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WSQ compression and decompression


The Agora WSQ - Wavelet Scalar Quantization - is a set of routines that implements the "WSQ Gray-scale Fingerprint Image Compression Specification", specified by the Federal Bureau of Investigation (FBI) in 1993.  The Agora WSQ software has achieved the FBI's certification of compliance to the standard.   This means that an image compressed with Agora may be decompressed and viewed with another vendor's standard compliant software, and vice versa.  The Agora WSQ technology ensures interoperability, and this benefits the customer.


In simple terms, WSQ is a image compression technique to reduce the size of a fingerprint image, sacrificing its quality as little as possible.  It was designed specificallytargeting fingerprint images, using their spectral characteristics to optimize the compression process. The process is "lossy", meaning that the reconstructed image isn't equal to the original; some information being lost. The WSQ algorithm was specially designed to minimize the loss of information, so that the reconstructed image be as close as possible to the original; the differences frequently being imperceptible.  The use of other compression algorithms such as JPG to compress fingerprints results in higher losses affecting the features.  This reduces the accuracy of identification.  One reason to use WSQ is to maintain the image quality and therefore the accuracy of identification.  The other one other one is interoperablity


With Agora the size reduction factor is adjustable, typically being set to the FBI recommended reduction of fifteen times (15x). This means that a 512x512 image, originally occupying 256 KB, can be reduced to approximately 17 KB.  In large data bases, the saved space is enormous.   Higher compression ratios may be used, but it is not recommended because the image quality starts to diminish.

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