Fingerprint identification system

A method of detecting and recording the location of minutia in a fingerprint image comprising the steps of

• scanning a gray scale image of a fingerprint,
• determining the direction of fingerprint ridges at multiple, spaced apart locations within the fingerprint,
• determining the spacing of fingerprint ridges at said multiple, spaced apart locations,
• orienting a filter over each of said multiple locations by reference to said ridge direction at each of said locations,
• adjusting the area of said filter by reference to the spacing of said ridges at each of said locations whereby said filter observes a predetermined number of ridges,
• said filter having an output level which is a function of relative angle of ridges adjacent the location being observed,
• and recording those locations indicating non-parallel ridges as an indication of minutia.

Apparatus for locating minutiae contained in a fingerprint image comprising means for determining the direction of fingerprint ridges at multiple locations,

• means for determining the spacing of said fingerprint ridges at each of said multiple locations,
• means responsive to said direction determining means and said spacing determining means for detecting a phase discontinuity in the ridge flow of the fingerprint image at each of said multiple locations, wherein said means for determining the phase discontinuity in the ridge flow of fingerprint image, which indicates a ridge ending or bifurcation, comprises
• a Gabor filter having a high level output when observing parallel fingerprint ridge flow and a low output when the ridge flow is not parallel,
• a Minutiae Filter having a low level output when observing parallel fingerprint ridge flow and a high output when the ridge flow is not parallel,
• means responsive to said direction determining means for aligning said Gabor Filter and said Minutiae Filter with the fingerprint at each of said multiple locations,
• means responsive to said spacing determining means for adjusting the size of said Gabor Filter and said Minutiae Filter calculation kernel to view a predetermined number of fingerprint ridges, and
• means for determining the ratio of the outputs of said filters as they are aligned at each of said multiple locations to identify minutiae, and
• means for recording the location of said phase discontinuities.

A method for creating and recording for future use an image state map containing image quality and areas of minutiae locations of a fingerprint image comprising the steps of

• converting a fingerprint image into a digitized gray scale image comprising a plurality of individual pixels,
• determining the quality of the fingerprint image at regularly spaced individual pixels,
• determining the quality of minutiae located on said fingerprint image,
• determining the location of minutiae within said fingerprint image,
• recording on said state map those areas where no minutiae are detected,
• identifying on said state map those areas where minutiae are present,
• and recording on said state map those areas where the quality of the image is too poor to reliably determine the presence or absence of minutiae or where minutiae were detected having a quality value below a predetermined value.

A method of determining the location of core and delta features in an image of a fingerprint comprising the steps of

• scanning a gray scale image of a fingerprint,
• measuring and mapping ridge angle and ridge frequency and associated image quality,
• computing a gradient map,
• finding and rank ordering gradient features and measuring and recording associated image quality, and
• applying vector field mathematics of Direct Estimation of Orientated Patterns to said gradient map to determine core and delta type to each gradient feature.

Apparatus for recording in machine readable form the existence and location of cores and deltas in an image of a fingerprint, said apparatus including

• means for converting a fingerprint image into a digitized gray scale image comprising a plurality of individual pixels,
• means for determining the ridge angle and quality of the fingerprint image at regularly spaced individual pixels to create a Ridge Angle Map and an image quality map,
• means for computing the gradients of said Ridge Angle Map to derive the location of possible cores and deltas,
• means for sorting the gradients according to size,
• means for creating a vector field representation of said fingerprint image,
• means for detecting and measuring the curling of said vector field, and
• means responsive to said detecting means for identifying cores and deltas.