| 1. |
- Fahlcrantz, Carl-Magnus, et al.
(författare)
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The Influence of Mean Reflectance on Perceived Print Mottle
- 2003
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Ingår i: Journal of Imaging Science And Technology. - 8750-9237. ; 47:1, s. 54-59
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Tidskriftsartikel (refereegranskat)abstract
- The perceived magnitude of a stimulus detected by the human visual system is, according to Fechner's Law, proportional to the logarithm of its physical intensity. This suggests that the perceived mottle in a printed image depends not only on the reflectance variation of the image, but also on its mean reflectance level. One possible approach is therefore to use the reflectance variation divided by the mean reflectance level, dR/R, as an estimate of the perceived mottle in an image. However, practical use of this method indicates that perceived mottle may be overestimated in dark and underestimated in light images. The present study therefore attempts to establish a better relationship between perceived mottle and mean reflectance level. A set of halftone patches was constructed by digital simulation, and then visually evaluated. Results suggest that the measured variation should be divided by a power function, with an exponent less than 1, of the mean reflectance to obtain the best correlation between visual and instrumental evaluation. The highest correlation was attained using the inverse square root, i.e., an exponent equal to 0.5.
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| 2. |
- Gooran, Sasan, 1965-
(författare)
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A Novel Hybrid AM/FM Halftoning Based on Multi-level Halftoning
- 2006
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Ingår i: Journal of Imaging Science And Technology. - 8750-9237. ; 50:2, s. 157-167
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Tidskriftsartikel (refereegranskat)abstract
- A digital gray scale image generally consists of 256 different gray tones. Printers and image setters normally generate much fewer levels and mostly only two levels. Therefore, in order to be able to display a digital cone-tone image by a multilevel device it has to be transformed into an image with fewer levels. The technique doing this transformation is called multi-level halftoning, and in the case of bilevel devices it is simply called halftoning. In this paper we propose a novel (bilevel) halftoning technique that is based on multilevel halftoning. The proposed method can also be categorized as belonging to hybrid amplitude modulated (AM)/ frequency modulated (FM) techniques. In this method the original digital image is firstly halftoned by a multilevel FM halftoning. Each level in the multilevel halftoned image is then replaced by a halftone table (microcell). An approach for extending any bilevel FM halftoning method to a multilevel method is also presented in this paper. The performance of the proposed method is examined by a number of illustrations where nonmodified error diffusion and our FM method are used. The problem with maze-like artifacts that occur when our FM halftoning, or similar methods such as DBS, are used as the macroscreen is discussed and a simple solution is introduced. An approach for extending the proposed method to be used in situations where the halftone dots cannot be produced smaller than a specific size is also proposed and examined. This modified version of the method can be useful for flexography, where the dots normally cannot be produced smaller than a critical size.
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| 3. |
- Gooran, Sasan, 1965-
(författare)
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Dependent color halftoning : Better quality with less ink
- 2004
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Ingår i: Journal of Imaging Science And Technology. - 8750-9237. ; 48:4, s. 354-362
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Tidskriftsartikel (refereegranskat)abstract
- When a color image is halftoned its color channels are normally halftoned independently. The dots in different channels are placed independent of each other and consequently the final result may not be of high quality even if a. well performing monochromatic halftoning method has been used. In this article we propose a method that halftones the channels of the color image in a context dependent manner. Since the yellow ink on a white paper is hardly visible, only cyan and magenta separations need to be halftoned dependently. We also show that dependent color halftoning not only increases the halftone image quality but also decreases the amount of ink needed to reproduce different colors.
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| 4. |
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| 5. |
- Tran, Linh Viet, et al.
(författare)
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Kernel density estimators for hue based image retrieval
- 2005
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Ingår i: Journal of Imaging Science And Technology. - 8750-9237. ; 49:2, s. 185-188
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Tidskriftsartikel (refereegranskat)abstract
- Color is widely used for content-based image retrieval. In these applications the color properties of an image are characterized by the probability distribution of the colors in the image. These probability distributions are very often estimated by histograms although the histograms have many drawbacks compared to other estimators such as kernel density methods. In this article we investigate whether using kernel density estimators instead of histograms could give better retrieval results based on hue descriptors of color images. In this article we introduce the Fourier series coefficients as descriptors of hue distributions. We argue that under certain conditions these coefficients are optimal in a least squared error sense. We will also apply Parseval formula to compute the similarity of two distributions directly from these Fourier coefficients. Our experiments show that this modification of the kernel based similarity estimation has better retrieval performance than the histogram methods and we will also show that the method is insensitive to parameter changes as long as they are selected in a reasonable range. © 2005, IS&T - The Society for Imaging Science and Technology.
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| 6. |
- Yang, Li, 1961-
(författare)
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A unified model of optical and physical dot gain in print color reproduction
- 2004
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Ingår i: Journal of Imaging Science And Technology. - 8750-9237. ; 48:4, s. 347-353
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Tidskriftsartikel (refereegranskat)abstract
- A unified model coping with both physical and optical dot gains on print color tone reproduction is proposed. The physical dot gain, is approximated by a quadratic function of nominal dot percentages. The function, for each color, is characterized by a single parameter depending on printing technologies as well as ink-paper interactions, and has a symmetric form around where the nominal dot percentage is 50%. The parameter can be derived from the best fit for the model to measured data, such as spectral reflectance values or CIEXYZ tristimulus values. Applications to a color laser printer (on office copy paper) reproduces the experimental dot gain curves fairly well. Dependence on physical dot percentage, a summation of the nominal dot percentage and the corresponding physical dot gain, results in the optical dot gain and in turn the overall dot gain asymmetric forms, plotted against the nominal dot percentages. Furthermore, theoretical analysis reveals fundamental differences between physical and optical dot gains. Therefore, effects of optical dot gain can not be accurately represented by any physical extension in printing practices.
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| 7. |
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| 8. |
- Yang, Li, et al.
(författare)
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Simulation of optical dot gain in multichromatic tone production
- 2001
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Ingår i: Journal of Imaging Science And Technology. - 8750-9237. ; 45:2, s. 198-204
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Tidskriftsartikel (refereegranskat)abstract
- Optical dot gain (light scattering or Yule-Nielsen effect) is an important effect influencing the quality of tone reproductions. Based on probability descriptions on the light scattering, a framework is established for describing this effect on the reflectance and color appearance of a chromatic halftone image. General expressions for the reflectance and CIEXYZ tristimulus values have been derived. Simulations for images printed with 2 inks have been carried out by applying Gaussian type of point spread function (PSF). Dependence of the optical dot gain on the optical properties of substrate and inks, the dot geometry etc., have been studied in detail.
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| 9. |
- Yang, Li, 1961-
(författare)
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Spectral model of halftone on a fluorescent substrate
- 2005
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Ingår i: Journal of Imaging Science And Technology. - 8750-9237. ; 49:2, s. 179-184
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Tidskriftsartikel (refereegranskat)abstract
- The color rendition of a halftone image depends on, among other things, physical and optical dot gains and fluorescence of substrates. A unified model describing spectral reflectance of a print is proposed with consideration of these effects. In this model the effects of either physical or optical dot gain are characterized by a single parameter, while those of fluorescence by two sets of spectral parameters, one for fluorescence of bare paper and one for fluorescence of a print solid. This model is tested and further illustrated with applications to images generated by a laser color printer on ordinary office papers. © 2005, IS&T - The Society for Imaging Science and Technology.
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