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FOCUS AND SIGNAL TO NOISE RATIO MEASUREMENT TECHNIQUES

IP.com Disclosure Number: IPCOM000025962D
Original Publication Date: 1989-Apr-30
Included in the Prior Art Database: 2004-Apr-04
Document File: 2 page(s) / 81K

Publishing Venue

Xerox Disclosure Journal

Abstract

The Contrast Transfer Function, (CTF), a direct measurement value for focus, is measured in an electronic input scanner by scanning a test pattern of lines, extending generally parallel with the slow scan direction, with no relative motion between the scanning element and the test pattern. The output of the scanning process is directed through the device thresholding operation. A series of successive scan lines of data are produced in this manner, each scan line of data produced with a successively incremented threshold level applied to the data. The output of the thresholding operation is examined at a plurality of photosite locations to determine maximum and minimum transition points associated with the variation of threshold levels. Upon detection of the maximum and minimum, CTF is calculated numerically by using the threshold transition values.

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FOCUS AND SIGNAL TO NOISE RATIO MEASUREMENT TECHNIQUES Richard B. Eaton

Proposed Classification U.S. Cl. 358 Int. Cl. H04n

The Contrast Transfer Function, (CTF), a direct measurement value for focus, is measured in an electronic input scanner by scanning a test pattern of lines, extending generally parallel with the slow scan direction, with no relative motion between the scanning element and the test pattern. The output of the scanning process is directed through the device thresholding operation. A series of successive scan lines of data are produced in this manner, each scan line of data produced with a successively incremented threshold level applied to the data. The output of the thresholding operation is examined at a plurality of photosite locations to determine maximum and minimum transition points associated with the variation of threshold levels. Upon detection of the maximum and minimum, CTF is calculated numerically by using the threshold transition values.

Focus is examined qualitatively by printing the successive scan line data produced with successively varied threshold level applied to the data with a binary output printer in normal operation. Transition points are then indicated by the change from one condition to the other, such as from black to white. The pattern produced appears roughly as a sawtooth function. The slope of the sawtooth from base to apex increases with improved focus.

Signal to noise ratio may be measured in an electronic input scanner by...