GB2339103A

GB2339103A - Colour proofer and calibration method therefore

Info

Publication number: GB2339103A
Application number: GB9910498A
Authority: GB
Inventors: Masayuki Mutoh; Akihiko Onuma
Original assignee: Silver Seiko Ltd
Current assignee: Silver Seiko Ltd
Priority date: 1998-05-19
Filing date: 1999-05-06
Publication date: 2000-01-12
Also published as: GB2339103A8; GB9910498D0; JPH11326056A; DE19922718A1

Description

2339103 COLOR PROOFER AND CALIBRAT10N METHOD THE R.EFOR This invention

relates to a color proofer which calibrates a color print, and more particularly, to a digital color PTOOfer (hereinafter referred to as color proofer) which directly calibrates a color print from computer data, and to a calibration method for a gradation reproduction characteristic and a color reproduction characteristic of a color procifer.

In recent years, employment of digital or electronic processing in printing has advancecL and a color proofer which directly performs calibration from computer data and Outputs a result of the calibration has appeared in place of prior conventional techniques such as anvil block calibration or chemical proof.

A color proofer, for example, of the inkjet type is recited in Masayuki Mutoh, "Digital Full Color Prinicr'SRjet'", a Collection of'Papers ofJapanHardcopy'97, the P- lectropholographic Society of Japan, pp. 153-156.

Since a color proofer calibrates a print and outputs a result of the calibration, it is required to provide a printed proof output with a l6gh degree of reproducibility. Particularly, the gradation reproduction characteristic and the color reproduction characteristic are important, and the color proofer is required to have modification functions for these characteristics.

The gradation reproduction function and the color rcproduction function of a color proofer by a computer may be performed by the computer processor or may be preformed by an TPIJ (linage Processing Unit), which is a dedicated image data proccssing apparatus, incorporated in the color I- r I procifer, as described in the above mentioned document.

The IPU includes, for example, as shown in FIG- 18, three processing blocks forming a color modification table 181, a gradation correction table 182 and a pseudo gradation generator 183 which arc connected in series. Upon printing, image data of C (cyan), M (magenta), Y (yellow) and K (black) are input at the left side in FIG. 18 and are pipeline processed in real time by the blocks 18 1, 182 and 183 before being output on the right side of FIG. 18 for input to a proofer engine (not shown). The pseudo gradation generator 183 is provided to perform dither processing and/or error diffUsion processing to express a gradation and has no direct relation to the present invention.

The color modification table 18 1 is a four dimensional (or threedimensional) look-up table (LUT) which uses input image data of C, M, Y, K (or C, M, Y) as an input address and ha.q modified output image data of C., M, Y, K stored at each address thereof in a corresponding relationship to the address.

The gradation correction table 192 includes one-dimensional tables, independent of one another, for C, M, Y, K each table of which uses input image data as an input address and has Is corrected output image data stored aveach address thereof in a corresponding relationship to the address.

Table data of the color modification table 181 and the gradation correction table 182 are produced by the computer and downloaded into the tables.

The table data of the color modification table 181 and the gradation correction table 182 are 2L) produced in the following procedure (1) A test chart (gradation patch) to be used for measurement of a raw gradation reproduction characteristic of the PTOofer engine including the pseudo gradation generator 183 is output as a print.

(2) The grad4tion patch obtained in (1) above is measured with a densitometer to obtain a raw gradation reproduction characteristic (density data).

(3) Gradation correction table data to be used for conversion into an optimum gradation 2- reproducibility characteristic are produced from the radation reproduction characteristic (density data) of (2) above in accordance with an algorithm prepared in advance and are downloaded into the gradation correction table 182 in the IPU.

(4) A test chin (color patch) to be used for measurement of a color reproduction characterimic of the color proofer including the pseudo gradation generator 183 and the gradation correction table 182 of (3) above is output as a print.

(5) The color patch obtained in (4) above is measured with a chromaticity meter to obtain a color reproduction characteristic (chromaticity data).

(6) Color modification table data to be used for conversion into an optimum color to reproduction characteristic are produced from the color reproduction characteristic (chromaticity data) of (5) above in accordance with another algorithm prepared in advance and are downloaded into the Color modification table 181 in the TPU.

(7) Where a host computer processor performs the color modification function and the gradation correction function, data processing based on the gradation correction table 182 obtained in (3) above and the color modification table 181 obtained in (6) above is executed by the host computer.

Where a plurality or large number of color proofers of the same model are manufactured for market, it is impossible to produce gradation correction table data and color modification table data peculiar to each of the color proofers when the amount of operation for production of the tables and later maintenance operations are taken into considcration, Accordingly, gradation correction table data and color modification table data are produced for a representative color proofer, and these table data arc applied to all of the color PTOOfers.

The conventional color procifer described above is disadvantageous in that, since it uses a densitometer and a chromaticity meter to measure a test chart (a gradation patch and a color patch), intervention of an operator is required and this is cumbersome.

The conventional color proofer is disadvantageous further in that, if color proofers; placed on 3- I the market are subject to some variation to the color reproduction characteristic and the radiation reproduction characteristic thereof, then a densitometer and a chromaticity meter as well as software for production of table data must be provided for the marketed proofers, and consequently, very cumbersome operation is required for re-calibration. Further, periodic maintenance is impossible.

The conventional color proofer is disadvantageous also in that, where a plurality of color proofers have a difference in color reproduction characteristic and gradation reproduction characteristic, it is impossible to provide a optimum color reproduction characteristics and gradation reproduction characteristics for all color proofers.

It is an object of the present invention to provide a color proofer which can measure the density and/or the chromaticity at a plurality of positions of a printed image.

In order to attain the object described above according to one aspect of the present invention, there is provided a color proofer which successively measures density and/or chromaticity at a Is plurality of designated positions of a print irnage, The color proofer having the above described structure and/or function is advantageous in that measurement necessary for calibration can be performed automatically.

According to another aspect of the present invention, there is Provided a color proofer which includes facilities for measuring density and/or chroinaficity at selected positions on a print image, gradation correction facilities and/or Color modification facilities, and a host computer interface for alloNving gradation correction data and/or color modification data produced by ahost computerbased on density data and/or chromaticity data measured by the density measurement facilities and/or the chromaticity measurement facilities to be sent to the gradation correction facilities and/or the color modification facilities.

The color proofer having the construction just described is advantageous in that calibration I I optimum to the color proofer can be automatically performed by producing calibration data from data measured with calibration software incorporated in the host computer in advance and pcrfbrming calibration of the color proofer with the thus produced calibration data.

According to a further aspect of the present invention, there is provided a color proofer, comprising density measurement facilities and/or chromaticity measurement facilities, positioning facilities for moving the density measurement facilities and/or the chromaticity measurement facilities to a selected position of a print image, gradation correction facilities and/or color modification facilities, and a telecommunication line interface for allowing gradation correction data and/or color Triodification data produced by a remotely located calibration computer based on density data and/or chromaticity data measured by the density measurement facilities and/or the chromaticity measurement facilities to be set to the gradation correction facilities and/or the color modification facil.ities, The color prooflr having the construction just described is advantageous in that calibration of the color PTOOfer can be performed remotely through. the tclecommuni cation line interface.

According to a still further aspect of the present invention, there is provided a color proofer, comprising density measurement facilities and/or chromaticity measurement facilities, positioning facilities formoving the density measurement facilities and/or the chromaticity measurement facilities to a selected position of a print image, gradation correction facilities and/or color modification facilities, and gradation corTection data production facilities and/or color modification dataproduction facilities forproducing gradation correction data and/or color modification data based on density data and/or chromaticity data measured by the density measurement facilities and/or the chromaticity measurement facilities and setting the produced gradation correction data and/or color modification data to the gradation correction facilities and/or the color modification facilities The color proofer having the construction just described is advantageous in that it can perform optimum calibration to the color proofer itself in a stand-alone fashion without requiring a computer.

According to a yet further aspect of the present invention, there is provided a calibration method for a color proofer which includes density measurement means, positioning means for moving the density measurement means to a selected position of a print image, a host computer interface, and gradation correction means, comprising the steps of printing gradation patches, moving the density measurement means to a selected patch position, producing patch data, measuring a density by means of the density measurement means, transferring the measured density data and the patch data to a host computer through the host computer interface, producing gradation correction data by the host computer, transferring the produced gradation correction data to the color proofer through the host computer interface, receiving the gradation correction data transfer-red thereto and setting the same to the gradation correction means, and discharging the gradation patches.

According to a yet further aspect of the present invention, there is provided a calibration method for a color proofer which includes chromaticity measurement means, positioning means for moving the chromaticity measurement means to a selected position of a print image, a host computer interface, and color modification means, comprising the steps of printing color patches, moving the chromaticity measurement means to a selected patch position, producing patch data, measuring a chromaticity by means of the chromaticity measurement means, transferring the measured chromaticity data and the patch data to a host computer through the host computer interface, producing color modification data by thehost computer, transferring the produced color modification data to the color proofer through the host computer interface, receiving the Color modification data transferred thereto and setting the same to the color modification means, and discharging the color patches.

According to a yet further aspect of the present invention, there is provided a calibration method for a color proofer which includes density measurement means, chromaticity measurement means, positioning means for moving the density measurement means and the chromaticity measurement means to a selected position of a print image, a host computer interface, gradation correction means, and color modification means, comprising the steps of printing gradation patches, F I mo%ring the density measurement means to a selected patch position, prodlicing patch data, measuring a density by means of the density measurement means, transferring the measured density data and the patch data to a host computer through the host computer interface, producing gradation correction data bythe host computer, transferring the produced gradation correction data to the color proofer through the host computer interface, receiving the gradation correction data transferred thereto and setting the same to the gradation correction means, discharging the gradation patches, printing color patches, moving the chromaticity measurement means to a selected patch position, producing patch data, measuring a chromaticity by means of the chromaticity measurement means, transferring the measured chromaticity data and the patch data to the host computer through the host computer interface, producing color modification data by the host computer, transferring the produced color modification data to the color procifer through the host computer interface, receiving the color modification data transferred thereto and setting the same to the color modification means, and discharging the color patches.

According to a yet further aspect of the present invention, there is provided a calibration )5 method for a color proofer which includes density measurement means, chromaticity measurement means, positioning means for moving the density measurement means and the chromaticity mcasurcmcnt means to a selected position of a print image, a telecommunication line interface', gradation correction means, and color modification means comprising the sieps of printing gradation patches, moving the density measurement means to a selected patch position, producing patch data, measuring a density by means of the density measurement means, transferring the measured density data and the patch data to a calibration computer located at a remote place through the telecommunication line interface, producing gradation correction data by the calibration computer, transferring the produced gradation correction data to the color proofer through the telecommunication fine interface, receiving the gradation correction data transferred thereto and 2.5 setting the same to the gradation correction means, discharging the gradation patches, printing color patches, moving the chromaticity measurement means to a selected patch position, producing patch I data, measuring a chromaticity by means of the chromaticity measurement means, tra'nsferring the measured chromaticity data and the patch data to the calibration computer through the telecommunication line interface, producing color modification data by the host computer, transferring theproduced color modification data to the color proofcrthrough the telecommunication line interface, receiving the color modification data transferred thereto and setting the same to the color modification means, and discharging the color patches.

According to a yet further aspect of the present invention, there is provided a calibration method for a color proofer which includes density measurement means, positioning means for moving the density measurement means to a selected position of a print image, gradation correction data production means, and gradation correction means, comprising the steps of printing gradation patches, moving the density measurement means to a selected patch position, producing patch data, measuring a densitybymeans ofthe density measurement rritans, producing gradation correction data from the measured density data by the gradation correction data production means, setting the produced gradation correction data to the gradation correction means, and discharging the gradation patches.

According to a yet further aspect of the present invention, there is provided a calibration method for a color proofer which includes chromaticity measurement means, positioning means for moving the chromaticity measurement means to a selected position of a print image, color modification data production means, and color modification means, comprising the steps of priming color patchcs, moving the chromaticity measurement means to a selected patch position, producing patch data, measuring a chromaticity by means of the chromaticity measurement means, producing color modification data from the measured chromaticity data by the color modification data production means, setting the produced color modification data to the color modification means, and discharging the color patches.

According to a yet further aspect of the present invention, there is provided a calibration method for a color proofer which includes density measurement means, chromaticity measurement -9.

means, positioning means for moving the density measurement means and the chromaticity measurement means to a selected position of a print image, gradation correction data production means, color modification data production means, gradation correction means, and color modification means, comprising the steps of printing gradation patches, moving the density i measurement means to a selected patch position, producing patch data, measuring a density by means of the density measurement means, producing gradation correction data frorn the measured density data by the gradation correction data production means, setting the produced gradation correction data to the gradation correction means, discharging the gradation patches, printing color patches, moving the chromaticity measurement means to a selected patch position, producing patch data, measuring a chromaticity by means of the chromaticity measurement means, producing color modification data from the measured chromaticity data by the color modification data production means, setting the produced color modification data to the color; nodification means, and discharging the color patches.

The above and other objects, features and advantages of the present invention will become apparent from (he following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.

FIG, I i.5 a perspective view showing a basic construction of a color proofer to which the present invention is applied; FIG. 2 is a diagrammatic view Ulustrating a test chart (gradation patches and color patches) which is used in the color proofer; FIG. 3 is a block diagram showing a detailed construction of a control apparatus of the color proofer, FIG. 4 Is a flow chart illustrating a metbod of producing a gradation correction table using a host computer in the color proofer,FIG. 5 is a flow chart illustrating a method of producing a color correction table using the host computer in the color proofer-, FIG, 6 is an illustration of the arrangement of FIGS. 6A and 6B.

FIGS, 6A and 613 are flow charts illustrating a method of producing a gradation correction table and a color modification table using the host computer in the color proofer, FIG. 7 is a circuit block diagram showing a detailed construction of a modified form of the control apparatus of the color proofer-, FIG. 8 is an illustration of the arrangement of FIGS, 8A and 8B.

FIGS. SA and 8B arc flow charts illustrating a method of producing a gradation correction table and a color modification table using a calibration computer in the color proofer wherein the control apparatus of FIG. 7 is incorporated, FIG. 9 is a circuit block diagram showing a detaded construction of another modified form of the control apparatus of the color proofer, FIG 10 is a flow chart illustrating a method of producing a gradation correction table using a gradation correction table data unit in the color proofer wherein the control apparatus of FTG, 9 is incorporated; FIG. 11 is a flow chart illustrating a method of producing a color modification table using a color modification table data unit in the color proofer wherein the control apparatus of FIG. 9 is incorporated; FIG. 12 is an illustration of the arrangement of FIGS. 12A and 12'13.

FIGS. 12A and 12D are flow charts illustrating a method ofproducing a gradation correction table and a color modification table using a gradation correction table data unit and a color modification table data unit in the colorproofer wherein the control apparatus of FIG. 9 is incorporated', FIG. 13 is a circuit block diagram showing a detailed construction of a further modified form of the control apparatus of the color proofer; 10- I I FIG. 14 is a block diagram shoiving a construction of a gradation correction table which can be incorporated in the color prooter in order to make a gradation reproduction characteristic smooth; FIG, 15 is a diagrammatic view showing a construction of another gradation correction table which can be incorporated in the color proofer in order to allow addition of random noise; FIG. 16 is a block diagram showing a construction of a color modification table having an in(erpolation function which can be incorporated in the color proofer, FIG. 17 is a block diagram showing a conNtruction of a color conversion module which can be provided, when needed, in the color proofer; FIG. 18 is a circuit block diagram of an IPU, In the drawirigs:

Referring first to FIG. 1, there is shown a basic construction of one embodiment of a color procifer to which the present invention can be applied. The Color proofer includes, as a proofer engine thereof, a rotary drurn type printer wherein a continuous jet type inkjet head which can print an ink dot ofa variable diameter such as disclosed, for example, in Japanese Patent Publication No,24871/1994 (U.S. Patent No.4,620,196) or Japanese Patent Laid-Open No. 83046/1976 (U.S.

Patent No. 4,673,951).

In particular, the color procifer shown in FIG. I includes, as principal components fficreof, a recording drum I which rotates writh paper wrapped 1herearound, a drum motor 2 for rotating the recording drum 1, a shaft encoder 3 for detecting rotation ofthe recording drum 1, a print head 4 in the form or a continuous jet type ink jet head for jetting an ink- jet toward the recording drum I to record an image on the paper wrapped around the recording drum 1, a feed mechanism 5 for movably positioning the print head 4 in an axial direction of the recording drum 1, a stepping motor 6 for driving the feed mechanism 5, a measurement head 7 provided on the print head 4 for movement in the axial direction ofthe recording drum I by the feed mechajsm 5, a control apparatus 8 including anIPU and so forth for controlling operation ofthe entire color proofer. The color proofer has a host -H- computer 9 connected thereto.

in the color proofer shown in FIG. 1, the measurement head 7 is coupled to the feed mechanism 5 for the print head 4 so that it may be moved in an axial direction of the recording drum I &irnilarly to the print head 4. Here, the measurement head 7 may be the same structure as the print head 4.

The measurement head 7 has a densitometer, a chromaticity meter or a spectrophotometer mounted thereon, and an arbitrary position (coordinates: (XV)) of a point in a print image on paper wrapped on the recording drum I can be designated for measurement by movement of the measurement head 7 in an axial direction (X direction) by the stepping motor 6 and relative movement of the measurement head 7 in a circumfitrential direction (Y direction) by rotation of the recording drum 1. Then the density and/or the chromaticity at the designated position can be nwasured. It is to be that, in the color proofer described below, the measurement head 7 has a spectrophotometer 71 (refer to 1FIG. 3) such that density data and chromaticity data are calculated based on a spectral reflection factor R(X) measured by the spectrophotometer 71 The control apparatus 8 is connected to the host computer 9, and performs, in addition to controlling of an ordinary printing operation, designation of (X, Y) coordinates to move the measurement head 7 to an arbitrary position relative to the print image and read the density and the chromaticity at the position and then executes data processing and so forth of the color proofer, While the densiitomcter, chromaticity meter or spectrophatometer 71 mounted on the measurement head 7 may be a measurement head of the contact type which contacts with the face of a print image to perform measumment of the same, preferably a measurement head of the non contact type is used in order to aHow measurement of the density and/or the chromaticity of a test chart immediately after it is printed.

Referring to FIG. 2, a test chart (gradation patches or color patcbes) used in the color proofer to which the present invention is applied is a chart of patches printed with image data (C, M, Y, K) at positions designated with coordinates (X, Y). Four different gradation color patches for C, Y, K are prepared and each includes patches of different densities of a single color. Meanwhile, for a test chart of color patches, only one kind of test chart is prepared, and patches of different colors based on image data are prepared and disposed on the single test chart.

Tt is to be noted that, when a conventional color matching software tool is used to perform color amendment, color patches associated with the soflware tool to be used are employed.

Referring to FIG. 3, there is shown a detailed construction of the control apparatus 8 of the color proofer to which the present invention is applied- The control apparatus 8 includes a measurement position generation unit I I for generating a measurement position (X, Y) of a test chart, a measurement patch data generation unit 12 for receiving the measurement position (X, Y) and generating measurement patch data (C, M, Y, K), a density- chromaticity calculation urt 13 for receiving a spectral reflection factor R(;L) measured by the spectrophotometer 71 of the measurement head 7 and for calculating and outputting density data D(C), D(M), D(Y), D(K) and chromaticity data L', a, b, a host computer interface 14 for outputting the measurement patch data (C, M, Y, K) from the measurement patch data generation unit 12 and the density data D(C), D(M), D(Y), D(K) and the chromaticity data L, a, b from the densitychromaticity calculation unit 13 to the host computer 9 and for receiving color modification table data (CNM) and gradation correction table data (C, M, YK) fiom the host computer 9 and outputting the received data a color modification table 15 for receiving image data (C, M, Y, K) and outputting color modified image, data (C, M, Y, K) color modified with the image data (C, M, Y, K), a gradation correction table 16 for receiving the color modified image data (C, M, Y, K) and outputting gradation corrected image data (C, M, Y, K) gradation corrected with the color modified image data (C, M, N% K), and a pseudo gradation generator 17 for receiving the gradation corrected image data (C, K Y, K), generating a pseudo gradation with the gradation corrected image data (C, M, Y, K) and outputting the pseudo gradation to the proofer engine. It is to be noted that the position values X and Y generated by the measurement position generation unit I I are input to the measurement head 7 and a drum control unit (not shown) for controlling the drum motor 2., respectively, so that they are used to determine a 13- measurement timing of a test chart.

FTG, 4 illustrates a method of producing the gradation correction table 16 using the host computer 9 in the color proofer to which the present invention is applied. This method includes a gradation patch printing step S 10 1. a measurement head predetermined patch position moving step S102, a patch data producing step S 103, a spectral reflection factor measuring step S 104, a density data converting step S105, a density data and patch data transferring step SI06, a gradation correction table data producing step S 107, a gradation correction table data transferring step S 1 08,a gradation correction table data setting step S 109, and a gradation patch discharging step S I 10.

FIG. 5 illustrates a method of producing the color modification table 15 using the host computer 9 in the color proofer to which the present invention is applied. The method of FIG. 5 includes a color patch printing step S20 1, a measurement head predetermined patch position moving step S202, a patch data producing step S203, a spectral reflection factor measuring step S204, a chromaticity data converting step S205, a chromaticity data and patch data transferring btep S206, a color modification table data producing step S207, a color modification table data transferring step S208, a color modification table data setting step S209, and a color patch discharging step S210, FIGS. 6A and 6B, arranged as shown in FIG. 6, illustrate a method of producing the gradation correction table 16 and the color modification table 15 using the host computer 9 in the color proofer to which the present invention is applied, This method includes a gradation patch printing step S i0l, a measurement head predetermined patch position movingstep S102, apatch data producing step S 103, a spectral refection factor measuring step S 104, a density data converting step S105, a density data and patch data transferring step S1D6, a gradation correction table data producing step S 107, a gradation correction table data transferring step S 108, a gradation coff ection table data setting step S 109, a gradation patch discharging step S I 10, a color patch printing step S201, a measurement head predetermined patch position moving step S202, a patch data producing step S203, a spectral reflection factormeasuring step S204, a chromaticity data converting step S205, a chromaticity data and patch data transferring step S206, a color modification table data producing step S207, a color modification table data transferring step S209, a color modification table data setting step S209, and a color patch discharging step S21 0.

Subsequently, a calibration operation of the color proofer having the constniction described above is described.

(1) Gradation patches are printed (step S101) while the paper is held -, Tapped on the recording drum 1, (2) The measurement position generation unit I I generates (Y, Y) coordinates, and the spectrophotometer 71 is adjusted to a predetermined patch position by movement (X) of the measurement head 7 and rotation (Y) of the recording drum I (step S102). Then, a spectral reflection factor RO.) is measured (step S 103).

(3) The (X, Y) coordinates generated in (2) above are input to the measurement patch data generation unit 12, and patch data (C, M, Y, K) corresponding to the coordinates are output from the measurement patch data generation unit 12 (step S 103).

(4) The spectral reflection factor R(k) measured in (2) above is input to the density chromaticity calculation unit 13 by which it is converted into density data D(C), D(M), D(Y), D(K) (step S 105).

(5) The control apparatus 8 transfers the patch data(C, M, Y, K) obtained in (3) above and the density data D(C), D(M), D(Y), D(K) obtained in (4) above as a set to the bost computer 9 through the host computer interface 14 (si ep S 106) (6) The control apparatus 8 executes the operations of (1) to (5) above repetitively for all of the gradation patches of the four colors C, Nt Y, K (repeats the steps S102 to S106). If the gradation patches for the four colors are printed on a single paper sheet, then a printing operation is performed once and measurement is executed for the four colors.

(7) The host computer 9 produces gradation correcfion table data (C, M, Y, K) independently of one another for the different colors of C, M, Y, K based on the patch data (C' M, V, V.) and the density data D(C), D(M), D(Y), D(K) received in (5) above using an algorithm incorporated therein (step S 107), and transf:rs the gradation correction table data (C, M', Y, K) to the color proofer (step S 108). The gradation correction table data are produced so that the input/output characteristic of the density maybe linear, or the gradation correction table data are produced so that the input/output characteristic of the area ratio may be linear and a dot gain is added so that an intermediate portion of the input/output characteristic may have some swell.

(8) The control apparatus 8 receives the gradation correction table data (C, K Y, K) produced in (7) above through the host computer interface 14 and sets the data to the gradation correction table 16 in the I PU (step S 109).

(9) The control apparatus 8 discharges the print of the gradation patches for which the measurement is completed (step S I 10).

(10) Color patches are printed (step S201). The paper is held wrapped on the recording drum 1.

(11) A similar operation to that in (2) above is performed (steps S202 and S204).

(12) (X, Y) coordinates generated in (11) above are input to the measurement patch data generation unit 12, from which patch data (C, M, Y, K) corresponding to the coordinates is output (step S203).

(13) A spectral reflection factor Ro) measured in (11) above is input to the density chromaticity calculation unit 13, by which it is converted into chromaticity data (L, a, b) (step S205).

(14) The control apparatus 8 transfers the patch data (C, M, Y, K) obtained in (12) above and the chromaticity data (L, a, b) obtained in (13) above as a set to the host computer 9 through the host computer interface 14 (step S206).

(15) The control apparatus 8 executes the operations of (11) to (14) above repetitively for all of the color patches (repeats the steps S202 to S206).

(16) The host computer 9 produces color modification table data (CNM) based on the patch data (C, M, Y, K) and the chromaticity data (L, a, b) received in (14) above using an algorithm incorporated therein (step S207), and transfers the color modification table data (CMYK) to the control apparatus 8 (step S208). The color modification table data (CMYK) are produced, for example, in the following manner. In particular, the host computer 9 has a target ICC (International Color Consortium) profile representative of a color reproduction characteristic of a target printing machine. The host computer 9 produces a proofer ICC. profile representative of the color reproduction characteristic of the color proofer from the received patch data (C, K Y, K) and chromaticity data (L,a, b). For the production of a proofer ICC profile, a conventional color matching software too] is used. The host computer 9 produces color modification table data (CMYK) from the target ICC profile and the proofer ICC profile using an algorithm incorporated therein.

(17) The control apparatus 8 receives the color modification table data produced in (16) above through the host computer interface 14 and sets them to the color modification table 15 in the IPU (step S209).

(18) The control apparatus 8 discharges the print of the color patches for which the measurement is completed (step S210).

FIG. 7 shows a detailed construction of a modification to the control apparatus 8 described hereiriabove with reference to FIG. 3. The modified control apparatus 8 of FIG. 7 is different from the control apparatus 8 of FIG. 3 in that it includes a telecorrumnication line interface (modem) 14' in place of the host computer interface 14, Thus, the color proofer which includes the modified control apparatus 8 of FIG. 7 is connected by a telecommunication line to a computer (hereinafter referred to as calibration computer) 9' for calibration installed in a calibration center at a remote place. The calibration computer 9' accommodates a plurality of such color proofers and calibrates (remote calibralion) the individual color proofers based on patch data (C, K Y, K) and density data (D(C), D(M), D(Y), D(K)) as well as patch data (C, M, Y, K) and chromaticity data (L, a', b) sent thereto from the color proofers over the telecommunication line.

Since theremaining portion of the color proofcr in which the modified control apparatus 9 of FIG.

17.

7 is incorporated is similar in construction to that of the color proofer in which the control apparatus 8 of FIG. 3 is incorporated, overlapping description of it is omitted here to avoid redundancy.

FIGS. 8A and 813, assembled as shown in FIG. 8, illustrate a method of producing the gradation correction table 16 and the color modification table 15 using the calibration computer 9' in the color proofer in which Lhe modified control apparatus 8 of FTG. 7 is incorporated, Referring to FTGS. 8A and 8B, the method includes a gradation patch printing step S 101, a measurement head predetermined patch position moving step S102, a patch data producing step S103, a spectral refection factor measuring step S 104, a density data converting step SI 05, adewity data andpatchdata transrerring step S 106', a gradation correction table data producing step S1 07, a gradation correction table data transferring step S 108', a gradation correction table data setting step S 109, a gradation patch discharging step Sl 10, a color patch printing step S201, a measurement head predetermined patch position moving step S202, a patch data producing step S203, a spectral reflection factor measuring step S204, a chromaticity data converting step S205, a chromaticity data and patch data transferring step S206', a color modification table data producing step S207, a color modification table data transferring step S209', a color modification table data setting step S209, and a color patch discharging step S2 10.

The calibration operation of the color proofer which includes the modified control apparatus 8 of FIG. 7 is similar to that of the color proofer which includes the control apparatus 8 of FIG, 3 except that the communication between the modified control apparatus 8 of the color proofer and the calibration computcr 9' and the communication between the control apparatus 8 of the color proofer and the host computer 9 are different from each other, that is, the operations in steps S 106' and S 106, S108'and S 108, S206'and S206, and S208'and S208 are different from each other in that the transfer steps S106, S 108'and S208'are by the telecommunications line interface 14'instead of through a direct host connection interface. Accordingly, overlapping description of the calibration operation is omitted here to avoid redundancy.

FIG. 9 shows a detailed construction of ano(her modification to the control apparatus 8 -Is- described hereinabove with reference to FIG. 3. The modified control apparatus 8 of FIG. 9 is different from the control apparatus 8 of FTG. 3 in that it includes, in order to provide a built-in file data production function to the color proofeT in which the modified control apparatus 8 is incorporated (or to the control apparatus 8 itself), a gradation correction table data production unit 18 and a color modification table data production unit 19 in place of the host computer interface.14 shown in FIG. 3 (or in place of the telecommunication line interface 14' of the modified control apparatus 8 of FIG. 7). Since the remaining portion of the color proofer in which the modified control apparatus 8 of]G. 9 is incorporated is similar in construction to that of the color proofer in wWch the control apparatus 8 of FIG. 3 is incorporated, overlapping description of it is ornitted here to avoid redundancy.

FIG. 10 illustrates a method of producing the gradation correction table 16 in the color proofcr in which the modified control apparatus 9 of FIG. 9 is incorporated, Referring to FIG. 10, the illustrated method includes a gradation patch printing step S101, a measurement head predetermined patch position moving step S102, a patch data producing step S103, a spectral refection factor measuring step S 104, a density data converting step S 105, a gradation correction table data producing step S 107', a gradation correction table data setting step S 109, and a gradation patch discharging step S I 10.

FIG. I I illustratcs a method of producing the color modification table 15 in the color proofer in which the modified control apparatus 8 of FIG. 9 is incorporated. Referring to FIG. 11, the illustrated method includcs a Color patch printing step S201, a measurement head predetermined patch position moving step S202, a patch data producing step S203, a spectral reflection factor measuring step S204, a chromaticity data converting step S205, a color modification table data producing step S207 a color modification table data setting step S209, and a color patch discharging step S210.

FIGS. 12A and 12B, assembled as shown in FIG- 12, illustrate a method of producing the gradation correction table 16 and the color modification table IS in the color proofer in which the 19- modified control apparatus 8 of FIG. 9 is incorporated, The method of FIGS. 12A and 12B includes a gradation patch printing step S 10 1, a measurement head predeteffnined patch position movingstep S 102, a patch data producing step S 103, a Spectral refection factor measuring step S 104, a density data converting step S103, a gradation correction table data producing step SIOT, a gradation correction table data setting step S 109, a gradation patch discharging step S 110, a color patch printing step S201, a measurement head predetermined patch position moving step S202, a patch data producing step S203, a spectral reflection factor measuring step S204, a chromaticity data converting step S205, a color modification table data producing step S207', a color modification table data setting step S209, and a color patch discharging step S21 0.

The calibration operation of the color proofer which includes the modified control apparatus 8 of FIG. 9 is similar to that of the color procifer which includes the control apparatus 8 or FIG. 3 except that production of gradation correction table data and color modification table data is performed in the control apparatus 8 (steps SIOT and S20T). Consequently, the steps S106, Slog, S206 and S208 which relate to communication of data are omitted, and the steps 107 and 207 are modified. Thus, further detailed description of the calibration operation is omitted here to avoid redundancy.

FIG- 13 shows a detfli ed construction of a further modification to the control apparatus 8 described hereinabove with reference to FIG. 3. The modified control apparatus 9 ofFIG. 13 is different from the control apparatus 8 of FIG, 3 in that chromaticity data (L', &, b) are input as input image data to the color proofer, in which the modified control apparatus 8 of FIG. 13 is incorporated, in place of image data (C, M, V, K). Consequently, the color modification table 15 receives the chromaticity data (L, a, b) as input data thereto and outputs image data (C, K Y, K), and color modification table data (L, a, b) calculated by the host computer 9 are set to the color modification table 15. Consequently, the host computer 9 need not necessarily include a target 2.5 ICC profile. it is to be noted that the color modification table 15 in the color proofer in which the modified control apparatus 8 of FIG. 13 is incorporated can be applied similarly to the color proofer in which the modified control apparatus 8 of FIG. 7 is incorporated and color modification table data arc produced by the calibration computer 9' installed at a remote place.

Subsequently, a calibration operation of the color profile in which the modified control apparatus 8 of FIG. 13 is incorporated is described, It performs such operations as those of (1) to (15) performed by the color proofer in which the control apparatus 8 of FIG. 3 is incorporated.

(16) The host computer 9 produces color modification table data (L, a, b) based on patch data (C, M, Y, K) and chromaticity data (L", a, b) received in (14) described hereinabove using an algorithm built therein and transfers the produced color modification table data (L, a, b) to the control apparatus 8. The color modification table data (L, a, b) are produced in the following manner. in particular, in each color patch, values of patch data (C, M, Y, K) and ideal chromaticity data (L, a, b) are provided in a corresponding relationship to each other, If the values of the patch data (C, M, Y, K) which correspond to chromaticity data (L, a, b) of a printed patch are determined from the correspondence data (C, M, Y, K/L, a, V), then color modification table data (L a, b) are obtained.

Thereafter, the color proofer similarly performs such operations as those of (17) and (18) C C performed by the color proofer in which the control apparatus 8 of FIG. 3 is incorporated.

FIG. 14 shows a construction of the gradation correction table 16 of the color proorer to which the present invention is applied where the gradation correction table 16 is constructed so as to have a smooth gradation reproduction characteristic. Referring to FIG. 14, the gradation correction table 16 shown receives input irmge data of 8 bits (256 gradations) for each of the colors of C, K Y, K and outputs image data of 10 to 12 bits (1,024 to 4,096 gradations) and is connected to a pseudo gradation generator 17 having a pseudo gradation expressive power (the size of a dither matrix or the like) which is varied by designation of a resolution. Employment of the gradation correction table 16 of the type described can compensate for a non- linmFity of the proofer engine.

Consequently, thepseudo gradation expressive force can be increased and the gradation reproduction characteristic of the proofer engine can be made linear. For example, a gradation expression of 10 bits (1,024 gradations) is allowed with respect to an input of 8 bits (256 gradations), and a gradation correction table 16 wilth which, from among 1,204 output points, those 256 points which provide a linear relationship between an input and an output are seJected is produced.

FIG. 15 shows another construction of the gradation correction table 16 of the color proofeT to which the present invention is applied where the gradation correction table 16 is constructed so as to allow addition of random noise Referfing to FIG. 15, the gradation correction table 16 shown includes four 16-bit address x 10-bit to 12-bit RAMs (PLandom.Accm Memories) of 64 KW (words) independent of one another for the four colors of C, M, Y, K and each including 256 memory planes of 10 to 12 bits having input addresses provided by input image data of 8 bits for one color (256 W x 10-bit to 12-bit memory planes), Input image data of 8 bits is input in parallel as an address to the 256 memory planes, and data of a memory plane selected with random data of 9 bits is output as output image data of 10 to 12 bits. If the input/output characteristics of the 256 memory planes are modulated with different noise data from one another, then diffierent memory planes are selected for different pixels, and random noise is added to an output image. The random data to be used for selection of a memory plane is generated in the control apparatus 8 (not shown in FIGS. 3, 7, 9 and 13).

FIG. 16 shows the color modification table 15 of the color proofer to which the present invention is applied where the color modification table 15 has an interpolation function. Referring to FIG. 16, the color modification table 15 shown includes a color modification table (three dimensional LUT) 15' and an interpolation calculation unit 20. If the m1or modification table 15 is formed from a three-dimensional LUT of 8 bits for each of L, a, b, then a large capacity RAM of 64 MB (22' x 4 bytes) is required. Therefore, in the color modification table 15' shown in FIG. 16, the color modification table I 5'is formed from a three-dimensional LUT of 6 bits for each of L, a, b (capacity: 21' x 4 bytes = I NS), and missing gradations which appeaT due to absence of the two least significant bits are interpolated by the interpolation calculation unit 20. The interpolation calculation is preferably performed three-dimensionally, and any suitable known algorithm may be used.

FIG. 17 shows a construction of a color conversion module which is suitably provided where needed in the color proofer to which the present invention is applied, Referring to FIG. 17, the color conversion module is generally denoted at 21 and converts three color signals of R (red), G (green), B (blue) or C, M, Y into four color signals of C, M, Y, K. To this end, the color conversion module 21 includes a K generation section 22 for inverting a minimum value of (C, M, Y) or a maximum value of (R, G, B) and multiplying the value obtained by the inversion by a coefficient for each input data section to generate a K component, and a UCR (Under Color Removal) section 23 for reducing the color data (where R, G, B data are input, after they are inverted) at a fixed ratio in accordance with the value of K generated by the K generation section 22.

The color conversion module 21 described above may be disposed in a stage preceding to the color modification table 15 in any of the control apparatus 8 described hereinabove with reference to FIGS. 3, 7, 9 and 13. Where the color proofer is used to print an output of a scanner or a digital is camera, three signals of R, G, B are input. A] so print data are not sometimes in the form offour color signals (C, K Y, K) but in the form of three color signals (C, M, Y) which include no separate K component. In such an instance, the color conversion module 21 should be disposed in a stage preceding to the color modification table 15.

It is to be noted that, while the color proofer described above employs a rotary drum type printer in which a continuous jet type ink jet head is incorporated as a proofer engine, as can be recognized from the contents of the description, the present invention is not linfited to the specific embodiment, but can be applied apparently to color proofers in which any of printers, plotters and so forth of the rotary drum type, serial type and so forth in which any of recording methods including DOD (Drop On Demand) type inkjet recording, electrophotographic recording, thermal transfer recording, and silver salt photographic recording is employed is used as a proofer engine.

While a preferred embodiment of the present invention has been described using specific -23.

terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the following claims.

Claims

Claims:

1. A color proofer, characterized in that it comprises:

density measurement means (7, 13) and/or chromaticity measurement means (7, 13); means (11) for designating a plurality of positions of a print image; and positioning means (2, 6) for successively moving said density measurement means (7, 13) and/or said chromaticity measurement means (7, 13) to the designated positions of the print image to allow said density measurement means (7 13) and/or said chromaticity measurement means (7, 13) to measure a density and/or a chromaticity at each of the designated positions.

2. A color proofer as set forth in claim 1, characterized in that a proofer engine is a rotary drum type printer in which a continuous jet type ink jet head (4) is incorporated.

3. A color proofer as set forth in claim I or 2, characterized in that a measurement head (7) in which said density measurement means (7, 13) and/or said chromaticity measurement means (71 13) are incorporated is formed as a unitary member together with a print head (4).

4. A color proof er a set forth in any one of claims 2 5 1 to 3, characterized in that said density measurement means (7) 13) and/or said chromaticity measurement means (7, 13) are of the contactless type.

5. A color proofer, characterized in that it comprises:

density measurement means (7, 13) and/or chromaticity measurement means (7, 13); positioning means (2, 6) for moving said density measurement means (7, 13) and/or said chromaticity measurement means (7, 13) to a selected position of a print image; gradation correction means (16) and/or color modification means (15); and a host computer interface (14) for allowing gradation correction data and/or color modification data produced by a host computer (9) based on density data and/or chromaticity data measured by said density measurement means (7, 13) and/or said chromaticity measurement means (7, 13) to be set to said gradation correction means (16) and/or said color modification means (15).

6. A color proofer, characterized in that it comprises:

density measurement means (7, 13) and/or chromaticity measurement means (7, 13); 26 positioning means (2, 6) for moving said density measurement means (7, 13) and/or said chromaticity measurement means (7, 13) to a selected position of a print image; gradation correction means (16; 182) and/or color modification means (15; 181); and a telecommunication line interface (14') for allowing gradation correction data and/or color modification data produced by a remotely located calibration computer (9') based on density data and/or chromaticity data measured by said density measurement means (7, 13) and/or said chromaticity measurement means (7, 13) to be set to said gradation correction means (16) and/or said color modification means (15).

7. A color proofer, characterized in that it comprises:

density measurement means (71 13) and/or chromaticity measurement means (7, 13); positioning means (2, 6) for moving said density measurement means (7, 13) and/or said chromaticity measurement means (7, 13) to a selected position of a print image; gradation correction means (16; 182) and/or color modification means (15; 181); and 27 gradation correction data production means (18) and/or color modification data production means (19) for producing gradation correction data and/or color modification data based on density data and/or chromaticity data measured by said density measurement means (7, 13) and/or said chromaticity measurement means (7, 13) and setting the produced gradation correction data and/or color modification data to said gradation correction means (16; 182) and/or said color modification means (15; 181).

8. A color proofer as set forth in any one of claims 5 to 7, characterized in that said color modification means (15) includes a three- dimensional look-up table (15') which receives input image data of L, a, b as an address and outputs data at the address as output image data of C, M, Y, K.

9. A color proof er as set forth in any one of claims 5 to 7, characterized in that said color modification means (15) includes a threedimensional look-up table (15') which receives higher order bits of input image data of L, a, b as an address, the number of the higher order bits being smaller than the number of bits of the input image data, and outputs data at the address as output image data of C, MI Y, K, and an interpolation calculation unit (20) for interpolating the output image data of said three- 28 dimensional look-up table (15') with the input image data.

10. A color proof er as set forth in any one of claims 5 to 7, characterized in that said gradation correction means (182) includes a one-dimensional table for each of the colors of C, M, Y, K which receives input image data of the color as an address, the one-dimensional tables for the colors of C, M, Y, K being independent of one another, and outputs data at the address as output image data composed of a number of bits larger than the number of bits of the address.

11. A color proof er as set forth in any one of claims 5 to 7, characterized in that said gradation correction means (182) includes a plurality of one-dimensional tables for each of the colors of C, M, Y, K to all of which input image data of the color is inputted in parallel as an address, the one-dimensional tables for the colors of C, M, Y, K being independent of one another, one of said onedimensional tables being selected at random with random data for each pixel, data of the selected one-dimensional table being outputted as the output image data.

12. A color proof er as set forth in any one of claims 5 to 9, characterized in that it further comprises a module (21) for receiving three color signals of C, M, Y or R, G, B, said module (21) including a K generation section 29 (22) and an under color removal section (28) by which the received three color signals are converted into four color signals of C, M, Y, K, an output of said module (21) being inputted to said color modification means (15).

13. A calibration method for a color proofer which includes density measurement means (7, 13), positioning means (2, 6) for moving said density measurement means (7, 13) to a selected position of a print image, a host computer interface (14), and gradation correction means (16), characterized in that it comprises the steps of: printing gradation patches; moving said density measurement means (7, 13) to a selected patch position; producing patch data-, measuring a density by means of said density measurement means (7, 13); transferring the measured density data and the patch data to a host computer (9) through said host computer interface (14); producing gradation correction data by said host computer (9); transferring the produced gradation correction data to said color proof er through said host computer interface (14); receiving the gradation correction data transferred thereto and setting the same to said gradation correction means (16); and discharging the gradation patches.

14. A calibration method for a color proofer which includes chromaticity measurement means (7, 13), positioning means (2, 6) for moving said chromaticity measurement means (7, 13) to a selected position of a print image, a host computer interface (14), and color modification means (15), characterized in that it comprises the steps of: printing color patches; moving said chromaticity measurement means (7, 13) to a selected patch position; producing patch data; measuring a chromaticity by means of said chromaticity measurement means (7, 13); transferring the measured chromaticity data and the patch data to a host computer (9) through said host computer interface (14); producing color modification data by said host computer (9); transferring the produced color modification data to said color proofer through said host computer interface 31 (14); receiving the color modification data transferred thereto and setting the same to said color modification means (15); and discharging the color patches.

15. A calibration method for a color proofer which includes density measurement means (7, 13), chromaticity measurement means (7, 13), positioning means (2, 6) for moving said density measurement means (7, 13) and said chromaticity me asurement means (7, 13) to a selected position of a print image, a host computer interface (14), gradation correction means (16), and color modification means (15), characterized in that it comprises the steps of: printing gradation patches; moving said density measurement means (7, 13) to a selected patch position; producing patch data; measuring a density by means of said density measurement means (7, 13); transferring the measured density data and the patch data to a host computer (9) through said host computer interface (14); producing gradation correction data by said host 32 computer (9); transferring the produced gradation correction data to said color proof er through said host computer interface (14); receiving the gradation correction data transferred thereto and setting the same to said gradation correction means (16); discharging the gradation patches; printing color patches; moving said chromaticity measurement means (7, 13) to a selected patch position; producing patch data; measuring a chromaticity by means of said chromaticity measurement means (7, 13); transferring the measured chromaticity data and the patch data to said host computer (9) through said host computer interface (14); producing color modification data by said host computer (9); transferring the produced color modification data to said color proofer through said host computer interface (14); receiving the color modification data transferred thereto and setting the same to said color modification 33 means (15); and discharging the color patches.

16. A calibration method for a color proofer which includes density measurement means (7, 13), chromaticity measurement means (7, 13), positioning means (2, 6) for moving said den-sity measurement means (7, 13) and said chromaticity measurement means (7, 13) to a selected position of a print image, a telecommunication line interface (14'), gradation correction means (16), and color modification means (15), characterized in that it comprises the steps of: printing gradation patches; moving said density measurement means (7, 13) to a selected patch position; producing patch data; measuring a density by means of said density measurement means (7, 13); transferring the measured density data and the patch data to a calibration computer (9') located at a remote place through said telecommunication line interface (14'); producing gradation correction data by said calibration computer (9'); transferring the produced gradation correction data to said color proofer through said telecommunication line 34 interface (14'); receiving the gradation correction data transferred thereto and setting the same to said gradation correction means (16); discharging the gradation patches; printing color patches; moving said chromaticity measurement means (7, 13) to a selected patch position; producing patch data; measuring a chromaticity by means of said chromaticity measurement means (7, 13); transferring the measured chromaticity data and the patch data to said calibration computer (9') through said telecommunication line interface (14'); producing color modification data by said host computer (9); transferring the produced color modification data to said color proofer through said telecommunication line interface (14'); receiving the color modification data transferred thereto and setting the same to said color modification means (15); and discharging the color patches.

17. A calibration method for a color proofer which includes density measurement means (7, 13), positioning means (2, 6) for moving said density measurement means (7, 13) to a selected position of a print image, gradation correction data production means (18), and gradation correction means (16), characterized in that it comprises the steps of: printing gradation patches; moving said density measurement means (7, 13) to a selected patch position; producing patch data; measuring a density by means of said density measurement means (7, 13); producing gradation correction data from the measured density data by said gradation correction data production means (18); setting the produced gradation correction data to said gradation correction means (16); and discharging the gradation patches.

18. A calibration method for a color proofer which includes chromaticity measurement means (71 13), positioning means (2, 6) for moving said chromaticity measurement means (7, 13) to a selected position of a print image, color modification data production means (19), and color modification means (15), characterized in that it 36 comprises the steps of: printing color patches; moving said chromaticity measurement means (7, 13) to a selected patch position; producing patch data; measuring a chromaticity by means of said chromaticity measurement means (7, 13); producing color modification data from the measured chromaticity data by said color modification data production means (19); setting the produced color modification data to said color modification means (15); and discharging the color patches.

19. A calibration method for a color proofer which includes density measurement means (7, 13), chromaticity measurement means (7, 13), positioning means (2, 6) for moving said density measurement means (7, 13) and said chromaticity measurement means (7, 13) to a selected position of a print image, gradation correction data production means (18), color modification data production means (19), gradation correction means (16), and color modification means (15), characterized in that it comprises the steps of: printing gradation patches; 37 moving said density measurement means (7, 13) to a selected patch position; producing patch data; measuring a density by means of said density measurement means (7, 13); producing gradation correction data from the measured density data by said gradation correction data production means (18); setting the produced gradation correction data to said gradation correction means (16); discharging the gradation patches; printing color patches; moving said chromaticity measurement means (7, 13) to a selected patch position; producing patch data; measuring a chromaticity by means of said chromaticity measurement means (7, 13); producing color modification data from the measured chromaticity data by said color modification data production means (19); setting the produced color modification data to said color modification means (15); and discharging the color patches.

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