JP2002361999A - Color chart for evaluating printing and method for forming the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a color chart in consideration of the arranging way of color patches facilitating the adjustment of the supply amount of ink at the time of printing of the color chart for evaluating printing characteristics. SOLUTION: When the color patch to be arranged at a certain position is determined, the corrected reference value of the consumption quantity of ink of the color patch to be arranged at a target position is calculated according to the difference between the consumption quantity of ink of the color patch already arranged adjacent to the position and the predetermined reference value of the consumption quantity of ink and a properly set error diffusion matrix and the color patch having a color nearest thereto and not yet arranged is selected to be arranged at that position. The color chart is designed or formed by repeating this procedure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print evaluation color chart formed by arranging a large number of patches of different colors in a tile pattern and a method of designing and producing the color chart.

[0002]

2. Description of the Related Art In general, when performing offset multicolor printing, printing plates of respective colors are prepared, and overprinting is performed step by step on a common sheet of paper from the printing plates. Is done. Color reproduction, which is the color development of printed matter, is based on ink,
Because it depends on various factors such as paper and printing conditions, if you want to know the print color reproduction, print an image part called a color control patch (hereinafter referred to as a color patch) that shows a certain color tone in a certain area. Is measured. Usually, a large number of color patches having various color tones are prepared, printed as a color chart in a tiled manner, and collectively measured. For example, in the case of four-color printing, Cyan, Magenta, Y
In the case where the density levels of ellow and Black (CMYK) are changed in five stages, 5 <4> color patches are arranged in a tile pattern on a two-dimensional plane and printed.

[0003] A color chart composed of patches of a large number of colors is usually created so as to change stepwise spatially because of its ease of creation. When making a color chart, it is easy to create the original data and it is easy to handle the printed color chart,
Normally, the chart is configured so that adjacent patches are different colors in which only one dot% of the CMYK dot% is different. FIG. 4 shows a layout of such a conventional color chart. A partial chart in which combinations of 5 × 5 halftone dot percentages of C and M are combined into one group while fixing the dot area percentages of Y and K, and a set of 5 × 5 halftone dot percentages of Y and K Together, the entire chart is configured.

On the other hand, FIG. 5 shows a simple schematic diagram of offset printing. As shown in FIG. 5, the ink supply device sets the supply amount by dividing the supply amount in the printing width direction by controlling the opening and closing amounts of the divided blades. A unit for controlling each blade is called an ink key, and the ink supply amount is set by appropriately adjusting the opening of the ink key. The ink supply amount is related to the amount of ink of the halftone dots to be formed, that is, the ink film thickness. In order to obtain an offset print with stable color tone reproduction, it is necessary to adjust the ink supply amount so that the ink film thickness is constant.

[0005]

The problem here is that even if the ink supply amount is kept constant, it is not always possible to obtain an offset print with stable color tone reproduction. This is because the ink consumption varies depending on the picture area of the printing plate surface, and the ink film thickness of the formed halftone dot varies even with the same ink supply amount. Therefore, when printing a general offset print, the printing machine operator appropriately adjusts the opening degrees of the plurality of ink keys arranged in the print width direction according to the print so as to offset the bias of the ink consumption in the print width direction. I do. This adjustment operation is a troublesome operation that requires skill because the visual evaluation and manual adjustment are repeated until the test-printed printed material sufficiently approaches the color tone of the printed sample.

Similarly, when a conventional color chart is printed, a portion where a light color is printed (a portion consuming a small amount of ink) and a portion where a dark color is printed (a portion consuming a large amount of ink) are used. Therefore, it is necessary to adjust an appropriate ink supply amount by an opening of an ink key of a printing press.
Moreover, since the color chart is printed in order to evaluate the printing characteristics of the printing press, there is no point in adjusting the color chart if it is accurate. .

The present invention has been made in view of such problems, and when printing a color chart for evaluating printing characteristics, a color patch which makes it easy to adjust the ink supply amount is provided. An object of the present invention is to provide a method for creating a color chart in consideration of the arrangement.

[0008]

According to a first aspect of the present invention, there is provided a method for designing or creating a print evaluation color chart formed by arranging a number of different color patches in a tile pattern. When determining a color patch to be arranged at a certain position, the difference between the ink consumption of the already arranged color patches adjacent to the position and a predetermined reference value of the ink consumption, and an error determined appropriately. According to the diffusion matrix, a correction reference value of the ink consumption of the color patch to be arranged at the target position is calculated, and a color patch which has the closest color to this and has not been arranged is selected and arranged at that position, This is a method of designing or creating a color chart by repeating this procedure.

In the printing plate of the color chart formed by the above method, since the ink consumption is distributed evenly in the printing width direction, it is sufficient that the ink supply amount is uniform in the printing width direction. It is not necessary to set the adjustment for each ink key, and the adjustment before printing becomes easy. still,
The amount of ink consumed per unit area is considered to be proportional to the sum of the areas of the halftone dots in the unit area. Therefore, it is considered that the ink consumption per area of the color patch is simply proportional to the dot area ratio (dot area%).

A second invention for solving the problems is a print evaluation color chart designed or created by the method of the first invention and formed by arranging a large number of patches of different colors in tiles.

According to a third aspect of the present invention, there is provided a print evaluation color chart designed or formed by the method of the first aspect of the invention, in which a plurality of patches of different colors are arranged in a tile pattern. Original film or printing plate.

According to a fourth aspect of the present invention, there is provided a computer readable recording medium in which printing plate making data for outputting an original film or a printing plate according to the third aspect of the invention is recorded in a data structure and format that can be interpreted by an output device. is there.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart illustrating the procedure of the color patch configuration method according to the present invention. FIG.
, The outline of the method of the present invention will be described.

First, the layout of the color chart, the number of color patches to be used, and the color to be used (color patch list) are determined, and the average ink consumption (only ink amount and (May be written) and set it as a reference value (S1).
0). To determine the color patch list means to determine the number of possible dot% values of each color for one color patch
To determine the values of four integers nc, nm, ny, nk and nc × nm × ny × nk = M colors of each color patch constituting the entire color patch, that is, the value of halftone dot area% of each color of CMYK. It is. Next, the pointer is set to the first position of the color patch layout (S12), and a color patch to be assigned thereto is arbitrarily selected from the color patch list (S1).
4). The selected color patch is excluded from the color patch list.

Next, a deviation is calculated by subtracting a reference value (or a modified reference value) from the ink consumption of the assigned color patch (S16). Then, from the diffusion matrix determined as the deviation, a correction reference value for a patch assigned to a position adjacent to the current pointer position (four positions in the case of two dimensions) is calculated (S18). A color patch having the ink consumption closest to the correction reference value is selected from the color patch list as a color patch to be allocated to an adjacent position (S20). The selected color patch is excluded from the color patch list. When the color patch list becomes empty, the process ends (S22). If not, the pointer is moved (S24) and step S1 is performed.
Return to 6.

In the color patch created in this manner, the ink consumption in any partial area is suppressed within a certain range around the reference value, so that the ink supply amount from each ink blade set by each ink key is set. Is constant, the ink film thickness of the halftone dot can be made constant, and stable offset printing can be performed.

The procedure of FIG. 1 will be described with a specific example. As the simplest example, seven patches of a single color (10, 30, 40,
70, 80, 90, and 100) will be described as a one-dimensional array (Irohanihohet) shown in FIG. First, the reference value is 60 from the average value of the dot area ratio of each patch in the patch list. This state is illustrated in FIG. Here, one patch is randomly selected from the color patch list and assigned to the first cell, i. Here is 80
It is assumed that is selected. Remove 80 from the patch list.
Then, 80 is assigned to a and the deviation from the reference value is calculated. The deviation is calculated as (reference value of b)-(dot area% of patch allocated to b) = 80-60 = 20 (FIG. 2)
(B)).

Next, a corrected reference value for b adjacent to b is calculated. Here, it is assumed that the diffusion matrix is determined as shown in FIG. Therefore, all the deviations in A propagate to B on the right. Specifically, (reference value) − (deviation of a) = 60−2
0 = 40 is calculated. Therefore, a patch closest to the correction reference value 40 of b is selected from the color patch list. Since 40 is included in the color patch list, this is assigned to b. Remove 40 from the patch list. The deviation from the reference value in B is calculated again. The deviation is (correction reference value of b) − (dot area ratio of patch assigned to b) =
It is calculated as 40-40 = 0 (FIG. 2 (C)).

Next, a corrected reference value for C next to B is calculated. This is (reference value)-(deviation of b) = 60-0 = 6
It is calculated as 0 (FIG. 2 (D)). Therefore, the patch 70 closest to the correction reference value 60 of C is selected from the color patch list. 70 is assigned to C, and 70 is excluded from the patch list. Thereafter, the same process is repeated to obtain an array of one-dimensional single-color patches as shown in FIG.

When a moving average is calculated for every three consecutive cells in the array of FIG. 2E, the values are 63.3, 46.6, 63.3, 43.3, and 66.6, indicating that there is not much bias. This is because when the deviation of the patch at a certain position from the reference value is large, a patch that absorbs the deviation is arranged next to the patch. As the number of color patches increases, the bias can be further reduced.

Next, the case of a fifth power patch will be described. The layout is a 25 × 25 two-dimensional array as shown in FIG. The layout order is one line processing to the right from the cell (A) to (A) in the upper left corner, and when one line is completed, the processing moves down by one stage and proceeds to the right again from (B) to (B). The color patch is CMYK four-dimensional, and the reference value and the deviation are also four-dimensional values (both the reference value and the deviation are processed for each color plate). FIG. 8 shows a color patch list. The reference value is (50, 50, 50, 50). As the two-dimensional diffusion matrix, the Floyd & Steinberg type shown in FIG. 7 is used.

First, one patch is randomly selected from a color patch list. Suppose (0, 50, 75, 100) is selected. This is allocated to the cell (A), and the selected color patch is excluded from the list. Next, the pointer is moved by one, and the deviation is calculated. The deviation is (0, 50, 75, 100)-
(50, 50, 50, 50) = (-50, 0, 25, 50).

The deviation to be propagated to the neighboring cells is calculated by multiplying by the weighting coefficient of the diffusion matrix in FIG. 7 (processing step corresponding to S16 in FIG. 1). For example, the deviation to be propagated to the cell on the right (Ab) is 7/16 × (−50, 0, 25, 50) = (− 2)
2, 0, 11, 22), the modified reference value for cell (A) is (because there are no other propagated deviations), (50, 50, 50,
50) − (− 22, 0, 11, 22) = (72, 50, 39, 28) (processing step corresponding to S18). Therefore, the patch closest to (72, 50, 39, 28) from the color patch list is assigned to the cell (A). When the distance is calculated by the Euclidean distance, (75, 50, 50, 25) is selected from the color patch list shown in FIG. 7 (processing step corresponding to S20). Note that the distance may be selected based on a defined distance other than the Euclidean distance.

The color patches (0, 50, 75, 100) are
As a result of allocating to cell (A), cell (B) and cell (B)
The deviation propagating in (b) propagates from 5/16 × (−50, 0, 25, 50) = (− 16, 0, 8, 16)... A from the weighting factors of the diffusion matrix in FIG. B deviation 1/16 x (-50,0,25,50) = (-3,0,2,3) ... deviation of B b propagating from A b. The deviation that propagates from A
In addition, since deviations that propagate from A, A, and B occur in B, the correction reference values are calculated by summing the deviations. The patch of the color closest to the correction reference value is selected from the color patch list and assigned to the current position, and the assigned color patch is excluded from the color patch list. Hereinafter, as shown in the flow of FIG. 1, the pointer is moved by one again (processing step corresponding to S24), and the same processing (S16 to S20 and S2 in FIG. 1) is performed.
Repeat 4). The color chart created by the above process is different from the conventional color chart of FIG. 4 in that the color patches are seemingly arranged randomly.

[0025]

According to the color chart for printing evaluation produced by the method of the present invention, the ink consumption is almost uniform in any part of the chart. This has a remarkable effect that the ink key adjustment and setting operation when printing the evaluation chart is remarkably easy.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a method of the present invention.

FIG. 2 is an explanatory diagram of a procedure for designing a one-dimensional color chart.

FIG. 3 is a one-dimensional error diffusion matrix.

FIG. 4 is an example of a conventional color chart composed of a number of color patches.

FIG. 5 is an explanatory diagram of an ink supply mechanism in the offset printing press.

FIG. 6 is a layout of a color chart composed of 25 × 25 patches.

FIG. 7 is an example of a two-dimensional error diffusion matrix.

FIG. 8 is an example of a color patch list.

Claims (4)

[Claims] 1. A method for designing or creating a print evaluation color chart formed by arranging a large number of patches of different colors in a tile pattern, wherein a color patch to be arranged at a certain position is determined. According to the difference between the ink consumption amount of the already arranged color patch adjacent to the position and the predetermined reference value of the ink consumption amount, and the ink of the color patch to be arranged at the target position according to an appropriately determined error diffusion matrix. A method of calculating a correction reference value of consumption, selecting an unarranged color patch having a color closest to the consumption amount, arranging the color patch at that position, and repeating or repeating this procedure to design or create a color chart. 2. A print evaluation color chart formed by arranging a number of different color patches in a tile pattern, designed or created by the method of claim 1. 3. An original film or printing plate for printing a printing evaluation color chart formed by arranging a number of patches of different colors in a tile pattern by the method of claim 1. 4. A computer-readable recording medium in which printing plate making data for outputting the original plate film or printing plate according to claim 3 is recorded in a data structure and format that can be interpreted by an output device.