These specifications are for the purpose of accrediting current live-and card-scan equipment integrated into automated booking stations. The complete Interim IAFIS Image Quality Specification consists of all requirements given in this document, plus all non-conflicting requirements given in the full IAFIS Image quality Specification, Appendix F, of the "Electronic Fingerprint Transmission Specification."

IQS 2.1 Geometric Image Accuracy

The absolute value of the difference "D", between the actual distance "X" between any two points on a target and the distance "Y" between those same two points as measured on the output scanned image of that target, shall mee t the following requirements for the value D:

Where: D, X, Y are in inches and D = |Y-X|

The requirement corresponds to a positional accuracy of ± 1.5% for distances between 0.07 and 1.5 inches, and a constant ±0.001 inches (1/2 pixel) for distances less than or equal to 0.07 inches.

IQS 2.2 Modulation Transfer Function

The MTF shall be measured using test chart number M-13-60-1X manufactured by Sine Patterns, Inc., or by using any other suitable sine wave or square wave target. If using the M-13-60-1X target, the calibration curve is constructed by performing a least s quares linear regression curve fit between the image gray levels of the useful density patches in the test target and the corresponding density patch values on the target.

IQS 2.3 Signal-to-Noise Ratio - no change from Appendix F

Both the ratio to signal to white noise standard deviation and the ratio of signal to black noise standard deviation of the digital scanner shall be greater than or equal to 125 using the following procedure:

(1) A random 0.25 inch x 0.25 inch test field within the image area is chosen and the white reference target, Munsell3 N9-white matte, is placed in the test field.

(2) A white test population of 8-bit reflectance values from at least 1000 samples within the test field are collected. The average values and standard deviation are computed from this test population.

(3) Steps 1 and 2 are repeated for the black reference target, Munsell N3 - black matte.

(4) The signal to noise ratio (SNR) is computed as the difference between average white and average black values, alternately divide by the white noise standard deviation ('white SNR') and the black noise standard deviation ('black SNR').

IQS 2.4 Gray-Scale Range of Image Data

At least 80% of the captured individual fingerprint images shall have a gray-scale dynamic range of at least 150 gray levels. For this requirements section, 'dynamic range' is defined as the total number of gray levels that have signal content from the f ingerprint image. Fingerprint card format lines, boxes and text shall be excluded from the dynamic range computation and white surround in the immediate vicinity of a given fingerprint shall be included in the dynamic range computation.

IQS 2.5 Gray-scale Linearity - no change from Appendix F

Using the 14 gray patches in the Sine Patterns, Inc. test target M-13-60-1X as the scanner input (independent variable), with their manufacture-supplied reflectance values, none of the corresponding 14 scanner output gray levels (dependent variable) shall deviate by more than 7.65 gray levels from a linear, least square regression line fitted between the two variables. The output sample values within an area of at least 0.25 x 0.25 inches shall be utilized to compute the average output gray level for eac h patch.

IQS 2.6 Output Gray Level Uniformity

- no change from Appendix F Output gray level uniformity shall be determined by scanning both a white reference target, Munsell N9-white matte, and a black reference target, Munsell N3 - black matte. The scanner shall be set up such that the white reference target is below scanner saturation level, and the black reference target is above scanner dark current level in the respective tests.

Using the white target as the scanner input, the following three requirements shall be met:

(1) The outputs of any two adjacent rows or columns of length 9 pixels or greater shall not have mean gray levels that differ by more than 2.5 gray levels.

(2) For all pixels within a 0.25 inch x 0.25 inch area ('quarter inch area') located in any region of the total scanner field of view, no individual pixel's gray level shall vary from the mean gray level by more than 22.0 gray levels.

(3) For any two non-contiguous quarter inch areas located anywhere in the total scanner field of view, the mean gray levels of the two quarter inch areas shall not differ by more than 12.0 gray levels.

And, using the black target as the scanner input, the following three requirements shall be met:

(1) The outputs of any two adjacent rows or columns of length 9 pixels or greater shall not have mean gray levels that differ by more than 1.0 gray levels.

(2) For all pixels within a 0.25 inch x 0.25 inch area ('quarter inch area') located in any region of the total scanner field of view, no individual pixel's gray level shall vary from the mean gray level by more than 8.0 gray levels.

(3) For any two non-contiguous quarter inch areas located anywhere in the total scanner field of view, the mean gray levels of the two quarter inch areas shall not differ by more than 3.0 gray levels.

Footnote:
³ Munsell-Macbeth, P.O. Box 230, Newburgh, NY 12551, Phone: (914)565-7660