APPENDIX H

DESCRIPTORS AND FIELD EDIT SPECIFICATIONS

FOR TYPE-7 LOGICAL RECORDS

FGP - FINGER POSITION. This mandatory fixed-length field shall occupy the 7th through 12th bytes of a Type-7 record. It shall contain possible finger positions beginning the least-most byte of the field (byte seven of the record). The decimal code number for the known or most probable finger position shall be taken from Table 5 of the standard “Data Format for the Interchange of Fingerprint Information”, ANSI/NIST-CSL 1-1993. The number shall be entered as a binary number, right justified and left zero filled withing the eight-bit byte. Up to five additional finger positions may be referenced by entering the alternate finger positions in the remaining five bytes using the same format. If fewer than five finger position references are to be used, the unused bytes shall be filled with the binary equivalent of “255". The code “0" (for “Unknown finger”) shall be used to reference every finger position from one through ten.

CGA - GRAYSCALE COMPRESSION ALGORITHM. This mandatory one-byte field shall occupy the 18th byte of a Type-7 record. It shall be used to specify the type of grayscale compression algorithm used (if any). A binary “0" denotes no compression. Otherwise, the contents of this byte shall be a binary representation for the number allocated to the particular compression technique used by the interchange parties. The FBI maintains a registry relating these number to the compression algorithms.

HLL - HORIZONTAL LINE LENGTH. This mandatory two-byte field shall occupy the 14th and 15th bytes of the Type-7 record. It shall be used to specify the number of pixels contained on a single horizontal line of the transmitted image.

IDC - IMAGE DESIGNATION CHARACTER. This mandatory one byte binary field shall be used to identify the image data contained in this record. The IDC contained in this field shall be a binary representation of the IDC found in the file content field of the Type-1 record.

IMG - IMAGE DATA. This binary field shall contain all of the high-resolution grayscale image data. Each pixel of the uncompressed image shall be quantized to eight bits (256 gray levels) contained in a single byte. If compression is used, the pixel data shall be compressed in accordance with the compression technique specified in the CGA field. This completes the high-resolution image description for a single image.

IMP - IMPRESSION TYPE. This mandatory one-byte field shall occupy the sixth byte of a Type-7 record. The code selected from Table 4, in the ANSI/NIST standard referenced above, describes the manner by which the fingerprint image information was obtained.

ISR - IMAGE SCANNING RESOLUTION. This mandatory one-byte field shall occupy the thirteenth byte of a Type-7 record. It shall contain a binary value of “0" if the minimum scanning resolution is used and a “1" if the native scanning resolution is used.

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LEN - LOGICAL RECORD LENGTH. This mandatory four-byte binary field shall contain the length of the logical record specifying the total number of bytes, including every byte of all the fields contained in the record.

VLL - VERTICAL LINE LENGTH. This mandatory two-byte field shall occupy the 16th and 17th bytes of the Type-7 record. It shall be used to specify the number of horizontal lines contained in the transmitted image.

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TABLE H-1. FIELD LIST FOR TYPE-7 (MISCELLANEOUS IMAGE) LOGICAL RECORDS

Under the condition column: O = Optional; M = Mandatory; C = Conditional, see notes

Under the character type column: A = Alpha; B = Binary; N = Numeric; S = Special Characters

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