A recently introduced algorithm for multirate vector quantization is used for coding image pyramids. The algorithm, called alphabet- and entropy-constrained vector quantization (AECVQ), operates by optimally choosing sub-codebooks from a large generic codebook. Simulations using 1-D AR and speech samples and full-band image data have shown the performance of AECVQ to be equal to that of entropy-constrained VQ (ECVQ); however, the ECVQ,which is also the best existing vector quantizer, is a single-rate coder. Excellent results at 1 bpp and below, judged both visually and using peak-to-peak SNR criterion, have been obtained by coding image pyramids using the AECVQ algorithm. These results demonstrate significant improvements over existing schemes. Although an AECVQ-based image coding scheme is considerably complex, it can be implemented in real time using current VLSI technology.
A compression technique based on a pyramidal expansion is presented. The elementary functions of the expansion form a class of pyramidal Gabor functions partitioning the frequency domain into different regions. Still images and moving image sequences are coded by Selecting and quantizing the coefficients in this expansion. Computer simulation of the proposed method show good quality reconstruction of both still images and image sequences.
A model is developed for estimating the displacement field in spatio-temporal image sequences that allows for affine shape deformations of corresponding spatial regions and for affine transformations of the image intensity range. This model includes the block matching method as a special case. The model parameters are found by using a least-squares algorithm. We demonstrate experimentally that the affine matching algorithm performs better in estimating displacements than other standard approaches, especially for long-range motion with possible changes in scene illumination. The algorithm is successfully applied to various classes of moving imagery, including the tracking of cloud motion.
We apply a model-based image coding scheme to the scene of a human walker. In our scheme, the motion of a whole human body is represented in 3-D stick motion. We concentrate on the following subjects: modeling of a walker by a stick model, the motion analysis algorithm based on the stick model, and the scheme to reconstruct continuous stick motion by the analyzed results. We determine both the form of a 3-D human stick model and how the model walks, and define the parameters of the model to represent the real motion in the scene. Then, we propose a three-layer motion representation scheme by using three stick models with different degrees of coarseness. Also, we present an algorithm for estimating the parameters of these stick models from monocular moving pictures. With this algorithm, the parameters of each model are estimated efficiently in the order of coarseness of model. We have applied his scheme to two experimental scenes where the identical walker is walking straight to the different direction. While the estimated 3-D motion has included some errors, the availability of this motion representation scheme to the model-based image coding system has been confirmed.
TOPICS: Optical filters, Linear filtering, Video coding, Digital filtering, Video, Image compression, Image filtering, Finite impulse response filters, Infinite impulse response filters, Signal to noise ratio
In many applications involving storage and transmission of digital images, there is an explicit need for data compression. Subband coding has emerged as one suitable technique for satisfying this need. Initially, image subband coders were based on FIR filter banks employing the quadrature mirror filters (QMF) of Johnston. To reduce the complexity associated with these subband coders, we have introduced image subband coders based on two types of IIR filter banks. The first is a tree structured filter bank, whereas the other is a fully parallel construction. The computational complexity ofthese filter banks is examined. The computational complexity of the llR-based structures is significantly lower than their FIR counterparts. Furthermore, we introduce multiplier-free IIR filter banks realizing even further complexity reductions. For the bit-efficient representation of the subband signals of both our still image and video coders, we propose a simple scheme similar to the ones employed for DCT-based coding in the CCITT H.261 recommendation and the emerging ISO/JPEG standard. In demonstrating the performance of our coders, we present simulation results at less than 0.5 bits per pel for still image coding and 64 to 200 kbps for coding of video. The performance of our low-complexity IIR structures is found to be comparable to structures based on FIR filters.
Well-known block transforms and perfect reconstruction orthonormal filter banks are evaluated based on their frequency behavior and energy compaction. The filter banks outperform the block transforms for the signal sources considered. Although the latter are simpler to implement and already the choice of the existing video coding standards, filter banks with simple algorithms may well become the signal decomposition technique for the next generation video codecs, which require a multiresolution signal representation.
An efficient subband image decomposition method for monochrome and color images made possible by mathematical morphology is described. The input signal spectrum is decomposed into four-subband and two-subband images by using two different sets of structuring elements. Then each band image can be decimated and coded effectively for data transmission. This subband pyramid scheme preserves the number of pixels as that in the original image Also, the data structure itself is very compact. The advantages of morphology over the linear filtering approach are its direct geometric interpretation, simplicity, and efficiency in hardware implementation. Some image examples are presented to show the effectiveness of this approach.
We present a bandwidth compression scheme suitable for transmission of radiometric data collected bytoday's sensitive and high-resolution sensors. Specific design constraints associated with this application are requirements for (1) near-lossless coding, (2) handling of a high dynamic range, and (3) placement of an upper bound on maximum coding error, as opposed to the average or rms coding error. In this approach both the spectral and spatial correlations in the data are exploited to reduce its bandwidth. Spectral correlation is first removed via the Karhunen-Loève (KL) transformation. An adaptive discrete cosine transform coding technique is then applied to the resulting spectrally decorrelated data. Because the actual coding is done in the transform domain, each individual coding error spreads over an entire block of data when reconstructed. This helps to reduce significantly the maximum error and, as such, makes this approach very suitable for this application. A useful by-product of this approach is that it readily provides some feature classification capability, such as cloud typing, through the interpretation of KL-transformed images. Since each KL-transformed image is a linear combination of all the spectral images, it represents a blend of information present in the entire spectral image set. As such, it could solely render some useful information not readily detectable from the ensemble of spectral images. This may be of particular utility for situations in which a photo interpreter may not have the time or the opportunity to inspect the entire set of images.
In this paper, a hybrid image coding scheme combining the advantages of both classified vector quantization (CVQ) and discrete cosine transform (DCT) is proposed. An image vector is classified according to its content activity. Vectors of low activity (shade vectors) are coded using CVQ. For vectors of high activity (edge vectors), DCT is used. To enhance the visual quality of the decoded image, the modulation transfer function (MTF) of the human visual system (HVS) model is incorporated into the DCT coding algorithm. Simulation results showed that the proposed approach allowed good subjective image quality to be obtained at relatively low bit rates. The improvement in quality is even more pronounced at low bit rates, if this
After three years of active and constructive international competition, a consensus was reached by the International Standards Organization (ISO) and the International Consultative Committee for Telephone and Telegraph (CCITT) in 1988 on one compression technique for still images. The collaboration of the CCITT and ISO took the form of the JPEG (Joint Photographic Expert Group), which is now referred to as the ISO/IEC JTC1/SC2/WG1O. Since then, the large-scale development of compatible interactive applications has begun to expand rapidly. A discussion of the JPEG standard is presented in the first part with an explanation of all the basic tools available in the standard. Then, to demonstrate the potential of the JPEG standard, two typical applications are described. One of them concerns the application to the printing industry currently under development in Japan, and the other deals with the large-scale introduction of photovideotex in Europe. Finally, other areas of active development around JPEG are briefly summarized to give the reader references and an overview of the evolving propagation of this worldwide standard.
We have studied the video packet loss due to excessive queueing delay in a single statistical multiplexer. The underlying video codec is assumed to separate its outputs into high-priority data and low-priority data so that the loss of low priority will cause a modest picture degradation. In conjunction with such hierarchical coding, the video multiplexer employs a control scheme that selectively discards low-priority data to alleviate the possibility of overload. The quality of the received pictures is measured by the expected underload period and the expected number of high-priority arrivals during an overload period. The former quantity measures the mean period that the received picture stays free of serious disturbance by packet loss due to excessive queueing delay, while the
latter is an indicator of the picture area affected. We have analyzed the performances of such a system under the given control scheme. Our analysis shows that the simple congestion control based on selective packet discarding can significantly prolong the underload period and reduce the number of high-priority losses in the overload period. To further reduce the number of high-priority arrivals in overload periods, we propose a control scheme that blocks all arrivals once they exceed the maximum delay. Moreover, the underload period can be dramatically prolonged by reducing the packetization buffer at the network input end. These results show that transporting video by the ATM technique is very promising.
We introduce a new class of linear-nonlinear combinational filters, called FIR stack hybrid (FSH) filters, which greatly enlarges the family of FIR median hybrid (FMH) filters. The optimal FSH filtering theory under the mean absolute error (MAE) criterion is studied. A general two-step method to synthesize optimal FSH filters is developed. In the first step, the probabilities needed in the optimal filter design are estimated based on images. In the second step, the linear program (LP) required to solve the best filter is avoided by using a good suboptimal algorithm that only needs data comparisons. A sufficient condition under which the suboptimal routine can result in optimal solutions is given, and this condition is shown to hold in most practical cases. To demonstrate the efficiency of the proposed approach, a group of FSH filters are synthesized for the standard image "Bridge." The task is to restore the image from impulsive or Gaussian noise. By checking the sufficient condition, each filter is found to be optimal in the minimum MAE sense. Testing results of some synthesized filters show that the optimal FSH filters can do a much better job than the corresponding FMH filters in both noise environments.
We propose algorithms for estimating the phase of a deterministic signal using its bispectrum. The bispectrum of a signal is the (discrete) Fourier transform of its triple correlation. While second-order statistics (e.g., correlation function, power spectrum, etc.) do not provide any information about the phase of the signal, third-order statistics (e.g., triple correlation, bispectrum, etc.) allow the recovery of the phase of the signal. We showthatthe applicability oftwo commonly used algorithms for phase estimation using the bispectrum is restricted to signals with simple phase characteristics. We propose algorithms for estimating the phase of arbitrary signals such as images, by taking into account the ambiguity due to the use of the principal value of the phase component. The resulting estimated phase is incorporated into a restoration filter. Image lines and images are used in our experiments to test the effectiveness of the proposed algorithms.
Blazed zone plates have been manufactured in germanium. A suitable surface relief pattern was first generated by recording in photoresist the circular fringes transmitted by a Fabry-Pérot interferometer. By scanning the fringe pattern and recording a series of exposures, we were able to generate a triangular groove profile. This was then transferred to the germanium substrate by ion-beam etching. By this means, diffraction efficiencies in excess of 80% have been achieved at 10μm for zone plates working in transmission and on axis.
We propose a real-time phase visualization technique using a phase conjugating mirror. An image of the phase derivative is formed in a coherent optical differentiation system and reflected by the phase conjugating mirror. After passage of the reflected light through the original phase object, its phase variation is compensated and its amplitude vanation only remains. This amplitude value is the derivative of the phase function and is fed to a second coherent optical integration system. An image inradiance of the output of this system is proportional to the square of the phase variation. This allows a neal-time quantitative visualization of actual object phase. There are no limitations to the phase objects in relation to the fine structures and large variations. Design of the setup for implementation of phase visualization is discussed. Computer simulations and experimental results are demonstrated.
An easily implemented and easily manageable system for timeresolved holographic interferometry is presented. The system consists of a multiple-pulsed Q-switched ruby laser and a rotating disk having radial slits with a constant angular separation. The disk is used to scan the reference beam along a holographic plate, thereby achieving spatial multiplexing. Since the influence on the beam is negligible and a single slit is illuminated by every laser pulse, there is no need for synchronization. The interferometric pattern is achieved by removing the disk and exposing a reference image on the holographic plate. The system may serve as an excellent tool for full-field dynamic measurements. A simple experiment has been performed showing a sequence of momentary interference patterns on a vibrating plate.
A design of a four-mirror optical system for submicron lithography using a KrF excimer laser beam (λ = 248 nm) is presented. By thirdorder aberration theory, analytic solutions for a telecentric, flat-field, anastigmatic four-spherical-mirror system (reduction magnification 5 x ) are found. Aspherization is carried out to the spherical mirror surfaces in order to reduce the residual higher order aberrations and vignetting effect. We obtain a reflection system useful in submicron lithographic application.