In this paper we propose a mathematical framework for multi-bit aperiodic clustered dot halftoning based on the Direct Multi-bit Search (DMS) algorithm. A pixel validation map is provided to the DMS algorithm to guide the formation of homogeneous clusters. The DMS algorithm operates without any user defined guidance, iteratively choosing the best drop absorptance level. An array of valid pixels is computed after each iteration that restricts the selection of pixels available to the DMS algorithm, improving the dot clustering. This process is repeated throughout the entire range of gray levels to create a visually pleasing multi-bit halftone screen. The resultant mask exhibits smoother appearance and improved detail rendering, compared to conventional clustered dot halftoning. Much of the improvements originate from the improved sampling of the aperiodic hybrid screen designs.
In many halftoning applications there is a need to generate a dispersed pattern of dots that is pleasing to the eye. We propose a method based on Riesz energy minimization that produces superior patterns than other techniques such as Direct Binary Search and k-means. We illustrate the proposed technique and discuss implementation issues including nonlinear programming techniques and memory-constrained implementations.
In this paper, we study the feasibility for using programmable Graphics Processing Unit (GPU) technology
for image halftoning, in particular implementing the computationally intense Direct Multi-bit Search (DMS)
Screen algorithm. Multi-bit screening is an extension of binary screening, in which every pixel in continuoustone
image can be rendered to one among multiple output states. For example, a 2 bit printer is capable
of printing with four different drop sizes. In our previous work, we have extended the Direct Binary Search
(DBS) to the multi-bit case using Direct Multi-bit Search (DMS) where at every pixel the algorithm chooses the
best drop output state to create a visually pleasing halftone pattern without any user defined guidance. This
process is repeated throughout the entire range of gray levels while satisfying the stacking constraint to create
a high quality multi-bit screen (dither mask). In this paper, we illustrate how employing Graphics Processing
Units (GPU) can speed-up intensive DMS image processing operations. Particularly, we illustrate how different
modules can be been parallelized. The main goal of many of the previous articles regarding DBS is to decrease
the execution time of the algorithm. One of the most common approaches is to decrease the neighborhood size
or filter size. The proposed parallel approach allows us to use a large neighborhood and filter size, to achieve
the highest halftone quality, while having minimal impact on performance. In addition, we also demonstrate
processing several non-overlapping neighborhoods in parallel, by utilizing the GPU's parallel architecture, to
further improve the computational efficiency.
In this paper, we describe adding constraints to the Direct Binary Search (DBS) algorithm. An example of
a useful constraint, illustrated in this paper, is having only one dot per column and row. DBS with such constraints requires greater than two toggles during each trial operation. Implementations of the DBS algorithm traditionally limit operations to either one toggle or swap during each trial. The example case in this paper produces a wrap-around pattern with uniformly distributed ON pixels which will have a pleasing appearance with precisely one ON pixel per each column and row. The algorithm starts with an initial continuous tone image and an initial pattern having only one ON pixel per column and row. The auto correlation function of Human Visual System (HVS) model is determined along with an initial perceived error. Multiple operation pixel error processing during each iteration is used to enforce the one ON pixel per column and row constraint. The constraint of a single ON pixel per column and row is used as an example in this paper. Further modification of the DBS algorithm for other constraints is possible, based on the details given in the paper. A mathematical framework to extend the algorithm to the more general case of Direct Multi-bit Search (DMS) is presented.
The ability of a sensor device is affected significantly by the surroundings and environment in which it is placed.
In almost all sensor modalities, some directions are better observed by a sensor than others. Furthermore, the
exact impact on the sensing ability of the device is dependent on the position assigned to the sensor. While
the problem of determining good coverage schemes for sensors of a field have many good solutions, not many
approaches are known to address the challenges arising due to location specific distortion. In this paper, we look
at the problem of incorporating terrain specific challenges in sensor coverage, and propose a geometric solution
to address them.
Recently, several watermarking schemes have been proposed that embed a watermark into two halftone images such that the watermark can be extracted by overlaying these halftone images. The watermark images in these schemes are binary images and the pixels in the two halftone images are correlated or not depending on whether the corresponding pixel in the watermark is on or off. In these schemes, the watermark is binary and does not contain detailed features. Furthermore, the extracted watermark contains residual patterns from the two images which reduces the fidelity of the extracted watermark image. This paper proposes a watermarking algorithm that addresses these problems. In addition, the proposed scheme admits more general watermark extraction functions and allows embedding of multiple watermark
A secure Internet infrastructure and IBM image watermarking technology have been integrated for the production and authentication of duplication-resistant hard copy documents that may be transmitted to remote sites before being printed. Envisioned applications include the issuance of certificates, contracts, public records, receipts, coupons, ...even college transcripts.
Recently, a number of authentication schemes have been proposed for multimedia data such as images and sound data. They include both label based systems and semifragile watermarks. The main requirement for such authentication systems is that minor modifications such as lossy compression which do not alter the content of the data preserve the authenticity of the data, whereas modifications which do modify the content render the data not authentic. These schemes can be classified into two main classes depending on the model of image authentication they are based on. One of the purposes of this paper is to look at some of the advantages and disadvantages of these image authentication schemes and their relationship with fundamental limitations of the underlying model of image authentication. In particular, we study feature-based algorithms which generate an authentication tag based on some inherent features in the image such as the location of edges. The main disadvantage of most proposed feature-based algorithms is that similar images generate similar features, and therefore it is possible for a forger to generate dissimilar images that have the same features. On the other hand, the class of hash-based algorithms utilizes a cryptographic hash function or a digital signature scheme to reduce the data and generate an authentication tag. It inherits the security of digital signatures to thwart forgery attacks. The main disadvantage of hash-based algorithms is that the image needs to be modified in order to be made authenticatable. The amount of modification is on the order of the noise the image can tolerate before it is rendered inauthentic. The other purpose of this paper is to propose a multimedia authentication scheme which combines some of the best features of both classes of algorithms. The proposed scheme utilizes cryptographic hash functions and digital signature schemes and the data does not need to be modified in order to be made authenticatable. Several applications including the authentication of images on CD-ROM and handwritten documents will be discussed.
The aim of this paper is to present a mathematical discussion of some aspects of digital printing, and other related problems such as analog/digital data conversion. In particular, we present results on the boundedness of the errors generated by error diffusion (and related) algorithms, and discuss the relationship between some of the mathematical questions arising in digital printing and some classical mathematical problems such as symbolic dynamics, the chairman assignment problem, and coding theory.
Decision making in the treatment of scoliosis is typically based on longitudinal studies that involve the imaging and visualization the progressive degeneration of a patient's spine over a period of years. Some patients will need surgery if their spinal deformation exceeds a certain degree of severity. Currently, surgeons rely on 2D measurements, obtained from x-rays, to quantify spinal deformation. Clearly working only with 2D measurements seriously limits the surgeon's ability to infer 3D spinal pathology. Standard CT scanning is not a practical solution for obtaining 3D spinal measurements of scoliotic patients. Because it would expose the patient to a prohibitively high dose of radiation. We have developed 2 new CT-based methods of 3D spinal visualization that produce 3D models of the spine by integrating a very small number of axial CT slices with data obtained from CT scout data. In the first method the scout data are converted to sinogram data, and then processed by a tomographic image reconstruction algorithm. In the second method, the vertebral boundaries are detected in the scout data, and these edges are then used as linear constraints to determine 2D convex hulls of the vertebrae.
We propose a watermarking scheme which allows the watermarked image to be authenticated by an authentication agent without revealing to the authentication agent the human-readable content of the image by combining privacy control with watermarking and authentication mechanisms. This watermarking scheme has universal applicability to data sets such as image, video and audio bit streams. The watermark can be made to be imperceptible to humans. Usage of public key cryptography allows the authentication agent to authenticate without the capabilities to watermark an image.