基于球面全景图的三维实景制作.doc

基于球面全景图的三维实景制作摘要：三维实景也叫虚拟现实（Virtual Reality）全景，是基于序列图片的数字三维全景技术。它使用专门的鱼眼镜头拍摄序列真实图片，经过拼接融合生成球面全景图。本文结合三维全景制作相关流程，探讨了与之相关的理论与关键技术，形成了一整套全景影像获取、拼接、发布技术流程,最后与*大学档案馆的数字化建设相结合，介绍了三维全景系统的关键制作步骤。关键词：虚拟现实 图像拼接 图像融合 球面全景图Abstract: Three-dimensional virtual reality is also called the Virtual Reality, its a digital three-dimensional panoramic technology based on sequence images. It uses specialized fish-eye lens to shoot sequences of real pictures, through the fusion splicing generates a spherical panorama. In this paper, based on three-dimensional panoramic production related processes discussed the associated theories and key technologies, formed a complete set of panoramic imaging gets, splicing, publication technology process, finally combined with the digital construction of * University Archives,introduced the keysteps in the production ofthree-dimensionalpanorama system.Keywords: Virtual reality Image stitching Image matching Spherical Panoramic Image1 引言广义上的全景就是视角范围超过人的正常视角的图像，本文我们说的全景特指水平视角360，垂直视角180的图像。360全景最大的三个特点是： 1、全：全方位，用户可观看左右 360，上下180球型范围内的所有景致； 2、景：实景，在现场采集的一系列照片基础上经过拼接合成得到的最大限度的保留了场景真实性的全景照片； 3、360：360环视的效果，虽然照片都是平面的，但是通过软件处理之后得到的360实景，却能给人以三维立体的空间感觉，使观者犹如身在其中。 由于它给人们带来全新的真实现场感和交互式的感受，故可广泛应用于三维电子商务，如在线的房地产楼盘展示、虚拟旅游、虚拟教育、医疗、航空等领域。在地质勘测、军事侦察、医学微创手术、航空航天以及视频会议等多个领域都发挥着重要作用。1 Introduction Panorama in a broad sense is the image perspective beyond the normal , panoramic of this article we say especially a horizontal angle of 360 , 180 vertical perspective image. Three largest features of the 360 panorama are:1. Entire: Omni-directional, users can watch around 360 , 180 spherical range up and down all of the landscape;2. Scenery: Outdoor scene, panorama basedona series of photoscollectedand throughthe mosaicsynthesishas retainedthe authenticity of the scene;3. 360: The effect of 360 look around, although the pictures are flat, but the 360 virtual when processed through the software will bring a person with three-dimensional feeling, just like the Viewer is in it.2 三维全景关键技术2 The key technology of three-dimensional panorama2.1 The general process ofpanorama generation 2.1 全景图生成一般流程本文系统在基于IBR方法基础上，先利用数码相机+鱼眼镜头采集场景序列图片，然后把多幅全景图投影到合适的空间模型，本文采用的是球面投影模型，再把拼接处理过的全景图组织成虚拟的全景空间，用户通过场景中导航图标可以在这个虚拟空间进行前进、后退、转弯、切换场景等漫游；每个场景都可以进行360环视、变焦浏览等操作。综上所述，基于全景图技术的虚拟场景生成过程可以用图2.1表示。The system in this paper isbased on the IBR method,and use thedigital camera withfisheye lensacquisitionsequence of scenes, Then put a number of images projected onto the appropriate space model of panoramic image, we use the spherical projection model this paper, Then treated stitching panorama organized into virtual panoramic space, Users navigate through the scenario icon can be forward, backward, turn, switch scenes roaming in this virtual space; Each scene can be 360 degrees around, zoom browsing operations etc. In summary, virtual scene generation process based on panorama technology can be represented by Figure 2.1确定图像的生成方式计算机绘制普通相机全景相机投影变换拼接融合生成全景图链接全景图浏览虚拟场景图2.1 全景图生成流程图Figure 2.1 Flowchart of panoramas generate 2.2 全景图像采集全景图像的拍摄要求360无死角的视角角度，所以对全景设备有着较高的要求，总体来说在图像的采集过程中要求有以下几点1：1、拍摄角度要恰当，相机应大致位于一个场景的中心位置。2、拍摄水平角度图像时，要尽可能的避免平转数码相机时镜头的偏斜和俯仰，尽量保持相机水平旋转。3、相机要尽可能的绕光心旋转。偏离光心引入的误差会导致插值图像时的重影和定位困难。 4、拍摄时光圈和焦距要固定不变。不同的光圈会使拍摄的不同方向的照片亮度、对比度和色彩差异较大。5、同一场景的序列图像必须有重叠部分，一般重叠区域约为30%-50%之间，这样拼接图像的时候才有足够的匹配点。 6、同一场景的采集时间要尽快，间隔不要太久，以免风云变色，带来外界环境变化，影响拼接效果。7、在拍摄时，场景中尽量不要出现移动的物体。2.2 Panoramic image acquisitionPanoramashooting requires360 no dead angle ofview,therefore has a higher requestto thepanoramic equipment, In generalthe image acquisition processrequirementsare as follows1:The camera angle to be appropriate, the camera should be roughly located in the center of a scene.When shootingHorizontal angle image,to avoid as much as possibledeviationand pitch when the digital camera pan,and try tokeep the camerarotation.Rotation around the optical center of the camera as much as possible. Errorintroduced by deviating from the optical center will cause interpolation image ghosting and difficult to locate.When shooting, aperture and focal length to be fixed. Different aperture would make photos of the different direction of brightness, contrast and color quite different.Sequenceimages of the same scenemusthave overlapping parts. General overlap area approximately 30% to 50%, so when stitching images have enough matching points.Acquisition time of the same scene as soon as possible, not too long intervals, in order to avoid the situation discoloration, bringing the external environment changes that affect splicing effect.In filming, try not to appear moving object in the scene.球面全景空间的视点空间对应单一视点处的球面范围，要获取该范围内的实景图，需要固定照相机或摄像机的位置，平转照相机或摄像机，每旋转一定的角度，拍摄一张照片2，完成水平360景象的拍摄后，需要将相机从最初的水平位置向上翻转90，使镜头朝上拍一张此场景天空的照片。但是由于拍摄天空时的镜头比拍摄水平方向时的镜头要高，所以要把相机往下调一点。完成对天空的拍摄后，再将三脚架向后移动一定距离，把相机向下旋转到最大角度（大约75左右）拍一张地的照片，这样就完成了一个场景的360拍摄。拍摄实景图像使用的器材包括三脚架、水平仪和数码相机等。如图2.2所示。View space in spherical panoramic space corresponding to the singleview pointof Sphericalrange,to get thereal mapin the range,you need fixedcamera orcamera position, swingthe camera, rotatesa certain angle,take a photo 2, Complete thelevel360 degreesceneshooting,the camera needs tobeturned up 90 degreesfrom the originalhorizontal position,make the lens upward to shoot sky of this scene. However, due to the lens when shooting the sky higher than shooting horizontal, so put the cameradowna bit. After completing the shoot to the sky, and then moving the tripod backward at a distance，put the camera down to its maximum angle (about 75 or so) to take a photo of earth, this completesa scene of360 shooting. Shooting real images using equipment includes tripods, levels and digital cameras, etc. As shown in Figure 2.2.图2.2 拍摄实景图像装置图Figure 2.2 Diagram of apparatus to taken real images 2.3 球面投影球面全景图的投影是将鱼眼照片上的点映射到球面模型上(如图2.3所示)，所有的投影线都是与球面垂直的，所以没有如传统平面图像中的光轴3。因此，只要在球面视图中可见，空间中的每个点都能在球面投影中展示出来。2.3 Spherical projection Spherical panorama projection is to map the points on the fisheye photos to spherical model (as shown in figure 2.3), All projection lines are perpendicular to the sphere s, so there is no optical axis like tradition plane image3. Therefore, as long as visible in the spherical view, each point in the space can be displayed in the stereographic projection.图2.3 球面变换示意Figure 2.3 spherical transform indication如图2.3所示，相机位于半径为 f 的球体中心，相机的拍摄方向即投影的方向由极角 (相机视线与相机坐标系Z 轴的夹角)和方位角 (相机视线在相机坐标系中 XY 平面内的投影与 X 轴的夹角)决定。在球面投影中，相机坐标系与球面坐标系是一样的。假设 P 在世界坐标系中的坐标为： (1)P 在球面上的投影点 p 的球面坐标可以表示为: (2)推导出: (3)这里 。由此，可以通过该公式算出照片上任意点 P 在投影球面的对应点 p 的坐标。2.3.1 而我等均为地哦我去山东龙口就爱死爹我As shown in figure 2.3, the camera is located in the center of a sphere with a radius of f, Camera shooting direction that is projection direction is determined by the polar Angle(The angle between the camera line of sight and Camera coordinate system z axis)and azimuth Angle(The angle between the camera line of sight in the camera coordinate system XY plane and the X axis). In spherical projection, the camera coordinate system and the spherical coordinate system is the same. Assume that the coordinates of P in the world coordinate system is: (1)The spherical coordinates of the projection point p of P can be expressed as: (2)Can be deduced: (3)Here.Thus, the coordinates of anypoint P correspondsP in projectionsurface Can be calculated by the formula.2.4全景图拼接简单地说，图像拼接就是把采集到的一些有相互重叠区域的图像序列变成一副无缝的360全景图。对于由于经济原因而采用非全视角相机拍摄的图片来说，图像的拼接是构建360虚拟全景空间的一个重要步骤，拼接质量的好坏，决定了能否给用户一个逼真的、真实的浏览效果。一般来说，图像拼接的误差应小于一个像素。由于拍摄到的相邻的图片之间存在一定区域的重叠，如图2.4所示，可以以此为拼接方法的入手点，用拼接工具识别出相邻图片的重叠区域，从而达到生成全景图的目的。为了达到让人满意的拼接效果，重叠区域大小要适当，对于图像特征明显的图片，重叠区域可以小一些，反之，就要大一些。一般情况下，相邻两幅图像的重叠部分应该在30%50%之间。2.4 Panorama stitching In brief, image stitching is to put sequence of overlapping images into a seamless 360panoramas. Images which for economic reason that use non-full-view camera shoot, image stitching is an important step to build 360 virtual panorama space, stitchingquality,decides whetherto give users a realistic and authentic view. In general, image stitching error should be less than one pixel. Because of there is a certain area of overlap between adjacent images, as shown in figure 2.4, we can take this as a starting point of stitching method, with splicing tool to identify the overlap of adjacent images, so as to achieve the purpose of generating panorama. In order to achieve satisfactory splicing effect, overlapping region size should be appropriate, for Images which have significant feature, overlapping area can be smaller, conversely, will greatly. In general, the overlap between two images should be between 30% - 50%.图2.4 全景图拼接示意图2.5图像融合对图像进行匹配之后，只是完成了对图像的定位。如果这时只根据拼接算法求得的两幅图像上下和水平方向的平移参数将两幅图简单的叠加起来，由于相邻图像之间存在的亮度差异和拍摄时三脚架旋转对拍摄图像带来的影响等原因，就会出现合成的图像有清晰的边界，拼接痕迹明显等让我们不能接受的现象。而图像融合4就是在图像匹配之后对图像像素值进行处理，目的是在保证图像的质量不发生改变的前提下消除图像拼接后出现的拼接痕迹。2.5 Image Fusion After the image matching, just completed the positioning of the image. At this time, if you simply overlay two images together only according to vertical and horizontal translational parametersobtainedby stitching algorithm, Due to brightness differences exist between adjacent images and effects of rotation on a tripod when shooting images and other reasons, there will bethe synthetic images haveclear boundaries,obvious splicing traces, which we obviously cannot accept phenomenon. Image fusion is to processing image pixels after image matching, objective is to removing splicing traces under the premise of guarantee the quality of the image does not change. 3 应用实例本节将结合相关理论和算法实现一个全景图漫游系统，本系统是大学校史馆的三维全景漫游系统。为广大校友提供了一个足不出户便可身临其境的浏览母校历史的平台。系统中对关键图片和文字配有多边形热区，用户通过点击想要细致阅读查看的区域，即可弹出相应的放大图片或相关视频文件。不仅方便了用户查看，更增加了系统的生动性和真实感。系统主界面如图所示：3 Application examples This section will combine related theories and algorithms to achieve a panorama roaming system, this system is a three-dimensional panoramic roaming system of xx university History Museum. For our alumni provides a platform for immersive browsing alma mater history without leaving home. In this system, key image and text are equipped with polygon hot spot, users by clicking on the area which he want careful reading, the corresponding enlarge images or related video files will pop up. Not only convenient for users to view,