NCJ Number
191261
Journal
Journal of Forensic Identification Volume: 51 Issue: 4 Dated: July/August 2001 Pages: 378-384
Date Published
2001
Length
7 pages
Annotation
Using color filters in black and white photography has long been known to enhance contrast; this method can be simulated with color photographs by using the channel mixer adjustment in Adobe Photoshop (computer software).
Abstract
The author often uses a Nikon 950 digital camera to photograph prints, because it has excellent macro capabilities. It can photograph from 2 cm away; however, the author cannot find filters or step-down rings to accommodate the lens size. His solution to this is to photograph the evidence in color and then use Adobe Photoshop's Channel Mixer to simulate the effects of black and white film with color filters. The author has used Adobe Photoshop Version 5.5 to do this, but this technique can be adapted for use in other applications, such as Paint Shop Pro and Corel Photo-Paint. The image must be a digital one, and this can be achieved either by photographing directly with a digital camera or by scanning traditional film into Photoshop. Photoshop offers several ways to create black and white images from color images, each creating different results. The user can change the mode of the image to grayscale, which renders all colors to gray, depending on their luminosity; or the user can desaturate the color from the image to render all colors with the same brightness level equally gray. The same rule that applies to filters then applies in the digital manipulation of color; adding more of any color channel (red, green, blue) makes tones rich in that color get lighter. The effect of using 100 percent or more of any channel is similar to using a filter of that color over the lens of a camera that contains black and white film. This article explains how this technique was used by the author with digital photographs of bloodstains. 6 figures and 3 references