Dithering Method Research Articles

Dual-mode adaptive-SVD ghost imaging.

In this paper, we present a dual-mode adaptive singular value decomposition ghost imaging (A-SVD GI), which can be easily switched between the modes of imaging and edge detection. It can adaptively localize the foreground pixels via a threshold selection method. Then only the foreground region is illuminated by the singular value decomposition (SVD) - based patterns, consequently retrieving high-quality images with fewer sampling ratios. By changing the selecting range of foreground pixels, the A-SVD GI can be switched to the mode of edge detection to directly reveal the edge of objects, without needing the original image. We investigate the performance of these two modes through both numerical simulations and experiments. We also develop a single-round scheme to halve measurement numbers in experiments, instead of separately illuminating positive and negative patterns in traditional methods. The binarized SVD patterns, generated by the spatial dithering method, are modulated by a digital micromirror device (DMD) to speed up the data acquisition. This dual-mode A-SVD GI can be applied in various applications, such as remote sensing or target recognition, and could be further extended for multi-modality functional imaging/detection.

Optimized dithering approach for 3D shape measurement using a phase-based chaos genetic algorithm.

A binary defocusing method has a significant impact on improving 3D shape measurement quality for digital fringe projector (DFP) techniques. In this paper, an optimization framework using the dithering method is presented. This framework utilizes genetic algorithm and chaos maps to optimize the bidirectional error-diffusion coefficients. It can effectively avoid quantization errors of binary patterns in a specific direction and obtain the fringe patterns with better symmetry and higher quality. In the process of the optimization, chaos initialization algorithms are used to generate a series of bidirectional error-diffusion coefficients as initial individuals. Additionally, mutation factors generated by chaotic maps, compared with the mutation rate, determine whether the individual position will mutate. Both simulations and experiments demonstrate that the proposed algorithm can improve the quality of phase and reconstruction at different defocus levels.

High-quality 3D shape measurement by kernel-optimized high sinusoidal similarity dither patterns

The error-diffusion dithering technique is widely used in three-dimensional (3D) measurement. The sinusoid similarity of dithering fringe patterns greatly affects measurement accuracy, while the traditional dithering methods lack this quality. In this paper, we present a kernel-optimized dithering technique based on the Floyd-Steinberg dithering method and establish an optimization strategy considering both intensity and phase aspects to generate high-quality sinusoidal fringes for 3D measurement by utilizing the binary defocusing technique. Both simulations and experiments demonstrate that the proposed method could improve the performance of 3D measurement effectively under different defocusing amounts, especially in narrow strips.

Telescopes Alignment Using the Sharpness Function Method Based on Undersampled Images

In astronomy, the images are sometimes undersampled. In the previous research works, image reconstructions have to be employed to recover the lost information from a set of undersampled images to achieve a high-resolution image using dithering or drizzle methods, which increase the complexity of alignment processes and make the real-time correction impossible. In this paper, the telescope is aligned by changing the positions of the secondary mirror using sharpness function method combined with the stochastic parallel gradient descent algorithm based on both well-sampled and undersampled images without image reconstructions. To improve the accuracy and robustness of the alignment, a new metric called relative root mean square error is proposed. Both numerical simulations and experiments are implemented, and the alignment precisions are measured by wavefront residual errors using Shack-Hartmann wavefront sensors. The results show that the correction processes can converge stably and quickly whether the images are well-sampled or undersampled. In experiments, the average wavefront error is 0.0595 λ for undersampled images and 0.0548 λ for well-sampled images after the telescope alignment, indicating that the misalignments are well compensated for both well-sampled and undersampled images.

A Low-cost Dithering Method for Improving ADC Linearity Test Applied in uSMILE Algorithm

Analog-to-digital converters (ADCs) are an important component in electronics design. One of the difficulties being faced is to be able to accurately and cost-effectively test the continually higher performance of ADCs under budget constraints. Test time for static linearity is a major portion of the total test cost. Our group proposed an ultrafast segmented model identification of linearity error (uSMILE) algorithm for estimating linearity, which reduces test time dramatically compared to the conventional method. However, this algorithm produces large estimation errors in low resolution ADCs (10-12 bits) when the input is a ramp signal, for which the quantization noise of ADC becomes a dominant part in the total noise. In this study, we propose three types of distribution dithering methods added to the ramp input signal to reduce the estimation error when uSMILE was applied to low resolution ADCs. Fixed pattern was proved to be the most efficient and cost-effective method by comparing with the Gaussian, uniform, and fixed-pattern distributions. The simulation results indicate that the estimation error can be significantly reduced in a 12-bit SAR ADC with effective dithering. Furthermore, a hardware evaluation board with commercial ADC products was used to validate the effectiveness of the fixed-pattern dithering methods, and our measurement shows the INL estimation error can be reduced to less than 0.1 LSB. Such dithering method relaxes the input requirement of uSMILE algorithm which dramatically reduces the test setup cost.

カラー画像に対する組織的ディザ法における閾値移動処理の研究 : 無線技術 : 画像処理・画像応用

カラー画像に対する組織的ディザ法における閾値移動処理の研究 : 無線技術 : 画像処理・画像応用

Dithering method for reproducing smoothly changing tones and fine details of natural images on woven fabric

This paper introduces novel methods to improve the aesthetic appearance of rendered grayscale digital images on woven fabric by smoothly changing tones and improving the reproducibility of fine details. The methods are based on stepping dithering, a recently developed dithering method for automatically generating jacquard weave patterns for arbitrary given images. The existing stepping dithering method suffers from two problems. The first problem is the visually unappealing repetition of patterns for input images containing low frequency, smooth gradation regions. The second problem is the low reproducibility of small structures with high frequency relative to mask size. This paper proposes new methods for faithfully rendering arbitrary natural images on jacquard fabric by solving the pattern repetition and low reproducibility problems. The new methods combine two approaches. The first problem is addressed by optimizing the distribution of thresholds in dither masks, while the second problem is addressed by adopting a dynamic binarizing process for an appropriate area of the stepping dither mask. The experiments described herein show that the proposed method successfully improves the appearance of the resulting woven fabric.

74‐3: Development of New Error‐Diffusion Dithering Method for Reflective Memory‐In‐Pixel (MIP) LCD

We have developed an error‐diffusion dithering method for a reflective MIP LCD to provide a high‐quality moving image. We have restricted error diffusing area within several segments defined on the image without deterioration of the image quality, and successfully resolved the fluttering problem in moving image.

Dithering techniques in automatic recognition of speech corrupted by MP3 compression: Analysis, solutions and experiments

A large portion of the audio files distributed over the Internet or those stored in personal and corporate media archives are in a compressed form. There exist several compression techniques and algorithms but it is the MPEG Layer-3 (known as MP3) that has achieved a really wide popularity in general audio coding, and in speech, too. However, the algorithm is lossy in nature and introduces distortion into spectral and temporal characteristics of a signal. In this paper we study its impact on automatic speech recognition (ASR). We show that with decreasing MP3 bitrates the major source of ASR performance degradation is deep spectral valleys (i.e. bins with almost zero energy) caused by the masking effect of the MP3 algorithm. We demonstrate that these unnatural gaps in spectrum can be effectively compensated by adding a certain amount of noise to the distorted signal. We provide theoretical background for this approach where we show that the added noise affects mainly the spectral valleys. They are filled by the noise while the spectral bins with speech remain almost unchanged. This helps to restore a more natural shape of log spectrum and cepstrum, and consequently has a positive impact on ASR performance. In our previous work, we have proposed two types of the signal dithering (noise addition) technique, one applied globally, the other in a more selective way. In this paper, we offer a more detailed insight into their performance. We provide results from many experiments where we test them in various scenarios, using a large vocabulary continuous speech recognition (LVCSR) system, acoustic models based on gaussian-mixture model (GMM) as well as on deep-neural network (DNN), and multiple speech databases in three languages (Czech, English and German). Our results prove that both the proposed techniques, and the selective dithering method, in particular, yield consistent compensation of the negative impact of the MP3 compressed speech on ASR performance.

Dithered Quantization via Orthogonal Transformations

Dithered quantization is a technique used to reduce or eliminate the statistical dependence between the signal and quantization error. This is most often achieved via adding pseudo-random noise prior to quantization. The present work develops a different dithering method, where dithering is accomplished by applying an orthogonal transformation to a vector of samples prior to quantization, and applying its inverse to the output of the quantizer. Focusing on uniform scalar quantization, it is shown that for any quantization rate, the proposed architecture approaches second-order independence, i.e., asymptotically vanishing correlation, as the dimension of the vector of samples processed jointly grows.

An Improved Size Invariant (n, n) Extended Visual Cryptography Scheme

In this paper, the authors have presented a (n, n) extended visual cryptography scheme where n numbers of meaningful shares furnish a visually secret message. Initially they have converted a grayscale image into binary image using dithering method. Afterwards, they have incorporated pixel's eight neighboring connectivity property of secret image during formation of meaningful shares. The scheme is able to generate the shares without extending its size. This approach has enhanced the visual quality of the recovered secret image from n numbers of shares. The scheme has been tested with some images and satisfactory results are achieved. The scheme has improved the contrast of the recovered secret image than a related (n, n) extended visual cryptography scheme.

Cross-correlation frequency-resolved optical gating of white-light continuum (500–900 nm) generated in bulk media by 1053 nm laser pulses

We have efficiently characterized the white-light continuum (WLC) generation covering 500–900 nm in a bulk sapphire plate using 280 fs pulse duration, 1053 nm center-wavelength seed laser pulses. We have acquired the well-optimized smoother region of the WLC spectrum successfully by using an FGS-900 color glass filter (Edmund Optics, Inc.). We have suppressed the spectral components below 500 nm and over 900 nm including an intense 1053 nm residual seed laser peak of the WLC spectrum. The experimental artifacts have been avoided by suppressing the intense 1053 nm seed laser. We employed the sum frequency generation cross-correlation frequency-resolved optical gating (SFG-XFROG) technique for characterization. The XFROG measurement was carried out by introducing the crystal dithering method up to 10° in 2° intervals to obtain the phase matching effectively over the filtered and smoother region of the WLC spectrum. This well-optimized WLC region covering 500–900 nm has significant importance for use as a seed pulse in an optical parametric chirped pulse amplification (OPCPA) system.

Active phase locking of thirty fiber channels using multilevel phase dithering method.

An active phase locking of a large-scale fiber array with thirty channels has been demonstrated experimentally. In the experiment, the first group of thirty phase controllers is used to compensate the phase noises between the elements and the second group of thirty phase modulators is used to impose additional phase disturbances to mimic the phase noises in the high power fiber amplifiers. A multi-level phase dithering algorithm using dual-level rectangular-wave phase modulation and time division multiplexing can achieve the same phase control as single/multi-frequency dithering technique, but without coherent demodulation circuit. The phase locking efficiency of 30 fiber channels is achieved about 98.68%, 97.82%, and 96.50% with no additional phase distortion, modulated phase distortion I (±1 rad), and phase distortion II (±2 rad), corresponding to the phase error of λ/54, λ/43, and λ/34 rms. The contrast of the coherent combined beam profile is about 89%. Experimental results reveal that the multi-level phase dithering technique has great potential in scaling to a large number of laser beams.

A 4.2 mW 50 MS/s 13 bit CMOS SAR ADC With SNR and SFDR Enhancement Techniques

This paper presents a SAR ADC with 71 dB SNDR and 85 dB SFDR at 50 MS/s while keeping low power consumption of 4.2 mW. To achieve high resolution without large increase of power, several SNR and SFDR enhancement techniques are proposed. Firstly, the ADC repeats comparison of LSB by using redundant DAC to average comparator noise and improve SNR. The technique also corrects settling error adaptively, which extends operation speed to 50 MHz even though extra comparison period is added for averaging. Secondly, simple filtering method for reducing DAC noise is introduced to achieve further improvement of SNR. Finally, new dithering method is proposed to enhance SFDR. Injecting noise-shaped, multi-valued and uniform-distributed dither to input of the ADC, spurs caused by capacitance mismatches of DAC can be suppressed more effectively compared with conventional dithering. These techniques can be realized by simple circuits in addition to a basic SAR ADC configuration and do not need high power consumption. The chip is fabricated in a 90 nm CMOS process and occupies 0.1 mm 2 including all correction logic. The ADC achieved a peak figure of merit (FoM) of 168.7 dB.

Interactive Material Design Using Model Reduction

We demonstrate an interactive method to create heterogeneous continuous deformable materials on complex three-dimensional meshes. The user specifies displacements and internal elastic forces at a chosen set of mesh vertices. Our system then rapidly solves an optimization problem to compute a corresponding heterogeneous spatial distribution of material properties using the Finite Element Method (FEM) analysis. We apply our method to linear and nonlinear isotropic deformable materials. We demonstrate that solving the problem interactively in the full-dimensional space of individual tetrahedron material values is not practical. Instead, we propose a new model reduction method that projects the material space to a low-dimensional space of material modes. Our model reduction accelerates optimization by two orders of magnitude and makes the convergence much more robust, making it possible to interactively design material distributions on complex meshes. We apply our method to precise control of contact forces and control of pressure over large contact areas between rigid and deformable objects for ergonomics. Our tetrahedron-based dithering method can efficiently convert continuous material distributions into discrete ones and we demonstrate its precision via FEM simulation. We physically display our distributions using haptics, as well as demonstrate how haptics can aid in the material design. The produced heterogeneous material distributions can also be used in computer animation applications.

2076630 An Enhanced Ultrasound Technique For Functional Evaluation Of Spermatogenesis

The only quantitative method used today to assess testicular function is Johnsen scoring of testicular histopathology. We propose that the heterogeneity found in testicular ultrasound images correlates with testicular function. To evaluate this heterogeneity we employ a noninvasive process that uses a dithering technique in which the pixels of an ultrasound image are transformed into a binary map. We then apply an algorithm to this binary map to determine Dynamic Range (DR) values. These DR quantities are used to assess levels of heterogeneity in gray scale ultrasound images. The purpose of this paper is to evaluate the correlation of DR with testicular histopathology. A retrospective review of all men who underwent testicular biopsy at our institution as part of a fertility evaluation was performed. All patients had ultrasound images taken preoperatively. The average DR for a single testis was obtained by performing the dithering method on five different ultrasound images and then averaged. The histologic specimens were reviewed by a single pathologist using a modified Johnsen criteria (0 to 10, >7 normal and ≤7 impaired spermatogenesis) to assess for the degree of impaired spermatogenesis. Pearson correlation, linear regression and Student’s t-test were obtained. Testicular biopsies were performed on a total of 32 patients. Complete data was available for 55 testes. A statistically significant negative correlation was found between DR and Johnsen scores (R2=0.29, Pearson r=-0.52, p<0.01). Johnsen scores ≤7 are associated with a mean DR=3.51. Whereas Johnsen scores ≥8 were associated with a mean DR=2.51. Intratesticular DR correlates with impaired spermatogenesis on testis biopsy. Evaluation of testicular ultrasound images through use of a dithering technique provides functional information. Potential exists for this non-invasive technique for real time assessment of testicular function.

1113 ディザ近似手法を用いた色の組み合わせを制限しないカラーユニバーサルデザイン : 可変ディザ近似および最適ディザサイズ導出手法(OS9-1 ヒューマンインタフェース・ユーザビリティ1)

The previous dithering method for color universal design, lightness contrast dithering approximation, has problems that it changes all of the background of pictures and it is difficult for color vision handicapped person to perceive the detail drawing patterns of pictures in a particular dither size. Therefore in this study, methods of variable dithering and optimal size derivation are proposed. The hypotheses are that using variable dithering method, which decreases the lightness contrast as the distance from the edge of drawing patterns increases, the appearance of pictures for the person with normal color vision is changed less than previous dithering method and also color vision handicapped person can perceive the drawing patterns, and optimal dither size is derived from the shape of the drawing patterns. Color patterns with three lightness contrasts and three dither sizes generated by variable dithering method are evaluated about appearance for normal color vision and visibility for the color vision handicapped. Also, patterns with seven dither sizes including the sample generated by optimal dither size derivation method are evaluated about visibility for the color vision handicapped. The results confirmed the hypothesis about variable dithering method. On the other hand, the results also showed that the sample generated by optimal dither size method does not have optimal visibility. In this study, it is hypothesized that optimal dither size is derived from only the shape of the drawing patterns, but other parameters, for example lightness contrast, should be taken into account.

Driving technology for improving motion quality of active-matrix organic light-emitting diode display

This paper reports transient response characteristics of active-matrix organic light emitting diode (AMOLED) displays for mobile applications. This work reports that the rising responses look like saw-tooth waveform and are not always faster than those of liquid crystal displays. Thus, a driving technology is proposed to improve the rising transient responses of AMOLED based on the overdrive (OD) technology. We modified the OD technology by combining it with a dithering method because the conventional OD method cannot successfully enhance all the rising responses. Our method can improve all the transitions of AMOLED without modifying the conventional gamma architecture of drivers. A new artifact is found when OD is applied to certain transitions. We propose an optimum OD selection method to mitigate the artifact. The implementation results show the proposed technology can successfully improve motion quality of scrolling texts as well as moving pictures in AMOLED displays.

Research on Halftone Technique of Digital Images

Halftone is the key technique for low-resolution equipment like fax machines and printers to reconstruct grayscale images with black and white binary data. Images produced by classic error diffusion algorithm have more abundant color than those made by ordered dithering method. But the problems still exits that there can distortions and false contour phenomenon and fuzzy edges. This paper puts forward an advanced error diffusion algorithm based on bidirectional feedback and improves its feedback type through adding correction factors. The simulation results show that the bidirectional feedback error diffusion algorithm with correction factors better inhibited the phenomenon of distortions and false contour. Directional texture is also improved greatly.

Novel Evaluation of Digital Halftone Image Qualities by Psychological Analysis

Monochrome binary halftone images express multiple levels with halftones produced by distributing black and white pixels. In this paper, for the subjective evaluation of halftone qualities, binary halftone images are considered as pointillistic images of visible black-and-white pixels. Visual impressions given by the pixel distribution are measured by the semantic differential (SD) method in a psychological manner. An experiment for measuring subjective impressions of subjects by using selected 30 SD items was conducted on several binary halftone images that were produced by three kinds of the typical halftoning methods: two error-diffusion methods and a kind of random dither method. The sample data are analyzed statistically by factor analysis. As a result, two common factors are found out and interpreted as the sensitivity factor and the activity factor, respectively. Also, the result of variance analysis demonstrates that the two common factors are able to describe the difference among the three halftoning methods.