• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.329-332
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• 2000

In this paper, we made 5W 2stage power amplifier for IMT-2000 repeater. We designed this amplifier by harmonic balanced simulation using nonlinear model to minimize distortion. After simulation, we acquired 47㏈m 1㏈ compression point at 2110 ~ 2170MHz single tone input. In addition, the ACPR of this amplifier was good. The test result was 47㏈m 1㏈ compression point, 42.6㏈ gain, -36.16㏈c ACPR at 2.5MHz, -44.34㏈c ACPR at 5MHz and -51.67㏈c ACPR at 7.5MHz.

• Journal of IKEEE
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• v.11 no.4
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• pp.219-226
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• 2007

An efficient block based two-layer JPEG encoding algorithm is proposed to compress high dynamic range (HDR) images in this work. The proposed algorithm separates an input HDR image into a tone-mapped low dynamic range (LDR) image and a ratio image, which represents the quotients of the original HDR pixels divided by the tone-mapped LDR pixels. Then, the tone-mapped LDR image is compressed using the standard JPEG scheme to preserve backward compatibility and the ratio image is encoded to minimize a cost function that models the perception of each block with different quantization parameters in the human visual system (HVS). Simulation results show that the proposed algorithm provides better performance than the conventional method, which encodes the ratio image without any prior information of blocks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.12
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• pp.1054-1064
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• 2012

HDR (high dynamic range) tone mapping algorithms are used in image processing that reduces the dynamic range of an image to be displayed on LDR (low dynamic range) devices properly. The retinex is one of the tone mapping algorithms to provide dynamic range compression, color constancy, and color rendition. It has been developed through multi-scale methods and luminance-based methods. Retinex algorithms still have drawbacks such as the emphasized noise and desaturation. In this paper, we propose a multi scale tone mapping algorithm for enhancement of contrast, saturation, and noise of HDR rendered images based on visual brightness functions. In the proposed algorithm, HSV color space has been used for preserving the hue and saturation of images. And the algorithm includes the estimation of minimum and maximum luminance level and a visual gamma function for the variation of viewing conditions. And subjective and objective evaluations show that proposed algorithm is better than existing algorithms. The proposed algorithm is expected to image quality enhancement in some fields that require a improvement of the dynamic range due to the changes in the viewing condition.

• Journal of Biomedical Engineering Research
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• v.15 no.2
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• pp.175-182
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• 1994

The international standard for digital compression and coding of continuous-tone still image known as JPEG (Joint Photographic Experts Group) standard is investigated for medical image archiving and communication. The JPEG standard has widely been accepted in the areas of electronic image communication, computer graphics, and multimedia applications, however, due to the lossy character of the JPEG compression its application to the field of medical imaging has been limited. In this paper, the JPEG standard is investigated for medical image compression with a series of head sections of magnetic resonance (MR) images (256 and 4096 graylevels, $256 {\times}256$size). Two types of Huffman codes are employed, i. e., one is optimized to the image statistics to be encoded and the other is a predetermined code, and their coding efficiencies are examined. From experiments, compression ratios of higher than 15 were obtained for the MR images without noticeable distortion. Error signal in the reconstructed images by the JPEG standard appears close to random noise. Compared to existing full-frame bit-allocation technique used for radiological image compression, the JPEG standard achieves higher compression with less Gibb's artifact. Feature of the progressive image build-up of the JPEG progressive coding may be useful in remote diognosis when data is transmitted through slow public communication channel.

• Speech Sciences
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• v.11 no.2
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• pp.19-25
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• 2004

Hearing aids play an very important role in aural rehabilitation for hearing impaired person who could not be medically treated. Especially, hearing aids with dynamic range compression (level dependent frequency response: LDFR) method concentrated dynamic output range of receiver into the narrowing dynamic range of sensorineural hearing impaired person. Thus, if aided hearing threshold level is improved and uncomfortable loudness level rises, then the users of hearing aids are favored with extended dynamic range. This study aims to evaluate audiological benefits in dynamic range compression hearing aids. To achieve this, pure tone and speech audiometry were examined to 15 children and 3 adults with narrow dynamic range moderate-to-severe binaural sensorineural hearing loss.

• The Transactions of the Korea Information Processing Society
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• v.3 no.6
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• pp.1624-1635
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• 1996

Palletized color images are the dominant type of the image used on Internet and World-Wide Web. In spite of this, most image compression and progressive transmission algorithm have been designed for continuous-tone images. Pallettize images. Palletized images differ from continuous-tone images in such a aspect that values are lookup table indices a new pyramid structure for compression and progressive transmission of a palletized image. In the proposed pyramid structure, the color of a node at higher level is the one that occupies the most part in 4 sons and each node is represented by a type code and several color codes. Since the proposed method do not exploit spatial correlation in an image, it is ideally applied to lossless compression and progressive transmission of palletized images. We have confirmed this through the experimental results.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.01a
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• pp.207-210
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• 2009

An efficient algorithm to compress high dynamic range (HDR) videos is proposed in this work. We separate an HDR video sequence into a tone-mapped low dynamic range (LDR) sequence and a ratio sequence. Then, we encode those two sequences using the standard H.264/AVC codec. During the encoding, we allocate a limited amount of bit budget to the LDR sequence and the ratio sequence adaptively to maximize the qualities of both the LDR and HDR sequences. While a conventional LDR decoder uses only the LDR stream, an HDR decoder can reconstruct the HDR video using the LDR stream and the ratio stream. Simulation results demonstrate that the proposed algorithm provides higher performance than the conventional methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.8
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• pp.669-679
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• 2013

When an image is converted from HDR (high dynamic range) to LDR (low dynamic range), a tone mapping process is the essential component. Many TMOs (tone mapping operators) have been motivated by human vision which has lower physical luminance range than that in real scene. The representative of human vision properties which motivate TMOs is the local adaptation. However, TMOs are ultimately compressing image information such as contrast, saturation, etc. and the compression causes defects in image quality. In this paper, in order to compensate the degradation of the image which is caused by TMOs, the visual acuity-based edge stop function is proposed for applying the property of human vision to base-detail separation. In addition, using CSF (contrast sensitivity function) which represents the relationship among spatial frequency, contrast sensitivity, and luminance, the sharpness filter is designed and adaptively applied to the detail layer in regard to surround luminance.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.267-268
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• 2007

A dynamic range compression algorithm using Markov random field (MRF) modeling to display high dynamic range (HDR) images on low dynamic range (LDR) devices is proposed in this work. The proposed algorithm separates foreground objects from the background using the edge information, and then compresses the color differences across the edges based on the MRF modeling. By minimizing a cost function using belief propagation, the proposed algorithm can provide an effective LDR image. Simulation results show that the proposed algorithm provides good results.

• Journal of Korea Multimedia Society
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• v.2 no.3
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• pp.308-319
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• 1999

In this paper we propose a new color inverse halftoning for color prints halftoned by clustered-dot. The proposed method divide channel image into blocks and then extract moire region according to its strength. To get more natural continuous tone image in human vision, the proposed method smooths the extracted moire region in proportion to moire strength. It can also preserve the significant edges well by considering edge information of color halftone image in the process of inverse halftoning. Experimental results show that the proposed method can make more improved inverse halftoning. Experimental results show that the proposed method can make more improved inverse halftoning image than the results of previous works. It could be applied to field of multimedia application, such as digital library construction, color print image compression and multimedia authoring.