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(Work performed in collaboration with the United States Secret Service)
Wide-field Chemical Imaging combines molecular spectroscopy and digital imaging for the chemical analysis of materials. The nondestructive technique requires little to no sample preparation thus decreasing potential contamination and increasing the efficiency of sample analysis. It also provides high spatial and spectral resolution data as well as qualitative and quantitative chemical information on both organic and inorganic species. Forensic scientists are able to utilize these advantages along with fluorescence and visible absorbance modalities to increase material analysis capabilities.
Conventional fingerprint imaging systems collect data at one specific color (single barrier filter configuration). By contrast, wide-field Chemical Imaging separates an image into individual wavelengths in a qualitative manner. This enables the examiner to discern usable information from a background on a pixel by pixel basis. Unwanted background response including intrinsic fluorescence, texture and colors can be minimized.
- Improved contrast between ridge detail & background
- Improved contrast on difficult backgrounds (patterned or fluorescent)
- Scan numerous emission wavelengths without having to change filters
Conventional fingerprint detection and enhancement is commonly performed using excitation from a suitable forensic light source, with direct image capture on photographic film or via a high sensitivity charge-coupled device (CCD) camera. For luminescent prints, a suitable barrier filter is required that blocks the reflected excitation light and only transmits the weak fingerprint emission. With wide-field Chemical Imaging, the liquid crystal tunable filter (LCTF) eliminates the need for barrier filters.
Figure 1. shows a $10 bill with a fingerprint visually obscured by the dark background. Chemical Imaging provides a means to minimize background contributions, resulting in enhanced ridge detail in the print.
The Condor™Wide-field Chemical Imaging System combines molecular,spectroscopic and imaging information by recording images of the sample as a function of wavelength. Through the use of an LCTF, a fully resolved spectrum, unique to the material, is recorded for each pixel location in the image. Contrast in the resulting chemical image is due to the varying amounts of absorption or emission which occurs at a given wavelength of light. This contrast provides structural, quantitative and compositional information. An advantage of a wide-field Chemical Imaging system is that the LCTF is computer controlled, therefore the parameters for a particular series of experiments needs set up only once. With limited knowledge of a particular fingerprint’s absorption or luminescence or any interference from the background, the system can be set up to analyze the fingerprint over a wide spectral range. The operator can then utilize the software to isolate the maximum absorption or emission of a treated fingerprint, thereby optimizing image contrast.
CI Xpert ™ software takes advantage of variability present at multiple wavelengths to further enhance image contrast through the use of multivariate statistical tools.
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