Showing papers on "Human visual system model published in 1999"

Perceptual watermarks for digital images and video

Abstract: The growth of new imaging technologies has created a need for techniques that can be used for copyright protection of digital images and video. One approach for copyright protection is to introduce an invisible signal, known as a digital watermark, into an image or video sequence. In this paper, we describe digital watermarking techniques, known as perceptually based watermarks, that are designed to exploit aspects of the the human visual system in order to provide a transparent (invisible), yet robust watermark. In the most general sense, any watermarking technique that attempts to incorporate an invisible mark into an image is perceptually based. However, in order to provide transparency and robustness to attack, two conflicting requirements from a signal processing perspective, more sophisticated use of perceptual information in the watermarking process is required. We describe watermarking techniques ranging from simple schemes which incorporate common-sense rules in using perceptual information in the watermarking process, to more elaborate schemes which adapt to local image characteristics based on more formal perceptual models. This review is not meant to be exhaustive; its aim is to provide the reader with an understanding of how the techniques have been evolving as the requirements and applications become better defined.

Fair benchmark for image watermarking systems

Abstract: Since the early 90s a number of papers on 'robust' digital watermarking systems have been presented but none of them uses the same robustness criteria. This is not practical at all for comparison and slows down progress in this area. To address this issue, we present an evaluation procedure of image watermarking systems. First we identify all necessary parameters for proper benchmarking and investigate how to quantitatively describe the image degradation introduced by the watermarking process. For this, we show the weaknesses of usual image quality measures in the context watermarking and propose a novel measure adapted to the human visual system. Then we show how to efficiently evaluate the watermark performance in such a way that fair comparisons between different methods are possible. The usefulness of three graphs: 'attack vs. visual-quality,' 'bit-error vs. visual quality,' and 'bit-error vs. attack' are investigated. In addition the receiver operating characteristic (ROC) graphs are reviewed and proposed to describe statistical detection behavior of watermarking methods. Finally we review a number of attacks that any system should survive to be really useful and propose a benchmark and a set of different suitable images.

Top-Down Attentional Guidance Based on Implicit Learning of Visual Covariation

Abstract: The visual environment is extremely rich and complex, producing information overload for the visual system. But the environment also embodies structure in the form of redundancies and regularities that may serve to reduce complexity. How do perceivers internalize this complex informational structure? We present new evidence of visual learning that illustrates how observers learn how objects and events covary in the visual world. This information serves to guide visual processes such as object recognition and search. Our first experiment demonstrates that search and object recognition are facilitated by learned associations (covariation) between novel visual shapes. Our second experiment shows that regularities in dynamic visual environments can also be learned to guide search behavior. In both experiments, learning occurred incidentally and the memory representations were implicit. These experiments show how top-down visual knowledge, acquired through implicit learning, constrains what to expect and guide...

Perceptual watermarks for digital images and video

Abstract: The growth of new imaging technologies has created a need for techniques that can be used for copyright protection of digital images. One approach for copyright protection is to introduce an invisible signal known as a digital watermark in the image. In this paper, we describe digital image watermarking techniques known as perceptually watermarks that are designed to exploit aspects of the human visual system in order to produce a transparent, yet robust watermark.

Motion streaks provide a spatial code for motion direction

Abstract: Although many neurons in the primary visual cortex (V1) of primates are direction selective, they provide ambiguous information about the direction of motion of a stimulus. There is evidence that one of the ways in which the visual system resolves this ambiguity is by computing, from the responses of V1 neurons, velocity components in two or more spatial orientations and then combining these velocity components. Here I consider another potential neural mechanism for determining motion direction. When a localized image feature moves fast enough, it should become smeared in space owing to temporal integration in the visual system, creating a spatial signal-a 'motion streak'-oriented in the direction of the motion. The orientation masking and adaptation experiments reported here show that these spatial signals for motion direction exist in the human visual system for feature speeds above about 1 feature width per 100 ms. Computer simulations show that this psychophysical finding is consistent with the known response properties of V1 neurons, and that these spatial signals, when appropriately processed, are sufficient to determine motion direction in natural images.

A perceptually based physical error metric for realistic image synthesis

Abstract: We introduce a new concept for accelerating realistic image synthesis algorithms. At the core of this procedure is a novel physical error metric that correctly predicts the perceptual threshold for detecting artifacts in scene features. Built into this metric is a computational model of the human visual system's loss of sensitivity at high background illumination levels, high spatial frequencies, and high contrast levels (visual masking). An important feature of our model is that it handles the luminance-dependent processing and spatiallydependent processing independently. This allows us to precompute the expensive spatially-dependent component, making our model extremely efficient. We illustrate the utility of our procedure with global illumination algorithms used for realistic image synthesis. The expense of global illumination computations is many orders of magnitude higher than the expense of direct illumination computations and can greatly benefit by applying our perceptually based technique. Results show our method preserves visual quality while achieving significant computational gains in areas of images with high frequency texture patterns, geometric details, and lighting variations.

Perceptual distortion metric for digital color video.

Abstract: In this paper I present a distortion metric for color video sequences. It is based on a contrast gain control model of the human visual system that incorporates spatial and temporal aspects of vision as well as color perception. The model achieves a close fit to contrast sensitivity and contrast masking data from several different psychophysical experiments for both luminance and color stimuli. The metric is used to assess the quality of MPEG-coded sequences.

A deblocking filter with two separate modes in block-based video coding

Abstract: This paper presents a method to remove blocking artifacts in low bit-rate block-based video coding. The proposed algorithm has two separate filtering modes, which are selected by pixel behavior around the block boundary. In each mode, proper one-dimensional filtering operations are performed across the block boundary along the horizontal and vertical directions, respectively. In the first mode, corresponding to flat regions, a strong filter is applied inside the block as well as on the block boundary because the flat regions are more sensitive to the human visual system (HVS) and the artifacts propagated from the previous frame due to motion compensation are distributed inside the block. In the second mode, corresponding to other regions, a sophisticated smoothing filter which is based on the frequency information around block boundaries, is used to reduce blocking artifacts adaptively without introducing undesired blur. Even though the proposed deblocking filter is quite simple, it improves both subjective and objective image quality for various image features.

Data hiding in images with adaptive numbers of least significant bits based on the human visual system

Abstract: We propose in this paper a novel method for embedding multimedia data (including audio, image, video, or text; compressed or non-compressed) into a host image. The classical LSB concept is adopted, but with the number of LSBs adapting to pixels of different graylevels. A piecewise mapping function according to human visual sensitivity of contrast is used so that adaptivity can be achieved without extra bits for overhead. The leading information for data decoding is few, no more than 3 bytes. Experiments show that a large amount of bit streams (nearly 30%-45% of the host image) can be embedded without sever degradation of the image quality (33-40 dB, depending on the volume of embedded bits).

Wavelet based watermarking method for digital images using the human visual system

Abstract: A wavelet based multiresolution watermarking method using the human visual system (HVS) is proposed, with the number of watermarks embedded proportional to the energy contained in each band. Experiments show that the proposed three-level wavelet based watermarking method is robust to some attacks such as, for example, joint photographic experts group (JPEG) compression, smoothing and cropping, collusion.

DWT-based technique for spatio-frequency masking of digital signatures

Abstract: The growth of the Internet and the diffusion of multimedia applications requires the development of techniques for embedding identification codes into images, in such a way that it can be granted their authenticity and/or protected the copyright. In this paper a novel system for image watermarking, which exploits the similarity exhibited by the Digital Wavelet Transform with respect to the models of the Human Visual System, for robustly hiding watermarks is presented. In particular, a model for estimating the sensitivity of the eye to noise, previously proposed for compression applications, is used to adapt the watermark strength to the local content of the image. Experimental results are shown supporting the validity of the approach.

Exploiting the cross-correlation of RGB-channels for robust watermarking of color images

Abstract: In the last few years, digital watermarking has been proposed as a solution to the problem of copyright protection of multimedia data against unauthorized uses. In the field of image watermarking, research has been mainly focused on grey-scale image watermarking, whereas the extension to the color case is usually accomplished by marking the image luminance, or by processing each color channel separately. In this paper, a DCT domain technique expressly devised for watermarking of color images is presented, which exploits the characteristics of the human visual system and the correlation between the RGB image channels. Experimental results are presented to demonstrate the validity of the new approach with respect to algorithms operating on image luminance only.

A software-only videocodec using pixelwise conditional differential replenishment and perceptual enhancements

Abstract: Designing a videocodec involves a four-way tradeoff among computational complexity, data rate, picture quality, and latency. Rapid advancement in very large-scale integration technology has provided CPUs with enough power to accommodate a software-only videocodec. Accordingly, computational complexity has resurfaced as a major element in this tradeoff. With a view toward significantly reducing computational complexity relative to standards-based videocodecs, we introduce a pixelwise conditional differential replenishment scheme to compress video via perception-sensitive decomposition of difference frames into a facsimile map and an intensity vector. Our schemes, which apply techniques from facsimile, are transform free. Some of them also involve no motion compensation and hence are completely free of block-based artifacts and particularly computationally economical. The fusion of our facsimile-based video-coding schemes and spatio-temporal perceptual-coding techniques facilitates powerful software-only video conferencing on today's medium- and highend personal computers. Indeed, assuming that a frame-capture driver has been provided, our motion-compensation-free approach has yielded a software-only, full-duplex, full-color videoconferencing system that conveys high-quality, CIF/Q-NTSC-sized video at 30 frames per second on 200-MHz Pentium PCs sending less than 300 Kbps in each direction. We also present new spatio-temporal compression techniques for perceptual coding of video. These techniques, motivated by the classical psychological experiments that led to formulation of the Weber-Fechner law, allow videocodec systems to capitalize on properties of the human visual system. Some of our spatiotemporal perceptual techniques not only apply to our proprietary pixelwise conditional differential replenishment schemes that we describe for video conferencing but also can readily be incorporated into today's popular video standards.

Specification and dialogue control of visual interaction through visual rewriting systems

Abstract: Computers are increasingly being seen not only as computing tools but more so as communication tools, thus placing special emphasis on human-computer interaction (HCI). In this article, the focus is on visual HCI, where the messages exchanged between human and computer are images appearing on the computer screen, as usual in current popular user interfaces. We formalize interactive sessions of a human-computer dialogue as a structured set of legal visual sentences, i.e., as a visual language, and show how rewriting systems can be generalized to specify both the pictorial and the computational aspects of visual languages. To this end, Visual Conditional Attributed Rewriting (VCARW) systems are introduced, and use for specification of visual languages. These specifications are given as inputs to a procedure illustrated in the article as a system of algorithms, which automatically generates control mechanisms of the interaction, thus favoring the design of more reliable and usable systems.

Data embedding in text for a copier system

Abstract: In this paper, we present a scheme for embedding data in copies (color or monochrome) of predominantly text pages that may also contain color images or graphics. Embedding data imperceptibly in documents or images is a key ingredient of watermarking and data hiding schemes. It is comparatively easy to hide a signal in natural images since the human visual system is less sensitive to signals embedded in noisy image regions containing high spatial frequencies. In other instances, e.g. simple graphics or monochrome text documents, additional constraints need to be satisfied to embed signals imperceptibly. Data may be embedded imperceptibly in printed text by altering some measurable property of a font such as position of a character or font size. This scheme however, is not very useful for embedding data in copies of text pages, as that would require accurate text segmentation and possibly optical character recognition, both of which would deteriorate the error rate performance of the data-embedding system considerably. Similarly, other schemes that alter pixels on text boundaries have poor performance due to boundary-detection uncertainties introduced by scanner noise, sampling and blurring. The scheme presented in this paper ameliorates the above problems by using a text-region based embedding approach. Since the bulk of documents reproduced today contain black on white text, this data-embedding scheme can form a print-level layer in applications such as copy tracking and annotation.

Designing JPEG quantization tables based on human visual system

Abstract: In this paper, a quantization table based on the human visual system is designed for the baseline JPEG coder By incorporating the human visual system with the uniform quantizer, a perceptual quantization table is derived The quantization table is easy to adapt to the specified resolution for viewing and printing Experimental results indicate that the HVS-based quantization table can achieve improvements in PSNR about 02-20 dB without increasing the complexity in both encoder and encoder

Balancing fusion, image depth and distortion in stereoscopic head-tracked displays

Abstract: Stereoscopic display is a fundamental part of virtual reality HMDsystems and HTD (head-tracked display) systems such as thevirtual workbench and the CAVE. A common practice instereoscopic systems is deliberate incorrect modeling of user eyeseparation. Underestimating eye separation is frequentlynecessary for the human visual system to fuse stereo image pairsinto single 3D images, while overestimating eye separationenhances image depth. Unfortunately, false eye separationmodeling also distorts the perceived 3D image in undesirableways. This paper makes three fundamental contributions tounderstanding and controlling this stereo distortion. (1) Weanalyze the distortion using a new analytic description. Thisanalysis shows that even with perfect head tracking, a user willperceive virtual objects to warp and shift as she moves her head.(2) We present a new technique for counteracting the shearingcomponent of the distortion. (3) We present improved methodsfor managing image fusion problems for distant objects and forenhancing the depth of flat scenes.CR Categories and Subject Descriptions: I.3.7 [ComputerGraphics] Three-Dimensional Graphics and Realism - VirtualReality; I.3.6 [Computer Graphics] Methodology and Techniques– Ergonomics; I.3.6 [Computer Graphics] Methodology andTechniques – Interaction Techniques; I.3.3 [Computer Graphics]Picture/Image Generation – Viewing AlgorithmsAdditional Keywords: virtual reality, stereoscopic display,head-tracking, image distortion

Development of an image/threshold database for designing and testing human vision models

Abstract: Models that predict human performance on narrow classesof visual stimuli abound in the vision science literature.However, the vision and the applied imaging communities need robust general-purpose, rather than narrow, computational human visual system (HVS) models to evaluate image fidelity and quality and ultimately improveimaging algorithms. Psychophysical measures of image quality are too costly and time consuming to gather to evaluate the impact each algorithm modification mighthave on image quality.Several general-purpose early HVS models currently existbut direct comparisons of the models on the same data setsare rarely made, making it difficult to evaluate their utility. Moreover, researchers designing a new model are confronted with the decision of what data set to use to set model parameters. To address these issues about 60 researchers interested in vision modeling have formed agroup tentatively called Modelfest. One of the group'sgoals is to develop a public database of test images withthreshold data from multiple laboratories for designingand testing HVS models. The data set will be available on

Interindividual Variation in Human Visual Performance

Abstract: The responses of 20 young adult emmetropes with normal color vision were measured on a battery of visual performance tasks. Using previously documented tests of known reliability, we evaluated orientation discrimination, contrast sensitivity, wavelength sensitivity, vernier acuity, direction-of-motion detection, velocity discrimination, and complex form identification. Performance varied markedly between individuals, both on a given test and when the scores from all tests were combined to give an overall indication of visual performance. Moreover, individual performances on tests of contrast sensi tivity, orientation discrimination, wavelength discrimination, and vernier acuity covaried, such that proficiency on one test predicted proficiency on the others. These results indicate a wide range of visual abilities among normal subjects and provide the basis for an overall index of visual proficiency that can be used to determine whether the surprisingly large and coordinated size differences of the components of the human visual system (Andrews, Halpern, & Purves, 1997) are reflected in corresponding variations in visual performance.

Perceived quality and bandwidth characterization of layered MPEG-2 video encoding*

Abstract: The current Internet is not well suited for the transmission of high quality video such as MPEG-2 because of severe quality degradation during network congestion episodes. One possible solution is the combination of layered video coding with the Differentiated Services (DiffServ) architecture; different video layers are mapped into different priority levels, and packets with different priorities receive a different dropping treatment in the network. It is expected that with layering and priority dropping, graceful degradation of video quality will be experienced during congestion episodes. We consider various layering mechanisms defined in the MPEG-2 standards; namely, temporal scalability, data partitioning (DP) and Signal to Noise Ratio (SNR) scalability. The main issue in this paper is how layers should be created to maximize perceived video quality over a given range of network conditions. Key to our study is the use of real life video sequences and a video quality measure consisting of a perceptual distortion metric based on the Human Visual System (VHS). Our results show that video quality is sensitive to how layering is accomplished, and that there is an optimum layering that maximizes the quality for a given network condition. Our results also show that layering can achieve higher network loading for a given minimum quality target than non-layered video, and can achieve graceful degradation over a wider range of network conditions. We have also seen that the wider the range of network conditions is, the higher is the number of layers required in order to remain at the highest possible quality level for each network condition. In particular, we demonstrate how three or four layers achieve better results than two layers; however, additional layers beyond four provide marginal improvement. Therefore, from a practical point of view, three or four layers are sufficient to attain most of the benefits of layering. We compare the various scalability techniques in terms of complexity and video quality. Temporal scalability, which restricts the layering to be done at frame boundaries, is the simplest to implement and introduces no overhead, but performs poorly compared to data partitioning, which allows the grouping of coefficients into layers independent of the frames they belong to. This shows that, contrary to customary belief, dropping data in B frames prior to dropping data in P or I frames is a poor layering technique. DP is much simpler to implement and introduces significantly lower overhead than SNR scalability. However, SNR scalability provides higher quality than DP when network conditions are particularly poor.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Can Audio Enhance Visual Perception and Performance in a Virtual Environment

Abstract: Does the addition of audio enhance visual perception and performance within a virtual environment? To address this issue we used both a questionnaire and an experimental test of the effect of audio on recall and recognition of visual objects within different rooms of a virtual environment. We tested 60 college-aged students who had normal visual acuity, color vision, and hearing. The between-participants factor was audio condition (none, low fidelity, and high fidelity). The questionnaire results showed that ambient sounds enhanced the sense of presence (or “being there”) and the subjective 3D quality of the visual display, but not the subjective dynamic interaction with the display. We also showed that audio can enhance recall and recognition of visual objects and their spatial locations within the virtual environment. These results have implications for the design and use of virtual environments, where audio sometimes can be used to compensate for the quality of the visual display.

Variable-Resolution Displays for Visual Communication and Simulation

Abstract: The spatial resolution of the human visual system decreases as a function of angular distance from the direction of gaze. This fact can be exploited in various applications to increase image compression, to increase image processing speed, and to decrease access time for image data. This paper describes a multiresolution pyramid method for creating variable resolution displays in real time using general purpose computers. The location of the high resolution region(s) can be dynamically controlled by the user with a pointing device (e.g., a mouse or an eye tracker) or by an algorithm. Our method has a number of advantages: high computational speed and efficiency, smooth artifact-free variable resolution, and compatibility with other image processing software/hardware. Applications to video communications (MPEG) and graphic simulation are described.

Quality assessment of motion rendition in video coding

Abstract: This paper addresses the issue of testing and quality assessment of motion rendition in digital video coding. Motion estimation and compensation are critical modules in video coders, as they are the most demanding resources and largely account for the visual quality of the resulting compressed stream. The testing of such modules is thus very important. A computational metric, based on a spatiotemporal model of the human visual system and of human motion sensing, is proposed and used to evaluate MPEG-2 compressed video. The metric is able to assess the quality of motion rendition and exhibits a good correlation with subjective data.

Visual cryptography and threshold schemes

Abstract: Visual cryptography is a secret sharing scheme that uses the human visual system to perform computations. In this article, we present some background to traditional secret-sharing schemes, then explain visual schemes, describing some of the basic construction techniques used. topics discussed include: two out of two scheme, two out of n schemes, and graph access structures.

Spectral sensitivities of the normal human visual system, color‐matching functions and their principles, and how and why the two sets should coincide

Abstract: The objectives of this article are (1) to help reestablish in technical thinking the three spectral sensitivity curves, dating from Helmholtz, of the normal human visual system (particularly their peak wavelengths); (2) to remind the reader of the principles of the sets of three color-matching functions (CMFs) comprising a CIE Standard Observer, and to make these principles more easily understandable; (3) to show how the visual data comprising today's Standard Observers lead directly to the peak wavelengths of the spectral sensitivity curves; (4) to use modern color-matching data to restore essential details to CMFs damaged by manipulation over the years; (5) to suggest that coincidence of corrected CMFs and the actual spectral sensitivities of the normal human visual system (a feature long tacitly assumed by color scientists of the past) is close at hand; and (7) to point out that CMFs embody a wealth of significance concerning the nature of the spectral response of the normal human visual system, despite the fact that they do not work well as weighting functions in the practice of colorimetry. The color-matching data of the CIE 1964 10° Standard Observer are used to reproduce the visual matches upon which it is based, and to model the principles of CMFs in general. The CIE 1964 data are treated as if they had been collected directly from modern-day visual matching experiments, in which an accurate, high-resolution, absolute spectral power distribution (SPD) of every viewed light is measured, and power content of each component of the light determined. The experimental units and dimensions of the resulting three CMFs are established. The significance of CMF plots above and below the zero-power level, and of the spectral shapes of the CMFs, is shown. The positions in wavelength of the nominal maximum of the red, green, and blue CMF, for a wide range of wavelengths of real spectral primaries, are noted (following MacAdam) to be “amazingly similar.” Then the much-manipulated data of the CIE Standard Observers are left behind, and modern raw unmanipulated visual data are analyzed in the same manner. The results yield characteristics of CMFs that are more representative of the normal human visual system than are those of the CIE Standard Observers. The peak heights of the nominal maxima of the red, green, and blue CMF, for the same wide range of primaries, are importantly significant also. They serve to define, at least approximately, the forms of the three spectral sensitivities, assuming the traditional model of the visual system. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 139–156, 1999