Instructions

U.are.U SDK - Developer Guide 27
The C/C++ APIs
Advanced Diagnostics
The majority of applications should use the dpfj_identify function to implement both identification and
verification. However, in a few special cases, e.g., using multi-modal biometrics, or doing statistical risk assessment,
the
dpfj_compare function allows you to compare two FMVs to determine their actual degree of dissimilarity. This
is useful for accuracy testing and diagnostics and is not intended to be used in final applications for actual fingerprint
recognition. The
dpfj_compare function returns a dissimilarity score with values:
• 0 = fingerprints are NOT dissimilar (i.e., they MATCH perfectly).
•
maxint (#7FFFFFFF or 2147483647) = fingerprints are completely dissimilar (i.e., DO NOT match).
• Values close to 0 indicate very close matches, values closer to
maxint indicate very poor matches.
The table below shows the relationship between the scores returned from
dpfj_compare and the false match error
rates observed in our test. The dissimilarity score distribution is estimated based on our internal testing, and may not be
representative of the actual rate that will be observed in deployment.
Wavelet Scalar Quantization (WSQ) Compression
The U.are.U SDK provides compression of fingerprint images with the WSQ algorithm. This compression is available
in two ways:
1 Using code developed by NIST. This code is included within the U.are.U C/C++ API.
2 Using the WSQ1000 SDK from Aware, Inc. on the target system. If the WSQ 1000 SDK is installed, the U.are.U
functions will call the WSQ 1000 functions to do compression and decompression instead of the native NIST-based
code. However, see additional information on “Raw” WSQ compression on page 28.
Crossmatch does not redistribute the Aware WSQ1000 SDK, it must be acquired and installed separately.
The typical sequence to compress an image would be:
•
dpfj_start_compression
• dpfj_set_wsq_bitrate or dpfj_set_wsq_size - Set the desired size for the compressed image
•
dpfj_compress_fid or dpfj_compress_raw - Compress the FID or raw image
•
dpfj_get_processed_data - Retrieve the compressed image
n dpfj_finish_compression
The typical process to decompress an image would be:
•
dpfj_start_compression
• dpfj_expand_fid or dpfj_expand_raw - Decompress an FID or raw image
•
dpfj_get_processed_data - Retrieve the expanded image
•
dpfj_finish_compression
Dissimilarity Score False Match Rate
2147483
.1%
214748
.01%
21474
.001%
2147
.0001%
Function Description
dpfj_compare Compare two FMDs; supported formats are: Gold SDK, One Touch SDK, ANSI
and ISO.
Function Description
dpfj_start_compression Initiates WSQ compression and allocates resources.