Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
  • G06V40/00—Recognition of biometric, human-related or animal-related patterns in image or video data
  • G06V40/10—Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
  • G06V40/12—Fingerprints or palmprints
  • G06V40/13—Sensors therefor
  • G06V40/1324—Sensors therefor by using geometrical optics, e.g. using prisms
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
  • G06V40/00—Recognition of biometric, human-related or animal-related patterns in image or video data
  • G06V40/10—Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
  • G06V40/12—Fingerprints or palmprints
  • G06V40/1335—Combining adjacent partial images (e.g. slices) to create a composite input or reference pattern; Tracking a sweeping finger movement
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
  • G06V40/00—Recognition of biometric, human-related or animal-related patterns in image or video data
  • G06V40/10—Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
  • G06V40/12—Fingerprints or palmprints
  • G06V40/1347—Preprocessing; Feature extraction
  • G06V40/1359—Extracting features related to ridge properties; Determining the fingerprint type, e.g. whorl or loop

Definitions

• the present invention relates to a system, apparatus, and method for the collection of friction ridge signatures from a subject. More particularly, the present invention relates to a low power consumption, small size, and low weight friction ridge capturing device and method for the collection of friction ridge signatures from a subject. Most particularly, the present invention relates to a low power consumption, compact, and portable digital friction ridge capturing apparatus, system and method for the collection of friction ridge signatures with a platen area of at least 3.0 square inches.
• Friction ridge impressions from a subject's fingers are commonly known as fingerprints. Animals also commonly have unique friction patterns on their footpads. In dogs and cats, for example, these patterns are called paw prints.
• Digital scanning systems that capture friction ridge impressions collectively termed herein as 'fingerprints', are old in the art. Many of these systems were designed to capture a smaller area of one or two fingerprints while others were designed to capture a much larger area. Such existing systems commonly use optical imaging, capacitance, infrared radiation, ultrasound, or other means to capture fingerprints. Many optical imaging systems are designed to capture one or two fingerprints at a time. These systems are termed 'single print devices' herein. For example, the manufacturers listed in Table 1 provide optical devices that scan one or two fingerprints at a time.
• CMOS complementary Metal Oxide Semiconductor
• the host computer or other control device is referred to as a host computer.
• There may be other components of a prior art system such as, e.g., polarizing filters, corrective optics, and holographic gratings.
• Most commercially available large format optical systems today follow this single digit system configuration. That is, they use a light source, prismatic body, TIR, camera(s), and host computer to create fingerprint images.
• "capable of capturing more than two fingerprints simultaneously” means optical devices having a surface capture area exceeding 3.0 square inches.
• large format fingerprint capture system This type of system is referred to as a large format fingerprint capture system.
• large format fingerprint capture systems include those that capture palm prints and writer's edge.
• Large format fingerprint devices typically capture fingerprints from multiple fingers simultaneously and therefore, the area upon which the subjects place their fingers must be large enough to accommodate the maximum number of fingers to be captured simultaneously. Usually, this number is four, but Cross Match Technologies provides a system that is able to capture the fingerprints in two groups of two fingerprints apiece. In effect, this Cross Match Technologies system captures four fingerprints simultaneously.
• Livescan systems one common form of large format fingerprint system, typically use a glass or plastic surface, termed a platen, upon which the subject's fingers are rolled or pressed.
• Images of the fingers' ridges are typically captured from underneath the platen by one or multiple cameras and are then converted into digital files. Images of rolled fingers are called rolled prints and images of pressed fingers are called slaps. Livescan devices are available from the sources listed in TABLE 2.
• U.S. Patent No. 3,200,701 to White discloses one such system.
• U.S. Patent No. 4,933,976 to Fishbine et al discloses a configuration comprising a prismatic-based TIR device for fingerprint capture.
• Fishbine et al. disclose a method that combines successively captured images into one image array.
• U.S. Patent Nos. 5,548,394, 5,629,764, 5,650,842, 6,178,255, and 6,407,804 all disclose variations of the TIR based prismatic platen device used to capture fingerprint images.
• the image may be generated using TIR or light dispersion from the friction ridges.
• a reference light source is an edge lit light panel manufactured by Hewlett-Packard that is illuminated by red Light Emitting Diodes (LEDs)
• LEDs Red Light Emitting Diodes
• the object plane to be imaged (the fingerprint) and the image plane of the camera are not parallel, centered, and perpendicular to a common axis.
• optics within the device must correct the positions of the object and/or image planes before the camera captures an image or the system must employ an algorithmic solution for correcting the perspective distortion introduced into the image.
• the size and weight of the device increase. For example, see U.S. Patent Nos. 5,650,842 and 6,407,804.
• the depth of field In the later cases, to avoid an unfocused image the depth of field must be deep enough for the entire object area to be in focus. Since the image is not optically corrected for perspective distortion, the depth of field requirement is driven by the three dimensional geometry of the platen, the optics used between the platen surface and the camera, and the geometric relationship between the camera and the platen surface. Typically, lenses that allow larger depths of field have focal lengths such as 30 mm or greater with corresponding f-stops often greater than 4.0. Long focal length lenses often result in a distance from the object plane to the image plane that is too large to put the entire device into a physically compact solution.
• the majority of existing optical fingerprint systems rely on LEDs for light sources. Light illuminating the platen may be either diffuse or collimated. Electricity consumers in a fingerprint device include the light source(s), the camera(s), frame grabber electronics, magnetic stripe readers, barcode readers, radio frequency identification modules, proximity card readers, smartcard readers, displays, platen heaters, platen blowers, and servomotors, if present. In total, the power used by such systems is above 10 watts for all existing large format fingerprint systems. Therefore, prior art large format fingerprint devices are powered by external power sources connected via separate cabling since power provided over a single data/control/power cable will either be insufficient or the battery on the attached computer will be drained too quickly.
• prior art systems cannot be powered only from the computer to which the device is attached.
• Most of the patented systems described above are either not compact or not lightweight and therefore they cannot be considered as portable. To be moved, these devices often require a protective case. In existing instances, the device and case weigh over 30 pounds.
• many devices must be re-calibrated once the device has been moved and reinstalled. Such re-calibration is required due to the presence of moving parts or the possibility that parts have moved relative to one another.
• Such systems also commonly address the issue of condensation on the platen. Such condensation occurs when the dew point around the platen/finger is too high relative to the ambient temperature of the prism and therefore moisture from the finger condenses on the prism.
• the system, apparatus, and method of the present invention preferably provides these features by: 1. balancing depth of field and lens focal length requirements; 2. algorithmically correcting image aberrations on the lens periphery via hardware, firmware or software; 3. algorithmically correcting perspective image distortions via hardware, firmware or software; 4.
• the camera requires at most about 2 watts and preferably at most about 1.8 watts; 5. minimizing the number of internal components as well as their weight and size so that the device weighs at most about 10 lbs and has a volume at most about 400 in 3 and preferably weighs at most about 7 lbs, more preferably less than 5 lbs and preferably has a volume less than about 325 in.
• the electrical components such as light source, camera, magnetic stripe reader, radio frequency identification (RFID) module, proximity card reader, smartcard reader, platen heater, platen blower, and barcode reader
• RFID radio frequency identification
• the present invention overcomes the deficiencies of prior art large format finge ⁇ rint devices by providing a finge ⁇ rint capture apparatus, system and method that is low power, compact, and lightweight and has a platen area greater than about 3.0 square inches, e.g., from about 3 to about 24 square inches. Further, the present invention is typically powered, controlled, and exchanges data over a single data/control/power connection to a host PC.
• the large format finge ⁇ rint device is directly connected to a completely disconnected (not plugged in to a wall power outlet or other external power source) portable PC, such as a laptop having a battery power source.
• a wireless interface e.g.
• the device may have no physical connection ports. If desired, the device exchanges data and accepts control functions via internet and/or satellite connectivity to a computer processor. In some embodiments the device may have an internal computational capability so it can direct finge ⁇ rint capture and finge ⁇ rint matching within the device using finge ⁇ rint templates that are delivered over a wired or wireless network attached to the device. Typical applications of such devices would be access control and tracking applications. The matching templates and algorithm could be updated over the electronic interface.
• the primary device components of the present invention combine to minimize required power, size and weight.
• the device of the present invention comprises a light source, a prism, a camera (including the lens), a housing, and a host computer.
• Optional elements comprise holographic elements such as gratings and holographic optical elements (HOEs), a battery subsystem, an image processing subsystem, optical filters, magnetic stripe reader, RFID module, proximity card reader, smartcard reader, barcode reader, a platen heater, a platen blower, and mirrors used to divert the image beam.
• holographic elements such as gratings and holographic optical elements (HOEs)
• a battery subsystem such as gratings and holographic optical elements (HOEs)
• an image processing subsystem such as gratings and holographic optical elements (HOEs)
• optical filters such as gratings and holographic optical elements (HOEs)
• magnetic stripe reader such as gratings and holographic optical elements (HOE
• aspect ratio changes may be used to minimize the depth of field, as taught by U.S. Patent Nos. 5,629,764 and 6,061,463 inco ⁇ orated herein by reference.
• aspect ratio, image aberration, and perspective corrections can be made algorithmically via hardware, firmware and software as provided for in the present invention.
• Ojanen, see Appendix A teaches one way of removing image aberrations and perspective distortions via such algorithms.
• technology may be used to maximize the amount of light generated per watt, as taught, by U.S. Patent Nos.
• a simple optical system has an object 1005, a lens 1001, a focus 1002, and an image 1006.
• the distance along the optical axis from the principal point to the object is the object distance 1004, o, and the distance along the optical axis from the principal point to the image is the image distance 1003, i.
• the angle ⁇ 1009 and the index of refraction n are properties of the prism 1010.
• a real object 1005 at the prism surface is imaged as a virtual object 1012.
• the Ojanen algorithm relies on the capture of a high accuracy image of a fixed array of dots of a particular size. By knowing the size and locations of the dots within a grid, the systematic discovery of barrel and pincushion distortions can be characterized by running a least squares algorithm on the error between the observed dot locations and sizes and the known dot locations and sizes. Correction of the distortions is then completed using the returned least squares parameters.
• the present invention employs a perspective correction algorithm in addition to the Ojanen algorithm.
• depth of field issues in some embodiments do not drive the lens requirement so a shorter focal distance lens can be used at the expense of potentially increasing aberrations. But, since such aberrations are predictable, they can be reasonably corrected using software that implements the Ojanen algorithm.
• f-stop setting Another important side effect of a shorter focal length lens is the f-stop setting. Since a low depth of field is required, a lower f-stop lens is used so that more efficient use is made of the light and thus size and power requirements are further reduced.
• the system power requirements of the present invention are reduced to the point that the device can be run within the limits of the power supplied via common computer interfaces such as FireWire and USB, e.g., USB-2, (Fire Wire can provide up to 50 watts of power and USB up to 2.5 watts).
• the unanticipated and non-obvious innovation of the present invention is enabling the finge ⁇ rint device to be powered by a completely disconnected laptop computer while maximizing the battery life of the laptop and thereby extending the useful amount of time the system can be used.
• the invention provides for a device that consumes at most about 3.0 watts of power, preferably at most about 2.5 watts of power.
• the light uses at most about 1 watt, preferably at most about 0.7 watts and the camera uses at most about 2 watts, preferably at most about 1.8 watts.
• a CCFL is used as one alternative to LED light sources.
• Other light sources include electroluminescent sources and lasers.
• the power source for this light is an electrical inverter that taps power off from the power originating from the host computer interface.
• a single CCFL is used to illuminate a light pipe that partially collimates the light before sending the light into a prism.
• This CCFL and light pipe construction as described in U.S. Patent Nos. 5,359,691, 5,390,276, and 5,854,872 generates enough light at a low power to serve as the system light source for the apparatus, system and method of the present invention.
• the rated lifetime of such CCFL's is about 10,000 hours of operation. As with LEDs, the rated lifetime is the amount of time the light is on at the rated power until the light output is one half of the original output.
• the light source emit enough light for the apparatus, system and method of the present invention, it also is delivered in a very compact size and thus contributes to the size of the apparatus, system and method of the present invention.
• the light source load comprises the electrical inverter and the CCFL.
• such a subsystem is needed in the case where more power is needed than the computer interface can provide.
• This can be the case, for instance, in an embodiment comprising at least one of a magnetic stripe reader, an RFID module, a proximity card reader and a smartcard reader to read demographic data from the back of a driver's license and an embodiment comprising a one dimensional or two dimensional barcode reader to read the demographic data from the bar code on the back of a driver's license.
• images are captured with either a one-dimensional (line scan) or two-dimensional (area scan) camera.
• Preferred embodiments comprise area scan cameras to increase system robustness by avoiding the use of moving parts.
• the image generated must be large enough to capture the entire object area at a prescribed resolution.
• the camera uses the light provided by the light pipe to capture images of rolled and slapped impressions of finge ⁇ rints.
• the electrical interface to the camera also comprises the control signals that operate the camera, operate the magnetic stripe reader, operate the barcode reader, operated the RFID module, operate the proximity card reader, operate the smart card reader, and turn the light source on and off. That is, in a preferred embodiment, all power, control, and data to be exchanged between the host computer and the finge ⁇ rint device are exchanged via the single connection between the computer and the device.
• control logic to capture finge ⁇ rints is how to determine when to start capturing a print and when to stop capturing a print.
• this control logic is implemented in software since the frame rate of the images delivered by the camera is high enough to allow processing on the host computer that algorithmically identifies a starting frame and an ending frame for each finge ⁇ rint capture.
• the real frame rate is 20 frames or more per second, which results in a 12-13 or more processed frames per second rate.
• the real frame rate is at least 6 frames per second which results in an at least 4 processed frames per second rate.
• the apparatus, system and method of the present invention provide a light source and camera combination that has a power and light efficiency that allows a large format finge ⁇ rint device to be powered, controlled, and to exchange data digital image frames over a single connection, such as a USB 2.0 cable connection.
• Alternative embodiments include FireWire 1.0, FireWire 2.0 and next generation peripheral interfaces.
• Alternative embodiments also include a power subsystem wherein a battery or capacitor is charged during periods of low power consumption and when more power is required more power is drawn from the power subsystem.
• non-volatile memory is included inside the device so that statistical and diagnostic data can be collected and monitored.
• the number of times the light source switches on and off is maintained in non-volatile memory so that a predetermined maintenance schedule can be followed.
• FIG. 1 illustrates a light source that can run on low power efficiently
• FIG. 2 illustrates a large format finge ⁇ rint device according to the present invention
• FIGs. 3A-B illustrate a large format finge ⁇ rint device in which a holographic grating has been inco ⁇ orated according to an embodiment of the present invention
• FIG. 4 illustrates a large format finge ⁇ rint device with either a battery subsystem or a capacitor that powers the electrical consumers of the device, according to an embodiment of the present invention
• FIGs. 5A and 5B illustrate a large format finge ⁇ rint device inco ⁇ orating a two-dimensional barcode reader with imaging capability, according to alternative embodiments of the present invention
• FIG. 6 illustrates a large format finge ⁇ rint device inco ⁇ orating a magnetic stripe reader, according to an embodiment of the present invention
• FIG. 7 illustrates an embodiment of the present invention comprising a device- resident computer processor and a device-resident non- volatile memory.
• FIGs. 8A-D are a flow diagram of the method of the present invention.
• FIG. 9 illustrates a slip case for covering the device.
• FIGs. 10A-B illustrate how changing the angle of the image sensor minimizes depth of field.
• FIG. 11 A-E illustrates a preferred compact embodiment of the device.
• FIG. 12 illustrates an alternative preferred compact embodiment of the device based upon the device in FIG. 11.
• FIG. 13 illustrates a possible case for the device which can be generated using an extrusion.
• the present invention focuses on the use of optical imaging to provide an optical finge ⁇ rint scanning apparatus, system and method for capturing more than two finge ⁇ rints simultaneously.
• a camera as used herein is minimally the combination of a lens and an image capture capability.
• image capture capability includes an image sensor and a frame grabber that converts the sensed image data to a digital format, e.g., an image frame.
• image capture capability is provided by film.
• Digital cameras optionally have interfaces to transfer digitized images to a system for processing.
• An image frame as used herein is data output by the camera that represents at least a portion of the scene, which the camera is capturing
• a capture sequence as used herein is a series of at least one image frame provided by the camera from which at least one image frame is selected for generating an output composite image.
• a physical connection port as used herein is a connector whereby a cable or other physical electronic communication mechanism is operatively attached to the connector.
• a roll capture sequence as used herein is a capture sequence used to generate a composite rolled finge ⁇ rint image.
• a slap capture sequence as used herein is a capture sequence used to generate a slap finge ⁇ rint image.
• FIG. 1 illustrating an embodiment of such a light pipe, shows a backlighting assembly system using a linear light source such as a cold cathode fluorescent lamp (CCFL) 92.
• a beam expander 6 has a width approximately equal to the width of the platen of the finge ⁇ rint capture device. The beam expander 6 expands the linear light source into a plane light source.
• a mirror reflector 100 is wrapped around the lamp 92 to collimate light in one dimension.
• Divergent angle rotating elongated microprism structure 16 is created on the top surface to rotate the light beams so that output light is collimated in both dimensions.
• Microprisms 94 located on the bottom surface are used to reflect light out.
• a side of the light pipe opposing the lamp is coated with a reflecting film 102 to reflect light back towards the microprism side and reflecting film 102 may be made to tilt towards the bottom surface so that essentially all of the light will be reflected out by the microprisms 94.
• the first preferred embodiment has especially low power consumption, consuming at most between 3.0 and 10.0 watts, preferably at most about 2.5 watts, to lower battery drain on a host computer not connected to an electrical outlet.
• the first preferred embodiment includes a camera 204 having a lens and optionally a filter 251, an efficient light source 201 that consumes at most about 1 watt, preferably at most about 0.7 watt, and emits sufficient light for the camera 204 to obtain an acceptable image, a prism 202, an optional light control film 250 inte ⁇ osed between said light source 201 and said prism 202, and an interface 205 to a host computer 206.
• light emitted by the efficient light source 201 enters the prism 202, is controlled by the light control film 250 and intersects the prism surface (platen) 207 at an angle greater than the critical angle.
• Light intersecting the finge ⁇ rint ridges 220 is scattered or absorbed while light that hits surface 207 of the prism with no ridges present is reflected.
• the reflected light then exits the prism 202 in a direction 208 towards an optional mirror 213 that reflects the light along optical axis 214 in a direction towards the camera 204 and optionally the filter 251.
• the optional mirror 213 is typically a precision dichroic mirror so that the mirror can additionally help remove ambient light that enters the system.
• the filer 251 substantially blocks ambient light from entering the camera.
• mirror 213 and filter 251 pass only green light.
• light source 201 emits a red light then mirror 213 and filter 251 pass only red light.
• filter 251 can also filter infrared light. Some of the scattered light may also exit the prism in a direction of the mirror 213.
• the camera 204 captures a frame and transmits the frame to the host computer 206. Typical lenses for the camera have an f-stop of 3.0 to 8.5.
• an external stimulus causes a device according to the present invention to turn on the light source 201 before beginning finge ⁇ rint capture and turn off the light source 201 after the host computer is done interacting with the device.
• the preferred manner to control the light is via a software control from the host computer 206.
• This host computer 206 directs the device to change a switch that allows or disallows electricity to flow to the light thereby Inrriing the light on and off.
• a record of counts and other data is typically maintained in a non-volatile memory 203 that is located in the camera 204 electronics or elsewhere on the device. These counts are used to track the need for system maintenance.
• Such counts include, but are not limited to, amount of time the light source is on, the number of each type of finge ⁇ rint captured or rescanned, the number of times the light source was switched on, the number of times the light source was switched off, and the number of times the device detected that the light was off when it should have been on.
• Other data stored typically includes the device serial number, manufactured date, manufactured location, date and time latest used, and driver software version number.
• a diagnostic software or firmware component typically interrogates these counts in the non-volatile memory 203 to determine if the counts indicate device maintenance is needed.
• This diagnostic component in an alternative embodiment, is also configured to perform tests to identify possible system errors. This diagnostic component outputs a diagnostic report based on the test results and the values of the counts.
• the diagnostic report can be viewed and browsed on a screen 210 of an attached host computer 206 or can be printed and, in any event, can be stored in a persistent storage (not shown) by the host computer 206.
• the efficient light source 201 is preferably a CCFL using a light pipe (dimensionally flat, high and uniform output) or alternatively and LED or other source providing a semi-collimated light source as adapted from the teachings of U.S. Patent Numbers 5,359,691, 5,390,276, and 5,854,872 and other collimated light sources.
• the patents teach light sources that inject light into the side of a light pipe. Microstructures within the light pipe and the light guide connecting the light source to the light pipe redirect the incident light into predefined directions.
• the arrangement and geometry of the microstructures enable the light pipe to output light from the light pipe surface in a substantially collimated fashion.
• the conical angles at which light leaves the surface of the light pipe are predetermined by the arrangement and geometry of the microstructures.
• the microstructures are typically microprisms.
• the light pipe configuration used for the present invention optionally also includes a filter to restrict light emanating from the filter surface to primarily semi-collimated light in a cone that diverges from the normal to the surface of the light pipe by approximately 30 degrees in each direction.
• an automatic feedback loop is used to control light source intensity 201 since light output varies over time.
• This feedback loop is implemented by at least one of an optoelectronic feedback loop for controlling input power to the light source 201 and a device-resident or host computer 206 resident software for adjusting the exposure time of the camera 204.
• an optoelectronic feedback loop for controlling input power to the light source 201 and a device-resident or host computer 206 resident software for adjusting the exposure time of the camera 204.
• Microsemi 2381 Morse Avenue, Irvine, CA 92614, sells silicon chips that can easily be inco ⁇ orated into an optoelectronic light feedback loop.
• the apparatus, system and method of the present invention preferably captures finge ⁇ rints using image processing operations as trigger conditions. For example, placing fingers of the subject on the platen could start a capture sequence, and the subject removing contact with the platen could end the capture sequence or when a substantially similar image occurs more than a pre-determined number of times could end the capture sequence.
• Image detection and capture processing operations are implemented in at least one of software, firmware, a dedicated circuit or a functionally dedicated chip. These operations are implemented on at least one of the host computer 206, a network computing resource 219, a frame grabber (not shown) that captures the frames, or within the device itself 200.
• the interface 205 to the host computer 206 is a single tether 205 that handles data, control, and power for the light source 201, camera 204, platen heater, platen blower, and optional devices.
• Optional devices include a barcode reader 501 and a magnetic stripe reader 601.
• the interface comprises at least one of USB (USB-2) connection or FireWire and their variants or other interface for exchanging data and conveying power to operate.
• USB USB-2
• FireWire USB 2
• the interface may include Ethernet and its variants as well as optical fiber, suitable to enable high resolution images to be captured and transmitted for processing over the tether 205.
• the interface can be any that provides the interconnectivity between the capture device of the present invention and a target system that performs at least one of receipt of captured images, and processing of received images.
• a protective covering (not shown) which comprises one of a coating placed directly onto the device, a coating placed directly onto the device combined with a removable cover, and a lightweight snap-on carrying case that the device easily slips into and out of.
• the images captured can include at least one of a single digit, up to 8 digits simultaneously, a palm print, a writer's edge, and all the slaps and rolls and footprints and nose prints required of an apparatus, system and method according to the present invention.
• camera lenses 204 may introduce imaging defects such as barrel and pincushion distortion.
• the present invention may employ a suitable correction algorithm such as a correction algorithm substantially similar to that published by Ojanen, the entire contents of which are hereby inco ⁇ orated by reference, or other suitable correction algorithm.
• a suitable correction algorithm such as a correction algorithm substantially similar to that published by Ojanen, the entire contents of which are hereby inco ⁇ orated by reference, or other suitable correction algorithm.
• a pre-print describing this Ojanen algorithm and software that implements this algorithm may be found at http://www.math.rutgers.edu/ ⁇ oianen/ and is included in Appendix A.
• the first step in applying the algorithm is to scan a reference target on the device, which contains multiple geometric elements of known size and spacing with respect to one another. The size and spacing of these geometric elements is designed to capture barrel and pincushion distortions. For example, a rectangular array of circles measuring 0.5 mm in diameter and spaced 2.5 mm apart is used.
• a second preferred embodiment of the present invention includes an efficient light source 201, a prism 202, a holographic grating
• the holographic grating 301 on an upper surface of the prism 202 and a light-transmitting substrate 302 on the holographic grating 301, a camera 204 having a lens, and an interface 205 to a host computer 206, and the host computer 206.
• the holographic grating 301, light transmitting substrate 302 and the upper surface 221 of the prism 202 together form a platen.
• the holographic grating 301 is attached by an adhesive to the upper surface 221 of the prism 202 and to the lower surface of the light transmitting substrate 302 by an adhesive (not shown).
• the holographic grating 301, light transmitting substrate 302 and the prism 202 are made of glass or acrylic polymer.
• light emitted by the efficient light source 201 enters the prism 202 intersecting the prism surface 221 at an angle greater than the critical angle. Then, the light passes through a holographic grating 301 and the light transmitting substrate 302 on the surface of the prism 202, hits the finger ridges 220, and is scattered/absorbed or hits the surface of the substrate
• the holographic grating 301 is adapted from the teaching of U.S. Patent No. 5,629,764.
• the holographic grating 301 allows the size of the system to be reduced since the depth of field requirement is now near zero.
• the holographic grating 301 is significantly advantageous to the compactness (and portability) of the present invention.
• An additional alternative to the second preferred embodiment and the above- mentioned alternative employs a holographic optical element (HOE) with a lensing function.
• HOE holographic optical element
• Such an HOE serves a very similar function to the holographic grating 301 but, in addition, it has a focusing ability built in so that part of the function of the lens can be off-loaded onto the HOE.
• FIG. 4 is substantially similar to that of FIG. 3B but shows a power subsystem 401 based upon a Lithium ion battery 402. hi this subsystem, a Microsemi LX2201 chip, or similar chip, can be effectively used to provide power to the electrical consumers in the system. If enough power enters the system through the tether 205, this power is directed to the appropriate electronic components using a switching implementation driven by software and firmware resident on the device 400.
• FIG. 5 A illustrates a built-in barcode reader 501 that is a second image capturing device in the camera.
• the window 502 is placed in a location behind a light blocker 503 that physically prohibits the light from disturbing the finge ⁇ rint image.
• a location is behind the camera 204 that captures the finge ⁇ rint image.
• a covering is designed into the case so that the window 502 is covered when not in operation.
• the case may provide parallel grooves flanking the window and a sliding cover is slidably located in said grooves. The grooves are sufficiently long such that the cover may slide from a first position which fully covers the window to a second position which fully exposes the window.
• the power for the barcode reader 501 is tapped off of the power subsystem 401.
• the control logic that interfaces to the camera 204 and the barcode reader 401 is written as firmware, in a preferred embodiment. This firmware communicates with the camera 204 and the barcode reader 401 in their native formats. For instance, the HHP barcode reader mentioned above communicates with a serial interface that is implemented on a Silicon Imaging camera.
• FIG 5B is an alternative embodiment of the barcode embodiment in which a movable mirror 504 is used to redirect the optical path of the finge ⁇ rint-capturing camera 204 through a secondary window 505.
• the camera 304 can begin capturing images of scenes through the secondary window 204. Captured images may be processed on the host computer 206 with any number of barcode reading software packages.
• a magnetic stripe reader 601 is included in the device. Since these readers are typically low power consumers and non-optical in nature, the magnetic stripe reader 601 can be placed in any location that does not interfere with finge ⁇ rint capture.
• the magnetic stripe reader 601 draws power from the power source 401 much as the barcode reader 501 and light source 201 do.
• the magnetic stripe reader 601 also has the option of being turned on and off in software.
• Applications of the magnetic stripe reader 601 include fraud prevention since a credit card can be scanned and finge ⁇ rints verified at the same time. Also, driver's licenses that encode demographic data in the magnetic stripe can be read.
• Sixth Embodiment In a sixth preferred embodiment, illustrated in FIG. 7, the present invention further comprises at least one of a device-resident computer processor 701 and a device-resident non-volatile memory 203 for storing minutiae used for matching.
• the device illustrated in FIG. 11 has a magnesium extruded case 1101. Inside of this case, a prism bracket 1103 holds the prism 1102 and light source 1104 so that the prism is flush with the surface of the case 1101 or extends slightly beyond the case. The prism bracket is loaded with the light source 1104 by placing the ears 1113 of the light source into the ear slots 1117 on the prism bracket 1103.
• the prism 1102 is slid into the prism bracket so that the prism is flush with the tabs and the retaining sill on the prism bracket.
• the completed prism bracket is slid onto the extrusion so that the radiused edge 1116 of the bracket fits into the scallop 1124 of the case 1101.
• the prism bracket is swung up into place using this hinge joint and the prism bracket is fastened to the case 1101 using machine screws (not shown) in holes 1115,
• the camera bracket 1122 has the lens threaded into the through hole 1123.
• a board level camera is secured in place onto camera bracket 1122 on the opposite side of the lens and the entire camera bracket assembly is mounted onto the camera mount 1121 by screwing the camera bracket to the camera mount through adjustment slot 1120.
• the inverter required for the light pipe can be mounted on the front side of camera mount 1119 as well.
• the electrical connections within the system are completed and adjustments for the locations of the components are made so as to ensure the camera is capturing the platen area properly.
• light originating at the light source 1104 enters the prism 1102 and intersects the platen surface. Light, which totally internally reflects is directed toward the camera around the optical axis 1105.
• the device illustrated in FIG. 12 can have the image sensor 1209 mounted at an angle that has been calculated to minimize the depth of field requirement.
• FIG. 12 is otherwise identical to FIG. 11. As illustrated in FIG. 12, the body of the lens 1108 remains parallel to the optical axis 1105 but, a board level camera 1110 on which the image sensor 1209 is mounted is rotated by about three degrees with respect to the pe ⁇ endicular to the optical axis 1105.
• a slip-case 900 is provided to cover the portable device when it is not in use.
• the slip-case 900 comprises a pair of tabs 902 to lock into a corresponding pair of cutouts 901 located in the handles 209 of the portable device.
• the slip-case is typically made of any suitably protective hard polymer.
• the device is dip-coated with an elastomer or other protective polymer (not shown). Case As illustrated in FIG.
• the device case can be manufactured as a metal or plastic extrusion.
• the case can be manufactured using a variety of processes including injection molding, Thixomolding, die casting, and investment casting.
• Thixomolding is a type of injection molding for metals.
• Previous approaches to manufacturing such a case have not used extrusion since the resulting device size is too large and/or the tolerances on the extrusion have not been good enough to yield a precision device.
• the desired shape needs to be able to fit within a 12 inch diameter circle since material for creating the extrusion is delivered as at most a 12 inch ingot (a cylinder of material).
• FIGs. 8A-8D are a flow chart describing a preferred embodiment of the method of the present invention.
• the host computer initializes 801 the camera 204 before beginning any finge ⁇ rint capture session. This first step establishes a camera connection during which the diagnostic data is read from the non-volatile data store 203.
• a request 802 that includes but is not limited to: capture a finge ⁇ rint of a given type 803 et seq., retrieve a captured image 830, retrieve diagnostic data 828-829, or end capture session 831-833.
• the capture finge ⁇ rint request 803 et seq. varies according to the type of finge ⁇ rint being captured. Several capture types exist but all such captures fit in either a roll or a slap format. In the following, a composite image is defined as an image formed from one or more image frames.
• a composite image includes an output image created from a sequence of scans from a linear sensor, a rolled print generated from a series of images, or even a single slap image that was the result of one processed image frame.
• These formats determine the processing steps of the method to be performed.
• the different capture types translate to different camera configuration settings. Configuration settings include area of platen to be captured, clock rate at which pixels are captured, and camera exposure time.
• the system begins capturing frames from the camera 204 and a calibration process compares the current frame with the previous frame.
• the system calculates a metric that measures the change in the luminance of the light source 201 in the middle of each captured frame.
• a pre-set tolerance i.e., levels-off
• the rate of increase drops below a pre-set threshold
• the light 201 is deemed to be "on”.
• luminance levels may be measured again and adjustments to the exposure setting of the camera 204 are made until the luminance levels reach a pre-set threshold level. Exposure adjustment is necessary as light source 201 brightness decreases over time.
• the software reports that a maintenance check is required. If the session initialized properly, the settings of the camera 204 for exposure, frame time and viewing window (based on the finge ⁇ rint capture type) are set for a roll image 806 or a slap image 818. At this point, the system captures a blank frame from the camera 204 and keeps this frame as a reference gain image for a roll image 807 or a slap image 819. The process of capturing a roll or slap print now commences. Roll Capture (FIG.
• Typical finge ⁇ rinting systems implement a foot pedal 212, touch screen 211, mouse, a key on a keypad, or buttons 210 to begin and end, i.e., "trigger", the start and/or stop of a finge ⁇ rint capture.
• Such switching mechanisms can be located on or in the device or external to the device on a computer, for instance.
• Embodiments of this invention may support these modes even using different modes to signal a beginning and an end.
• the preferred embodiments rely on an automatic or "self- generated" trigger that offers the end-users complete independence from physically manipulating other devices.
• This trigger implemented in one of software, firmware, or hardware, eliminates the need for manually signaling the start and end of a roll. Triggers to start and/or stop a fmge ⁇ rint capture sequence are determined by statistics captured from frame sequences obtained by the camera. These statistics measure frame direction and relative frame movement between successive frames obtained by the camera to determine the type of finge ⁇ rint being captured. Once the type of finge ⁇ rint being captured is known and the device is initialized for that type of finge ⁇ rint capture, the camera obtains a sequence of frames and that sequence is analyzed for triggers. These automatic triggers may be used in conjunction with the other existing switching mechanisms described above. In one embodiment, the process for initializing a roll occurs 808.
• the subject positions the center of the finger on the platen so that the subject sees the finge ⁇ rint centered in the viewing window of the client's user interface.
• the subject then rolls the finger in one direction to the nail bed of the finger and then completely rolls the finger in the opposite direction to the nail bed on the other side.
• the finge ⁇ rint roll is complete and the finge ⁇ rint system returns to the client software to let the subject know that the finge ⁇ rint roll is complete.
• the host computer 206 continuously captures frames 809 from the camera 304. For each frame, the image is preprocessed with offset and gain correction 810 before a fmge ⁇ rint-locating algorithm is applied.
• the fmge ⁇ rint-locating algorithm analyzes the each frame for finge ⁇ rint data and if the subject has placed a finger on the platen, then the system locates the finge ⁇ rint 811 in the frame and generates coordinates that describe a bounding box around the finge ⁇ rint. To compute the finge ⁇ rint location in each frame, two histograms are generated. The histograms are based upon image variance and are calculated only on each row and column index that is evenly divisible by the estimated finge ⁇ rint ridge width.
• the variance of the grayscale values of the pixels is calculated over an area roughly equal to the width of two ridges on the current frame for every pixel whose row and column is evenly divisible by the estimated ridge width, and whose area resides entirely within the current frame. If the variance of the pixel is greater than a pre-set threshold, then the associated positions in each histogram are incremented. Once the two histograms have been generated, the first and last entries in each histogram that are above a pre-set tolerance provide a rectangle encompassing the location of the finge ⁇ rint.
• the automatic trigger process employs the current and previous finge ⁇ rint bounding box locations to determine finger travel distance and direction between frames.
• the center column of each finge ⁇ rint is calculated as the middle of the corresponding bounding box determined by step 811.
• the centers of the current and previous locations are compared to determine if the finge ⁇ rint is moving and if so, which direction the finger is moving. If the Euclidian distance between the centers of the locations is less than or equal to a predetermined number of pixels, the finge ⁇ rint is determined to be stopped. If the current frame center is greater than a predetermined number of pixels right of the previous frame, the finge ⁇ rint is determined to be rolling right. If the current frame center is greater than a predetermined number of pixels left of the previous frame, the finge ⁇ rint is determined to be rolling left.
• the predetermined number of pixels is typically at least about 10.
• a half roll in one direction is started with a frame whose roll direction is either left or right (the direction of the half roll).
• the half roll is composed of a sequence of frames that have a direction of either stopped or direction of the half roll.
• the half roll is completed when the current frame's roll direction is opposite the direction of the half roll. If the half roll has a sufficient number of frames with a roll direction equal to the half roll direction, the full roll is begun and the capture sequence is started. Otherwise, the software returns to waiting for a half roll.
• the full roll is composed of a sequence of frames with roll directions opposite the direction of the half roll direction, not including stopped. The full roll is completed when the roll direction of a frame is not equal to the direction of the full roll or a sufficient number of stationary frames have been captured.
• the software accepts the full roll as complete. If the number of frames is insufficient, the system cancels the full roll and returns to waiting for a half roll. If at any point during the rolls the finger is removed from the platen, the software returns to waiting for a half roll.
• the composite image that represents the finge ⁇ rint roll is initialized. As frames from the camera are captured, they are processed by applying offset and gain, finge ⁇ rint location, and trigger condition analysis. If the cancel condition is indicated then the current finge ⁇ rint roll is halted and the process returns to the beginning of the finge ⁇ rint roll process 808.
• the composite image is post-processed 814 814A 815 815 A 815B. If there is no trigger condition set then the current frame is merged into the composite image 813 813.1-813.5 to create a composite roll image from a sequence of frames. The process of grabbing and processing frames continues in this manner until the roll end trigger occurs. The roll end trigger signals the end of the capture sequence.
• merging 813 into a composite image is done in five steps: 1) identifying where the current composite image and new finge ⁇ rint image overlap, 2) calculating the direction of the roll, 3) computing an initial splice line by roughly aligning the finge ⁇ rint ridges between the composite image and new fmge ⁇ rint image, 4) use a quality metric to refine the splice line from the top to the bottom of the image, 5) combine the new image frame into the merged composite image using mo ⁇ hing along the splice line.
• Overlap area 813.1 The overlap area between the merged composite image and the new finge ⁇ rint image has been described above.
• Roll direction 813.2 The direction of the roll can be determined by computing which side the new finge ⁇ rint image is located. For example, if the new finge ⁇ rint image is located on the left side of the composite image then the roll direction is to the left.
• Initial splice line 813.3 Create an initial splice line based on the endpoints where the new finge ⁇ rint image and the composite finge ⁇ rint image intersect in the overlap area then compute the slope of this new splice line segment. Compute the center of this new splice line segment. Determine which two finge ⁇ rint ridges, near the center of the new image and the merged composite image, have the best alignment.
• a metric that can be used is the local gray scale average along the splice line. This center location of the splice line is updated so to this identified best match point so that splice line refinement can occur at this reliable anchor point. Copy this new splice line and its center location and call it the composite splice line.
• this refinement region iterate from a threshold number of pixels left of the splice point to a threshold number of pixels to the right of the splice point.
• Form a splice line segment candidate from the iterated pixel to the starting position on the splice line.
• One similarity metric computes the pixel intensity average of the two areas and compares the averages. The result of the comparison is a score that represents how close these two areas match, which represents how well the ridges line up.
• This process iterates to the top of the overlap area and from the center of the splice line segment to the bottom of the overlap area.
• the result is a final composite splice line based on the initial splice line.
• Morphine (merging) into composite image 813.5 The existing composite image and new finge ⁇ rint image form a new composite image.
• the initial splice line and composite splice line control what region of the composite image gets blended with the new finge ⁇ rint image region. Iterate from the bottom of the overlap region to the top of the overlap region along both splice lines simultaneously. For each row consider the pixels on that row between the splice lines and a pre-determined threshold number of pixels outside of the splice lines.
• the merging method to create the rolled finge ⁇ rint from a sequence of frames typically comprises the following steps.
• the first frame is copied to the composite image.
• the bounding boxes, located as described above for locate print 811, for the current and previous finge ⁇ rint locations are intersected to form an overlap area.
• the left of the overlap area is equal to the maximum of the left coordinates of the two bounding boxes.
• the top of the overlap area is equal to the maximum of the top coordinates of the two bounding boxes.
• the right of the overlap area is equal to the minimum of the right coordinates of the two bounding boxes.
• the bottom of the overlap area is equal to the minimum of the bottom coordinates of the two bounding boxes.
• the center columns of the overlap area in the current frame and composite image are examined to find where finge ⁇ rint ridges intersect the columns. These intersections are compared between the new frame and the composite image and they are used to perform a dynamic stretch on the current frame. If the current frame and composite image are too dissimilar then the merging is aborted and the subject is warned that the finger is moving too drastically. In this case, a new roll capture is automatically started.
• the current frame is stretched so that the ridges roughly intersect with the existing ridges from the composite image and the current image is mo ⁇ hed with the composite image to produce a new composite image.
• the final composite image becomes the finge ⁇ rint roll image.
• adjacent opposed dark edges of two sequential bounding boxes are compared by taking a histogram to analyze each dark edge and a matching algorithm is used to match ridges to obtain an image such that the finge ⁇ rint ridges are continuous.
• Image processing techniques remove image defects introduced by the camera and the lens. Six main processing steps occur: deviant pixel correction, offset and gain correction, high pass filtering, aberration correction, perspective correction, and noise filtering.
• Offset and gain correction 810 Applying offset and gain is a pixel by pixel operation.
• Deviant pixel correction 814 Most cameras contain imperfections on the sensory chip. These imperfections manifest themselves as intensity values that differ greatly from the normal expected intensity values. These deviant pixels are beyond a threshold away from the average intensity value of a neighborhood of pixels. Deviant pixel correction involves two steps.
• the first step involves initializing the deviant pixel subsystem.
• the second step is the correction of individual frames.
• Initialization which occurs in the session initialization 801, requires an offset image acquired in camera initialization.
• the grayscale value of each pixel in the image below the second row and above the second to last row is compared to an average grayscale value of the two pixels above and two pixels below the current pixel. If the grayscale value of the current pixel significantly differs from the average of the other four pixels, the current pixel's location is added to a cached list for use in the second step.
• Deviant pixel correction of the individual frames is relatively simple.
• High pass filtering 814A Edge details of the finge ⁇ rint ridges may be enhanced at the cost of increasing noise in the image frame.
• An approach to enhancing the edges is applying a high pass filter as is commonly known in the image processing field. Such filters convolve a high pass filter with the image. Typical high pass filters used may have a kernel size of 3, 5, or 7. The strength of the high-pass filter being used is driven by the application requirements.
• Aberration correction 815 The camera lens also introduces image defects such as pincushion or barrel distortions.
• Parameters for correction of these defects are identified during calibration at the time of device manufacture and these parameters are stored in the non- volatile memory 203.
• camera initialization these parameters are read and the defect model is initialized.
• the output coefficients and the defect model are used to correct a captured image using an algorithm such as the Ojanen algorithm. Correction amounts to local averaging in neighborhoods defined by the defect model and the output coefficients.
• an inte ⁇ olation method such as bi-linear inte ⁇ olation or nearest neighbor can be used to create an output pixel for each neighborhood.
• Perspective correction 815 A Perspective correction of the image may also be performed.
• a mathematical description of the perspective model identified by the algorithm can be used in conjunction with an inte ⁇ olation algorithm such as bi-linear inte ⁇ olation to generate the final corrected composite image. Correction in the image occurs after the final roll or slap has been captured.
• the perspective correction can be geometrically modeled as a three-dimensional relationship between planes. Once measured, the mathematical description of these planes can be used in conjunction with bi-linear inte ⁇ olation to create a perspective corrected composite image.
• the initialization step 801 preferentially precomputes the perspective correction parameters for each pixel so that in full operation extra time would not have to be spent on calculating needed weights repeatedly.
• Noise filtering 815B The noise filter algorithm convolves the image with an averaging convolution kernel, hi the convolution operation, the variance within the neighborhood is used in conjunction with a fixed threshold. If the variance exceeds the threshold then the original pixel is left unchanged otherwise, the pixel is assigned the value of the convolution.
• the convolution kernel size is established experimentally according to an application's requirements.
• the image processing steps may have their order changed and merging of the composite rolled image may occur at any stage of processing the frame.
• Slap Capture (FIG. 8C): When acquiring a slap print, similar processing steps to that of the roll capture are performed. From the subject's perspective the subject places the target fingers or thumb on the platen. Frames from the camera are continuously captured and processed until the trigger condition indicates a good slap capture. For each frame captured, offset and gain correction are applied and the frame is analyzed for the presence of a trigger condition. This analysis involves calculating the variance of sub windows within the full frame. Each sub window is square with the length of the sides roughly equal to the width of two finge ⁇ rint ridges.
• Sub windows are centered on every pixel whose row and column index is evenly divisible by the ridge width and whose sub window area resides entirely within the current frame. If a pixel's variance is greater than a certain threshold then a count is incremented and the same operation is performed on the previous image in the same location. If the pixel's variance in the previous image is also greater than the threshold, a second count is also incremented. The ratio of the number of pixels that are above the variance threshold in both images to the number of pixels that are above the variance threshold in only the current image is used to determine how similar the two images are. If the images are similar enough for a small sequence of a few frames, the current frame has the capture condition set and the best frame (frames) is (are) saved.
• the process of capturing and processing frames continues 821 to 824.
• the final captured frame is post processed 825 825 A 826 826A 826B as described above for roll capture 814 814A 815 815 A 815B.
• the software updates diagnostic data in non-volatile memory 827, saves the image and indicates the capture is complete 828 to the host program and processes a new request 802.
• the image processing steps may have their order changed and merging of the composite rolled image may occur at any stage of processing the frame.
• the present invention applies to large format finge ⁇ rint/handprint/footprint scanning as well as pet imaging applications. Other extensions of this technology to other applications are also possible.
• the same invention can be applied in newborn applications in which the footprints of newborns are digitally captured, in applicant processing applications for capture and submission of fmge ⁇ rints for criminal background pmposes, for arrestee or detainee applications, for verification of the person's identity when the collected prints are matched against a database of prints, for access control applications, and for applications to sampling pet paws or pet noses to maintain identities of animals with certified pedigrees.
• Many times demographic data must be collected in conjunction with the finge ⁇ rints so that the finge ⁇ rints can be associated with a name, address, identification number, etc. Such demographic data allows expedited matching in many database systems.
• the mapping may image (e.g., due to incorrect cropping during depend on the focus distance; for zoom lenses in scanning of a slide). I
• test sheet that is photographed consists of a rectangular grid of black dots, see Figure 5 .
• An example of a photograph of the sheet is shown in Figure 6. From a digital image it is easy to compute
• Figure 3 Combination of barrel and pincushion disthe locations of the centers of the dots in the distortions. torted image, we call these ⁇ Aji- The goal is then to choose the parameters of the mapping F in (1) so that F maps the set ⁇ z t ⁇ i to a rectangular grid of
• Figure 6 Target sheet photographed with a 20mm
• Figure 4 Mapping rays through a pinhole. . a ° r ⁇ r
• the software was written using mostly Matlab. There are three main parts: initialization, optimization, and correction.
• the initialization part com Figure 5 Target sheet putes the centers of the dots in the distorted image and passes them to the optimization part.
• the result of the optimization essentially the function ⁇ (r) contains all the information that is needed to undistort images created with a particular lens.
• a stand-alone C program was written for correcting images based on the parameters of ⁇ (r).
• the software can create "displacement maps" for Adobe Photoshop, so the correction can be done in any image processing program.nas a Photoshop compatible displace filter. To apply corrections to images only the C proinverse mapping of F (certainly each factor in (1) gram or a displacement map is needed. is invertible).
• Figure 7 ⁇ (r) for the lens used in Figure 7.
• Figure 8 Transverse magnification M(r).
• Figures 9 and 10 show an example of a zoom lens at directly into the firmware of a digital camera. This the 20mm setting both before and after correction. would allow more freedom in designing the lens but
• the function ⁇ (r) for this lens is shown in Figure 7 still allow excellent image quality. and the transverse magnification in 8. Note how dM/dr changes sign, hence the lens has both barrel and pincushion distortion.
• Figure 3 note the similarity with the middle "square" [1] E. Hecht, Optics, 3rd ed., Addison-Wesley, in Figure 3. 1998.
• Lens design is inherently a process of compromise between not only the specifications of the lens but also different aberrations. In many cases it appears that high distortion is tolerated when low cost or long zoom ranges are desired. The method described here shows, notably, that distortion is very easy to correct digitally. Even with a rudimentary setup we have achieved near perfect results. With a complete description email: Harr . O j anenoiki . f i of the lens ray tracing techniques could be used to web: www. iki . fi/Harri . Oj anen/
• Figure 9 Original image formed with a 20mm lens.
• Figure 11 Image formed with a 28mm lens.

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