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Automatic Identification of Screen Ruling on Printed Copy

IP.com Disclosure Number: IPCOM000010902D
Publication Date: 2003-Jan-30
Document File: 9 page(s) / 247K

Publishing Venue

The IP.com Prior Art Database

Abstract

When processing images which need to be descreened it is necessary to select the screen ruling of the origination before the scan as this determines the scan resolution and enables optimum screen filtering to be used. This requires the user to know what the screen resolution is of the origination. Most users can not tell what the screen resolution is simply by looking at the origination and require the aide of a manual tool to determine the screen. This in itself can be difficult to use and can be a time consuming process to conduct (ie. Find the manual tool, select a suitable area, twist the tool to give the desired result). It is possible to measure the screen ruling by analysing a high resolution scan of a small area of the image. Thus the screen ruling can be determined automatically without user intervention. This process consists of 1. Automatically identifying a suitable region for close examination from a low resolution preview that has not been descreened 2. Scanning the suitable region at a high enough resolution not to alias the screen and calculate the screen ruling from the Fourier transform.

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FFEI

        � � � Automatic Identification of screen ruling on printed copy

M Gouch � � � � � � � � � 15th March 1999

Introduction        ......................................................................................... 2

Theory behind process......................................................................... 2

Identify suitable region for close examination        ................................... 2

Target requirement........................................................................ 2

Process        ....................................................................................... 2

Calculate the screen resolution        ....................................................... 3

Target requirement........................................................................ 3

Process        ....................................................................................... 3

Primary calling process / methods / API        ................................................ 7

Call “IdentifyCropPoint” with the low resolution image.        ....................... 7

Pass the new scanned data into “GetScreenRuling”        ......................... 8

Introduction

When processing images which need to be descreened it is necessary to select the screen ruling of the origination before the scan as this determines the scan resolution and enables optimum screen filtering to be used.� This requires the user to know what the screen resolution is of the origination.� Most users can not tell what the screen resolution is simply by looking at the origination and require the aide of a manual tool to determine the screen.� This in itself can be difficult to use and can be a time consuming process to conduct (ie. Find the manual tool, select a suitable area, twist the tool to give the desired result).

It is possible to measure the screen ruling by analysing a high resolution scan of a small area of the image.� Thus the screen ruling can be determined automatically without� user intervention.

This process consists of

1.       Automatically identifying a suitable region for close examination from a low resolution preview that has not been descreened

2.       Scanning the suitable region at a high enough resolution not to alias the screen and calculate the screen ruling from the Fourier transform.

Theory behind process

Identify suitable region for close examination

Target requirement

The ideal region is a flat tint region which has the screen present in all three channels.�

A flat tint is preferable as we do not need to discriminate between high frequency image detail and screen frequency when it comes to calculating the screen frequency from the high resolution scan.

Also we need to discriminate between flat tints with screens and flat tints produced from spot colours.

Process

Sub devide� the low resolution image into tile segments. Each segment should cover the same area, on the copy, as the area we will examine at the high resolution to measure the screen ruling.

Examine tile segments of the low resolution i...