Applied Mechanics and Materials Vol. 469

Abstract: To meet the requirements of real-time on-line detection, an algorithm for hot stamping image recognition was proposed based on projection with adaptive threshold. Firstly CCD collects digital image, then convert RGB images into HSV space, and extract V channel. The initial threshold was set according to the error on the first location of matching region. In the subsequent template matching process, the threshold would be update; the smallest D-value point is the best match. The experiment results show that the improved algorithms can identify hot stamping area and greatly increase the matching velocity, having certain guiding significance to hot stamping quality detection based on machine vision.

Abstract: A resolution test-chart for digital camera has been developed based on the knife-edge method. RAW images have been acquired with NikonD7000 DSLR and Canon G12. Set the device color-space to Adobe RGB, and convert the image data to LAB color-space using Adobe RGB profile. The Fourier transfer of the LAB tonal value were computed under MATLAB environment. Then by analyzing the L/C/H (Derived from LAB space ) and the Modulation Transfer Function (MTF), we can get the resolution characteristics of the Nikon D7000 and Canon G12 camera.

Abstract: 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.

Abstract: Different rendering conditions (e.g., changes in lighting conditions or atmospheric conditions, changes of the imaging system) often cause significant color differences between two images. In the prepress process, the brightness and hue between two images should be adjusted to be as similar as possible. Currently, we generally use image processing software such as PhotoShop to adjust the image manually, it’s complex and time consuming. In this paper, the color correction algorithm based on histogram matching was put forward and implemented. Only one image needed to be adjusted well previously as the reference image, and the mapping relationship was established on pixels between the histogram of the source images and the reference image, then the source images would have the histograms similar to that of the reference image, so that the images would have similar color characteristic and achieve image color correction finally. The experimental result showed that the realized color correction algorithm was effective, it could not only maintain the visual effect of images, but also eliminate the color differences between the reference image and the source images.

Abstract: The paper suggested an algorithm to extract the golden region with tone change in an image as a printing plate information of metallic ink. It is based on HSV color space. A statistical hue range of golden color was used to separate the golden regions from the image, and Otsu algorithm was applied to acquire the tone of golden regions. The golden target regions are acquired by multiplication pixel by pixel between processed H values and the processed S values. The experiments were carried out on various images with different textures and background characteristics, and the segmentation effect were compared and analyzed also. They showed that the suggested algorithm is suitable for both simple and complex texture area. The color difference between image’s background and target influences the result of extraction, he large color difference is more suitable for segmentation.

Abstract: The study on the method of the color measurement of gold and silver foil paper is important to control color quality in the printing industry. The methods used in the experiments were to study the role of the gold tone and silver tone by studying the influence of gold tone and silver tone with different content on the chromatic value of normal color ink with different tone and different saturation. In the experiments, chromatic value of SPIN and SPEX respectively in the diffuse light conditions of color measurement could represent the chromatic value of the ink containing gold or silver ink. Then the difference of L values between SPIN and SPEX was defined as lightness difference. The ratio of the difference of saturation between SPIN and SPEX to their sum was defined as saturation ratio. Therefore, the Correlation Properties between lightness difference and saturation ratio was quantified. The result shows that with the quantity of gold and silver ink increasing, saturation ratio has linear relation with lightness difference for the same color. Similarly, with the saturation of normal ink colors increasing, saturation ratio has linear relation with lightness difference for a series of colors containing the same quantity of gold and silver ink .

Abstract: The prediction of color appearance is the basic theory and technology in modern color science field. The aim of this study is to evaluate the color appearance of packaging and printing atlas. This paper took high gloss double-sided coated paper color printing atlas as the experimental samples. The color samples are measured using ACS color-matching instrument under different light sources (D65, A and TL84), then based on color science and visual psychophysics methods, establishing the datasets of the samples’ color appearance. We use mathematical statistics methods, correlation coefficient R² and coefficient of variation CV, to evaluate the visual prediction results in the color atlas, under three different light sources.

Abstract: The effects of aluminum foil packaging materials on color reproduction were mainly studied from the following two aspects in this topic: (1) through the study of CIEl976 chroma space, color difference evaluations of 7 kinds of colors for aluminum foil were compared with that of coated paper, based on the established color libraries of coated paper. (2) Four different spectrophotometers of X-Rite were used to measure L^*、 a^*、 b^* of different colors, analyzing the effects of different spectrophotometer on color reproduction. Research has proved that: (1) the method which color was transferred to the aluminum foil, according to the established color libraries of coated paper, is feasible, and there was no difference between two colors on aluminum foils by visual inspection, the chromatic aberration was less than 1. (2) From the measurements, aspheric photometers like X-Rite939, Spectroeye, X-Rite500 cannot be used for color measurement on aluminum foil, the error is bigger than SP64, and accuracy is lower. (3) Through the total color difference analysis of four instruments on magenta, the ball SP64 portable spectrophotometer is the most suitable equipment for color reproduction on aluminum foil packaging materials.

Abstract: In order to improve for the inadequacy of traditional evaluation methods, this paper researched a kind of color-difference evaluation method for the food package printing matter based on human visual characteristics. Research method is as follow: the reference image and the target image were transformed to the opposite color space, and were dealt with the human eye Contrast Sensitive Function (CSF) spatial filter. The modified three opposite color component of images were transformed into the CIE XYZ space image after CSF spatial filtering processed; finally the image was transformed to the CIELAB space image. The color-difference of the target image was calculated according to color-difference formula. The color-difference result of image is the calculation result with human visual characteristics filtering processed; it combines subjective evaluation with objective evaluation. The research could provide practical and effective evaluation method for the field of food package printing matter.

Abstract: This research is to find out the relationship between objective measurement contrast and clarity to the human eye perception, via the analysis of different tone background and white text, based on the text contrast properties in ISO 13660 standard, to do some basic research for the black background of print quality evaluation. Experimental results show that perceived sharpness and contrast into positive correlation, the greater the contrast, the sharpness perception will increase accordingly， but it is not linear relation, in contrast, under the condition of smaller contrast, small changes of contrast will cause great changes in the perception of the definition, with the increase of contrast, perceived definition changes tend to be gentle, it is important to note that contrast is of the biggest objective measurement results in background of 100% black tone, whereas the human eye subjective sense of clarity is not the best, it turns out that the best sense of clarity in background tone value is around 90%.