Design of Farthest-Point Masks for Image Halftoning

In an earlier paper, we briefly presented a new halftoning algorithm called farthest-point halftoning. In the present paper, this method is analyzed in detail, and a novel dispersion measure is defined to improve the simplicity and flexibility of the result. This new stochastic screen algorithm is loosely based on Kang's dispersed-dot ordered dither halftone array construction technique used as part of his microcluster halftoning method. Our new halftoning algorithm uses pixelwise measures of dispersion based on one proposed by Kang which is here modified to be more effective. In addition, our method exploits the concept of farthest-point sampling (FPS), introduced as a progressive irregular sampling method by Eldar et al. but uses a more efficient implementation of FPS in the construction of the dot profiles. The technique we propose is compared to other state-of-the-art dither-based halftoning methods in both qualitative and quantitative manners

Structure-aware halftoning

our result faithfully preserves the texture details as well as the local tone. All images have the same resolution of 445×377. This paper presents an optimization-based halftoning technique that preserves the structure and tone similarities between the original and the halftone images. By optimizing an objective function consisting of both the structure and the tone metrics, the generated halftone images preserve visually sensitive texture details as well as the local tone. It possesses the blue-noise property and does not introduce annoying patterns. Unlike the existing edge-enhancement halftoning, the proposed method does not suffer from the deficiencies of edge detector. Our method is tested on various types of images. In multiple experiments and the user study, our method consistently obtains the best scores among all tested methods.

Digital halftoning using fibonacci-like sequence pertubation and using vision-models in different color spaces

A disadvantage in error diffusion is that it creates objectionable texture patterns at certain gray levels. An approach, threshold perturbation by Fibonacci-like sequences, was studied. This process is simpler than applying a vision model and it also decreases the visible patterns in error diffusion. Vector error diffusion guarantees minimum color distance in binarization provided that a uniform color space is used. Four color spaces were studied in this research. It was found that vector error diffusion in two linear color spaces made no reduction in the quality of halftoning compared with that in CIEL*a*b* or CIEL*u*v* color spaces. A luminance vision MTF and a chroma vision MTF were used in model-based error diffusion to further improve the halftone image quality

Stippling by Example

In this work, we focus on stippling as an artistic style and discuss our technique for capturing and reproducing stipple features unique to an individual artist. We employ a texture synthesis algorithm based on the gray-level co-occurrence matrix (GLCM) of a texture field. This algorithm uses a texture similarity metric to generate stipple textures that are perceptually similar to input samples, allowing us to better capture and reproduce stipple distributions. First, we extract example stipple textures representing various tones in order to create an approximate tone map used by the artist. Second, we extract the stipple marks and distributions from the extracted example textures, generating both a lookup table of stipple marks and a texture representing the stipple distribution. Third, we use the distribution of stipples to synthesize similar distributions with slight variations using a numerical measure of the error between the synthesized texture and the example texture as the basis for replication. Finally, we apply the synthesized stipple distribution to a 2D grayscale image and place stipple marks onto the distribution, thereby creating a stippled image that is statistically similar to images created by the example artist

Image Quality Dependence on Partial Coherence in a Projection Printer

A study has been made of the printed images from a projection printer whose light source can be varied to provide illumination of various levels of partial coherence. The coherence interval for five light source configurations was measured with a shearing interferometer at the object plane of the printer. Many test images were made with the printer for each of the five degrees of partial coherence and results showing image quality as a function of coherence interval have been reported. It was found that with an 11µm coherence interval the image forming characteristics were typical of an incoherent instrument and could be adequately explained by a linear transfer function. An increasing departure from linearity was seen as the coherence interval increased to 71µm. This could be best seen as an increase in ringing around edge images and emphasized high frequencies in sine wave images. For coherence intervals greater than 71µm few changes occurred in the image microstructure indicating that the printing characteristics are essentially those of a coherent system. Tri-bar resolving power showed a factor of two drop from the incoherent to the coherent imaging condition. Image microstructure effecting the macro tone reproduction was observed and concluded to be an example of the half tone effect

Isotropic Surface Remeshing

International audienceThis paper proposes a new method for isotropic remeshing of tri- angulated surface meshes. Given a triangulated surface mesh to be resampled and a user-specified density function defined over it, we first distribute the desired number of samples by generalizing error diffusion, commonly used in image halftoning, to work directly on mesh triangles and feature edges. We then use the resulting sam- pling as an initial configuration for building a weighted centroidal Voronoi tessellation in a conformal parameter space, where the specified density function is used for weighting. We finally create the mesh by lifting the corresponding constrained Delaunay trian- gulation from parameter space. A precise control over the sampling is obtained through a flexible design of the density function, the latter being possibly low-pass filtered to obtain a smoother grada- tion. We demonstrate the versatility of our approach through vari- ous remeshing examples

Implications of lead isotope variation in lead white from 17th century Dutch paintings

Lead white is a lead (Pb) carbonate that has been extensively used throughout human history. Analysing lead isotope ratios of lead white potentially gives information on the provenance of the lead constituting the pigment. The extensive use of lead white in oil paintings until the 20th century, combined with lead isotope analysis, provides information not only on the provenance of the lead in the pigment but also on painting making processes, trading of lead, lead white throughout history and attribution and authentication. This research presents a comprehensive study of the application of lead isotope analysis to: - Improving analytical precision and sensitivity of lead isotope analysis - Investigating the heterogeneity of lead isotope ratios in lead white used within a single painting - Study of the time-dependant variation of lead isotope ratios of lead white in 17th century Dutch paintings - Use of lead isotope analysis of lead white in combination with other analytical techniques to study paintings The proposed development of improved and more sensitive analytical methods lead to the creation of a new sampling tool, named “micro-scalpel” that allows sampling from cross-sections. This instrument reduces the amount of pictorial material taken during the sampling, and allows the operator to selectively sample from one pictorial layer at a time. Simultaneously the analytical method was improved, increasing the sensitivity of the instrument (multi collector inductively coupled plasma mass spectrometer or MC ICPMS) with the application of a lead double spike (DS) technique and the use of a 1013 Ω resistor amplifiers. Due to the improved analytical sensitivity, the sample size required for analysis was reduced by a factor of ten with the use of 1013 Ω resistor amplifiers, while maintaining accuracy and precision. The new method was used to investigate the heterogeneity of lead isotope ratios within a single painting. The study was conducted on five Netherlandish paintings from the 17th century. Each painting was sampled several times (n. 5-20) in different areas. The data were then compared to the analysis of powdered lead white (historical Venetian lead white from the end of the 16th century rescued from a shipwreck). The study determined that the lead isotope ratios of the Venetian lead white pigment were homogeneous. In contrast, four out of the five paintings contain lead white samples that were outside analytical, identifying lead isotope ratios heterogeneity within the painting. The results suggest that the pigment, processed and used in the artist’s studio prior to painting could have been in contact with other lead-bearing compounds that altered the original isotopic composition. These findings suggest multi-sampling strategy, and the need of a database to compare data to have a reliable interpretation of lead isotope ratios. The lead isotope analysis of 77 dated Dutch paintings from 27 artists allowed assessment of the time-dependent variation of lead isotope ratios of lead white and the creation of a database. The lead isotope compositions recorded a clear time dependence identifying a shift in lead isotope ratios during the period 1642-1647, and a second change is indicated after 1680. The changes in lead isotope ratios in lead white were connected to historical events. For example, the period 1642-47 coincides with the English Civil War in the country that was the main producer of lead at the time. The identification of a time-dependent variation of lead isotope ratios of lead white gives the possibility to distinguish early and late works by individual artists active in the 17th century