In this paper we first describe the pinhole camera model that considers cameras as central projection systems. In order to perform accurate measurements, the linear camera model and the Zhang's method are improved in order to take nonlinear parameters into account and compensate the distortion contribute. This method is very diffused as it requires a simple setup and it allows to calibrate cameras using a simple and fast procedure, but it does not consider lenses distortions, that must be taken into account with short focal lenses, commonly used in video surveillance systems.

One of the most used camera calibration method is the Zhang's method, that allows the estimation of the linear parameters of the camera model. The most important one is the camera calibration, which is the estimation of the parameters defining the camera model. Yet, different methodological issues must be considered in order to perform accurate measurements using images. Video surveillance systems are commonly used as important sources of quantitative information but from the acquired images it is possible to obtain a large amount of metric information. Results show no significant difference between the two calibration approaches working with fish-eye camera in test field, while evidence of differences was found in the measurement on the actual cases. The height of four known persons was measured and used as reference value for validation. Moreover, two actual cases, both characterized by common low-resolution and distorted images, were also analyzed. Both approaches were applied to several frames acquired by a fish-eye camera and then measuring the height of five different people. The performance of the software in correcting distorted images is compared with a technique of single view self-calibration.

A stable and reliable approach of camera calibration is needed since investigators have to deal with different cameras while inspecting the crime scene. This study focuses on the aspect of camera calibration to verify human height extraction by Amped FIVE software, which is adopted by the Forensic science laboratories of Carabinieri Force (RaCIS), Italy. A weak model, which is not able to properly describe and correct the lens distortion, could introduce systematic errors. More specifically, those introduced by lens distortion are present in wide-field-of-view lens such as VSCs. In this study, some aspects of human height extraction from VSC video frames are analyzed with the aim of identifying and mitigating error sources that can strongly affect the measurement. Video surveillance camera (VSC) is an important source of information during investigations especially if used as a tool for the extraction of verified and reliable forensic measurements.

Amped five trial version