Latent fingerprint detectors and fingerprint scanners therefrom

Abstract

An automatic fingerprint system includes an optical sensor having a first light source that provides a collimated beam for interrogating a first sample surface, and a camera including a lens and a photodetector array having a camera field of view (FOV CAMERA )large enough to image the first sample surface. The camera is critical angle positioned relative to the first light source to receive specular reflection (glare) from the first sample surface to generate image data from the glare. The first light source and camera have substantially equal and opposite numerical apertures (NAs), A computer or processor that includes reference fingerprint templates receives a digitized form of the image data, and includes data processing software for (i) comparing the image data to reference fingerprint templates to determine whether the image data includes at least one fingerprint and (ii) for generating a fingerprint image if the fingerprint is determined to be present.

1 . A latent fingerprint detection system, comprising:
 a first light source that illuminates a sample surface such that the sample surface produces specular reflection; and   an optical detector arranged at a critical alignment angle relative to the first light source such that the optical detector captures the specular reflection from the sample surface and generates image data using essentially only the specular reflection to generate image data of the sample surface; and   an image processor that:
 analyzes said generated image data to determine if said generated image data includes a fingerprint; and 
 produces image data of the fingerprint responsive to a determination that said analyzed image data includes a fingerprint. 
   
     
     
         2 . The system of  claim 1 , wherein said first light source and said optical detector have substantially equal and opposite numerical apertures. 
     
     
         3 . The system of  claim 1 , wherein the optical detector is aligned relative to said sample surface at an alignment angle that is substantially equal to an angle of reflection from the sample surface of the light provided by said first light source. 
     
     
         4 .- 10 . (canceled) 
     
     
         11 . The system of  claim 1 , wherein said image processor analyzes said image data of the sample surface to determine if said image data includes a fingerprint by performing slope detection. 
     
     
         12 . The system of  claim 1 , further comprising a second light source that illuminates a sample surface such that the sample surface produces diffuse reflection. 
     
     
         13 . The system of  claim 1 , further comprising:
 at least one scanner mechanically coupled to said optical detector for scanning said optical detector across a plurality of regions of interest on said sample surface.   
     
     
         14 .- 17 . (canceled) 
     
     
         18 . A method of detecting surface contaminants using specular reflection, comprising:
 illuminating a sample surface with a first light source such that the sample surface produces specular reflection;   arranging an optical detector at a critical alignment angle relative to the first light source such that the optical detector captures the specular reflection from the sample surface and generates image data using essentially only the specular reflection to generate image data of the sample surface;   analyzing said generated image data of the sample surface to determine if said generated image data includes an image of a surface contaminant; and   producing image data of the contaminated area responsive to a determination that said analyzed image data includes an image of a surface contaminant.   
     
     
         19 . The method of  claim 18 , wherein said arranging further comprises configuring said first light source and said optical detector such that they have substantially equal and opposite numerical apertures. 
     
     
         20 . The method of  claim 18 , wherein said arranging further comprises aligning said optical detector relative to said sample surface at an alignment angle that is substantially equal to an angle of reflection from the sample surface of the light provided by said first light source. 
     
     
         21 .- 27 . (canceled) 
     
     
         28 . The method of  claim 18 , wherein said surface contaminant comprises a fingerprint and said analyzing includes performing slope detection on said image data of the sample surface. 
     
     
         29 . The method of  claim 18 , further comprising second illuminating a sample surface with a second light source such that the sample surface produces diffuse reflection. 
     
     
         30 . The method of  claim 18 , wherein said surface contaminant is a fracture or physical defect in the sample surface. 
     
     
         31 . The method of  claim 18 , wherein illuminating a sample surface with a first light source further comprises illuminating said sample surface with a plurality of parallel aligned fluorescent tubes aligned fluorescent tubes arranged to collimated light as well as non-collimated light. 
     
     
         32 .- 33 . (canceled) 
     
     
         34 . A latent fingerprint detection system, comprising:
 a light source alignment portion configured to align a light source at an illumination angle relative to a sample surface such that said light source illuminates said sample surface so that the sample surface produces specular reflection; and   a specular reflection discriminator configured to direct the produced specular reflection to an optical detector aligned relative to said sample surface at an alignment angle that is substantially equal to an angle of reflection of the produced specular reflection such that the directed specular reflection does not saturate the optical detector; and   the optical detector captures the specular reflection from the sample surface and generates image data using essentially only the specular reflection to generate image data of the sample surface.   
     
     
         35 . The system of  claim 34 , further comprising an image processor that:
 analyzes said image data of the sample surface to determine if said image data includes a fingerprint; and   generates image data of the fingerprint responsive to a determination that said analyzed image data includes a fingerprint.   
     
     
         36 . The system of  claim 35 , wherein said image processor analyzes said image data of the sample surface to determine if said image data includes a fingerprint by performing slope detection. 
     
     
         37 . The system of  claim 34 , further comprising:
 at least one scanner mechanically coupled to said optical detector for scanning said optical detector across a plurality of regions of interest on said sample surface, where said scanner is configured to maintain the critical alignment angle during scanning.   
     
     
         38 . The system of  claim 34 , wherein the discriminator includes an optical arrangement coupled to the optical detector and where the optical arrangement has a numerical aperture of zero. 
     
     
         39 . The system of  claim 34 , wherein the numerical apertures of the light source and the optical detector are substantially equal and opposite. 
     
     
         40 . The system of  claim 34 , wherein the specular reflection discriminator includes a partial reflector that is arranged to:
 direct a portion of illumination from said light source towards the sample surface in a direction perpendicular to the sample surface; and   direct a portion of specular reflection from the sample surface into the optical detector, which is arranged to detect light coming in a perpendicular direction from the sample surface.   
     
     
         41 . The system of  claim 1 , wherein said first light source comprises a broadband light source. 
     
     
         42 . The system of  claim 1 , wherein the first light source provides a collimated beam of light. 
     
     
         43 . The system of claim  5 , wherein said collimated beam comprises a narrowband beam. 
     
     
         44 . The system of  claim 1 , wherein said first light source comprises a narrowband light source including an ultraviolet (UV) wavelength. 
     
     
         45 . The system of  claim 1 , wherein said first light source comprises:
 a broadband light source; and   a spectral filter in optical communication with the broadband light source.   
     
     
         46 . The system of  claim 1 , wherein said first light source is a laser operating at a wavelength of less than 600 nm. 
     
     
         47 . The system of claim  5 , wherein the collimated beam is an infra-red (IR) beam including at least one of a wavelength at 3.42 μm, 5.71 μm, 6.9 μm, or 8.8 μm. 
     
     
         48 . The system of  claim 1 , wherein the first light source is a plurality of parallel aligned fluorescent tubes arranged to collimated light as well as non-collimated light. 
     
     
         49 . The system of  claim 1 , wherein said optical detector includes an optical arrangement that directs and focuses incoming light onto a detector portion, and where a numerical aperture of said optical arrangement is zero. 
     
     
         50 . The system of  claim 1 , further comprising:
 a second light source that illuminates the sample surface such that the same surface produces specular reflection; and   a third light source that illuminates the sample surface such that the sample surface produces specular reflection;   wherein the sample surface is thermal printer dye film; and   wherein a wavelength band of at least one light source substantially matches an absorption spectrum of said dye film.   
     
     
         51 . The system of  claim 1 , wherein the sample surface is glossy paper. 
     
     
         52 . The method of  claim 18 , wherein said first light source comprises a broadband light source. 
     
     
         53 . The method of  claim 18 , wherein said first light source comprises a broadband light source. 
     
     
         54 . The method of claim  22 , wherein providing a collimated beam of light includes providing a narrowband beam. 
     
     
         55 . The method of  claim 18 , wherein said illuminating including providing narrowband light in an ultraviolet (UV) wavelength. 
     
     
         56 . The method of  claim 18 , wherein said illuminating including providing broadband light; and
 spectrally filtering said broadband light such that said sample surface is illuminated with spectrally filtered light.   
     
     
         57 . The method of  claim 18 , wherein said illuminating including illuminating the sample surface with a laser operating at a wavelength of less than 600 nm. 
     
     
         58 . The method of  claim 18 , wherein said illuminating including illuminating the sample surface with an infra-red (IR) beam including at least one of a wavelength at 3.42 μm, 5.71 μm, 6.9 μm, or 8.8 μm. 
     
     
         59 . The method of  claim 18 , wherein said arranging further ding setting a numerical aperture of said optical detector to zero. 
     
     
         60 . A method of detecting latent fingerprints using specular reflection, comprising:
 arranging a first light source such that it illuminates a sample surface so that the sample surface produces specular reflection;   arranging an optical detector at a critical alignment angle relative to the first light source such that the optical detector captures the specular reflection from the sample surface and generates image data using essentially only the specular reflection to generate image data of the sample surface;   analyzing said generated image data of the sample surface to determine if said generated image data includes an image of a fingerprint; and   producing image data of the fingerprint responsive to a determination that said analyzed image data includes an image of a fingerprint.