1,077 research outputs found
Evaluation of the effectiveness of HDR tone-mapping operators for photogrammetric applications
[EN] The ability of High Dynamic Range (HDR) imaging to capture the full range of lighting in a scene has meant that it is being increasingly used for Cultural Heritage (CH) applications. Photogrammetric techniques allow the semi-automatic production of 3D models from a sequence of images. Current photogrammetric methods are not always effective in reconstructing images under harsh lighting conditions, as significant geometric details may not have been captured accurately within under- and over-exposed regions of the image. HDR imaging offers the possibility to overcome this limitation, however the HDR images need to be tone mapped before they can be used within existing photogrammetric algorithms. In this paper we evaluate four different HDR tone-mapping operators (TMOs) that have been used to convert raw HDR images into a format suitable for state-of-the-art algorithms, and in particular keypoint detection techniques. The evaluation criteria used are the number of keypoints, the number of valid matches achieved and the repeatability rate. The comparison considers two local and two global TMOs. HDR data from four CH sites were used: Kaisariani Monastery (Greece), Asinou Church (Cyprus), Château des Baux (France) and Buonconsiglio Castle (Italy).We would like to thank Kurt Debattista, Timothy Bradley,
Ratnajit Mukherjee, Diego Bellido Castañeda and TomBashford
Rogers for their suggestions, help and
encouragement.
We would like to thank the hosting institutions: 3D
Optical Metrology Group, FBK (Trento, Italy) and UMR
3495 MAP CNRS/MCC (Marseille, France), for their
support during the data acquisition campaigns.
This project has received funding from the European
Union’s 7
th Framework Programme for research,
technological development and demonstration under
grant agreement No. 608013, titled “ITN-DCH: Initial
Training Network for Digital Cultural Heritage: Projecting
our Past to the Future”.Suma, R.; Stavropoulou, G.; Stathopoulou, EK.; Van Gool, L.; Georgopoulos, A.; Chalmers, A. (2016). Evaluation of the effectiveness of HDR tone-mapping operators for photogrammetric applications. Virtual Archaeology Review. 7(15):54-66. https://doi.org/10.4995/var.2016.6319SWORD546671
Layered 3D: tomographic image synthesis for attenuation-based light field and high dynamic range displays
We develop tomographic techniques for image synthesis on displays composed of compact volumes of light-attenuating material. Such volumetric attenuators recreate a 4D light field or high-contrast 2D image when illuminated by a uniform backlight. Since arbitrary oblique views may be inconsistent with any single attenuator, iterative tomographic reconstruction minimizes the difference between the emitted and target light fields, subject to physical constraints on attenuation. As multi-layer generalizations of conventional parallax barriers, such displays are shown, both by theory and experiment, to exceed the performance of existing dual-layer architectures. For 3D display, spatial resolution, depth of field, and brightness are increased, compared to parallax barriers. For a plane at a fixed depth, our optimization also allows optimal construction of high dynamic range displays, confirming existing heuristics and providing the first extension to multiple, disjoint layers. We conclude by demonstrating the benefits and limitations of attenuation-based light field displays using an inexpensive fabrication method: separating multiple printed transparencies with acrylic sheets.Dolby Laboratories Inc.Samsung ElectronicsAlfred P. Sloan Foundatio
3D Shape Measurement of Objects in Motion and Objects with Complex Surfaces
This thesis aims to address the issues caused by high reflective surface and object with motion in the three dimensional (3D) shape measurement based on phase shifting profilometry (PSP). Firstly, the influence of the reflectivity of the object surface on the fringe patterns is analysed. One of the essential factors related to phase precision is modulation index, which has a direct relationship with the surface reflectivity. A comparative study focusing on the modulation index of different materials is presented. The distribution of modulation index for different material samples is statistically analysed, which leads to the conclusion that the modulation index is determined by the diffuse reflectivity.
Then the method based on optimized combination of multiple reflected image patterns is proposed to address the saturation issue and improve the accuracy for the reconstruction of object with high reflectivity.A set of phase shifted sinusoidal fringe patterns with different exposure time are projected to the object and then captured by camera. Then a set of masks are generated to select the data for the compositing. Maximalsignal-to-noise ratio combining model is employed to form the composite images pattern. The composite images are then used to phase mapping.Comparing to the method only using the highest intensity of pixels for compositing image, the signal noise ratio (SNR) of composite image is increased due to more efficient use of information carried by the images
Capturing and viewing gigapixel images
We present a system to capture and view "Gigapixel images": very high resolution, high dynamic range, and wide angle imagery consisting of several billion pixels each. A specialized camera mount, in combination with an automated pipeline for alignment, exposure compensation, and stitching, provide the means to acquire Gigapixel images with a standard camera and lens. More importantly, our novel viewer enables exploration of such images at interactive rates over a network, while dynamically and smoothly interpolating the projection between perspective and curved projections, and simultaneously modifying the tone-mapping to ensure an optimal view of the portion of the scene being viewed.publishe
Lighting in the third dimension : laser scanning as an architectural survey and representation method
This paper proposes tridimensional (3D) laser scanning to architects and lighting designers as a lighting
enquiry and visualization method for existing built environments. The method constitutes a complement
to existing lighting methods by responding to limitations of photometric measurements, computer
simulation and HDR imagery in surveying and visualizing light in actual buildings. The research explores
advantages and limitations of 3D laser scanning in a case study addressing a vast, geometrically complex
and fragmented naturally and artificially lit space. Lighting patterns and geometry of the case study are
captured with a 3D laser scanner through a series of four scans. A single 3D model of the entire space is
produced from the aligned and fused scans. Lighting distribution patterns are showcased in relation to
the materiality, geometry and position of windows, walls, lighting fixtures and day lighting sources.
Results and presented through images similar to architectural presentation drawings. More specifically,
the lighting distribution patterns are illustrated in a floor plan, a reflected ceiling plan, an axonometry
and a cross-section. The point cloud model of the case study is also generated into a video format
representing the entire building as well as different viewpoints. The study shows that the proposed
method provides powerful visualization results due to the unlimited number of images that can be
generated from a point cloud and facilitates understanding of existing lighting conditions in spaces
HDRFusion:HDR SLAM using a low-cost auto-exposure RGB-D sensor
We describe a new method for comparing frame appearance in a frame-to-model
3-D mapping and tracking system using an low dynamic range (LDR) RGB-D camera
which is robust to brightness changes caused by auto exposure. It is based on a
normalised radiance measure which is invariant to exposure changes and not only
robustifies the tracking under changing lighting conditions, but also enables
the following exposure compensation perform accurately to allow online building
of high dynamic range (HDR) maps. The latter facilitates the frame-to-model
tracking to minimise drift as well as better capturing light variation within
the scene. Results from experiments with synthetic and real data demonstrate
that the method provides both improved tracking and maps with far greater
dynamic range of luminosity.Comment: 14 page
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