Characterization of total dot gain gives a good insight to the study of paper and print. In this article, we propose three approaches based on the Murray-Davies model to obtain total dot gain. In the first approach, the total gain is approximated by minimizing the root-mean-square between the calculated spectrum and the reflected spectrum measured by the spectrophotometer. The other two approaches are based on microscale images captured by a high resolution camera. These two approaches differ in their schemes on how to obtain the gray tone of the full-tone ink. By the use of microscale images, the authors also illustrate the shape of the effective dot area for the investigated paper substrate. They also study the histograms of the reflected and transmitted microscale images. This comparison shows that although the transmitted image has less optical dot gain compared to the reflected image, the transmittance also incorporates some small amount of optical dot gain. V C 2011 Society for Imaging Science and Technology.[DOI: xxx] INTRODUCTIONCharacterization of total dot gain is an important issue in the study of paper properties and print characteristics. Most of the proposed models in literature are based on spectral models, which calculate the lateral propagation of light into the paper substrate (optical dot gain) and the spreading of the inks (physical dot gain) according to their superposition with the other inks. [1][2][3][4][5] In this article, we present three different approaches for computing the total dot gain. One of the approaches uses reflectance spectrum obtained by a spectrophotometer and the other two use reflected microscale images captured by a high resolution camera. The idea of using microscale images to characterize the dot gain is already examined by Arney et al. 6 ; in their approach, they have added an unprinted (paper) stripe at the side of the halftone area in order to find the border between dots and paper. In one of the proposed microscale image approaches in this paper, we attach two stripes to the halftone area, namely unprinted stripe and 100% ink stripe. In the second microscale image approach, we propose another model that does not require the 100% ink stripe. In this approach, the gray tone of the 100% ink for each halftone patch is calculated
Ink spreading and lateral light scattering in the substrate a↵ect the color of a halftone print. One of the most important phenomena which a↵ects the print result is dot gain, meaning that printed dots appear larger than the dots in the digital bitmap. This is partly due to the ink spreading and ink penetration into the substrate, resulting in an enhancement of the physical dot size, referred to as the physical dot gain. Lateral propagation of light in paper, causes printed dots to appear larger than their physical size, which is called optical dot gain. Characterization of total dot gain, i.e. the combination of physical and optical dot gain, is an important issue in the study of paper properties and print characteristics. Many models based on macroscopic measurements are reported in the literature to separately characterize both physical and optical dot gains. The aim of this study is to go beyond the macroscopic models, and to study the halftone prints on a microscopic scale, by using microscale images captured by a high-resolution camera.In this dissertation, three approaches based on the Murray-Davies model are proposed to obtain the total dot gain. In the first approach, by minimizing the root-mean-square di↵erence between the calculated spectrum and the reflected spectrum measured by the spectrophotometer, the total dot gain is approximated. The other two approaches are based on microscale images captured by a high-resolution camera. These two approaches di↵er in their schemes on how to obtain the gray tone of the full tone ink. By the use of microscale images, it is also possible to illustrate the shape of the e↵ective dot area for the investigated paper substrate.A novel approach based on the histogram of microscale images is also proposed to separate physical from optical dot gain. Attaining the physical dot gain characteristic makes it possible to determine the actual physical dot shape, by which the Modulation Transfer Function (MTF) of the paper substrate is estimated. The proposed approach is validated by comparing the estimated MTF of eleven o↵set printed coated papers to the MTF obtained from the unprinted papers using measured and Monte-Carlo simulated edge response.Another potential usage based on the separation of physical from optical dot gain, is to study the characterization of di↵erent color inks.ii
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