Assessing the quality of 3D reconstructed models remains a key challenge in multimedia applications, especially in the context of cultural heritage, where visual fidelity and perceptual realism are equally crucial. This study investigates how reconstruction parameters, as well as existing objective quality metrics, align with human perception. In addition, we analyze how perceived quality and user interaction are related. A dataset of 3D models was generated by varying the number of input images, mesh complexity, and texture resolution. Results from a subjective study show that texture resolution significantly affects perceived quality, whereas variations in number of images and mesh complexity have a limited impact. Furthermore, interaction behavior was found to vary with perceived quality, with participants spending more time and exploring larger viewing angles for models receiving higher scores. These findings highlight the need for perceptually grounded, interaction-aware evaluation methodologies and provide guidelines for future perceptual optimization of 3D reconstruction pipelines.

Extended reality technologies are increasingly used in cultural heritage for preserving and accessing sites and artworks, where 3D model acquisition and rendering are key. Despite progress in reconstruction methodologies, a standardized approach to quality assessment is still missing. This study aims to evaluate objective quality metrics —both image-based and model-based, Full Reference and No Reference— applied to 3D models generated using the Structure from Motion algorithm. By varying parameters such as the number of images, number of triangles, and texture resolution, we examine the impact of these factors on metric outcomes, aiming to assess their reliability in cultural heritage applications.

In this work, we propose a demo of an immersive videoconference system using Free Viewpoint Video (FVV) technology. It makes use of the FVV Live system, which covers the entire FVV pipeline (capture, view rendering, and visualization) while working in real-time. The FVV Live system consists of nine cameras that capture an environment and a view renderer that uses the information from the cameras to generate a synthetic view at an arbitrary point.It is designed as a hybrid demo. While the capture and rendering processes take place at our premises, FVV Live can be visualized through devices connected to the Internet.The system allows immersive navigation of a virtual scene with 6 degrees of freedom, and interaction with live-captured avatars integrated in such scene. For this purpose, it uses WebRTC connections to update the position of the virtual camera and to receive the FVV Live view encoded as a video.Additionally, the user will be recorded by a simple camera and microphone setup, and the generated streams will be transmitted to our premises through the same WebRTC server. This way, people being recorded by FVV Live will be able to see and hear the user, enabling bidirectional communication.

FVV Live is a novel end-to-end free-viewpoint video system, designed for real-time operation, using consumer-grade cameras and hardware, which enables low deployment costs and easy installation for immersive event-broadcasting or videoconferencing. All the blocks of the system have been designed to maximize perceptual video quality, overcoming the limitations imposed by hardware and network, which impact directly the accuracy of depth data and thus the quality of virtual view synthesis. Therefore, it does not sacrifice perceptual video quality with respect to high-end counterparts. The results presented in this paper correspond to an implementation with nine stereo-based depth cameras. However, the design of the acquisition block of FVV Live allows scalability for an arbitrary number of cameras. In addition, FVV Live presents low motion-to-photon and end-to-end delays, which enables a responsive free-viewpoint navigation and bilateral immersive communications. Moreover, the visual quality of FVV Live has been assessed through subjective assessment with satisfactory results, and additional comparative tests show that it is preferred over state-of-the-art DIBR alternatives.

Many computer vision and human-computer interaction applications developed in recent years need evaluating complex and continuous mathematical functions as an essential step toward proper operation. However, rigorous evaluation of these kind of functions often implies a very high computational cost, unacceptable in real-time applications. To alleviate this problem, functions are commonly approximated by simpler piecewise-polynomial representations. Following this idea, we propose a novel, efficient, and practical technique to evaluate complex and continuous functions using a nearly optimal design of two types of piecewise linear approximations in the case of a large budget of evaluation subintervals. To this end, we develop a thorough error analysis that yields asymptotically tight bounds to accurately quantify the approximation performance of both representations. It provides an improvement upon previous error estimates and allows the user to control the tradeoff between the approximation error and the number of evaluation subintervals. To guarantee real-time operation, the method is suitable for, but not limited to, an efficient implementation in modern graphics processing units, where it outperforms previous alternative approaches by exploiting the fixed-function interpolation routines present in their texture units. The proposed technique is a perfect match for any application requiring the evaluation of continuous functions; we have measured in detail its quality and efficiency on several functions, and, in particular, the Gaussian function because it is extensively used in many areas of computer vision and cybernetics, and it is expensive to evaluate.

In Structure-from-Motion (SfM) applications, the capability of integrating new visual information into existing 3D models is an important need. In particular, video streams could bring significant advantages, since they provide dense and redundant information, even if normally only relative to a limited portion of the scene. In this work we propose a fast technique to reliably integrate local but dense information from videos into existing global but sparse 3D models. We show how to extract from the video data local 3D information that can be easily processed allowing incremental growing, refinement, and update of the existing 3D models. The proposed technique has been tested against two state-of-the-art SfM algorithms, showing significant improvements in terms of computational time and final point cloud density.

Abstract In the context of 3D reconstruction, we present a static multi‐texturing system yielding a seamless texture atlas calculated by combining the colour information from several photos from the same subject covering most of its surface. These pictures can be provided by shooting just one camera several times when reconstructing a static object, or a set of synchronized cameras, when dealing with a human or any other moving object. We suppress the colour seams due to image misalignments and irregular lighting conditions that multi‐texturing approaches typically suffer from, while minimizing the blurring effect introduced by colour blending techniques. Our system is robust enough to compensate for the almost inevitable inaccuracies of 3D meshes obtained with visual hull–based techniques: errors in silhouette segmentation, inherently bad handling of concavities, etc.

We introduce an innovative, semi-automatic method to transform low resolution facial meshes into high definition ones, based on the tailoring of a generic, neutral human head model, designed by an artist, to fit the facial features of a specific person. To determine these facial features we need to select a set of "control points" (corners of eyes, lips, etc.) in at least two photographs of the subject's face. The neutral head mesh is then automatically reshaped according to the relation between the control points in the original subject's mesh through a set of transformation pyramids. The last step consists in merging both meshes and filling the gaps that appear in the previous process. This algorithm avoids the use of expensive and complicated technologies to obtain depth maps, which also need to be meshed later.

In this paper, we explore the challenges posed by wide baseline camera configurations for depth-image-based rendering, which should provide greater freedom for choosing the virtual viewpoint in a Free Viewpoint Video context, compared with the usual camera configurations intended for use in 3DTV settings. We implement a backward mapping approach with a custom filtering scheme based on median filters. Whilst the results back our initial assumption that this camera configuration provides good mobility, we show that the usual encoding for depth information referred to a global reference system is wrong and reference systems local to each camera should be used instead.

We present an innovative system to encode and transmit textured multi-resolution 3D meshes in a progressive way, with no need to send several texture images, one for each mesh LOD (Level Of Detail). All texture LODs are created from the finest one (associated to the finest mesh), but can be reconstructed progressively from the coarsest thanks to refinement images calculated in the encoding process, and transmitted only if needed. This allows us to adjust the LOD/quality of both 3D mesh and texture according to the rendering power of the device that will display them, and to the network capacity. Additionally, we achieve big savings in data transmission by avoiding altogether texture coordinates, which are generated automatically thanks to an unwrapping system agreed upon by both encoder and decoder

Our recently proposed wavelet-based L-infinite-constrained coding approach for meshes ensures that the maximum error between the vertex positions in the original and decoded meshes is guaranteed to be lower than a given upper bound. Instantiations of both L-2 and L-infinite coding approaches are demonstrated for MESHGRID, which is a scalable 3D object encoding system, part of MPEG-4 AFX. In this survey paper, we compare the novel L-infinite distortion estimator against the L-2 distortion estimator which is typically employed in 3D mesh coding systems. In addition, we show that, under certain conditions, the L-infinite estimator can be exploited to approximate the Hausdorff distance in real-time implementations.

3D triangle meshes are extremely used to model discrete surfaces, and almost always represented with two tables: one for geometry and another for connectivity. While the raw size of a triangle mesh is of around 200 bits per vertex, by coding cleverly (and separately) those two distinct kinds of information it is possible to achieve compression ratios of 15:1 or more. Different techniques must be used depending on whether single-rate vs. progressive bitstreams are sought; and, in the latter case, on whether or not hierarchically nested meshes are desirable during reconstruction.

Most current multi-player 3D games can only be played on dedicated platforms, requiring specifically designed content and communication over a prede-fined network. To overcome these limitations, the OLGA (On-Line GAming) consortium has devised a framework to develop distributive, multi-player 3D games. Scalability at the level of content, platforms and networks is exploited to achieve the best trade-offs between complexity and quality. Besides, stan-dardized content compression formats (MPEG-4, JPEG 2000) are used in OLGA's framework, enabling easy deployment over existing infrastructure, while keeping hooks to well-established practices in the game industry.

Truly hierarchical three-dimensional model coding (3DMC) techniques based on subdivision surfaces have, over merely progressive ones, the advantage of yielding pyramidally nested meshes that inherently approximate the surface of a three-dimensional (3-D) object at increasing levels of detail (LODs). Such a nesting makes it natural to edit (hence animate) the model at different LODs. From a compression efficiency viewpoint, it is also the most advantageous, because it permits us to group into hierarchical sets the 3-D details needed to reposition the new vertices predicted along the subdivision process. We first review extensively previous work on both progressive and hierarchical 3DMC. We then describe our hierarchical 3DMC technique based on subdivision surfaces, which is inspired by the set partitioning in hierarchical trees (SPIHT) coding scheme and has in turn inspired the wavelet subdivision surfaces tool of MPEG-4's Animation Framework eXtension (AFX). We finally compare our technique with several others.

SS (subdivision surfaces) are a powerful modelling paradigm for truly hierarchical (instead of merely progressive) 3D surface (as opposed to mesh) coding. Two SS-based tools of the MPEG-4 animation framework extension allow us to derive a piecewise smooth surface from an initial control mesh: if the subdivision process is run in its predefined form, the initial mesh is simply smoothed; if 3D details are added to the positions of the new vertices appearing after each subdivision step, a particular target surface may be approximated with an increasing accuracy. In both cases, multiresolution editing/animation is possible.

This paper presents the first results of the Authoring744 research initiative, which uses MPEG-7 to synthesize MPEG-4 content. The objective is to use MPEG-7 content descriptions to synthesize content, instead of creating descriptions by analyzing existing content. The output uses MPEG-4 XMT as the representation format, which is further used to create an MPEG-4 binary format, which can in turn be played.

We build on state of the art methods for multiresolution embedded coding of images, such as Said and Pearlman's (1996) set partitioning in hierarchical trees, and combine them with ideas for 3D objects modelling with subdivision surfaces, to obtain a new technique for hierarchical 3D model coding. The compression ratios we obtain are better than or similar to previously reported ones but, perhaps more importantly, the truly hierarchical coding of 3D objects we propose allows their efficient multiresolution animation. This kind of technique could have a major impact on VRML and MPEG-4, the two ISO standards that now deal with the coding of 3D objects, which are in both cases static and linearly approximated by polygonal meshes. In future versions of those standards, that will have to address the coding of dynamic 3D objects, these will most likely be modelled with higher order primitives such as subdivision surfaces.