High dynamic range imaging for face matching

Human facial recognition in the context of surveillance, forensics and photo-ID verification is a task for which accuracy is critical. In most cases, this involves unfamiliar face recognition whereby the observer has had very short or no exposure at all to the faces being identified. In such cases, recognition performance is very poor: changes in appearance, limitations in the overall quality of images - illumination in particular - reduces individuals’ ability in taking decisions regarding a person’s identity. High Dynamic Range (HDR) imaging permits handling of real-world lighting with higher accuracy than the traditional low (or standard) dynamic range (LDR) imaging. The intrinsic benefits provided by HDR make it the ideal candidate to verify whether this technology can improve individuals’ performance in face matching, especially in challenging lighting conditions. This thesis compares HDR imaging against LDR imaging in an unfamiliar face matching task. A radiometrically calibrated HDR face dataset with five different lighting conditions is created. Subsequently, this dataset is used in controlled experiments to measure performance (i.e. reaction times and accuracy) of human participants when identifying faces in HDR. Experiment 1: HDRvsLDR (N = 39) compared participants’ performance when using HDR vs LDR stimuli created using the two full pipelines. The findings from this experiment suggest that HDR (µ =90.08%) can significantly (p< 0.01) improve face matching accuracy over LDR (µ =83.38%) and significantly (p<0.05) reduce reaction times (HDR 3.06s and LDR 3.31s). Experiment 2: Backwards-Compatibility HDR (N = 39) compared par ticipants’ performance when the LDR pipeline is upgraded by adding HDR imaging in the capture or in the display stage. The results show that adopt xi ing HDR imaging in the capture stage, even if the stimuli are subsequently tone-mapped and displayed on an LDR screen, allows higher accuracy (capture stage: µ =85.11% and display stage: µ =80.70%), (p<0.01) and faster reaction times (capture stage: µ =3.06s and display stage: µ =3.25s), (p< 0.05) than when native LDR images are retargeted to be displayed on an HDR display. In Experiment 3: the data collected from previous experiments was used to perform further analysis (N = 78) on all stages of the HDR pipeline simultaneously. The results show that the adoption of the full-HDR pipeline as opposed to a backwards-compatible one is advisable if the best values of accuracy are to be achieved (5.84% increase compared to the second best outcome, p<0.01). This work demonstrates scope for improvement in the accuracy of face matching tasks by realistic image reproduction and delivery through the adoption of HDR imaging techniques

PRELIMINARY EVALUATION OF HDR TONE MAPPING OPERATORS FOR CULTURAL HERITAGE

[EN] The ability of High Dynamic Range (HDR) imaging to capture the full range of lighting in a scene has led to an increasing interest in its use 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 objects under harsh lighting conditions, as significant geometric details may not have been captured accurately in under- and over-exposed regions of the images. HDR imaging offers the possibility to overcome this limitation. 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 photogrammetric algorithms, and in particular keypoint detection techniques. The evaluation criteria used are the number of keypoints and the number of valid matches achieved. The comparison considers two local and two global TMOs.Suma, R.; Stavropoulou, G.; Stathopoulou, E.; Van Gool, L.; Georgopoulos, A.; Chalmers, A. (2016). PRELIMINARY EVALUATION OF HDR TONE MAPPING OPERATORS FOR CULTURAL HERITAGE. En 8th International congress on archaeology, computer graphics, cultural heritage and innovation. Editorial Universitat Politècnica de València. 343-347. https://doi.org/10.4995/arqueologica8.2015.3582OCS34334

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

Subjective evaluation of high dynamic range imaging for face matching

Human facial recognition in the context of surveillance, forensics and photo-ID verification is a task for which accuracy is critical. Quite often limitations in the overall quality of facial images reduces individuals' ability in taking decisions regarding a person's identity. To verify the suitability of advanced imaging techniques to improve individuals' performance in face matching we investigate how High Dynamic Range (HDR) imaging compares with traditional low (or standard) dynamic range (LDR) imaging in a facial recognition task. An HDR face dataset with five different lighting conditions is created. Subsequently, this dataset is used in a controlled experiment (N=40) to measure performance and accuracy of human participants when identifying faces in HDR vs LDR. Results demonstrate that face matching accuracy and reaction time are improved significantly by HDR imaging. This work demonstrates scope for realistic image reproduction and delivery in face matching tasks and suggests that security systems could benefit from the adoption of HDR imaging techniques

Fifty shades of HDR

From relatively unknown, just 5 years ago, High Dynamic Range (HDR) video is now having a major impact on most aspects of imaging. Although one of the five components of the specification for UHDTV, ITU-R Recommendation BT.2020 in 2012, it is only when it became apparent that HDR could help accelerate the slow penetration of 4K into the TV and home-cinema market, that HDR suddenly started to gain significant attention. But what exactly is HDR? Dynamic range is defined as the difference between the largest and smallest useable signal. In photography this has meant the luminance range of the scene being photographed. However, as HDR grows as a “marketing tool” this definition is becoming less “black & white”. This paper considers the different ways in which the term HDR is now being exploited; the challenges of achieving a complete efficient HDR pipeline from capture to display for a variety of applications; and, what could be done to help ensure HDR algorithms are future proof as HDR technology rapidly improves

Data provenance in photogrammetry through documentation protocols

Documenting the relevant aspects in digitisation processes such as photogrammetry in order to provide a robust provenance for their products continues to present a challenge. The creation of a product that can be re-used scientifically requires a framework for consistent, standardised documentation of the entire digitisation pipeline. This article provides an analysis of the problems inherent to such goals and presents a series of protocols to document the various steps of a photogrammetric workflow. We propose this pipeline, with descriptors to track all phases of digital product creation in order to assure data provenance and enable the validation of the operations from an analytic and production perspective. The approach aims to support adopters of the workflow to define procedures with a long term perspective. The conceptual schema we present is founded on an analysis of information and actor exchanges in the digitisation process. The metadata were defined through the synthesis of previous proposals in this area and were tested on a case study. We performed the digitisation of a set of cultural heritage artefacts from an Iron Age burial in Ilmendorf, Germany. The objects were captured and processed using different techniques, including a comparison of different imaging tools and algorithms. This augmented the complexity of the process allowing us to test the flexibility of the schema for documenting complex scenarios. Although we have only presented a photogrammetry digitisation scenario, we claim that our schema is easily applicable to a multitude of 3D documentation processes

Status of the plastic scintillator detector for the HERD experiment

Future satellite experiments for cosmic-ray and gamma-ray detection will employ plastic scintillators to discriminate gamma-rays from charged particles and to identify nuclei up to Iron. The High Energy Cosmic Radiation Detector (HERD) facility will be one of those new experiments and it will be installed onboard the Chinese Tiangong Space Station (TSS). The main goal of the HERD experiment is to detect charged cosmic-rays up to PeVand gamma-rays up to hundred GeVs. The plastic scintillator detector (PSD) surrounds the inner detectors on five sides. For energies above a few GeVs a high detector segmentation is required in order to avoid the back-splash effect, due to the interaction between high energy particles and the innermost calorimeter. Each PSD basic element (bar or tile) is coupled to several Silicon Photomultipliers (SiPMs) for the detection of scintillation light. In 2021 we have performed a beam test campaign to test all the subdetectors of the HERD experiment at CERN PS and SPS. We tested two different PSD prototypes, one with a long bar geometry and the other with a squared tile geometry. In both prototypes two scintillating materials (BC-404 and BC-408) were used. Both the prototypes were equipped with SiPMs of two different sizes (MPPC S14160-3050 and S14160-1315) and they were read-out by the CAEN Citiroc-based board DT5550 W. In this work we will describe the PSD design along with the beam test results

The High Energy cosmic-Radiation Detector (HERD) Trigger System

The High Energy cosmic-Radiation Detection (HERD) facility is a next generation spaceborne detector to be installed onboard the Chinese Space Station for about 10 years. HERD will address major problems in fundamental physics and astrophysics, providing precise measurements of charged-cosmic rays up to PeV energies, performing indirect searches for dark matter in the electron spectrum up to few tens of TeV and monitoring the gamma-ray skymap for surveys and transient searches. HERD is composed of a 3D imaging calorimeter (CALO) surrounded by a scintillating fiber tracker (FIT), a plastic scintillator detector (PSD) and a silicon charge detector (SCD). In addition, a transition radiation detector (TRD) is placed on a lateral side to provide accurate energy calibration. Based on this innovative design, the effective geometric factor of HERD will be one order of magnitud larger than that of current space-based detectors. The HERD trigger strategy is designed to accomplish the scientific goals of the mission, and is based on trigger definitions that rely on the energy deposited in CALO and the PSD. The trigger performances are evaluated using a detailed Monte Carlo simulation that includes the latest HERD geometry. In addition, alternative trigger definitions based on the event topology can be established thanks to the photodiode readout of CALO crystals. The feasibility of these topological triggers is also investigated and presented

The Plastic Scintillator Detector of the HERD space mission

The High Energy cosmic-Radiation (HERD) detector is one of the prominent space-borne instruments to be installed on-board the Chinese Space Station (CSS), around 2027. Primary scientific goals regarding this initiative include: precise measurements of cosmic ray (CR) energy spectra and mass composition, at energies up to the PeV range; contributions to high energy gamma-ray astronomy and transient studies; as well as indirect searches for Dark Matter (DM) particles via their possible annihilation/decay to detectable products. HERD is configured to accept incident particles from both its top and four lateral sides. Owing to its pioneering design, an order of magnitude increase in acceptance is foreseen, with respect to previous and ongoing experiments. The Plastic Scintillator Detector (PSD) constitutes an important sub-detector of HERD, particularly aimed towards anti-coincidence (discriminating incident photons from charged particles), while providing precise charge measurement of incoming cosmic-ray nuclei in a range of Z = 1-26. Main requirements concerning its design, include: high detection efficiency, broad dynamic range and good energy resolution. In order to select the optimal layout, two geometries are currently under investigation: one based on long scintillator bars and the other on square tiles, with both layouts being readout by Silicon Photomultipliers (SiPMs). Ongoing activities and future plans regarding the HERD PSD will be presented in this work. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0