Image enhancement of ninhydrin-processed and colored fingerprints

Abstract

Image enhancement of a pre-processed and colored ˆngerprint with complex background patterns has high demand in appraisal evaluation of forensic evidence. This paper focuses on image enhancement of ninhydrin-processed ˆngerprints on periodic-patterned backgrounds. Contrast adjustment usually does not work well for separation between ˆngerprints and periodic-patterned backgrounds because of similarity in their color scales and / or superposing patterns. As alternative methods of contrast more enhanced ˆngerprints than the contrast adjustment does. If some periodic patterns remain after the processing of each approach, these patterns can be removed by using frequency ˆltering based on 2-dimensional Fast Fourier Transformation. It is eŠective to apply the hue-based approach ˆrst and, if the enhancement of ˆngerprints is not su‹cient, then it is recommended to use the PCA-based approach both in RGB and CIELAB color space. Proposed methods are easy to be conducted when an RGB image including a colored ˆngerprint is given by a common digital camera or ‰atbed scanner. Our methods can also be used even when an image for background subtraction is not available. Proposed methods expand the capability of utilizing colored ˆngerprints processed by ninhydrin for the forensic evidence.