汉代建筑画像石的频率域自适应分解数字修复技术

摘要

画像石作为汉代石质建筑构件,其刻画的内容包含丰富的建筑题材,是古建研究的重要参考资料.画像石经历两千多年各种病害侵蚀,导致其画面信息残缺不全,继续恶化将会使画像石所传承的历史信息消失殆尽.因此急需利用现有残存信息进行画面内容复原,重建完整的汉代画像石图像.数字修复是种非接触无损信息补全技术,可从能量泛函与纹理合成两个角度对缺失信息进行数字填充.但是任意单一方案均难以满足汉代画像石修复既要结构信息过渡自然又要保证纹理细节的质感的需求.频率域自适应分解数字修复技术,将汉代画像石图像在频率域DCT分解为纯结构与纯纹理两部分,分别用CDD曲率扩散技术重建结构信息;用Criminis样本块合成技术重建纹理信息;并将二者IDCT重构以获得最终修复效果.数字修复过程中,用Contourlet轮廓波系数计算前景、背景、雕刻和病害四种不同对象的纹理能量参数E.针对不同E值范围,对DCT分解位置、CDD曲率点扩散方向以及Criminisi合成样本大小等技术指标进行自适应动态调整.该技术充分考虑了汉代画像石复杂的缺损机制,相比固定分解位置和单一的扩散方向及不变的样本尺寸,其修复过程更加灵活,仿真实验结果更加符合格式塔视觉心理学原则.其数字修复结果作为实体修复的效果图,可避免直接修复对汉代画像石造成的二次损害.%As the Han Dynasty building components,the stone relief expresses the traditional architecture figures which have important information for the architects to research.More than two thousand years past,the information has been missing on and on.It is accurately needed to reconstruct the missing information.The left info includes lots of texture info and structure info.Digital image inpainting is a new technology that can restore the missing information without touching the real stone relief.But it is difficult to repair both structure info and texture info in the same time nether using neither PDE nor exemplar synthesis.DCT is used in adaptive frequency decomposed inpainting to decompose the stone relief image into pure structure part and pure texture part,then inpaint the structure info using CDD and inpaint the texture info using Criminis's exemplar synthesis.Finally IDCF the two parts together to get the total result.When the Han dynasty relief is inpainted,Contourlet coefficient is used to design an energy parameter to calculate the texture complexity value of foreground,background,embossed and crack blocks.And then is (E) used (E) to choose a perfect decompose position adaptively.The energy parameter (E)also helps to choose the order of CIDD diffusing and the size of exemplar patches adaptively.The result of digital inpainting is more active than the methods which have invariant decompose position,diffusing order and exemplar size.It obeys the principle of Gestalt and can be used as an effect picture to repair the real Han dynasty stone relief,this can protect the relief from second time damage when it is repaired directly.