Method and device for reducing smear in a rolled fingerprint image

Claim 1

A method of reducing smear in a rolled fingerprint image represented by a rolled image array, comprising the steps of: sequentially generating frames of an optical image signal which includes data values characteristic of light intensities of corresponding locations of an optical image, wherein the optical image includes a fingerprint image of a finger rolling on a surface; determining, for each frame of the optical image signal, a freeze column representing a line positioned between leading and trailing edges of the fingerprint image and oriented transverse to a direction of roll of the rolling finger; sequentially updating an interim array that is an accumulation of the frames of the optical image signal and characteristic of an interim image of a rolled fingerprint, a current update of the interim array being formed by reducing pixel values of the interim array by a portion of the difference between corresponding data values from a current frame of the optical image signal and the pixel values of the interim array if the corresponding data values of the current frame of the optical image signal are less than the pixel values of the interim array; and generating the rolled image array by transferring portions of the interim array to the rolled image array, wherein the transferred portion of the current update of the interim array extends forward in the direction of finger roll from the freeze column determined from a preceding frame of the optical image signal that preceded the current frame of the optical image signal.

Claim 2

A method of reducing smear in a rolled fingerprint image represented by a rolled image array, comprising the steps of: sequentially generating frames of an optical image signal which includes data values characteristic of light intensities of corresponding locations of an optical image, wherein the optical image includes a fingerprint image of a finger rolling on a surface; determining, for each frame of the optical image signal, a freeze column representing a line positioned between leading and trailing edges of the fingerprint image and oriented transverse to a direction of roll of the rolling finger; sequentially updating an interim array that is an accumulation of the frames of the optical image signal and characteristic of an interim image of a rolled fingerprint, a current update of the interim array being formed by reducing pixel values of the interim array by a portion of the difference between corresponding data values from a current frame of the optical image signal and the pixel values of the interim array if the corresponding data values of the current frame of the optical image signal are less than the pixel values of the interim array; and generating the rolled image array by transferring portions of the interim array to the rolled image array, wherein the transferred portion of the current update of the interim array extends forward in the direction of finger roll from the freeze column determined from a preceding frame of the optical image signal that preceded the current frame of the optical image signal.

Claim 19

A method of generating a rolled fingerprint image array characteristic of a rolled fingerprint image, comprising the steps of: generating a series of frames of an optical image signal characteristic of an optical image of a finger rolling on a surface at sequential times, wherein the frames include data, the value of each datum being characteristic of a light intensity of a corresponding location of the optical image of the rolling finger; determining a freeze column from each frame, wherein each freeze column is representative of a position between leading and trailing edges of the corresponding optical image of the rolling finger; sequentially updating an interim array in an image memory with the frames as they are generated, the interim array being characteristic of an interim image of a rolled fingerprint that has a leading edge and a trailing edge, including first updating the interim array by transferring a first one of the optical image signals to the image memory, and then further updating the interim array by reducing pixel values of the interim array with a portion of the difference between corresponding data values of a current frame and the pixel values of the interim array if the corresponding data values of the current frame indicate a darker image than the pixel values of the interim array; associating the freeze columns determined from the frames with corresponding updates of the interim array; and sequentially updating the rolled fingerprint image array in an output memory with the updates of the interim array by sequentially transferring a portion of each update of the interim array to the output memory, including transferring a portion of the first update of the interim array that extends in a direction of finger roll rearward from approximately the freeze column associated with the first updated interim array, and then transferring a portion of a subsequent update of the interim array that extends forward in the direction of finger roll from approximately the freeze column associated with a preceding update of the interim array.

Claim 20

A method of generating a rolled fingerprint image array characteristic of a rolled fingerprint image, comprising the steps of: generating a series of frames of an optical image signal characteristic of an optical image of a finger rolling on a surface at sequential times, wherein the frames include data, the value of each datum being characteristic of a light intensity of a corresponding location of the optical image of the rolling finger; determining a freeze column from each frame, wherein each freeze column is representative of a position between leading and trailing edges of the corresponding optical image of the rolling finger; sequentially updating an interim array in an image memory with the frames as they are generated, the interim array being characteristic of an interim image of a rolled fingerprint that has a leading edge and a trailing edge, including first updating the interim array by transferring a first one of the optical image signals to the image memory, and then further updating the interim array by reducing pixel values of the interim array with a portion of the difference between corresponding data values of a current frame and the pixel values of the interim array if the corresponding data values of the current frame indicate a darker image than the pixel values of the interim array; associating the freeze columns determined from the frames with corresponding updates of the interim array; and sequentially updating the rolled fingerprint image array in an output memory with the updates of the interim array by sequentially transferring a portion of each update of the interim array to the output memory, including transferring a portion of the first update of the interim array that extends in a direction of finger roll rearward from approximately the freeze column associated with the first updated interim array, and then transferring a portion of a subsequent update of the interim array that extends forward in the direction of finger roll from approximately the freeze column associated with a preceding update of the interim array.

Claim 24

A device for reducing smear in a rolled fingerprint image represented by a rolled image array, comprising: an imaging system for sequentially generating frames of a series of electronic signals characteristic of an optical image that includes a fingerprint image of a finger rolling on a surface; means for sequentially generating frames of an optical image signal in response to the electronic signals, each optical image signal including data, the value of each datum being characteristic of a light intensity of a corresponding location of the optical image; an image capture system responsive to the optical image signals for sequentially updating an interim array characteristic of an interim image of a rolled fingerprint that has a leading edge and a trailing edge, a current update of the interim array being formed from a preceding update of the interim array and a current frame of the optical image signal by reducing pixel values of the preceding update of the interim array with a portion of the difference between the corresponding data values of the current frame and the pixel values of the preceding update of the interim array if the corresponding data values of the current frame are characteristic of darker images than the pixel values of the preceding update of the interim array; means for determining, for each frame of the optical image signal, a freeze column representing a line positioned between leading and trailing edges of the fingerprint image and oriented transverse to a direction of roll of the rolling finger; and means for generating the rolled image array by transferring a portion of the current interim array to the rolled image array, wherein the transferred portion of the current interim array extends forward in the direction of finger roll from the freeze column determined from a preceding frame of the optical image signal that preceded the current frame of the optical image signal.

Claim 25

A device for reducing smear in a rolled fingerprint image represented by a rolled image array, comprising: an imaging system for sequentially generating frames of a series of electronic signals characteristic of an optical image that includes a fingerprint image of a finger rolling on a surface; means for sequentially generating frames of an optical image signal in response to the electronic signals, each optical image signal including data, the value of each datum being characteristic of a light intensity of a corresponding location of the optical image; an image capture system responsive to the optical image signals for sequentially updating an interim array characteristic of an interim image of a rolled fingerprint that has a leading edge and a trailing edge, a current update of the interim array being formed from a preceding update of the interim array and a current frame of the optical image signal by reducing pixel values of the preceding update of the interim array with a portion of the difference between the corresponding data values of the current frame and the pixel values of the preceding update of the interim array if the corresponding data values of the current frame are characteristic of darker images than the pixel values of the preceding update of the interim array; means for determining, for each frame of the optical image signal, a freeze column representing a line positioned between leading and trailing edges of the fingerprint image and oriented transverse to a direction of roll of the rolling finger; and means for generating the rolled image array by transferring a portion of the current interim array to the rolled image array, wherein the transferred portion of the current interim array extends forward in the direction of finger roll from the freeze column determined from a preceding frame of the optical image signal that preceded the current frame of the optical image signal.