Cropping WSQ: Options and Impacts
April 2007
Margaret Lepley, The MITRE Corporation
ABSTRACT
Wavelet Scalar Quantization (WSQ) is a wavelet-based compression algorithm used by the FBI
with a large and growing archive of WSQ fingerprint images, often collected in a
digital 10-print file that contains a 4-finger flat impression as well as single
finger rolled images. Sometimes a sequence error occurs and a single finger
image is obviously incompatible with the 4-finger view of the same finger.
When this occurs, past practice with hardcopy has been to crop a section of the
4-finger image to replace the erroneous single finger image. At other times,
when a 4-finger flat scanner is used, only the 4-finger image may be available.
This report studies various methods of cropping a 4-finger electronic WSQ file,
and determines which method and operational instructions best maintain image
quality. Other aspects of fingerprint cropping, such as automatically finding the
crop location, and removal of other fingerprints or writing outside the print of
interest are not addressed in this report.
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