WO1991014577A1 - Dispositif d'enregistrement thermique - Google Patents

Dispositif d'enregistrement thermique Download PDF

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Publication number
WO1991014577A1
WO1991014577A1 PCT/GB1991/000476 GB9100476W WO9114577A1 WO 1991014577 A1 WO1991014577 A1 WO 1991014577A1 GB 9100476 W GB9100476 W GB 9100476W WO 9114577 A1 WO9114577 A1 WO 9114577A1
Authority
WO
WIPO (PCT)
Prior art keywords
data
input gradation
optical density
gradation
heating elements
Prior art date
Application number
PCT/GB1991/000476
Other languages
English (en)
Inventor
John Edward Baxendale
Original Assignee
Dowty Maritime Limited
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 Dowty Maritime Limited filed Critical Dowty Maritime Limited
Publication of WO1991014577A1 publication Critical patent/WO1991014577A1/fr

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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
    • H04N1/401—Compensating positionally unequal response of the pick-up or reproducing head
    • H04N1/4015—Compensating positionally unequal response of the pick-up or reproducing head of the reproducing head
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/315—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of heat to a heat sensitive printing or impression-transfer material
    • B41J2/32—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of heat to a heat sensitive printing or impression-transfer material using thermal heads
    • B41J2/35—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of heat to a heat sensitive printing or impression-transfer material using thermal heads providing current or voltage to the thermal head
    • B41J2/355—Control circuits for heating-element selection
    • B41J2/36—Print density control

Definitions

  • This invention relates to thermal recording apparatus for recording a grey scale image using a thermal recording head, and to a method of compensating for spurious heating effects in thermal recording apparatus.
  • Known thermal recording heads comprise a linear array of heating elements each of which can be selectively energised from an electric current source so as to heat a portion of a recording medium and produce a spot or printed pixel along a print line. Successive lines are printed by moving the recording head and recording medium relative to one another. The greyness or optical density of each spot is controlled by controlling the electrical energy applied to each heating element in accordance with gradation data corresponding to the image to be recorded.
  • the present invention is based on an appreciation of the fact that the variation in the performance of the heating elements is not simply due to
  • heating elements comprising thick or thin film elements on a ceramic substrate with an insulating wear resistant surface glaze, are found to vary in surface geometry and also in the thickness of the heating film and surface glaze. These variations effect the thermal properties of the heating elements independently of their resistance. Thus variations in the performance of each heating element is best compensated for by reference to correction data derived from measurement of the optical density of spots recorded by the heating elements.
  • thermal recording apparatus comprises a plurality of heating elements each operative to record a spot on a recording medium corresponding to input gradation data, and a correction memory storing gradation correction data for producing a corresponding output to each heating element in accordance with the input gradation data and the identity of each heating element, said gradation correction data corresponding to measurements of the optical density of spots recorded by said heating elements
  • the gradation correction data stored in the memory consists of individual corrected values of input gradation data for each combination of heating element and grey level of the input gradation data, these corrected values being stored in the memory in the form of a look-up table so that the address of each heating element serves to access the corresponding corrected value for the particular grey level of the input gradation data.
  • the corrected values of the input gradation data are derived by averaging the optical density of the spots recorded by all the heating elements at one particular grey level of the input gradation data before any correction is applied, and comparing the optical density of each spot with the average optical density value so as to produce a correction ratio for each heating element.
  • An equation is then used which relates the input gradation data to corrected values in terms of the correction ratio for each heating
  • SUBSTITUTESHEET element so as to generate the corrected values for all the other grey levels of the input gradation data.
  • This equation is established from an analysis of the optical density measurements of the spots recorded by the heating elements at different grey levels of the input gradation data, and once established it is found to apply to any recording head employing the same type of heating element.
  • Figure 1 is a schematic drawing of the drive circuit of a thermal recording head according to the invention
  • Figure 2 is a graph showing the variation in optical density of the spots recorded by a prior art recording head at different grey levels
  • Figure 3 is a graph showing the average and lightest and darkest optical densities for each
  • the thermal recording head 1 is of a known type and comprises a plurality of heating elements fabricated on a ceramic substrate as a linear array so as to record a line of spots or pixels on a recording medium.
  • the heating elements may be fabricated using thick film technology in which the heating elements are still screen printed, or thin film technology in which the heating elements are deposited by vacuum evaporation. In both cases, an insulating, wear-resistant surface glaze is formed over the heating elements.
  • the recording medium may be thermally sensitive paper or plastic film on which the image is recorded directly, or thermally sensitive carrier film from which the image is transferred to paper. In all cases, the grey level or optical density of a spot formed on the recording medium is generally proportional to the heat emitted by the heating element.
  • a recording head drive unit 2 serves to control energisation of the heating elements in accordance with image data received via a a connection 3 from
  • the image data is quantised in terms of levels on a grey scale, and the drive unit 2 energises the heating elements with energies corresponding to these grey levels or gradation data so as to record the required image.
  • the buffer memory 4 typically stores sufficient data to record one line of the image at a time, this data being supplied via a data input 5 in conjunction with address data at an address input 6 so that the gradation data is related to the corresponding heating elements that are to be energised.
  • the recording head is of known construction.
  • the uniformity of the head in recording grey scales can be evaluated by energising all of the heating elements at each successive grey level and measuring the optical density of the resulting spots.
  • the results of these tests at grey levels 1 to 15 are plotted in Figure 2, and illustrate how the optical density i varies across the width w of the recording head, and how this variation becomes more pronounced at higher grey levels.
  • Figure 3 illustrates normalised values of the average optical density i and the lightest and the darkest optical densities for each grey level.
  • the illustrated recording head is adapted to counter the described non-uniformity of grey level recording by providing a correction memory 7 which stores correction data derived from optical density measurements.
  • the memory 7 takes the form of an EPROM and is configured as a look-up table so as to respond to input image data at data input 8 and heating element address data at address input 9 and produce corresponding corrected gradation data at output 10 which is applied to the data input 5 of the buffer memory 4.
  • the correction data is derived from the optical density measurements of the spots recorded by the heating elements at a predetermined grey level without the correction memory 7 being effective, for example, the optical density measurements i
  • SUBSTITUTE SHEET shown in Figure 2 for grey level 10.
  • This equation is used to calculate the corrected output data C for each heating element at each grey level of the input gradation data D.
  • the equation quoted above may be used with a different value for the factor A; for example, with 1 ⁇ A 2 although preferably 1.1 ⁇ A ⁇ 1.2.
  • the recording head has a 16 level grey scale, but the invention is especially applicable to apparatus for high quality, high resolution recording which would preferably use a larger number of grey levels, for example, 121 levels.
  • Additional grey levels may be obtained using the known technique of "dithering" between adjacent grey levels in an array of successive lines. For example, an array of eight spots, four each on successive lines adjacent one another, may be recorded at levels selected from either of two adjacent levels so as to produce up to seven intermediate levels.
  • the recording head will preferably have a large number of heating
  • SUBSTITUTE SHEET elements typically, there can be 8, 12, 16 or 24 heating elements per millimetre with a typical overall total of 3967 heating elements.
  • the optical density measurements made on the spots produced by the heating elements may be made using an optical reflection densitometer that is scanned along the line of spots.

Landscapes

  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Electronic Switches (AREA)
  • Recording Measured Values (AREA)
  • Heat Sensitive Colour Forming Recording (AREA)

Abstract

Procédé de compensation des effets de réchauffement inégaux se produisant dans les éléments de réchauffement (1) d'un dispositif d'enregistrement thermique excité par des données (8) d'échelonnement d'entrée, comprenant la mesure de la densité optique des taches enregistrées par les éléments de réchauffement quand ils sont excités, l'utilisation desdites mesures de densité optique pour calculer des données de correction d'échelonnement pour chaque élément de réchauffement, la mise en mémoire desdites données de correction d'échelonnement pour produire des sorties (3) corrigées afin d'exciter les éléments de réchauffement en réponse aux données d'échelonnement d'entrée. La mémoire de correction (7) peut être une table de recherche mémorisant des valeurs corrigées, chacune d'entre elles correspondant à l'identité d'un élément de réchauffement en particulier et d'un niveau particulier des données d'échelonnement d'entrée. Les valeurs corrigées se calculent par la moyenne de la densité optique des taches enregistrées par les éléments de réchauffement sur un niveau de gris, en comparant la densité optique de chacune des taches avec la moyenne pour produire un rapport de correction en appliquant une équation de correction pour tous les niveaux de gris.
PCT/GB1991/000476 1990-03-29 1991-03-27 Dispositif d'enregistrement thermique WO1991014577A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9007014.5 1990-03-29
GB909007014A GB9007014D0 (en) 1990-03-29 1990-03-29 Thermal recording apparatus

Publications (1)

Publication Number Publication Date
WO1991014577A1 true WO1991014577A1 (fr) 1991-10-03

Family

ID=10673459

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1991/000476 WO1991014577A1 (fr) 1990-03-29 1991-03-27 Dispositif d'enregistrement thermique

Country Status (3)

Country Link
AU (1) AU7489691A (fr)
GB (2) GB9007014D0 (fr)
WO (1) WO1991014577A1 (fr)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0535769A1 (fr) * 1991-09-23 1993-04-07 Eastman Kodak Company Procédé pour compenser les tolérances des résistances dans l'impression d'images multi-tons
EP0541064A2 (fr) * 1991-11-04 1993-05-12 Eastman Kodak Company Module de tête d'impression thermique
DE4302652A1 (fr) * 1992-01-31 1993-08-05 Ricoh Kk
EP0601658A1 (fr) * 1992-12-09 1994-06-15 Agfa-Gevaert N.V. Procédé de calibrage des éléments chauffants d'une tête thermique d'un système d'impression
EP0627319A1 (fr) * 1993-05-28 1994-12-07 Agfa-Gevaert N.V. Procédé pour corriger le manque d'uniformité dans un système d'impression thermique
EP0673774A2 (fr) * 1994-03-25 1995-09-27 Eastman Kodak Company Compensation des chutes de tension dues à l'emplacement de l'élément chauffant résistif dans les têtes d'impression thermiques
EP0810775A2 (fr) * 1995-06-22 1997-12-03 Texas Instruments Incorporated Améliorations dans un procédé de compensation d'éléments d'image défectueux dans une matrice d'éléments d'image d'un dispositif d'enregistrement d'images
FR2752653A1 (fr) * 1996-08-12 1998-02-27 Alps Electric Co Ltd Dispositif de detection d'image et procede de correction de nuance
EP0848544A1 (fr) * 1996-12-16 1998-06-17 Alps Electric Co., Ltd. Procédé de correction de l'effet d'ombre pour un dispositif de lecture d'image et appareil de traitement d'image pour le traitement de l'image lue
US5796420A (en) * 1993-05-28 1998-08-18 Agfa-Gevaert Method for correcting across-the-head uneveness in a thermal printing system
US6116714A (en) * 1994-03-04 2000-09-12 Canon Kabushiki Kaisha Printing head, printing method and apparatus using same, and apparatus and method for correcting said printing head

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7369145B2 (en) 2005-01-10 2008-05-06 Polaroid Corporation Method and apparatus for controlling the uniformity of print density of a thermal print head array

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0183680A2 (fr) * 1984-11-29 1986-06-04 Polaroid Corporation Procédé et appareil d'inscription thermique
EP0210627A2 (fr) * 1985-08-01 1987-02-04 General Electric Company Système d'écriture de film avec commande en boucle fermée pour des images électroniques
EP0317268A2 (fr) * 1987-11-16 1989-05-24 Canon Kabushiki Kaisha Appareil d'enregistrement d'images

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2854318B2 (ja) * 1989-04-28 1999-02-03 キヤノン株式会社 画像記録装置

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0183680A2 (fr) * 1984-11-29 1986-06-04 Polaroid Corporation Procédé et appareil d'inscription thermique
EP0210627A2 (fr) * 1985-08-01 1987-02-04 General Electric Company Système d'écriture de film avec commande en boucle fermée pour des images électroniques
EP0317268A2 (fr) * 1987-11-16 1989-05-24 Canon Kabushiki Kaisha Appareil d'enregistrement d'images

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Patent Abstracts of Japan, unexamined applications, M field, Volume 11, No. 213, July 10, 1987, The Patent Office Japanese Governm *

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0535769A1 (fr) * 1991-09-23 1993-04-07 Eastman Kodak Company Procédé pour compenser les tolérances des résistances dans l'impression d'images multi-tons
EP0541064A2 (fr) * 1991-11-04 1993-05-12 Eastman Kodak Company Module de tête d'impression thermique
EP0541064A3 (en) * 1991-11-04 1993-07-21 Eastman Kodak Company Thermal print head unit
DE4302652A1 (fr) * 1992-01-31 1993-08-05 Ricoh Kk
DE4302652C2 (de) * 1992-01-31 1999-01-21 Ricoh Kk Verfahren zur Aufzeichnungsdichte-Korrektur einer Aufzeichnungseinrichtung sowie Aufzeichnungsdichte-Korrekturvorrichtung zur Durchführung dieses Verfahrens
EP0601658A1 (fr) * 1992-12-09 1994-06-15 Agfa-Gevaert N.V. Procédé de calibrage des éléments chauffants d'une tête thermique d'un système d'impression
US5796420A (en) * 1993-05-28 1998-08-18 Agfa-Gevaert Method for correcting across-the-head uneveness in a thermal printing system
EP0627319A1 (fr) * 1993-05-28 1994-12-07 Agfa-Gevaert N.V. Procédé pour corriger le manque d'uniformité dans un système d'impression thermique
US6116714A (en) * 1994-03-04 2000-09-12 Canon Kabushiki Kaisha Printing head, printing method and apparatus using same, and apparatus and method for correcting said printing head
US6409300B2 (en) 1994-03-04 2002-06-25 Canon Kabushiki Kaisha Printing head, printing method and apparatus using same, and apparatus and method for correcting said printing head
US6616257B2 (en) 1994-03-04 2003-09-09 Canon Kabushiki Kaisha Printing head, printing method and apparatus using same, and apparatus and method for correcting said printing head
EP0673774A3 (fr) * 1994-03-25 1996-02-21 Eastman Kodak Co Compensation des chutes de tension dues à l'emplacement de l'élément chauffant résistif dans les têtes d'impression thermiques.
EP0673774A2 (fr) * 1994-03-25 1995-09-27 Eastman Kodak Company Compensation des chutes de tension dues à l'emplacement de l'élément chauffant résistif dans les têtes d'impression thermiques
EP0810775A2 (fr) * 1995-06-22 1997-12-03 Texas Instruments Incorporated Améliorations dans un procédé de compensation d'éléments d'image défectueux dans une matrice d'éléments d'image d'un dispositif d'enregistrement d'images
EP0810775A3 (fr) * 1995-06-22 1998-04-29 Texas Instruments Incorporated Améliorations dans un procédé de compensation d'éléments d'image défectueux dans une matrice d'éléments d'image d'un dispositif d'enregistrement d'images
EP1069759A2 (fr) * 1995-06-22 2001-01-17 Texas Instruments Incorporated Améliorations dans un procédé de compensation d'éléments d'image défectueux dans une matrice d'éléments d'image d'un dispositif d'enregistrement d'images
EP1069759A3 (fr) * 1995-06-22 2001-11-14 Texas Instruments Incorporated Améliorations dans un procédé de compensation d'éléments d'image défectueux dans une matrice d'éléments d'image d'un dispositif d'enregistrement d'images
FR2752653A1 (fr) * 1996-08-12 1998-02-27 Alps Electric Co Ltd Dispositif de detection d'image et procede de correction de nuance
EP0848544A1 (fr) * 1996-12-16 1998-06-17 Alps Electric Co., Ltd. Procédé de correction de l'effet d'ombre pour un dispositif de lecture d'image et appareil de traitement d'image pour le traitement de l'image lue

Also Published As

Publication number Publication date
GB9106528D0 (en) 1991-05-15
GB9007014D0 (en) 1990-05-30
GB2243265A (en) 1991-10-23
AU7489691A (en) 1991-10-21

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