三維模型之鉛筆畫風格非相片寫實繪圖技術

Abstract

本文提供一套鉛筆畫風格的繪圖系統，表現三維實體的邊界面模型，以鉛筆畫型態呈現，配合電腦與繪圖介面讓使用者可即時互動，使用者可以即時任意轉動、拉遠、拉近此模型，並透過貼圖參數與筆觸的調整，選擇喜好的效果。 本文將整個顯像的過程分成兩大部份：(1)物體特徵線的產生與筆觸表現。(2)表現物體可見表面的影線法著色。在製作鉛筆畫的過程中，先依據使用者的視角即時找出代表三維物體的特徵線，其包含褶皺、輪廓與邊界線，配合連接特徵線的機制將之連成較長線條，最後藉由線條中的控制點與使用者設定的寬度計算筆觸外型，並使用鉛筆畫線條的圖片與貼圖技術形成鉛筆筆觸的紋路。在物體表面著色的過程，先計算組成物體表面網格，從每個網格頂點的主切線方向，使用影線法多重貼圖與三角混色法跟卡通渲染法在網格內處理貼圖效果，擴及全部表面而產生鉛筆畫的陰影效果。

This paper presents a pencil painting style rendering for non-photorealistic 3D surface models with the computer graphic interface . The user can arbitrary rotate, zoom out , and zoom in the model. By adjustment of the texture parameter and the thickness of the bush stroke, the user can design the styling of the rendering as he likes. The process of this rendering system is divided into two stages: Stage 1: Determine the characteristic lines of the model and the presentation of the brush strokes. Stage 2: Present surface shading of the model. The characteristic lines of the 3D model are traced from the triangles mesh to meet the user’s visual angle first , which include crease lines ,silhouette lines and boundary lines , then the short characteristic lines are connected to longer lines . Finally, the outlines of the strokes are counted according to the control points and the width that the user defined. The pencil style painting with the texture mapping technique is designed to form the brush strokes. In the surface shading stage, we calculate the main tangent directions of vertexes of model meshes, and the techniques which produce the shadow including hatching, multitexture , 3-way blending and toon-shading are applied to the pencil style painting for every individual mesh of all surfaces. Finally , the rendering of whole picture will be established.