Volume 37, Issue 4 (July 1992)
Forensic Photography and Nighttime Visibility Issues
Photographic demonstrative evidence can be of great value in bringing an understanding to the court regarding visibility issues involved in a nighttime scene. However, there are a number of criteria that must be satisfied to ensure the results accurately represent the visibility conditions. The use of a slide duplicating film results in good contrast fidelity and an extended luminance range. With appropriate calibration, the resulting slides can be projected with neutral-density filters used to reduce the projector output such that the luminance of the screen image is made equal to the luminance that would have existed at the scene. This is important because the thresholds of vision are heavily dependent upon adaptation level. Angular fidelity is achieved by calculating the viewing distance, which will give all scene objects their true angular size. A procedure is described that allows a numerical evaluation of the fidelity of the resulting projected images with respect to threshold observation of scene detail. This numerical evaluation procedure may also be useful in seeking the exclusion of nighttime photos that do not meet the criteria.