Quality Assessment of Deblocked Images

Changhoon Yim,Bovik, A C IEEE 2011 IEEE TRANSACTIONS ON IMAGE PROCESSING - Vol.20 No.1

<P>We study the efficiency of deblocking algorithms for improving visual signals degraded by blocking artifacts from compression. Rather than using only the perceptually questionable PSNR, we instead propose a block-sensitive index, named PSNR-B, that produces objective judgments that accord with observations. The PSNR-B modifies PSNR by including a blocking effect factor. We also use the perceptually significant SSIM index, which produces results largely in agreement with PSNR-B. Simulation results show that the PSNR-B results in better performance for quality assessment of deblocked images than PSNR and a well-known blockiness-specific index.</P>

Adaptive CU splitting and pruning method for HEVC intra coding

Yim, Changhoon,Kim, Gaewon Institution of Electrical Engineers 2014 Electronics letters Vol.50 No.10

Coding unit (CU) splitting and pruning for complexity reduction in high-efficiency video coding (HEVC) intra coding is dealt with. Adaptive determination of the threshold values for splitting and pruning in each CU is proposed based on the depth level information of neighbour CUs, whose values are determined from a fixed parameter in the previous method. Simple preconditions for splitting and pruning are also proposed to improve coding efficiency. Simulation results show that the proposed method gives significant improvement of computational complexity with much smaller reduction of coding efficiency compared with the previous method.

DCT 영역에서의 POCS에 근거한 디지털 영상 후처리

임창훈 건국대학교 산업기술연구원 2005 건국기술연구논문지 Vol.30 No.-

Even though post-processing methods based on projections onto convex sets (POCS) have shown good performance for blocking artifact reduction, it is infeasible to implement POCS for real-time practical applications. This paper proposes DCT domain post-processing method based on POCS. The proposed method shows very similar performance compared to the conventional POCS method, while it reduces tremendously the computational complexity. DCT domain POCS performs the lowpass filtering in the DCT domain, and it removes the inverse DCT and forward DCT modules. Through the investigation of lowpass filtering in the iterative POCS method, we define kth order lowpass filtering which is equivalent to the lowpass filtering in the kth iteration, and the corresponding kth order DCT domain POCS. Simulation results show that the kth order DCT domain POCS without iteration gives very similar performance compared to the conventional POCS with k iterations, while it requires much less computations. Hence the proposed DCT domain POCS method can be used efficiently in the practical post-processing applications with real-time constraints.

Packet-Level Layer-Based Interleaving Unequal Forward Error Correction (LIU-FEC) for Robust Wireless Scalable Video Transmission

Ha, Hojin,Yim, Changhoon Springer-Verlag 2014 WIRELESS PERSONAL COMMUNICATIONS Vol.77 No.3

Fast intra prediction method by adaptive number of candidate modes for RDO in HEVC

Chung, Byungjin,Yim, Changhoon Elsevier 2018 Information processing letters Vol.131 No.-

<P><B>Abstract</B></P> <P>The intra prediction of high efficiency video coding (HEVC) selects the candidate modes through rough mode decision (RMD) among 35 modes for intra coding. The fixed number of candidate modes after the RMD might be inefficient, because the rate-distortion optimization (RDO) process using candidate modes still takes about 35% of total encoding time.</P> <P>In this letter, we propose an efficient method to reduce the number of candidate modes adaptively by adjusting the threshold for Hadamard cost (HC). The threshold is determined using the weight based on the standard deviation of gray level of pixels in prediction unit. The proposed method performs the RDO process using the reduced number of candidate modes having smaller HC than the threshold. Simulation results show that the proposed method gives about 16% complexity reduction with just 0.08% BD-rate increase compared with the original HEVC test model. The proposed method gives significant improvement of BD-PSNR and BD-rate with similar complexity reduction compared with the previous state-of-the-art method.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We propose an efficient method to reduce the number of candidate modes adaptively. </LI> <LI> The proposed method gives about 16% complexity reduction compared with the HM. </LI> <LI> The proposed method gives significant improvement of BD-PSNR and BD-rate compared with the existing methods. </LI> </UL> </P>

Priority Tries for IP Address Lookup

Hyesook Lim,Changhoon Yim,Swartzlander, Earl E IEEE 2010 IEEE Transactions on Computers Vol.59 No.6

<P>High-speed IP address lookup is essential to achieve wire speed packet forwarding in Internet routers. The longest prefix matching for IP address lookup is more complex than exact matching because it involves dual dimensions: length and value. This paper presents a new formulation for IP address lookup problem using range representation of prefixes and proposes an efficient binary trie structure named a priority trie. In this range representation, prefixes are represented as ranges on a number line between 0 and 1 without expanding to the maximum length. The best match to a given input address is the smallest range that includes the input. The priority trie is based on the trie structure, with empty internal nodes in the trie replaced by the priority prefix which is the longest among those in the subtrie rooted by the empty nodes. The search ends when an input matches a priority prefix, which significantly improves the search performance. Performance evaluation using real routing data shows that the proposed priority trie is very good in performance metrics such as lookup speed, memory size, update performance, and scalability.</P>

Image Dehazing from Depth Estimation using Convolutional Neural Networks

Yejin Kim,Changhoon Yim 대한전자공학회 2021 IEIE Transactions on Smart Processing & Computing Vol.10 No.2

Image dehazing is a process that removes haze effects from images. In this paper, we propose a new paradigm that uses depth information to generate the transmission map for image dehazing. Other methods for image dehazing estimate the transmission map directly. We propose the generation of transmission map indirectly from the depth map using the properties of an atmospheric scattering model to obtain a dehazed image. Depth information can be estimated using established methods that employ convolutional neural networks (CNNs) based on deep learning. Experimental results show that more sophisticated transmission maps can be generated from depth maps without any post-processing. The proposed method can provide improved subjective image dehazing results without any darkening effects compared to previous methods.

히스토그램 평활화 전처리 기반 단순 선형 반복적 군집화를 이용한 슈퍼픽셀 영상 분할

백지연(Jiyeon Baek),임창훈(Changhoon Yim) 대한전자공학회 2018 대한전자공학회 학술대회 Vol.2018 No.6

Superpixel segmentation means dividing an image into many fragments which have similar property. In this paper, we propose a superpixel segmentation method using simple linear iterative clustering (SLIC) with contrast limited adaptive histogram equalization. This method uses histogram equalization as a pre-processing step for clustering. Simulation results show that the proposed method generates superpixels which have more concise boundary coherence compared with the existing SLIC method.

IP 주소 검색을 위한 가중 이진 프리픽스 트리

임창훈,임혜숙,이보미,Yim Changhoon,Lim Hyesook,Lee Bomi 한국통신학회 2004 韓國通信學會論文誌 Vol.29 No.11B

IP 주소 검색은 인터넷 라우터의 필수적인 기능의 하나로서, 라우터 전체의 성능을 결정하는 중요한 요소이다. 소프트웨어에 기반한 IP 주소 검색 방식의 성능 평가 기준 중 가장 중요한 것은 라우터의 처리 속도를 보장해 주는 의미를 갖는 최대 메모리 접근 횟수이다. 이진 프리픽스 트리 방식(BPT)은 최대 메모리 접근 횟수에 있어서 기존의 다른 소프트웨어에 기반한 방식 중 우수한 방식이지만, 트리의 구조가 불균형적이 되는 단점이 있다. 본 논문에서는 기존의 BPT 방식의 트리 생성 과정에 가중치 개념을 추가하여, 완전 균형 트리에 매우 근접하는 트리를 생성하는 가중 이진 프리픽스 트리 (WBPT) 방식을 제안한다. 제안하는 WBPT 방식은 기존의 소프트웨어에 근거한 방식들에 비교하여 최대 메모리 접근 횟수에 있어서 가장 적은 성능을 보인다. 또한 3만 개 정도의 프리픽스에 대해서 L2 캐쉬에 저장이 가능한 정도의 작은 메모리 크기를 요구하구 프리픽스의 추가, 삭제가 용이하므로 실제적인 라우터의 IP 검색을 위하여 사용될 수 있는 방식이다. IP address lookup is one of the essential functions on internet routers, and it determines overall router performance. The most important evaluation factor for software-based IP address lookup is the number of the worst case memory accesses. Binary prefix tree (BPT) scheme gives small number of worst case memory accesses among previous software-based schemes. However the tree structure of BPT is normally unbalanced. In this paper, we propose weighted binary prefix tree (WBP) scheme which generates nearly balanced tree, through combining the concept of weight to the BPT generation process. The proposed WBPT gives very small number of worst case memory accesses compared to the previous software-based schemes. Moreover the WBPT requires comparably small size of memory which can be fit within L2 cache for about 30,000 prefixes, and it is rather simple for prefix addition and deletion. Hence the proposed WBPT can be used for software-based If address lookup in practical routers.

Complement Bloom Filter for Identifying True Positiveness of a Bloom Filter

Hyesook Lim,Jungwon Lee,Changhoon Yim IEEE 2015 IEEE communications letters Vol.19 No.11

<P>The use of Bloom filters in network applications has increased rapidly. Since Bloom filters can produce false positives, the trueness of each positive needs to be identified by referring to an off-chip hash table. This letter proposes a new method for identifying the trueness of Bloom filter positives. We propose the use of an additional Bloom filter programmed for the complement set of the given set. In querying an input, if the complement Bloom filter produces a negative result, the input is a member of the given set since Bloom filters never produce a false negative. When both Bloom filters produce positives, a hash table needs to be referred to in our method. We provide a mathematical analysis, whereby the probability of referring to a hash table converges to the summation of the false positive probabilities of each Bloom filter. We provide the simulation result that the rate of referring to a hash table in our method is the order of 10<SUP>-5</SUP> for Bloom filter sizing factor 32.</P>