Research And Implementation On A Material Light Measurement System Basde On Hemispherical Model

Realistic rendering effect has been one of the core content of computer graphics,mainly used in virtual reality,video effects,graphics simulation,advertising,computer games,etc.How to achieve photo-level renderings is a hot topic in rendering in recent years.Material is a combination of surface visual attributes,including the surface of the color,texture,smoothness,transparency,reflectivity and refractive index,etc.Rendering is to transform the shots,which composed of points of view,the light source,3D scene,character,material,into a highly realistic continuous frame,by simulating the physical process of the light propagation in the 3D scene.Because different materials,that have different types,properties or texture,will produce different rendering effects,more realistic material library must be used for rendering,in order to achieve photo-level renderings.The measurement of realistic material refers to capture all kinds of information of the material in the real world through the material acquisition system.Those information will be stored into the bidirectional texture function,in order to construct a BTF material library based on measurement.Through the rendering engine,the three-dimensional model is rendered using the obtained bidirectional texture function,so that it can realistically represent real-world objects and scenes.In recent years,more and more BTF material libraries are built to provide realistic rendering services in universities domestic and foreign.Those BTF material acquisition systems existed have the same principles,but they have different structure and emphases.This article selected topics from the National 863 Program "research and application of photorealistic rendering system" project and the National Natural Science Foundation Project "physical material light modeling and measurement method research".The hemispherical material light measurement system,which performing lighting measurement for objects that existed in the real world by constructing various lighting characteristics,is a system integrated with software and hardware.This system can efficiently acquire the state of the upper hemisphere of one object,utilizing multiple measurements at different angles of the same material.After that,it will build a physical material model in the computer to obtain data of the material model.At last,these data will attach to the surface of a virtual 3D object to show a highly realistic rendering effect.This system now is applied to various fields,including product design,apparel design,digital media design,etc.The main content of this paper is describing the design and implementation of the hemispherical pattern material light measurement system.Then putting forward the device of hemispherical mode material light measurement and its method of material collection and measurement.This paper focuses on key issues that restrict the application of multi-camera measurement in the field of realism modeling.Building the equipment and its shooting environment of the hemispherical material light measurement,following connecting the CNC system to control equipment shooting objects in the real world.Designing the material acquisition methods and processes in multi-angle and multi-lighting condition,then optimizing it.Completing continuous acquisition mode and custom acquisition mode.Achieving the pre-requisite work for collecting target material via system control and physical implementation,including camera detection and correction,light initialization and switch control,light source color temperature experiment,light source correction,calibration of camera and light source shooting ambient irradiance,etc.The analysis of this paper focuses on parameter selection and data transmission.Among them,the image information of the target under various light characteristics is get.BTF data is processed,and geometric feature is extracted.Photo-level rendering effect is obtained using different rendering methods.