Evaluating high dynamic range (HDR) processing with regards to the presence of individualizing characteristics in shoeprint impressions
Kristin Rogahn, Forensic Scientist
Ventura County Sheriff’s Office
Forensic Sciences Laboratory
Ventura, CA
See also the instructional video "Using High Dynamic Range (HDR) in Crime Scene and Evidence Photography"
Abstract:
Difficult lighting situations that lead to challenging photographic conditions are common at crime scenes. It is imperative that the photographer accurately documents the scene details despite vast differences between the brightest areas and the darkest shadows. High Dynamic Range (HDR), unlike painting with light, is a method for processing a series of photographs into one image that captures the fullest range of highlights and shadows present in the original impression. HDR is a method used to increase the span between shadows and highlights in an image by taking more than one picture of the same scene – shots that maximize shadows, maximize mid-tones, and maximize highlights – and then merging them into one unified picture with tremendous tonal range. This research found that HDR processing of multiple images does not produce a significant increase in detailed information compared with viewing the same images in Photoshop. However, exposure (auto)bracketing increases the ability to capture more detailed images of footwear impressions than a single image alone, and allows the use of HDR software for rapid processing and comparison.