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Browse Prior Art Database

High Frequency Information Detector/Discriminator

IP.com Disclosure Number: IPCOM000044553D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Fox, SJ: AUTHOR [+2]

Abstract

This article describes a device and method which detects and discriminates between halftones (HT) and high frequency line copy (LC) information. For each pel (picture element), an optimum high frequency operator (HF(R)), is applied. If HF(R) is greater than a predetermined threshold T1, the pel is classified as a high frequency pel. For each high frequency pel, four directional high frequency operators are generated. The maximum and minimum values for the four operators are determined. A high frequency gradient, G = MAX - MIN, is computed for each high frequency pel. G is then compared against a second predetermined threshold level, T2. If G is greater than T2, then the pel is characterized as a line copy. If the pel is less than T2, then the pel is characterized as an HT.

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High Frequency Information Detector/Discriminator

This article describes a device and method which detects and discriminates between halftones (HT) and high frequency line copy (LC) information. For each pel (picture element), an optimum high frequency operator (HF(R)), is applied. If HF(R) is greater than a predetermined threshold T1, the pel is classified as a high frequency pel. For each high frequency pel, four directional high frequency operators are generated. The maximum and minimum values for the four operators are determined. A high frequency gradient, G = MAX - MIN, is computed for each high frequency pel. G is then compared against a second predetermined threshold level, T2. If G is greater than T2, then the pel is characterized as a line copy. If the pel is less than T2, then the pel is characterized as an HT. A common type of high frequency information is very small or very thin lettering or graphics (i.e., two-point text). Text this size may be considered as high frequency information for a system with a scanning resolution of less than 500 pixels per inch. As such, the line copy-type information requires a thresholder adopted to line copy and designed to enhance its black-white-black transitions. A problem lies in the fact that this high frequency line copy information appears to the system as almost identical to the high frequency pattern of many halftone line screens. The small black dots on a white background which make up the halftone screen (or halftone carrier) pattern have a significant frequency overlapped with, for example, two-point and four-point text. For optimum operation, one wants to threshold the line copy so as to enhance the black-white contours. On the other hand, the desired thresholding technique for halftone is to minimize or eliminate the black-white transitions and reproduce only the gray continuous tone information contained therein. With reference to Figs. 1 and 3, a symmetrical high frequency operator (HF(S)) is calculated for several different radii....