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WO1997018666A1 - Procede de tramage - Google Patents

Procede de tramage Download PDF

Info

Publication number
WO1997018666A1
WO1997018666A1 PCT/SE1996/001451 SE9601451W WO9718666A1 WO 1997018666 A1 WO1997018666 A1 WO 1997018666A1 SE 9601451 W SE9601451 W SE 9601451W WO 9718666 A1 WO9718666 A1 WO 9718666A1
Authority
WO
WIPO (PCT)
Prior art keywords
picture
screens
screening
screen
screening according
Prior art date
Application number
PCT/SE1996/001451
Other languages
English (en)
Swedish (sv)
Inventor
Björn KRUSE
Original Assignee
Forskarpatent I Linköping Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Forskarpatent I Linköping Ab filed Critical Forskarpatent I Linköping Ab
Priority to AU76594/96A priority Critical patent/AU7659496A/en
Publication of WO1997018666A1 publication Critical patent/WO1997018666A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40—Picture signal circuits
    • H04N1/405—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40—Picture signal circuits
    • H04N1/405—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
    • H04N1/4055—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a clustered dots or a size modulated halftone pattern

Definitions

  • Picture reproduction in print is in most cases done with a very limited number of colours. For the reproduction of black and white pictures only one colour is necessary, normally black, while reproduction of colour picture requires at least three printing colours.
  • the object of the screen is to distribute the colour over the surface, surface modulation, so that the resulting impression of the screened picture coincides with that of the original.
  • the tone value 50% is desired the area is in principle to be divided so that half of the area is covered with colour and half of the area is bare (without colour).
  • This dividing of the area can be carried out in a number of different ways.
  • a usual method of digital screening is to imitate the effect of differently large screen points that one achieves at optical screening.
  • Another way is to emulate the light sensitive particles in a film. In the latter case the result receives a random character. In the former case the result is regularly arranged as a lattice.
  • the original picture is separated in its colour components, most frequently cyan, magenta and yellow that are each screened separately. Because of the risk of moire patterns different techniques are used to modify the conventional screens, for instance by the use of different screen angles of the separations . If non-periodic screens are used the moire problem is minimised already from the start .
  • the method depends on the original picture being divided into segments for which different screening methods are suitable.
  • the separating into segments can be done based on local richness of detail, tone value or some other property of the picture or the media.
  • Each point in the picture area belongs to one of the different segments. In the transition zones between two segments a point may partly belong to two or several segments.
  • the local variation may be given a threshold so that a segment is constituted by detail, in the picture with great variation, S 2 , while the second segment has a lower local variation, S 1 .
  • the local variation may be given a threshold so that a segment is constituted by detail, in the picture with great variation, S 2 , while the second segment has a lower local variation, S 1 .
  • t 2 is a threshold that rules the size of the variation. Only points with a greater local variation belong to. S 2 .
  • the segment S 1 is in this case constituted by the remaining picture points, that is those that do not belong to .
  • the variation may be constituted by the variation measure known from statistics but may also be calculated in other ways It should be observed that the segments are not necessarily hanging together. How fragmented they are is ruled by the character of the original picture . In a more complicated case with three segments S 1 , S 2 and S 3 , the definition could be the following.
  • S 1 remaining points In this case the picture is separated into three segments. One, S 3 , where there is a large richness of detail, one, S 2 , where the richness of detail is less but where the tone value is higher than the threshold value t 2 and finally S 1 constituted by the remaining points where we have a low tone value and little variation.
  • S 3 where there is a large richness of detail
  • S 2 where the richness of detail is less but where the tone value is higher than the threshold value t 2
  • S 1 constituted by the remaining points where we have a low tone value and little variation.
  • the number of segments may of course be larger. In the following we allow n to define the number of segments S 0 , S 1 and
  • each point (x,y) in the area belongs to one and only one segment. If, however, 0.0 ⁇ S 1 (x,y) ⁇ 1 .0 the point (x,y) lies in a transition zone between the two segments.
  • the value of S i (x,y) may be associated to how close the point is to the inner of the segment. A large value close to 1.0, means that the point is closer to the inner of the segment while a lower value means that it is further away.
  • the border zone may for instance be made by low pass filtration of the segment in question . At the transition between two segments values between 0.0 and 1.0 result defining the degree of belongingness .
  • R 1 , R 2 ... R n be n number of screens belonging to respective segments.
  • the screens may explicitly be defined as matrixes or functions of (x,y) so that a screen value between 0.0 and 1.0 can be calculated for each picture point.
  • the screen may for instance be a conventional screen, a stocastic screen or a screen that has been made in some other optional way.
  • R is the starting point for an optimising (minimising) of the difference between the original picture and the screened version of the original picture.
  • the screened picture is obtained by comparing the picture point value with the corresponding screen point value (threshold screening) .
  • RP denote the screened picture.
  • D(x,y) to be the difference between the original and screened version added over a surrounding N:
  • N is a surrounding of the point (x,y) If the original picture were binary D would be ⁇ 0 at optimum. If P however is a picture with half tones D will never be zero everywhere. Our requirement for optimum is instead that
  • is small in each point.
  • Point enlarging is an effect at the producing of films, plates and in printing by the interacting of the colour with the paper. When illuminated an effect is added depending on optical spreading effects in the paper substrate.
  • the first effect is normally called mechanical point enlarging while the latter is called optical point enlarging .
  • a simple correction of the point enlarging can be made in the tone value of the picture, as is common today, however the point enlarging is dependent both on the shape of the screen and the size of the screen points.
  • a compensation that in this meaning takes detailed regard to shape and size can only be executed under the optimising phase above . It is not until the picture is screened that the real look of the actual points are known.
  • G(RP) is a generally unlinear function over an environment of each point in RP.
  • the function G is such that is compensates for the point enlarging actually obtained.
  • the function has a different form depending on actual printing media and printing press. For instance the influence of the physical point enlarging on RP can be described as:
  • RP' is now no longer binary but shows an extended zone outside each screen point, that depending on the coefficients c ⁇ ⁇ may have different extension .
  • the influence of the optical point enlarging on RP' may for instance be described as :
  • the coefficients d ⁇ ⁇ are ruled by the optical spreading properties of the paper.
  • the function G may also take in regard the remaining frequency response of the screen function. A simple generalisation of this is to allow G also to be dependent on the specific screen function.

Landscapes

  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Spectrometry And Color Measurement (AREA)
  • Printing Methods (AREA)
  • Facsimile Image Signal Circuits (AREA)

Abstract

L'invention se rapporte au tramage numérique et électronique d'images, utilisé notamment dans l'impression, et dans lequel différents types de trames sont mélangés pour obtenir une seule et même image. Dans des zones de l'image présentant une structure détaillée, on utilise une trame fine, alors que pour des zones plus grandes présentant une structure moins détaillée d'échelles de gris ou de couleur, on utilise une trame plus grossière. Les trames plus grossières peuvent être également utilisées pour les parties de l'image qui doivent être très claires (par exemple, les tons de la peau et les parties brillantes). En faisant en sorte que les trames soient des multiples entiers les unes des autres, on obtient automatiquement une transition en douceur et certains points d'image feront partie des deux trames.
PCT/SE1996/001451 1995-11-13 1996-11-12 Procede de tramage WO1997018666A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU76594/96A AU7659496A (en) 1995-11-13 1996-11-12 Screening method

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9504016A SE9504016L (sv) 1995-11-13 1995-11-13 Rastreringsförfarande
SE9504016-8 1995-11-13

Publications (1)

Publication Number Publication Date
WO1997018666A1 true WO1997018666A1 (fr) 1997-05-22

Family

ID=20400185

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1996/001451 WO1997018666A1 (fr) 1995-11-13 1996-11-12 Procede de tramage

Country Status (3)

Country Link
AU (1) AU7659496A (fr)
SE (1) SE9504016L (fr)
WO (1) WO1997018666A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0828379A3 (fr) * 1996-09-04 1999-01-20 Canon Information Systems, Inc. Obtention de demi-teintes par sélection de matrices de tremblement basée sur le gradient
EP0946049A1 (fr) * 1998-03-24 1999-09-29 Hewlett-Packard Company Traitement d'images
EP2464092A1 (fr) * 2010-12-10 2012-06-13 Canon Kabushiki Kaisha Appareil et procédé de traitement d'images

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5055942A (en) * 1990-02-06 1991-10-08 Levien Raphael L Photographic image reproduction device using digital halftoning to screen images allowing adjustable coarseness
US5408338A (en) * 1992-02-19 1995-04-18 Ricoh Company, Ltd. Image processing unit processing pixel data according to scan line density

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5055942A (en) * 1990-02-06 1991-10-08 Levien Raphael L Photographic image reproduction device using digital halftoning to screen images allowing adjustable coarseness
US5408338A (en) * 1992-02-19 1995-04-18 Ricoh Company, Ltd. Image processing unit processing pixel data according to scan line density

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0828379A3 (fr) * 1996-09-04 1999-01-20 Canon Information Systems, Inc. Obtention de demi-teintes par sélection de matrices de tremblement basée sur le gradient
EP0946049A1 (fr) * 1998-03-24 1999-09-29 Hewlett-Packard Company Traitement d'images
EP2464092A1 (fr) * 2010-12-10 2012-06-13 Canon Kabushiki Kaisha Appareil et procédé de traitement d'images
US8749851B2 (en) 2010-12-10 2014-06-10 Canon Kabushiki Kaisha Image processing apparatus and image processing method

Also Published As

Publication number Publication date
SE9504016L (sv) 1997-05-14
AU7659496A (en) 1997-06-05
SE9504016D0 (sv) 1995-11-13

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