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...at we are given a pair of rectified images as input. Recent references on stereo camera calibration and rectification include [130, 70, 131, 52, 39]. 2.2. Representation A critical issue in understanding an algorithm is the representation used internally and output externally by the algorithm. Most stereo correspondence methods compute a univalued disparity function d(x, y) with respect to a reference image, which could be one of the input images, or a “cyclopian” view in between some of the images. Other approaches, in particular multi-view stereo methods, use multi-valued [113], voxel-based [101, 67, 34, 33, 24], or layer-based [125, 5] representations. Still other approaches use full 3D models such as deformable models [120, 121], triangulated meshes [43], or level-set methods [38]. Since our goal is to compare a large number of methods within one common framework, we have chosen to focus on techniques that produce a univalued disparity map d(x, y) as their output. Central to such methods is the concept of a disparity space (x, y, d). The term disparity was first introduced in the human vision literature to describe the difference in location of corresponding features seen by the left and right eyes...

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... they rely on the presence of specific image features such as edges and hence generate only sparse reconstructions [28], or they place strong constraints on the input viewpoints relative to the scene =-=[29, 30]-=-. Our implementation of the Space Carving Algorithm also uses plane sweeps, but unlike all previous methods the algorithm guarantees complete reconstructions in the general case. Our approach offers s...

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...projecting it into the input images, and evaluating the amount of mutual agreement between those projections. A simple measure of agreement is the variance of the projected pixels in the input images =-=[8, 11]-=-. Other methods compare images two at a time, and use windowmatching metrics such as sum of squared differences or normalized cross correlation [20, 23, 31]. An interesting feature of scene-space wind...

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...G can be done using polyhedral CSG, but this is very hard to do in a robust manner. A more common method used to convert silhouette contours into visual hulls is volume carving [22] [8] [29] [19] [5] =-=[27]-=-. This method removes unoccupied regions from an explicit volumetric representation. All voxels falling outside of the projected silhouette cone of a given view are eliminated from the volume. This pr...

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...a scene element between di#erent cameras. This constraint, called photoconsistency, is obviously quite powerful. Two well-known recent algorithms 2 that have used photo-consistency are voxel coloring =-=[23]-=- and space carving [16]. Voxel coloring makes a single pass through voxel space, first computing the visibility of each voxel and then its color. There are some constraints on the camera geometry, nam...

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...ws, inverting (10) is far easier. First, the volume containing the geometry of the scene is partitioned into voxels. Then, the occupancy of each voxel is determined using the voxel coloring algorithm =-=[16]-=-, where each voxel is projected into the various images and deemed to be occupied or not depending on the consistency of measurements from the various images. At the end of the voxel coloring approach...

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...xel approaches, a recent algorithm computes discrete slices of the visual hull using graphics hardware for acceleration [9]. Other approaches improve the shape using splines [17] or color information =-=[18]-=-. If the primary purpose of a shape representation is to produce new renderings of that shape from different viewing conditions, then construction of an explicit model is not necessary. The image-base...