Dither Matrix Research Articles

A digital driving method using pulse‐density modulation with a random dither matrix for higher motion image quality

AbstractWe propose a new digital driving technique using pulse‐density modulation (PDM) with a random dither matrix for evenness of luminance uniformity and higher motion image quality. As a digital driving technique, pulse‐width modulation (PWM) is conventionally used for active‐matrix organic light‐emitting diode (AMOLED) displays in order to improve luminance uniformity. However, in PWM driving, it is difficult to realize high‐frame‐rate driving for improving motion image quality. On the other hand, it is considered that PDM driving method is effective to obtain high motion image quality because of non‐frame‐refreshing property. In the present paper, we proposed a PDM driving technique using a random dither matrix and evaluated the relationship between the display image quality and the driving frequency in the proposed method through simulations. As a result, it is confirmed that good image quality can be obtained by using a blue‐noise mask as a random dither matrix at a practical driving frequency. Moreover, we demonstrated the proposed technique using an actual AMOLED panel.

Dither matrix estimation based on pixel histograms of halftones

A dithering halftone is typically binary and generated by comparing the continuous-tone levels with periodic thresholds, which are two-dimensional repetition of a basic threshold matrix called the dither matrix. In many applications it is required to estimate the thresholds (that is, the period and the dither matrix) for a halftone. The period can be estimated conventionally by examining the autocorrelation functions or Fourier spectra. This paper focuses on the estimation of the dither matrix. In this paper, we regard the dithering at every site as a testing of getting a black halftone pixel and then estimate the dither matrix based on the pixel histograms of the halftone. Such a pixel-histogram based approach (PHA) is in contrast to the conventional full-dot-pattern based approach (FDPA), which is based on block histograms. The use of pixel histograms provides better efficiency: the usage of more information (on the whole rather than partial image data), the stronger resistance to the damage caused by the size increasing of dither, and the simpler computation. The experimental results show that compared with the FDPA, our PHA has higher percentages of successful estimates, is less damaged by the increase of dither size, and is computationally simpler.

PERANCANGAN APLIKASI PENYISIPAN CITRA BERWARNA PADA QR CODE DENGAN METODE HALFTONE

The project is made in the form of a software application that accepts input color image to be processed into Halftone QR-Code. Halftone QR-Code is a composite image of the QR-Code and halftone image that can be recognized by QR-Code Scanner. QR-Code image generated using the Library Massagingtoolkit-QRCode with alphanumeric text input degan various versions QR-Code in accordance with a lot of character input. The input image is processed into a halftone image with methods Ordered Dithering variation dither matrix 4 x 4 and 8 x 8. The image of the QR-Code and halftone images will be processed into QR-Code Halftone Pattern Assignment method. Output generated by the application Halftone QR-Code tested with QR-Code ZXing Library and QRAFTER application on Iphone 6s Plus and QR. The average rate of overall success with the test scenario ZXing QR-Code Library by 94%. The average rate of overall success with the test scenario QRAFTER application on Iphone 6s Plus from the laptop screen and hardcopy respectively by 100%.

Hybrid Approach for PRNGs using BBS and Dithering Technique

Objectives: The cryptographically secure pseudo-random number generator Blum Blum-Shub (BBS) is a simple algorithm with a strong security proof, all of number generators that produced by BBS will be converted to (0, 1) using simplest form called Parity (even parity bit and odd parity bit).This approach proposed new method for extending bit space acquired from BBS based on dither matrix instead of (Parity) feature with saving of strength and security of crypto-key. Methods/Statistical Analysis: We used dithering techniques (2*2, 4*44) that provide continuous image of higher colors on a display of less color depth, for improving numbers that generated by BBS. And used some of statistical tests for measuring crypto-key strength such (run, poker, serial and frequency tests).The proposal algorithm has been programmed using c#.net 2013 Findings: This approach provides high extended on number space that generated from BBS by using Dithering techniques (2*2, 4*4), with saving of crypto-key randomness and guarantee passing of statistical tests, dithering techniques (8*8) is unsuitable for this purpose. Although, it provides height extension but decrease the randomness of key numbers. Application/Improvements: This approach proposed to replace (Parity) property with dithering techniques. It’s replaces max of gray level in dithering such (256) in 8 bit image with value of n , (p*q) in BBS , this may convert the domain of any number sets to dithering domain to be suitable for purpose. Keywords: Blum-Blum-Shub, Cryptography, Cryptography Key, Dithering, Pseudo Random Number generation (PRNGs)

Forced Random Sampling: fast generation of importance-guided blue-noise samples

In computer graphics, stochastic sampling is frequently used to efficiently approximate complex functions and integrals. The error of approximation can be reduced by distributing samples according to an importance function, but cannot be eliminated completely. To avoid visible artifacts, sample distributions are sought to be random, but spatially uniform, which is called blue-noise sampling. The generation of unbiased, importance-guided blue-noise samples is expensive and not feasible for real-time applications. Sampling algorithms for these applications focus on runtime performance at the cost of having weak blue-noise properties. Blue-noise distributions have also been proposed for digital halftoning in the form of precomputed dither matrices. Ordered dithering with such matrices allows to distribute dots with blue-noise properties according to a grayscale image. By the nature of ordered dithering, this process can be parallelized easily. We introduce a novel sampling method called forced random sampling that is based on forced random dithering, a variant of ordered dithering with blue noise. By shifting the main computational effort into the generation of a precomputed dither matrix, our sampling method runs efficiently on GPUs and allows real-time importance sampling with blue noise for a finite number of samples. We demonstrate the quality of our method in two different rendering applications.

Revealing information by averaging.

We present a method for hiding images in synthetic videos and reveal them by temporal averaging. The main challenge is to develop a visual masking method that hides the input image both spatially and temporally. Our masking approach consists of temporal and spatial pixel by pixel variations of the frequency band coefficients representing the image to be hidden. These variations ensure that the target image remains invisible both in the spatial and the temporal domains. In addition, by applying a temporal masking function derived from a dither matrix, we allow the video to carry a visible message that is different from the hidden image. The image hidden in the video can be revealed by software averaging, or with a camera, by long-exposure photography. The presented work may find applications in the secure transmission of digital information.

Optimal parameters based stochastic dot model for tone compensation of dither matrix

The image outputs of a laser printer are accompanied with nonlinear phenomena such as dot gains and losses. As a result, a laser printer model is necessary to suppress such nonlinear distortions. This paper proposes the optimal parameters based stochastic dot model (OPSDM) and applies it to the tone compensation of dither matrices. In the proposed model, Munsell value is taken as intermediate value and a conversion method for the printouts is established at first. Then, no printer model of printout result is measured, and recurrent parameters of model are modified to obtain the optimal parameters of the stochastic dot model of printer by calculating the minimum Munsell value error between the measure result and simulated result of model. Finally, the dither matrix thresholds are modified to make the simulated result of every gray level with dither matrix close to the given level. The results of experimental indicate that the modified dither matrix with proposed model can significantly restrain the influence of the nonlinear characteristics of printer.

Tone compensation of amplitude modulation matrix via minimal Munsell value error based laser printer model

A laser printer model is required to help suppress non-linear distortions associated with laser printer outputs. A minimal Munsell value error based printer model is proposed and applied to compensate for the tone of the amplitude modulation (AM) matrix. A conversion method for printouts is established with Munsell values as intermediate values. Then, through recurrent parameter modifications and simulations, the optimal parameters of the stochastic dot model of the printer are obtained by calculating the minimum Munsell value error. Finally, the dither matrix is converted to a binary pattern with a given grey level, and the AM matrix thresholds are modified to make the simulated grey level of the binary pattern close to the given grey level. An experimental assessment of the proposed method, in which the difference between the corresponding Munsell values of printouts and ideal values is analysed, indicates that the method can significantly restrain the influence of non-linear characteristics of printers.

Embedding of computer-generated hologram in a dithered image

We have developed an encryption method using a computer-generated hologram (CGH) embedded in a dithered image. First, confidential information is converted into a CGH. Next, the CGH data undergo two separate dithering processes in parallel: one corresponding to CGH white pixels and one corresponding to CGH black pixels. The results from both processes are used to form a dither matrix for creating the final dithered and encoded image. In this way, confidential information can be embedded into the image. The confidential information can be extracted using a technique similar to CGH optical reconstruction.

An Improved Hierarchical Segmentation Method for Remote Sensing Images

This paper presents an inversed quad tree merging method for hierarchical high-resolution remote sensing image segmentation, in which bottom-up approaches of region based merge techniques are chained. The image segmentation process is mainly composed of three sections: grouping pixels to form image object/region primitives in imagery using inversed quad tree, initializing neighbor list and region feature variables and then hierarchical clustering neighboring regions. This segmentation algorithm has been tested on the QuickBird images and been evaluated and it exhibits good efficiency over initialization of neighbor list for quad tree node/region primitives. This paper also provides a brief proof of the good efficiency of a sorted merge list which can be viewed as an alternative for dither matrix to randomly distribute region merging pairs which is adopted in e-Cognition.

Hierarchical graph color dither

Suppose a dispersed-dot dither matrix is treated as a collection of numbers, each number having a position in space; when the numbers are visited in increasing order, what is the distance in space between pairs of consecutive numbers visited? In Bayer’s matrices, this distance is always large. We hypothesize that this large consecutive distance is important for good dispersed-dot threshold matrices. To study the hypothesis, matrices that have this quality were generated by solving a more general problem: given an arbitrary set of points on the plane, sort them into a list where consecutive points are far apart. Our solution colors the nearestneighbor graph, hierarchically. The method does reproduce Bayer’s dispersed-dot dither matrices under some settings and, furthermore, can produce matrices of arbitrary dimensions. Multiple similar matrices can be created to minimize repetitive artifacts that plague Bayer dither while retaining its parallelizability. The method can also be used for halftoning with points on a hexagonal grid, or even randomly placed points. It can also be applied to artistic dithering, which creates a dither matrix from a motif image. Unlike in the artistic dither method of Ostromoukhov and Hersch, the motif image can be arbitrary and need not be specially constructed.

P‐126: Advanced Image‐Processing Method for Hybrid Color LCDs

AbstractThe hybrid color LCD (HC‐LCD) mode, which we have proposed in the previous papers, can display the RGB three primary colors using only two kinds of sub‐pixels of green (G) and magenta (M). We have also proposed the spatial dither method customized for the HC‐LCD, which utilizes plural pixels and their color mixing of both binary red (or blue) color and magenta color with analog grayscale. However, this dither method substantially degrades the display resolution in displaying the intermediate colors according to the size of the dither matrix. This paper shows the advanced image‐processing method using two pixels and their continuous hue changes in the magenta sub‐pixel, that we have not fully utilized so far. The degradation of the display resolution can be reduced by this method and image quality can be dramatically improved especially in the photograph of human face or skin.

Training-Based Descreening

Conventional halftoning methods employed in electrophotographic printers tend to produce Moiré artifacts when used for printing images scanned from printed material, such as books and magazines. We present a novel approach for descreening color scanned documents aimed at providing an efficient solution to the Moiré problem in practical imaging devices, including copiers and multifunction printers. The algorithm works by combining two nonlinear image-processing techniques, resolution synthesis-based denoising (RSD), and modified smallest univalue segment assimilating nucleus (SUSAN) filtering. The RSD predictor is based on a stochastic image model whose parameters are optimized beforehand in a separate training procedure. Using the optimized parameters, RSD classifies the local window around the current pixel in the scanned image and applies filters optimized for the selected classes. The output of the RSD predictor is treated as a first-order estimate to the descreened image. The modified SUSAN filter uses the output of RSD for performing an edge-preserving smoothing on the raw scanned data and produces the final output of the descreening algorithm. Our method does not require any knowledge of the screening method, such as the screen frequency or dither matrix coefficients, that produced the printed original. The proposed scheme not only suppresses the Moiré artifacts, but, in addition, can be trained with intrinsic sharpening for deblurring scanned documents. Finally, once optimized for a periodic clustered-dot halftoning method, the same algorithm can be used to inverse halftone scanned images containing stochastic error diffusion halftone noise.

ディザ画像への計算機ホログラムの埋込み

We have developed a method of encryption using computer-generated holograms (CGH) embedded in dithered image. First, the confidential information is converted into a CGH. Next, the CGH data undergoes two separate dithering processes in parallel: one corresponding to CGH white pixels and one corresponding to CGH black pixels. The results from both processes are used to form a dither matrix for creationg th final ditherd and encoded image. In this way, the confidential information can be embedded into the image. The confidentioal information can be extracted using a technique similar to CGH optical reconstruction.

Table Look-Up Method of Inverse Halftoning for Ordered Dither Images by Utilizing Flat Area Detection and Dither Matrix Addresses

Table Look-Up Method of Inverse Halftoning for Ordered Dither Images by Utilizing Flat Area Detection and Dither Matrix Addresses

Comprehensive Halftoning of 3D Scenes

The display of images on binary output hardware requires a halftoning step. Conventional halftoning algorithms approximate image values independently from the image content and often introduce artificial texture that obscures fine details. The objective of this research is to adapt a halftoning technique to 3D scene information and thus to enhance the display of computer generated 3D scenes. Our approach is based on the control of halftoning texture by the combination of ordered dithering and error diffusion techniques. We extend our previous work and enable a user to specify the shape, scale, direction, and contrast of the halftoning texture using an external buffer. We control texture shape by constructing a dither matrix from an arbitrary image or a procedural texture. Texture direction and scale are adapted to the external information by the mapping function. Texture contrast and the accuracy of tone reproduction are varied across the image using the error diffusion process. We halftone images of 3D scenes by using the geometry, position, and illumination information to control the halftoning texture. Thus, the texture provides visual cues and can be used to enhance the viewer's comprehension of the display.

Dot Allocations in Dither Matrix with Wide Color Gamut

The color gamut in bi-level digital printers depends on the allocation of the CMY primary ink dots placed in dithering matrices. The typical color mixture model is based on Neugebauer theory, where CMY dots are placed at random, but recent digital printers don't obey that theory. The simplest method used in digital printers is “coaxial” allocation, where the CMY ink dots are placed in the same positions in each color dither matrix. The coaxial model produces sharp edges, but may generate too many secondary colors with unsaturated chromaticities. A mixture of C and M inks may produce a more brilliant bluish color when the C and M dots are placed side-by-side to avoid overlapping. In this article, “min-med”, “min-max” and “min” models with side-byside dot allocation are discussed. These are designed to suppress the occurrence of secondary colors. The corresponding color gamuts are analyzed and compared.

Dot Allocations in Dither Matrix with Wide Color Gamut

Dot Allocations in Dither Matrix with Wide Color Gamut

A new bi-level quantizing method for document images

An adaptive bilevel quantizing technique for images containing text and continuous-tone areas in the same page is proposed. At first, the original document image is divided into M*M pixel blocks and whether a block is a continuous-tone area or not is determined by using two features, the density of black pixels in the block and the differential value to neighbors. Then, continuous-tone areas are made binary by using the multistep dither matrix. Finally, the remaining area, which includes text and figures, is quantized to bilevel.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Embedding the attribute information into a dithered image

AbstractAttribute information is indispensable data in the collection and storage of a large amount of image information. If these data are stored together with the image, handling of the materials would become simpler and more reliable. This paper proposes a method to embed the attribute information into a dither image by using the difference of the threshold values of the dither matrix when a multilevel image is binarized. This method can embed the attribute information of about 2 kbytes (equivalent to about 25 percent of the data for the image) into a dithered image of 256 × 256 pixels. The embedded information can be displayed or printed separately at any time. This method can restore the dither image almost perfectly by using the property of the ordered dither method.