Lens correction techniques and their application in forensic photogrammetry

In the field of forensics, digital media, such as images and videos, can become key pieces of evidence in any investigation. However, to correctly use images and videos for analysis and measurement, the images must be geometrically true. As such, it is essential to perform correction of the distortion of the images caused by the lens of the camera, as is recommended by forensic photography best practices and guidelines. In order to quantify the error associated with this correction, 3 techniques were compared: control point, straight-line, and manual lens correction. An idealized digital image was first created with no distortion, which was then distorted to 10 varying severities. Each resulting image was then corrected by each of the 3 techniques to attempt to remove the distortion. The level of distortion remaining was quantified by examining specific pixel locations before distortion and after correction. The results of the study found that the control point technique outperformed both others, with the manual technique outperforming the straight-line method. In regard to the application in forensics, the control point technique is the most accurate and also provides camera location information, and thus is the most suitable for use.