Kyung-Chan Jin

Mixing and Simplex Search for Optimal Illumination in Machine Vision

Mixed-color illumination affects the quality of images in industrial vision system and it is important to optimize color and intensity for image acquisition. This study used simplex search to find the optimal illumination in a short amount of time. A typical color mixer synthesized various color of lights by changing the inputs of RGB power LEDs and passing the lights through an optical system. The image quality under mixed-color illumination was calculated according to the sharpness. For the purpose of optimal illumination using simplex search, a probe network was organized with N + 1probing points for N inputs. The shape of the probe network, simplex, was varied through procedures of extension, contraction, and shrinkage. The inputs of the color mixer were changed until the size of the simplex became smaller than a threshold. The simplex search was tested for commercial semiconductor patterns, and was useful for finding the optimal illumination.

TDC module for time-of-flight

Time-to-digital (TDC) technique was proposed to measure time-of-flight (TOF) that can determine the distance which is produced by the associated particle imaging (API) techniques including neutron methods with neutron generator and secondary radiation detection. The purpose of API method is for the elemental analysis and TDC shows the location of target object. In order to manage high resolution TDC timing, we used the propagation delay on the internal wires of field programmable gate array (FPGA) chips, utilized the place and route (P&R) delay difference. By setting P&R area constraints, we generated two precise ring oscillators with slightly different frequencies. The time difference between two ring oscillators is the time bin resolution of TDC. The multi-channel number of alpha-gamma event depends on the size of FPGA gates and configurable. Experimental results showed that the time interval of two ring oscillators of FPGA is about 100 ps, and varied by the lock detection between the operating frequencies of two ring oscillators that differ within 100 ps. After implementation of TDC counter TOF tagging schemes such as time stamp and control logic were generated and the event rate at each channel was more than 1 MHz. Finally, we investigated that TOF FPGA was useful in the multi-channel analyzer to measure the time interval between alpha-gamma of API system.

FPGA-based forward and back-projection operators for tomographic reconstruction

Artifacts in computerized tomography (CT), such as metal streak effects, can also be reduced using the iterative reconstruction approach. The main issue in iterative method is the computation cost by efficient implementation of the forward and back-projection operations, which are the dominant cost in all iterative reconstruction algorithms. We designed a field programmable gate array (FPGA)-based operators for iterative forward and back-projection method to solve the artifact model. The projection method in CT reconstruction is to retrieve the volumetric image based on observed projection image and makes reconstruction errors minimize. The FPGA-based operators contain only the iterative reconstruction operations from tomographic projections, and the filtering of detector data and the geometry correction between detector and object are done by host CPU processor. For FPGA design, we used Impulse C package, C-to-FPGA tool including the use of streaming and pipelining for high performance. We evaluated the FPGA-based projection on Shepp-Logan phantom data with metal streak artifact. Simulation results show that the FPGA-based operators can reduce the computation time of iterative reconstruction, while still providing accuracy comparable to CPU or GPU-based reconstruction.

Post-processing to reduce missing wedge effect using total variation minimization

The use of X-ray inspection for analyzing faults in printed circuit board components is becoming more important with the ongoing development of 3D integrated circuits. Achieving optimal X-ray inspection for a slab-like flat object depends on selecting an appropriate computed tomography (CT) geometry, such as an off-centered cone-beam geometry. However, because the use of flat components in tomographic reconstruction restricts the range of viewing angles, CT leads to the missing wedge problem, which causes missing angle artifacts in reconstructed 3D data. In this paper, we propose the use of post-processing to reduce the missing wedge effect via total variation minimization, when sinogram images have equal quality at all viewing angles and the accessible tilt range is restricted only by the physical limits of the oblique-view CT system. We demonstrate that axial slice reconstruction using the proposed processing method substantially reduces the missing wedge effect and that the proposed method provides overall image quality superior to that achieved with existing denoising methods.

Open-Source Hardware Module Application for Remote Monitoring of Disaster Prevention

Since the natural disasters such as floods, droughts, heat wave and cold wave are increasing, the need for risk management is necessary to minimize the damage with utilizing IT technology. Also, the monitoring services of disaster response type have been developed and applied. Recently, the open source hardware based on the signal of the sensor, or the monitoring studies have been carried. In this paper, by analyzing a low-cost open source hardware platform such as Beagle board, we examine the utilization of the hardware-based module for sensor monitoring.

Oblique Angle Artifact Reduction Using Wavelet-Based Filtering in Off-Centered Circular Geometry of Cone Beam Computed Tomography

A tomographic methodology for inspection of TSV (Through Silicon Via) process wafers is developed by utilizing an X-ray source. In conventional X-ray computed tomography (CT), the scanning axis of X-ray source and detector is approximately parallel to the long axis of the phantom and perpendicular to the plane of X-ray source. However, because TSV projection data are captured by angling the phantom bed relative to the plane of X-ray beam, the conventional CT geometry can not produce the visible projection images and results in a poorer resolution in TSV phantom. In such cases, an off-centered circular trajectory geometry of cone beam computed tomography (CBCT) is more effective. However, each projection is transversely truncated, bringing errors and artifacts in reconstruction. In this paper, the wavelet-based filtering as the adaptive denoising filter of compressed sensing (CS) enhancement is proposed for the off-centered circular trajectory scanning geometry. In the experiment, TSV imaging of nanofocus CT (nCT) is used to evaluate the accuracy and practicability of the proposed method, which is equipped with an off-centered flat panel detector. Results show that artifact enhancement is acceptable for practical use, and the image quality appears sufficient for specific diagnostic requirements. It provides a novel solution for wafer inspection CBCT system, in order to reduce the effect of oblique angle artifact.

Forward projection model for noisy computerized tomography projection enhancement

The noise in a low-radiation dose can be enhanced by an iterative reconstruction technique using forward and back projection models. This work investigated an iterative reconstruction approach using a forward projection model based on a contrast limited adaptive histogram equalization (CLAHE). Using the CLAHE technique, the projection image was processed to remove the noise, and then the preprocessed image was used as input to reconstruct the slice images. Finally, we evaluated the proposed method and found that compared to conventional reconstruction techniques, the proposed method led to improved image quality, concurrent with a reduction in the Poisson noise distribution, as demonstrated by phantom studies.

Reduction of Missing Wedge Artifact in Oblique-View Computed Tomography

The manufacturer need for high-speed interconnection in three-dimensional integrated circuits (3D ICs) warrants inspection with through-silicon via (TSV) technology. Because the use of a flat component in tomographic reconstruction restricts the range of viewing angles, the computed tomography (CT) system produces limited-view projection images, which causes missing angle artifacts in the reconstructed 3D data. In this paper, we propose a total variation (TV) approach for tomographic image reconstruction. The proposed approach improves the image quality when the sinogram images have equal quality at all viewing angles and the accessible tilt range is restricted only by the physical limits of the oblique-view CT system. This method employs a bowtie TV (b-TV) penalty, which establishes a desirable balance between smooth and piecewise-constant solutions in the missing wedge region. Finally, the images resulting from the proposed method are shown to be smooth with sharp edges and fewer visible artifacts. Furthermore, the overall image quality is higher than those of images obtained by existing TV methods.

Generating selected color using RGB, auxiliary lights, and simplex search

ABSTRACT A mixed light source generates various colors with the potential to adjust the intensities of multiple LEDs, which makes it possible to generate arbitrary colors. Currently, PCs and OSs provide color selection windows that can obtain the red, green, and blue (RGB) or hue, saturation, and lightness (HSL) color coordinates of a user’s selection. Mixed light sources are usually composed of primary-colored LEDs with LEDs in auxiliary colors such as white and yellow used in a few cases. The number of LED inputs and the dimming levels are greater than the number of elements in the color coordinate when using auxiliary-colored LEDs, which causes an under-determined problem. This study proposes a method to determine the dimming levels of LEDs based on a simplex search method (SSM). Commercial LEDs have different optical power values and impure color elements, even if they are RGB. Hence, the characteristics of the LEDs were described using a linear model derived from the tri-stimulus values (an XYZ color coordinate model) and dimming levels. Color mixing models were derived for an arbitrary number of auxiliary-colored LEDs. The under-determined problem was solved using an SSM without an inverse matrix operation. The proposed method can be applied to a machine vision system and an RGBW light mixer for semiconductor inspection. The dimming levels, obtained using the proposed method showed better optical responses than those derived using other methods.

Open source monitoring hardware for sensor interface

Open source hardware (OSHW) has been created by the design movement and is a promising technology as it applies a compatible concept to a variety of components. Also, OSHW is intended to enable anyone to study specific hardware, makes modifications, and share hardware changes with peers. In this paper, we present the sensor interface application of OSHW. To develop embedded systems using the concept of OSHW, we developed and tested a monitoring module based on the Beaglebone Black for a chip inspection system. The developed module can be used in low power monitoring, and can obtain a more flexible sensor interface in the on-line chip fault inspection and isolation process.