The FreeRef-1 system is an innovative technology designed for forensic photography that enables contactless placement of size references and accurate measurements in photographs, particularly useful in situations where traditional methods may contaminate or alter the evidence. The system consists of a projector and custom-made software that work together to facilitate the documentation of evidence at crime scenes or in forensic laboratories.
How the FreeRef-1 System Works
The FreeRef-1 projector is equipped with five 1 mW green lasers that project beams parallel to the camera lens at known center distances. These lasers create a square pattern of four dots that maintains a constant size regardless of the distance from the camera, which serves as a size reference. The projector also includes a mechanism to adjust the distance of the lasers from the lens, allowing users to select the size of the projected dot pattern to fit the item being photographed. Additionally, the projector has a "mode-laser" that helps the software determine whether the projector was used in Small (S) or Large (L) mode, based on the relative position of the mode-laser dot to the four reference dots.
The FreeRef-1 software, developed in Matlab, automates the process of detecting the laser dots in photographs. It uses the camera's EXIF information, along with the locations of the detected laser dots, to calculate the horizontal and vertical rotations of the plane on which the laser dots are visible (the projection plane) with respect to the camera sensor. With these rotations known, the software can determine a transfer function from pixel-space dimensions in the 2D photograph to real-world 3D locations on the projection plane, allowing for accurate measurements that account for perspective effects.
The user interface of the software enables users to perform measurements with just two mouse clicks, automatically drawing and labeling the measured distance. The software ensures that original files are never accidentally overwritten, preserving the integrity of the chain of evidence.
Applications and Benefits
The FreeRef-1 system is particularly suitable for forensic applications such as traffic accident investigations, damage investigations on ship bows, placing real-world size references in 3D scans, and measuring crop growth in greeneries. Its contactless and projection-angle-tolerant features offer many benefits, including time savings, reduced manpower, increased measurement accuracies, and minimized contamination risks. The system is expected to be priced similarly to a regular external camera flash, around EUR 500, making it a cost-effective solution for forensic professionals.
In summary, the FreeRef-1 system represents a leap forward in forensic photography, providing a safer, faster, and more accurate method for documenting evidence without the need for physical size references, which can be cumbersome and risk contaminating the scene.
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