Cheol Lee

We propose a ghost-free high dynamic range (HDR) image synthesis algorithm using a low-rank matrix completion framework, which we call RM-HDR. Based on the assumption that irradiance maps are linearly related to low dynamic range (LDR) image exposures, we formulate ghost region detection as a rank minimization problem. We incorporate constraints on moving objects, i.e., sparsity, connectivity, and priors on under- and over-exposed regions into the framework. Experiments on real image collections

We have measured optical transmission and reflection spectra of large scale graphene grown by chemical vapor deposition technique over the extensive frequency range from far-IR to uv (4 meV–6.2 eV). Large scale graphene exhibits an excitonic absorption peak in the uv-region (ℏω=4.6 eV) and the constant interband absorption with σ1(ω)=e2/4ℏ in the IR-visible region, respectively. In the far-IR range, Drude peak is observed, and its strength ωp,2d2 indicates the induced carrier density N2d=1.95×10

Matrix completion is a rank minimization problem to recover a low-rank data matrix from a small subset of its entries. Since the matrix rank is nonconvex and discrete, many existing approaches approximate the matrix rank as the nuclear norm. However, the truncated nuclear norm is known to be a better approximation to the matrix rank than the nuclear norm, exploiting a priori target rank information about the problem in rank minimization. In this paper, we propose a computationally efficient trun

This paper presents a hybrid flash file system (HFFS) based on both NOR flash and NAND flash memory. In a conventional NAND flash-based flash file system, there is a trade-off between life span and durability in the frequent writing of small amounts of data. Because NAND flash supports only a page-level I/O, at least one page is wasted in the synchronous writing of small amounts of data. The wasting of pages reduces the utilization and life span of the NAND flash. To alleviate the utilization pr

A gradient domain tone mapping algorithm is proposed to display high dynamic range (HDR) video sequences in low dynamic range (LDR) devices in this work. The proposed algorithm obtains a pixelwise motion vector field and incorporates the motion information into the Poisson equation. Then, by attenuating large spatial gradients, the proposed algorithm can yield a high-quality tone-mapped result without flickering artifacts. Simulation results show that the proposed algorithm provides a better per

An optimized brightness-compensated contrast enhancement (BCCE) algorithm for transmissive liquid crystal displays (LCDs) is proposed in this paper. We first develop a global contrast enhancement scheme to compensate for the reduced brightness when the backlight of an LCD device is dimmed for power reduction. We also derive a distortion model to describe the information loss due to the brightness compensation. Then, we formulate an objective function that consists of the contrast enhancement ter

An efficient algorithm to compress high dynamic range (HDR) videos is proposed in this work. We employ the motion information to separate an HDR video sequence into a tone-mapped low dynamic range (LDR) sequence and a ratio sequence. Then, those two sequences are encoded using the standard H.264/AVC codec. During the encoding, we allocate the limited bit budget to the LDR sequence and the ratio sequence optimally to maximize the qualities of the LDR and HDR sequences. Conventional LDR devices us

In this work, we designed and implemented schemes that defer writing of metadata in order to realize an efficient and reliable NAND flash file system. The conventional NAND flash file systems synchronously write their metadata in the NAND flash for reliability; however, the synchronous writing of metadata generates excessive garbage. We propose the scheme for merging the writing of metadata so as to reduce the garbage of the NAND flash while ensuring file system consistency. The proposed scheme

Great effort has been devoted in recent years to improve the electrical conductivity of graphene for use in practical applications. Here, we demonstrate the hole carrier density of CVD graphene on a SiO2/Si substrate increases by more than one order of magnitude to n = 3 × 10(13) cm(-2) after irradiation with a high energy 5 MeV proton beam. As a result, the dc-resistance (R) of graphene is reduced significantly by 60%. Only a negligible amount of defect is created by the irradiation. Also the h

We propose a novel power-constrained RGB-to-RGBW conversion algorithm for emissive RGBW displays. We measure the perceived color distortion using a color difference model in a perceptually uniform color space, and compute the power consumption for displaying an RGBW pixel on an emissive display. The main contribution is to formulate the optimization problem to minimize the color distortion subject to the constraint on the power consumption. Then, we solve it efficiently to convert an image in re