Characteristic of a Bullet´s Digital Images Under the Illumination of Different Wavelengths

When a gun is fired, it makes special marks on its bullet casing and projectile. We call these marks as firearm fingerprints. These firearm fingerprints can be distinguished as we identify a person from his fingerprints. The fireball firearm identification system, which is digital imaging and surface profiling information system for forensic ballistics identification, consists of CCD camera, microscope, ring-light source, stepper motor, projectile specimen, graphic capture card and a computer. The fireball system works in line-scan manner. It can take images of cylindrical projectiles and cartridge cases for identification, while it is difficult to deal with the cylindrical projectiles and cartridge cases by traditional method. In this paper in order to find which wavelength light is the best light for the digital images of projectiles, we use the fireball system under the light illumination which wavelength is from 400 nm to 700 nm. For simplicity, the projectiles are motionless. Experiment reveals that the longer wavelength light has better effect on the digital images. The high quality of images of projectiles is the basis for their accurate identification.