NCJ Number
206162
Journal
Law Enforcement Technology Volume: 31 Issue: 6 Dated: June 2004 Pages: 38,40,42-46,48
Date Published
June 2004
Length
8 pages
Annotation
This article describes digital image resolution and discusses the forensic importance of quality digital images.
Abstract
Resolution is a misunderstood term in the burgeoning industry of digital imagery. Resolution is vitally important because it affects image quality, authenticity, and enhancement processes in law enforcement. Failing to understand resolution, therefore, can have deleterious outcomes for law enforcement. For example, while law enforcement agencies may spend thousands of dollars on high-resolution digital cameras, they print their images on inexpensive paper using inkjet printers, resulting in a poor quality digital image. Defense attorneys are learning how to challenge the integrity of digital images, thus law enforcement should consider resolution throughout the entire process, including printing. The author presents a crash course in resolution basics in order to clear up the confusion surrounding the issue of digital image resolution. The difference between pixels and dots is described and the importance of resolution is illustrated with the two-line test. The quality of the output device and the resolution of the original image determines the final size and quality of the digital image. The Federal Bureau of Investigation’s (FBI) requirements of the minimum resolution of latent prints is described, along with the requirement that the digital images be printed in life size in order to see the value of the resolution. The author goes on to consider how large to print images, including the limitations presented by current cameras on the market, and then discusses the debate surrounding the loss of imaging quality. The main argument in this debate is that the loss of image quality is inconsequential unless using a low-image quality setting. However, in the case of forensic applications, any degradation in image quality affects how clearly details are displayed. When purchasing cameras, not only should law enforcement agencies look for high-resolution cameras, they should also consider the image storage capacity and whether images are stored using a low-resolution JPG format, which allows more images to be stored in exchange for loss of detail. For the best forensic results, cameras that provide either RAW or TIF image file format settings are the best choice. Finally, the printer quality is often the lowest common denominator in any digital imaging system. Figures