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Using Multicoloured Halftone Screens for Offset Print Quality Monitoring
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
2005 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In the newspaper printing industry, offset is the dominating printing method and the use of multicolour printing has increased rapidly in newspapers during the last decade. The offset printing process relies on the assumption that an uniform film of ink of right thickness is transferred onto the printing areas. The quality of reproduction of colour images in offset printing is dependent on a number of parameters in a chain of steps and in the end it is the amount and the distribution of ink deposited on the substrate that create the sensation and thus the perceived colours. We identify three control points in the offset printing process and present methods for assessing the printing process quality in two of these points:

• Methods for determining if the printing plates carry the correct image

• Methods for determining the amount of ink deposited onto the newsprint

A new concept of colour impression is introduced as a measure of the amount of ink deposited on the newsprint. Two factors contribute to values of the colour impression, the halftone dot-size and ink density. Colour impression values are determined on gray-bars using a CCD-camera based system. Colour impression values can also be determined in an area containing an arbitrary combination of cyan magenta and yellow inks. The correct amount of ink is known either from a reference print or from prepress information. Thus, the deviation of the amount of ink can be determined that can be used as control value by a press operator or as input to a control system.

How a closed loop controller can be designed based on the colour impression values is also shown.

It is demonstrated that the methods developed can be used for off-line print quality monitoring and ink feed control, or preferably in an online system in a newspaper printing press.

Place, publisher, year, edition, pages
Institutionen för teknik och naturvetenskap , 2005. , 104 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1147
Keyword [en]
Datorteknik, multicolour printing, printing process, colour images, colour impression, CCD-camera
Keyword [sv]
Datorteknik
National Category
Computer Engineering
Identifiers
URN: urn:nbn:se:liu:diva-5573ISBN: 91-85297-25-9 (print)OAI: oai:DiVA.org:liu-5573DiVA: diva2:21386
Presentation
2005-02-10, 00:00 (English)
Supervisors
Note
Report code: LiU-TEK-LIC-2005:02.Available from: 2005-01-20 Created: 2005-01-20 Last updated: 2009-04-14
List of papers
1. Unsupervised colour image segmentation applied to printing quality assessment
Open this publication in new window or tab >>Unsupervised colour image segmentation applied to printing quality assessment
2005 (English)In: Image and Vision Computing, ISSN 0262-8856, Vol. 23, no 4, 417-425 p.Article in journal (Refereed) Published
Abstract [en]

We present an option for colour image segmentation applied to printing quality assessment in offset lithographic printing by measuring an average ink dot size in halftone pictures. The segmentation is accomplished in two stages through classification of image pixels. In the first stage, rough image segmentation is performed. The results of the first segmentation stage are then utilized to collect a balanced training data set for learning refined parameters of the decision rules. The developed software is successfully used in a printing shop to assess the ink dot size on paper and printing plates.

Keyword
Colour image segmentation; Fuzzy clustering; Quality inspection; Colour printing
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-13768 (URN)10.1016/j.imavis.2004.11.003 (DOI)
Available from: 2005-01-20 Created: 2005-01-20
2. A New Method for Colour Measurements in Graphic Arts
Open this publication in new window or tab >>A New Method for Colour Measurements in Graphic Arts
1999 (English)In: Color Research & Application, ISSN 1520-6378, Vol. 24, no 3, 185-196 p.Article in journal (Refereed) Published
Abstract [en]

This article presents a method for colour measurements directly on printed half-tone multicoloured pictures. The article introduces the concept of colour impression. By this concept we mean the CMY or CMYK vector (colour vector), which lives in the three- or four-dimensional space of printing inks. Two factors contribute to values of the vector components, namely, the percentage of the area covered by cyan, magenta, yellow, and black inks (tonal values) and ink densities. The colour vector expresses integrated information about the tonal values and ink densities. Values of the colour vector components increase if tonal values or ink densities rise and vice versa. If, for some primary colour, the ink density and tonal value do not change, the corresponding component of the colour vector remains constant. If some reference values of the colour vector components are set from a preprint, then, after an appropriate calibration, the colour vector directly shows how much the operator needs to raise or lower the cyan, magenta, yellow, and black ink densities in order to correct colours of the picture being measured. The values of the components are obtained by registering the RGB image from the measuring area and then transforming the set of registered RGB values to the triplet or quadruple of CMY or CMYK values, respectively. Algorithms based on artificial neural networks are used for performing the transformation. During the experimental investigations, we have found a good correlation between components of the colour vector and ink densities.

Keyword
colour printing, colour classification, neural networks, graphic arts
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-13769 (URN)10.1002/(SICI)1520-6378(199906)24:3<185::AID-COL5>3.0.CO;2-1 (DOI)
Available from: 2005-01-20 Created: 2005-01-20
3. Intelligent Monitoring of the Offset Printing Process
Open this publication in new window or tab >>Intelligent Monitoring of the Offset Printing Process
2004 (English)In: Neural Networks and Computational Intelligence - Proceedings, 2004, 173-178 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, we present a neural networks and image analysis based approach to assessing colour deviations in an offset printing process from direct measurements on halftone multicoloured pictures--there are no measuring areas printed solely to assess the deviations. A committee of neural networks is trained to assess the ink proportions in a small image area. From only one measurement the trained committee is capable of estimating the actual amount of printing inks dispersed on paper in the measuring area. To match the measured image area of the printed picture with the corresponding area of the original image, when comparing the actual ink proportions with the targeted ones, properties of the 2-D Fourier transform are exploited.

Keyword
Neural modelling, Neural network committee, Fourier transform, Offset lithographic printing
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-13770 (URN)
Available from: 2005-01-20 Created: 2005-01-20 Last updated: 2009-02-05
4. Modelling and Control of the Web-Fed Offset Newspaper Printing Press
Open this publication in new window or tab >>Modelling and Control of the Web-Fed Offset Newspaper Printing Press
Show others...
2003 (English)In: TAGA Proceedings, 2003, 179–194- p.Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-13771 (URN)
Available from: 2005-01-20 Created: 2005-01-20

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