Chul Hee Park

Color Restoration of RGBN Multispectral Filter Array Sensor Images Based on Spectral Decomposition

A multispectral filter array (MSFA) image sensor with red, green, blue and near-infrared (NIR) filters is useful for various imaging applications with the advantages that it obtains color information and NIR information simultaneously. Because the MSFA image sensor needs to acquire invisible band information, it is necessary to remove the IR cut-offfilter (IRCF). However, without the IRCF, the color of the image is desaturated by the interference of the additional NIR component of each RGB color channel. To overcome color degradation, a signal processing approach is required to restore natural color by removing the unwanted NIR contribution to the RGB color channels while the additional NIR information remains in the N channel. Thus, in this paper, we propose a color restoration method for an imaging system based on the MSFA image sensor with RGBN filters. To remove the unnecessary NIR component in each RGB color channel, spectral estimation and spectral decomposition are performed based on the spectral characteristics of the MSFA sensor. The proposed color restoration method estimates the spectral intensity in NIR band and recovers hue and color saturation by decomposing the visible band component and the NIR band component in each RGB color channel. The experimental results show that the proposed method effectively restores natural color and minimizes angular errors.

Edge enhancement algorithm for low-dose X-ray fluoroscopic imaging

BACKGROUND AND OBJECTIVE Low-dose X-ray fluoroscopy has continually evolved to reduce radiation risk to patients during clinical diagnosis and surgery. However, the reduction in dose exposure causes quality degradation of the acquired images. In general, an X-ray device has a time-average pre-processor to remove the generated quantum noise. However, this pre-processor causes blurring and artifacts within the moving edge regions, and noise remains in the image. During high-pass filtering (HPF) to enhance edge detail, this noise in the image is amplified. METHODS In this study, a 2D edge enhancement algorithm comprising region adaptive HPF with the transient improvement (TI) method, as well as artifacts and noise reduction (ANR), was developed for degraded X-ray fluoroscopic images. The proposed method was applied in a static scene pre-processed by a low-dose X-ray fluoroscopy device. First, the sharpness of the X-ray image was improved using region adaptive HPF with the TI method, which facilitates sharpening of edge details without overshoot problems. Then, an ANR filter that uses an edge directional kernel was developed to remove the artifacts and noise that can occur during sharpening, while preserving edge details. RESULTS The quantitative and qualitative results obtained by applying the developed method to low-dose X-ray fluoroscopic images and visually and numerically comparing the final images with images improved using conventional edge enhancement techniques indicate that the proposed method outperforms existing edge enhancement methods in terms of objective criteria and subjective visual perception of the actual X-ray fluoroscopic image. CONCLUSIONS The developed edge enhancement algorithm performed well when applied to actual low-dose X-ray fluoroscopic images, not only by improving the sharpness, but also by removing artifacts and noise, including overshoot.

Simple and accessible analytical methods for the determination of mercury in soil and coal samples.

Simple and accessible analytical methods compared to conventional methods such as US EPA Method 7471B and ASTM-D6414 for the determination of mercury (Hg) in soil and coal samples are proposed. The new methods are consisted of fewer steps without the Hg oxidizing step consequently eliminating a step necessary to reduce excess oxidant. In the proposed methods, a Hg extraction is an inexpensive and accessible step utilizing a disposable test tube and a heating block instead of an expensive autoclave vessel and a specially-designed microwave. Also, a common laboratory vacuum filtration was used for the extracts instead of centrifugation. As for the optimal conditions, first, best acids for extracting Hg from soil and coal samples was investigated using certified reference materials (CRMs). Among common laboratory acids (HCl, HNO3, H2SO4, and aqua regia), aqua regia was most effective for the soil CRM whereas HNO3 was for the coal CRM. Next, the optimal heating temperature and time for Hg extraction were evaluated. The most effective Hg extraction was obtained at 120°C for 30min for soil CRM and at 70°C for 90min for coal CRM. Further tests using selected CRMs showed that all the measured values were within the allowable certification range. Finally, actual soil and coal samples were analyzed using the new methods and the US EPA Method 7473. The relative standard deviation values of 1.71-6.55% for soil and 0.97-12.11% for coal samples were obtained proving that the proposed methods were not only simple and accessible but also accurate.

G-Channel Restoration for RWB CFA with Double-Exposed W Channel

In this paper, we propose a green (G)-channel restoration for a red–white–blue (RWB) color filter array (CFA) image sensor using the dual sampling technique. By using white (W) pixels instead of G pixels, the RWB CFA provides high-sensitivity imaging and an improved signal-to-noise ratio compared to the Bayer CFA. However, owing to this high sensitivity, the W pixel values become rapidly over-saturated before the red–blue (RB) pixel values reach the appropriate levels. Because the missing G color information included in the W channel cannot be restored with a saturated W, multiple captures with dual sampling are necessary to solve this early W-pixel saturation problem. Each W pixel has a different exposure time when compared to those of the R and B pixels, because the W pixels are double-exposed. Therefore, a RWB-to-RGB color conversion method is required in order to restore the G color information, using a double-exposed W channel. The proposed G-channel restoration algorithm restores G color information from the W channel by considering the energy difference caused by the different exposure times. Using the proposed method, the RGB full-color image can be obtained while maintaining the high-sensitivity characteristic of the W pixels.

Color Restoration for Infrared Cutoff Filter Removed RGBN Multispectral Filter Array Image Sensor

Imaging systems based on multispectral filter arrays(MSFA) can simultaneously acquire wide spectral information. A MSFA image sensor with R, G, B, and near-infrared(NIR) filters can obtain the mixed spectral information of visible bands and that of the NIR bands. Since the color filter materials used in MSFA sensors were almost transparent in the NIR range, the observed colors of multispectral images were degraded by the additional NIR spectral band information. To overcome this color degradation, a new signal processing approach is needed to separate the spectral information of visible bands from the mixed spectral information. In this paper, a color restoration method for imaging systems based on MSFA sensors is proposed. The proposed method restores the received image by removing NIR band spectral information from the mixed wide spectral information. To remove additional spectral information of the NIR band, spectral estimation and spectral decomposition were performed based on the spectral characteristics of the MSFA sensor. The experimental results show that the proposed method restored color information by removing unwanted NIR contributions to the RGB color channels.

Kernel-based image upscaling method with shooting artifact reduction

This paper describes the interpolation algorithm which contains shooting or ringing artifact suppression based on windowed sinc interpolator. In general, the windowed sinc interpolator can achieve better performance by using wider window. However, using wide window causes more ripples that produce unwanted defects such as ringing or shooting artifact. Therefore, shooting reduction technique is proposed in this paper for using wider windows to improve the performance without shooting artifact. The proposed algorithm can suppress shooting artifact by using median sinc interpolator and it can be also used as a post processor for many kernel-based interpolation methods. The resulted image shows that the proposed algorithm can maintain local details and suppress shooting artifact in the image well.

A method of RGB color Conversion of Image obtained Horizontally arranged RWB image sensor Using dual Sampling

This Paper proposes a vehicle detection system and a license plate recognition system from CCTV images installed on public roads. Since the environment of this system acquires the image in the general road environment, the stable condition applied to the existing vehicle entry / exit system is not g...

Least Square based Multi-spectral Color Interpolation Algorithm for RGB-NIR Image Sensors

The use of near-infrared (NIR) band gives us additional invisible information to discriminate objects and enables us to recognize objects more clearly under low light conditions. To acquire color and NIR bands together in a single image sensor developed from a conventional color filter array (CFA), we use a multispectral filter array (MSFA) in the RGB-NIR sensors and design a color interpolation algorithm to fill the information about the multi-spectral (MS) bands from the subsampled MSFA image. Aliasing in the MSFA image caused by the subsampled bands is minimized by balancing the energy of the bands. A panchromatic (PAN) image is generated by filtering the low-pass kernel to the MSFA image. This PAN image without chrominance signals, which contains the most high-frequency in the MSFA image, is used to reconstruct the MS images by solving the least square cost function between the PAN and MS images. The experiments show that the proposed algorithm estimates the high-resolution MS images very well.

Photodiodes integration on a suspended ridge structure VOA using 2-step flip-chip bonding method

In this works, we have demonstrated a VOA integrated with mPDs, based on silica-on-silicon PLC and flip-chip bonding technologies. The suspended ridge structure was applied to reduce the power consumption. It achieves the attenuation of 30dB in open loop operation with the power consumption of below 30W. We have applied two-step flipchip bonding method using passive alignment to perform high density multi-chip integration on a VOA with eutectic AuSn solder bumps. The average bonding strength of the two-step flip-chip bonding method was about 90gf.

Video resampling algorithm for simultaneous deinterlacing and image upscaling with reduced jagged edge artifacts

In this paper, we propose a video resampling method for simultaneous deinterlacing and image upscaling. The proposed method is composed of two steps: the initial image magnification step and the edge enhancement step. In order to convert an interlaced image into a display format image, a filtering strategy, which resizes images with arbitrary ratios and reduces the overall computational load, is performed region adaptively using local characteristics such as motion or motionless regions. After the initial step, the proposed jagged edge correction (JEC) method is applied to the initially upscaled images to correct the stair-like artifacts (jagged edges) which are caused by ignoring any edge information in diagonal edge regions during the linear filtering process. Moreover, this method can be very useful for various upscaling applications to improve edge quality since it can be used in combination with other common interpolation techniques, such as cubic spline techniques. Experimental results show that the proposed method substantially reduces the jagged edges of the converted images and provides steep and natural-looking edge transitions.