wavelet Transformation (cont.)
d2
h2
v2h1
d1v1
a3d3h3
v3
Original imageNxN
Wavelet coefficientsNxN
d = diagonal detail: filtering in both x and y directions using h (n)h = horizontal detail: filtering in x-direction using h (n) and in y direction using h (n)v = vertical detail: filtering in x-direction using h (n) and in y
direction using h (n)a = approximation: filtering in both x and y directions using h (n)
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OriginalImage
Example of 2D Wavelet Transformation Example of 2D Wavelet Transformation
Original image
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LH1
HL1
HH1
LL1LL1
Example of 2D Wavelet Transformation (cont.) Example of 2D Wavelet Transformation (cont.)
The first level wavelet decomposition
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LL2
LH1
HL1
HH1
LH2 HH2
HL2LL2
Example of 2D Wavelet Transformation (cont.) Example of 2D Wavelet Transformation (cont.)
The second level wavelet decomposition
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LH1 HH1
LH2 HH2
HL2
HL3
HH3LH3
LL3
HL1
The third level wavelet decomposition
Example of 2D Wavelet Transformation (cont.) Example of 2D Wavelet Transformation (cont.)
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Example of 2D Wavelet TransformationExample of 2D Wavelet Transformation
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Examples: Types of Wavelet TransformExamples: Types of Wavelet Transform
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Haarwavelets
Symlets
Daubechieswavelets
Biorthogonalwavelets
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Wavelet Transform Coding for Image CompressionWavelet Transform Coding for Image Compression
Wavelet transform Quantizer Symbol
encoderInput image
(NxN)
Compressedimage
Inverse wavelet
transform
Symboldecoder
Decompressedimage
Decoder
Encoder
Unlike DFT and DCT, Wavelet transform is a multiresolution transform.
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Wavelet Transform Coding Example Wavelet Transform Coding Example
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
(CR = 38:1) (CR = 67:1)
Error ImageRMS Error = 2.29
Zoom details
No blockingArtifact
Error ImageRMS Error = 2.96
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Wavelet Transform Coding Example (cont.) Wavelet Transform Coding Example (cont.)
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
(CR = 108:1) (CR = 167:1)
Error imageRMS Error = 3.72
Error imageRMS Error = 4.73
Zoom details
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Wavelet Transform Coding vs. DCT Coding Wavelet Transform Coding vs. DCT Coding
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
(CR = 67:1) (CR = 67:1)
Zoom details
Error imageRMS Error = 2.96
Wavelet DCT 8x8
Error imageRMS Error = 6.33
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Type of Wavelet Transform and PerformanceType of Wavelet Transform and Performance
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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No. of Wavelet Transform Level and PerformanceNo. of Wavelet Transform Level and Performance
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(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
Threshold Level and PerformanceThreshold Level and Performance
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(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Table 8.14 (Cont’)
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Table 8.19 (Con’t)
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Lossless Predictive Coding Model Lossless Predictive Coding Model
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Lossless Predictive Coding Example Lossless Predictive Coding Example
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Lossy Predictive Coding Model Lossy Predictive Coding Model
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Delta Modulation Delta Modulation
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Linear Prediction Techniques: Examples Linear Prediction Techniques: Examples
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Quantization Function Quantization Function
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Lloyd-Max Quantizers Lloyd-Max Quantizers
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Lossy DCPM Lossy DCPM
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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DCPM Result Images DCPM Result Images
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.
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Error Images of DCPM Error Images of DCPM
(Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition.