Light Field Camera as Tool for Forensic Photogrammetry

Abstract

<p><strong>Abstract.</strong> Light field cameras record both the light intensity received by the sensor and the direction in which the light rays are travelling through space. Recording the additional information of the direction of Light rays provides the opportunity to refocus an image after acquisition. Furthermore, a depth image can be created, providing 3D information for each image pixel. Both, focused images and 3D information are relevant for forensic investigations. Basic overview images are often acquired by photographic novices and under difficult conditions, which make refocusing of images a useful feature to enhance information for documentation purposes. Besides focused images, it can also be useful to have 3D data of an incident scene. Capital crime scenes such as homicide are usually documented in 3D using laser scanning. However, not every crime scene can be identified as capital crime scene straight away but only in the course of the investigation, making 3D data acquisition of the discovery situation impossible. If this is the case, light field images taken during the discovery of the scene can provide substantial 3D data. We will present how light field images are refocused and used to perform photogrammetric reconstruction of a scene and compare the generated 3D model to standard photogrammetry and laser scanning data. The results show that refocused light field images used for photogrammetry can improve the photogrammetry result and aid photogrammetric processing.</p>

Optical Blur Disturbs – The Influence of Optical-Blurred Images in Photogrammtry

“…To analyse whether and how much photogrammetric procedures are influenced by optical blur it was decided to use two different camera systems, a standard digital single lens reflex camera and a Lytro Illum. Both systems were used in two different scenarios, one close range scene, derive from a staged forensic scenery (Sieberth et al, 2018) (Figure 1 (a)), another for camera calibration (Figure 1 (b)). The camera calibration setup was based on the configuration presented in Sieberth et al (2014a), which analysed the influence of motion blur upon photogrammetric procedures.…”

“…It has been shown previously that plenoptic cameras can be used in photogrammetric applications (Sieberth et al, 2018;Zeller et al, 2017Zeller et al, , 2014. In the research presented in this paper, images acquired with a Lytro Illum camera will be used to explore the influence of optical blur and manually changing the aperture on normal photogrammetric procedures.…”

“…Forensic scene: The staged forensic scene was set up in an indoor room, containing table and a clothed mannequin (Sieberth et al, 2018). Within the scene, three measurement crosses were distributed evenly within the working volume, each providing two distances of known length between the coded target points.…”

“…The DSLR camera, (Nikon D700) was equipped with a 50mm lens (Nikkor 50mm f/1.8 G). The procedure was carried out using aperture f/4.5 and fixed focus, and then acquiring 58 overlapping close range photos of the scene (Sieberth et al, 2018). Then, the Lytro Illum was set to a focal length of 50 mm and focused once on the scene and then 58 overlapping images were acquired in similar fashion to the DSLR procedure.…”

Validation of Close-Range Photogrammetry for Architectural and Archaeological Heritage: Analysis of Point Density and 3D Mesh Geometry

“…The Darktable [51] open-source software was used to develop the photographs. The values for white balance, sharpness, contrast, brightness [52] and illumination parameters were adjusted. Moreover, Agisoft Metashape [53] was used for the image processing to produce 3D models from oriented and scaled images with random control points.…”