Frequency signature analysis of samples from different image categories.

<p>The first column displays a sample image of monochrome graphic art (A), natural scenes from the Groningen database (F), face photographs (K), scientific illustrations (P), object photographs (U), cartoons (Z) and plant photographs (E'). The second column shows the corresponding power spectra (B, G, L, Q, V, A', F'). The low spatial frequencies are represented at the center and darker shades represent higher power. The sector parts shown schematically in <a href="" target="_blank">Fig. 2D</a> were analyzed. For all images in the same category, the three columns on the right side represent the mean power for each sector of the power spectrum (C, H, M, R, W, B', G'; for numbering of the sectors, refer to <a href="" target="_blank">Fig. 2D</a>); the mean sector slope values (D, I, N, S, X, C', H'); and the mean sector error of the line approximation (E, J, O, T, Y, D', I'). The whisker plots represent mean values and their standard deviation. The image shown in A is an engraving by the 15th century artist Martin Schongauer and was reproduced with permission from “Das Berliner Kupferstichkabinett”, Akademischer Verlag, Berlin, 1994 (inventory number: 916-2; © Staatliche Museen zu Berlin, Kupferstichkabinett). F displays an example from the Groningen database of natural scenes <a href="" target="_blank">[38]</a>. K is a photograph similar to those of the AR face database <a href="" target="_blank">[45]</a> and shows one of the authors (M.K.), to avoid conflicts with the rights of the persons photographed for the AR database. The scientific illustration in P, the object photograph in U, and the plant photograph in E' are from the study by Redies et al. <a href="" target="_blank">[12]</a>. Images are reproduced with permission from the authors. Z displays a propaganda cartoon from the Japan Times (from the year 1942; downloaded from Wikimedia Commons).</p>




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