Browse Prior Art Database

Digital Filter For Edge Enhancement In Photodiode Array Scanners

IP.com Disclosure Number: IPCOM000048528D
Original Publication Date: 1982-Feb-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Habegger, MA: AUTHOR

Abstract

In diode array scanners, the contrast response of the scanner tends to roll off as the spatial frequency of the scanned image approaches the Nyquist frequency. The Nyquist frequency is here defined as an image bar pattern having the same spatial frequency as the spatial frequency of the array. In other words, there is a transition from black to white for each adjacent diode pair. It is known that as the image spatial frequency approaches the Nyquist frequency, the lens and diode array scanner combination loses its ability to resolve the image and the contrast goes to zero. The circuit described herein compensates for this roll off of contrast by detecting the signal level difference between the target pel (picture element) being sampled and its adjacent pels.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 2

Digital Filter For Edge Enhancement In Photodiode Array Scanners

In diode array scanners, the contrast response of the scanner tends to roll off as the spatial frequency of the scanned image approaches the Nyquist frequency. The Nyquist frequency is here defined as an image bar pattern having the same spatial frequency as the spatial frequency of the array. In other words, there is a transition from black to white for each adjacent diode pair. It is known that as the image spatial frequency approaches the Nyquist frequency, the lens and diode array scanner combination loses its ability to resolve the image and the contrast goes to zero. The circuit described herein compensates for this roll off of contrast by detecting the signal level difference between the target pel (picture element) being sampled and its adjacent pels. The difference is added to the target pel signal to boost the contrast.

Fig. 1 above shows the contrast signal produced by the diode array and lens combination as a function of the spatial frequency of the image data. As the spatial frequency increases to the Nyquist frequency, curve 10 indicates how the contrast rolls off to zero. Curve 12, on the other hand, indicates the boost effect that can be given to the contrast by the digital filter shown in Fig. 2. The ideal result is represented by the dashed line 14 showing a flat contrast response out to Nyquist frequency.

The function of the filter in Fig. 2 is to sum the target pel video level E2 with its difference from the video levels of adjacent pels. The...