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Image Enhancement and Adobe Photoshop: Using Calculations to Extract Image Detail

NCJ Number
Journal of Forensic Identification Volume: 57 Issue: 4 Dated: July/August 2007 Pages: 493-505
Jill Smith
Date Published
July 2007
13 pages
This article presents step-by-step instructions, along with a case example, of how to use Adobe Photoshop to clarify image details while reducing distracting background patterns during forensic print analysis.
Adobe Photoshop contains an often ignored calculations function that allows forensic investigators to enhance subject images while subtracting background images. The easily applied mathematical functions utilize color channels to help visualize the subject more clearly. The basic concept is that one or more channels (colors) containing primarily background images can be subtracted while the other channels containing the subject image can be enhanced. The enhancement technique works best on color images. The example provided is of a footwear impression captured at the scene of an assault. The footwear impression is in blood while the background in this case is a woodgrain pattern on the floor. The author recommends that forensic examiners experiment with the many channel blends in an effort to gain familiarity with the calculations function, which will ultimately help in the prediction of outcomes when using blending modes. The author presents step-by-step instructions for subtracting the woodgrain floor pattern from the image while enhancing the bloodstain footwear image. Following the 17-step procedure, the author offers calculations for the blending modes that further enhance the image quality. Figures