Digital Filter For Edge Enhancement In Photodiode Array Scanners
Original Publication Date: 1982-Feb-01
Included in the Prior Art Database: 2005-Feb-08
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.