Recently, inkjet-printing industry demands high-speed and single-pass printing that requires simultaneous jetting of a large number of ejectors. As a result, the jetting reliability has become an important issue in most industrial inkjet-printing applications. To ensure the jetting reliability, a real-time monitoring of the jetting status is needed. Since the monitoring process should not interrupt the printing process, the monitoring time for all of the nozzles should be less than 1 second. For this purpose, the authors developed two module prototypes to monitor the commercial inkjet heads with 1024 nozzles: (1) a head driver with an internal self-sensing capability; (2) an external monitoring module that can be used for third-party drivers. To deal with a large number of nozzles effectively, the authors are proposing a parallel sensing scheme that can be used to monitor multi-head jetting. Lastly, the authors verified our monitoring scheme by using a drop visualization system for a comparison of the monitoring results with the droplet jetting images.
Most existing image quality assessment algorithms are designed for distorted images, while there is no special assessment for enhanced images. However, the existing assessment indices are related to image enhancement methods. In an attempt to design a quality assessment algorithm for enhanced images, deep research into the correlation between image enhancement and image quality has been carried out. Based on the four major features of image enhancement methods, which are lightness, contrast, saturation and sharpness, a new enhanced image quality assessment (EIQA) index which combines multiple similar features is proposed. Experimental results show that the proposed assessment index has a good consistency with the subjective score and has excellent performance for enhanced image quality assessment. In current research, the SROCC (Spearman’s rank correlation coefficient) and PLCC (Pearson linear correlation coefficient) of the proposed index are both greater than 0.7. Moreover, the algorithm has high operating efficiency.
Three-ply paperboard was coated using hydroxypropylated starch (HPS) and styrene–butadiene latex as polymeric components and kaolin or synthetic layered silicate as the functional pigment. The coatings were designed to modify the surface characteristics of the substrate to enhance the printability and barrier properties and prevent the migration of mineral oil. The substrates were printed with aqueous dye-based inkjet inks and the ink–substrate interaction and print quality characteristics such as print density, mottling, bleeding, and wet and dry ink rub resistance were determined. The coated substrates showed extraordinarily high print density values and reasonable good dry rub resistance, but low wet ink adhesion, which was ascribed to dissolution of the coating–ink interface. Water vapor transmission rate (WVTR) determinations confirmed that the coatings were sensitive to moisture, since the WVTR values more than doubled when the relative humidity was increased from 50% to 75%. The highest print density (2.66 in the 100% black area) was achieved on silicate-filled coatings, which was 97% higher than that of the uncoated reference. On kaolin-containing coatings, the print density was 60% higher than that of the uncoated reference. The AFM images revealed not only that the starch–silicate coatings were remarkably smooth, but also that they were more homogeneous than the pure starch coating. Although the resistance of the studied coatings to liquid oils was in most cases only moderate, the migration of a gaseous mineral oil simulant through the coated sample was low. A small addition of synthetic silicate effectively prevented the migration of mineral oil in the liquid phase through coatings with a solely starch binder. This work demonstrates that starch-based coatings can be designed for high-quality inkjet printing with dye-based inks and that such coatings can simultaneously inhibit the migration of mineral oil in packaging applications, suitable for e.g., hybrid printing applications.
As part of a study aimed at selecting inksets for printing fabrics for outdoor use, pigment-based and disperse dye-based inksets were evaluated on polyester fabric via textile inkjet printing. Colorimetric attributes were recorded for each color, as well as the mixed colors generated through RIPMaster V11 software. Color Table (CTB) profiles were created to compare spot colors and International color consortium (ICC) profiles were created to evaluate color gamut volumes. Four-color and seven-color disperse dye-based inksets were evaluated, along with six-color and eight-color pigment-based inksets . Four-color and seven-color combination of disperse and pigment inksets were compared. As expected, the addition of colors to the basic four-color inkset increased the color gamuts significantly. It was also found that the disperse dye-based inkset provided deeper colors, and excellent wet and dry crock fastness. However, light fastness from the disperse dye-based inksets was not as high as the levels obtained using pigment-based inksets.
A computational color constancy algorithm for digital image enhancement is proposed. This algorithm imitates the inner complex behaviors of the human visual system and ends up expressing one cost function. The algorithm approaches the human visual system with mathematical optimization and reduces the number of parameters that are needed to enhance digital images compared with automatic color equalization by including an automatic thresholding called Otsu’s method. It is shown through experiments that the proposed algorithm has good performance in terms of color/lightness constancy and image contrast.
The properties of ink dots determine the color performance of inkjet printed fabrics. The purpose of this study was to enhance the color performance of pigment inkjet printing using the electrostatic attraction force. A cationic modifier was used to pretreat cotton fabric prior to inkjet printing with pigment inks in which the pigment particles were negatively charged on the surface. The spreading test of pigment ink droplet (4.0 μL) was conducted both on the untreated and modified fabrics. The effective porosity of cotton fabric was calculated and its correlation with the Zeta potential of pigment inks was studied. The ink dots on the inkjet printed fabrics were observed under a digital microscope. The colorimetric attributes demonstrated that keeping the pigment particles on the fabric surface by the electrostatic attraction force was helpful to improve the color performance of pigment inkjet printing. The 2-dimensional color gamut of (a∗, b∗) was enlarged by 13.4% on the modified fabric as compared to the untreated fabric.