The investigation of low light imaging is of high importance in the field of color science from different perspectives. One of the most important challenges that arises at low light levels is the issue of noise or, more generally speaking, low signal-to-noise ratio (SNR). In the present work, effects of different image sensor noises, such as photon noise, dark current noise, read noise, and quantization error are investigated in low light color measurements. In this regard, a typical image sensor is modeled and employed for this study. A detailed model of noise is considered in the process of implementing the image sensor model to guarantee the precision of the results. Several experiments have been performed over the implemented framework and the results show the following: first, photon noise, read noise, and quantization error lead to uncertain measurements distributed around the noise free measurements and these noisy samples form an elliptical shape in the chromaticity diagram; second, even for an ideal image sensor, in very dark situations, stable measurement of color is impossible due to the physical limitation imposed by the fluctuations in photon emission rate; third, dark current noise reveals dynamic effects on color measurements by shifting their chromaticities towards the chromaticity of the camera black point; fourth, dark current dominates the other sensor noise types in the image sensor in terms of affecting measurements. Moreover, an SNR sensitivity analysis against the noise parameters is presented over different light intensities.
The electronic display industry has begun a migration towards higher color gamut devices driven by LED, OLED, quantum dot and laser technologies capable of generating near monochromatic color stimuli in the traditional red, green, blue three-channel paradigm. The use of highly selective spectral stimuli, however, poses a risk to the consistency of visual experience amongst a group of disparate, but otherwise normal, color observers. Several models of spectral color vision have surfaced in recent research and are helping investigators to better understand the implications for color experience variability. The present research serves to summarize various color difference indices that may be useful in predicting the magnitude of observer response inconsistencies and applies them to simulations of current electronic displays as examples of potential concerns these new high-gamut technologies might raise. In particular, various laser-based displays are shown to perform with significantly increased observer variability versus traditional ITU-R Rec. 709 and SMPTE 431 RGB-primary displays utilized in the cinema industry. Further, observer metamerism can be reduced significantly with proper optimization of a multichannel projection system comprising seven explicitly designed primary spectra.
The authors propose a method of image rendering to predict the incomplete chromatic-adaptation effect for paintings. A simple model of incomplete chromatic adaptation is developed to predict the appearance of the paintings under the illumination of an incandescent light source and to produce the full color image on a display device. The authors extend the von Kries framework to incomplete chromatic adaptation. An index parameter representing the degree of incomplete chromatic adaptation is defined based on the color temperature of the black-body radiators. First, the optimum value of the index parameter is determined by visual experiments on memory matching using real paintings and color patches, so that the color image produced on the display is matched to the original appearance of objects in a real scene. This approach is shown to have better performance in comparison with the traditional CIECAM02. Next, an algorithm is presented to estimate the index parameter of the incomplete adaptation index based on the image data of colorimetric rendering for a target painting. It is found that the index parameter can be estimated using only three features extracted from the color image. The color images rendered with the estimated parameter are used to predict the incomplete chromatic-adaptation effect for the original painting under the incandescent light source. The feasibility of the proposed method is confirmed based on a series of experiments using a variety of paintings.
In this article, the authors reproduce gloss unevenness on a paper surface by expanding the Torrance–Sparrow model, which is based on the measurement and analysis of mesoscopic facets on paper. As the conventional Torrance–Sparrow model only considers macroscopic and microscopic facets, the authors expand the model to be able to consider mesoscopic facets. The normal vectors of mesoscopic facets on a paper surface were measured by using a collimator lens system with a small pinhole aperture, and the authors obtained the normal vector map by moving the stage for the paper. Gloss unevenness was reproduced by generating the same probability distribution as the measured distribution of the normal vectors. As a result, the authors succeeded in reproducing gloss unevenness using an expanded Torrance–Sparrow model.
A study was conducted to better understand the toner charging process under dynamic conditions. A second study was conducted to better understand how toner chargeability is affected by the aging of the components in the printer cartridge of single component electrophotography-based toner printing systems. In this article the authors report on both of these studies. In these systems, toner is tribocharged, i.e., charged by friction by contact with the component surfaces in the printer cartridge. Through a series of experiments it was observed that the nip between the developer and the supply roller is the primary charging region, which was further augmented by the metering blade. In the second study a significant reduction in the charging ability of the toner was observed as the printing cartridge aged due to wear of the toner and the charge contributing components in the cartridge. As efforts continue to be made to place single component toner development technology at the forefront of affordable, reliable, and high quality printing, it has become very important to better understand these issues.
Printed metal grid conductors can be used in thin, flexible and large-area lighting sources based on, e.g., light-emitting electrochemical cells (LECs). Similar to organic light-emitting diodes (OLEDs), LECs are thin-film electroluminescent devices, which can be processed from solution. However, LECs have a simpler architecture, and do not rely on air-sensitive charge-injection layers or metals for electron injection. This offers simplicity for manufacturing process, cost-efficiency and easier large-scale manufacture. Printing methods such as inkjet and flexography are suitable for manufacturing the metal grid conductors needed in LEC devices. The goal of this article is to evaluate the potential of flexographic and inkjet printing to manufacture metal grid conductors on an industrial scale. Printing equipment that can be up-scaled to industrial scale is used and the printing conditions are modified to meet the device requirements. The performance and properties of inkjet and flexographic printed conductors are compared. Finally, the performance of full LEC devices is evaluated. As a conclusion, both inkjet and flexographic printing were found to be suitable for fabricating metal grid conductors since the surface roughness, layer thickness and electrical performance met the target values when the printing conditions were carefully optimized. Some compromises had to be made between adhesion, surface roughness, layer thickness and process reliability requirements. Finally, the performance of inkjet printed LEC devices has been demonstrated.
Large format inkjet printing systems have evolved over the last decade and now offer high levels of speed and print and color quality. There are, however, no established standards or test protocols with which to evaluate this technology, and users must rely on manufacturers’ marketing claims and counter claims. Wide and grand format devices may use solvent inks, UV-curable inks (cured via exposure to ultra-violet light), or latex ink. The media typically used by this category of device range from card stock to cast or calendared vinyl to rigid media. Inks used may be CMYK (cyan, magenta, yellow, black), light inks, metallic, or white. Viewing distances for these products range from point of purchase to greater distances for street signs, banners, and billboards. This research first identifies test areas that are relevant to this type of printing system; next, test procedures are developed; and finally, practical testing using commercially available large format roll to roll and flatbed inkjet printing systems is conducted. The aim of this research is to provide real practical data from the field as input to the ISO committee that is developing ISO 15311 that relates to Large Format Signage Printing.
As part of the IDEAlliance Inkjet RoundUP, 24 sets of different print samples were obtained from the following supplier companies: Agfa, Durst, EFI, Epson, Fujifilm, HP, Mimaki, Mutoh, Océ, Roland, and Seiko. Tests were conducted for different test areas including color gamut, color management accuracy, print uniformity, repeatability from day to day, CMYK cross-hair registration, ink consumption, print speed, rub resistance as it relates to floor graphics, and weathering as applicable for outdoor signage. Individual test results are presented, and while we do not seek to create “winners” and “losers”, we seek to identify achievable and appropriate “pass/fail” metrics for international standards and local certification/validation programs. In general, for color management, for example, we see that the systems produced extremely accurate color accuracy and are able to match GRACoL to within 1–2 CIEDE2000.
This research also seeks to identify a color characterization data set that can accurately represent the color characteristics of wide format inkjet printing. There exist well-established data sets for offset and gravure printing (for example SWOP, FOGRA, Japan Color), but there are no accepted data sets for large format inkjet printing. One standard being developed, ISO 15339, proposes Characterization Reference Print Condition 7 (CRPC 7) for “Extra large gamut printing processes”. In this research, we evaluate the applicability of using CRPC 7 to represent the color response of commercial large format inkjet printing systems.