JPH03240392A - Color printing system utilizable for duplication of computer forming picture - Google Patents

Abstract

PURPOSE: To generate a hue value in a range between 0 and 360 deg. to the hue value of an original image from R, G and B values, to generate an output color value by using it, to minimize a processing time and the required capacity of memory and to accurately create a printed matter that coincides with the original image. CONSTITUTION: The original image is shown on a color monitor, and R, G and B pixel data are stored in a storage unit 13 via a computer 12. The data are sent to a computer 16 via a storage unit 15, the computer 15 processes pixel data and stores output data that is used for image duplication in a storage unit 17, and a storage unit 19 reads the data and sends it to a color processing system 20. The computer 16 generates a hue value in a range between 0 to 360 deg. from R, G and B values, also decides a cleanliness factor and an intensity term and generates a color output. A film that is created from data of the system 20 by a recording device 21 is duplicated by a printer 22, and the duplicate is sent to a viewbox 24 and compared with the original image. When it does not coincide, calibration data of the computer 16 is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a related invention of Japanese Patent Application No. 1-121632, hereinafter referred to as the related application.

[Industrial application field]

The present invention relates to color printing systems, and more particularly to systems that can be used to accurately and reliably reproduce images generated by a computer and displayed on a color monitor.

The system of the present invention easily and accurately produces prints that visually match the original image produced on a color monitor screen while minimizing the time required for processing operations and minimizing memory requirements. make it possible to create

Furthermore, the system represents significant improvements in terms of simplicity of operation and ease of use, particularly in terms of calibration methods that allow for direct, fast, and accurate calibration.

[Prior Art and Problems to be Solved by the Invention] As disclosed in the above-mentioned related application, the types of images that an artist produces on a computer's color monitor screen using a "coloring" program or the like, Various methods for reproducing images have been used or proposed in the past. One method used to date is to send a digital image to a color film recorder to create a slide, then place the slide on a conventional color separation scanner (scanner) to create a lithographic image. Color separation halftone film is processed to produce printing plates. This type of operation is tedious and, more importantly, does not consistently produce accurate color reproductions.

Also, the values of red, green and blue, i.e. rRGB, and the values of cyan, magenta, yellow and black, i.e. r
A few methods have been proposed that on the surface seem suitable for use with computer systems, such as converting to CMYK J values.However, the previously proposed conversion methods are very complex. When attempting to convert a complex, computer-generated signal or similar signal into a signal suitable for reproduction in color printing, it would appear to be extremely difficult to obtain satisfactory results. It is.

The aforementioned related application discloses a fast and accurate conversion of data, such as that provided to a computer monitor screen, into data for controlling a printing operation so that an accurate reproduction of the original image is obtained. In this system,
The color output value is derived from the component color values of the pixels of the original image as produced on a color monitor screen.The tone correction value is preferably determined by a look-up table, and the tone correction value is derived from the color output value. It is used to generate a gray color and achieve gray balance over the entire range of gray (hereinafter referred to as gray). And in this system, accurate gray balance is obtained from all color inks except black ink, and over a very wide range.

However, black may be added to provide optimal contrast and to facilitate accurate reproduction of the original image. As disclosed (black color is added as a function of the gray element corresponding to the screen color with the least effective intensity).

As further disclosed in the related application, a color correction system can be used after the process of obtaining accurate gray balance, and the color correction system can be used to obtain a balance that approximates the optimum balance by using a scale that operates with a linear characteristic. Color correction values, including color values, can be used to accurately reproduce the colors of the original image. Additionally, the color correction values include selected values that are added to provide optimal balance and highly accurate color reproduction. The selected value is
It also works on screen and ink colors, and on selected other colors such as bright red, purple and brown.

Additional important features of the related application are the use of a viewing box to view the reproduction in parallel with a monitor under standard lighting conditions, and the ability to quickly and accurately calibrate the system while retaining the original image. Concerning a sequentially executable calibration procedure that provides highly reliable reproduction of .

SUMMARY OF THE INVENTION The present invention has the general purpose of improving the system of related applications.

The system according to the present invention retains some of the advantages characteristic of the system of the related application, but also includes changes that simplify the operation and calibration process, making it easier to perform accurate color corrections. It is being done. The most important modification is the generation of hue values and the determination of output color data as a function of this hue value. In particular, the hue value corresponds to a rotation angle from a certain reference hue, ranging from 0° to 3°.
It is determined to be within a range of 60°. The reference hue is, for example, a pure red hue. Therefore, for example, if 0″' or 360″ indicates red, a value of 120° indicates green, and a value of 240° indicates blue.

According to a unique feature of the invention, a hue term is generated by a predetermined function of the hue value for each of the three output primaries used in the reproduction. Each such hue term is generated using, for example, a look-up table and then used to control the corresponding output color.

For example, the system of the present invention can be used to control the use of cyan, magenta, and yellow, or rCMYJ ink colors, similar to those shown in related applications, and to the assumed approximate relationship of CMY ink colors to ROB screen colors. It is useful to be partially based. The hypothetical relationships are that cyan has a negative or inverse relationship with red, magenta has a negative or inverse relationship with green, and yellow has a negative or inverse relationship with blue. When determining the value of each of the CMY values, one of the RGB values has an inverse relationship to one of the CMY values and is used as a primary color value. Especially R, G and B
The values of R are used as original values for the determination of the output values of C, M and Y, respectively, facilitating the determination of values for performing approximate color matching. In the system of the present invention, the hue term is R
It is used to change or modify the terms obtained from the GB values, thereby controlling the C, M and Y output values.

Further features include: for generating color-corrected output data;
It is concerned with the determination and use of cleanness and intensity terms in relation to the hue term. For example, cleanliness and intensity terms are preferably used to modify the terms derived from the RGB values, thereby controlling the C, M and Y values.

The objects, features, and advantages of the present invention thus far described, as well as those not previously described, will become more apparent from the following detailed description in conjunction with the accompanying drawings.

〔Example〕

In FIG. 1, the reference numeral 10 generally refers to the system in which the invention is actually implemented. An original image in the desired format is generated on the screen of color monitor 11 using computer 12, arranged as shown in the related application. Reference is made here to the disclosure content of related applications. Each pixel data of the image in the form of red, green and blue pixel data groups is stored using the storage unit 13 on a suitable storage medium such as a magnetic disk or magnetic tape. As indicated by the dashed line 14, the disk,
The tape or other storage medium is then transported by physical means to a storage unit 15 that operates to transfer the data from the storage medium to the memory of the second computer 16. The computer 16 processes red, green and blue pixel data,
Generate output data used to reproduce images. The computer 16 is supplied with calibration data defining the relationship between the characteristics of the monitor 11 and the known or assumed characteristics of the ink used in the halftone reproduction of the original image.

The output data generated by computer 16 includes data defining a black component and at least three color components for control of halftone reproduction of an image. For example, the output data controls cyan ink, magenta ink, yellow ink, and even black ink. However, the present invention
It can also be used to control printing processes that use additional inks, such as light cyan and pink inks, and is not limited to controlling four types of ink processes.

The output data generated by the computer 16 is stored by a storage unit 17 on a suitable medium which is conveyed by physical means to another storage unit 19 as indicated by the dashed line 18. Storage unit 19 is operative to read output data to a standard type color processing system associated with halftone film recorder 21. The film produced by recording device 21 is then used to make one or more copies using printing press 22, which can be either a production printing press or a proofing press.

As indicated by dashed line 23, the reproduction produced by printing press 22 is transported by physical means to view box 24 where it is compared side-by-side with the original image on color monitor 11. Both view box 24 and color monitor 11 are preferably under standard lighting conditions, as indicated by dashed rectangle 26 in FIG. If the duplicate image does not exactly match the original image, modifying the calibration data provided to computer 16 using the methods previously described;
Try to get a more accurate copy. - Once a satisfactory replication has been obtained or the reliability of the calibration data has been established,
Other original images can be copied as is.

Additionally, the system stores calibration data in a file corresponding to the identification number of the particular ink used. The filed calibration data is returned for use by computer 15 whenever subsequent inks are subsequently used. Additionally, the filed calibration data is returned to provide initial calibration data when using previously unused ink combinations that are similar to the combinations identified in the file.

FIG. 2 of the related application shows a monitor 1, a computer 12
, shows how the storage unit 13 and the viewing box 24 are arranged on the table and in the room or enclosure so as to provide the standard lighting conditions 26 mentioned above. It is desirable that the walls be flat and have a neutral color that does not cause reflection. Additionally, an indirect lighting arrangement is used to avoid reflections from the screen surface of the color monitor as well as reflections from the viewing box 24, within which the reproduction is placed. The lighting is very dim, but sufficient if excessive contrast between the screen, the reproduction and the background wall surface is avoided.

As disclosed in related applications, view box 24
is standard 50, the intensity of which is variable using the intensity control knob.
It is desirable to have a light bulb in the computer 1
2 is also connected to the keyboard and status monitor.

Preferably, computer 12 includes a disk drive for use with portable disks, and more preferably a hard disk. Additionally, the computer 12 is connected to a graphics tablet and associated pack, which the artist uses to produce the desired images on the screen of the color monitor 11.

The standard ``Paint'' software is used for this purpose.

There may also be a scanner to scan an existing painting and generate a corresponding image on the screen for modification by the artist. This type of computer graphics device arrangement is very flexible and allows the artist to create original images in the desired format that are easily modified and quickly reproduced.

When carrying out the present invention, a calibration program is configured to run on a computer 1 to create or modify a calibration data file.
2 is loaded. The calibration data file is loaded or stored on a portable disk within the computer 12 hard disk and/or computer 12 disk drive. During calibration, an original test image is generated on the monitor screen for comparison with a replica of this original test image within the view box 24 created by the system of the present invention. The system of the present invention provides an orderly proofing method for any particular combination of inks used in the reproduction process so that errors can be easily and immediately detected and corrected by direct translation into an accurate proof. It is possible.

The calibration data file can then be stored and returned for use at any time as long as such particular combination of inks continues to be used.

FIG. 2 is a flow diagram illustrating the digital processing operations performed by computer 16 in the described system IO. The original image file is first loaded from storage unit 15 into the memory of computer 16 and organized into successive groups of pixel data to correspond to the order required by color processing system 20.

Each group of pixel data includes consecutive R, G, and B groups of data. These data are 8 bytes in the system described so far. The data each have a value from 0 to 255 and define the effective intensity of the corresponding color component of the pixel. It will be appreciated that the present system is not limited to the use of data in 8-bit byte format, but may also use data groups of bits larger or smaller than 8 bits.

The numerical values of such pixel data bytes are referred to below as R, G and B values or collectively as RGB values. In the systems described so far and in prior art systems, there is a complementary or inverse relationship to the actual strength. That is, the value of zero corresponds to the maximum intensity of the actual color component, 25
A value of 5 corresponds to the minimum intensity of the color components of the actual screen. When all three RGB values are the maximum value, it corresponds to a black pixel, and when all three RGB values are the minimum value, it corresponds to a white pixel. If two of the RGB values are the maximum values,
If the third is zero, the corresponding pixel is one color of maximum saturation.

After loading the pixel data set and detecting the end-of-file mark, the gray and saturation factors are determined, and subsequent methods include black printing, generation and use of color removal terms, accurate tone replication, gray Used to perform balance and color correction. Unless stated in the alternative, these methods do not necessarily have to be performed in the order described. For example, black printing to determine a black output value may be performed after the output color value or the method for generating the output color value.

The gray and saturation factors, CF and SF determination process will be explained.

The first step in the method described is the determination of gray and saturation factors. The gray factor corresponds to the lowest intensity of the red, green or blue component of the pixel. That is, it corresponds to the largest one of the RGB values. This is used to control black printing, and is also used to determine color removal and cleanliness, which is used to control color printing.

The saturation factor corresponds to the red component color, green component color, or blue component color that has the greatest intensity. That is, R
It corresponds to the smallest of the GB values. This is not used to control black printing, but is used to determine the cleanliness and intensity terms used to control color printing.

Next, the black printing process will be explained.

In the illustrated operation, the next step is to determine a black output value for printing black ink. The black output value is a function of the gray factor, with a value of 0 being the darkest black, and a value of 255 being the brightest. A typical shape of this function is shown in the graph of FIG. 3 by line 28. In this example, the black color starts at the midpoint of the gray factor and rises sharply into the shadows. Preferably, this output value is generated using a look-up table in the memory of computer 15, where the gray value is used to access a memory location containing data defining the black output value.

Next, the process of removing the base color and the gray component will be explained.

In controlling the color components generated as described above, color removal values are also generated as a function of the gray factor. The color removal value CR corresponds to the ratio of the background color removal (IICR) to the gray component removal (GCR), and the gray factor G
Generated as a function of F. A typical example of this function is the fourth
As shown in the figure. As shown in the figure, the value CR is the line 29
is a linear function of the gray factor shown by the line 30
This function typically increases from 0 at the midtone point to a value of about 40% at the shaded end, as shown in the figure. As explained above, the value CR is used to eliminate either the RlC or B values before the tonal reproduction values are generated from the RGB values.

Next, the process of color tone reproduction will be explained.

Before discussing tonal reproduction in detail, it should be noted that in the system being described, output color values are generated and these are
It controls cyan, magenta, and yellow inks, expressed as values, M values, and Y values, or collectively as CMY values. In the described system, any such output color value is derived in part from a tonal value derived from one of the RGB values to an assumed inverse approximation relationship of the CMY ink colors to the RGB screen values. Based on this, accurate tonal reproduction, gray balance, and color correction are derived from hue values that are generated separately from RGB values in part.

Before carrying out tonal correction, the R, G and B tonal values are changed by adding the color removal (ICR) described above to obtain the corrected tonal values R', C;' and B' shown in Figure 2. The equation is:

R'=R0CR G'=G+CR B'=B0CR where CR is a function of the gray factor CF, a representative example of which is shown in FIG.

In the described system, the next step is to determine further modified tone values R1, G1 and B1. Color reproduction is very important. No matter what kind of image you create, if the color tone is not accurately reproduced, the image will never look good. Color reproduction also depends on the characteristics of the device used to output the image. The values R1, G1 and B1 are functions of the values of R', G' and B', respectively, and are preferably generated using a look-up table.

In FIG. 5, lines 31, 32 and 33 show typical relationships of the values of R1, Gl and G to the values of R', G' and B'.

Due to the above-mentioned inverse relationship between CMY colors and R0B colors, the equation becomes as follows.

C=255-RI M=255-CI Y=255-81 Next, the gray balance correction process will be explained.

The second most important consideration in color separation is the ability to reproduce grays across the tonal scale from lightest to darkest. At each point on the tonal scale, for a set of colors used to reproduce in ink, vehicle, or other medium,
Each has a combination of values that creates gray. If each output color is pure, such as cyan, magenta or yellow,
Equal values result in gray. This usually does not occur and the colors will be mixed to some extent.

- For boat fishing, it is good to determine the magenta and yellow values as a function of cyan. This is because cyan is usually the most mixed color and always has the highest value. In the system described, the equation for the cyan value remains as is, and the new G2 value and B2 as a function of G1 and B1 are
A value is generated and subtracted from 255 to obtain the control values for the cyan and yellow values.

In the graph of FIG. 6, lines 34 and 35 show a typical example where the ratio of the G2 value and the corresponding Gl value to Bl value of 82 is less than 1 for magenta and yellow control.

Line 36 represents the case where the ratio between the ordinate and the abscissa is 1 and corresponds to the constant R1 tone value used for cyan control. Although the straight line indicates that the function is linear, it is understood that the function may be non-linear and may be generated by a look-up table or the like. Now, the formula becomes:

C=255-RI M=255-G2 Y=255-82 Next, the color correction process will be explained.

In color separation, color always needs to be independent of gray, and vice versa. To do this,
Any term used to modify color by definition
In pure gray it must be erased. According to a very important feature of the invention, the color is modified for each pixel based on the hue value. Hue values represent only color angle and are independent of gray. In particular, for the hue value H, the red vector is at an angle of 0°, and the green vector is at an angle of 2π/3 radians (12
0°), the blue vector is 4π/3 radians (2
40°).

Based on the R value, the formula for hue is as follows.

If G>B then H=90- (180(A/π))G<
If B, H=270- [:180(A/π)) However, A is expressed in radians by the following formula: Arcta
If n is expressed in degrees, the equation becomes as shown in FIG.

Additional terms are used to define a more complete color modification equation. The gray factor GF and SF factor are RG in advance.
They are defined as the maximum and minimum values of the B value, respectively. The other term is called the degree of gray and represents the percentage of gray in the RGB set.

Gr = (255-GF) / (255-S
F) Cleanliness is the inverse of gray: CL-1-Gr The last term is intensity, which represents the percentage of color depth.

I = 1- (S F/255) The color separation formula can be expressed as follows.

Cyan = 255-R1 [1+(1, CL, H function set)] Magenta = 255-G2 (1+(1, CL, H
function set)] Yellow = 255-82 (1+(1,
M) of the function of CL, H]1, the terms of the set of functions of CL, H must be canceled when it is a perfect gray, where R-C,=B. When it is completely gray, GF=SF, so the gray level is 1 and the cleanliness is 0. Therefore, this term disappears. The function required for H is typically non-linear and determined by a look-up table or the like. The functions of (2) and CL are determined in the same way, but linear functions may be used depending on the required accuracy. The function of H can be positive or negative depending on whether color is added or subtracted.

The general formula is:

C=255 R1(1+IcCLcHc:IM-2
55G 2 (1+INCLNHNl]Y= 255
B 2 (1+IyCLJh) However, IC, IN and ■ are functions of ■, and CLc, CLH and C
L is a function of CL and Hc.

Hs and H7 are functions of H.

In a practical test with some available inks, Ic, iT
The terms 4 and 1v are equal to I, CLc.

It is known that satisfactory results can be obtained when the terms CLM and CL are expressed as CL''. Therefore, under appropriate conditions, the following simplified formula can be used satisfactorily. .

C= 255-R1 (1+ICL4He) M= 255
G 2 [1+ICL”HM)Y = 255-
B 2 (1+ICL”)lv) - HC, HM and H
The V lookup table can be generated interactively using a calibration method of the type disclosed in detail in related applications.

The object of the test is the output for a color proof that is evaluated against a computer displayed image. The lookup values are modified until a satisfactory result is obtained.

With the system of the invention, the calibration method becomes very simple,
It can be done much faster than others. This is possible because each operating step and lookup value or associated control value acts on a proof that can be determined visually, whereas the control values in other operating steps are essentially This is because we are trying not to affect it as much as possible.

In other words, this is a conversion method in which there is no mutual influence between processes in the correction process, and results that are as visually accurate as possible can be obtained immediately.

The generation and use of hue values is of particular importance. This is because hue modification is important in obtaining visually accurate reproductions. In the system of the present invention, differences in hue between the original image and the proof can be easily detected visually and appropriate changes in control values can be determined and implemented.

The look-up table for H is preferably created by increasing the hue in 1" increments, resulting in 360 values. A sample diagram of the hue correction coefficient is shown in FIG. 7. However, it is easy to understand that in reality it is common to use smooth curves.
The illustration is for cyan printing. A similar diagram, but with different curves, applies to magenta and yellow printing.

It goes without saying that other control values can be used in place of or in addition to the control values included in the lookup table for defining the various functional relationships that have been explained so far, and the idea that is characteristic of the present invention can be used. It will also be appreciated that other modifications and changes may be made without departing from the spirit and scope.

〔Effect of the invention〕

The present invention makes it possible to accurately reproduce the colors of an original computer-generated image, and to facilitate this task.

[Brief explanation of drawings]

1 is a schematic block diagram of a color print reproduction system used in carrying out the present invention; FIG. 2 is a flow diagram illustrating processing operations performed in accordance with the present invention; and FIG. Figure 4 is a graph explaining the relationship between the terms used for black printing and the gray factor, Figure 4 is a graph explaining the relationship between the color removal term and the gray factor, and Figure 5 is a graph explaining the relationship between the term used for black printing and the gray factor. FIG. 6 is a graph illustrating the further modification of a term to obtain gray balance, and FIG. FIG. 6 is a sample diagram showing the shape of the relationship obtained between the correction coefficient and the hue value in FIG. In the figure, 11... Color monitor 12... Computer, 13... Storage unit, 15... Storage unit, 16... Computer, 17... Storage unit, 19... Storage unit, 20 ... Color processing system, 21 ... Halftone film recording device, 22 ... Printing machine, 24 ... View box. Black printing tone reproduction gray balance red tribute green shea] blue magellan red

Claims (1)

[Claims] 1. Defining R, G, and B values that are variable within a certain range and correspond to the intensity values of the red, green, and blue component colors of individual pixels of the original image, respectively. providing original image digital data in the form of a plurality of groups of input data; and digitally processing the plurality of groups of input data;
a plurality of groups of input data producing from each group of input data output digital data having output values comprising at least three output color values for controlling the reproduction of individual pixels of the original image by at least three output colors; A method of image reproduction comprising a processing step, the processing of the plurality of input data generating from the R, G and B values hue values corresponding to hues of individual pixels of the original image. and using the hue values in generating the output color values. 2. The image reproduction method according to claim 1, wherein the hue value is generated to be in the range of 0° to 360° and corresponds to a rotation angle from a certain reference hue. 3. The step of generating the hue value is based on the target value being one of the R, G and B values and the remaining two being the two residual values, from twice the target value to the second value. The value obtained by subtracting the remaining value is √
generating a first value that is the arctangent (tan^-^1) of the ratio of the value divided by 3 and the difference between the two residual values;
and the step of adding either 0° or 180° to the value obtained by subtracting the first value from the constant value, depending on which of the two residual values is larger. 4. The processing of the multi-group input data includes generating an intensity term from the R, G, and B values that is related to the intensity of any color component of an individual pixel of the original image; A method as claimed in claim 1, in which the intensity value is used together with the hue value when generating an output color value. 5. The method of claim 4, wherein the intensity term corresponds to the maximum of the intensity levels represented by the R, G, and B values. 6. Processing the multiple groups of input data to generate the output data includes generating a clean term related to the ratio of maximum to minimum intensity levels represented by the R, G, and B values; A method as claimed in claim 1, including the step of using the cleaning value in conjunction with the hue value when generating the output color value. 7. Processing the plurality of input data to generate the output data includes generating first, second and third tone values from a predetermined function of the R, G and B values; A method as claimed in claim 1, including the step of using the tone value in conjunction with the hue value when generating the output value. 8. The step of processing the plurality of input data to generate the output data generates an intensity term related to the intensity of any color component of an individual pixel of the original image from the R, G, and B values. 8. The method of claim 7, further comprising the step of using the intensity value along with the tone value and the hue value in generating the output color value. 9. Processing the plurality of input data to generate the output data includes generating a clean term related to the ratio of maximum to minimum intensity levels represented by the R, G, and B values; 8. The method of claim 7, including the step of using the clean term in conjunction with the tone value and the hue value when generating the output color value. 10. The method of claim 1, wherein the output value includes a black output value in addition to at least the three output color values. 11. The processing step of the plurality of groups of input data includes the R, G
11. A method as claimed in claim 10, including the step of generating a gray factor corresponding to a minimum value of the intensity level represented by the values of and B, and using the gray factor in generating the black output value. 12. Processing the plurality of input data to generate the output data includes generating first, second and third tone values as predetermined functions of the R, G and B values; 11. The method of claim 11, comprising: generating first, second, and third modified tonal values as a function of a gray factor; and using the modified tonal values together with the hue value in generating the output value. Image duplication method described in. 13. generating a color removal term as a predetermined function of the gray factor;
12. The method of claim 11, wherein the color removal value is added to the first, second, and third tone values when generating a modified tone value. 14. Using the modified tonal values generates first, second and third further modified tonal values by a predetermined function of the first, second and third modified tonal values, respectively. 12. The image duplication method according to claim 11, comprising the step of: 15. The step of using the modified tonal value comprises generating at least two additional modified tonal values by a predetermined function of at least two of the first, second and third modified values. 15. The image duplicating method according to claim 14, further comprising the step of performing balance correction. 16. The processing of said plurality of input data to produce said output data includes forming first, second, and third tones by predetermined functions of said R, G, and B values that generally act inversely. using the first tone value together with the hue value when generating a cyan output color value; using the second tone value together with the hue value when generating a magenta output color value; 2. A method as claimed in claim 1, including the steps of: using a yellow output color value; and using the third tone value in conjunction with the hue value when generating a yellow output color value. 17. Generating first, second, and third hue values for modifying the tone value by a predetermined function of the hue term when generating the cyan, magenta, and yellow output color values; 17. The image duplication method according to claim 16, further comprising: 18. generating from the R, G and B values an intensity term related to the intensity of any color component of each individual pixel of the original image, and generating the cyan, magenta and yellow output color values; 18. The method of claim 17, wherein the intensity term is used together with the first, second and third hue terms when generating the image. 19. The processing step of the plurality of groups of input data includes the R, G
and B, using the gray factor in generating the black output value to generate the cyan, magenta and yellow output color values. 19. The image reproduction method of claim 18, further comprising: generating first, second and third modified tone values for use in conjunction with the hue and intensity terms by a predetermined function of the gray factor when . 20. The image reproduction method of claim 19, wherein each of the predetermined functions is modifiable independently of other functions of the predetermined functions for calibration purposes.