JP2003011397A - Method of defining printer media and inking intensity compatibility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a linear tone scale derived in an independent color space and referenced from a shade of an unprinted substrate in relation to quantification of a printed tone scale for each individual color in a printing system. SOLUTION: In order to determine a threshold for excessive ink coverage of the printing system on a specified substrate, a subjective evaluation of acceptable threshold for bleed, cockle, show through, and image density is executed. An ink in each dependent color in this system is limited in a part of all upper ink limits and a color of a paper is used as a reference point to calibrate the tone scale for each color in this system and to generate the tone scale conversion in a different combination of both of graphics and text with respect to each color.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to image processing, and more particularly to optimizing the quality of a substrate specific image in a printing system.

[0002]

Ink jet printing systems are known. In this system, the printhead defines one or more rows of orifices that receive a conductive recording fluid, such as aqueous ink, from a pressurized fluid supply manifold and eject the received fluid as a row of parallel streams. To do. A printer using such a print head is
By selectively charging and deflecting the drops in each stream, depositing at least a portion of the drops on the print receiving medium, the rest of the drops impinges on a drop capture device, thereby rendering the graphics Has achieved regeneration.

[0003]

This is especially true of ink jet printing systems, where some printing systems require that the amount of ink or other colorant applied to the substrate be limited. There is. For high speed ink jet printing systems that use aqueous dye inks, ink limitation is of particular interest in terms of avoiding substrate degradation. Excessive moisture can cause the paper to stretch and wrinkle. This problem is due to the fast roll-to-roll (roll
More serious due to web tension in the to roll system. The balance between ink loading, print speed, web tension, drying power, etc. must be carefully maintained. The present invention solves two related problems. First
In addition, the present invention identifies an upper ink limit for the above parameters. Second, it linearizes the tone scale of each ink in the system from substrate color to maximum ink. In the past, the dependency between the ink and the substrate was not clear. This problem was exacerbated in high speed ink jet systems, which gave large amounts of water to the paper in a short time.

In the prior art, the upper ink limit for a small number of selected substrates was preset by the printer manufacturer. High speed digital presses operate with a large number of substrates of unknown ink compatibility. Moreover, the color of those substrates that have not yet been printed can change significantly. Also, the ink colors available in the system can change regularly.

Therefore, a calibration procedure that is universal for any combination of ink, substrate, and machine configuration.
It is desirable to have a technology that can solve the problem of ation procedures).

[0006]

SUMMARY OF THE INVENTION The present invention provides a printed tone for each individual color in a printing system.
Regarding quantification of scale. In particular, in accordance with the present invention, a novel approach for producing a linear tone scale derived in an independent color space and referenced to the shade of an unprinted substrate is disclosed. Further, the present invention provides methods and means for ensuring compatibility with print media by limiting the amount of colorant applied to the substrate.

According to one aspect of the invention, there is provided a method of determining an upper ink limit for a printing system on a particular substrate. This decision is bleed, wrinkled (cockl
e), show through, image density (image
density) based on a subjective assessment of the acceptable threshold. This method fixes printing parameters such as speed, dryer temperature, web tension, and works with pre-defined test patterns printed on a particular substrate. The present invention also includes the ability to limit each independent color ink in the system to a fraction of the total ink cap. Furthermore, the present invention allows the color of the paper to be used as a reference point to calibrate the tone scale of each color in the system. Still further, the invention facilitates producing a separate set of tone scale transformations for both graphics and text for each color in the system.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The present invention optimizes the image quality of a printer as a function of the inking system and the substrate that receives the ink. A single page test pattern has been created that enables you to accomplish this task. This test page is printed with the printer under the same operating conditions as the actual print job to be optimized. This pattern can be used to print inks on various substrates.
Construct to cover a practical and usable range of loading. In this way, the uncharacterized substrate is identified with an upper ink limit for graphics, an optimal text print density, and a tone scale calibration for each ink in this system based on the color of the unprinted substrate. It can be quantified through a series of steps.

Any suitable test pattern can be selected to achieve the objectives of the present invention with any number of patterns.
The present invention discloses general methods and principles applied to any such test pattern that include the properties required for the evaluation described herein.

Referring to FIG. 1, the first step in calibration is to determine the shape of the tone curve for each ink in the system, relative to the color of the unprinted substrate. This pattern is scanned with a spectrophotometer to determine the three-dimensional color coordinates of the substrate and each test patch. A test patch is a dynamic
A linear increase over the range with respect to the level of inking applied. Depending on the printing system, this can be achieved through various ink splash scattering techniques. In the case of binary ink jet printing systems, error diffusion and / or dither algorithms can be used to obtain the required ink distribution on the substrate.

Experiments have confirmed that there is typically a non-linear relationship between the amount of ink applied to the substrate and the overall intensity of the reflected color.
Here, the unit scale of the tone scale is defined as the unit distance between the substrate color and a particular color sample when plotted in a three-dimensional independent color coordinate system. A typical tone scale curve is illustrated in FIG. The substrate color coordinates are shown at 3. Curve 4 is
It is typical for coordinates obtained from a graded inking scale printed on a test page. A plurality of discrete points 5 are measured from the sample. Curves are then fitted to these discrete points using a curve fitting algorithm such as the least squares method. The largest ink point corresponding to black text at position 6 represents the largest distance from the substrate color. However, it is generally not possible to print at this maximum intensity due to system limitations such as the ability to dry the substrate. In FIG. 2, the ink cutoff point (ink cutoff po
int) 7 and the ink critical point 18 is shown as the realistic maximum ink point for color text. For reference purposes only, a second curve 8 representing another ink in the same printing system is also shown. Similarly, it will be appreciated that any number of such curves representing any ink color can be shown.

The upper limit of ink for graphics printing is
Determined from test pattern. This is the intensity of the image, bleeding between colors, reverse text.
It is based on the judgment such as fill in, wrinkle of paper, and see-through on the back side of paper. In the pattern,
Generally, there are multiple options to indicate the usable range of ink loading on various substrates. Only one critical value is selected for a given job. The selection process is determined as the maximum acceptable value for the constraint. The constraints vary for each test parameter depending on the actual job data. For example, bleeding can be important when there is heavy text on a dark background. Wrinkles can be very important in image graphics applications. Show through is important in double printing, and so on.

When the operator selects an overall ink limit for graphics, the individual ink limit is derived by dividing the overall ink limit by three and assigning the same value to all colors in the system.
Test patterns are constructed to facilitate this derivation. For example, each different ink cap image (8) shown as part of the test pattern in FIG. 1 is designed so that the primary ink caps are equal to 33% of the total ink caps in this photograph. ing. To further illustrate this example, a given image on a test page can have an ink cap of 150% for each pixel in the image. 1
One pixel is made up of ink contributions from the three primary colors and black. Each of these inks contains 50
It is set to the individual ink upper limit of%. In this case, it is assumed that the colors represented by the 200% overall ink limit can all also be represented by the 150% overall ink limit. This is because black is not an independent color. Black is used to represent some combination of the three primary colors pixel by pixel. Another choice would have different ink caps, but the relative distribution between colors remains constant for all choices.

The next test pattern used to determine the ink cap is the color to color ink bleed pattern. In this pattern, the primary color ink is
Each is printed over the previously printed ink in this system to form a grid pattern. Orthogonal grid lines are printed at the maximum critical point for each individual primary color. The user
You must check the feathering of the edges by looking at the intersections of different color inks. This feathering increases the width of the grid lines in the area of overlap with another color. In general, the inks are tuned to have the same physical properties so that preferential bleeding from one color to another does not occur. However, some substrates, especially those with coated substrates, may be more prone to feathering than others. The diagonals on the grid pattern are set at the typical inking level for text and represent the printed text on a colored background. Dithered feathering should also be noted as part of the ink cap determination. Again, the decision is application-based. The evaluation of this pattern is important in the case of text documents printed on a colored background. In the case of graphics images, its importance is rather low.

The test pattern page is also used to evaluate text bleed. The background color is printed with the upper ink limit of the graphics for each of the three primary colors (cyan, magenta, yellow). The text at the center of the square is printed with each combination of two of the three primary colors. This is accomplished simply by removing the third color in the text area. The purpose of this pattern is to look for a fillin of the text with a third unprinted color due to bleeding between colors. If the text is filled with unprinted color (s), the upper ink limit should be lowered to the point where all the text in the pattern is readable. Although this pattern is set to the graphics ink critical limit, text filling is an accurate indication that there is excessive bleeding that degrades edge definition in the graphics image.

Finally, the patterns on the test page are used to evaluate wrinkles and show throughs. The test pattern is printed using the three primary colors and black. However, each color is 75% of the upper limit ink criticality independent of graphics. The total ink coverage in this patch is 300% (75% x 4),
For each independent trial, it represents 75% of the total ink limit, which is 400%. Cyan, magenta,
Total usable area of yellow, black (CMYK) system (gamu
Most colors in t) can be printed with 300% ink loading. Because black is redundant. Wrinkles are determined by looking and / or feeling the flatness of the surface of the printed substrate over the test patch area from the back side (which is the non-printed side). Similarly, show-through is determined by looking at or measuring the darkness of the opposite side (which is the unprinted side) of the substrate opposite the test patch area.

The printer operator is required to select an upper ink limit for graphics based on these test patterns and the nature of the job to be printed. The value is entered into the software utility,
This software utility divides the overall selected ink upper limit into three parts and applies the limit to each of the primary colors and black. It is assumed here that any color in the entire printable area can be exactly approximated with a complete coverage of 3 out of 4 colors in this system. Black is redundant and is used to reduce overall ink consumption and provide a single color for black text. In this way, the ink criticality of FIG. 2 is determined.

In general, it is desirable for the tone scale to have a linear relationship over the entire range of printable densities. To achieve this, an input / output transfer function is derived. This transfer function operates on incoming continuous tone color data before it is converted to binary form using some splash scattering algorithm such as error diffusion or a dither matrix. The first step in obtaining a linear tone response is to generate a function that describes the actual tone scale between the paper white and the upper ink limit for each ink. This curve 4 in FIG. 2 is
It is inverted in curve 15 of FIG. By transforming the input image data with a look-up table that is the inverse of the original tone curve non-linearity, the resulting tone response to the new transformed data is linear.
This new transformed linear tone curve is shown at 16 in FIG. This curve passes through the substrate color point 3 and the ink critical point 7 in the L * a * b * independent color coordinate system. This color coordinate system is well known to those skilled in the art as a standard for defining and transmitting color information. In the processed color printing system, the same process is repeated for each primary color and black. 1
Systems containing spot colors that are one or more non-primary colors can be calibrated using the same procedure.

The requirements for good image quality for text differ significantly from those for graphics. The text is typically monochrome and is typically printed in black. It is desirable to have the inking level high enough to allow the individual droplets derived from the binary conversion algorithm to overlap each other. This can be achieved by forcing black text to be printed at a higher density ink limit than is used for graphics. The test page is used to determine the black ink limit. This part of the test page contains various font sizes and point sizes. Each sample is printed with a different amount of black ink. The operator must select the darkest color text while avoiding edge misalignment as a result of excess ink being carried along irregularities on paper fibers or other surfaces.
This point is the upper third of the tone scale range
It is generally found in. From this value, the associated software algorithm assigns the ink limit for colored text to approximately the black text threshold. The reason for this allocation is that the processed color ink made up of two inks can be printed without possible feathering. The software applies one additional condition to the ink cap determination for colored text. In order to obtain characters that have completed formation after the splash-scattering algorithm has been applied to text data printed using only one primary color, the black text is colored text even if it is above the critical point 50. A minimum threshold concentration is imposed above the critical point. Both the black text ink upper critical point 6 and the other primary text ink critical point 18 are shown in FIG. Applying the same curve fitting and conversion routines used for graphics to these new curves gives a linear tone response to the text data. As already mentioned, the diagonal lines in the test pattern can also be used to show interactions in printing black and colored text on top of the background image data. Obviously, if one wants to print a particular spot color with optimum density, the test pattern can be modified to replace this color with black.

Determining the ink caps for graphics and text is a somewhat subjective judgment based on the type of printing included in the job. A typical graphics image is shown in FIG. Excessive ink causes loss of detail in shadow areas. The magnified area A shows an appropriate ink cap to maintain image detail. Section B shows the same magnified area, but in this case the upper ink limit is chosen so that details in the shadow are masked. FIG. 6 shows the same conditions when printing text on a dark background. The text in area A is easier to read than the text in area B. The text in area B is filled with the background color. The reason is that the upper limit of the ink is too high. The images and tests of FIGS. 5 and 6 are shown for illustrative purposes only. However, it will be apparent to those skilled in the art that other similar patterns can be used to achieve the same result.

The derivation of the tone scale curve from the spectrophotometric scan and the subjective determination of the upper ink limit work in conjunction with the appropriate image processing software required to define the integrated workflow. The entire tone scale calibration process is shown in FIG. The novel features given in the disclosure in this application are part of the overall workflow solution.

The process defined in FIG. 4 is serial in nature. Starting with the ink and substrate specifications for a particular job, we end up with the actual printing of the processed imaged data specific to the ink / media.
After each step in the workflow, a first test pattern is printed, as shown in FIG. As already explained, the tone scale color blocks are measured using a spectrophotometer. The operator visually determines the upper color limits for the graphics image and the preferred text color. This data is input to characterization software that derives two sets of curves or input / output transfer functions. One set is for graphics images and the other set is for text. For each of the system's primary colors for both text and graphics stored on the server, along with unmodified graphics and text data,
A separate look up table (LUT) may be generated. In the process shown in FIG. 4, after the transfer function is generated from the characterization software, the RIP
This appropriate function in operates on and transforms graphics and text image data. Finally, a splash-scattering algorithm such as error diffusion or dither matrix is applied to the transformed continuous tone data to reduce it to binary data. This binary file is an exact representation of the original continuous tone data, but adjusted for a particular substrate printed at a particular speed. Finally, these image files are loaded into the printer data system and imaged on the press.

The calibration technique according to the present invention has many advantages. The tone scale is linearized based on the measurement of the delta "E" from the color of the substrate in the L * a * b * color space, which allows for accurate calibration of any ink color on any substrate. It will be possible. Single page
Wrinkle, show through, bleed,
An ink cap is determined based on a number of ink / substrate parameters, including image quality and the like. These patterns are defined to represent the expected results for a particular upper ink limit. This ink cap test pattern contains an image representing the entire usable range of ink loading on various substrates, thereby
The operator can make a decision based on the comparison.
In the preferred embodiment of the invention, this pattern can and should be run at the same print speed as the actual job. Separate calibration curves are generated for both text and graphics from the same test page. Therefore, the software that prepares the job uses a separate transformation for each
Dual text / graphics modes are available.

The present invention has been described in detail above with particular reference to its preferred embodiments. However, it should be understood that modifications and variations are possible without departing from the spirit and scope of the invention.

[Brief description of drawings]

FIG. 1 illustrates a typical set of test patterns used for calibration according to the present invention.

FIG. 2 is a typical tone scale curve.

FIG. 3 is an inversion of the curve of FIG.

FIG. 4 is a block diagram of the calibration process of the present invention.

FIG. 5 shows an exemplary image with correct and excess ink limits.

FIG. 6 illustrates exemplary text with correct and excessive ink limits.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/23 101 H04N 1/40 D 5C074 1/46 B41J 3/00 B 5C077 1/60 H04N 1/46 Z 5C079 (72) Inventor Terry Wozniak 45502, Springfield, Fairfield Pike, Ohio, USA 3222 (72) Inventor Christopher El Watkins, State of Ohio 45324, Fairborn, Grisham Lane 1271, Appointment Sea F Term (Reference) 2C056 EA11 EC76 EE03 2C061 AQ05 KK04 KK18 KK28 2C262 AA02 AA24 AB12 AC07 BA09 BC07 BC10 BC19 CA13 EA11 FA13 FA18 2G020 AA08 DA02 DA03 DA04 DA12 DA43 5B057 CA01 CA08 CB01 ADB A4 CB08 DB09 CE08 BB16 DD03 DD08 DD24 EE08 FF15 GG01 HH04 5C077 MM27 MP08 PP36 PP37 TT05 5C079 HA18 HB08 KA12 LB01 MA10 NA03 PA03

Claims (10)

[Claims] 1. A method of determining compatibility between printer media and inking strength in a printing system, the steps of identifying a printer and a substrate for use in color printing, the identified printer and the identified substrate. Printing a color test pattern of a plurality of test patches using the plurality of test patches; generating a tone scale curve for each ink in the color test pattern using the plurality of test patches; 1 constraints on the identified printer and board
A step of selecting one, a step of determining an ink upper limit based on the ink and the substrate parameter, a tone scale is generated using the ink upper limit,
Calibrating the color of any ink on any substrate for the printing system. 2. The method of claim 1, wherein the tone
The step of generating a scale curve comprises: plotting the color test pattern in the L * a * b * color space with respect to the color of the substrate; and measuring the Euclidean distance from the color of the substrate as a measure of color intensity. And a step of using as a. 3. The method of claim 1, further comprising scanning the color test pattern with a spectrophotometer to determine three-dimensional color coordinates of each of the plurality of test patches and the substrate. A method comprising. 4. The method of claim 1, wherein the step of determining an upper ink limit determines a first ink upper limit for suitable color text and a second ink upper limit for graphics. A method comprising the steps of :. 5. The method of claim 1, wherein the color test pattern comprises image and graphics data that group together a usable range of ink loading on a range of acceptable substrates for color printing operations. Including, including a test pattern to determine an appropriate ink cap on a particular substrate. 6. A method of determining compatibility between a printer medium and inking strength in a printing system, the method comprising: identifying a printer having a plurality of inks for color printing and a substrate; Printing a color test pattern using the identified substrate; generating a tone curve for each of the plurality of inks using a portion of the color test pattern; Determining a threshold for excess ink coverage for the identified printer and substrate using a portion of the pattern; and defining a range of tone scales for the plurality of inks on the identified substrate. Recalibrating so that it is below a threshold of a good ink coverage. how to. 7. The method of claim 6, wherein the test pattern comprises a subpattern printed with increasing ink coverage levels to identify a threshold for the excess ink coverage. And how to. 8. The method of claim 6, wherein the test pattern reveals when ink bleeding is excessive due to ink coverage above a threshold for the excess ink coverage. A method comprising: 9. The method of claim 6, wherein the test pattern reveals when the dry time is excessive due to ink coverage above a threshold for the excess ink coverage. A method comprising. 10. The method of claim 6, wherein the test pattern reveals when the paper is overcurved due to ink coverage above a threshold for the excess ink coverage. A method comprising: