• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2015.07a
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• pp.499-500
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• 2015

동영상 부호화에서 중요하고 매우 높은 비중을 차지하는 화면 간 예측에서는 휘도와 색차 성분에서 다양한 tap의 보간 필터를 사용한다. 본 논문에서는, 현재 표준인 HEVC(High Efficiency Video Coding)에서 쓰이는 보간 필터인 DCT-IF(Discrete Cosine Transform-based Interpolation FIlter)에 알아보고 tap 수에 따른 성능을 분석한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.6C
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• pp.857-864
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• 2004

Many image compression standards such as JPEG, MPEG or H.263 are based on the discrete cosine transform (DCT) and quantization method. Quantization error. is the major source of image quality degradation. The current dequantization method assumes the uniform distribution of the DCT coefficients. Therefore the dequantization value is the center of each quantization interval. However DCT coefficients are regarded to follow Laplacian probability density function (pdf). The center value of each interval is not optimal in reducing squared error. We use mean of the quantization interval assuming Laplacian pdf, and show the effect of correction on image quality. Also, we compare existing quantization error to corrected quantization error in closed form. The effect of PSNR improvements due to the compensation to the real image is in the range of 0.2 ∼0.4 ㏈. The maximum correction value is 1.66 ㏈.

• Journal of Broadcast Engineering
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• v.21 no.1
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• pp.51-59
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• 2016

This paper presents a method of DCT-based illuminant compensation to enhance the accuracy of face recognition under an illuminant change. The basis of the proposed method is that the illuminant is generally located in low-frequency components in the DCT domain. Therefore, the effect of the illuminant can be compensated by controlling the low-frequency components. Moreover, a directional high-order local pattern descriptor is used to detect robust features in the case of face motion. Experiments confirm the performance of the proposed algorithm got up to 95% when tested using a real database.

• Journal of Advanced Navigation Technology
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• v.17 no.1
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• pp.69-79
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• 2013

In this paper, DCT(Discrete Cosine Transform) and CAVLC(Context Adaptive Variable Length Coding) are co-designed as hardware IP with software operation of the other modules in H.264/AVC codec. In order to increase the operation speed, a new method using SHIFT table is proposed. As a result, enhancement of about 16(%) in the operation speed is obtained. Designed Hardware IPs are downloaded into Virtex-4 FX60 FPGA in the ML-410 development board and H.264/AVC encoding is performed with Microblaze CPU implemented in FPGA. Software modules are developed from JM13.2 to make C code. In order to verify the designed Hardware IPs, Modelsim program is used for functional simulation. As a result that all Hardware IPs and software modules are downloaded into the FPGA, improvement of processing speed about multiples of 16 in case of DCT hardware IP and multiples of 10 in case of CAVLC compared with software-only processing. Although this paper deals with co-design of H/W and S/W for H.264, it can be utilized for the other embedded system design.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.285-288
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• 2002

Compression of magnetic resonance images (MRI) has proved to be more difficult than other medical imaging modalities. In an average sized hospital, many tora bytes of digital imaging data (MRI) are generated every year, almost all of which has to be kept. The medical image compression is currently being performed by using different algorithms. In this paper, Fuzzy C-Means (FCM) algorithm is used for the Vector Quantization (VQ). First, a digital image is divided into subblocks of fixed size, which consists of 4${\times}$4 blocks of pixels. By performing 2-D Discrete Cosine Transform (DCT), we select six DCT coefficients to form the feature vector. And using FCM algorithm in constructing the VQ codebook. By doing so, the algorithm can make good time quality, and reduce the processing time while constructing the VQ codebook.

• Journal of Broadcast Engineering
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• v.7 no.2
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• pp.168-180
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• 2002

This paper proposes a novel method to detect unauthorized copies of digital images. This copy detection scheme can be used as either an alternative approach or a complementary approach to watermarking. A test image is reduced to 8$\times$8 sub-image by intensity averaging, and the AC coefficients of its discrete cosine transform (DCT) are used to compute distance from those generated from the query image, of which a user wants to find copies. Copies may be Processed to avoid copy detection or enhance image quality. We show ordinal measure of DCT coefficients, which is based on relative ordering of AC magnitude values and using distance metrics between two rank permutations, are robust to various modifications of the original image. The optimal threshold selection scheme using the maximum a posteriori (MAP) criterion is also addressed.

• The Transactions of the Korea Information Processing Society
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• v.7 no.8
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• pp.2341-2348
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• 2000

The special effects on the compressed :vII'EG domain become one of the interesting problems. In this paper, we developed minimal deCilder to effect in DCT compressed domain, proposed the video effects including wipe, dissolve, and zooming. To increase the expandability and portabilitv, the minimal decoder and the effects arc implemented to filters of COM based DirectShow.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10b
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• pp.245-250
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• 1992

In this paper, we present a nev algorithm for the fast computation of the discrete cosine transform(DCT). This algorithm consists of the three dimensional prime factor-decomposed algorithm(PFA) and three dimensional common factor-decomposed algorithm(CFA). We can compute N-point DCT for the number N decomposable Into three relative prime numbers using PFA and into three common numbers using CFA. We also show input and output index mapping for the three decomposition. it results in requiring fever multiplicaions than the previous algorithms. Particularly, for the large number N, it is more powerful in reducing the number of multiplication.

• Proceedings of the IEEK Conference
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• 2000.11c
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• pp.89-92
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• 2000

The wireless network has bursty and high error rates. Due to the quite limited bandwidth in wireless networks, images are usually transmitted as a compressed version with VLC(variable length coding). Loss of coded data can affect a decoded image to a large extent, making concealment of errors caused by data loss an important issue. This paper presents a error concealment technique for DCT(Discrete Cosine Transform) based image coding. First, a method to estimate the missing DC coefficients of a JPEG coded image which is required for decoding the compressed image, is suggested and evaluated. Second, the missing data is interpolated by exploiting the probability of being nonzero and the correlation between adjacent blocks. In addition, since the these technique is computational efficient, it conserves system resources and power consumption, which are restrictive in mobile computers.

• Proceedings of the KIEE Conference
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• 2006.04a
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• pp.21-23
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• 2006

Due to development of Internet network environments and data compression techniques, the size and amount of multimedia data has greatly increased. They are compressed before transmission or storage. Dealing with these compressed data such as video retrieval or indexing requires the decoding procedure most of the time. In video retrieval and indexing a color histogram is one of the most frequently used tools. We propose a novel scheme for extracting color histograms from images transformed into the compressed domain using $8{times}8$ DCT(Discrete Cosine Transform). In this scheme an averaged version of original image is obtained by filtering DCT coefficients with a filter we destined.