## 1 Introduction  
Because industrial metals are usually composed of a large number of crystal grains with anisotropic elasticity and plasticity, an inhomogeneous microscopic deformation occurs as a result of external mechanical loads and internal thermal stresses. The development of inhomogeneous deformation causes various damages, such as localized plastic deformation, surface roughness, microcracking, and necking. It is therefore important to investigate microscopic elastic and plastic deformation behaviors. Recently, experimental and analytical methods for inhomogeneous deformation of metals have progressed remarkably. The first is the electron backscatter diffraction (EBSD) method, by which the distribution of crystal orientation on the surface of the specimen is acquired [1]. The misorientation of each grain and the Schmid factor, which is defined as the normalized shear stress on a slip plane assuming that the stress is uniform throughout the material, are good indicators of the activity of crystallographic slip. The second one is the digital image correlation (DIC)method. The strain on surface grains can be evaluated based on the digital images acquired before and after deformation [2]. Currently, DIC is widely used as a powerful contactless method for the evaluation of the deformation of materials. The third method is crystal plasticity finite element (CPFE) analysis [3]. If the geometry and crystal orientation of grains are known, it is possible to simulate their elastic and plastic deformation with CPFE analysis, where the elastic deformation is expressed by the generalized Hooke's law, and the plastic deformation is assumed to occur by a combination of crystallographic slips on planes with high-resolved shear stress. Several studies have used these methods. For example, [PERSON] et al. carried out tensile tests on dog-bone aluminum specimens with enlarged crystal grains, and simulated the microscopic deformation behavior using the three-dimensional CPFE analysis [4]. As the number of grains in the specimen was not very large, the crystal orientation and geometry of all grains in the specimen were measured and modeled. Deformation and surface roughness were well simulated by the analysis, but the agreement was not perfect. The main reason for the difference seems to be imperfect modeling of grain geometry inside the specimen, which caused variable stress distribution in the material. Regarding normal polycrystalline metals, complete three-dimensional measurement and analysis of grains is still very difficult. [PERSON] et al. simulated the heterogeneous deformation of pure titanium using the CPFE method [5; 6]. The crystal orientation of surface grains was measured using the EBSD method, and a quasi-three-dimensional model was generated. Microscopic plastic deformation and slip activities were also simulated. However, the agreement was unsatisfactory because the simulation did not consider the crystal orientation or geometries of grains underneath the specimen surface. The importance of subsurface grains in the deformation of surface grains has also gained attention due to precursory finite element analyses by [PERSON] et al. [7]. More-accurate comparisons between the CPFE method and experiments, using high-resolution DIC, were performed for small specimens of tantalum oligocrystals by [PERSON] et al. [8]. It was concluded that an accurate reproduction of the initial microstructure and proper modeling of the grain boundary properties are very important for simulating the deformation behavior of oligocrystals, including the regions adjacent to the grain boundaries. Recently, DIC has been used for small specimens deformed in the scanning electron microscope (SEM) [9; 10; 11; 12]. High-resolution SEM images enable us to evaluate the in-plane strain tensors of specimen surfaces during loading. Further, crystallographic investigations are also possible, with the help of EBSD data. Various methods for minimization of image distortion and noise reduction have been proposed, which have greatly improved accuracy.