김휘용 교수

Evaluation of coding efficiency is traditionally modeled as a continuous rate-distortion (R-D) function, where the peak signal-to-noise ratio (PSNR) is adopted as the quality measure. Although the PSNR-versus-bitrate curve offers some useful tradeoff information between video quality and coding bit-rates, it does not take human perceptual experience into account. In this work, by following the recent image/video quality assessment framework based on the just-noticeable-difference (JND) notion, w

The proliferation of deep learning-based machine vision applications has given rise to a new type of compression, so called video coding for machine (VCM). VCM differs from traditional video coding in that it is optimized for machine vision performance instead of human visual quality. In the feature compression track of MPEG-VCM, multi-scale features extracted from images are subject to compression. Recent feature compression works have demonstrated that the versatile video coding (VVC) standard

A contour-like artifact called false contour is often observed in large smooth areas of decoded images and video. Without loss of generality, we focus on detection and removal of false contours resulting from the state-of-the-art High Efficiency Video Coding codec. First, we identify the cause of false contours by explaining the human perceptual experiences on them with specific experiments. Next, we propose a precise pixel-based false contour detection method based on the evolution of a false c

With the aid of rapid development in optical and display devices, Holography has become an emerging technology to represent 3D objects providing the most natural and realistic depth illusion to the users. To reproduce a light field of objects, a hologram records the interference patterns between the object and reference wavefields. Especially for computer-generated holograms, they contain vast amount of data and must be efficiently compressed for storage or transmission. Although several coding

Video of higher frame rates (HFR) reduces the visual artifact in large screen display at the cost of a higher coding bit rate (or transmission bandwidth). In this work, we propose a perceptual quality driven frame rate selection (PQD-FRS) method that assigns a time-varying frame rate to a sequence so as to reduce its transmission cost. The objective of the PQD-FRS method is to offer perceptually indistinguishable experience for a certain percentage of viewers. We first conduct a subjective test

HEVC is a next generation video coding standard designed with modern coding techniques to be especially efficient for coding high-resolution video such as 4 K/8 K-ultra high- definition (UHD) video. Among the advanced coding tools of HEVC, tiles and wavefront parallel processing (WPP) have been newly adopted for parallel processing of such high-resolution (4 K/8 K-UHD) video. To realize UHD video services over portable devices with limited battery power, it is essential to implement multi-core-b

Motion compensation (MC) is a critical component in terms of computational complexity and memory bandwidth. The MC complexity of High Efficiency Video Coding (HEVC) for UHD contents significantly increased more than that of AVC/H.264. This paper reveals and analyzes a feature of generalized P and B pictures in HEVC and introduces a simple and effective method for MC complexity reduction that can be exploited at both the encoder and decoder without affecting the compression performance. The propo

Compressing digital holograms have growing attention nowadays due to their huge amount of original data sizes. Although many progresses have been reported for full-complex holograms, the coding performance for phase-only holograms (POHs) has been quite limited so far. In this paper, we present a very efficient compression method for POHs. It extends the conventional video coding standard HEVC (High Efficiency Video Coding) in such a way that the standard can be able to compress not only the natu

Textured meshes are widely used in computer graphics to represent 3D scenes, with UV mapping playing a crucial role in establishing a bijective mapping between the 3D mesh surface and a 2D texture. This mapping not only allows for the enhancement of rendering quality but also enables the compression of mesh textures using standard 2D image or video codecs. However, when reconstructing meshes from real-world multiview images, the resulting UV texture maps often suffer from fragmentation due to ge

Recently, the convergence of the broadcasting and telecommunication has been issued. As representative convergence models, the broadcasting with bi-directional return path and IPTV with TPS(triple player service) service have been already developed and penetrated into the consumers. In advance to the tendency, TV-anytime forum standardized the system and method for bi-directional return path service which allows a consumer to access to interactive content, such as the Internet and interactive te

Abstract Because of its convenience and compatibility with various image processing techniques, digital image representation of holograms is generally used in digital holography, and thus, quality assessment of digital holograms is an essential issue. This study proposes a new objective quality metric for digital phase hologram image processing. The proposed metric is based on a newly defined phase distortion created by taking the 2 π periodicity of phase information into account. The experiment

Unmanned aerial vehicles like drones are one of the key development technologies with many beneficial applications. As they have made great progress, security and privacy issues are also growing. Drone tacking with a moving camera is one of the important methods to solve these issues. There are various challenges of drone tracking. First, drones move quickly and are usually tiny. Second, images captured by a moving camera have illumination changes. Moreover, the tracking should be performed in r

Robustness to noise and/or illumination variations has been a major issue with change detection. We present a novel change detection scheme that is robust to both noise and illumination changes. The major difference of our method compared to the existing ones is that our algo- rithm globally estimates and compensates for the illumination changes between two input images, whereas the previous approaches rely on some local change metrics for illumination-independent detection. Spe- cifically, a pi