text: Gabor filters (GFs) play an important role in many application areas for the enhancement of various types of images and the extraction of Gabor features. For the purpose of enhancing curved structures in noisy images, we introduce curved GFs that locally adapt their shape to the direction of flow. These curved GFs enable the choice of filter parameters that increase the smoothing power without creating artifacts in the enhanced image. In this paper, curved GFs are applied to the curved ridge and valley structures of low-quality fingerprint images. First, we combine two orientation-field estimation methods in order to obtain a more robust estimation for very noisy images. Next, curved regions are constructed by following the respective local orientation. Subsequently, these curved regions are used for estimating the local ridge frequency. Finally, curved GFs are defined based on curved regions, and they apply the previously estimated orientations and ridge frequencies for the enhancement of low-quality fingerprint images. Experimental results on the FVC2004 databases show improvements of this approach in comparison with state-of-the-art enhancement methods.
  @cite_41: Fingerprint image enhancement is a crucial step in automatic fingerprint recognition. A large number of approaches for filtering the fingerprint image have been suggested. Most of them perform oriented band pass filtering. However, such filters, for example, Gabor filters, may create spurious ridge structure information. This is harmful for the feature extraction and therefore is harmful for the automatic fingerprint recognition. This paper examines the properties of applying the Gabor filter in the fingerprint image enhancement. It shows that the nonsinusoidal-shaped ridge structure, the ridge frequency estimation error, and the small filter size are the causes of creating spurious ridge structures. As a solution, we suggest an adaptive oriented low pass filter instead of the Gabor filter to avoid producing undesired harmful side effects for the automatic fingerprint recognition.
  @cite_5: A new technology evaluation of fingerprint verification algorithms has been organized following the approach of the previous FVC2000 and FVC2002 evaluations, with the aim of tracking the quickly evolving state-of-the-art of fingerprint recognition systems. Three sensors have been used for data collection, including a solid state sweeping sensor, and two optical sensors of different characteristics. The competition included a new category dedicated to ”light” systems, characterized by limited computational and storage resources. This paper summarizes the main activities of the FVC2004 organization and provides a first overview of the evaluation. Results will be further elaborated and officially presented at the International Conference on Biometric Authentication (Hong Kong) on July 2004.
  @cite_29: A major new professional reference work on fingerprint security systems and technology from leading international researchers in the field. Handbook provides authoritative and comprehensive coverage of all major topics, concepts, and methods for fingerprint security systems. This unique reference work is an absolutely essential resource for all biometric security professionals, researchers, and systems administrators.
  @cite_13: The National Institute of Standards and Technology in conjunction with the Federal Bureau of Investigation has developed a new database of grayscale fingerprint images and corresponding minutiae data. The database contains latent fingerprints from crime scenes and their matching rolled fingerprint mates. In all there are 258 latent cases. Each case includes the latent image, the matching tenprint image, and four sets of minutiae that have been validated by a professional team of latent examiners. One set of minutiae contains all minutiae points on the latent fingerprint; the second set contains all minutiae points on the tenprint mate; the other two sets contain the minutiae points in common between the latent fingerprint and tenprint mate. In all there are 27,426 minutiae recorded across the set of tenprints with 5460 minutiae in common with their matching latent fingerprint. All data files are formatted according to the ANSI NISTITL 1-2000 standard using Type-1, 9, 13, & 14 records. Software utilities are provided to read, write, and manipulate these files. The database can be used to develop and test new fingerprint algorithms, test commercial and research AFIS systems, train latent examiners, and promote the ANSI NIST file format standard.
summary: Enhancement of low quality images (occurring e.g. in all databases of FVC2004 @cite_5 ) and very low quality prints like latents (e.g. NIST SD27 @cite_13 ) is still a challenge. Techniques based on contextual filtering are widely used for fingerprint image enhancement @cite_29 and a major difficulty lies in an automatic and reliable estimation of the local context, i.e. the local orientation and ridge frequency as input of the GF. Failure to correctly estimate the local context can lead to the creation of artifacts in the enhanced image @cite_41 which consequently tends to increase the number of identification or verification errors.