DE60121421T2 - Method for calibrating a thermal printer - Google Patents

Description

FIELD OF THE INVENTION

The The present invention relates to a method of applying heat energy to a recording medium using a thermal head with energized heating elements that can be individually addressed. The The invention particularly relates to a method for calibrating a Halbtonthermodruckers. In particular, the recording medium is a thermographic material, and the method for thermal Printing concerns thermography.

GENERAL STATE OF THE ART

The Recording of thermal images or the thermography is a recording process in which images through the use of imagewise modulated Thermal energy be generated. Thermography deals with materials, which are not sensitive to light, but sensitive to heat or thermosensitive are and in which image-wise Heat is sufficient a visible change in a thermosensitive imaging material via a chemical or physical To bring about a process, which changes the optical density.

The Most of the direct thermographic recording materials are of the chemical type. When heating to a certain transformation temperature finds an irreversible Reaction takes place and a colored picture is produced.

At the Direct thermal printing can be heating of the thermographic recording material resulting from image signals which converted into electrical impulses and then by a driver circuit selectively transferred to a thermal print head. The thermal printhead consists of microscopic thermal resistance elements, the electrical energy over the joule effect in heat convert. The so in heat signals converted electrical impulses manifest themselves as on the surface of the thermographic material, e.g. Paper, transferred heat, in the leading to the color development chemical reaction takes place. This principle is described in "Handbook of Imaging Materials "(edited by Arthur S. Diamond - Diamond Research Corporation - Ventura, California, USA, printed by Marcel Dekker, Inc. 270 Madison Avenue, New York, ed. 1991, pp. 298-299).

One particularly interesting direct thermal imaging element used an organic silver salt in combination with a reducing agent. With such a material one obtains an image because the silver salt under the influence of heat is developed to metallic silver.

One Thermal printer varies the pressure energy to the density of the thermal printing to control. The task is to print predictable densities with smallest increments to over the wished Density range to produce an almost continuous gray scale. The control is usually a two-step process.

A traditional technique for calibrating a thermal printer is like follows.

First a first calibration page is printed with a border setting, to the desired Maximum density and a complete Range of print settings. At the next step will be by visually examining the printed page determines if this the desired Limit setting is. The normal task is the minimum exposure to find the required area for the full range Densities to print. The lower the limit setting, the more For example, the gray scale in the printed film is continuous. The process printing and setting the maximum limit setting is repeated, until a desired Limit setting is determined.

When next becomes a second calibration page with the selected limit system setting and with a subset of printing system settings that are the full Cover range of print settings, printed. The resulting Densities of the printed page are then measured and for the full Range of pressure settings a pressure setting-to-density table created. An expenditure lookup table used to do this can adjust the exposure to the desired density for a Any digital image value is produced using the pressure setting-to-density table. After that prints the Thermal printer pages with this output lookup table to view the desired To produce densities while the same maximum exposure is appropriate.

If however, the maximum exposure is changed, the calibration process needs be repeated.

In EP 453 714 For example, the amount of energy supplied to the printing elements for a given gradation number can be changed to accommodate variable characteristics of different recording materials. This is based on test prints to map the input data to the adjustment signal sent to each heating element of the printhead.

One Problem that arises with this calibration technique is that Calibration data for a certain marginal tax rate is specific. If this Setting changed must be the whole process of consecutive prints, to the desired Limit control setting for maximum density and calibration to be repeated. If different users want different maximum densities requires as well each a separate calibration. Such repeated calibrations are inefficient, expensive and unproductive.

TASKS OF INVENTION

A Object of the present invention is to provide an improved calibration method for recording a Image on a thermal imaging element using a thermal head with energized heating elements.

A Another object of the invention is that the calibration method the ability has to generate a single calibration page and from that to derive sufficient information to calibrate individual page Prints about one huge Range of densities to produce.

Further Objects and advantages of the present invention will become apparent the description and the drawings.

SHORT PRESENTATION THE INVENTION

The mentioned above Tasks are performed by a calibration method as claimed in the claims 1 defined characteristics realized. Specific features for preferred embodiments of the invention are in the dependent claims explained.

Further Advantages and embodiments The present invention will become apparent from the following description.

SHORT DESCRIPTION THE DRAWINGS

The Invention will be described below with reference to the accompanying Drawings describing the scope of the present Do not limit the invention should.

It demonstrate

1 a preferred embodiment of a calibration method according to the present invention and

2 a graph showing experimentally measured densities and finally obtained densities in relation to printer data.

DETAILED DESCRIPTION OF THE INVENTION

In the interest of good understanding, it is mentioned that in this patent document an index "i" is often used in relation to certain data (eg printer data P _i , density Di, thermal head data TH _i , re-scaled thermal head data Th _i ', etc.), whereas Index "j" is used to indicate a user-related variable (eg Prefnew _j , a desired density Dwant _j , ...). Of course, in some situations a combination of both indices can be used (eg a density D _ji ). In order to make reading the patent as easy as possible, such a combined index "ji" is often simplified to a single index "i", although one skilled in the art may well understand that implicitly means a combined index "ji".

First, attention is directed to the drawings where 1 a preferred embodiment of a calibration method according to the present invention and wherein 2 Figure 12 is a graph showing experimentally measured densities and finally obtained densities in relation to printer data. Regarding 1 a so-called "disk formation" and a so-called "duty cycle" (indicated in this drawing with "DC") are described in full depth, eg in EPA-01000003.2 (in the name of Agfa-Gevaert); an example of a "user's taste" (indicated by the abbreviation "U" in this drawing) is explained, for example, in EP-0536822 (Agfa-Gevaert), a type of "compensation" (in this drawing, "TPH control Compensations ") and the meaning of a" thermal head applied voltage "(indicated in this drawing with" V _TH ") are explained in full depth eg in EP-0714780 (Agfa-Gevaert). For the sake of brevity, no redundant descriptions are repeated for the technical terms.

In the present specification, the term "reference pressure power Pref" means the power derived under reference conditions comprising V _TH Rref and Dcref, and more particularly the time-averaged power derived during a time slice of 100%.

• – Beliefern des Thermodruckers mit einem thermographischen Material m, mehreren Druckerdaten P_i, die jeweils als ein Pixel mit einer Dichte D_ji aufgezeichnet werden sollen, und Standardreferenzwerte zum Drucken von Parametern Π umfassend einen Wert Pref für eine Referenzdruckleistung;
• – Drucken eines Kalibrierungsmusters für die mehreren Druckerdaten P_i, wobei das Kalibrierungsmuster einen mehrstufigen Dichtekeil derart umfasst, dass ein ganzer Bereich einer Beziehung D_ji (P_i) zwischen den Druckerdaten P_i und der Dichte D_ji abgedeckt ist;
• – Messen einer Dichte Dexp_i (siehe 2) für jedes Feld des Dichtekeils des Kalibrierungsmusters in Relation zu den mehreren Druckerdaten P_i und Speichern einer ersten Menge S1 = (Pref, P_i, Dexp_i) in einem ersten Speicher M1; – Berechnen für eine gegebene Dichte Dwant_j (siehe 2, die veranschaulicht, dass Dwant_j 2,50 oder 3,00 beträgt) eines entsprechenden Werts Prefnew_j für die Referenzdruckleistung und Speichern einer zweiten Menge S2 = (Dwant_j, Prefnew_j) in einem zweiten Speicher M2;

Berechnen für die gewünschte Dichte Dwant_j für alle Druckerdaten P_i einer entsprechenden Dichte D_ji und Speichern einer dritten Menge S3 = (Dwant_j, Prefnew_j, P_i, D_ji) in einem dritten Speicher M3.According to the present invention and with reference to 1 and 2 comprises a method of calibrating a thermal printer comprising a thermal head having a plurality of energizable heating elements

• Supplying the thermal printer with a thermographic material m, a plurality of printer data P _i to be respectively recorded as a pixel having a density D _ji , and standard reference values for printing parameters Π including a value Pref for a reference printing power;
• Printing a calibration pattern for the plurality of printer data P _i , the calibration pattern comprising a multi-level density key such that a whole range of a relationship D _ji (P _i ) between the printer data P _i and the density D _{ji is} covered;
• - Measuring a density Dexp _i (see 2 for each field of the density wedge of the calibration pattern in relation to the plurality of printer data P _i and storing a first set S1 = (Pref, P _i , Dexp _i ) in a first memory M1; Calculate for a given density Dwant _j (see 2 illustrating that Dwant _{j is} 2.50 or 3.00) of a corresponding value Prefnew _j for the reference printing power and storing a second quantity S2 = (Dwant _j , Prefnew _j ) in a second memory M2;

Calculate for the desired density Dwant _j for all printer data P _{i of} a corresponding density D _ji and store a third set S3 = (Dwant _j , Prefnew _j , P _i , D _ji ) in a third memory M3.

Under consideration the notes about the indices "i", "j" and "ji" become all other embodiments instead of using a combined index "ji" with a single index "i".

When Comparative example, the just mentioned embodiment is now also with individual indexes "i" reformulated.

• – Beliefern des Thermodruckers mit einem thermographischen Material m, mehreren Druckerdaten P_i, die jeweils als ein Pixel mit einer Dichte Di aufgezeichnet werden sollen, und Standardreferenzwerte zum Drucken von Parametern Π umfassend einen Wert Pref für eine Referenzdruckleistung;
• – Drucken eines Kalibrierungsmusters für die mehreren Druckerdaten P_i, wobei das Kalibrierungsmuster einen mehrstufigen Dichtekeil derart umfasst, dass ein ganzer Bereich einer Beziehung Di (P_i) zwischen den Druckerdaten P_i und der Dichte Di abgedeckt ist;
• – Messen einer Dichte Dexp_i für jedes Feld des Dichtekeils des Kalibrierungsmusters in Relation zu den mehreren Druckerdaten P_i und Speichern einer ersten Menge S1 = (Pref, P_i, Dexp_i) in einem ersten Speicher M1;
• – Berechnen für eine gegebene Dichte Dwant_j eines entsprechenden Werts Prefnew_j für die Referenzdruckleistung und Speichern einer zweiten Menge S2 = (Dwant_j, Prefnew_j) in einem zweiten Speicher M2;
• – Berechnen für die gewünschte Dichte Dwant_j für alle Druckerdaten P_i einer entsprechenden Dichte Di und Speichern einer dritten Menge S3 = (Dwant_j, Prefnew_j, P_i, Di) in einem dritten Speicher M3.

Thus, the invention may be reworded as a method of calibrating a thermal printer comprising a thermal head having a plurality of energizable heating elements, the method comprising the steps of:

• Supplying the thermal printer with a thermographic material m, a plurality of printer data P _i to be respectively recorded as a pixel having a density Di, and standard reference values for printing parameters Π comprising a value Pref for a reference printing power;
• Printing a calibration pattern for the plurality of printer data P _i , the calibration pattern comprising a multi-level density key such that a whole range of a relationship Di (P _i ) between the printer data P _i and the density Di is covered;
• - measuring a density Dexp _i for each field of the density wedge of the calibration pattern in relation to the plurality of printer data P _i and storing a first set S1 = (Pref, P _i , Dexp _i ) in a first memory M1;
• Calculating for a given density Dwant _j a corresponding value Prefnew _j for the reference pressure power and storing a second quantity S2 = (Dwant _j , Prefnew _j ) in a second memory M2;
• Calculating for the desired density Dwant _j for all printer data P _{i of} a corresponding density Di and storing a third set S3 = (Dwant _j , Prefnew _j , P _i , Di) in a third memory M3.

• – Beliefern mit einem thermographischen Material m, mehreren Druckerdaten P_i zur Aufzeichnung und Standardreferenzwerten zum Drucken von Parametern Π umfassend einen Wert Pref für eine Referenzdruckleistung;
• – Drucken eines Kalibrierungsmusters für die mehreren Druckerdaten P_i, wobei das Kalibrierungsmuster einen mehrstufigen Dichtekeil derart umfasst, dass ein ganzer Bereich einer Beziehung Di (P_i) zwischen den Druckerdaten P_i und der Dichte Di abgedeckt ist;
• – Messen einer Dichte Dexp_i für jedes Feld des Dichtekeils des Kalibrierungsmusters in Relation zu den mehreren Druckerdaten P_i und Speichern einer ersten Menge S1 = (Pref, P_i, Dexp_i) in einem ersten Speicher M1;
• – Transformieren der Druckerdaten P_i in Thermokopfdaten TH_i (siehe 1) gemäß einer Transformation H, die H(P_i) ≥ TH₀ und H (P_m) ≥ H(P_n) für P_m > P_n anwendet, wobei TH₀ ein Mindestwert von zu adressierenden Thermokopfdaten ist und wobei P_m und P_n willkürliche Werte der Druckerdaten P_i sind;
• – Finden eines Werts THDwant_j für die Thermokopfdaten TH_i entsprechend der gewünschten Dichte Dwant_j;
• – Berechnen bei der gewünschten Dichte Dwant_j eines entsprechenden Werts Prefnew_j für die Referenzdruckleistung unter Berücksichtigung von Pref, von THDwant_j und THmax, wobei THmax ein Höchstwert von Thermokopfdaten ist, die adressiert werden können, und Speichern einer vierten Menge S4 = (Dwant_j, Prefnew_j) in einem vierten Speicher M4;
• – Berechnen für die gewünschte Dichte Dwant_j für alle verfügbaren Druckerdaten P_i einer entsprechenden Dichte Di und Speichern einer sechsten Menge S6 = (Dwant_j, Prefnew_j, P_j, D_j) in einem sechsten Speicher M6.

In a preferred embodiment according to the present invention, a method of calibrating a thermal printer comprising a thermal head having a plurality of energizable heating elements, the method comprising the steps of:

• Supplying a thermographic material m, a plurality of printer data P _i for recording and standard reference values for printing parameters Π comprising a value Pref for a reference printing power;
• Printing a calibration pattern for the plurality of printer data P _i , the calibration pattern comprising a multi-level density key such that a whole range of a relationship Di (P _i ) between the printer data P _i and the density Di is covered;
• - measuring a density Dexp _i for each field of the density wedge of the calibration pattern in relation to the plurality of printer data P _i and storing a first set S1 = (Pref, P _i , Dexp _i ) in a first memory M1;
• - Transforming the printer data P _i in thermal head data TH _i (see 1 ) according to a transformation H applying H (P _i ) ≥ TH ₀ and H (P _m ) ≥ H (P _n ) for P _m > P _n , where TH _{0 is} a minimum value of thermal head data to be addressed, and P _m and P _{n are} arbitrary values of the printer data P _i ;
• Finding a value THDwant _j for the thermal head data TH _i corresponding to the desired density Dwant _j ;
• Calculating at the desired density Dwant _j a corresponding value Prefnew _j for the reference printing power taking into account Pref, THDwant _j and THmax, where THmax is a maximum value of thermal head data that can be addressed and storing a fourth set S4 = (Dwant _j , Prefnew _j ) in a fourth memory M4;
• Calculate for the desired density Dwant _j for all available printer data P _{i of} a corresponding density Di and store a sixth set S6 = (Dwant _j , Prefnew _j , P _j , D _j ) in a sixth memory M6.

It can be displayed that the contents of memory M2 in practice often equal to the contents of memory M4. The same goes for for the Contents of memory M3 and M6.

• – Beliefern mit einem thermographischen Material m, mehreren Druckerdaten P_i zur Aufzeichnung und Standardreferenzwerten zum Drucken von Parametern Π umfassend einen Wert Pref für eine Referenzdruckleistung;
• – Drucken eines Kalibrierungsmusters für die mehreren Druckerdaten P_i, wobei das Kalibrierungsmuster einen mehrstufigen Dichtekeil derart umfasst, dass ein ganzer Bereich einer Beziehung Di (P_i) zwischen den Druckerdaten P_i und der Dichte Di abgedeckt ist;
• – Messen einer Dichte Dexp_i für jedes Feld des Dichtekeils des Kalibrierungsmusters in Relation zu den mehreren Druckerdaten P_i und Speichern einer ersten Menge S1 = (Pref, P_i, Dexp_i) in einem ersten Speicher M1;
• – Transformieren der Druckerdaten P_i in Thermokopfdaten TH_i gemäß einer Transformation H, die H(P_i) ≥ TH₀ und H(P_m) ≥ H(P_n) für P_m > P_n anwendet, wobei TH₀ ein Mindestwert von zu adressierenden Thermokopfdaten ist und wobei P_m und P_n willkürliche Werte der Druckerdaten P_i sind;
• – Finden eines Werts THDwant_j für die Thermokopfdaten TH_i entsprechend der gewünschten Dichte Dwant_j;
• – Berechnen bei der gewünschten Dichte Dwant_j eines entsprechenden Werts Prefnew_j für die Referenzdruckleistung unter Berücksichtigung von Pref, von THDwant_j und THmax, wobei THmax ein Höchstwert von Thermokopfdaten ist, die adressiert werden können, und Speichern einer vierten Menge S4 = (Dwant_j, Prefnew_j) in einem vierten Speicher M4;
• – Umwandeln der Thermokopfdaten TH_i in umskalierte Thermokopfdaten TH_i' unter Berücksichtigung von TH_i, THDwant_j und THmax;
• – Neuberechnen der umskalierten Thermokopfdaten TH_i' in umskalierte Druckerdaten P_i' gemäß einer Transformation H' gekennzeichnet durch H' (TH') ≥ 0 und H'(TH'_m) ≥ H'(TH'_n) für TH'_m ≥ TH'_n;
• – Speichern einer Relation S5 zwischen den umskalierten Druckerdaten P_i' und der gemessenen Dichte Dexp_i (von S1) in einen fünften Speicher M5;
• – Ableiten der Relation S5 (im Speicher M5) für die gewünschte Dichte Dwant_j für alle verfügbaren Druckerdaten P_i einer entsprechenden Dichte Di und Speichern einer sechsten Menge S6 = Dwant_j, Prefnew_j, P_j, D_j) in einem sechsten Speicher M6.

In a preferred embodiment according to the present invention, a method of calibrating a thermal printer comprising a thermal head having a plurality of energizable heating elements, the method comprising the steps of:

• Supplying a thermographic material m, a plurality of printer data P _i for recording and standard reference values for printing parameters Π comprising a value Pref for a reference printing power;
• Printing a calibration pattern for the plurality of printer data P _i , the calibration pattern comprising a multi-level density key such that a whole range of a relationship Di (P _i ) between the printer data P _i and the density Di is covered;
• - measuring a density Dexp _i for each field of the density wedge of the calibration pattern in relation to the plurality of printer data P _i and storing a first set S1 = (Pref, P _i , Dexp _i ) in a first memory M1;
• Transforming the printer data P _i into thermal head data TH _i according to a transformation H applying H (P _i ) ≥ TH ₀ and H (P _m ) ≥ H (P _n ) for P _m > P _n , where TH _{0 is} a minimum value of thermal head data to be addressed and P _m and P _{n are} arbitrary values of the printer data P _i ;
• Finding a value THDwant _j for the thermal head data TH _i corresponding to the desired density Dwant _j ;
• Calculating at the desired density Dwant _j a corresponding value Prefnew _j for the reference printing power taking into account Pref, THDwant _j and THmax, where THmax is a maximum value of thermal head data that can be addressed and storing a fourth set S4 = (Dwant _j , Prefnew _j ) in a fourth memory M4;
• Converting the thermal head data TH _i into rescaled thermal head data TH _i 'taking into account TH _i , THDwant _j and THmax;
• Recalculating the rescaled thermal head data TH _i 'into rescaled printer data P _i ' according to a transformation H 'characterized by H' (TH ') ≥ 0 and H' (TH ' _m ) ≥ H' (TH ' _n ) for TH' _m ≥ TH '_n;
• Storing a relation S5 between the rescaled printer data P _i 'and the measured density Dexp _i (from S1) into a fifth memory M5;
• Deriving the relation S5 (in the memory M5) for the desired density Dwant _j for all available printer data P _{i of} a corresponding density Di and storing a sixth set S6 = Dwant _j , Prefnew _j , P _j , D _j ) in a sixth memory M6 ,

In one possible embodiment, the steps of supplying, printing a calibration pattern and measuring a density Dexp _i for each field of the density key are replaced by detecting a new value for a desired density Dwant _j .

• – Beliefern des Thermodruckers mit mehreren Bilddaten d zur Aufzeichnung auf dem thermographischen Material m;
• – erstes Umwandeln der Bilddaten d in Dichtedaten Di gemäß einer gewünschten Beziehung U zwischen jeder der Bilddaten d und einer entsprechenden Dichte Di;
• – zweites Umwandeln der Dichtedaten Di in Druckerdaten P_i unter Verwendung der (P, D_i) Informationen in einer vorausgegangenen Menge S3prev entsprechend Dwant_j;
• – Speichern der (zwei Mal) umgewandelten Bilddaten d als eine Menge S7 = (d, P_i) in einem siebten Speicher M7.

In another preferred embodiment according to the present invention, the step of printing a calibration pattern is preceded by the following steps:

• Supplying the thermal printer with a plurality of image data d for recording on the thermographic material m;
• First converting the image data d into density data Di according to a desired relationship U between each of the image data d and a corresponding density Di;
• Second converting the density data Di into printer data P _i using the (P, D _i ) information in a previous set S3prev corresponding to Dwant _j ;
• Storing the (twice) converted image data d as a set S7 = (d, P _i ) in a seventh memory M7.

In another preferred embodiment according to the present invention, the steps of first converting the image data d and secondly converting the density data Di by transforming according to T = S ^-1 o U (which means that the operation must first be performed U and after Operation S ^-1 , see also 1 ).

at yet another preferred embodiment according to the present invention Invention, the default reference values for print parameters Π are selected of the group from a reference value for a resistance Reref a heating element (e.g., Reref = 3000 Ω), a reference value DCref for one Duty cycle (e.g., Dcref = 70%) and a reference value Tref for a base temperature a heating element (e.g., Tref = 25 ° C).

In yet another preferred embodiment, calculating a corresponding value Prefnew _{j is} performed according to

In still another preferred embodiment according to the present invention, converting the thermal head data TH _i to rescaled thermal head data TH _i 'is carried out in accordance with

wobei N eine (eine Anzahl von Bits pro Wert darstellende) Bittiefe der Thermokopfdaten TH_i ist.In still another preferred embodiment according to the present invention, transforming the printer data P _i into thermal head data TH _{i is} carried out in accordance with

where N is a bit depth (representing a number of bits per value) of the thermal head data TH _i .

In still another preferred embodiment according to the present invention, the recalculation of the rescaled thermal head data TH _i 'is performed in rescaled printer data P _i ' according to

In another preferred embodiment according to the present invention, a method further comprises the step of searching two consecutive values of thermal head data TH _k and TH _i corresponding to the densities D _k and D _l including a desired density Dwant _j therebetween.

wobei N eine (eine Zahl von Bits darstellende) Bittiefe der Thermokopfdaten TH und M eine (eine Zahl von Bits darstellende) Bittiefe der Druckerdaten P_i ist und wobei M von N verschieden ist, vorzugsweise N > M.In another preferred embodiment, the step of transforming the printer data P _i into thermal head data TH _{i is} according to the following equation:

where N is a bit depth (representing a number of bits) of the thermal head data TH and M is one (a number of bits representing) bit depth of the printer data P _i and where M is different from N, preferably N> M.

at a particularly preferred embodiment is e.g. M = 10 or 12 and N = 13.

In a further preferred embodiment, a method of thermal recording by means of a thermal head comprising a plurality of energizable heating elements H _n and using a calibration method according to any one of the preceding disclosures.

at Yet another preferred embodiment comprises the thermographic Material on a support a heat sensitive Layer containing an organic silver salt and a reducing agent in the heat-sensitive Layer and / or in another optional layer.

A Device for the thermal recording of an image on a thermographic Material may use a method as described above.

In one possible embodiment, the output values Dh _k , Dh _kcm and Dh _{kcml relate to} values of an optical density and / or values of a pixel size to be reproduced on the thermographic material m.

One An attempt to test the performance of a calibration method according to the present invention Invention was carried out on a (commercially available from Agfa-Gevaert) Thermal printer Drystar3000 executed. The Results of the most important steps of the calibration procedure are listed in Table 1 (in the appendix, page 15).

One 27-step calibration wedge was at a reference pressure rating Pref of 75.6 mW printed. The 27 printer data values P1, P2,. P27 ranged between 411 and 1023. The 27 corresponding experimental Density values were between 0.23 and 3.49.

The 27 printer data values P1, P2, ..., P27 were divided into 27 thermal print head data values TH1, TH2, ..., TH27 transformed.

at In the example described above were the test results listed above from the single calibration page continues to use all to obtain the required information to high quality To guarantee prints at two different values from Dwant, e.g. Dwant = 2.50 and Dwant = 3.00.

It THDwant and Prefnew were calculated. For Dwant = 2.50, THDwant = 6950 and consequently Prefnew = 64.1 mW. For Dwant = 3.00 on the other hand THDwant = 7436 and Prefnew = 68.1 mW.

For each Dwant value, the rescaled P values (indicated by the symbol P ') were calculated and the expenditure lookup table used during printing is set to the appropriate energy to the desired density for one to produce any digital image value has been created.

Finally became the quality calibrated by printing with the two values of Dwant, i.e. 2.50 and 3.00, another test wedge, especially one 33-step test wedge, and by comparing the experimental Dense with the desired Densities. about across the whole density range was the difference between two corresponding densities never greater than 2%. This result clearly demonstrates that the objects of the present invention are realized are.

The Recording of thermal images according to the present This invention can be used to make both slides as well as printouts of the reflection type. In the field of hard copies will be thermographic recording materials based on an opaque (white, for example) Base used in the field of medical diagnosis monochrome (e.g., black) images on a transparent base find wide application, since such pressures expediently with the help of a Light box can be considered.

The Method of the present invention lends itself to a wide variety of printing techniques apply.

In "direct thermal printing", the method may be to represent an image of a human and medical image data received from a medical imaging device (eg, a medical imaging camera).

A Further application of the present invention includes the hard copy expression for the so-called non-destructive Testing (NDT - non-destructive Testing) based on, for example, radiographic or Ultrasound systems. Exemplary purposes of NDT include the study or quality control of materials, welded Connections or assemblies; the development of manufacturing processes; experimenting with research; Etc.

at a further preferred embodiment of the present invention the image data is graphic image data, e.g. from a computerized Publishing system to be received. Furthermore, a method according to the present Invention also in graphic plotters, in recorders, in computer printers, etc. are applied.

In still another preferred embodiment, the densities (such as D _ji , Dexp _i and Dwant _j ) relate to values of optical density and / or values of a pixel size to be reproduced on the thermographic material m.

Farther it is important to indicate that for the expert a so-called Heating element e.g. a resistive element, an inductive heating element, a pyrotechnic heating element or a high frequency heating element may include.

After this preferred embodiments of the present invention, it will be apparent to those skilled in the art now obvious that it made numerous modifications can be without from the scope of the invention as defined in the appended claims, departing.

Tabelle 1

Table 1

Claims (14)

A method of calibrating a thermal printer comprising a thermal head having a plurality of energizable heating elements, comprising the steps of: - supplying the thermal printer with a thermographic material m, a plurality of printer data P _i to be respectively recorded as a pixel having a density Di, and standard reference values for printing of parameters Π comprising a value Pref for a reference pressure power; Printing a calibration pattern for the plurality of printer data P _i , the calibration pattern comprising a multi-level density key such that a whole range of a relationship Di (P _i ) between the printer data P _i and the density Di is covered; - measuring a density Dexp _i for each field of the density wedge of the calibration pattern in relation to the plurality of printer data P _i and storing a first set S1 = (Pref, P _i , Dexp _i ) in a first memory M1; Calculating for a given density Dwant _j a corresponding value Prefnew _j for the reference pressure power and storing a second quantity S2 = (Dwant _j , Prefnew _j ) in a second memory M2; Calculating for the desired density Dwant _j for all printer data P _{i of} a corresponding density Di and storing a third set S3 = (Dwant _j , Prefnew _j , P _i , Di) in a third memory M3. The method according to claim 1, further directly after the measuring step with the further steps: - transforming the printer data P _i into thermal head data TH _i according to a transformation H comprising H (P _i ) ≥ TH ₀ and H (P _m ) ≥ H (P _n ) for P _m > P _n where TH _{0 is} a minimum value of thermal head data to be addressed and where P _m and P _{n are} arbitrary values of the printer data P _i ; Finding a value THDwant _j for the thermal head data TH _i corresponding to the desired density Dwant _j ; and wherein the following step of computing for a desired density Dwant _j, a corresponding value Prefnew _j for said reference printing power and storing a second set S2 = (Dwant _j, Prefnew _j) in a second memory M2 Pref, THDwant considered _j and THmax, wherein THmax is a maximum of thermal header data that can be addressed. The method of claim 2, wherein the final step according to claim 1 of calculating for said desired density Dwant _j, for each printer data P _i a corresponding density Di and storing a third set S3 = (Dwant _j, Prefnew _j, P _i, Di) third in a Memory M3 comprises the following steps: - converting the thermal head data TH _i into rescaled thermal head data TH _i 'taking into account TH _i , THDwant _j and THmax; Recalculating the rescaled thermal head data TH _i 'into rescaled printer data P _i ' according to a transformation H 'characterized by H' (TH ') ≥ 0 and H' (TH ' _m ) ≥ H' (TH ' _n ) for TH' _m ≥ TH '_n; Storing a relation 55 between the rescaled printer data P _i 'and the measured density Dexp _i (from S1) into a fifth memory M5; Deriving the relation S5 (in the memory M5) for the desired density Dwant _j for all available printer data P _{i of} a corresponding density Di and storing a sixth set 56 = Dwant _j , Prefnew _j , P _j , D _j ) in a sixth memory M6 , The method of any one of claims 1-3, wherein the step of printing a calibration pattern is preceded by the steps of: - providing the thermal printer with a plurality of image data d for recording on the thermographic material m; First converting the image data d into density data Di according to a desired relationship U between each of the image data d and a corresponding density Di; Second converting the density data Di into printer data P _i using the (P, Di) information in a previous set S3prev corresponding to Dwant _j ; Storing the (twice) converted image data d as a set S7 = (d, P _i ) in a seventh memory M7. The method of claim 4, wherein the steps of first converting the image data d and second converting the density data Di are performed by transforming according to T = S ^-1 o U. Method according to one of claims 1 to 3, wherein the standard reference values for print parameters Π are selected from the group of a reference value for a resistance Reref a heating element, a reference value DCref for a duty cycle and a Reference value Tref for a base temperature of a heating element. A method according to claim 2 or 3, wherein the calculation of a corresponding value Prefnew _{j is} carried out in accordance with

A method according to claim 2 or 3, wherein the conversion of the thermal head data TH _{i is performed} in rescaled thermal head data TH _i 'according to

A method according to claim 2 or 3, wherein transforming the printer data P _i into thermal head data TH _{i is} carried out in accordance with

where N is a bit depth (representing a number of bits per value) of the thermal head data TH _i . A method according to claim 2 or 3, wherein the recalculation of the rescaled thermal head data TH _i 'is performed in rescaled printer data P _i ' according to

The method of claim 2 or 3, further comprising the step of searching two consecutive values of thermal head data TH _k and TH _l which comprises, corresponding to the densities D _k and D _l wherein between a desired density Dwant _j is enclosed. The method of claim 2, wherein the step of transforming the printer data P _i into thermal head data TH _{i is} according to the following equation:

where N is a bit depth (representing a number of bits) of the thermal head data TH and M is a bit depth (representing a number of bits) of the printer data P _i and where M is different from N. Method for thermal recording by means of a thermal head comprising a plurality of energizable heating elements H _n and using a calibration method according to any one of the preceding claims. Method according to any one of the preceding Claims, wherein the thermographic material on a support comprises a heat-sensitive layer, containing an organic silver salt and a reducing agent in the heat-sensitive Layer and / or in another optional layer.