Inkjet technology has been used as a tool to manufacture printed electronics, and the size of the droplet should be properly measured and controlled in order to improve the print quality. To this end, the volume of an inkjet droplet can be measured by assessing an image of the droplet through the use of a visualization system. However, a vision-based method may have accuracy issues, so, in this study, an alternative method is proposed by using a microbalance to measure the droplet mass. The mass and the volume of the droplet are simultaneously measured for verification and comparison. Since the results of the proposed mass measurement method are susceptible to the evaporation of liquid on the microbalance, the accuracy of the measurement is improved by employing an evaporation compensation method. Finally, the effects of the jetting frequency on the measurement uncertainty of the mass and the volume of the droplet are investigated by using several jetting materials with different boiling temperatures.

Inkjet printing using water-based pigment ink has been carried out with laser exposure to dry the ink in a short period of time (approximately the same as the penetration time). Heating by near-infrared laser exposure is advantageous because it heats only the ink without heating the paper. As a result, the formation of cockles or creases in the paper is suppressed, and the optical density of printed images is improved. In addition, show-through to the back side of the paper is reduced, and bleeding is also suppressed. Furthermore, it is demonstrated that the favorable conditions for laser exposure are different on different types of paper because of the different penetration times; the mechanisms of the penetration and the drying are also discussed.

The visibility of images displayed on mobile devices can vary significantly according to the lighting conditions. Generally, the brightness of a mobile device is adjusted to enhance the visibility according to the intensity of the illumination. However, different brightness settings can be more suitable for different types of content, even under the same illumination. Accordingly, this article presents a method for adjusting the device brightness according to the features of the displayed app image. First, two subjective tests are performed under various lighting conditions to select the features related to the visibility of several app screenshots and to select a satisfactory range of device brightness for the same app screenshots. The relationship between the app image features and the satisfactory brightness levels is then analyzed. Thereafter, the images are categorized using two features: the average luminance and the advancing color ratio related to satisfactory brightness. The optimal device brightness for each category is then selected based on the maximum frequency of satisfactory device brightness. Experimental results show that the categorized app images with the optimal device brightness produce a high satisfaction ratio under various lighting conditions.

The problem of visual discomfort caused by watching stereoscopic 3D content must be addressed if 3D movies and TV are to become widespread. Previous research on visual discomfort has mostly relied on subjective assessment methods. Recently, more objective assessment methods for evaluating visual discomfort have been proposed which may avoid the ambiguities of subjective assessment methods. Nevertheless, subjective human factors are also important in analyzing visual discomfort. Thus, it is necessary to correlate objective measures with personal reports from subjects. In this article, the authors measure visual discomfort caused by watching stereoscopic 3D videos by integrating objective and subjective assessment methods with reference to depth and viewing time. To construct an objective assessment method, they detect eye-blinking with near-infrared video and then convert the eye-blinking data to a visual discomfort value by correlating them with the viewer’s discomfort response. The authors use questionnaires as a subjective assessment method of measuring physiological symptoms of visual discomfort. Using both the objective and the subjective assessment results, they then construct a visual discomfort estimation model which includes the parameters of depth and viewing time. Experimental results show that visual discomfort increases as the depth and viewing time increase. In addition, the visual discomfort estimation model shows lower residual errors than those obtained by using separate subjective and objective assessment models.

Preferred skin color reproduction is an important factor for improving the image quality of display devices and systems. Therefore, this article presents a race-selective preferred skin color reproduction method for the case of multiple races in a single image. First, the proposed method detects skin regions using a focus map and skin candidate map. Next, the race of each detected skin region is classified by comparing the Euclidean distance of the average chromaticity for each detected skin region with a database of racial skin colors. Based on this classification, the racial preferred skin color for each detected skin region is then selected from candidate racial preferred skin colors that are predefined in a database generated through an observer’s preference test. Finally, the skin color is reproduced toward the preferred skin color. Experimental results confirm that the proposed method can achieve race-selective preferred skin color reproduction in the case of multiple races in a single image.