彩色線條塗鴉藝術是一種線條畫的藝術風格：在微觀之下，多層次、無固定形狀、雜亂無章且各種單一顏色的塗鴉線條交疊在一起；在巨觀之下，它卻能表現出令人驚艷的彩色影像。在本研究中，我們提出了一套系統，透過決定塗鴉線條的調色盤顏色與排程線條塗鴉的圖層疊合順序，來合成彩色線條塗鴉藝術畫。我們從原始影像中分析塗鴉線條的調色盤顏色：先透過群集演算法與排序法將每個像素顏色分群排序後，得到數個彩色坡度漸層，再從漸層色中取出數個代表色，以作為重製坡度漸層的基本調色盤顏色。在本系統中的彩色線條塗鴉遞色技術中，我們最佳化了原始彩色坡度漸層色與使用調色盤顏色作為基本色來重製後的漸層顏色之顏色相似性。彩色線條塗鴉遞色技術透過使用了多個圖層的方式，在每個圖層中使用不同單色的塗鴉線條，層層疊加來實現。在研究結果中可以看出，經由我們的系統來產生之彩色線條塗鴉藝術影像，能夠有效的表現出彩色線條塗鴉藝術畫家所展現之藝術風格。

Color circular scribble art is an artistic line drawing form where the multi-layered, shapeless, disorderly, and mono-colored scribbles overlap together at microscopic scale and reveal astonishing colorful images at macroscopic scale. In this thesis, we propose a system to synthesize color circular scribble art through the determination of suggested palette colors and a scheduled drawing sequence to overlay layers of mono-colored scribbles to achieve a color circular scribble image. Color palette is generated through an analysis of the input color image. By clustering and sorting of each color pixels, color ramps are derived for selecting representative base colors in color scribbling and also in determining the combination of base colors to synthesize the remaining ramp colors. Our system optimized the color similarity through a novel color scribble dithering method with the representative base colors. The color scribble dithering is achieved by layering the selected based colors in a form of circular scribbles. The results shows that the generated color circular scribble images are comparable to those artworks created by skilled scribble artists.

[1] Chun-Chia Chiu, Yi-Hsiang Lo, Ruen-Rone Lee, and Hung-Kuo Chu. Tone-and featureaware circular scribble art. In Computer Graphics Forum (Proc. Pacific Graphics), volume 34, 2015.
[2] Alexei A Efros and William T Freeman. Image quilting for texture synthesis and transfer. In Proceedings of the 28th annual conference on Computer graphics and interactive techniques, pages 341–346. ACM, 2001.
[3] Theophano Mitsa and Kevin J Parker. Digital halftoning technique using a blue-noise mask. JOSA A, 9(11):1920–1929, 1992.
[4] Daniel L Lau, Gonzalo R Arce, and Neal C Gallagher. Green-noise digital halftoning. Proceedings of the IEEE, 86(12):2424–2444, 1998.
[5] Murat Mese and PP Vaidyanathan. Recent advances in digital halftoning and inverse halftoning methods. IEEE Transactions on Circuits and Systems I: Fundamental Theory and Applications, 49(6):790–805, 2002.
[6] Wai-Man Pang, Yingge Qu, Tien-Tsin Wong, Daniel Cohen-Or, and Pheng-Ann Heng. Structure-aware halftoning. ACM Transactions on Graphics (SIGGRAPH 2008 issue), 27 (3):89:1–89:8, 2008.
[7] Ignacio Ascencio-Lopez, Oscar Meruvia-Pastor, and Hugo Hidalgo-Silva. Adaptive incremental stippling using the poisson-disk distribution. Journal of Graphics, GPU, and Game Tools, 15(1):29–47, 2010.
[8] Adrian Secord. Weighted voronoi stippling. In Proceedings of the 2nd international symposium on Non-photorealistic animation and rendering, pages 37–43. ACM, 2002.
[9] Seok Jang and Hyun-Ki Hong. Stippling technique based on color analysis. In Pacific-Rim Conference on Multimedia, pages 782–793. Springer, 2005.
[10] Xiaolin Wu. Color quantization by dynamic programming and principal analysis. ACM Transactions on Graphics (TOG), 11(4):348–372, 1992.[11] R. W. Floyd and L. Steinberg. An adaptive algorithm for spatial greyscale. In Society for Information Display, volume 17, pages 75–77, 1976.
[12] Victor Ostromoukhov. A simple and efficient error-diffusion algorithm. In Proceedings of the 28th annual conference on Computer graphics and interactive techniques, pages 567–572. ACM, 2001.
[13] Jan Puzicha, Marcus Held, Jens Ketterer, Joachim M Buhmann, and Dieter W Fellner. On spatial quantization of color images. IEEE Transactions on Image Processing, 9(4): 666–682, 2000.
[14] Hao-Zhi Huang, Kun Xu, Ralph R Martin, Fei-Yue Huang, and Shi-Min Hu. Efficient, edgeaware, combined color quantization and dithering. IEEE Transactions on Image Processing, 25(3):1152–1162, 2016.
[15] Aaron Hertzmann, Charles E. Jacobs, Nuria Oliver, Brian Curless, and David H. Salesin. Image analogies. In Proceedings of the 28th Annual Conference on Computer Graphics and Interactive Techniques, SIGGRAPH ’01, pages 327–340, 2001. ISBN 1-58113-374-X.
[16] Emil Praun, Hugues Hoppe, Matthew Webb, and Adam Finkelstein. Real-time hatching. In Proceedings of the 28th annual conference on Computer graphics and interactive techniques, page 581. ACM, 2001.
[17] Paul Heckbert. Color image quantization for frame buffer display, volume 16. ACM, 1982.
[18] Michael Gervautz and Werner Purgathofer. A simple method for color quantization: Octree quantization. In New trends in computer graphics, pages 219–231. Springer, 1988.
[19] Holger Winnemöller, Sven C Olsen, and Bruce Gooch. Real-time video abstraction. In ACM Transactions On Graphics (TOG), volume 25, pages 1221–1226. ACM, 2006.
[20] Yuri Boykov, Olga Veksler, and Ramin Zabih. Fast approximate energy minimization via graph cuts. IEEE Transactions on pattern analysis and machine intelligence, 23(11): 1222–1239, 2001.
[21] Yuri Boykov and Olga Veksler. Graph cuts in vision and graphics: Theories and applications. In Handbook of mathematical models in computer vision, pages 79–96. Springer, 2006.