Volodymyr Fedak

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Artifacts suppression in images and video

• Volodymyr Fedak

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Introduction

• What is the problem?
• Why is it important?
• What did I do?
• What are the results?
• So what next?

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What is the problem?

• blocking
• ringing
• blurring
• flickering

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What is the problem?
F - 2
F - 1
F
F 1
F 2
Intra-frame processing
Inter-frame processing
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Why is it important ?
Postprocessing techniques

• motion-compensated algorithms iterative
  approaches based on the theory of projections
  onto convex set

• spatial-temporal algorithmsalgorithms that
  transform signal to frequency domain

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What did I do ?

• Analyse modern postprocessing techniques
• Implement most encouraging methods
• Compare results of mentioned algorithms
• Propose approaches for optimization

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Wavelet-based de-blocking and de-ringing
algorithm proposed by Alan and Liew

• Steps
• Detection of Block Discontinuities
• Threshold Maps Generation at Different Wavelet
  Scales
• low frequency filtering

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Non-Local Means
NLM is an improvement of Bilateral filtering
C(y, x) - geometric relationship S(I(y), I(x)) -
luminance ratio I(y) pixel luminance

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Non-Local Means
N(x) - window surrounding pixel x Q(x) is a
search window around pixel x
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Non-Local Means Parameters

• h - determines the amount of averaging (h
  increases amount of blocking artifacts decrease).
• N (x) the match window/patch when N(x)
  increases, blocking artifacts of the processed
  sequence decreases very slowly
• Q(x) the search window/patch when Q(x)
  increases, artifacts of the processed sequence
  decreases very slowly for an increasing value of
  the search window size, and we have a large
  amount of computation time.

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Possible ways for optimization

• Extended NLM to the temporal domain . Use
  together with motion-compensation algorithm but
  apply some quality coefficient to the motion
  vector.
• Add smart patch/search window size choosing
  algorithm.
• Use Hierarchical block matching algorithm to find
  similar windows for speeding-up NLM

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Any questions ?