Seung Taek Kim

An Optical Mixer and RGB Control for Fine Images using Grey Scale Distribution

We considered the issue of color mixing from the viewpoint of gray scale images and investigated the effect of the mixed light. The goal of this study was to improve the quality of the grey scale images by using mixed RGB illumination. The mixing mechanism and image quality were formulized and applied to a machine vision system with an RGB mixer. The RGB mixer was made of RGB LEDs, a power AMP, a mixing chamber, and a bundle of optical fibers. The intensity of the RGB light was adjusted by varying the 12 bit DAC voltage. The optical characteristics of the RGB LEDs were measured by a spectrometer. The color variation of the mixed light was monitored by a chromatic meter. Grey scale images were captured and analyzed under various lighting conditions provided by the mixer. The optimal illumination was determined by the distribution of the grey scale in the captured image. The chromatic diagram showed that various colors can be generated, and the image histogram showed that the mixed light can increase the quality of the grey scale image.

3D Body Scanning Measurement System Associated with RF Imaging, Zero-padding and Parallel Processing

Abstract This work presents a novel signal processing method for high-speed 3D body measurements using millimeter waves with a general processing unit (GPU) and zero-padding fast Fourier transform (ZPFFT). The proposed measurement system consists of a radio-frequency (RF) antenna array for a penetrable measurement, a high-speed analog-to-digital converter (ADC) for significant data acquisition, and a general processing unit for fast signal processing. The RF waves of the transmitter and the receiver are converted to real and imaginary signals that are sampled by a high-speed ADC and synchronized with the kinematic positions of the scanner. Because the distance between the surface and the antenna is related to the peak frequency of the conjugate signals, a fast Fourier transform (FFT) is applied to the signal processing after the sampling. The sampling time is finite owing to a short scanning time, and the physical resolution needs to be increased; further, zero-padding is applied to interpolate the spectra of the sampled signals to consider a 1/m floating point frequency. The GPU and parallel algorithm are applied to accelerate the speed of the ZPFFT because of the large number of additional mathematical operations of the ZPFFT. 3D body images are finally obtained by spectrograms that are the arrangement of the ZPFFT in a 3D space.

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.