Subjectivity¹ is problematic when evaluating fingerprints², and quality is in the eye of the examiner. But three computer programs used together can give fingerprint³ grading unprecedented⁴ consistency⁵ and objectivity, according to Penn State researchers. "People leave behind all kinds of fingerprints, and the job of a forensic⁶ examiner is then to look at a fingerprint and identify a person who could have left it," said Akhlesh Lakhtakia, Charles Godfrey Binder⁷ Professor of Engineering Science and Mechanics, Penn State. "Various scenarios⁸ can be envisioned（预期，展望） where a fingerprint can be seriously altered. Once it is altered, it can conceivably lead the examiner to a false conclusion."

 

Fingerprints usually undergo environmental weathering and smudging（弄脏，弄模糊）. The condition of a fingerprint affects how reliable a match can be between a collected print and prints on record. Knowing a fingerprint's dependability can minimize the chance of a wrongful or delayed conviction.

 

Lakhtakia's team created a process using three inexpensive computer programs to grade a fingerprint for the availability of ridge⁹ detail for subsequent identification. Computerized grading ensures standardized¹¹ evaluation¹² to a degree finer than any human can accomplish. They report their results in the current issue of Forensic Science International.

 

"The quality of a fingerprint can be graded finer than on a zero, one, two, three scale," Lakhtakia explained. "Two point three per cent is worse than fifteen per cent, but both could be graded as a zero by the naked eye. Humans can't grade finer than the zero to three scale. But computers can."

 

The three separate computer programs include the FBI's Universal Latent Workstation -- usually free to qualified¹³ agencies, the open-source image editor GIMP and a simple custom program written in Mathematica to count pixels.

 

Investigators¹⁴ photograph the fingerprint -- developed for visualization¹⁵ or not -- and run the picture through the Universal Latent Workstation. This program creates a simplified map of the fingerprint by designating colors to four area types. The background area is black, areas with definite ridges¹⁶ are white, and debatable regions are yellow and blue.

 

The GIMP editor converts the map file into an image file with red-green-blue color values. The RGB values are stored as number clusters that a computer program can easily translate into binary¹⁷ sequences（二元序列） useable in a mathematical equation.

 

A pixel-counting algorithm in Mathematica calculates the total percentage of white pixels from imported RGB pictures, essentially¹⁸ creating a grading scale ranging from 0 to 100. A high-quality fingerprint would have a high number of white pixels, while a potentially unreliable print would mostly appear in yellow and blue.

 

The ease and relative speed of this grading system may help to standardize¹⁰ fingerprint quality assessment¹⁹ in an inexpensive, efficient manner.

 

"The next step of this kind of research is, is there false detail created by development techniques?" Lakhtakia said. "That can happen. Looking at the thin-film technique that my group has developed, I don't imagine so, but we would obviously have to prove it."

 

Other researchers from Penn State on this project include Drew Pulsifer, graduate student in engineering science and mechanics; Sarah Muhlberger, fingerprint technician; Stephanie Williams,recent graduate in forensic science; and Robert Shaler, retired²⁰ professor of forensic science.

 

The U.S. Department of Justice funded this research.

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