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標題: 彩色至灰階影像轉換之研究
The Study of Color to Gray-Scale Image Transform
作者: 賁致修
Pen, Chih-Hsiu
關鍵字: 彩色至灰階轉換;Color-to-grayscale conversion;對比增強;contrast enhancement
出版社: 電機工程學系所
引用: [1]Metzger, W.: Laws of Seeing. The MIT Press, Cambridge (2006) [2]Gilchrist, A., Kossyfidis, C., Bonato, F., Agostini, T., Cataliotti, J., Li, X., Spehar, B., Annan, V., Economou, E.: An anchoring theory of lightness perception. Psychol. Rev. 106, 795–834 (1999) [3]Wyszecki, G., Stiles, W.: Color Science, Concepts and Methods, Quantitative Data and Formulae. Wiley, New York (2000) [4]Cadik, M.: Perceptual evaluation of color-to-grayscale image conversions. Computer Graphics Forum 27(7), 1745–1754 (2008) [5]David, H.: The Method of Paired Comparisons. Oxford University. Press, London (1988) [6]Bala, R., Eschbach, R.: Spatial color-to-grayscale transform preserving chrominance edge information. In: Color Imaging Conference,IS&T—The Society for Imaging Science and Technology,pp. 82–86 (2004) [7]Grundland, M., Dodgson, N.: Decolorize: fast, contrast enhancing, color to grayscale conversion. Pattern Recogn. 40(11), 2891–2896(2007) [8]Gooch, A., Olsen, S., Tumblin, J., Gooch, B.: Color2gray: salience-preserving color removal. ACM Trans. Graph. 24(3), 634–639 (2005) [9]Kim, Y., Jang, C., Demouth, J., Lee, S.: Robust color-to-gray via nonlinear global mapping. ACM Trans. Graph. 28(5), (2009) [10]Kuhn, G.R., Oliveira, M.M., Fernandes, L.A.F.: An improved contrast enhancing approach for colortograyscale mappings. Vis. Comput. 24(7), 505–514 (2008) [11]Wu‧J,Shen‧X,Liu‧L:Interactive two-scale color-to-gray.In:Springer-Verlag (2012) [12]Neumann, L.Cadik, M., Nemcsics, A.: An efficient perceptionbased adaptive color to gray transformation. In: Proceedings of Computational Aesthetics 2007, pp. 73–80. Eurographics Association, Banff (2007) [13]Rasche, K., Geist, R., Westall, J.: Detail preserving reproduction of color images for monochromats and dichromats. IEEE Comput. Graph. Appl. 25(3), 22–30 (2005) [14]Rasche, K., Geist, R., Westall, J.: Re-coloring images for gamuts of lower dimension. Comput. Graph. Forum 24(3), 423–432(2005)

Most methods that convert color images to grayscale images use the intensity value directly for the converted grayscale value. When two pixels have different colors but the same intensity values, the conversion causes the original contrast to disappear. In addition, human visual system has a tendency of regarding regions with similar colors or structures as a whole.

To solve the aforementioned problem and incorporating the characteristics of the human visual system into the color conversion, this thesis proposes a color-to-grayscale conversion method that considers the influence between image blocks. The method divides an image into several different blocks to calculate an overall grayscale value for each block. Then, it uses the color of a pixel and the probability that a pixel belongs to each block to better differentiate each pixel after grayscale conversion.

The first step is to divide an image into two blocks. The grayscale value of each block is calculated by minimizing the energy of the difference between the grayscale value after conversion and the color distance before conversion. The second step further divides each block into two subblocks. Each pixel in a subblock is paired with a representative pixel in another subblock. Two weights for the chrominance values are calculated by minimizing the energy of color distances before and after conversion. In the third step, the grayscale value for each block is calculated by combining the grayscale value calculated in the first step, the weighted chrominance values calculated in the second step, and the difference between the intensity values before and after conversion. Finally, the grayscale value for each block is multiplied by the probability that a pixel belongs to each block to form the final grayscale value.

In the experiments, we find that adjusting a parameter in the first step increases the contrasts among different blocks. On the other hand, the probability that a pixel belongs to each block cannot be too small or too large because it makes the influence among block either too weak or too strong. The experimental results show that the method can be adjusted to fit different conversion needs.
其他識別: U0005-1507201314395000
Appears in Collections:電機工程學系所

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