Browse Prior Art Database

IMPROVED HALF-TONE FREQUENCY DETECTION

IP.com Disclosure Number: IPCOM000025796D
Original Publication Date: 1988-Feb-29
Included in the Prior Art Database: 2004-Apr-04
Document File: 6 page(s) / 289K

Publishing Venue

Xerox Disclosure Journal

Abstract

In the reproduction of copies of an original from video image data created, for example, by electronic raster input scanning from an original document, one is faced with the limited resolution capabilities of the reproducing system and the fact that output devices are mostly binary. This is particularly evident when attempting to reproduce half-tones, lines and continuous tone images. Of course, an image data processing system may be tailored so as to offset the limited resolution capabilities of the reproducing apparatus used, but this is dificult due to the divergent processing needs required by the different types of image which may be encountered. In this respect, it should be understood that the image content of the original document may consist entirely of high frequency half-tones, low frequency half-tones, continuous tones, or line copy, or a combination, in some unknown degree, of some or all of the above. In the face of these possibilities, optimizing the image processing system for one image type in an effort to offset the limitations in the resolution capability of the reproducing apparatus used, may not be possible, requiring a compromise choice which may not produce acceptable results. Thus, for example, where one optimizes the system for low frequency half-tones, it is often at the expense of degraded reproduction of high frequency half-tones, or of line copy, and vice versa.

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 33% of the total text.

Page 1 of 6

XEROX DISCLOSURE JOURNAL

IMPROVED HALF-TONE: FREQUENCY DETECTION Ying-Wei Lin
Anthony F. Calarco

:A, INPUZT

COMPLEMENT

DELAY #l 102-y

Proposed Classification
U.S. C1.358 Int. C1. H04n

NOISE ADDER

I ADJUSTMENT I *4+A

1

I

I

106-4

Volume 13 Number 1 January/February 1988

18

 TO IMAGE PROCESSING CONTROLLER

43

[This page contains 1 picture or other non-text object]

Page 2 of 6

IMPROVED HALF-TONE FREQUENCY DETECTION (Cont'd)

In the reproduction of copies of an original from video image data created, for example, by electronic raster input scanning from an original document, one is faced with the limited resolution capabilities of the reproducing system and the fact that output devices are mostly binary. This is particularly evident when attempting to reproduce half-tones, lines and continuous tone images. Of course, an image data processing system may be tailored so as to offset the limited resolution capabilities of the reproducing apparatus used, but this is dificult due to the divergent processing needs required by the different types of image which may be encountered. In this respect, it should be understood that the image content of the original document may consist entirely of high frequency half-tones, low frequency half- tones, continuous tones, or line copy, or a combination, in some unknown degree, of some or all of the above. In the face of these possibilities, optimizing the image processing system for one image type in an effort to offset the limitations in the resolution capability of the reproducing apparatus used, may not be possible, requiring a compromise choice which may not produce acceptable results. Thus, for example, where one optimizes the system for low frequency half-tones, it is often at the expense of degraded reproduction of high frequency half-tones, or of line copy, and vice versa.

In US-A 4,194,221 to Stoffel, this problem was addressed by applying a discrimination function instructing the image processing system as to the type of image data present and particularly, an auto correlation function to the stream of pixel data, to determine the existence of high frequency half- tone image data. Such a function is expressed as:

t = fast

t=o

where


n = the bit or pixel number; p = the pixel voltage value; and t = the pixel position in the data stream.

Stoffel describes a method of processing automatically a stream of image pixels representing unknown combinations of high and low frequency half- tones, continuous tones, and/or lines to provide binary level output pixels representative of the image. The described function is applied to the stream of image pixels and, for the portions of the stream that contained high frequency half-tone image data, notes large number of closely spaced peaks in the resultant signal. The correlator circuits described in Stoffel's referred

DISCLOSURE XEROX 44 JOURNAL

Volume 13 Number 1 January/February 1988

[This page contains 1 picture or other non-text object]

Page 3 of 6

IMPROVED H...