Dwsq takes as input a file containing a WSQ-compressed grayscale fingerprint image. Once read into memory, the lossy-compressed pixmap is decoded and reconstructed using Wavelet Scalar Quantization as described in the FBI's Criminal Justice Information Services (CJIS) document, "WSQ Gray-scale Fingerprint Compressions Specification," Dec. 1997. This is the only fingerprint compression format accepted by the FBI IAFIS system.
Upon completion, two different output image file formats are possible, a NIST IHead file (the default) or a raw pixmap file (specified by the -raw_out flag). In addition, a specially formatted text file, called a NISTCOM, is created with extension ".ncm". The NISTCOM file contains relevant image attributes associated with the decoded and reconstructed output image. (See NISTCOM OUTPUT below.)
All switch names may be abbreviated; for example, -raw_out may be written -r.
the extension of the decompressed output file. To construct the output filename, dwsq takes the input filename and replaces its extension with the one specified here.
the input WSQ file to be decompressed.
specifies that the decoded and reconstructed image should be stored to a raw pixmap file.
Upon successful completion, dwsq, creates a specially formatted text file called a NISTCOM file. A NISTCOM is a text-based attribute list comprised of (name, value) pairs, one pair per text line. The first line of a NISTCOM always has name = "NIST_COM" and its value is always the total number of attributes included in the list. These attributes are collected and merged from two different sources to represent the history and condition of the resulting reconstructed image. The first source is from an optional NISTCOM comment block inside the WSQ-encoded input file. This comment block can be used to hold user-supplied attributes. The WSQ encoder, cwsq, by convention inserts one of these comment blocks in each compressed output file it creates. (The utility rdwsqcom can be used to scan a WSQ file for any and all comment blocks.) The second source of attributes comes from the decompression process itself. In general, attribute values from this second source are given precedence over those from the first.
The NISTCOM output filename is constructed by combining the basename of the input WSQ file with the extension ".ncm". By creating the NISTCOM file, relevant attributes associated with the decoded and reconstructed image are retained and easily accessed. This is especially useful when dealing with raw pixmap files and creating image archives. The following is an example NISTCOM generated by dwsq:
NIST_COM 7 PIX_WIDTH 500 PIX_HEIGHT 500 PIX_DEPTH 8 PPI 500 LOSSY 1 COLORSPACE GRAY