JP3691322B2 - Color correction method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color printing proof (color printing proof or proof) in which a color image for proofreading is formed on a proofing paper before producing a color printed matter using a printing paper by a color printing machine using a rotary press or the like. The present invention relates to a color correction method that is suitable for application to a printing proof creation system that creates a printing proofer (also simply referred to as a proof) or a printing proofer (also simply referred to as a proofer) such as a color printer.
[0002]
[Prior art]
Conventionally, proofs for proofing colors etc. in the stage before creating a color print with a color printing machine in which a color image based on a halftone dot image as a product is formed on a printing paper (formal paper that will be the final product) Proof) is created by a printing proofer such as a color printer which is an image output device.
[0003]
The printing proofer is used because a color image is easily formed on a proof paper (recording sheet) in a short time without the need to make a plate-making film or printing plate (PS plate) as in a printing machine. This is because a hard copy, that is, a proof can be created.
[0004]
In order to form a proof color image on a calibration paper, image data dependent on the device [printing (ink, printing machine, paper, etc.), photograph, image sensor, CRT, LED, etc.], for example, CMYK (cyan, magenta) , Yellow, black) image data is temporarily measured by a standard print profile (such as a four-dimensional look-up table) given by a manufacturer or the like. After conversion to image data and XYZ image data mathematically interconvertible with this, a printing proofer profile (hereinafter also simply referred to as a proofer profile), for example, a printer profile (three-dimensional lookup table) Device-dependent image data for color printers, for example, RGB (red, green, blue) image data And, and so as to create a (also referred to as a calibration for the printer.) Color printer using image data of the device-dependent by proof which the color image is formed on paper calibration (proof).
[0005]
In this way, it is possible to confirm the color of the printed matter related to the printing press by a proof printing (proof) of the color printer in the pre-printing process.
[0006]
[Problems to be solved by the invention]
By the way, since the color reproduction range by the printing machine is different from the color reproduction range of the printing proofer, the range that cannot be reproduced by the printing proofer is determined by gamut mapping (color reproduction area mapping). Link with the user profile.
[0007]
When a proof corresponding to the color of the target printed material is output from the printing proofer using the linked profile in this way, if the color match is not sufficient, it depends on the device before the linked profile. The tone adjustment (tone curve adjustment) is finely adjusted for each of the image data CMYK.
[0008]
However, this fine adjustment work is time-consuming because it is not clear where and how much correction should be made with respect to the color shift, and it may not be possible to correct even by fine adjustment. There is a problem that there is.
[0009]
The present invention has been made in view of such problems, and provides a color correction method that makes it possible to easily and surely match the color of the proof by the proofer with the color of the target printed matter. The purpose is to do.
[0010]
[Means for Solving the Problems]
This invention
After the input image data that depends on the printing conditions is converted to colorimetric value data by the print profile, the colorimetric value data is converted to image data that depends on the proofer conditions by the proofer profile, and the proofing is performed from the proofer by the image data. In a color correction method for improving color reproduction accuracy in a system that outputs and simulates print color reproduction,
Converting image data dependent on printing conditions for outputting a printing color chart measured at the time of creating the printing profile into image data depending on proofer conditions via the printing profile and the proofer profile;
Supplying the image data to the proofer and outputting a proof color chart from the proofer;
Measuring the proof color chart to create a print color reproduction profile simulated by the proofer;
Obtaining a difference between the print color reproduction profile and the print profile for the entire color space of the input image data depending on the printing conditions;
Correcting the colorimetric value data using the obtained difference; and
(Invention of Claim 1).
[0011]
According to the present invention, a color chart for creating a printing profile is output from a proofer as a proof. The proof is color-measured in the same manner as the original print profile to obtain a conversion relationship between the image data and the colorimetric value data depending on the proof condition, that is, a print profile (print color reproduction profile). Then, the difference between the original print profile and the print color reproduction profile obtained from the proof is obtained for the entire color space of the input image data depending on the printing conditions, and the obtained difference is used to output from the print profile. The colorimetric data is corrected.
[0012]
By correcting the colorimetric data in this way, it is not necessary to adjust the tone curve for each color, and the proof color can be easily and reliably matched with the color of the target printed matter.
[0013]
In this case, in the step of correcting the colorimetric value data using the obtained difference, the obtained difference is added to the original print profile (subtracted because the sign is reversed). The new print profile (modified print profile) is used. By using this modified printing profile, it is no longer necessary to adjust the tone curve for each color without using extra memory, etc., and the color of the proof matches the target print easily and reliably. (Invention of claim 2).
[0014]
In addition, a value obtained by multiplying the difference by a weighting factor depending on the value of the input image data depending on the printing condition in the entire color space (difference multiplied by the weighting factor) is added to the original print profile and corrected. By using the print profile, it is possible to match colors more accurately (the invention according to claim 3).
[0015]
The difference between the print color reproduction profile and the print profile is not obtained for the entire color space of the input image data depending on the print conditions, but is a colorimetric value color space that is a color space of the colorimetric value data. By calculating for the whole, it is also possible to correct the image data depending on the proofer condition by using the obtained difference instead of correcting the colorimetric value data (the invention according to claim 4). .
[0016]
In this case, corrected colorimetric value data in the colorimetric value color space is obtained from the obtained difference and the print profile, the proofer profile is corrected by the corrected colorimetric value data, and the proofer profile is corrected by the corrected proofer profile. By correcting the image data depending on the conditions, it is possible to output from the proofer a proof that matches the target printed matter by only correcting the proofer profile without correcting the print profile. Described invention).
[0017]
Even in this case, corrected colorimetric value data in the colorimetric value color space is obtained from the difference and the print profile, and the corrected colorimetric value data is multiplied by a weighting factor depending on the colorimetric value color space. By correcting the proofer profile with color value data and correcting the image data depending on the proofer condition with the corrected proofer profile, there is a possibility that colors can be matched more accurately. (Invention of claim 6).
[0018]
Furthermore, in the present invention, the difference between the colorimetric value data obtained by measuring the proof color chart and the colorimetric value data of the print color chart is calculated for the entire color space of the input image data depending on the printing conditions. It is also possible to correct the colorimetric value data using the obtained difference (the invention according to claim 7).
[0019]
According to the present invention, it is not necessary to create a print color reproduction profile.
[0020]
In this case as well, the print profile can be corrected by the difference, and the colorimetric value data can be corrected by the corrected print profile.
[0021]
Further, the weighting coefficient depending on the value of the input image data depending on the printing condition in the entire color space is applied to the difference, the difference multiplied by the weighting coefficient is added to the printing profile, the printing profile is corrected, It is also possible to correct the colorimetric value data by using a corrected printing profile.
[0022]
Further, the weighting factor is set to a value of 1 in the color reproduction range of the printing proofer, and is set to a value of 0 in a range other than the color reproduction range (or the color of the printing proofer). By setting the value to 1 in the reproduction range and gradually decreasing from the value 1 as the distance from the color reproduction range is increased (the invention according to claim 11), there is a possibility that colors can be matched more accurately. Is obtained.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0024]
FIG. 1 shows a schematic overall configuration of a print proof creation system 10 to which an embodiment of the present invention is applied.
[0025]
The print proof creation system 10 basically includes an electronic plate collecting device 6 and a color image recording device 8 connected via a communication interface such as Ethernet.
[0026]
The electronic plate collecting apparatus 6 includes a workstation (W / S) 12 as the main body of the electronic plate collecting apparatus, and the W / S 12 outputs the color scanner 2 functioning as an image input device and each of the CMYK 4 plate originals. A film printer 4 is connected.
[0027]
On the other hand, the color image recording device 8 stores a print profile and a printer profile, which will be described later, and a host computer (H / C) 14 mainly functioning as a color conversion means, and a proof image output device (a proof print output device or a print). And a printer 16 functioning as a proofer or simply a proofer.
[0028]
Each of the W / S 12 and the host computer 14 includes a display which is a display device (not shown), a main body having a CPU / memory (storage means), and a keyboard and a mouse which are input devices.
[0029]
The color scanner 2 connected to the W / S 12 reads a document image on a stencil sheet (not shown) on which a ruled line in which characters and photographs are inserted is read and from other document images. A color image such as a picture, a character, or a graphic is read, and image data (device-dependent image data) after four-color (CMYK) color separation is sent to the W / S 12.
[0030]
The W / S 12 displays the stencil board image read by the color scanner 2 on the display. The user electronically collects an image based on the image data on the block mount image using a keyboard and a mouse, and creates an electronic plate-collected image for one page, a so-called imposition pattern.
[0031]
Data representing the imposition pattern is supplied to the film printer 4. The film printer 4 outputs a high-quality CMYK plate for printing, corresponding to the imposition pattern data.
[0032]
Usually, a printing plate is produced from this printing film original plate, and the produced printing plate is mounted on a rotary press, that is, a printing machine 7 and applied with ink. Then, the ink applied to the printing plate is transferred to the printing paper Pa to complete the color printed matter Pm on which the image IM is formed.
[0033]
In this case, the work for producing the color printed matter Pm using the printing machine 7 is a very large work and the cost is high. For this reason, a color image recording device 8 as a proofer for color printing is used for the purpose of confirming the finish of the color printed matter Pm before actual printing by the printing press 7.
[0034]
Therefore, an image edited / collected using W / S 12 has description language data (image data in a description language) describing image information for one page including position information, color information (including density information), and the like. Is supplied to the host computer 14 as PDL (Page Description Language) data.
[0035]
The host computer 14 performs color conversion processing and the like, and the image data subjected to the color conversion processing and the like is supplied to a printer 16 (also referred to as a printing proofer body or a proofer).
[0036]
The printer 16 outputs a hard copy HC based on the supplied image data. In this embodiment, the hard copy HC is obtained by forming the image IM on the image receiving sheet RS.
[0037]
FIG. 2 shows a schematic configuration of main functions of the host computer 14. This host computer 14 functions as the color conversion means 20. That is, the host computer 14 decodes the PDL data supplied from the W / S 12 by a raster image processor (RIP) (not shown) and develops a bitmap, and CMYK image data (device-dependent image data) as each scanned image data. ).
[0038]
Each CMYK image data is supplied to the color conversion means 20 in which a print profile 26 and a printer profile 36, which are color conversion LUTs (look-up tables), are set.
[0039]
The color conversion means 20 is input device-dependent image data, in this case, image data depending on printing conditions, for example, CMYK color image data Iin = Iin (C, M, Y, each of which is half-net data. , K) is image data depending on the proofer condition which is device-dependent image data [in this embodiment, image data depending on the printer condition, for example, image data of each color of RGB (hereinafter, also simply referred to as RGB image data). .) Iout = Iout (R, G, B)], and then output to the printer 16.
[0040]
In this case, the standard print profile 26 constituting the color conversion means 20 uses the supplied CMYK color image data Iin (C, M, Y, K) as colorimetric value data which is device-independent image data. As XYZ colorimetric value data Icv = Icv (X, Y, Z).
[0041]
Of course, the print profile 26 does not convert the image data Iin into the XYZ colorimetric value data Icv, but converts it into Lab colorimetric value data Icv = Icv (L, a, b) that can be mathematically converted to this. It can also be a print profile.
[0042]
The XYZ colorimetric value data Icv converted by the print profile 26 is converted from device-independent image data to device-dependent image data by a printer profile 36 as a printer color conversion unit constituting the color conversion unit 20. Iout = Iout (R, G, B).
[0043]
In addition, four look-up tables (LUTs) for one-dimensional conversion for converting the gradation of the image data Iin for each color of CMYK for each color of CMYK may be inserted before the print profile 26. Further, the print profile 26 Insert a one-dimensional LUT for each colorimetric value XYZ to correct the difference in paper color (ground color) when you want to use the desired print book instead of the standard print book at the subsequent stage. Also good.
[0044]
As shown in FIG. 1, the RGB image data Iout converted by the printer profile 36 constituting the color conversion means 20 is supplied from the host computer 14 to the printer 16 so that the image IM is transferred from the printer 16 onto the image receiving sheet RS. A hard copy HC is output as a proof (proof print) on which is formed.
[0045]
In this embodiment, as the printer 16, for example, light is emitted corresponding to the RGB image data Iout, and on the photosensitive material (not shown) by each RGB laser light that is intensity-modulated according to the RGB image data Iout. A latent image is exposed and recorded by scanning, and water is applied to the photosensitive material on which the latent image is exposed and recorded, and then combined with the image receiving sheet RS, and heat developed and transferred to form a visible image on the image receiving sheet RS. It is used.
[0046]
Next, a procedure for creating a standard print profile (hereinafter also referred to as an original print profile or an original print profile) 26 set in the color conversion unit 20 and a correction method for correcting the original print profile 26 are described. Will be described with reference to the process diagram of FIG. 3 (first embodiment).
[0047]
In order to correct the original print profile 26, the printer profile 36 needs to be calibrated. The calibrated printer profile 36 is created as follows. For each RGB color of the RGB image data Iout supplied to the printer 16, the value is changed in a predetermined increment from 0 value to the maximum value (for example, 255), and as shown in FIG. A patch 40 is formed on the image receiving sheet RS to create a color chart Cpf.
[0048]
Each color patch 40 formed on the color chart Cpf is measured by a colorimeter 42 to obtain XYZ colorimetric value data, and a conversion table of RGB image data and XYZ colorimetric value data (or Lab colorimetric value data) is created. To do. This conversion table is inversely converted and subjected to interpolation processing as necessary, thereby obtaining an LUT for converting XYZ colorimetric value data (colorimetric value data Icv in FIG. 2) into RGB image data Iout. it can. This LUT is set as the printer profile 36 (step S1).
[0049]
Next, a method for creating the original print profile 26 will be described. The original print profile 26 is a colorimetric value table when the CMYK halftone data is changed at a certain step. For example, when creating a table of colorimetric values in 10% increments with CMYK halftone data, 11 for four CMYK colors with halftone values changed to 0, 10,..., 100%. ^Four = It is necessary to obtain colorimetric values for 14641 colors. In practice, however, a film having only a few hundred colors is created by the film printer 4, and then a printing plate is created. The printing plate 7 is used on the standard printing paper Pa using the printing plate. A standard ink is used to print and form a color chart Cpa on which color patches 44 are formed (see FIG. 1), and each color patch 44 is measured by the colorimeter 42 and the colorimetric value table in 10% increments. That is, a standard original print profile 26 [in FIG. 2, non-linear for converting CMYK print image data Iin (C, M, Y, K) into colorimetric value data Icv (X, Y, Z)] A four-dimensional (four-dimensional three-dimensional conversion) LUT] is created (step S2).
[0050]
By using the original print profile 26 and inputting the halftone data C, M, Y, K constituting the print image data Iin = Iin (C, M, Y, K), the XYZ colorimetry is performed. Value data Icv = Icv (X, Y, Z) can be converted.
[0051]
As described above, the original print profile 26 requires extremely large color measurement in order to create a document with high conversion accuracy. For this reason, a standard original print profile 26 is usually provided by the manufacturer. “Standard” means, for example, art paper, coated paper, matte paper, high-quality paper, etc. as the paper type, as well as 2-3 types of ink with a high market share, and as a printing machine Similarly, it means a case where a printing machine 7 having a high market share is used at room temperature.
[0052]
Next, in order to create the original print profile 26, the printer 16 outputs a color chart Cpa ′ similar to the printed color chart Cpa (step S3).
[0053]
In this case, the CMYK halftone data when the printed color chart Cpa is created is converted into CMYK image data (in other words, the color chart measured when the original print profile 26 is created) by the host computer 14. Device-dependent image data for outputting Cpa), and the converted CMYK image data is converted into RGB image data Iout, which is device-dependent image data for the proofer, through the original print profile 26 and printer profile 36. . Based on the RGB image data Iout, the printer 16 outputs a color chart Cpa ′ in which a color patch 44 ′ having the same arrangement as the color patch 44 of the color chart Cpa in printing is formed.
[0054]
The color patches 44 'constituting the color chart Cpa' are measured in the same manner as the original print profile 26 to obtain colorimetric values XYZ (step S4).
[0055]
As a result, the conversion relationship between the CMYK image data of the printer 16 as the printing proofer and the colorimetric values is obtained from the color chart Cpa ′ having the color patch 44 ′, and the print color reproduction profile 26 ′ reproduced by the printer 16 is obtained. It is obtained (step S5).
[0056]
Next, in the entire CMYK space (C is 0 to 255, M is 0 to 255, Y is 0 to 255, and K is 0 to 255), the image data values of the CMYK all space are input. , Output colorimetric values T0 (C, M, Y, K) of the original print profile 26 as a target, and output colorimetric values T1 (C, M, Y) of the print color reproduction profile 26 '. , K) = difference Δ (C, M, Y, K) from X1, Y1, Z1 = T1 (C, M, Y, K) −T0 (C, M, Y, K) = (X1−X0, Y1-Y0, Z1-Z0) are obtained (step S6).
[0057]
Next, considering the color reproduction range of the printer 7 and the color reproduction range of the printer 16, the corrected print profile 26A is obtained by multiplying the difference Δ by a predetermined weight (weight coefficient) w (step S7). ), And is added to the original print profile 26 (subtracted because the sign is actually reversed), and the addition result is set as a corrected print profile (corrected print profile) 26A (step S8).
[0058]
In this case, as indicated by a solid line in the schematic diagram of FIG. 4, the weight w is, for example, a weight w1 that takes a value 1 within the color reproduction range of the printer 16 and takes a value 0 outside the color reproduction range of the printer 16 ( C, M, Y, K) or a weight w2 (C, M, Y) that takes a value that gradually decreases from a value 1 to a value 0 as the distance from the color reproduction range of the printer 16 increases, as indicated by a one-dot chain line. , K). In FIG. 4, the horizontal axis CMYK value of 0% corresponds to the paper value of the image receiving sheet RS of the printer 16, and the horizontal axis CMYK value of 100% corresponds to the ink value of the printing machine 7. To do.
[0059]
The output colorimetric value of the corrected print profile 26A multiplied by the weights w = w1 and w2 set in this way is set as T2 (C, M, Y, K), and the overall output measurement of the corrected print profile 26A is set. When the color value is Tout, for example, the output colorimetric value Tout when the weight w is w = w1 can be obtained by the following equations (1) and (2).
[0060]
Tout = T2 = T0-1 × Δ (within the reproduction range of the printer profile) (1)
Tout = T0 (outside printer profile reproduction range) (2)
As described above, according to the embodiment described above, as shown in the schematic diagram of FIG. 5, each color patch 44 of the color chart Cpa printed by the printing machine 7 is measured by the colorimeter 42 to obtain CMYK image data. The original print profile 26 is created as a target to be the output colorimetric value T0 for converting the colorimetric value data into colorimetric value data.
[0061]
Next, using this original print profile 26 and the printer profile 36 with an output RGB value of P0, a color chart as a proof from the printer 16 using the CMYK image data when the printed color chart Cpa is created. Cpa 'is output.
[0062]
Next, the color chart Cpa 'is color-measured to create a print color reproduction profile 26' having an output colorimetric value T1 when the color chart Cpa printed by the printer 16 is reproduced.
[0063]
Next, in consideration of the color reproduction range of the printing machine 7 and the printer 16, the weights w = w1 and w2 are set, and the output colorimetric value indicated by the above-described equations (1) and (2) becomes Tout. A corrected print profile 26A is created.
[0064]
By setting the corrected print profile 26A and the printer profile 36 as the corrected color conversion means 20A (see FIG. 2) of the host computer 14, the image of the hard copy HC that is the output of the printer 16 becomes the target. Even if the image IM on the color printed material Pm has a different color shift with a plurality of colors having different hues, it is easily corrected by using the corrected color conversion means 20A. Color matching is possible.
[0065]
The above is the description of the first embodiment. In order to facilitate understanding of the second and third embodiments described below, the first embodiment is illustrated in the block diagram of FIG. Based on this, it will be described again as Lab colorimetric values instead of XYZ colorimetric values (in the block diagram of FIG. 6, the blocks enclosed by double squares represent “processing (processing by hardware or software)”, which is a single layer. Each block enclosed by a square represents a “profile” or “table” as storage means).
[0066]
In FIG. 6, a color as a printed matter in which each color patch 44 is formed by performing printing processing (step S <b> 11) by the printing machine 7 (see FIG. 1) based on the chart printing data Ich that is input image data Iin depending on the printing conditions. A chart (print color chart) Cpa is created. Here, the number of chart print data Ich, in other words, the number of color patches 44 is several hundred as described above.
[0067]
Next, each color patch 44 in the printing color chart Cpa is measured by the colorimeter 42 to obtain the printing color chart Lab colorimetric data Lab1 (step S12).
[0068]
Next, an input image that corresponds to the print color chart Lab colorimetric data Lab1 subjected to color measurement and the chart print data Ich for outputting the print color chart Cpa and depends on the print conditions in the entire print color space by interpolation processing. The original print profile 26 having a correspondence relationship with the output colorimetric value data Icv corresponding to the data Iin is created (step S13: corresponding to the process of step S2 above).
[0069]
Next, the chart print data Ich, which is image data depending on the printing conditions for outputting the print color chart Cpa colorimetrically measured when the original print profile 26 is created, is printed with the print profile 26 and the printer profile (proofer profile) 36. Is converted into image data Iout depending on the proofer condition, the image data Iout is supplied to the printer 16 as a proofer, and a proof color chart Cpa ′ is output from the printer 16 (corresponding to the processing in step S3 above). .)
[0070]
Next, each color patch 44 'constituting the proof color chart Cpa' is measured by the colorimeter 42 (step S14: corresponding to the process of step S4), and the measured proof color chart Lab colorimetric data Lab2 is measured. And a print color reproduction profile 26 'in the entire print color space simulated by the printer 16 as a proofer from the chart print data Ich as the input image data Iin are created by the same profile creation process as in step S13 (step S15: This corresponds to the process in step S5).
[0071]
Next, the difference between Lab colorimetric value data Icv = Lab3 and Lab colorimetric value data Lab4 when the print color reproduction profile 26 'and the print profile 26 are passed through the entire input image data Iin depending on the printing conditions. Δ (Lab3−Lab4 = ΔLΔaΔb) is obtained for the entire print color space of the input image data Iin depending on the printing conditions (step S16: corresponding to the processing of step S6).
[0072]
The CMYK image data Iin thus obtained is converted into a difference (difference data) Δ = ΔLΔaΔb of Lab colorimetric value data Icv (CMYK → ΔLΔaΔb), the difference table 51 of the print color space, the original print profile 26, and Is added to the adder 52 to obtain a corrected print profile 26A ', whereby a corrected Lab colorimetric value data Icv' can be obtained for the entire print color space of the input image data Iin. 26A 'can be obtained.
[0073]
In this case, the difference table 51 of the print color space can be used by applying the above-described weighting factor w1 or weighting factor w2.
[0074]
That is, as shown in FIG. 7 as a modification, a table (weight coefficient table) in which a multiplier 60 for the weight coefficient w is inserted between the difference table 51 in the print color space and the adder 52 and the weight coefficient w is stored. 62 can be inserted into the input image data Iin and the multiplier 60. The weighting coefficient table 62 outputs the weighting coefficient w1 or w2 shown in FIG. 4 corresponding to the value of the input image data Iin, and supplies it to the other input of the multiplier 60 in which the difference Δ is supplied to one input. To do.
[0075]
The print color space difference table 51 and the original print profile 26 and the adder 52, or the print color space difference table 51, the original print profile 26, the weighting factor table 62, and the multiplier 60 are added. The printing profile 26A ′ composed of the device 52 can be integrated into one corrected printing profile 26A that can convert the CMYK input image data Iin into the corrected colorimetric value data Icv ′.
[0076]
By using the integrated corrected print profile 26A and printer profile 36, the input image data Iin of the entire print color space can be converted into RGB image data Iout depending on the corrected printer conditions.
[0077]
FIG. 8 is a block diagram for explaining the second embodiment. The example in FIG. 8 is the same as the example in FIG. 6 up to the process before the difference generation process (step S17) as compared with the example in FIG.
[0078]
In the example of FIG. 8 (second embodiment), in the difference generation process in step S17, the corresponding difference Δ in the entire print color space is not obtained as in the difference generation process in step S16, but the entire colorimetric value space. The corresponding difference Δ (the difference Δ corresponding to the Lab colorimetric value data Icv) is obtained.
[0079]
The Lab colorimetric value data Icv thus obtained is converted into differential data Δ = ΔLΔaΔb (Lab → ΔLΔaΔb), the colorimetric color space difference table 53, and the Lab data obtained from the difference data ΔLΔaΔb and the printing profile 26. A modified printer profile 36A ′ composed of an adder 54 for adding the colorimetric value data Icv and the original printer profile 36 is created.
[0080]
According to the printer profile 36A ′, printer-dependent image data Iout can be obtained from the corrected Lab colorimetric value data Icv ″ obtained for the entire colorimetric value color space of the Lab colorimetric value data Icv. .
[0081]
Also in this case, as shown as a modification of FIG. 9, the weighting coefficient table 66 and the multiplier 64 are inserted, and the above-described weighting coefficient w1 or weighting coefficient is added to the colorimetric value color space difference table 53. Can be used over w2. In this case, the horizontal axis of the weighting factors w = w1 and w2 is not the CMYK axis but the Lab axis (see FIG. 4) which is a colorimetric value.
[0082]
Also in this case, the colorimetric value color space difference table 53, adder 54 and printer profile 36, or the colorimetric value color space difference table 53, adder 54, printer profile 36, weight coefficient table 66, and multiplier 64 are used. The Lab colorimetric value data Icv output from the print profile 26 can be integrated into one corrected printer profile 36A that can be converted into image data Iout depending on the corrected printer conditions.
[0083]
By using the original print profile 26 and the integrated printer profile 36A, it is possible to convert the input image data Iin of the entire print color space into RGB image data Iout depending on the corrected printer conditions.
[0084]
FIG. 10 shows a block diagram for explaining the third embodiment. In the first and second embodiments described above, when the difference Δ is obtained, the print color reproduction profile 26 ′ is created and obtained. In this third embodiment, the difference Δ is obtained as the print color reproduction profile. 26 'is not created, in other words, the print color reproduction profile 26' is not used.
[0085]
That is, in the example of FIG. 10 (third embodiment), the entire print color space is directly obtained from the print color chart Lab colorimetric data Lab1 obtained in step S12 and the proof color chart Lab colorimetry data Lab2 obtained in step S14. The difference Δ is obtained.
[0086]
The CMYK image data Iin obtained in this way is converted into colorimetric value data ΔLΔaΔb (CMYK → ΔLΔaΔb). The modified print profile 26A ′ having a configuration in which the difference table 55 of the print color space and the print profile 26 are combined by the combiner 56. Thus, a print profile 26A ″ that can obtain corrected colorimetric value data Icv ″ for the entire print color space of the input image data Iin can be obtained.
[0087]
Also in this case, as shown in the modification of FIG. 11, the weighting coefficient table 70 and the multiplier 68 are inserted, and the weighting coefficient w1 or the weighting coefficient w2 described above is added to the difference table 55 in the print color space. Can be used.
[0088]
10 and 11, the print color space difference table 55 and the original print profile 26 and the combiner 56, or the print color space difference table 55, the original print profile 26, the combiner 56, and the weighting factor table. Each of the print profiles 26A ″ including 70 and the multiplier 68 can be integrated into one corrected print profile 26A.
[0089]
The integrated corrected print profile 26A and printer profile 36 can convert the input image data Iin of the entire print color space into image data Iout (RGB) depending on the corrected printer conditions.
[0090]
In the example of FIG. 11, since the print color reproduction profile 26 'is not created, the profile creation process (step S15) is not required. For example, the algorithm of the profile creation process (steps S13 and S15) uses several hundred input data. Even if the algorithm corresponds to the above, the number of input data is not limited to several hundreds of input data, but when the number of color patches 44 of the color charts Cpa and Cpa ′ is increased, Since the difference table 55 of the printing color space can be created by the difference Δ corresponding to the patch 44, as a result, the color approximated by the printed matter Pm (the printing color reproduction accuracy in the simulation of the printed matter Pm is good). The effect that the copy HC can be created is achieved.
[0091]
【The invention's effect】
As described above, according to the present invention, it is possible to achieve the effect that the proof as the proofer output can easily and surely match the color of the printed matter as the target.
[0092]
Specifically, for example, a color chart corresponding to a printed color chart is output as a proof from a printing proofer. Then, this proof is color-measured to obtain a conversion relationship between device-dependent image data as a printing proofer and colorimetric value data, that is, a proof print profile (also referred to as a print color reproduction profile). Further, the difference between the print color reproduction profile and the original print profile is obtained in the print color space, and the obtained difference is added to the original print profile (subtracting because the sign is reversed). The new print profile (modified print profile).
[0093]
For this reason, by using this modified print profile, the proof color that is the output of the proofer is different from the color of the target printed matter in a plurality of colors that are close in hue. In addition, it is possible to achieve the effect that the color of the proof can be easily and surely matched with the color of the printed matter which is the target that has been difficult to be corrected by the conventional adjustment of the tone curve for each color.
[0094]
In the present invention, when the difference is obtained, it is obtained not in the print color space but in the colorimetric value color space and added to the original proofer profile of the obtained difference (because the sign is reversed, it is actually subtracted). A new proofer profile after correction (modified proofer profile) is used.
[0095]
For this reason, by using this corrected proofer profile, the proof color that is the output of the proofer is different from the color of the printed matter that is the target in different colors with different colors. In this case, it is possible to easily and surely match the color of the proof with the color of the target printed matter, which has been difficult to correct by adjusting the tone curve for each color.
[0096]
Further, according to the present invention, a color chart corresponding to the printed color chart for creating a print profile is output as a proof from the printing proofer. Then, the color of the proof and the printed color chart are measured to obtain a difference between colorimetric values in the print color space, and the obtained difference is added to the original print profile (the sign is reversed, so the subtraction is actually performed). .) Is used as a new print profile after correction (corrected print profile).
[0097]
Even with this configuration, when the color of the proof, which is the output of the proofer, is different from the color of the printed matter that is the target, the tone curve for each of the conventional colors is different. Thus, the effect that the color of the proof can be easily and surely matched with the color of the target printed matter, which has been difficult to be corrected by the adjustment of (5), is achieved.
[0098]
As described above, the color correction method according to the present invention is suitable for use in simulating the color of a printed matter created by a printing machine with a color reproduction accuracy with a proofer such as a printer before actual printing processing. .
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration including a print proof creation system to which an embodiment of the present invention is applied.
FIG. 2 is a block diagram showing a configuration of color conversion means.
FIG. 3 is a process diagram used for explaining the operation of the embodiment of the invention.
FIG. 4 is a diagram for explaining changing a weight according to a difference in a color reproduction range.
FIG. 5 is a diagram for schematically explaining the configuration of the embodiment of the present invention;
FIG. 6 is a block diagram for explaining the configuration of the first embodiment;
FIG. 7 is a block diagram for explaining a configuration of a modified example of the first embodiment;
FIG. 8 is a block diagram for explaining a configuration of a second embodiment;
FIG. 9 is a block diagram for explaining a configuration of a modified example of the second embodiment;
FIG. 10 is a block diagram for explaining a configuration of a third embodiment;
FIG. 11 is a block diagram for explaining a configuration of a modified example of the third embodiment.
[Explanation of symbols]
2 ... Color scanner 4 ... Film printer
6 ... Electronic plate collector 7 ... Printer
8. Color image recording device 10. Print proof creation system
12 ... workstation 14 ... host computer
16 ... Printer (printing proofer) 20 ... Color conversion means
20A: Color conversion means after correction 26: Original print profile
26 '... Print color reproduction profile reproduced by printer
26A, 26A ′, 26A ″... Print profile after correction
36 ... Printer Profile
36A, 36 '... Printer profile after correction
44, 44 '... color patch
Cpf Color chart (for printer profile creation)
Cpa ... printed color chart
Cpa '... Color chart reproduced by the printer
IM ... Image HC ... Hard copy
Pa ... Main printing paper Pm ... Color printed matter
RS ... Sheet

Claims (11)

After the input image data that depends on the printing conditions is converted to colorimetric value data by the print profile, the colorimetric value data is converted to image data that depends on the proofer conditions by the proofer profile, and the proofing is performed from the proofer by the image data. In a color correction method for improving color reproduction accuracy in a system that outputs and simulates print color reproduction,
Converting image data dependent on printing conditions for outputting a printing color chart measured at the time of creating the printing profile into image data depending on proofer conditions via the printing profile and the proofer profile;
Supplying the image data to the proofer and outputting a proof color chart from the proofer;
Measuring the proof color chart to create a print color reproduction profile simulated by the proofer;
Obtaining a difference between the print color reproduction profile and the print profile for the entire color space of the input image data depending on the printing conditions;
And a step of correcting the colorimetric value data using the obtained difference. The color correction method according to claim 1,
In the step of correcting the colorimetric value data using the obtained difference,
A color correction method comprising: correcting the print profile by adding the obtained difference to the print profile, and correcting the colorimetric value data by the corrected print profile. The color correction method according to claim 1,
In the step of correcting the colorimetric value data using the obtained difference,
Multiplying the obtained difference by a weighting factor depending on the value of the input image data depending on the printing conditions in the entire color space, and adding the difference multiplied by the weighting factor to the printing profile to correct the printing profile; A color correction method comprising the step of correcting the colorimetric value data with the corrected print profile. After the input image data that depends on the printing conditions is converted to colorimetric value data by the print profile, the colorimetric value data is converted to image data that depends on the proofer conditions by the proofer profile, and the proofing is performed from the proofer by the image data. In a color correction method for improving color reproduction accuracy in a system that outputs and simulates print color reproduction,
Converting image data dependent on printing conditions for outputting a printing color chart measured at the time of creating the printing profile into image data depending on proofer conditions via the printing profile and the proofer profile;
Supplying the image data to the proofer and outputting a proof color chart from the proofer;
Measuring the proof color chart to create a print color reproduction profile simulated by the proofer;
Obtaining a difference between the print color reproduction profile and the print profile for the entire colorimetric value color space which is a color space of the colorimetric value data;
And a step of correcting the image data depending on the proofer condition using the obtained difference. The color correction method according to claim 4.
In the step of correcting the image data depending on the proofer condition using the obtained difference,
Corrected colorimetric value data in the colorimetric value color space is obtained from the obtained difference and the print profile, the proofer profile is corrected by the corrected colorimetric value data, and the proofer condition is set by the corrected proofer profile. A color correction method comprising the step of correcting dependent image data. The color correction method according to claim 4.
In the step of correcting the image data depending on the proofer condition using the obtained difference,
Corrected calorimetric value data in the colorimetric value color space is obtained from the obtained difference and the print profile, and corrected colorimetric value data obtained by multiplying the corrected calorimetric value data by a weighting factor depending on the colorimetric value color space. A color correction method comprising: correcting the proofer profile by the step of correcting image data depending on the proofer condition by the corrected proofer profile. After the input image data that depends on the printing conditions is converted to colorimetric value data by the print profile, the colorimetric value data is converted to image data that depends on the proofer conditions by the proofer profile, and the proofing is performed from the proofer by the image data. In a color correction method for improving color reproduction accuracy in a system that outputs and simulates print color reproduction,
Converting image data dependent on printing conditions for outputting a printing color chart measured at the time of creating the printing profile into image data depending on proofer conditions via the printing profile and the proofer profile;
Supplying the image data to the proofer and outputting a proof color chart from the proofer;
Measuring the proof color chart to obtain colorimetric value data; and
Obtaining a difference between the colorimetric value data of the print color chart and the colorimetric value data of the proof color chart for the entire color space of the input image data depending on the printing conditions;
And a step of correcting the colorimetric value data using the obtained difference. The color correction method according to claim 7.
In the step of correcting the colorimetric value data using the obtained difference,
A color correction method comprising: correcting the print profile by adding the obtained difference to the print profile, and correcting the colorimetric value data using the corrected print profile. The color correction method according to claim 7.
Multiplying the obtained difference by a weighting factor depending on the value of the input image data depending on the printing conditions in the entire color space, and adding the difference multiplied by the weighting factor to the printing profile to correct the printing profile; A color correction method, wherein the colorimetric value data is corrected by the corrected print profile. The color correction method according to any one of claims 3, 6, and 9,
The color correction method according to claim 1, wherein the weighting factor is a value 1 in a color reproduction range of the printing proofer and a value 0 in a range other than the color reproduction range. The color correction method according to any one of claims 3, 6, and 9,
The color correction method according to claim 1, wherein the weighting factor is set to a value of 1 in the color reproduction range of the printing proofer, and gradually decreases from the value of 1 as the distance from the color reproduction range increases.

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