Volodymyr Fedak Artifacts suppression in images and video

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

What is the problem? blocking ringing blurring flickering

What is the problem? F - 2 F - 1 F F + 1 F + 2 Intra-frame processing… Inter-frame processing…

Why is it important ? De-coderArtifact detection Reducing artifacts Transform to original format Enhanced information postprocessingCoder parameters Compressed information Postprocessing techniques : -motion-compensated algorithms iterative approaches based on the theory of projections onto convex set -spatial-temporal algorithms algorithms that transform signal to frequency domain

What did I do ? Analyse modern postprocessing techniques Implement most encouraging methods Compare results of mentioned algorithms Propose approaches for optimization

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

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

Non-Local Means NLM could be presented: in general way: v(i) – noisy image W(i, j) - weighted average of pixels in the image v(j) – pixel luminance in terms of implementation: N(x) - window surrounding pixel x; Q(x) is a search window around pixel x;

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.

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

Any questions ?