This paper investigates an issue with the Wavelet Scalar Quantization (WSQ) compression algorithm which causes severe degradation of the compressed image. The problem was first noticed when compressing the two-thumb images from live-scan identification flats (ID Flats) captured with a 3-inch high platen device. If the thumbs were placed sufficiently close to the bottom edge of the platen during capture, the compression/decompression of the image could result in a severely degraded fingerprint image. In extreme cases all fingerprints in the image were lost. Testing on 3-inch identification slaps at NIST shows 2%-3% of the two-thumb captured images are affected by some level of degradation. This paper will explain why this occurs, show an example, and offer an algorithm modification to detect and prevent the problem. It is recommended that modifications to the WSQ specification and existing operational software be made to prevent degradation in future compressed images that are currently going undetected in automated capture systems.
Citation: NIST Interagency/Internal Report (NISTIR) - 7746Report Number:
NIST Pub Series: NIST Interagency/Internal Report (NISTIR)
Pub Type: NIST Pubs
WSQ, compression, fingerprint, thumb, slaps, identification flats, live-scan