This is a 1995 document located on the Biometric Consortium site:
ANSI Standard - Image Quality
The MIQR is being replaced with specifications that cover both card- and live-scan devices. The minimum scan rate in picture elements (pixels) per inch, the pixel depth in bits (i.e., number of bits which determines the number of gray levels possible per pixel), and the acceptable transmission rates are specified in Section 5 of the ANSI Standard. The minimum scan rate for ten-print records for submission to IAFIS and EFIPS is expressed in pixels per inch (PPI or P/in). Scan rates are often expressed in dots per inch or DPI, just another term for pixels per inch. One term, DPI, comes from the printing industry and the other, PPI, from the computer industry.
The ANSI standard specifies a minimum scanning resolution of 500 pixels per inch (P/in) 5 p/in for ten print submittals. However, the transmission rate is specified as a range from 500 p/in +/- 5 p/in to 520 p/in +/-5 p/in. This allows scanners operating at 600 p/in to be used as long as the transmitted data meets the ANSI Standard. These scan and transmission rates were arrived at by balancing forensic needs, the state of technology, and the cost of implementation. In 1995 the FBI will begin work on upward revisions to these scan and transmission rates for an anticipated 1998 update of the ANSI Standard. IAFIS is being designed to be able to contain images scanned at different data rates. Plans call for the scan and transmission rates for type 7 records (latent prints) to be as high as 1,000 DPI. |
