苗腾, 许童羽, 邓寒冰, 周云成, 徐静, 于越. 单图像的植物器官表观纹理生成系统研发[J]. 农业工程学报, 2020, 36(7): 208-216. DOI: 10.11975/j.issn.1002-6819.2020.07.024
    引用本文: 苗腾, 许童羽, 邓寒冰, 周云成, 徐静, 于越. 单图像的植物器官表观纹理生成系统研发[J]. 农业工程学报, 2020, 36(7): 208-216. DOI: 10.11975/j.issn.1002-6819.2020.07.024
    Miao Teng, Xu Tongyu, Deng hanbing, Zhou yuncheng, Xu jing, Yu yue. Development of an appearance texture generation system for single plant organ image[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2020, 36(7): 208-216. DOI: 10.11975/j.issn.1002-6819.2020.07.024
    Citation: Miao Teng, Xu Tongyu, Deng hanbing, Zhou yuncheng, Xu jing, Yu yue. Development of an appearance texture generation system for single plant organ image[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2020, 36(7): 208-216. DOI: 10.11975/j.issn.1002-6819.2020.07.024

    单图像的植物器官表观纹理生成系统研发

    Development of an appearance texture generation system for single plant organ image

    • 摘要: 为提高农业题材三维数字媒体内容制作效率,解决植物器官表观纹理制作流程繁琐的问题,研发了基于单图像的植物器官表观纹理生成系统。该系统分为漫反射强度纹理、透射纹理、高光纹理、法向量贴图、环境遮蔽图以及表观纹理实时可视化6个模块。漫反射强度纹理生成模块采用基于能量约束的本征图像分解方法将植物器官图像分解为漫反射纹理以及光照图;透射纹理生成模块以PROSPECT模型为理论基础,反演植物叶片透射与反射的统计学关系,利用漫反射纹理生成透射纹理;高光参数纹理生成模块采用交互式操作,基于用户对少量样本点的高光表观参数设定,根据概率插值出整个器官表面的高光参数,进而形成高光强度纹理和粗糙度纹理;法向量贴图模块在阴影恢复形状技术的基础上,综合低频和高频特征生成法向量贴图;环境遮蔽图生成模块通过简单的亮度倍增操作,将光照图转换成环境遮蔽纹理;表观纹理实时可视化模块利用上述生成的表观纹理进行实时的器官三维渲染,为用户提供反馈。系统仅需调节3个参数即可生成6种样式丰富的器官表观纹理,操作简捷,自动化程度高。在处理512×512分辨率的图像时,生成6种表观纹理的总计算时间小于8 s。结果表明,该系统可以通过简单的操作,高效生成三维植物可视化中常用的表观纹理,为农业题材的三维数字资源开发提供技术工具。

       

      Abstract: Abstract: This paper presents a plant organ appearance textures generation system using a single image to improve the efficiency of three-dimensional digital media content production and simplify the tedious process of producing the textured appearance of plant organs in images. The system consists of six modules: diffuse reflection texture, transmittance texture, specular textures, normal map, ambient occlusion (AO) map and real-time visualization. The system takes a single organ texture as input. Firstly, the input texture is decomposed into diffuse reflection texture and shading texture by the diffuse reflection texture module. The two textures thus obtained are also used as input images for other modules. Diffuse reflection texture module adopts an energy constrained intrinsic decomposition method, which is stable and quick. The transmittance texture module can transform a diffuse reflection texture into a transmittance texture. The core of the module is a transmittance empirical model based on the PROSPECT model, which is a widely used leaf-scale radiation transfer model. To obtain this empirical model, we first generate the spectral data of leaf reflectance and transmittance under different parameters by PROSPECT model and transform them into RGB color space. Then we invert the statistical formula of plant leaf transmittance and reflection by using weighted least squares regression. The formula yields the transmittance color by diffuse reflection color. Specular intensity and roughness parameter describe the directional characteristics of leaf surface reflection. In theory, these two parameters can't be accurately calculated from a single image. Therefore, specular textures module focuses on providing users with an interactive tool to speed up the generation of textures. We assume that the materials of leaf-blade regions that show similar diffuse reflectance are similar, as are their specular parameters. Therefore, in the specular textures module, the user interactively selects some sample points on the diffuse reflection texture, sets the specular intensity parameter and roughness parameter for these points, and then calculates these two specular parameters on the basis of the diffuse similarity between the other positions on the diffuse reflection texture and the selected sample points. Normal map module uses shading map to estimate a normal map. First, the shape from shading technique based on linear approximation is used to estimate the relative height of the organ surface from the shading map. Second, the organ surface height is filtered by Gauss blur to obtain the low-frequency features on the organ surface height. We estimate two normal maps by low frequency height feature and original height feature respectively. We overlay the two normal maps by linear interpolation to obtain the final normal mapWe observed that the concave and convex areas on the organ surface formed shadows in the shading map and these could be used as environmental shadows. Therefore, the system uses an illumination map S to generate a simple AO map. First, the brightness of the shading map is enhanced, and then, Gauss blur is used to get the final AO map. To facilitate users to evaluate the quality of the final product, that is the appearance of the texture, the real-time visualization module loads the generated appearance of the texture for real-time rendering to provide the users the WYSIWYG three-dimensional visualization results. Experiments show that our appearance of texture matches the appearance parameters in the three-dimensional rendering formula and can be directly applied to the generation of realistic digital images of plants in three-dimensional visualization software. Compared to the current commercial texture production software, the texture style generated by this system is more comprehensive, more in line with the production needs of digital images of plants, and more automated and user-friendly. It meets the need for rapid and accurate rendering of the textured appearance of plant organs and provides a technical tool for the development of three-dimensional digital image resources of agricultural specimens.

       

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