KEYWORDS: Digital watermarking, Digital holography, Holograms, 3D image reconstruction, Near field diffraction, Optical engineering, Wave propagation, Light wave propagation, Computer generated holography, Diffraction
Since holograms are very costly content, security against holograms is very important. Hologram watermarking has been researched for a long time as a security solution for the digital hologram distributed on the network as the hologram is digitized. We deal with a digital watermarking for digital hologram contents as ownership protection tool. Since holograms have different optical characteristics from natural images, a watermarking technique using these characteristics should be needed. We therefore selected Fresnel diffraction for this property. Both of the host holograms and the watermarks are diffracted more than once for each. The results are refracted to concentrate the diffracted data into the localized regions of the transformed plane so that the region occupied one region among them. From this process, we change and select the region of the watermark. We experimented our scheme with various test images for various attacks on data-manipulating attack and geometric attack. It is apparently recognizable for eye inspection. From the results, we expect the proposed watermarking scheme to be an appropriate solution for protecting the ownership of holograms.
We propose a new system that can generate digital holograms using natural color information. The system consists of a camera system for capturing images (object points) and software (S/W) for various image processing. The camera system uses a vertical rig, which is equipped with two depth and RGB cameras and a cold mirror, which has different reflectances according to wavelength for obtaining images with the same viewpoint. The S/W is composed of the engines for processing the captured images and executing computer-generated hologram for generating digital holograms using general-purpose graphics processing units. Each algorithm was implemented using C/C++ and CUDA languages, and all engines in the form of library were integrated in LabView environment. The proposed system can generate about 10 digital holographic frames per second using about 6 K object points.
In this paper, we proposed a new coding technique of digital hologram video using 3D scanning method and video compression technique. The proposed coding consists of capturing a digital hologram to separate into RGB color space components, localization by segmenting the fringe pattern, frequency transform using M×N (segment size) 2D DCT (2 Dimensional Discrete Cosine Transform) for extracting redundancy, 3D scan of segment to form a video sequence, motion compensated temporal filtering (MCTF) and modified video coding which uses H.264/AVC. The compressed digital hologram was reconstructed by both computer program and optic system. The proposed algorithm showed better properties after reconstruction with higher compression ratios than the previous researches.
We propose an efficient coding method of digital holograms (or fringe patterns) using standard compression tools for video and image. The fringe pattern is generated by a computer-generated hologram (CGH) algorithm with both an object image and its depth information. The proposed coding consists of preprocessing to separate RGB color space components, localization by segmenting the fringe pattern, frequency transform using M×N (segment size), 2-D discrete cosine transform (DCT) for extracting redundancy, segment scanning the segmented fringe pattern to form a video sequence, classification of coefficients, and hybrid video coding, which uses MPEG-2/4, H.264/AVC, differential pulse code modulation (DPCM), and lossless coding. The proposed algorithm illustrates that it has better properties for reconstruction, from four to eight times higher compression rate than previous research.
JPEG2000 was established as an international standard for still image compression by ISO/IEC/ITU-T. This paper
proposed a method to perform network adaptive context extraction with high speed, which takes the largest portion in
calculation of EBCOT. This algorithm is to extract the context for coefficients whose value is more than or equal to a
transfer factor about the network environment. The speed and network-adaptive power is up at the cost of degrading the
image quality about transfer factor. The transfer factor was from 20 to 1 with the image quality of between 50dB and
30dB, at which from 20% to 60% of the amount of calculation and data was reduced. Since the degradation in image
quality can be adjusted by the transmission factor, the proposed method is expected to be used effectively in conjunction
with the progressive transmission methods according to the image quality. Also by implementing hardware IP, it is
expected to be able to be used in designing a JPEG2000 system.