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Color Separation of Signature and Stamp Inks to Facilitate Handwriting Examination

NCJ Number
Journal of Forensic Sciences Volume: 48 Issue: 6 Dated: November 2003 Pages: 1396-1405
Alan Chaikovsky B.Sc.; Sharon Brown M.Sc.; Laser Sin David; Alex Balman M.A.; Avner Barzovski M.Sc.
Date Published
November 2003
10 pages
This article discusses new digital photography methods that may be used to facilitate handwriting examination.
The value of digital image processing in questioned document analysis has shown itself useful through various applications in an abundance of questioned document cases. There are no reports to date of how these image-processing methods can be applied to the separation of rubber stamp inks intersecting with handwritten signatures. The four most common color combinations discussed here are black or purple (stamp colors), and blue or black (signature). Four methods for dealing with these combinations are a traditional analog method, digital methods using the "RGB-HSB-CMYK" models, the digital L*a*b color method that is principally useful for separating blue, red or green writing inks from various stamp inks, and the digital method using the “Channel Mixer” function. When using analog technology in the photographic separation of an inked signature from the ink of a rubber stamp, one is confined to the use of certain light sources, filters, and films. The photographer can only assess the success of the photograph once it has been developed, a process that demands time and use of material. Digital photography and image processing software enable the photographer to view the resultant photograph in real time. An unsuccessful image can be discarded at the touch of a button, with little waste of time and effort. A quality photograph can be enhanced and processed using different color models and functions, enabling the document examiner to complete a handwriting comparison that previously would have been limited and confined. Using the analog method, only very specific combinations of colored ink may be separated. Using digital photography and software, most, if not all, of the common ink color combinations can be successfully separated. Each case should be approached individually until a satisfactory separation is achieved using one of the color models. The Channel Mixer method was found to be the most universal. 7 figures, 6 references