結果討論

在我們的研究方法中，彩色影像分割的結果影響輸出點畫細緻度的程度很大，尤 其在漸層的部分，如下圖 38 的天空部分，圖(a)的分割明顯比圖(b)粗糙，因此在漸層的 部分表現較差。

(a)

(b)

圖 38 (a) (h_s,h_r,m)(7,.5,20)。(b) (h_s,h_r,m)(20,2,15)

62 Spectrum）的測試，如圖 39，結果發現秀拉的色點並非是完美的藍雜訊性質，而是較 符合隨機卻不均勻分布的白雜訊（White Noise）性質。我們認為其原因在於秀拉作畫時，

63

改變，因此在分析光暈的研究上，目前我們並沒有想到一個較準確的實現辦法。而若要 以主觀判斷來增加光暈，我們目前可以以手動方式直接修改輸入圖片在邊緣位置的亮度 及色相來達成，如圖 41。

最後，本論文採用我們在第三章所建立的色彩統計模型的一個限制是，我們目前 的方法，如果在著色步驟時，搜尋到兩個以上與目標顏色最相似的代表色，其組成色並 不相同，則我們無法判斷出哪一個代表色的顏色組成方式與目標影像的整體顏色最為搭 配。若有此情況發生，我們則利用隨機的方式決定要採用的代表色。另外，因為我們已 對秀拉的點畫進行事前處利並儲存分析結果，此色彩統計模型為一個短期內無法更新的 固定資訊，因此對於大部分的狀況而言，同一個代表色的顏色組成只會有一種，無法隨 著不同影像的色調風格而改變其組成結構。

(a)

64

(b)

(a) (b) (c)

圖 40 (a)「馬戲團」局部圖，小丑的紅色頭髮在上方有明顯的深藍色光暈，但在同樣 背景的左側頭髮邊緣部分卻完全沒有光暈。(b)「大捷特島的星期日下午」局部圖，後方 穿西裝的男人與淺綠色草地有明顯的邊緣，卻沒有光暈；在前方的男人的深色帽子與後 方男人的深色西裝交界處有明顯的白色光暈，但是在加上光暈之前，此交界處的邊緣性 質十分不明顯。(c)「女模特兒」局部圖，在同樣的背景之下，右邊的女人與背景有著紫 色的光暈，而左邊的女人與背景卻是白色的光暈。

65

(a) (b)

(c) (d)

圖 41 手動增加光暈結果。(a)為原始圖片，(b)為利用繪圖軟體手動增加光暈的影像。(c) 和(d)分別為(a)和(b)的點畫結果。

66

第六章

貢獻與未來展望

6.1 貢獻

本論文提出了一個簡單而直覺的新方法來模擬藝術家點畫的顏色組合習慣與著色 方式。在前處理方面，我們分析了藝術家真實點畫的著色習慣與結構，避免產生不必要 的補色效果，並藉由學習這些收集來的資訊創造出藝術家沒有使用到的顏色，以及模擬 這些新顏色的組成結構，也建構了色彩統計模型儲存各種顏色組合資訊供查詢使用，以 符合能輸入任意彩色影像、並得到良好配色效果的標準。在方法上我們修改了多類藍雜 訊取樣的作法，配合彩色影像分割以及查詢前處理所建立的色彩統計模型，可以準確的 得知每個區域分割所要填入的顏色以及此顏色的組成結構與百分比密度，以完整的模擬 藝術家的著色習慣。在結構上，我們計算輸入影像的梯度方向與大小，並藉此調整色點 的旋轉方向以及排列方式，使得輸出的點畫結果保有良好的結構與邊緣特性。

6.2 未來展望

未來，我們希望可以更精確的分析由藝術家點畫收集而來的資訊，在產生藝術家 所沒有使用到的顏色時可以有更準確的定義方法，以完整的模仿藝術家的顏色組成結 構。另外，希望可以降低在彩色影像分割之後著色的不連續情形，使整體輸出點畫更加 流暢。最後，希望可以在實作方法上降低參數的設定量，使模擬過程更加自動化。

67

參考資料

[1] B. E. Bayer, "An optimum method for two level rendition of continuous tone pictures," IEEE International Conference on Communications, pp. 2611-2615, 1973.

[2] J. F. Jarvis, C. N. Judice, and W. H. Ninke, "A survey of techniques for the display of continuous tone pictures on bilevel displays," Computer Graphics and Image Processing, vol. 5, pp. 13-40, 1976.

[3] W. Floyd R, "An adaptive algorithm for spatial gray - scale," Proc.Soc.Inf.Disp., vol.

17, pp. 75-77, 1976.

[4] V. Ostromoukhov, "A simple and efficient error-diffusion algorithm," Proceedings of the 28th annual conference on Computer graphics and interactive techniques, pp.

567-572, 2001.

[5] M. P. Salisbury, M. T. Wong, J. F. Hughes, and D. H. Salesin, "Orientable textures for image-based pen-and-ink illustration," presented at the Proceedings of the 24th annual conference on Computer graphics and interactive techniques, 1997.

[6] A. A. Efros and W. T. Freeman, "Image Quilting for Texture Synthesis and Transfer,"

SIGGRAPH, 2001.

[7] A. Hertzmann, C. E. Jacobs, N. Oliver, B. Curless, and D. H. Salesin, "Image analogies," presented at the Proceedings of the 28th annual conference on Computer graphics and interactive techniques, 2001.

[8] Y. Chung-Ren, C. Ming-Te, L. Tong-Yee, and L. Wen-Chieh, "Stylized Rendering Using Samples of a Painted Image," Visualization and Computer Graphics, IEEE Transactions on, vol. 14, pp. 468-480, 2008.

[9] H. Lee, S. Seo, S. Ryoo, and K. Yoon, "Directional texture transfer," presented at the Proceedings of the 8th International Symposium on Non-Photorealistic Animation and Rendering, Annecy, France, 2010.

[10] O. Deussen, S. Hiller, C. V. Overveld, and T. Strothotte, "Floating Points: A Method for Computing Stipple Drawings," Computer Graphics Forum, vol. 19, pp. 41-50, 2000.

[11] Q. Du, V. Faber, and M. Gunzburger, "Centroidal Voronoi Tessellations: Applications and Algorithms," SIAM Review, vol. 41, pp. 637-676, 1999.

68

[12] A. Secord, "Weighted Voronoi stippling," presented at the Proceedings of the 2nd international symposium on Non-photorealistic animation and rendering, Annecy, France, 2002.

[13] S. Hiller, H. Hellwig, and O. Deussen, "Beyond Stippling — Methods for Distributing Objects on the Plane," Computer Graphics Forum, vol. 22, pp. 515-522, 2003.

[14] S. Jang and H.-K. Hong, "Stippling Technique Based on Color Analysis Advances in Multimedia Information Processing - PCM 2005." vol. 3768, pp. 782-793, 2005.

[15] C.-K. Yang and H.-L. Yang, "Realization of Seurat’s pointillism via non-photorealistic rendering," The Visual Computer, vol. 24, pp. 303-322, 2008.

[16] S. Seo and K. Yoon, "Color juxtaposition for pointillism based on an artistic color model and a statistical analysis," The Visual Computer, vol. 26, pp. 421-431, 2010.

[17] G. Arroyo, D. Martín, and M. V. Luzón, "A stochastic approach to simulate artists behaviour for automatic felt-tipped stippling," in Evolutionary Computation (CEC), 2010 IEEE Congress on, pp. 1-8, 2010.

[18] D. Roguljic and V. Papic, "Procedure for non-photorealistic rendering in pointillist style," in ELMAR, 2011 Proceedings, pp. 111-114, 2011.

[19] J. Hays and I. Essa, "Image and video based painterly animation," presented at the Proceedings of the 3rd international symposium on Non-photorealistic animation and rendering, Annecy, France, 2004.

[20] A. Hertzmann, "Painterly rendering with curved brush strokes of multiple sizes,"

presented at the Proceedings of the 25th annual conference on Computer graphics and interactive techniques, 1998.

[21] T.-Q. Luong, A. Seth, A. Klein, and J. Lawrence, "Isoluminant color picking for non-photorealistic rendering," presented at the Proceedings of Graphics Interface 2005, Victoria, British Columbia, 2005.

[22] S. Strassmann, "Hairy brushes," SIGGRAPH Comput. Graph., vol. 20, pp. 225-232, 1986.

[23] P. Haeberli, "Paint by numbers: abstract image representations," presented at the Proceedings of the 17th annual conference on Computer graphics and interactive techniques, Dallas, TX, USA, 1990.

[24] A. Hertzmann, "A survey of stroke-based rendering," Computer Graphics and Applications, IEEE, vol. 23, pp. 70-81, 2003.

69

[25] D. Kim, M. Son, Y. Lee, H. Kang, and S. Lee, "Feature-guided Image Stippling,"

Computer Graphics Forum, vol. 27, pp. 1209-1216, 2008.

[26] S. Y. Kim, R. Maciejewski, T. Isenberg, W. M. Andrews, W. Chen, M. C. Sousa, and D.

S. Ebert, "Stippling by example," presented at the Proceedings of the 7th International Symposium on Non-Photorealistic Animation and Rendering, 2009.

[27] M. D., "Stipple placement using distance in a weighted graph," Computational Aesthetics in Graphics, Visualization and Imaging, pp. 44-52, 2007.

[28] D. Martín, G. Arroyo, M. V. Luzón, and T. Isenberg, "Example-based stippling using a scale-dependent grayscale process," presented at the Proceedings of the 8th International Symposium on Non-Photorealistic Animation and Rendering, Annecy, France, 2010.

[29] A. Glassner, "Penrose tiling," Computer Graphics and Applications, IEEE, vol. 18, pp.

78-86, 1998.

[30] W.-M. Pang, Y. Qu, T.-T. Wong, D. Cohen-Or, and P.-A. Heng, "Structure-aware halftoning," presented at the ACM SIGGRAPH 2008 papers, Los Angeles, California, 2008.

[31] J. Chang, B. Alain, and V. Ostromoukhov, "Structure-aware error diffusion," presented at the ACM SIGGRAPH Asia 2009 papers, Yokohama, Japan, 2009.

[32] H. Li and D. Mould, "Contrast-aware Halftoning," Computer Graphics Forum, vol. 29, pp. 273-280, 2010.

[33] J. I. Yellott, "Spectral consequences of photoreceptor sampling in the rhesus retina,"

Science, vol. 221, pp. 382-385, 1983.

[34] S. Lloyd, "Least squares quantization in PCM," Information Theory, IEEE Transactions on, vol. 28, pp. 129-137, 1982.

[35] R. L. Cook, "Stochastic sampling in computer graphics," ACM Trans. Graph., vol. 5, pp. 51-72, 1986.

[36] M. Cohen, J. Shade, S. Hiller, and O. Deussen, "Wang Tiles for image and texture generation," in ACM SIGGRAPH 2003 Papers, San Diego, California, pp. 287-294 , 2003.

[37] A. Lagae and P. Dutré, "A procedural object distribution function," ACM Trans.

Graph., vol. 24, pp. 1442-1461, 2005.

[38] J. Kopf, D. Cohen-Or, O. Deussen, and D. Lischinski, "Recursive Wang tiles for

70

real-time blue noise," ACM Trans. Graph., vol. 25, pp. 509-518, 2006.

[39] V. Ostromoukhov, C. Donohue, and P.-M. Jodoin, "Fast hierarchical importance sampling with blue noise properties," ACM Trans. Graph., vol. 23, pp. 488-495, 2004.

[40] L.-Y. Wei, "Multi-class blue noise sampling," presented at the ACM SIGGRAPH 2010 papers, Los Angeles, California, 2010.

[41] D. Comaniciu and P. Meer, "Mean shift: a robust approach toward feature space analysis," Pattern Analysis and Machine Intelligence, IEEE Transactions on, vol. 24, pp. 603-619, 2002.

[42] B. Aslan and G. Zech, "Statistical energy as a tool for binning-free, multivariate goodness-of-fit tests, two-sample comparison and unfolding," Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, vol. 537, pp. 626-636, 2005.