Reduction of Background Features in Images of Fingerprints Using Combinations of Images Acquired Under Different Lighting Conditions

• NCJ Number: 199516
• Journal: Journal of Forensic Identification Volume: 53 Issue: 2 Dated: March/April 2003 Pages: 198-208
• Author(s): Bruce A. Comber
• Date Published: March 2003
• Length: 11 pages
• Publication Format: Article
• Publication Type: Report (Study/Research)
• Language: English
• Country: United States of America

Annotation

This article describes procedures in two cases in which background features in images of fingerprints were reduced to allow for a clearer image of the fingerprints.

Abstract

Images of a subject can be recorded under different lighting conditions that produce varying relationships of the brightness or darkness among the images. Images of the same subject produced under different lighting conditions can be combined in different proportions in an additive or subtractive manner to allow a feature, such as background printing or pattern, that is visible in both images to be significantly reduced in prominence. This technique is useful in reducing the visibility of features that interfere with other features of primary interest within an image, such as fingerprints. In one case described in this article, the image recorded was of white paper with a red star symbol bearing a ninhydrin developed fingerprint. Through experimentation, the red symbol was observed to reflect red light in the vicinity of 650 nm and absorb blue light in the vicinity of 450 nm. Images acquired under these conditions provided a significant difference in the appearance of the red symbol, allowing it to be eliminated. In the second case described, the image was of a piece of paper with writing across it in lead pencil, which obscured a fingerprint developed with DFO (a reagent producing a photoluminescent result) and later treated with ninhydrin. Two images were recorded, one under 505 nm incident light and the other with white light. The use of a 565 nm filter for both images tended to absorb the color of ninhydrin, producing contrast between the fingerprint (dark) and the background (light). The two images differed predominantly in the intensity of the fingerprint. The pencil marks were relatively consistent in that they remained dark. Any combination of the images resulted in the pencil marks remaining dark. Inverting one of the images, however, resulted in the fingerprint detail remaining strong while the pencil marks were eliminated. Details of the equipment and procedures used in these two cases are provided. 11 figures and 7 references