Abstract: A computer based image processing system uses an extraction process to include a pressure invariant feature for measuring distances between minutiae. The feature extraction process identifies one or more of the following features of the fingerprint: an orthogonal image contrast, a parallel image contrast, and a feature confidence. A ridge counter process, executing on the computer system, determines the number of ridges (ridge count) running across two given points and further qualifies (invalidates) this count if the confidence value of the pixels in the region adjoining the region is not reliable. The ridge count feature between minutiae is used for determining reliable features when matching fingerprints.

Abstract: A computer based image processing system uses an extraction process to extract one or more features from a target fingerprint image. The feature extraction process identifies one or more of the following features of the fingerprint: orthogonal image contrast, parallel image contrast, feature confidence, distance between two minutia, neighbor information, angle-distance between two minutia, angle-distance neighbor information, minutiae density, ridge length, ridge density, and wiggle factor. A pruner process, executing on the computer system, determines if one or more of the features meet any one or more of a set of pruning criteria, and that deletes the minutiae if the pruning criteria is met. The pruning process is based on (i) locations and image contrast, (ii) the distances, orientations of minutiae and (iii) spatial distributions of minutiae and ridges of the fingerprint. The minutiae that remain after the pruning can be used for feature matching.

Abstract: A fingerprint image is divided into blocks of pixels. The blocks are determined to be within the foreground or background of the image. Each of the foreground blocks are assigned a block direction. If an image consists of the complete impression of the fingerprint, there should exist at least one path (ridge), composes of foreground blocks, which lies on both half planes of a coordinate system with an origin at the centroid of the foreground and that comes sufficiently close to the x axis once the path crosses to the second half plane of the coordinate system.

Abstract: A fingerprint image is divided into blocks of pixels. The blocks are marked as directional or non-directional. The blocks are also determined to be within the foreground or background of the image. Contiguous regions of blocks that are in the foreground and are directional are selected. The quality measure is the ratio of the area of all these selected contiguous regions to the total area of the fingerprint image (i.e., the foreground.) The contribution of each of the blocks of the regions to the quality measure can be given by a distance from a block containing a reference point (a block of reference) within the foreground. Further, the block of reference can be located at the centroid of the foreground. Images are judged to be of poor quality if the quality measure is below a quality threshold and are judged to be of good quality if the quality measure is above the quality threshold. Optionally, poor quality images are examined further to determine if they are smudged or come from a dry finger.