RECONSTRUCTION OF WELD POOL SURFACE BASED ON SHAPE FROM SHADING

A valid image-processing algorithm of weld pool surface reconstruction according to an input image of weld pool based on shape from shading （SFS） in computer vision is presented. The weld pool surface information is related to the backside weld width, which is crucial to the quality of weld joint. The image of weld pool is recorded with an optical sensing method. Firstly, the reflectance map model, which specifies the imaging process, is estimated. Then, the algorithm of weld pool surface reconstruction based on SFS is implemented by iteration scheme and speeded by hierarchical structure. The results indicate the accuracy and effectiveness of the approach.

Research on an Algorithm of Shape from Shading

Shape from shading(SFS)is an important domain in computer vision.The paper presented an improved algorithm of shape from shading based on a single image according to an existed one.The presented algorithm enhanced the boundary constraints to eliminate the rotation distortion on the border of reconstructed object and introduced the factor of brightness error to weaken the influence irradiance equation’s nonlinearity on reconstructed errors.The reconstructed results verify the performance improvement in terms of accuracy by the input image of a synthetic image and a real image of weld.

Estimation of Illuminant Direction and Albedo from Shading

Assuming uniform albedo and Lambertian surface for the imaging model, a new robust method for estimation of illuminant direction and albedo from shading is presented. If there is a singular point with maximum intensity in an image, the method use shading information of the singular point and its neighbors to estimate directly the elevation of illuminant direction, surface albedo, and the bias brightness. Some experiment results on synthetic images are given to illustrate the new approach is accurate and robust.

Improving Shape from Shading with Interactive Tabu Search

Optimisation based shape from shading （SFS） is sensitive to initialization： errors in initialization are a signifi- cant cause of poor overall shape reconstruction. In this paper, we present a method to help overcome this problem by means of user interaction. There are two key elements in our method. Firstly, we extend SFS to consider a set of initializations, rather than to use a single one. Secondly, we efficiently explore this initialization space using a heuristic search method, tabu search, guided by user evaluation of the reconstruction quality. Reconstruction results on both synthetic and real images demonstrate the effectiveness of our method in providing more desirable shape reconstructions.

Improved shape from shading without initial information

The number of constraints imposed on the sur- face, the light source, the camera model and in particular the initial information makes shape from shading （SFS） very dif- ficult for real applications. There are a considerable number of approaches which require an initial data about the 3D ob- ject such as boundary conditions （BC）. However, it is difficult to obtain these information for each point of the object Edge in the image, thus the application of these approaches is lim- ited. This paper shows an improvement of the Global View method proposed by Zhu and Shi [1]. The main improvement is that we make the resolution done automatically without any additional information on the 3D object. The method in- volves four steps. The first step is to determine the singular curves and the relationship between them. In the second step, we generate the global graph, determine the sub-graphs, and determine the partial and global configuration. The proposed method to determine the convexity and the concavity of the singular curves is applied in the third step. Finally, we apply the Fast-Marching method to reconstruct the 3D object. Our approach is successfully tested on some synthetic and real im- ages. Also, the obtained results are compared and discussed with some previous methods.

Existence and Uniqueness in Shapefrom Shading

For the image of a smooth surface object fully contained within the field of view and illuminated in an arbitrary direction, this paper discusses the ekistence and uniqueness of the conditions for solving a shape-from-shading problem under the conditions that the Fourier series expansion of the image intensity contains only zero and first order terms in a polar coordinate system. Three theorems are established, one for the ekistence and two for the uniqueness of z-axis symmetric shape from shading.

Ocean surface wave measurements from fully polarimetric SAR imagery

A new method for the retrieval of ocean wave parameters from SAR imagery is developed,based on the shape-from-shading(SFS)technique.Previously,the SFS technique has been used in the reconstruction of 3D landform information from SAR images,in order to generate elevation maps of topography for land surfaces.Here,in order to retrieve ocean wave characteristics,we apply the SFS methodology,together with a method to orient the angular measurements of the azimuth slope and range slope,in the measurement of ocean surface waves.This method is applied to high resolution fine-quad polarization mode(HH,VV,VH and HV)C-band RADARSAT-2 SAR imagery,in order to retrieve ocean wave spectra and extract wave parameters.Collocated in situ buoy measurements are used to validate the reliability of this method.Results show that the method can reliably estimate wave height,dominant wave period,dominant wave length and dominant wave direction from C-band SAR images.The advantage of this method is that it does not depend on modulation transfer functions(MTFs),in order to measure ocean surface waves.This method can be used in monitoring ocean surface wave propagation through open water areas into ice-covered areas,especially the marginal ice zone(MIZ)in polar oceans.