Jung-Young Son’s research while affiliated with Konyang University and other places

In this work, two methods are proposed for solving the problem of one-dimensional barcode segmentation in images, with an emphasis on augmented reality (AR) applications. These methods take the partial discrete Radon transform as a building block. The first proposed method uses overlapping tiles for obtaining good angle precision while maintaining good spatial precision. The second one uses an encoder–decoder structure inspired by state-of-the-art convolutional neural networks for segmentation while maintaining a classical processing framework, thus not requiring training. It is shown that the second method’s processing time is lower than the video acquisition time with a 1024 × 1024 input on a CPU, which had not been previously achieved. The accuracy it obtained on datasets widely used by the scientific community was almost on par with that obtained using the most-recent state-of-the-art methods using deep learning. Beyond the challenges of those datasets, the method proposed is particularly well suited to image sequences taken with short exposure and exhibiting motion blur and lens blur, which are expected in a real-world AR scenario. Two implementations of the proposed methods are made available to the scientific community: one for easy prototyping and one optimised for parallel implementation, which can be run on desktop and mobile phone CPUs.

In this study, a 50 × 50 mm holographic optical element (HOE) with the property of a spherical mirror was recorded digitally on a silver halide photoplate using a wavefront printing method. It consisted of 51 × 96 hologram spots with each spot measuring 0.98 × 0.52 mm. The wavefronts and optical performance of the HOE were compared with those of reconstructed images from a point hologram displayed on DMDs of different pixel structures. The same comparison was also performed with an analog-type HOE for a heads-up display and with a spherical mirror. A Shack–Hartmann wavefront sensor was used to measure the wavefronts of the diffracted beams from the digital HOE and the holograms as well as the reflected beam from the analog HOE and the mirror when a collimated beam was incident on them. These comparisons revealed that the digital HOE could perform as a spherical mirror, but they also revealed astigmatism—as in the reconstructed images from the holograms on DMDs—and that its focusability was worse than that of the analog HOE and the spherical mirror. A phase map, i.e., the polar coordinate-type presentation of the wavefront, could visualize the wavefront distortions more clearly than the reconstructed wavefronts obtained using Zernike polynomials. The phase map revealed that the wavefront of the digital HOE was more distorted than those of the analog HOE and the spherical mirror.

We measured vertical and horizontal displacements of distant objects based on the moiré effect. The grid attached to the object was photographed and recorded on video camera. The video was processed later in the lab. The method is self-calibrated and does not need special equipment in the field (except for a regular videographer’s apparatus). The objectives of this study were to create a method for non-contact moiré measurement based on camera images and to find a way to deal with anomalous vibrations of structures. The experimental measurements of the fundamental frequency are in accordance with the theory of square beams. Tests with broken models were also conducted. The influence of two opposite factors on the fundamental frequency in the beams with cracks was estimated. In determining the pre-failure condition, the decay rate seems to be a more promising indicator than the fundamental frequency; however, this was only observed when a crack was near the fixed edge. The results and findings can be applied in measuring displacement in various objects; in public safety, and particularly, in distinguishing between normal and abnormal vibration in bridges.

The thermal properties of electrically heated carbon-fiber-reinforced mortar prisms with 0.5%, 1.0%, 1.5% and 2.0% of their volumes are investigated. Each prism dimension is 40 mm × 40 mm × 160 mm. When the constant power of 30W is applied to two conductive-gel strips painted on the prisms’ surfaces as the electrodes, for 5 min, the prisms show that: (1) their surface heating patterns have mostly the shape of two semi-circles centered at each of the electrodes; (2) their surface temperatures increase more for those with higher fiber percentages; (3) their surface’s average temperature increments are the highest for the first 1 min of heating; (4) the lines representing the lowest and highest temperature zones and one of the normal lines to two electrodes record the highest temperature increment for the first 1 min of heating; (5) the temperature ratio of two points on the surface of each of four different percentage prisms has almost an unchanging value for all heating time periods especially when the two points are close to the volume defined by two electrodes; (6) the average temperature increments decrease with time. These facts are for all percentage prisms.

Thermal images are used to visualise the crack forming processes in mortar prisms under the flexural strength test with a UTM (Universal Testing Machine). The surface temperature of the prisms increases as the stress on them increases. When the prisms are reinforced by carbon fibres, the aggregated fibres along the crack paths becomes distinctive due to their higher temperature compared with their surrounding mortar areas of the prisms. This enables to visualise the crack forming process. In this process, there is a moment of abrupt increase in the temperature gradient of the aggregated fibres. This moment matches closely to that of the crack on-set obtained from the video images of crack forming process taken with a panchromatic camera, with less than 2.2 % difference. The moment is also matched with that of sharp dropping in the force from the UTM after the peak. This sudden temperature gradient increase can be used to determine the crack on-set times of the prisms with a high accuracy.

The presence of monocular depth sense is identified with a light field imaging system which can project up to 8 different view images simultaneously to a viewer’s each eye. The depth of field of subjects’ eyes increases further as the number of simultaneously projected images to subjects’ each eye increases more, though the increasing rate is somewhat different for different subjects. The diopter values exceed more than those of real object as the number exceeds more than six for the binocular viewing while it is eight for monocular viewing. The increasing rate of the diopter values for the binocular viewing is more than that for monocular viewing. These results assure that a natural viewing condition can be incorporated in light field imaging systems. These results are derived from 7 subjects under age 35, having eye sight greater than 1.0.