JPH0974486A - Density conversion table generating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To include a required density area completely by adding density data through extrapolation even when the density data does not completely include a required density area in the case of generating a density conversion table based on the density data obtained through density measurement of color patch. SOLUTION: Plural density data strings including completely a required density area are prepared. When the density data obtained by measuring the density of a test pattern does not completely include a prescribed required density area, the optimum density data connected smoothly to the original data are selected among the prepared density data strings and extrapolated to the measured density data. Then the measured density data are used to generate a density conversion table.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of creating a density conversion table in a printer using a thermal head.

[0002]

2. Description of the Related Art It is known that in a printer, especially a printer using a thermal head, even if the same image data is printed, the density changes depending on the environmental conditions such as temperature and humidity. That is, although the output density depends on the environmental condition, it is clear that such density fluctuation is not preferable.

Therefore, it has been attempted to improve the density fluctuation due to such an environmental condition (for example, Japanese Patent Laid-Open No. Hei.
137002, JP-A-5-114962).

The method is as follows. First, a printer prints a predetermined test pattern image for each print color of cyan C, magenta M, yellow Y, and black K. The test pattern image is, for example, as shown in FIG.
Usually, the color patch is such that the density gradually changes by a predetermined density width as shown in FIG. Note that, in FIG. 3, it is assumed that the concentrations are lowered in the order of a, b, c, d, e, f, g, t, j, and l.

When a test pattern image as shown in FIG. 3 is printed for each print color, the density of each patch of the printed test pattern image is measured. As a result, density data of the test pattern image is obtained for each print color.

Now, assume that the density data of a certain print color is as shown by the black circles in FIG. For example, the density data indicated by A in the figure indicates that the density was D _k when the density of a patch printed with image data having a gradation value of k was measured. The same applies to other density data. It is assumed here that the image data has 256 gradations.

In FIG. 4, the curve indicated by the broken line is a smooth connection of the measured density data indicated by black circles for easy understanding. That is, this curve is the current input / output characteristic of the printer. Further, D _min and D _max are the minimum density and the maximum density that the printer wants to represent. That is, the required density range is between the minimum density D _min and the maximum density D _max .

Now, assuming that the target input / output characteristic of the printer is as shown by the solid line in FIG. 4,
For example, when the image data of the gradation value k is input, the density of D _k0 must be printed, but at the present time, the output density when the image data of the gradation value k is input is not D _k0 but D. _{It is k} .

Such density fluctuations are caused by environmental fluctuations. Therefore, a density conversion table is created to correct the input / output characteristics shown by the broken line in FIG. 4 to the target input / output characteristics shown by the solid line. It Naturally, this density conversion table is created for each print color. The method of creating the density conversion table from the density data obtained by measuring the printed test pattern image and the target input / output characteristics of the printer is well known, and a description thereof will be omitted.

[0010]

However, as in the case shown in FIG. 4, when the measured density of the printed test pattern image completely covers the entire required density range, that is, when the minimum gradation value When the density of the patch printed with the image data is D _min or less and the density of the patch printed with the image data of the maximum gradation value is D _max or more, the density data and the target input / output of the printer. It is possible to create a density conversion table from the characteristics, but when printing a test pattern image as described above, it is affected by the environment at that time, and the density of the printed test pattern image is measured. Since a measurement error also occurs in the device, the measured concentration data completely covers the entire required concentration range as shown in FIG. 5 due to these synergistic effects. If you do not want to occur. In each figure of FIG. 5, the solid line indicates the target input / output characteristic of the printer.

That is, in FIG. 5A, the density of the patch printed with the image data of the minimum gradation value is lower than D _min , but the density of the patch printed with the image data of the maximum gradation value is lower than D _max. Has become. However, in such a case, the density range shown by _DxU in the figure cannot be output even if the image data of any gradation value is input, so that the density conversion table cannot be created.

In FIG. 5B, the density of the patch printed with the image data of the maximum gradation value is higher than D _max , but the density of the patch printed with the image data of the minimum gradation value is higher than D _min. Therefore, the density conversion table cannot be created even in such a case because the density range shown by D _{x L} in the figure cannot be output even if the image data of any gradation value is high.

Further, in FIG. 5C, the density of the patch printed with the image data of the minimum gradation value is higher than D _min , and the density of the patch printed with the image data of the maximum gradation value is D _max. Since the density is _lower , the density range indicated by D _xU and D _xL in the figure cannot be output regardless of the image data of any gradation value. A conversion table cannot be created.

However, conventionally, no consideration has been given to the case where the measured density of the test pattern image thus printed does not completely cover the entire required density range. In the case as shown in each figure of FIG. 5, the density conversion table cannot be created, or the density conversion table cannot be output even if the density conversion table is created by some method. Met.

The present invention solves the above-mentioned problems, and creates a good density conversion table even when the measured density of the printed test pattern image does not completely cover the entire required density range. It is an object of the present invention to provide a method for creating a density conversion table that can be used.

[0016]

In order to achieve the above object, the method of creating a density conversion table of the present invention prints a test pattern having a predetermined density change for each print color, and prints the printed test pattern. In the density conversion table creation method that creates the density conversion table using the density data obtained by measuring the density of the test pattern, the density data obtained by measuring the density of the test pattern does not completely include the predetermined required density range. In this case, for the density range where the density data is insufficient, the density data that can be optimally connected is selected from a plurality of density data strings prepared in advance, and the selected density data is added to determine the predetermined density data. It is characterized by obtaining density data that completely covers the required density range of, and creating a density conversion table using the density data.

[0017]

In this method of creating the density conversion table, a plurality of density data strings completely covering the required density range are prepared. If the density data obtained by measuring the density of the test pattern does not completely cover the predetermined required density range, select the density data that can be optimally connected from the prepared density data sequence, The density data is added to the measured density data. This concentration data completely covers the required concentration range.

Then, a density conversion table is created using this density data. If printing is performed using this density conversion table, it is possible to print a color image according to the target input / output characteristics.

As described above, according to the present invention, when the measured density data of the printed test pattern does not completely include the required density range, the optimum density data is added to completely cover the required density range. Since the included density data can be created, a density conversion table can be created using this density data, and thus a stable image can be printed even when the usage environment fluctuates.

[0020]

Embodiments will be described below with reference to the drawings.
FIG. 1 is a flow chart showing a method for creating a density conversion table according to the present invention.

First, a test pattern image is printed for each print color (step S1), and the density of the test pattern image is measured (step S2). Up to this point, the process is the same as the conventional one, and the density data of each print color is obtained by this.

Next, smoothing processing is performed on the obtained density data (step S3). This smoothing process is a process for reducing the measurement error of the device for measuring the density. For example, paying attention to one density data, the density data of five points of the density data of interest and the density data of four points before and after the density data. A predetermined weighting is performed on the data to obtain an average value, and the process of replacing the target concentration data with the obtained average value is performed for all the concentration data. In addition, it goes without saying that other known smoothing processing may be performed.

Next, the smoothed density data is subjected to processing for maintaining the monotonic increasing property (step S4).
This processing is the same as the processing shown in the above-mentioned Japanese Patent Laid-Open No. 5-137002, in which the abnormal point is deleted and the density data before and after the abnormal point is deleted by an appropriate interpolation method, for example, a linear interpolation method. Replace.

Next, it is judged whether or not it is necessary to perform extrapolation processing on the density data (step S5). This extrapolation process is a feature of the present invention, the details of which will be described later. In this determination process, it is determined whether or not the density data obtained in step S4 completely includes the required density range. If it is determined that the density data completely includes the required density range, the extrapolation process is not required. In this case, after performing the smoothing process (step S7), the density data and the target of the printer are processed. A density conversion table is created based on the input / output characteristics (step S8). Since a conventionally known method may be used to create the density conversion table, the description thereof will be omitted. Also, step S7
The smoothing process of 1 may use the same method as the smoothing process of step S3.

However, if the density data obtained in step S4 does not completely include the required density range, extrapolation processing is performed (step S6). The extrapolation process will be described in detail below.

Now, assume that the density data obtained in step S4 are smoothly connected to form the curve shown by the broken line in FIG. Note that, in FIG. 2, only two density data are shown on the curve indicated by the wavy line, but it is natural that there are other density data.

By the way, in the curve shown by the wavy line in FIG. 2, the minimum concentration is lower than D _min , but the maximum concentration is lower than D _max , so this concentration data does not completely include the required concentration range. Therefore, the extrapolation processing in step S6 is performed to obtain the density data that completely covers the required density range.

In the present invention, a plurality of density data strings that define predetermined input / output characteristics are prepared in advance.
Here, it is assumed that three input / output characteristics are defined as shown by A, B, and C in FIG. As a matter of course, the input / output characteristic curves of A, B, and C are obtained by smoothly connecting predetermined density data. Further, it is natural that the density data forming the input / output characteristics prepared in advance is set so as to completely include the required density range.

Therefore, first, for each prepared input / output characteristic, data having the same density as the maximum value of the measured density data is searched (hereinafter, this data will be referred to as attention data). When the data of the same density exists, the data is set as the target data, and when the data of the same density does not exist, the data having the density closest to the density is set as the target data.

As shown in FIG. 2, _assuming that the maximum density of the measured density data is D ₀ , in the input / output characteristics shown by A and the input / output characteristics shown by B, the data shown by a _n and b _m respectively. Assuming that the density is D ₀ , the data indicated by a _n in the input / output characteristic indicated by A is determined as the attention data, and the data indicated by B
In the input / output characteristic indicated by, the data indicated by b _m is determined as the attention data.

However, in the input / output characteristic shown by C, the density is D
_Assuming that the data of ₀ does not exist, two data c _k and c _{k + 1} whose density is before and after D ₀ are obtained from the data of the input / output characteristic, and the density of these data and D ₀ are obtained.
And the density difference between the two is determined, and the one with the smaller density difference is determined as the data of interest. Here, it is assumed that the data indicated by c _k in FIG. 2 is determined as the attention data.

Next, for the measured density data, the slope between the density data indicated by P, which is the end point data, and the density data indicated by Q, which is the immediately preceding point, is determined. Now, let this inclination be m. In addition, for the data of each input / output characteristic prepared in advance, the slope between the target data and the next data is obtained.

For example, as shown in FIG. 2, in the input / output characteristic indicated by A, the next data of the target data a _n is a _{n + 1.}
Then, the slope between the data a _n and the data a _{n + 1} is calculated. Now, assume that this inclination is m _a .

Similarly, in the input / output characteristics indicated by B and C in FIG. 2, the data next to the target data is b.
_{m + 1,} When a c k _{+ 1,} obtaining the slope of these data attention data b _m, and c _k. Now, it is assumed that these inclinations are m _b and m _c , respectively.

Next, the slope closest to the slope m of the measured concentration data is calculated from the slopes m _a , m _b and m _c of the input / output characteristics thus obtained. Here, if m _a is the closest to m, this means that the input / output characteristic indicated by A is selected as the optimum data to be extrapolated to the measured concentration data.

In this way, the inclination of the end point portion of the measured concentration data and the inclination at the position corresponding to the end point portion of the measured concentration data in the input / output characteristics prepared in advance are compared by extrapolation to the measured concentration data. This is because the data to be connected is the most smoothly connected to the measured concentration data.

[0037] Therefore, when the input-output characteristic shown by A as described above is selected in FIG. 2, the attention data a _n
The data from the next data a _{n + 1} to a _max which is the last data of the selected input / output characteristic is moved in parallel,
Extrapolation is added to the measured concentration data so as to smoothly connect to the end point P of the measured concentration data. Specifically, the slope of the line segment connecting the point P and the extrapolated data a _{n + 1} coincides with the slope of the line segment connecting the end point P of the measured concentration data and the point Q immediately before it. You can do it.

As a result, it is apparent that the measured concentration data which completely covers the required concentration range and has a smooth input / output characteristic can be obtained.

The above is the extrapolation processing. When the extrapolation processing is completed, a density conversion table is created based on the density data obtained by this extrapolation processing and the target input / output characteristics of the printer ( Step S8).

In the above, the case where the maximum concentration of the measured concentration data does not reach the maximum concentration D _max of the required concentration range has been described, but the minimum concentration of the measured concentration data is required as shown in FIG. 5 (b). The same applies when the minimum density D _min in the density range is not reached. However, in this case, the slope of the input / output characteristic prepared in advance is performed using the data of interest and the data immediately preceding it, and the data to be extrapolated is the first of the selected input / output characteristics. Data, that is, the data from the lowest density data to the data immediately before the data of interest is used.

Further, as shown in FIG. 5 (c), the maximum density of the measured density data does not reach the maximum density D _max of the required density range, and the minimum density of the measured density data is the minimum density of the required density range. The same applies when D _min is not reached.

As the apparatus configuration for performing the above-described processing, a color printer and a density measuring apparatus for measuring the density of a test pattern image are provided as in the conventional case. For example, only the processing of step S2 in FIG. The density measuring device may be used, and the other processes may be performed by the color printer. It is also possible to perform the processing of steps S2 to S8 in FIG. 1 by the density measuring device and transfer the created density conversion table to the LUT of the color printer.

As described above, according to the present invention,
Even when the density data obtained by measuring the test pattern image does not completely include the required density range, it is possible to completely include the required density range by extrapolating the optimum density data. , It is possible to always create a density conversion table, and as a result, even if the usage environment changes and even if there is a measurement error in the density measuring device, it is possible to perform color printing with the target input / output characteristics. Become.

[Brief description of drawings]

FIG. 1 is a flowchart showing a density conversion table creating method according to the present invention.

FIG. 2 is a diagram for explaining the extrapolation processing in step S6 of FIG.

FIG. 3 is a diagram showing an example of a test pattern image.

FIG. 4 is a diagram for explaining the reason for creating a density conversion table.

FIG. 5 is a diagram for explaining the problem of the present invention.

Claims (1)

[Claims] 1. A density conversion table for printing a test pattern having a predetermined density change for each print color, and creating a density conversion table using density data obtained by measuring the density of the printed test pattern. In the method, when the density data obtained by measuring the density of the test pattern does not completely include the predetermined required density range,
For the density range where the density data is insufficient, select the density data that can be optimally connected from a plurality of density data sequences prepared in advance, and add the selected density data to the specified required density range. A density conversion table creating method, characterized in that density data completely including the above is obtained and a density conversion table is created using the density data.