## 1 Introduction  
With the development of computer technology, 3D video has become increasingly popular recently. It provides users with a more authentic and interactive viewing experience [1]. Free viewpoint video (FVV) has also drawn a lot of attention as it allows users to choose the viewpoint freely [2]. However, for FVV, it is unrealistic to obtain the video of arbitrary viewpoint through a series of cameras in practical application. Due to bandwidth limitations, only a certain number of viewpoints can be transmitted. How to generate high-quality FVV based on a limited number of viewpoints has become one of the research hotspots in the field of 3D video [3]. One practical way is to create virtual views on the receiving end. In this context, depth image based rendering (DIBR) is a better choice [4]. Depth image is usually represented by a single-channel grayscale image, which takes up less storage space than a 24-bit color image of the same size. Depth image encoding is more efficient than that of color image [5]. As discussed in Reference [4], the bit rate of depth image requires below 20% of the basic color image bit rate. Therefore, depth image requires less bandwidth than color image, which can speed up the video transmission. The core process of DIBR technology is 3D warping. As shown in Figure 1, it consists of two steps. First, all pixels in the reference image are re-projected into the world coordinate system according to the depth information. These points are then projected into the image plane of the virtual view based on the virtual camera parameters [6].  
In the 3D warping process, due to inaccurate depth values and occlusion relationship between objects, some artifacts appear in the synthesized virtual view, such as cracks, ghosts, holes and pixel overlapping [7]. Cracks are caused by the rounding errors of the float results, usually 1-2 pixels wide. Ghosts mean that pixels at the boundary of foreground are incorrectly projected into the virtual view as background pixels. The foreground and background textures are mixed due to errors of depth values. As a result of the positional relationship between the reference view and the virtual view, adjacent pixels with different depth values in the reference image will not be contiguous in the virtual view, which leads to two situations. One is the overlap of pixels, which will affect the occlusion relationship between objects in the virtual image if not processed. The other is that the region occluded by the foreground is exposed in the virtual view, resulting in a large hole called disocclusion. In addition, there is another type of hole that usually appears at the border of the virtual image. They are outside the imaging range of the reference view and are known as out-of-field regions (OFRs).  
In order to prevent artifacts and improve the quality of virtual view, in this paper, we propose a novel view synthesis method based on the DIBR process. First, a virtual image is generated by the original DIBR. The hole pixels at the boundary are marked and inversely projected into the reference view to calculate the extended region of the reference image and its depth image. The extended region is filled with pixels from the nearby source region, aiming to fill the OFRs in the virtual image. Second, unidirectional depth image preprocessing is applied to detect and remove the ghosts. In addition, the 3D warping process is modified to avoid cracks and pixel overlapping. Finally, a local background-first inpainting method is proposed to fill the disocclusions. This approach can prevent the penetration of the foreground objects. The rest of the paper is organized as follows. The related previous algorithms are discussed in Section 2. The proposed framework is presented in Section 3. Experimental results are provided in Section 4. Finally, the conclusions are given in Section 5.