JP2000278547A - Color correction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and surely watch a proof color by a proofer with a color of a printed matter by obtaining a difference between a printed color reproduction profile and a printing profile for an entire color space of input image data that depends upon a printing condition and correcting color measurement value data by using the obtained difference. SOLUTION: Each color patch 44 of a printed color chart Cpa is measured by a colorimeter and an original printing profile 26 which becomes an output value T0 for converting CMYK image data into color measurement value data is prepared. Next, a printer profile 36 where a RGB value of this original printing profile 26 output becomes P0 is used and a color chart Cpa' as a proof is outputted from a printer by CMYK image data of the time when the printed color chart Cpa is prepared. Then, this color chart Cpa' is color measured and a printing color reproduction profile 26', in which an output color measurement value becomes T1 when the printed color chart Cpa is reproduced, is prepared.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color printing proof in which a color image for proofing is formed on a proofing paper before a color print is produced by using a printing press by a color printing machine utilizing a rotary press or the like. The present invention relates to a color correction method suitable for application to a print proof creation system that creates color print proofs or proofs or simply proofs with a print proofer (also simply referred to as proofer) such as a color printer.

[0002]

2. Description of the Related Art Conventionally, a color image by a halftone image as a product is printed on a printing paper (official paper as a final product). Proof prints are created by a printing proofer such as a color printer as an image output device.

[0003] The use of a printing proofer does not require the production of a plate-making film or a printing plate (PS plate) as in a printing machine, and a color image can be easily formed on a proof paper (recording sheet) several times in a short time. This is because a formed hard copy, that is, a proof print can be created.

In order to form a color image for proofing on proof paper, image data depending on a device [printing (ink, printing machine, paper, etc.), photograph, image sensor, CRT, LED, etc.], for example, CMYK ( Cyan, magenta,
Yellow, black) colorimetric data, which is device-independent image data, for example, a Lab image, according to a standard print profile (such as a four-dimensional lookup table) given in advance by a maker or the like. After converting the data into XYZ image data that can be mathematically converted with the data, the color is converted by a proofer profile for printing (hereinafter, also simply referred to as a proofer profile), for example, a printer profile (three-dimensional lookup table). Device-dependent image data for the printer, eg, R
The image data is converted into GB (red, green, blue) image data, and a proof print (proof) in which a color image is formed on proof paper by a color printer (also referred to as a proof printer) is created using the device-dependent image data. I am trying to do it.

[0005] In this manner, the color of the printed matter relating to the printing press can be simulated by the proof printing (proof) of the color printer and confirmed in a process prior to the actual printing.

[0006]

Since the color reproduction range of the printing proofer differs from the color reproduction range of the printing proofer, the range that cannot be reproduced by the printing proofer is gamut mapping (color reproduction range). mapping)
Links the print profile and the proofer profile.

When a proof whose color corresponds to a target printed matter is output from a printing proofer by using the linked profile as described above, if the color matching is not sufficient partially, the preceding stage of the linked profile is used. Fine adjustment of gradation adjustment (tone curve adjustment) is performed on each of the device-dependent image data CMYK.

[0008] However, this fine adjustment requires time and effort because it is not clear where and how much to correct the color misregistration. There is a problem that it may not be possible.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has been made in consideration of the above-described problems, and has been made in consideration of the above circumstances. The aim is to provide a method.

[0010]

According to the present invention, after converting input image data depending on printing conditions into colorimetric value data by a print profile, the colorimetric value data is converted into an image dependent on proofer conditions by a proofer profile. In a color correction method for improving color reproduction accuracy in a system that simulates print color reproduction by outputting a proof from a proofer based on the image data and outputting a proof from the proofer, a print color chart measured at the time of creating the print profile is output. Converting the image data depending on the printing condition into image data depending on the proofer condition via the print profile and the proofer profile, and supplying the image data to the proofer, and proof color from the proofer. Outputting a chart; Creating a print color reproduction profile simulated by the proofer by measuring the color of the proof color chart; and calculating the difference between the print color reproduction profile and the print profile over the entire color space of the input image data depending on the print conditions. And a step of correcting the colorimetric value data using the obtained difference (the invention according to claim 1).

According to the present invention, a color chart for creating a print profile is output from a proofer as a proof. The color of this proof is measured in the same manner as the original print profile, and a conversion relationship between image data and colorimetric value data depending on the proof condition, that is, a print profile (print color reproduction profile) is obtained. Then, a 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 condition, and the print profile is output using the obtained difference. The colorimetric data is corrected.

By correcting the colorimetric data in this way, it is not necessary to adjust the tone curve for each color, and the color of the proof can be easily and reliably matched to the color of the target printed matter.

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 (actually subtraction because the sign is reversed). Is set as a new print profile after correction (corrected print profile). By using this modified print profile, it is not necessary to adjust the tone curve for each color without using extra memory, etc. as storage means, and the proof color can be easily and reliably matched to the target print. (The invention according to claim 2).

[0014] Further, a value obtained by multiplying the difference by a weight coefficient depending on a value of input image data depending on a printing condition in the entire color space (a difference obtained by multiplying the weight coefficient) is added to the original print profile. By using the corrected print profile, it is possible to more accurately match colors (the invention according to claim 3).

The difference between the print color reproduction profile and the print profile is not calculated for the entire color space of the input image data depending on the printing conditions, but the colorimetric value which is the color space of the colorimetric value data is used. By obtaining the entire value color space, instead of correcting the colorimetric value data, the obtained difference may be used to correct the image data depending on the proofer condition. Invention).

In this case, corrected colorimetric value data in the colorimetric color space is obtained from the obtained difference and the print profile, and the proofer profile is corrected with the corrected colorimetric data. By correcting the image data depending on the proofer condition, the proofer that matches the target print can be output from the proofer only by correcting the proofer profile without correcting the print profile ( The invention according to claim 5).

Also 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 the corrected colorimetric value data and correcting the image data depending on the proofer condition with the corrected proofer profile, it is possible to more accurately match colors. (Claim 6)
Described invention).

Further, according to the present invention, the difference between the colorimetric value data obtained by measuring the color of the proof color chart and the colorimetric value data of the print color chart is calculated based on the entire color space of the input image data depending on the printing conditions. , And the colorimetric value data may be corrected using the obtained difference (the invention according to claim 7).

According to the present invention, there is no need to create a print color reproduction profile.

In this case, it is also possible to correct the print profile based on the difference, and to correct the colorimetric value data using the corrected print profile.

Further, the difference is multiplied by a weight coefficient depending on the value of the input image data depending on the printing condition in the entire color space, and the difference obtained by multiplying the weight coefficient is added to the print profile to correct the print profile. Then, the colorimetric value data can be corrected using the corrected print profile (the invention according to claim 9).

Further, the weighting factor is set to a value of 1 in the color reproduction range of the printing proofer, and to a value of 0 in a range other than the color reproduction range (the invention according to claim 10). By setting the value to 1 in the color reproduction range of the proofer, and by gradually decreasing the value from the value 1 as the distance from the color reproduction range increases (the invention according to claim 11), it is possible to more accurately match colors. You have the potential to do it.

[0023]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic overall configuration of a print proof creating system 10 to which an embodiment of the present invention is applied.

The print proof creating 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.

The electronic collecting device 6 includes a workstation (W / S) 12 as a main body of the electronic collecting device.
The / S12 is connected to a color scanner 2 functioning as an image input device, a film printer 4 for outputting CMYK4 plate originals, and the like.

On the other hand, the color image recording device 8 stores a host computer (H / C) 14 which stores a printing profile and a printer profile to be described later and mainly functions as a color conversion means, and a proof image output device (proof printing output). And a printer 16 functioning as an apparatus or a printing proofer or simply a proofer.)

The W / S 12 and the host computer 14 each include a display as a display device (not shown), a main body having a CPU / memory (storage means), and a keyboard and mouse as input devices. I have.

The color scanner 2 connected to the W / S 12 reads an original image on an underlaying board (not shown) on which a rule, which is a range into which characters and photographs are inserted, is written, and also reads other images. A color image such as a picture, a character, or a figure is read from the document image, and image data (device-dependent image data) after four-color (CMYK) color separation is sent to the W / S 12.

The W / S 12 displays the copyboard image read by the color scanner 2 on a display.
The user electronically collects an image based on the image data using the keyboard and the mouse on the copy mount image, and creates an electronic copy image for one page, a so-called imposition pattern.

Data representing the imposition pattern is supplied to the film printer 4. The film printer 4 outputs a high-quality CMYK printing original film corresponding to the imposition pattern data.

Usually, a printing plate is prepared from the printing film original plate, and the prepared printing plate is mounted on a rotary press, that is, a printing press 7, and ink is applied thereto. Then, the ink applied to the printing plate is transferred to the printing paper Pa, and the color print Pm on which the image IM is formed is completed.

In this case, the operation of producing the color print Pm using the printing machine 7 is an extremely large-scale operation, and the cost is high. For this reason, the 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 machine 7.

Therefore, an image edited and collected by using the W / S 12 has description language data (descriptive language) describing one page of image information including position information, color information (including density information), and the like. PDL (Page Des
The data is supplied to the host computer 14 as cription language) data.

The host computer 14 performs a color conversion process and the like, and supplies the image data subjected to the color conversion process and the like to a printer (also referred to as a printing proofer body or proofer) 16.

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 an image IM on the image receiving sheet RS.

FIG. 2 shows a schematic configuration of a main function of the host computer 14. The host computer 14 functions as a color conversion unit 20. That is, the host computer 14 receives the P supplied from the W / S 12.
Raster image processor (R
The data is decoded by IP) and developed into a bitmap, and developed into CMYK image data (device-dependent image data), which are each scanned image data.

Each of the CMYK image data is
The print profile 26 and the printer profile 36, which are LUTs (look-up tables) for color conversion, are supplied to the color conversion means 20 in which they are set.

The color conversion means 20 inputs device-dependent image data, in this case, image data depending on printing conditions, for example, CMY each of which is halftone% data.
Image data of each K color Iin = Iin (C, M, Y, K)
Is image data that depends on proofer conditions that are device-dependent image data [In this embodiment, image data that depends on printer conditions, for example, image data of each color of RGB (hereinafter, also simply referred to as RGB image data) Iou.
t = Iout (R, G, B)] and then output to the printer 16.

In this case, the standard print profile 26 constituting the color conversion means 20 converts the supplied CMYK color image data Iin (C, M, Y, K) into device-independent image data. XYZ colorimetric value data as color value data Icv = Icv (X, Y, Z) is converted.

Of course, the print profile 26 does not convert the image data Iin into XYZ colorimetric value data Icv, but Lab colorimetric value data Icv = Icv (L, a, b) ) Can be used as the print profile.

X converted by the print profile 26
The YZ colorimetric value data Icv is stored in a printer profile 3 as a printer color conversion unit constituting the color conversion unit 20.
6, RGB image data Iout = Iou which is device-dependent image data from device-independent image data
Converted to t (R, G, B).

Note that, before the print profile 26, C
Four one-dimensional conversion look-up tables (LUTs) for performing tone conversion of the image data Iin of each color of MYK for each color of CMYK may be inserted. Alternatively, a one-dimensional LUT for correcting a difference in paper color (ground color) when a desired printing paper is to be used may be inserted for each colorimetric value XYZ.

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 as shown in FIG. 1, so that the printer 16 outputs a hard copy HC as a proof (proof print) in which the image IM is formed on the image receiving sheet RS. .

In this embodiment, the printer 16 emits light corresponding to, for example, RGB image data Iout, and receives light (not shown) using RGB laser light intensity-modulated in accordance with the RGB image data Iout. A latent image is exposed and recorded by scanning over the material, and water is applied to the photosensitive material on which the latent image has been exposed and recorded. Then, the latent image is combined with the image receiving sheet RS, and thermally developed and transferred to form a visible image on the image receiving sheet RS. Is used.

Next, a method of 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 means 20,
The procedure of a correction method for correcting the original print profile 26 will be described with reference to the process chart of FIG. 3 (first embodiment).

To correct the original print profile 26, it is necessary that the printer profile 36 be calibrated. The calibrated printer profile 36 is created as follows. For each of the RGB colors of the RGB image data Iout supplied to the printer 16, the value is changed from a value of 0 to a maximum value (for example, 255) at predetermined intervals, and as shown in FIG. The patch 40 is formed on the image receiving sheet RS to create the color chart Cpf.

Each color patch 40 formed on the color chart Cpf is measured by a colorimeter 42 to obtain XYZ colorimetric value data, and conversion between RGB image data and XYZ colorimetric value data (or Lab colorimetric value data). Create a table. By inverting this conversion table and performing interpolation processing as necessary, an LUT for converting XYZ colorimetric data (colorimetric data Icv in the example of FIG. 2) to RGB image data Iout can be obtained. it can. This LUT is set as the printer profile 36 (step S
1).

Next, a method of creating the original print profile 26 will be described. The original print profile 26 is CMYK
3 is a colorimetric value table when halftone% data of the color data is changed at certain intervals. For example, to create a table of colorimetric values in 10% increments using CMYK halftone% data, 11 ⁴ = 14641 colors for four CMYK colors with halftone% values changed to 0, 10,..., 100% It is necessary to determine the colorimetric value of the minute. However, in actuality, a film having only a few hundred characteristic colors is created by the film printer 4 and then,
A printing plate is prepared, and the printing machine 7 uses the printing plate to print color patches 44 on standard printing paper Pa using standard ink.
Is formed as a color chart Cpa on which color patches are formed (see FIG. 1). Each color patch 44 is measured by a colorimeter 42, and the colorimetric value table in increments of 10%, that is, the standard original print profile 26 [ In FIG. 2, CMYK
Non-linear data for converting print image data Iin (C, M, Y, K) into colorimetric value data Icv (X, Y, Z)
LUT] (step S2).

Using the original print profile 26, the print image data Iin = Iin (C, M, Y,
By inputting each halftone% data C, M, Y, and K constituting K), XYZ colorimetric value data Icv = Icv (X,
Y, Z).

As described above, the original print profile 26 is
Extremely large-scale colorimetry is required to create a product with good 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 paper types, and two or three types of inks having a high market share as inks, and further as a printing machine. Similarly, this means a case where the printing press 7 having a high market share is used at room temperature.

Next, a color chart Cpa 'similar to the printed color chart Cpa is output from the printer 16 to create the original print profile 26 (step S3).

In this case, the printed color chart Cpa
Of the CMYK halftone% data at the time of creating the original print profile 26, that is, device-dependent data for outputting the color chart Cpa measured at the time of creation of the original print profile 26. Image data), and the converted C
The MYK 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. Then, based on the RGB image data Iout, the printer 16 outputs a color chart Cpa 'in which color patches 44' having the same arrangement as the color patches 44 of the color chart Cpa in printing are formed.

The color patches 44 'forming the color chart Cpa' are measured in the same manner as the original print profile 26 to obtain colorimetric values XYZ (step S4).

Thus, the conversion relationship between the CMYK image data of the printer 16 as a printing proofer and the colorimetric values is obtained from the color chart Cpa 'having the color patches 44', and the printing color reproduction profile reproduced by the printer 16 is obtained. 26 'is obtained (step S5).

Next, the entire CMYK space (C is 0 to 255,
Output colorimetry of the original print profile 26 as a target obtained by inputting the image data values of the entire CMYK space when M is 0 to 255, Y is 0 to 255, and K is 0 to 255). Value T0 (C, M, Y, K) =
X0, Y0, Z0 and output colorimetric value T1 (C, M, Y, K) of print color reproduction profile 26 '= X1, Y1, Z1
Δ (C, M, Y, K) = T1 (C, M, Y,
K) -T0 (C, M, Y, K) = (X1-X0, Y1-
Y0, Z1-Z0) are obtained (step S6).

Next, the color reproduction range of the printing press 7 and the printer 1
Print profile 2 after correction taking into account the color gamut of
6A, a predetermined weight (weight coefficient) w is assigned to the difference Δ.
(Step S7), and the result is added to the original print profile 26 (subtracted because the sign is actually reversed).
The result of the addition is defined as a corrected print profile (corrected print profile) 26A (step S8).

In this case, as shown by the solid line in the schematic diagram of FIG. 4, for example, the weight w takes a value of 1 within the color reproduction range of the printer 16 and a value of 0 outside the color reproduction range of the printer 16.
Weight w1 (C, M, Y, K), or weight w2 (as shown by a dashed-dotted line) whose value gradually decreases from value 1 to value 0 as the distance from the color reproduction range of the printer 16 increases. C, M, Y, K). In FIG. 4, a value of 0% of the value of the horizontal axis CMYK corresponds to a value of the paper of the image receiving sheet RS of the printer 16, and the value of the horizontal axis CMYK is 0%.
A value of 100% corresponds to the value of the ink of the printing press 7.

The output colorimetric value of the corrected print profile 26A multiplied by the weights w = w1 and w2 set as described above is set as T2 (C, M, Y, K), and the entire corrected print profile 26A is set. Is set to Tout, for example, when the weight w is w = w1, the output colorimetric value To
ut can be obtained by the following equations (1) and (2).

Tout = T2 = T0−1 × Δ (within the reproduction range of the printer profile) (1) Tout = T0 (out of the reproduction range of the printer profile) (2) According to the above-described embodiment, As shown in the schematic diagram of FIG. 5, the output colorimeter converts the CMYK image data into colorimetric value data by measuring the color of each color patch 44 of the color chart Cpa printed by the printer 7 with the colorimeter 42. An original print profile 26 as a target having the value T0 is created.

Next, the original print profile 26,
Using the printer profile 36 whose output RGB value is P0, the printer 16 outputs a color chart Cpa 'as a proof from the CMYK image data when the printed color chart Cpa is created.

Next, the color chart Cpa ′ is measured and the color chart Cpa ′ printed by the printer 16 is measured.
A print color reproduction profile 26 'in which the output colorimetric value when pa is reproduced is T1 is created.

Next, weights w = w1 and w2 are set in consideration of the color reproduction range of the printing press 7 and the printer 16, and the output colorimetric values shown by the above equations (1) and (2) are calculated. Tout
Then, a modified print profile 26A is created.

By setting the corrected print profile 26A and the printer profile 36 as the corrected color conversion means 20A of the host computer 14 (see FIG. 2), the hard copy H output from the printer 16 is output.
C is the image I on the target color print Pm
Even if a plurality of colors having different hues are different from each other with respect to M, the corrected color conversion means 2
The use of 0A allows for easily corrected color matching.

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 will be described with reference to FIG. Based on the block diagram, description will be made again as Lab colorimetric values instead of XYZ colorimetric values (in the block diagram of FIG. 6, blocks surrounded by double squares indicate "processing (processing by hardware or software)"). The blocks enclosed by single squares represent "profiles" or "tables" as storage means, respectively.)

In FIG. 6, a printing process (step S1) is performed by the printing machine 7 (see FIG. 1) based on the chart print data Ich which is the input image data Iin depending on the printing conditions.
1) is performed to create a color chart (print color chart) Cpa as a printed matter on which each color patch 44 is formed. Here, the number of the chart print data Ich, in other words, the number of the color patches 44 is several hundred as described above.

Next, the color patches 44 in the print color chart Cpa are measured by the colorimeter 42 to obtain the print color chart Lab colorimetric data Lab1 (step S1).
2).

Next, the measured print color chart Lab
Output colorimetric value data corresponding to the colorimetric data Lab1 and the chart print data Ich for outputting the print color chart Cpa, and corresponding to the input image data Iin depending on the print conditions in the entire print color space by interpolation processing. Ic
An original print profile 26 corresponding to v is created (step S13: corresponding to the process of step S2).

Next, chart print data Ich, which is image data depending on print conditions for outputting a print color chart Cpa measured at the time of creation of the original print profile 26, is transmitted to the print profile 26 and the printer profile (proofer). The image data Iout is converted into image data Iout depending on the proofer condition via the profile 36, and the image data Iout is supplied to the printer 16 as a proofer, and the proof color chart Cpa 'is output from the printer 16 (the processing in the step S3). Corresponding to.).

Next, the proof color chart Cp
The color patches 44 'constituting a' are measured by the colorimeter 42 (step S14: corresponding to the process of step S4), and the measured proof color chart Lab colorimetric data Lab2 and the input image data Iin are used. A printer 16 which is a proofer from a certain chart print data Ich
A print color reproduction profile 26 'for the entire print color space simulated in (1) is created by the same profile creation processing as in step S13 (step S15: corresponding to the above-described step S5).

Next, 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. Then, a difference Δ (Lab3−Lab4 = ΔLΔaΔb) is obtained for the entire printing color space of the input image data Iin depending on the printing conditions (step S16: corresponding to the processing in step S6).

The CMYK image data Iin thus obtained is converted into a difference (difference data) Δ = ΔLΔaΔb of the Lab colorimetric value data Icv (CMYK → ΔLΔa).
Δb) By making a correction print profile 26A 'configured to add the difference table 51 of the print color space and the original print profile 26 by the adder 52, the entire print color space of the input image data Iin is corrected. Lab
A print profile 26A 'from which the colorimetric value data Icv' can be obtained can be obtained.

In this case, the printing color space difference table 51
Can be used by multiplying the weight coefficient w1 or the weight coefficient w2 described above.

That is, as shown as a modified example in FIG. 7, a multiplier 60 for the weight coefficient w is inserted between the difference table 51 of the print color space and the adder 52 to store the weight coefficient w (weight table). (Coefficient table) 62 can be inserted into the multiplier 60 with the input image data Iin. The weight coefficient table 62 outputs the weight coefficient w1 or w2 shown in FIG. 4 corresponding to the value of the input image data Iin, and supplies the weight coefficient w1 or w2 to the other input of the multiplier 60 in which the difference Δ is supplied to one input. I do.

The print color space difference table 51, the print profile 26A 'comprising the original print profile 26 and the adder 52, or the print color space difference table 51
The print profile 26A 'including the original print profile 26, the weight coefficient table 62, the multiplier 60, and the adder 52 can convert the CMYK input image data Iin into corrected colorimetric value data Icv'1. Into the two modified print profiles 26A.

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 the corrected RGB image data Iout depending on the printer conditions. .

FIG. 8 is a block diagram used for explaining the second embodiment. The example of FIG. 8 is the same as the example of FIG. 6 up to the processing before the difference generation processing (step S17) as compared with the example of FIG.

In the example of FIG. 8 (second embodiment), in the difference generation processing in step S17, the corresponding difference Δ is not determined in the entire print color space as in the difference generation processing in step S16, but the colorimetry is performed. The corresponding difference Δ in the entire value space
(Difference Δ corresponding to Lab colorimetric value data Icv).

The Lab colorimetric value data Icv obtained in this way is converted into difference data Δ = ΔLΔaΔb (L
ab → ΔLΔaΔb) Colorimetric value color space difference table 53
Then, an adder 54 for adding the difference data ΔLΔaΔb and the Lab colorimetric value data Icv obtained from the print profile 26, and a modified printer profile 36A ′ including the original printer profile 36 are created.

According to the printer profile 36A ', the corrected Lab colorimetric value data Icv "obtained for the entire colorimetric color space of the Lab colorimetric value data Icv.
Printer-dependent image data Iout.

In this case as well, as shown as a modification of FIG. 9, the weighting coefficient table 66 and the multiplier 64 are inserted, and the weighting coefficient w1 is added to the difference table 53 of the colorimetric value color space. Alternatively, the weight coefficient w2 can be used. Note that the weight coefficient w in this case is
The horizontal axis of = w1, w2 is not the CMYK axis but the colorimetric value, for example, the Lab axis (see FIG. 4).

Also in this case, the colorimetric value color space difference table 53, the adder 54, and the printer profile 3
6, or a colorimetric value color space difference table 53, an adder 54, a printer profile 36, and a weight coefficient table 6.
6 and the multiplier 64 integrate the Lab colorimetric value data Icv output from the print profile 26 into one corrected printer profile 36A that can convert the corrected colorimetric data Iout depending on the printer conditions. Can be.

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.

FIG. 10 is a block diagram used for explaining the third embodiment. In the above-described first and second embodiments, when calculating the difference Δ, the print color reproduction profile 26 ′ is created and determined.
In the embodiment, the difference Δ is not created in the print color reproduction profile 26 ′, in other words, the print color reproduction profile 2
6 'is obtained without using 6'.

That is, the example of FIG. 10 (third embodiment)
Then, the print color chart La obtained in step S12
The difference Δ in the entire print color space is directly obtained from the b color measurement data Lab1 and the proof color chart Lab color measurement data Lab2 obtained in step S14.

The CMYK image data Iin thus obtained is converted into colorimetric value data ΔLΔaΔb (CMY
K → ΔLΔaΔb) By correcting the difference table 55 of the print color space and the print profile 26 with the corrected print profile 26A ″ configured to be synthesized by the synthesizer 56, the entire print color space of the input image data Iin is corrected. It is possible to obtain a print profile 26A "from which the obtained colorimetric value data Icv""can be obtained.

Also in this case, as shown in the modification of FIG. 11, the weight coefficient table 70 and the multiplier 68 are inserted, and the above-described weight coefficient w1 or weight It can be used by multiplying by a coefficient w2.

As shown in FIGS. 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 and the combiner 56, Print profile 2 including weight coefficient table 70 and multiplier 68
6A '' can each be integrated into one modified print profile 26A.

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.

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) is several hundred. Is not limited to the hundreds of input data even if the number of color patches 44 of the color charts Cpa and Cpa 'is increased, Since the difference table 55 of the print color space can be created based on the difference Δ corresponding to the entire patch 44, as a result, the color is approximated to the print Pm (the print color reproduction accuracy in the simulation of the print Pm is reduced). (Good) The effect that the hard copy HC can be created is achieved.

[0091]

As described above, according to the present invention, the effect that the proofer output, which is the proofer output, can be easily and surely made to exactly match the color of the target printed matter can be achieved.

Specifically, for example, a color chart corresponding to the printed color chart is output as a proof from the printing proofer. Then, the proof is measured to obtain a conversion relationship between device-dependent image data as a printing proofer and colorimetric value data, that is, a printing profile of the proof (also referred to as a printing color reproduction profile). Further, a difference between the print color reproduction profile and the original print profile is obtained in a print color space, and the obtained difference is added to the original print profile (actually subtracted because the sign is reversed). Has a new print profile (corrected print profile).

Therefore, by using the corrected print profile, the color of the proof, which is the output of the proofer, differs from the color of the target printed matter by a plurality of colors having close hues. In this case, it is possible to easily and reliably match the color of the proof with the color of the target print, which has been difficult to correct by the conventional adjustment of the tone curve for each color. You.

Further, according to the present invention, when the above difference is obtained, the difference is obtained not in the print color space but in the colorimetric color space, and the obtained difference is added to the original proofer profile (in practice, the difference is subtracted because the sign is reversed). .) New proofer profile after modification (modified proofer profile)
I have to.

Therefore, by using the proofer profile after the correction, the proof color which is the output of the proofer is different from the color of the target printed matter by a plurality of colors having close hues to different colors. In this case, it is possible to easily and reliably match the color of the proof with the color of the target print, which has been difficult to correct by the conventional adjustment of the tone curve for each color. Is done.

Further, according to the present invention, a color chart corresponding to a printed color chart for creating a print profile is output as a proof from a printing proofer. Then, the color difference between the proof and the printed color chart is measured to determine the difference between the colorimetric values in the print color space, and the obtained difference is added to the original print profile (the sign is actually reversed, so the subtraction is actually performed). .) Is changed to a new print profile after correction (corrected print profile).

According to this configuration, even when the proof color output from the proofer is different from the target print color in a plurality of colors having close hues and different colors, the conventional proofer color In the color of the printed material, which was difficult to correct by adjusting the tone curve of
The effect that the colors of the proof can be easily and surely matched is achieved.

As described above, the color correction method according to the present invention is used for simulating the color of a printed matter created by a printing machine with a color proofer with a proofer such as a printer before the actual printing process. It is suitable.

[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 illustrating a configuration of a color conversion unit.

FIG. 3 is a process chart for explaining the operation of the embodiment of the present 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 schematically illustrating a configuration of an embodiment of the present invention.

FIG. 6 is a block diagram used for describing the configuration of the first embodiment.

FIG. 7 is a block diagram used for describing the configuration of a modification of the first embodiment.

FIG. 8 is a block diagram used for describing the configuration of a second embodiment.

FIG. 9 is a block diagram used to describe the configuration of a modification of the second embodiment.

FIG. 10 is a block diagram used to describe the configuration of a third embodiment.

FIG. 11 is a block diagram used for describing the configuration of a modification of the third embodiment.

[Explanation of symbols]

2 Color scanner 4 Film printer 6 Electronic collecting device 7 Printing machine 8 Color image recording device 10 Print proof creation system 12 Workstation 14 Host computer 16 Printer (printer proofer) 20 Color conversion Means 20A: Corrected color conversion means 26: Original print profile 26 ': Print color reproduction profile reproduced by the printer 26A, 26A', 26A "... Corrected print profile 36: Printer profile 36A, 36 '... Printer profile after correction 44, 44 ': Color patch Cpf: Color chart (for creating printer profile) Cpa: Printed color chart Cpa': Color chart reproduced by printer IM: Image HC: Hard copy Pa: Print paper Pm: empty Printed material RS ... sheet

Claims (11)

[Claims] 1. An image processing method comprising: converting input image data depending on printing conditions into colorimetric value data according to a print profile; converting the colorimetric value data into image data depending on proofer conditions using a proofer profile; In a color correction method for improving color reproduction accuracy in a system for simulating print color reproduction by outputting a proof from a proofer, an image depending on printing conditions for outputting a print color chart measured at the time of creating the print profile Converting the data into image data depending on proofer conditions via the print profile and the proofer profile; supplying the image data to the proofer; and outputting a proof color chart from the proofer; Proof color chart Creating a print color reproduction profile to be simulated by the proofer and 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 print condition. And correcting the colorimetric value data using the obtained difference. 2. The color correction method according to claim 1, wherein in the step of correcting the colorimetric value data using the obtained difference, the obtained difference is added to the print profile to correct the print profile. And a step of correcting the colorimetric value data using the corrected print profile. 3. The color correction method according to claim 1, wherein the step of correcting the colorimetric value data using the obtained difference depends on the printing condition in the entire color space. Multiplying a weighting factor depending on the value of the input image data, adding a difference obtained by multiplying the weighting factor to the print profile to correct a print profile, and correcting the colorimetric value data with the corrected print profile; A color correction method. 4. After converting input image data depending on printing conditions into colorimetric value data using a print profile, converting the colorimetric value data into image data depending on proofer conditions using a proofer profile. In a color correction method for improving color reproduction accuracy in a system for simulating print color reproduction by outputting a proof from a proofer, an image depending on a printing condition for outputting a print color chart measured at the time of creating the print profile Converting the data into image data depending on proofer conditions via the print profile and the proofer profile; supplying the image data to the proofer; and outputting a proof color chart from the proofer; Proof color chart Creating a print color reproduction profile to be simulated by the proofer by color, and calculating a difference between the print color reproduction profile and the print profile with respect to the entire colorimetric value color space that is the color space of the colorimetric value data. A color correction method comprising: using the obtained difference to correct image data depending on the proofer condition. 5. The color correction method according to claim 4, wherein the step of correcting the image data depending on the proofer condition using the obtained difference comprises: determining the colorimetric value from the obtained difference and the print profile. Calculating corrected colorimetric value data in a color space, correcting the proofer profile with the corrected colorimetric data, and correcting image data depending on the proofer condition with the corrected proofer profile. Color correction method. 6. The color correction method according to claim 4, wherein the step of correcting the image data dependent on the proofer condition by using the obtained difference comprises: determining the colorimetric value from the obtained difference and the print profile. Calculating corrected colorimetric value data in a color space, correcting the proofer profile with corrected colorimetric value data obtained by multiplying the corrected colorimetric value data by a weighting factor depending on the colorimetric value color space, and Correcting the image data depending on the proofer condition using a profiler profile. 7. After converting input image data depending on printing conditions into colorimetric value data using a print profile, converting the colorimetric value data into image data depending on proofer conditions using a proofer profile. In a color correction method for improving color reproduction accuracy in a system for simulating print color reproduction by outputting a proof from a proofer, an image depending on a printing condition for outputting a print color chart measured at the time of creating the print profile Converting the data into image data depending on proofer conditions via the print profile and the proofer profile; supplying the image data to the proofer; and outputting a proof color chart from the proofer; Proof color chart Obtaining colorimetric value data by coloration, and calculating 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 condition. A color correction method, comprising: a step of obtaining; and a step of correcting the colorimetric value data using the obtained difference. 8. The color correction method according to claim 7, wherein in the step of correcting the colorimetric value data using the obtained difference, the obtained difference is added to the print profile to correct the print profile. And correcting the colorimetric value data with the corrected print profile. 9. The color correction method according to claim 7, wherein the obtained difference is multiplied by a weight coefficient that depends on a value of input image data that depends on a printing condition in the entire color space, and the weight coefficient is multiplied. A color correction method comprising: correcting a print profile by adding a difference to the print profile; and correcting the colorimetric value data with the corrected print profile. 10. The color correction method according to claim 3, wherein the weighting coefficient has a value of 1 in a color reproduction range of the printing proofer, and the weight coefficient is a range other than the color reproduction range. In the color correction method, the value is set to 0. 11. The color correction method according to claim 3, wherein the weighting coefficient has a value of 1 in a color reproduction range of the printing proofer, and the weight coefficient increases as the distance from the color reproduction range increases. A color correction method characterized in that a value is gradually reduced from a value of 1.