Watermark embedding processes usually result in some degradation of the digital multimedia contents. Hence, they are not suitable for valuable and sensitive digital multimedia contents. Therefore, schemes combining signature with digital watermarking-like techniques have been proposed. Based on the general model for these combined schemes, a new scheme for image copyright protection by utilizing the pinned field of the protected image is proposed in this paper. The pinned field explores the texture information of the images and can be used to enhance the watermark robustness. Experimental results show that the proposed scheme works well under different signal-processing and geometric transformation attacks. On the other hand, in comparison with related schemes in the literature, our proposed scheme also has better performance. Furthermore, the proposed scheme is robust to both JPEG lossy compression and additive Gaussian noise.
An image authentication and tampering localization technique based on a wavelet-based digital watermarking procedure [Opt. Express 3(12), 491-496 (1998)] is proposed. To determine whether a given watermarked image has been tampered with or not, the similarity between the extracted and embedded watermarks is measured. If the similarity is less than a threshold value, the proposed sequential watermark alignment based on a coefficient stamping (SWACS) scheme is used to determine the modified wavelet coefficients corresponding to the tampered region. Then, the morphological region growing and subband duplication (MRGSD) scheme are used to include neighboring wavelet coefficients and then duplicate the wavelet coefficients in other subbands. The experimental results show that the proposed SWACS and MRGSD schemes can efficiently identify different types of image tampering. Moreover, the detection performance of the proposed system on various sizes of the watermark and tampered region is also evaluated.
A secure coding concept for pairwise images is revealed and implemented by the use of the proposed fractal mating coding scheme, in which the domain pools consist of the domain blocks selected from the pairwise images to explore both the intra- and interimage similarities. In addition to the pairwise relation, the mating ratios denoting the percentages of the domain blocks selected from both images are utilized. Further encryption can be achieved by the use of block mean permutation and mating of the fractal codes. The security level is high because the jointly coded images cannot be correctly reconstructed without all the required information. The computer experiments show that the coding performance can be greatly improved from conventional fractal coding schemes, and the intersecured purpose for pairwise images is successfully achieved.
Arbitrary shaped coding is an important issue of MPEG-4. In this study, an efficient shaped coding method, called the boundary block-searching (BBS) algorithm, which can enhance the coding efficiency of conventional padding schemes, is proposed. The proposed BBS algorithm assumes that boundary blocks have strong correlation even though they are not connected. For an input boundary block, the most similar block (only object pixels are considered) is sought from the previously coded data. Instead of being encoded by the use of discrete cosine transform, the boundary block is encoded by a position vector, which indicates the relative position of the most similar block. Therefore, the number of bits required to denote the boundary block is greatly reduced and low bit rate can be achieved. For two video sequences under different test conditions, simulation results show that the proposed BBS algorithm can greatly improve coding efficiency.
A parallelized random iteration algorithm that is explicit in the iterated function system (IFS) code is proposed to speed up the decoding of fractal images. In a conventional random iteration algorithm, the fractal image is serially decoded and may generate undesirable transient points. The proposed intrinsic parallel random iteration (IPRI) algorithm determines only one initial point and can avoid the transient points. Moreover, the contractive affine transformations (CATs) denoted by the IFS code can operate in parallel and simultaneously generate subimages. The parallel capability is basically proportional to the number of CATs. Two generalized methods of the proposed IPRI algorithm are provided to solve the nonuniformity problem due to the unequal probabilities among CATs. Finally, the proposed IPRI algorithm can cooperate with a previous parallel decoding algorithm to obtain higher parallel capability. Simulation results demonstrate the validity of the proposed IPRI algorithm.
The selection of initial blocks is one of the important issues in finite-state vector quantizers (FSVQs) for images. Conventional FSVQs use blocks located at fixed positions as initial blocks, which then are coded by the codewords in the super codebook. We propose an adaptive-initial-block (AIB) scheme to determine the initial blocks for gradient-match (GM) and side-match (SM) vector quantizers, which are two significant classes of FSVQs. According to the next-state functions used in GMVQs and SMVQs, the blocks with large boundary matching errors in original VQs are selected as the initial blocks. The error propagation effects can be reduced, and the coding performance is significantly improved. The simulation results show that the peak signal-to-noise ratios of coded images can be 2 dB higher than that of conventional GMVQs and SMVQs when the state codebook sizes are much smaller than that of the super codebook.
Dyadic displacements of an image can be regarded as a special type of permutations of pixel addresses. This property can be used to encrypt an image without information loss, damage, or addition. In this paper, a new optical image encryption technique based on dyadic permutations and holographic interference is proposed. First, we adopt holographic interference to record both the phase and amplitude of the Fourier transform of an input image as the intensity information. Then the recorded phase is processed through dyadic permutations based on exclusive-OR (XOR) operations. The original image can be successfully recovered by using the inverse procedure.
Conventional optical image verification systems based on the joint transform correlator (JTC) can only recover symmetric images in the output plane, which is an limitation to practical usage. In this paper, an optical asymmetric-image verification system based on the JTC is proposed. An additional phase mask is attached with a spatial light modulator (SLM), which displays the joint power spectrum as the amplitude information, to enable the reconstruction of an asymmetric image in the output plane. Two phase functions are paired and iteratively retrieved by the use of the projection onto constraint sets algorithm. One key is one of the joint functions in the input plane and acts as the key. The other phase is attached by the SLM. Compared with the image verification system based on the JTC architecture, the proposed system can obtain the asymmetric images in the output plane. In addition, the the proposed architecture can also yield the better image quality for symmetric images. Simulation results are given to verify the proposed method.
In this paper two architectures for optical image verification are roposed. Both architectures are modified from conventional joint transform correlators (JTCs) and can significantly improve the recovered image quality. First, an input phase-only function is Fourier transformed and then is interfered with a reference wave that is diffracted from a plane wave incident on another random phase mask. Second, two phase-only functions are placed at the two input sides of a beam splitter such that the interference patternof their Fourier transforms can be detected. The intensity of the interference pattern in both architectures can be recorded and then its Fourier-transform can be obtained in the output plane. To obtain a predefined target image in the output plane, the input phase function is iteratively retrieved by the use of the projection onto constraint sets algorithm. Simulation results show that the less mean squared error and better image quality are obtained for both the binary and grayscale images.
Deoxyribonucleic acid (DNA) sequences are difficult to analyze similarity due to their length and complexity. The challenge lies in being able to use digital signal processing (DSP) to solve highly relevant problems in DNA sequences. Here, we transfer a one-dimensional (1D) DNA sequence into a two-dimensional (2D) pattern by using the Peano scan algorithm. Four complex values are assigned to the characters “A”, “C”, “T”, and “G”, respectively. Then, Fourier transform is employed to obtain far-field amplitude distribution of the 2D pattern. Hereto, a 1D DNA sequence becomes a 2D image pattern. Features are extracted from the 2D image pattern with the Principle Component Analysis (PCA) method. Therefore, the DNA sequence database can be established. Unfortunately, comparing features may take a long time when the database is large since multi-dimensional features are often available. This problem is solved by building indexing structure like a filter to filter-out non-relevant items and select a subset of candidate DNA sequences. Clustering algorithms can organize the multi-dimensional feature data into the indexing structure for effective retrieval. Accordingly, the query sequence can be only compared against candidate ones rather than all sequences in database. In fact, our algorithm provides a pre-processing method to accelerate the DNA sequence search process. Finally, experimental results further demonstrate the efficiency of our proposed algorithm for DNA sequences similarity retrieval.
The technique of the multiple phases retrieval algorithm (MPRA) for designing optical security and verification systems is proposed in this paper. This technique is based on a 4-f optical correlator, which is a common architecture for optical image encryption and verification systems. In the proposed systems, however, two or more phase masks are iteratively retrieved by using the MPRA to obtain the target image. The convergent speed of the iteration process in the MPRA is significantly increased and the recovered image is much more similar to the target one than those in previous approaches. Moreover, the system security is increased since only the pair-wise retrieved phase masks can correctly recover the target images.
To avoid carrying two phase keys, one of the phase mask serves as the key and the other phase mask can be stored in the database of the security system as an active lock. Finally, according to our simulation results, the misalignment effects for the phase mask in the Fourier plane are more series than that in the input plane.
In this paper, the finite-state vector quantizers (FSVQs) with an extended super codebook obtained by applying the affine transformation to the codewords are proposed for the image coding framework. In designing the state codebook, each codeword in the super codebook in conventional FSVQs is affine-transformed (luminance shift, contrast scaling, and isometry operations) and thus a much larger virtual codebook is obtained. By using the matching criteria, such as the gradient match and the side match criteria in existing FSVQs, for the neighboring pixels in the block boundaries the much smaller state codebooks with different sizes can be constructed. Note that the rest parts of the proposed scheme are similar to those in the conventional FSVQs. On the other hand, much higher image quality can be obtained by using the extended virtual codebook. According to our simulation results, the peak-signal-to-noise ratio (PSNR) of the decoded images is significantly improved by 1--2 dB for the extended virtual codebook. However, the PSNRs are significantly reduced once the FSVQ with the gradient match and side match criteria are employed. Therefore we proposed another scheme that can improve the PSNR under the same bit rate. The simulation results show that the PSNR can be slightly increased. According to this scheme, we will propose efficient scheme to significantly increase the PSNR in our future work.
An image cryptosystem based on multiple phase-only computer-generated masks is proposed. The proposed cryptosystem is a hierarchical security system that uses multiple phase keys to produce multiple output images. The distant parameters between the phase keys are introduced to increase the system security. The proposed system achieves higher security because the phase keys must have their corresponding order and correct distant parameters to obtain the target image. The proposed system is safe even when an illegal user steals the whole phase keys but without the correct order and distant parameters. Aside from data encryption, the proposed system can also provide safe verification to identify the identity of the persons. The decryption process can be performed in digital methods or implemented by optics for the high speed. Simulation results are demonstrated to verify the proposed method.
In this paper, we propose the fractal-based gradient match vector quantizers (FGMVQs) and the fractal-based side match vector quantizers (FSMVQs) for the image coding framework. The proposed schemes are based upon the non-iterative fractal block coding (FBC) technique and the concepts of the gradient match vector quantizers (GMVQs) and the side match vector quantizers (SMVQs). Unlike the ordinary GMVQs and SMVQs, the super codebooks in the proposed FGMVQs and FSMVQs are generated from the affine-transformed domain blocks in the non-iterative FBC technique. The codewords in the state codebook are dynamically extracted from the super codebook with the side-match and gradient-match criteria. The redundancy in affine-transformed domain blocks is greatly reduced and the compression ratio can be significantly increased. Our simulation results show that about 10% - 20% bit rates in the non-iterative FBC techniques are saved by using the proposed FGMVQs and FSMVQs.
X-ray images of pistachio nuts on conveyor trays for product inspection are considered. The first step in such a processor is to locate each individual item and place it in a separate file for input to a classifier to determine the quality of each nut. This paper considers new techniques to: detect each item (each nut can be in any orientation, we employ new rotation-invariant filters to locate each item independent of its orientation), produce separate image files for each item [a new blob coloring algorithm provides this for isolated (non-touching) input items], segmentation to provide separate image files for touching or overlapping input items (we use a morphological watershed transform to achieve this), and morphological processing to remove the shell and produce an image of only the nutmeat. Each of these operations and algorithms are detailed and quantitative data for each are presented for the x-ray image nut inspection problem noted. These techniques are of general use in many different product inspection problems in agriculture and other areas.
Free-space digital optics is a new technology that exploits the ability of optics to handle thousands of light beams or information channels at once. This and other features of optics complement the strengths and weaknesses of purely electronic systems. A compact free-space optical system that uses array of microlens for chip-to-chip and board-to-board interconnections is proposed. Here the weakly diffracted Gaussian beam and wavelength division architecture are utilized to improve the channel density and reduce the crosstalk in a microlens interconnection system. Based on the simulation, we improve the channel capacity by 3.47 times (or reduce the crosstalk by 93.1 dB) while maintaining the same crosstalk (or channel density) compared with the conventional microlens interconnection system. As for the nonperfect filtering effect of different wavelengths at the detector plane, it is also studied to fully investigate the properties of the proposed scheme. The parameter sensitivity of the proposed system is studied for completeness. From the simulations, the relationship between the interconnection distance and spot size at the detector plane is wavelength-independent. In addition, the spot size is the most sensitive to the change of the microlens diameter compared with the other system parameters.
The output of an electronic holographic apparatus represents the magnitude and phase of the coherent light reflected from a three-dimensional object. The amplitude and phase can be fed into a spatial light modulator for three-dimensional object reconstruction, and the technique is thus named electronic holography. Resolution studies of recording and display devices for electronic holography are presented. The theoretical analysis for electronic holography is first carried out. Mathematically, the additive noise at the exposure of an electronic hologram is more serious than that at the reconstruction. Simulation is used to verify the theoretical results, and the resolution requirements for an electronic hologram are deduced. In our simulation, the point source is placed 500 mm in front of the recording device and the reference plane wave is tilted at angle π/4 in the -<i>y</i> direction with the normal to the recording plane. To discrimmate a two-point object with 0.17-mm separation, an 8-bit 256x256 charge injection device with a pixel size of 10 x 10 μm<sup>2</sup> is necessary. In addition, the additive noise from the ambient light during the exposure or reconstruction of an electronic hologram should be less than 1/100 of the signal amplitude for a 40-dB output SNR.
The exhaustive search process leads to a computational burden and therefore increases the complexity in the fractal image coding system. This is the main drawback to employ fractals for practical image compression applications. In this paper, an image compression scheme based on the fractal block coding and the simplified finite-state algorithm is proposed. For the finite-state algorithm that has been successfully employed in the vector quantization (VQ) technique, the state codebook (equivalent to the domain pool in the fractal image coding) is determined by a specific next-state function. In this research, we use the position of the range block to decide its domain pool. Therefore, a confined domain pool is limited in the neighboring region of the range block and thus the search process is simplified and faster. During the computer simulations, we consider two partition types, the single-level (8 X 8 blocks) and two-level (8 X 8 and 4 X 4 blocks) conditions. The simulation results show that the proposed scheme greatly reduces the computational complexity and improves the system performance.