The iridescence effect, produced by structural color, is difficult (if not impossible) to capture and print using traditional CMYK pigments. RGB pigments, nonetheless, generate structural colors by light interference. The layered surface structure generated by pigments’ particles reflects different wavelengths of light in different viewing angles. In printed media, pigments’ particles will collectively influence the optical response of the surface, depending on their size, orientation, structure, and dimensions, ultimately, affecting the visual characteristics of the image perceived by the observer. In this work, we have studied the influence of different halftones’ structures on printed images, produced with RGB inks via screen printing. We investigated the influence of different halftones’ structures in creating different spatial combinations of inks on the printed surface that reproduce the characteristics of iridescent effect of a headdress made of quetzal feathers. We applied first-order, second-order, and structure-aware FM halftones to compare how they influence the reproduction of the material qualities of the object represented in the image. The results show that the structure-ware halftones improve the representation of the image structures and details and, therefore, it could better convey the 3D surface features that produce iridescence effect in the original feathers of the headdress.
In this paper we investigate applying two deep generative models to digital halftoning with the aim of generating halftones with comparable quality to those generated with the direct binary search (DBS) algorithm. For the first framework, we apply conditional generative adversarial networks (cGANs) using two discriminators with different receptive field size and a generator consisting of densely connected blocks. For the second framework, deep autoregressive (AR) models, we propose mapping input images into a feature space using a single forward pass of a deep neural network and then applying a shallow autoregressive model at the end output. Our methods show promising results; halftones generated with our algorithms are less noisy than those generated with DBS screen and do not contain artifacts commonly associated with error diffusion type algorithms.
In previous work [1] , content-color-dependent screening (CCDS) determines the best screen assignments for either regular or irregular haltones to each image segment, which minimizes the perceived error compared to the continuous-tone digital image. The model first detects smooth areas of the image and applies a spatiochromatic HVS-based model for the superposition of the four halftones to find the best screen assignment for these smooth areas. The segmentation is not limited to separating foreground and background. Any significant color regions need to be segmented. Hence, the segmentation method becomes crucial. In this paper, we propose a general segmentation method with a few improvements: The number of K-means clusters is determined by the elbow method to avoid assigning the number of clusters manually for each image. The noise removing bilateral filter is adaptive to each image, so the parameters do not need to be tested and adjusted based on the visual output results. Also, some color regions can be clearly separated out from other color regions by applying a color-aware Sobel edge detector.
For mass production, multiple color halftoning screen printing (MCHSP) can be considered as the alternative textile printing technology when vivid color gradation is needed and cost for digital printing is concerned. Essentially, MCHSP utilizes the same equipment as traditional screen printing to print overlapped multiple color gradation under halftoning patterns by applying the dedicated treatments on color separation and calibration. In order to ensure the color quality, the equipment calibration and tone curve compensation are required to compensate the variables from equipment setup and heterogeneous fabrics. In this research, we provided the procedure of tone curve compensation to alleviate the discrepancy from heterogeneous fabrics. The experimental result based on 55 samples of 44 different fabrics shows the compensation effectiveness and reveal the distribution of average compensation percentage across fabrics.
FM (Frequency modulation) halftoning (aperiodic and dispersed-dots) is increasingly popular with traditional analog offset lithographic printing. There is a desire from customers in the commercial market to use this capability with high-end digital presses based on electrophotographic printing (EP) technologies. However, the inherent instability of the EP process challenges the achievement of satisfactory print quality with dispersed-dot, aperiodic halftoning. The direct binary search (DBS) algorithm is widely considered to represent the gold standard of dispersed-dot, aperiodic halftone image quality. In this paper, we continue our previous efforts to adapt DBS from dispersed-dots to clustered-dots to use with the Indigo liquid EP printing technology; we present a new screen design algorithm for aperiodic, clustered-dot halftoning based on Direct Bineary Search. Our screen design has a very good detail rendering capability and very stable halftone frequency overall. The halftone texture after applying screen is even better than directly using our previous work, clustered-dot halftoning.
To enable the track and trace of pages from a color printer, data must be embedded and recoverable across the entire page regardless of the content on that page. This paper describes a solution that allows low visibility and high detectability of databearing “dot signatures”. An analysis of optimum dot-color to background-color combinations uncovers the serendipitous method of “Blue Clipping,” operating only on the blue component, exploiting low visual sensitivity to the blue channel. Blue Clipping is compared to the method of yellow dots, and the problem of dot gain for shadow dots is addressed. While initially designed for enterprise printers, this new technology is also adding functionality to 3D objects. It enables visually pleasing yet robustly recoverable data markings from a small region anywhere on a printed surface, without the need for costly special inks.
In this paper, we propose a novel error diffusion halftoning algorithm for the conversion of cyan, magenta and yellow (CMY) ink amounts to a multi-bit halftone image. We adopt the idea of allowing multiple drops of colorants in order to achieve print results with better saturation, which is implemented by modifying the classic Floyd-Steinberg error diffusion algorithm. For better halftone texture and more efficient use of colorants, we add a dot-off-dot feature to the classic Floyd-Steinberg error diffusion. Blending-in the original input image with its DBS screened multilevel halftone image as a preprocessing step to dot-off-dot error diffusion is proposed as a measure to reduce halftone artifacts. Digitally simulated halftone images will be presented to illustrate the better halftone texture that can be achieved by applying the proposed algorithm.
Digital halftoning is a technique for converting a continuoustone image into a binary image with the aim of reproducing it on a binary output device. Error diffusion (ED) is an algorithm that has proven to be effective for the halftoning process, and it has been widely applied to digital printing tasks. However, in images reproduced by conventional ED algorithms based on signal processing theory, the total appearance of objects—which includes properties such as glossiness, transparency, and roughness—is often lost. In this paper, we propose an appearance-preserving ED algorithm to improve the quality of printed images. We consider a texture-preserving approach to effectively represent the total appearance of objects. In this study, we utilized different weights for the error distribution based on the texture strength to permit stable representation of the pixels relevant to the texture. Experimental results using printed images demonstrated that the proposed algorithm improved the quality of printed images relative to images produced by conventional techniques.