GB2542888A

GB2542888A - Fingerprint imaging

Info

Publication number: GB2542888A
Application number: GB1612804.3A
Authority: GB
Inventors: Marsh Nick
Original assignee: Mayor's Office For Policing And Crime
Current assignee: Mayor's Office For Policing And Crime
Priority date: 2015-07-24
Filing date: 2016-07-25
Publication date: 2017-04-05
Anticipated expiration: 2036-07-25
Also published as: GB201612804D0; GB2542888B; GB201513137D0

Abstract

An imaging apparatus comprises a camera, 20, and a housing, 10, in which is contained a support, 24, for a lifted fingermark (fingerprint, palm print, footprint, lift), spaced from the camera. A first light source, 22, is positioned on the same side of the support as the camera, such that when a fingermark, 30, is located in the support, light from the source may be reflected from the fingerprint into the camera. A light absorbent material (e.g. black velvet), 28, is placed beneath the support to improve the contrast of this image. A second light source, 26, is positioned on the opposite side of the support as the camera, such that when a fingermark is located in the support, light from the second light source may be transmitted through the fingermark into the camera. The housing may be divided into two compartments, 12, 14, with the support situated between the two compartments. The first and second light sources may be provided by separate light generators. The light absorbent material may be mounted on a movable member and its movement may expose the second light source.

Description

Fingerprint Imaging

The present specification relates to fingerprint imaging, particularly of fingerprints that have been transferred to a lifting tape or similar medium.

The retrieval of latent evidence at crime scenes to identify the perpetrator is intrinsic to a successful forensic investigation. Fingermarks are one of the key types of evidence that can be found. The retrieval of these from a scene generally involves manually powdering the scene with aluminium powder, which sticks to the fingermark. The aluminium powder is then 'lifted' using adhesive tape, preserving the pattern of the fingermark, and this tape is then stuck to a sheet of Cobex (RTM), (a thin clear plastic sheet of PVC) forming a sandwich with the aluminium-enhanced fingermark in the middle, known as a 'lift'.

The lift must either be manually transferred to a central place fingerprint bureau, or transmitted via 'scan and send' from a police station (a remote scanner), where it is scanned into the Automatic Fingerprint Identification System. (AFIS).

The lift is placed on a flatbed document scanner, controlled by dedicated software.

The software and scanner only provide for limited adjustments to made by the operator to try to ensure that the best capture has been made. The scanners are irregularly calibrated, and combined with incorrect lighting and are prone to produce less then the optimal results, on marks, which contain a full grey scale. They also produce an end result, which is in a JPEG compressed format and is therefore forensically questionable.

Alternatively, the lift may be photographed by a professional photographer, though this involves greater expense and delay.

Whether that fingermark is scanned at a police station or a central place fingerprint bureau, there is always a time delay between a mark being lifted and then loaded onto the AFIS system.

The object of the present invention is to provide a fast and convenient means of capturing a high quality image of the fingermark.

According to a first aspect of the present invention, there is provided a fingerprint imaging apparatus comprising; a camera, a housing, in which is contained a support for a fingermark or similar, spaced from the camera, an upper light source, positioned above the support such that when a fingermark is located in the support, light from the upper light source may be reflected from the fingermark into the camera, and a lower light source, positioned beneath the support such that when a fingermark is located in the support, light from the lower light source may be transmitted through the fingermark into the camera.

In some embodiments the housing is divided into an upper compartment and a lower compartment, with the support situated generally between the upper and lower compartments.

In some embodiments the upper light source and lower light source are provided by separate light generators.

In some embodiments the light absorbent material is provided on a moveable member, which is situated beneath the support in a first position, but may be moved to expose the lower light source in a second position.

In some embodiments a channel is provided in the side of the housing for the fingermark or the like and/or the support to be slid into position.

According to a second aspect of the present invention there is provided a method of imaging a fingerprint comprising the step of providing the apparatus of any preceding statement of invention. 'Fingermarks or the like' includes impressions left by any part of a body on other objects; while the tips of the fingers and thumbs are most commonly used, similar impressions left by the palm, sole of the foot, ears could also be used.

The term 'camera' here indicates any apparatus which is capable of capturing a still or moving image using electromagnetic radiation.

Terms such as 'upper', 'lower', 'top', 'back', 'above', 'beneath' and similar cognates refer to the orientation of the apparatus as shown in the diagrams, though it will be appreciated that the particular orientation of the camera to its environment is unimportant.

The invention will now be described, by way of example, with reference to the drawings, of which:

Figure 1 is a sectional side view of the image capture apparatus;

Figure 2 is a diagrammatic representation of the image in a first capture mode;

Figure 3 is a diagrammatic representation of the image in a second capture mode; and Figure 4 is a sectional side view of another embodiment of the image capture apparatus.

Referring to figure 1, the fingerprint imager comprises a camera 20 attached to a housing 10. The housing is divided into an upper section 12 and a lower section 14 by a dividing wall 15. The dividing wall includes an aperture 24 centrally located. One side of the housing 10 includes a longitudinal slot 16 just below, parallel to, the dividing wall 15. An image capture window 25 can slide from a position beneath the aperture 24, through the slot and extend out of, or be removed from, the housing. The image capture window is retained along a sliding path by for example grooves in the walls of the housing 10. The image capture window comprises a rigid frame with a an aperture capable of supporting a lift (for example, by being slightly smaller than the outer dimensions of the lift), and thereby avoid adding any pattern or artefact to the image of the lift. This avoids one of the problems of the use of a scanner, where imperfections, scratches, marks or dust of the scanner platen, and interference between the surfaces of the lift medium and the platter, cause anomalies and artefacts in the captured image.

The camera 20 is attached to the upper surface of the upper section, with the lens directed to the image capture window 25. An upper light source 22 is also included in the upper section, also directed to the image capture window 25. The upper light source is set to one side of the centre of the upper housing (which is occupied by the camera lens), so that light directed to the image capture window will be somewhat inclined from the vertical.

The lower section 14 contains a lower light source 26 located on a vertical wall of the lower section, for example by an array of LEDs behind an opaque scattering material, so as to provide a diffuse light source. The floor 28 of the lower section 14 is covered in a light absorbent material 28 such as black velvet. An angled glass plate 32 (typically set at 45° to the side wall) is provided, generally dividing the lower section 14.

The housing 10 is designed to exclude outside light from penetrating the housing. It may be made of metal or another robust material.

To use the apparatus, the image capture window 25 is slid outside the slot (in the direction of arrow e) so that it is exposed. A lift 30 is positioned on image capture window. The image capture window may have a depression or shape to receive the lift.

The image capture window, having the lift positioned on it, is then slid through the slot 16 into the housing, until it is located beneath the aperture 24 in the dividing wall 15.

The image is then illuminated. There are two modes of illumination. The first mode is when the lift is illuminated from above by the light 22 (generally indicated by arrow a) in the upper section 12. Referring to figure 2, some of this light is reflected by the material producing the fingermark towards the camera to form a bright image. During this mode of illumination, the lower light source is not illumined, so any light entering the lower section of the housing is absorbed by the black velvet floor of the lower housing beneath the angled glass plate. This produced a black background to the bright image of the fingermark, providing a good contrast.

This mode of illumination is particularly suitable for lifts whose fingermarks have been produced using aluminium fingerprint powder. The light source is positioned angled to maximise the amount of light reflected from the image capture window plane to the lens of the camera for the geometry of the upper housing. In this manner, a clear image can be produced relatively independently of the density of the aluminium powder, allowing faint fingermarks to be captured.

The second mode of illumination is when the lower light source is illuminated. A proportion of the light from the lower light source is directed to the glass plate (generally indicated by arrow b) (the proportion depending upon, amongst other factors, on the angle the glass plate and its coating), and then reflected upwards (generally indicated by arrow c) towards the fingermark on the image capture window, and depending on the geometry, some falls on the camera lens. Referring to figure 3, when a fingermark is placed on the image capture window and bottom lit in this manner, some of the light which falls on the material making up the fingermark will be scattered or absorbed. Light which does not fall on the material making up the fingermark passes unimpeded up towards the camera. This produces a dark image of the fingermark against a bright or white background.

This mode of illumination is particularly suitable for lifts whose fingermarks have been produced using black fingerprint powder. The lower light source is chosen to be relatively soft, so that the faint subtitles and variations in the fingermark image captured by the lens are not burnt out by an excessively intense background.

The camera output is connected to a display screen, so that the user can view the captured image when the image capture window has been placed in position underneath the aperture of the dividing wall. The camera is chosen to be capable of capturing an area of sufficiently high resolution, for example a 2 x 2inch (approximately 5cm by 5cm) area at lOOOppi, to be useful. The sensor plane to lift distance/will be dependant on the particular camera chosen A limited input means and user interface is provided to allow the user to make adjustments. In particular, this will allow the user to switch between the top lit and back lit modes depending on the type of fingerprint powder that has been used to produce the fingermark, so that the optimum image is captured. Once a user is satisfied, the user captures the image. Typically, this will be a uncompressed bit map file using a high greyscale gradation such as 16 bits, allowing the accurate capture of fine detail. The image may then be electronically transmitted to the AFIS (e.g. by a secure network transmission).

The two modes of illumination, in conditions where both the lighting and contrast can be optimised for the image capture and operating in a largely automatic manner, offer superior performance to conventional methods. In testing over a two month period 188 lifts, which had been previously scanned through two different scanner systems, with a negative outcome on the AFIS system, were re-examined using the described apparatus. 83% of the lifts, showed a noted improvement in the quality of the mark, and out of these, 6% were successfully identified and 24% were searched and eliminated from enquiries. In no case was a inferior result noted.

Referring to figure 4, in an alternative embodiment the lower section 14 contains a lower light source 27 located on a floor of the lower section, which as for the previous embodiment may be an array of LEDs behind an opaque scattering material, so as to provide a diffuse light source. A baffle 31 is covered in a light absorbent material 29 such as black velvet. The baffle 31 is suspended at one end on a pivot shaft 45 which is attached to the side walls of the lower section of the housing, and handle 44 runs in a groove 35. The groove 35 is an arc centred on the shaft 45, so that the baffle 31 can be pivoted between a lower position where it lies parallel and closely spaced to the floor of the lower section 14 of the housing, and an upper position 29' (shown in dotted line), where the baffle lies generally against a side wall of the lower section in a vertical position. The baffle may be moved between the upper and lower positions by the user grasping the handle 44.

When the user intends to illuminate the fingermark from above, the user ensures that the baffle 31 is in the lower position 29 so that the light absorbent material 29 forms a dark background to the fingermark while it is top-lit by the upper light source 22 in the manner previously described. Alternatively, when the user intends to illuminate the sample from beneath, the baffle 31 is moved to the upper position 29' so that path between the lower light source 27 and the image capture window (generally indicated by arrow d) is unimpeded, so that the lower light can back-light the fingermark as previously described.

The upper and lower light sources, as well as being provided in different locations (and directions), also ideally have different qualities, the upper light source may be LEDs in a relatively small area resembling a point source, while the lower light source is more diffuse. However, the characteristics could be varied, and the upper light course could for example be provided by an annular light ring. The light from the upper and lower light sources is ideally white, but other colours or specific spectra could be used.

It will also be realised that mirror light guides, prisms and similar means may be used to direct the light to the fingermark, which may allow a single light generator to be used to provide both the upper light source and lower light source by altering the manner that the light is directed.

In the embodiments described above, the image capture window 25 is configured to slide through a slot to allow the lift to be mounted. It will be apparent that alternative configurations could equally be provided, such as enabling the two sections of the housing to pivot open to allow the lift to be placed on the image capture window.

Many variations are possible without departing from the scope of the present invention as defined in the appended claims.

Claims

Claims:

1. An imaging apparatus comprising; a camera, a housing, in which is contained a support for a fingermark or the like, spaced from the camera, an upper light source, positioned above the support such that when a fingermark is located in the support, light from the upper light source may be reflected from the fingermark into the camera, a lower light source, positioned beneath the support such that when a fingermark is located in the support, light from the lower light source may be transmitted through the fingermark into the camera, and a light absorbent material provided beneath the support.

2. An apparatus according to claim 2, wherein the housing is divided into an upper compartment and a lower compartment, with the support situated generally between the upper and lower compartments.

3. An apparatus according to either previous claim, wherein the upper light source and lower light source are provided by separate light generators.

4. An apparatus according to any previous claim, wherein the light absorbent material is provided on a moveable member, which is situated beneath the support in a first position, but may be moved to expose the lower light source in a second position.

5. An apparatus according to any previous claim, wherein a channel is provided in the side of the housing for the fingermark or the like and/or the support to be slid into position.

6. A method of imaging a fingerprint comprising the step of providing the apparatus of any preceding claim.

7. An apparatus as herein described and illustrated.

8. A method as herein described and illustrated.