粉蠟筆畫下寬疏筆觸效應觀察研究

Abstract

本論文提出一個更真實模擬粉蠟筆寬疏筆觸的繪圖模擬方法。探討如何利用顏色變化來尋找出符合人類視覺的筆觸分區與修正蠟筆附蠟公式，進而呈現更真實的粉蠟筆寬疏筆觸。做法主要如下： 1. 將輸入圖像顏色分層簡化，並修正分層不佳的狀況 2. 將輸入圖像利用本系統提出的綜合方法，依照顏色變化程度分成三種筆觸區，分別對應寬疏筆觸、中筆觸與細筆觸。 3. 各種筆觸個給予一種角度，並加入人類作畫會有的隨機抖動產生筆觸軌跡 4. 依據筆觸軌跡並利用本系統的蠟筆附蠟模擬進行作畫，並對寬疏筆觸的效果做進一步的調整。 本論文所提出之方法處裡的圖片，其在背景區域的寬疏筆觸呈現效果令人滿意，符合真實粉蠟筆作畫時蠟筆橫持繪畫出的寬疏筆觸現象。

This thesis addresses three problems remaining in two pastel drawing simulating systems developed respectively in 2013 and 2014, during which issues that may incur in the simulation were explored and initial attempts of resolution were made, some of which without much success.

The major defect in the previous drawing manifested in the presentation of wide and long strokes, in sparse distribution and lighter shades, over the areas in the scene where color/shade variation being deemed as visually unperceivable. To be specific, the thesis tries to resolve the following 3 issues: (1) Applying wide pastel strokes with visually satisfying width, length and spacing in between over ‘low contrast’ areas in an image; (2) Identifying areas in an image, in a way more consistent with what would have been done in hand drawings, over which the wide pastel strokes in to be applied to; (3) Applying lighter shades of wide pastel strokes visually similar to the effect of wiping the paper very lightly and swiftly with a pastel

For (1), measures undertaken in the two piloting systems were discarded and an approach borrowed from a referential survey proved to be satisfactory. For(2), image segmentation in HSV color space used in the piloting systems are incorporated with two complementary segment measures in grey-level space, eliminating difficulties encountered in color space quantization over vast low color-contrast areas in the images (the blue sky, out-of-focus zones, etc.). For (3), instead of decreasing degree of saturation to make a shade(color) look lighter, as done in the old, an alternative without lowing color saturation was exploited with visual satisfaction. In all, the system proposed in the thesis achieves the wide-band pastel drawing effect visually similar to that by a hand-held piece of pastel butt sweeping very gently across the paper with its longitudinal section.