• Journal of the Korea Society of Computer and Information
• /
• v.23 no.1
• /
• pp.67-74
• /
• 2018

In this paper, we propose an efficient scene based non-uniformity correction algorithm which performs the offset correction using the uniform obtained from input scenes for Infrared camera. In general, pixel outputs of a infrared detector can not be uniform. Therefore, the non-uniformity correction procedure need to be performed to make the image outputs uniform. A typical non-uniformity correction method uses a black body at the laboratory to obtain the output of the infrared detector's pixels for two temperatures, HOT and COLD, and calculates the non-uniformity correction parameters. However, output characteristics of the Infrared detector changes while the Infrared camera is operated, the fixed pattern noise of the Infrared detector and dead pixels are generated. To remove the noise, the offset correction is generally performed. The offset correction procedure usually need the additional device such as a thermo-electric cooler, shutter, or non-uniformity correction lens. Therefore, we introduce a general scene based non-uniformity correction technique without additional equipment, and then we propose an improved non-uniformity correction algorithm based on image to solve the problem of the existing technique.

• Journal of Drive and Control
• /
• v.16 no.2
• /
• pp.72-79
• /
• 2019

Despite the development of electronic components and microprocessors, hydraulic actuators are still being applied in various applications. In some applications, there is a desire to apply a hydraulic actuator with a relatively small position error to the system. Various studies have been conducted to reduce the position error of hydraulic actuators. In this paper, the position error of the hydraulic actuator when the hydraulic oil pressure is supplied is defined as the offset generated by the servo valve, and the method for correcting the servo valve offset has been studied. A method for compensating the servo valve offset was proposed and it was verified through experiments that the position error of the hydraulic actuator was reduced. We also compared the servo valve offset correction method and controller using the PID control and disturbance observer used to reduce the position error of the hydraulic actuator. No-load test and load test were performed to confirm the performance of the servo valve offset correction method. The results of the study were compared with those obtained by using the disturbance observer and PID control.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.21 no.4
• /
• pp.972-983
• /
• 1996

This paper proposes a new technique for frequency offset correction for OFDM systems on a frequency selective fading channel. Frequency offset in OFDM introduces interchannel interference among the multiple subcarriers of OFDM signal. To compensate the interference, this paper describes an algorithm with two stages:acquisition and tracking. At both stages, the proposed algorithm oversamples the received OFDM signal to obtain a couple of demodulated symbol sets. At acquisition stage the frequency offset is reduced to half or less of the intercarrier spacings by matching the sign pattern of each element of the sets. Next, at tracking stage the frequency offset is corrected with a frequency detector which is controlled by the correlation of the two sets. It is shown that the proposed algorithm can correct the frequency offset in the event of uncertainty in the initial offset that exceeds one half of the intercarrier spacing. In addition, the proposed algorithm is robust to transmitted symbols and channel characteristics by using oversampled symbol sets.

• Korean Journal of Remote Sensing
• /
• v.38 no.2
• /
• pp.189-198
• /
• 2022

In this present study, we investigated the effect of the offset correction factor calculation method on the sulfur dioxide (SO₂) column density in the SO₂ retrieval algorithm of the Geostationary Environment Monitoring Spectrometer (GEMS) launched in February 2020. The GEMS operational SO₂ retrieval algorithm is the Differential Optical Absorption Spectroscopy (DOAS) - Principal Component Analysis (PCA) Hybrid algorithm. In the GEMS Hybrid algorithm, the offset correction process is essential to correct the absorption effect of ozone appearing in the SO₂ slant column density (SCD) obtained after spectral fitting using DOAS. Since the SO₂ column density may depend on the conditions for calculating the offset correction factor, it is necessary to apply an appropriate offset correction value. In this present study, the offset correction values were calculated for days with many cloud pixels and few cloud pixels, respectively. And a comparison of the SO₂ column density retrieved by applying each offset correction factor to the GEMS operational SO₂ retrieval algorithm was performed. When the offset correction value was calculated using radiance data of GEMS on a day with many cloud pixels was used, the standard deviation of the SO₂ column density around India and the Korean Peninsula, which are the edges of the GEMS observation area, was 1.27 DU, and 0.58 DU, respectively. And around Hong Kong, where there were many cloud pixels, the SO₂ standard deviation was 0.77 DU. On the other hand, when the offset correction value calculated using the GEMS data on the day with few cloud pixels was used, the standard deviation of the SO₂ column density slightly decreased around India (0.72 DU), Korean Peninsula (0.38 DU), and Hong Kong (0.44 DU). We found that the SO₂ retrieval was relatively stable compared to the SO₂ retrieval case using the offset correction value on the day with many cloud pixels. Accordingly, to minimize the uncertainty of the GEMS SO₂ retrieval algorithm and to obtain a stable retrieval, it is necessary to calculate the offset correction factor under appropriate conditions.

• Journal of the Korea Society of Computer and Information
• /
• v.18 no.10
• /
• pp.63-70
• /
• 2013

In this paper, we investigated frequency synchronization through computer simulation of digital M/W transmission system in multipath fading channel. we suggested frequency offset correction algorithm against frequency offset between transmitter and receiver, then evaluated the degree of constellation performance enhancement. From the performance evaluation, in case of large frequency offset, although adopting frequency offset correction scheme, residual frequency offset degraded system performance. As a result, according to frequency offset value between transmitter and receiver residual frequency offset affects system performance significantly. The results of this paper should be utilized for frequency synchronization criterion when frequency band of broadcasting system is rearranged.

• Journal of the Institute of Electronics Engineers of Korea SP
• /
• v.49 no.2
• /
• pp.35-44
• /
• 2012

Most recent infrared (IR) sensors have a focal-plane array (FPA) structure. Spatial non-uniformity of a FPA structure, however, introduces unwanted fixed pattern noise (FPN) to images. This non-uniformity correction (NUC) of a FPA can be categorized into target-based and scene-based approaches. In a target-based approach, FPN can be separated by using a uniform target such as a black body. Since the detector response randomly drifts along the time axis, however, several scene-based algorithms on the basis of a video sequence have been proposed. Among those algorithms, the state-of-the-art one based on Kalman filter uses one-directional warping for motion compensation and only compensates for offset non-uniformity of IR camera detectors. The system model using one-directional warping cannot correct the boundary region where a new scene is being introduced in the next video frame. Furthermore, offset-only correction approaches may not completely remove the FPN in images if it is considerably affected by gain non-uniformity. Therefore, for FPN reduction in IR videos, we propose a joint correction algorithm of gain and offset based on bi-directional warping. Experiment results using simulated and real IR videos show that the proposed scheme can provide better performance compared with the state-of-the art in FPN reduction.

• Proceedings of the KSRS Conference
• /
• 2004.10a
• /
• pp.471-474
• /
• 2004

Not all CCD pixels generate uniform value for the uniform radiance due to the different process of manufacture and each pixel characteristics. And the image data compression is essential in the real time image transmission because of the high line rate and the limited RF bandwidth. This pixel's nonuniformity and the loss compression make CCD pixel correction necessary in on-orbit condition. In the MSC system, the NUC unit, which is a part of MSC PMU, is charge of the correction for CCD each pixel. The correction is performed with the gain and the offset table for the each pixel and the each TDI mode. These correction tables are generated and programmed in the PMU Flash memory through the various image data tests at the ground test. Besides, they can be uploaded from ground station after onorbit calibration. This paper describes the principle of the table generation and the test way of the non-uniformity after NUC

• Journal of radiological science and technology
• /
• v.45 no.5
• /
• pp.397-405
• /
• 2022

Computed radiography (CR) systems, which convert an analog signal recorded on a cassette into a digital image, combine the characteristics of analog and digital imaging systems. Compared to digital radiography (DR) systems, CR systems have presented difficulties in evaluating system performance because of their lower detective quantum efficiency, their lower signal-to-noise ratio (SNR), and lower modulation transfer function (MTF). During the step of energy-storing and reading out, a baseline offset occurs in the edge area and makes low-frequency overestimation. The low-frequency offset component in the line spread function (LSF) critically affects the MTF and other image-analysis or qualification processes. In this study, we developed the method of baseline correction using mathematical morphology to determine the LSF and MTF of CR systems accurately. We presented a baseline correction that used a morphological filter to effectively remove the low-frequency offset from the LSF. We also tried an MTF evaluation of the CR system to demonstrate the effectiveness of the baseline correction. The MTF with a 3-pixel structuring element (SE) fluctuated since it overestimated the low-frequency component. This overestimation led the algorithm to over-compensate in the low-frequency region so that high-frequency components appeared relatively strong. The MTFs with between 11- and 15-pixel SEs showed little variation. Compared to spatial or frequency filtering that eliminated baseline effects in the edge spread function, our algorithm performed better at precisely locating the edge position and the averaged LSF was narrower.

• Journal of the Korea Society of Computer and Information
• /
• v.24 no.6
• /
• pp.11-19
• /
• 2019

In this paper, a new Scene-based Nonuniformity Correction (SBNUC) method is proposed by applying Image Roughness-like and Spatial Noise cost functions on deep neural network structure. The classic approaches for nonuniformity correction require generally plenty of sequential image data sets to acquire accurate image correction offset coefficients. The proposed method, however, is able to estimate offset from only a couple of images powered by the characteristic of deep neural network scheme. The real world SWIR image set is applied to verify the performance of proposed method and the result shows that image quality improvement of PSNR 70.3dB (maximum) is achieved. This is about 8.0dB more than the improved IRLMS algorithm which preliminarily requires precise image registration process on consecutive image frames.

• Korean Journal of Optics and Photonics
• /
• v.9 no.6
• /
• pp.408-412
• /
• 1998

As the radius of curvature of curved optical waveguide gets smaller, the loss increases at the junction of linear-curved waveguide by the cross sectional mode mismatch. The concept of lateral offset has been used widely to minimize it, and simple method of maximum matching has been efficient for most cases of silica waveguide with low optical confinement and large radius of curvature. Here, we analyzed that the propagation mode characteristics of the lateral offset and propagation mode characteristics of general case with effective index method and Airy function solution. As the normalized frequency varies, mode characteristics changes near the boundary of 1/V=0.7 and the simple matching of gaussian profile might give -35% of error at most. We proposed improved method with a new correction factor to improve the mode mismatch problem of conventional methods for general cases, and showed the convenience and feasibility of this method for the calculation of the lateral offset.