Optical Dot Research Articles

Dot Off Dot Screen Printing with RGBW Reflective Inks

Recent advances in pigment production resulted in the possibility to print with RGBW primaries instead of CMYK and performing additive color mixing in printing. The RGBW pigments studied in this work have the properties of structural colors, as the primary colors are a result of interference in a thin film coating of mica pigments. In this work, we investigate the angle-dependent gamut of RGBW primaries. We have elucidated optimal angles of illumination and observation for each primary ink and found the optimal angle of observation under diffuse illumination. We investigated dot off dot halftoned screen printing with RGBW inks on black paper and in terms of angle-dependent dot gain. Based on our observations, optimal viewing condition for the given RGBW inks is in a direction of around 30∘ to the surface normal. Here, the appearance of the resulting halftoned prints can be estimated well by Neugebauer formula (weighted averaging of the individual reflected spectra). Despite the negative physical dot gain during the dot off dot printing, we observe angularly dependent positive optical dot gain for halftoned prints. Application of interference RGBW pigments in 2.5D and 3D printing is not fully explored due to the technological limitations. In this work, we provide colorimetric data for efficient application of the angle-dependent properties of such pigments in practical applications.

An optical neural network using less than 1 photon per multiplication

Deep learning has become a widespread tool in both science and industry. However, continued progress is hampered by the rapid growth in energy costs of ever-larger deep neural networks. Optical neural networks provide a potential means to solve the energy-cost problem faced by deep learning. Here, we experimentally demonstrate an optical neural network based on optical dot products that achieves 99% accuracy on handwritten-digit classification using ~3.1 detected photons per weight multiplication and ~90% accuracy using ~0.66 photons (~2.5 × 10−19 J of optical energy) per weight multiplication. The fundamental principle enabling our sub-photon-per-multiplication demonstration—noise reduction from the accumulation of scalar multiplications in dot-product sums—is applicable to many different optical-neural-network architectures. Our work shows that optical neural networks can achieve accurate results using extremely low optical energies.

Optronic convolutional neural networks of multi-layers with different functions executed in optics for image classification.

Although deeper convolutional neural networks (CNNs) generally obtain better performance on classification tasks, they incur higher computation costs. To address this problem, this study proposes the optronic convolutional neural network (OPCNN) in which all computation operations are executed in optics, and data transmission and control are executed in electronics. In OPCNN, we implement convolutional layers with multi input images by the lenslet 4f system, downsampling layers by optical-strided convolution and obtaining nonlinear activation by adjusting the camera's curve and fully connected layers by optical dot product. The OPCNN demonstrates good performance on the classification tasks in simulations and experiments and achieves better performance than other current optical convolutional neural networks by comparison due to the more complex architecture. The scalability of OPCNN contributes to building deeper networks when facing complicated datasets.

Application of gradient method for separately analyzing optical and mechanical dot gain of electrophotography prints

Abstract The ultimate goal of each production process is to optimize all the subprocesses leading to the high quality final product. Within the printing process, dot gain is identified as one of the most important variables to control because of the extremely negative impact to middle tone contrast and the overall reproduction. Dot gain consists of two components, mechanical and optical dot gain, as a result of two different contributions. This article proposes a model for separately analyzing components of dot gain for electrophotography prints using gradient method, where the impact of printing technique and paper type will be examined. It is shown that mechanical dot gain for electrophotography prints can be satisfactorily approximated with Gaussian, whilst optical dot gain is once again confirmed to have the form of a Lorentzian.

Angular Color Prediction Model for Anisotropic Halftone Prints on a Metallic Substrate

Under specular reflection, non-isotropic halftones such as line halftones printed on an ink-receiving plastic layer superposed with a metallic layer change their colors upon in-plane rotation of the print. This color change is due to the orientation-dependent optical dot gain of the halftone. A strong dot gain occurs when the incident light is perpendicular to the halftone line structure. A color prediction model is proposed which predicts under specular reflection the color of cyan, magenta and yellow line halftones as a function of the azimuthal rotation angle, the incident angle and the line frequency. The model is calibrated by measuring 17 reflectances at the (25° : 25°) measurement geometry, with the incident light parallel to the halftone lines. The model has been tested for several azimuthal rotation and incident viewing angles, each time for 125 different cyan, magenta and yellow ink surface coverages. The obtained prediction accuracies are between ΔE94 = 3.5 and ΔE94 = 7.

Edge spread function for the paper-ink system

AbstractThe importance of accurate identification of the edge spread function for the paper-ink system is closely related with the possibility of separating mechanical and optical dot gain. Our approach is based on the precise fit of the edge spread function, ESF. Namely, all of the research so far incorporates symmetric ESF, in contrast to the research reported so far, in which only the symmetric ESF has been considered¸ which is not realistic, due to the presence of dot gain. This approach, based on image analysis, allows us to identify uniquely the domain of impact of each contribution. Six different paper-ink systems are analyzed and discussed, and all of them show a satisfactory correlation with the proposed model.

Research on optical simulation system for halftone printing dot with Monte Carlo method

The optical simulation system of printing dot is proposed, which could promote optical study of printing dots properties and improve printing quality. The optical simulation system was built based on Monte Carlo program that can simulate photons propagation path in paper. Once inputting the optical parameters of paper and ink, the optical dot simulation program will simulate millions of photons propagation path in prints. After analyzing statistical information of photons, dot morphology and dot reflective data can be obtained. The results showed that simulation system is versatile and easy to operate, besides the simulated dot shape and reflectance quite approached to realistic printing condition. The optical simulation system could sufficiently accomplish printing dot optical properties simulation, which provides a new way to predict and control printing quality.

A novel method for determining the optical component of the paper substrate point spread function

Knowledge of the actual shape of the point spread function (PSF) is of the utmost importance for paper and print quality assessment, since the PSF represents the degree of lateral scattering of light which is closely associated with the size of the optical dot gain. Importance of the correct shape of the PSF prompted us to propose a new experimental method for determining optical component of PSF of a paper substrate by studying the interaction of collimated light and paper and at the same time demonstrate superiority of the Lorentzian shaped PSF compared to the Gaussian, which is commonly used in the description of the PSF. Additionally, measured profile of the scattered light was compared with the profile obtained from Monte Carlo simulation for identical wavelength of incident light. Once the shape of the optical PSF was determined, FTIR spectra of samples were recorded and analysed, aiming to determine how the ratio of chemical and mechanical pulp influences the shape of the optical PSF. All results indicate better approximation of Lorentzian PSF compared to Gaussian, and imply correlation between the share of mechanical and chemical pulp in paper and characteristics of PSF.

Modeling coverage-dependent ink thickness in ink-jet printing

We propose a simple extension of the Murray-Davis halftone reflectance model that accounts for the change of ink dot reflectance due to ink spreading. Significant improvement of the prediction accuracy is obtained for a range of paper substrates and printer combinations compared to the classical Yule-Nielsen and Clapper-Yule models. The results show that ink dot thickness dependency is the main factor limiting the validity of the Murray-Davis model and that optical dot gain can be neglected when the model is calibrated for one specific printer, ink, and substrate combination. The proposed model provides a better understanding of the reflectance from halftone prints that contributes to the development of physical models for simpler and faster printer calibration to different substrates.

Research on secondary colour optical dot gain model in electrostatic digital colour printings

Research on secondary colour optical dot gain model in electrostatic digital colour printings

Classified Quantization Research on Dot Gain Characteristic

Dot gain divides into physical and optical dot gain. These two parts constitute the comprehensive dot gain in the process of printing. Ink spreading on the surface of paper is used for the analysis of physical dot gain and light scattering function model is used for optical dot gain. Trace the dots on the CTP plate and offset printing proof to analyze the influence of image micro-parameters caused by dot gain. Physical and optical dot gain are quantized to research the correlation between dot gain and shape of dot. It shows that: optical dot gain of AM dot accounts for a larger proportion; dot gain of all types has no relation with shape of dot. Besides, physical dot gain of FM dot accounts for a larger proportion than optical dot gain.

‘Optical Dot System’ as Assistance for Drivers to Visualize Affordance of Road Environment

‘Optical Dot System’ as Assistance for Drivers to Visualize Affordance of Road Environment

‘Optical Dot System’ to Assist Appropriate Speed for Bicycles

‘Optical Dot System’ to Assist Appropriate Speed for Bicycles

Research Methods of Determining the Dot Transfer Function of Multicolor Printer

Y_N model-based printer forward characterization, considering the influence of the physical dot gain and optical dot gain, it needs to determine the effective ink dot percentages and the factor n of Yule-Nielson model through single-channel ink limit and nonlinear optimal method. Based on the foregoing, we can determinate the dot transfer function of multicolor printer. Before Y_N model formula factor n and effective dot percentage being determined, it needs to get the sample by printing each primary color inks foot ladder. However, transferring ink to the substrate occurs obvious physical dot gain issues, while the paper absorbing ink ability is limited, so firstly implementing single channel ink quantity control for printer becomes particularly important. Considering the problem of the optical dot gain resulting model accuracy misfit, Y_N model introduces a parameter factor n to correction.

Analysis of Multilevel Screened Image Based on Informatics

With the technical progress in the fields of imaging and printing device, multilevel imaging and screening technologies are applied increasingly. The application of these technologies in printing field, which is as an information channel, can expand capability of information transfer. In order to obtain the characteristics of information transfer in image reproduction, in which multilevel screening technology is applied, the relationship among optical density, dot area and dot density is constructed. According to the basic definitions of information content and of information entropy, the relationship between information content/entropy and gray levels of screening dot is analyzed. Furthermore, multilevel FM screening images, which are with 4 levels, 8 levels and 16 levels and generated by a program, are analyzed and compared with bi-level screened images. The results show, that under lower imaging resolution, multilevel screening can achieve higher count of tone levels and information entropy. It is significant for the improvement of the capability of information transfer and reproduction quality of image.

Analysis of Optical and Physical Dot Gain by Microscale Image Histogram and Modulation Transfer Functions

The color of a print is affected by ink spreading and lateral light scattering in the substrate, making printed dots appear larger. Characterization of physical and optical dot gain is crucial for the graphic arts and paper industries. We propose a novel approach to separate physical from optical dot gain by use of a high-resolution camera. This approach is based on the histogram of microscale images captured by the camera. Having determined the actual physical dot shape, we estimate the modulation transfer function (MTF) of the paper substrate. The proposed method is validated by comparing the estimated MTF of 11 offset printed coated papers to the MTF obtained from the unprinted papers using measured and Monte Carlo simulated edge responses.

8 vertex HANS: An ultra-simple printer color architecture

The underlying non-linearity of how print colorants combine makes color control in printing significantly more complex than for other color imaging devices. While in additive systems a measurement of their few primaries and per-channel non-linearities versus luminance is a sufficient basis for predicting color output, printing typically requires the measurement of a large number of colorant combinations. This requirement for many measurements makes accurate color output more challenging and means that setting up a printing system's color control can be time consuming and costly. The solution presented in this paper involves a new use of the HANS approach, which instead of print optimization looks for simplifying print color formation and therefore also control. In a nutshell this can be achieved by only ever combining eight basic colorant patterns, which results in a display-like color gamut and allows for color control on the basis of their eight measurements and those of the printing system's optical dot gain.

Effective Dot Area’s Calculating Based on YNSN Model

Yule-Nielsen neugebauer spectrum(YNSN) model can describe the relation between dot area and spectrum reflectance, which can calculate the effective dot area. The modified index in the model still can’t be determined. The reciprocal of paper’s spectral reflectance at the range of visible light is adopted as the modified index in YNSN model in order to reduce the optical dot gain. By experiment, the modified YNSN mode can be used to calculate the effective dot area of light color. The research has a certain significance for controlling and testing printing color.

Theoretical Research of Color Reproduction on Concentric Dot

Concentric dot is a new shape of ink dot, which subdivides dot of AM screening into ring and space. Concentric dot has morphological characteristics and reproduction characteristics of AM dots and FM dots, also has excellent color reproduction characteristics. Compared with traditional solid dot, high saturation of concentric dot has been proven. However, the mechanism of this phenomenon is rarely reported. Taking AM dots as reference, this paper try to explain the high saturation of concentric dot theoretically from several aspects, and aims to reveal the mechanism of the color reproduction characteristics of concentric dots. Due to the low amount of ink, the surface of concentric dots is smoother, and achieves better reproduction of color. The distribution characteristics of ring and space result in dot gain both inside and outside of concentric dots, which have a positive impact on the color reproduction. Establishing the relationship of optical dot area and saturation, the difference of color reproduction characteristics between concentric dots and AM dots can be analyzed as the result of the different microstructure of two dots. Using the improved Clapper-Yule model and the law of Lambert-Beer, the conclusion above can be analyzed theoretically. On this basis, experiments are designed and carried out to prove the correctness of theoretical analysis. According to the research, several conclusions are made. The conclusions can be list as follow: different saturations of concentric dots and AM dots lead to different color reproduction, when optical dot area stays the same; different saturations of concentric dots and AM dots is mainly caused by the microstructures of the tow dots; Under the same condition of incident light, concentric dots of monochrome ink reflect more of the visible spectrum than AM dots after absorption, which reasonably explains the high saturation of concentric dots. The study is to reveal the principle of color reproduction of concentric dots with high saturation, providing a theoretical basis for the application of concentric screening technology.

Study on Optical Dot Gain Model Based on Point Spread and Probability Methods

Optical dot gain is the key point of halftone reconstruction study, and has always been a meaningful topic of theoretical study. The Yule–Nielsen formula is by far the most widely used research method of optical dot gain. However, solving the Yule–Nielsen parameter n remains a difficult problem. This paper disregards solving for the Yule–Nielsen parameter n, analyzes the light scattering and osmotic effect of halftone presswork, deduces the exact expressions of blank area of presswork, and determines the reflectivity of the dot part and halftone presswork according to the point spread function and probability method. Furthermore, this paper analyzes how the optical dot gain depends on the dot area coverage of presswork, ink layer transmittivity, and paper-based spectral reflectivity. In addition, a new algorithm model for optical dot gain is established. By employing the Clapper–Yule Model to calculate the spectral transmittance of printing ink and comparing it with the practical measured spectral reflectivity of the halftone presswork proof, the accuracy of the model established in this paper is fully verified.