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HALO-FREE DESIGN FOR RETINEX BASED REAL-TIME VIDEO ENHANCEMENT SYSTEM
~PDCN 2013~ February 11 – 13, 2013 Innsbruck, Austria Yuecheng Li1, Hong Zhang1, and Mingui Sun2 1Image Processing Center, Beihang University, Beijing, China 2Department of Neurosurgery, University of Pittsburgh, PA, USA
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Outline 1 Introduction and Problems 2 Strategies 3 Conclusions
2.1 Preventing Traditional Halo Artifacts 2.2 Preventing Motion Caused Halo Artifacts 3 Conclusions
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Outline 1 Introduction and Problems 2 Strategies 3 Conclusions
2.1 Preventing Traditional Halo Artifacts 2.2 Preventing Motion Caused Halo Artifacts 3 Conclusions
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Retinex Theory Observed Image Reflectance Illumination Retinex Theory:
1 Introduction and Problems Retinex Theory Retinex Theory: Derived from Color Constancy phenomenon. A prevailing theory in the field of image enhancement. At each pixel (x, y) in the image domain: Observed Image Reflectance Illumination Mathematically ill-posed problem.
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Retinex Theory Solution:
1 Introduction and Problems Retinex Theory Solution: Assumption: The reflectance image corresponds to the sharp details in the image while the illumination image is expected to be spatially smooth. Center/Surround mode (SSR, MSR, and MSRCR) : Gaussian Convolution.
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Traditional Halo Artifacts
1 Introduction and Problems Traditional Halo Artifacts Due to the isotropy of Gaussian filters. Improvements: Bilateral Filtering, mean-shift, variational approaches, etc. Original image Enhanced by using traditional retinex-based method
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Motion Caused Halo Artifacts
1 Introduction and Problems Motion Caused Halo Artifacts Our work: MSR is realized on FPGA FPGA based video enhancement system
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Motion Caused Halo Artifacts
1 Introduction and Problems Motion Caused Halo Artifacts Other applications: NASA Digital Signal Processors (DSP); real-time Enhanced Vision System (EVS). Tsutsui et al.: VLSI architecture; variation mode. consensus design: A pipeline structure, where current frame’s reflectance is derived from previous frame’s illumination, can save frame buffer and system delay. Motion caused halo artifacts Due to inter-frame motion, motion causes mismatch between previous frame’s illumination and current frame. Video: Two kinds of halo artifacts
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Outline 1 Introduction and Problems 2 Strategies 3 Conclusions
2.1 Preventing Traditional Halo Artifacts 2.2 Preventing Motion Caused Halo Artifacts 3 Conclusions
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Computation optimization Improved pipeline structure
2 Strategies Strategies Methods to prevent halo artifacts: Traditional halo artifacts: Motion caused halo artifacts: Bilateral Filtering Computation optimization Improved pipeline structure
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Outline 1 Introduction and Problems 2 Strategies 3 Conclusions
2.1 Preventing Traditional Halo Artifacts 2.2 Preventing Motion Caused Halo Artifacts 3 Conclusions
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Preventing Traditional Halo Artifacts
2 Strategies Preventing Traditional Halo Artifacts Bilateral filtering definition Supposing I is a given gray-scale image and p = (px, py) the 2-D pixel position, BF[·] is defined by: Ω is a neighboring domain; Wp is a normalization factor; Gs is a spatial Gaussian decreasing the influence of distant pixels; Gr is a range Gaussian decreasing the influence of pixels q with an intensity value different from Ip.
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Preventing Traditional Halo Artifacts
2 Strategies Preventing Traditional Halo Artifacts BF Based Retinex Supposing L is the illumination image and R the reflectance image, BF based Retinex model in logarithmic form can be expressed as: The computation is complex and heavy even for a single scale BF. Multi-scale is necessary.
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Preventing Traditional Halo Artifacts
2 Strategies Preventing Traditional Halo Artifacts Optimized separable BF based illumination estimator Separable BF Spatial Gaussian filter: three scales Range Gaussian filter: single scale Scales combining Single scale
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Preventing Traditional Halo Artifacts
2 Strategies Preventing Traditional Halo Artifacts Combing the three scales for spatial Gaussian filter Computation burden decreases to 1/3 without obvious performance sacrifice. a. Reflectance image by independent three scales b. Reflectance image by the combined scale
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Preventing Traditional Halo Artifacts
2 Strategies Preventing Traditional Halo Artifacts Performance comparison a. Source image b. Result by Traditional MSR c. Result by Optimized Separable BF Based Retinex
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Outline 1 Introduction and Problems 2 Strategies 3 Conclusions
2.1 Preventing Traditional Halo Artifacts 2.2 Preventing Motion Caused Halo Artifacts 3 Conclusions
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Preventing Motion Caused Halo Artifacts
2 Strategies Preventing Motion Caused Halo Artifacts Motion Caused Halo Artifacts Inter frame motion will produce spatial mismatch between previous frame’s illumination and current frame thus produce the motion caused halo artifacts. Commonly adopted pipeline structure
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Preventing Motion Caused Halo Artifacts
2 Strategies Preventing Motion Caused Halo Artifacts a b c d e f
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Preventing Motion Caused Halo Artifacts
2 Strategies Preventing Motion Caused Halo Artifacts Inspired In the scaled Retinex domain, image contents are generally illumination free. Hoi-Kok Cheung et al. promote H.264 with Retinex. motion estimation motion compensation prediction error coding Retinex Images
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Preventing Motion Caused Halo Artifacts
2 Strategies Preventing Motion Caused Halo Artifacts Proposed pipeline structure Rn-1 Rn gray-scale projection Cross correlation Motion vectors Motion compensation on Ln
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Preventing Motion Caused Halo Artifacts
2 Strategies Preventing Motion Caused Halo Artifacts ME Algorithm Efficient Gray-scale Projection algorithm: where the Grayn(j) and Grayn(i) correspond to the gray projection value of column j and row i respectively.
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Preventing Motion Caused Halo Artifacts
2 Strategies Preventing Motion Caused Halo Artifacts Effectiveness of gray-scale projection algorithm. Samples from images set for simulation
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Preventing Motion Caused Halo Artifacts
2 Strategies Preventing Motion Caused Halo Artifacts Both the source images and their reflectance are manually translated with vertical 10 pixels and horizontal 20 pixels respectively. Gray-scale projection algorithm is performed with the original images and their translated images to estimate the preset inter-frame motion. Average accuracy of gray-scale projection algorithm Being conducted on source images Being conducted On reflectance images Horizontal 68% 77% Vertical 69% 94%
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Preventing Motion Caused Halo Artifacts
2 Strategies Preventing Motion Caused Halo Artifacts Problem on boundary Results under traditional pipeline structure Results under the proposed pipeline structure with ME and MC
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Outline 1 Introduction and Problems 2 Strategies 3 Conclusions
2.1 Preventing Traditional Halo Artifacts 2.2 Preventing Motion Caused Halo Artifacts 3 Conclusions
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Conclusions Conclusions: Future work
Based on two ‘concepts: edge preserving and illumination-free reflectance Traditional halo artifacts is restrained by optimized separable BF Motion caused halo artifacts is alleviated by a modified pipeline structure with traditional ME algorithm Future work Solving the problem on image boundary; Further necessary optimization.
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Q/A
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