CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Japanese Patent Application No. 2020-209258, filed on Dec. 17, 2020. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

TECHNICAL FIELD

The present disclosure relates to a print method for printing an uneven portion having unevenness on a surface on a print medium.

DESCRIPTION OF THE BACKGROUND ART

Conventionally, there is known a printing and object-shaping system that performs a 2.5-dimensional operation between printing of a two-dimensional image and shaping of a three-dimensional object to print an unevenness shape having unevenness on a surface on a print medium (see, for example, Japanese Unexamined Patent Publication No. 2016-43618 (Patent Literature 1)). The printing and object-shaping system described in Japanese Unexamined Patent Publication No. 2016-43618 includes an inkjet head that ejects an ultraviolet-curable ink, and an ultraviolet light source that irradiates the ink ejected on a print medium with ultraviolet light. In this printing and object-shaping system, an ink layer formed by an ink ejected from an inkjet head and cured by ultraviolet light applied from an ultraviolet light source is sequentially stacked on a print medium to print an unevenness shape on the print medium.

In addition, conventionally, an embossing simulation apparatus that simulates an unevenness shape of a face material surface of an embossed wallpaper or leather is known (see, for example, Japanese Unexamined Patent Publication No. 2019-12378 (Patent Literature 2)). In the simulation apparatus described in Japanese Unexamined Patent Publication No. 2019-12378, in the simulation information table stored in the storage portion, the height of the unevenness shape on the face material surface of wallpaper, leather, or the like is represented in 8-bit (256 gradations) grayscale. Furthermore, conventionally, an image data conversion apparatus that converts color image data into black-and-white image data by gray-scaling is known (see, for example, Japanese Patent No. 6338194 (Patent Literature 3)). The image data conversion apparatus described in Japanese Patent No. 6338194 gray-scales color image data, prepares a histogram of luminance values for the gray-scaled image data, and executes predetermined processing based on the prepared histogram.

[Patent Literature 1]: Japanese Unexamined Patent Publication No. 2016-43618

[Patent Literature 2]: Japanese Unexamined Patent Publication No. 2019-12378

[Patent Literature 3]: Japanese Patent No. 6338194

SUMMARY

The inventor of the present application has studied a method for printing an uneven portion including a plurality of stacked ink layers and having unevenness on the surface on a print medium by an inkjet printer. For example, the inventor of the present application has studied the following print method as a method for printing a woodgrain uneven portion on the entire print medium (seeFIG. 4), or printing an uneven portion made of a picture of tigers on a part of the print medium (seeFIG. 5).

That is, when in the uneven portion3, a portion that gives thickness to the uneven portion3is defined as the thickly-piled portion3a,and the thickest portion in the thickly-piled portion3aincludes, for example, 10-layer-stacked ink layers (seeFIGS. 8B and 18B), first, grayscale image data is prepared being image data including the uneven portion3to be printed on the print medium2and being image data in which the thickness of the thickly-piled portion3ais represented by, for example, 256 gradations (8 bits) of grayscale. For example, the grayscale image data shown inFIG. 4and the grayscale image data shown inFIG. 5are prepared. In this case, for example, an operator prepares grayscale image data using a personal computer (PC) in which image preparation software is installed. In the grayscale image data shown inFIGS. 4 and 5, the density of the image increases as the thickness of the thickly-piled portion3aincreases.

Thereafter, a histogram of luminance values of the prepared grayscale image data is automatically prepared on the PC. That is, a histogram of the luminance values of the grayscale image data with the luminance value of 256 gradations (0 to 255) on the horizontal axis and the number of pixels on the vertical axis is prepared on the PC. The histogram shown inFIG. 6is a histogram of luminance values of the grayscale image data shown inFIG. 4, and the histogram shown inFIG. 17is a histogram of luminance values of the grayscale image data shown inFIG. 5. In the histograms shown inFIGS. 6 and 17, the luminance value increases as the density of the image increases.

Thereafter, the luminance values of 256 gradations of the created histogram are equally divided into 10, and a range of 10 luminance values (luminance value range) is set. That is, the luminance value of 256 gradations of the histogram is equally divided into 10 being is the same number as the number of stacking of the ink layers of the thickest portion in the thickly-piled portion3a,and 10 luminance value ranges are set. Specifically, luminance values of 256 gradations of the histogram are equally divided into 10, and as shown inFIGS. 6 and 17, a first luminance value range R1in which the luminance value is 255 or less and 229.5 or more, a second luminance value range R2in which the luminance value is less than 229.5 and 204 or more, a third luminance value range R3in which the luminance value is less than 204 and 178.5 or more, a fourth luminance value range R4in which the luminance value is less than 178.5 and 153 or more, a fifth luminance value range R5in which the luminance value is less than 153 and 127.5 or more, a sixth luminance value range R6in which the luminance value is less than 127.5 and 102 or more, a seventh luminance value range R7in which the luminance value is less than 102 and 76.5 or more, an eighth luminance value range R8in which the luminance value is less than 76.5 and 51 or more, a ninth luminance value range R9in which the luminance value is less than 51 and 25.5 or more, and a tenth luminance value range R10in which the luminance value is less than 25.5 and exceeds 0 are set.

Thereafter, printing is performed on the print medium2based on the set luminance value range. When printing is performed on the print medium2, for example, first, a color ink layer3bmade of the cured color ink is formed, and a thickly-piled portion3amade of the cured clear ink is formed thereon (seeFIGS. 8B and 18B). Since the color ink layer3bis composed of one ink layer, printing of the ink layer is performed once when the color ink layer3bis formed. In addition, as described above, since the thickest portion in the thickly-piled portion3ais composed of 10 ink layers, printing of the ink layer is performed 10 times when the thickly-piled portion3ais formed.

When the thickly-piled portion3ais formed, in the portion in which the luminance value is included in the first luminance value range R1in the grayscale image data, ink layers of 10 layers are printed from the first printing of the ink layer to the tenth printing of the ink layer, and the printed ink layers of 10 layers are sequentially stacked (see hatched portions inFIGS. 8A, 8B, 18A, and 18B). In addition, when the thickly-piled portion3ais formed, in the portion in which the luminance value is included in the second luminance value range R2in the grayscale image data, ink layers of 9 layers are printed from the second printing of the ink layer to the tenth printing of the ink layer, and the printed ink layers of 9 layers are sequentially stacked, in the portion in which the luminance value is included in the third luminance value range R3in the grayscale image data, ink layers of 8 layers are printed from the third printing of the ink layer to the tenth printing of the ink layer, and the printed ink layers of 8 layers are sequentially stacked, and in the portion in which the luminance value is included in the fourth luminance value range R4in the grayscale image data, ink layers of 7 layers are printed from the fourth printing of the ink layer to the tenth printing of the ink layer, and the printed ink layers of 7 layers are sequentially stacked (see hatched portions inFIGS. 8A, 8B, 18A, and 18B).

In addition, when the thickly-piled portion3ais formed, in the portion in which the luminance value is included in the fifth luminance value range R5in the grayscale image data, ink layers of 6 layers are printed from the fifth printing of the ink layer to the tenth printing of the ink layer, and the printed ink layers of 6 layers are sequentially stacked, in the portion in which the luminance value is included in the sixth luminance value range R6in the grayscale image data, ink layers of 5 layers are printed from the sixth printing of the ink layer to the tenth printing of the ink layer, and the printed ink layers of 5 layers are sequentially stacked, in the portion in which the luminance value is included in the seventh luminance value range R7in the grayscale image data, ink layers of 4 layers are printed from the seventh printing of the ink layer to the tenth printing of the ink layer, and the printed ink layers of 4 layers are sequentially stacked, in the portion in which the luminance value is included in the eighth luminance value range R8in the grayscale image data, ink layers of 3 layers are printed from the eighth printing of the ink layer to the tenth printing of the ink layer, and the printed ink layers of 3 layers are sequentially stacked, in the portion in which the luminance value is included in the ninth luminance value range R9in the grayscale image data, ink layers of 2 layers are printed at the ninth printing of the ink layer and the tenth printing of the ink layer, and the printed ink layers of 2 layers are stacked, in the portion in which the luminance value is included in the tenth luminance value range R10in the grayscale image data, an ink layer of 1 layer is printed at the tenth printing of the ink layer, and in the portion in which the luminance value is 0 in the grayscale image data, no ink layer is printed (see hatched portions inFIGS. 8A, 8B, 18A, and 18B).

FIG. 8Ais a diagram for illustrating print data on each printing from the first printing of the ink layer to the tenth printing of the ink layer in a predetermined longitudinal section of the thickly-piled portion3aprinted based on the luminance value range shown inFIG. 6. For example, in a portion where the luminance value of the grayscale image data is 250, ink layers of 10 layers are printed from the first printing of the ink layer to the tenth printing of the ink layer, in a portion where the luminance value of the grayscale image data is 140, ink layers of 6 layers are printed from the fifth printing of the ink layer to the tenth printing of the ink layer, and in a portion where the luminance value of the grayscale image data is 30, ink layers of 2 layers are printed by the ninth printing of the ink layer and the tenth printing of the ink layer.FIG. 8Bis a diagram for illustrating the unevenness state of the surface of the uneven portion3when the thickly-piled portion3ais printed according to the print data shown inFIG. 8A.

In addition,FIG. 18Ais a diagram for illustrating print data on each printing from the first printing of the ink layer to the tenth printing of the ink layer in a predetermined longitudinal section of the thickly-piled portion3aprinted based on the luminance value range shown inFIG. 17. For example, in a portion where the luminance value of the grayscale image data is 250, ink layers of 10 layers are printed from the first printing of the ink layer to the tenth printing of the ink layer, and in a portion where the luminance value of the grayscale image data is 228, ink layers of 9 layers are printed from the second printing of the ink layer to the tenth printing of the ink layer.FIG. 18Bis a diagram for illustrating the unevenness state of the surface of the uneven portion3when the thickly-piled portion3ais printed according to the print data shown inFIG. 18A.

In the case of the grayscale image data shown inFIG. 4, as shown inFIG. 6, since there is no deviation in frequency distribution over the entire region of the luminance values of 256 gradations (that is, since there is no histogram bias), even if the luminance values of 256 gradations are equally divided into 10 and 10 luminance value ranges are set as described above, and printing is performed as described above, the number of stacking of the ink layers in the portion constituting the thickly-piled portion3ahas variation as shown inFIG. 8B. Therefore, in the case of the grayscale image data shown inFIG. 4, even if the printing is performed as described above, as shown inFIG. 8B, the unevenness of the surface of the uneven portion3is clear, and the unevenness feeling appears on the surface of the uneven portion3.

On the other hand, in the case of the grayscale image data shown inFIG. 5, as shown inFIG. 17, the frequency of the luminance values in the range from 255 to 150 and the frequency when the luminance value is 0 are large, and there is a bias in the frequency distribution (that is, there is a histogram bias). Therefore, when the luminance value of 256 gradations is equally divided into 10, 10 luminance value ranges are set, and printing is performed as described above, as shown inFIG. 18B, the number of stacking of the ink layers in the portion constituting the thickly-piled portion3ais less likely to cause variation. Therefore, in the case of the grayscale image data shown inFIG. 5, when printing is performed as described above, as shown inFIG. 18B, the unevenness of the surface of the uneven portion3is not clear (that is, the surface of the uneven portion3is flat), and the unevenness feeling is less likely to appear on the surface of the uneven portion3.

Thus, the present disclosure provides a print method for printing an uneven portion having unevenness on a surface on a print medium, the print method making it possible to clarify the unevenness of the surface of the uneven portion and express the unevenness feeling of the surface of the uneven portion regardless of whether there is a bias or there is no bias in a histogram of luminance values of grayscale image data in which the thickness of a thickly-piled portion being a portion for giving a thickness to the uneven portion is represented by a grayscale of predetermined gradations.

According to an aspect of the invention, a print method of the present disclosure is a print method for printing an uneven portion constituted by a plurality of stacked ink layers and having unevenness on a surface of the uneven portion on a print medium by an inkjet printer, the print method including: when a portion that gives a thickness to the uneven portion in the uneven portion is a thickly-piled portion, the number of stacking of the ink layers of a thickest portion in the thickly-piled portion is N, and a natural number of N or less is M, an image data preparation step of preparing grayscale image data being image data including the uneven portion and being image data representing a thickness of the thickly-piled portion with a grayscale of predetermined gradations; a histogram preparation step of preparing a histogram of luminance values of the grayscale image data prepared in the image data preparation step; a luminance value range setting step of dividing a luminance value of the predetermined gradations of the histogram prepared in the histogram preparation step into N and setting a range of N luminance values; and a printing step of performing printing on the print medium based on a luminance value range being a range of a luminance value set in the luminance value range setting step. The printing step includes performing printing of the ink layer N times when the thickly-piled portion is formed. A luminance value of a darkest portion in the grayscale image data is maximum. The luminance value range including a maximum luminance value being a maximum value among luminance values of the predetermined gradations is set as a maximum luminance value range, and the luminance value range not including a luminance value of 0 but including a luminance value of 1 is set as a minimum luminance value range. A luminance value of a darkest portion in the grayscale image data is included in the maximum luminance value range. When the thickly-piled portion is formed in the printing step, in a portion in which a luminance value is included in the M-th luminance value range from the maximum luminance value range toward the minimum luminance value range in the grayscale image data, printing of the ink layers of (N−M+1) layers from an M-th printing of the ink layer to an N-th printing of the ink layer is performed, and in a portion in which a luminance value is 0 in the grayscale image data, printing of the ink layer is not performed. The luminance value range setting step includes adjusting a division position of a luminance value of the predetermined gradations while checking the histogram displayed on a display that is predetermined.

In addition, according to another aspect of the invention, a print method of the present disclosure is a print method for printing an uneven portion constituted by a plurality of stacked ink layers and having unevenness on a surface of the uneven portion on a print medium by an inkjet printer, the print method including: when a portion that gives a thickness to the uneven portion in the uneven portion is a thickly-piled portion, the number of stacking of the ink layers of a thickest portion in the thickly-piled portion is N, and a natural number of N or less is M, an image data preparation step of preparing grayscale image data being image data including the uneven portion and being image data representing a thickness of the thickly-piled portion with a grayscale of predetermined gradations; a histogram preparation step of preparing a histogram of luminance values of the grayscale image data prepared in the image data preparation step; a luminance value range setting step of dividing a luminance value of the predetermined gradations of the histogram prepared in the histogram preparation step into N and setting a range of N luminance values; and a printing step of performing printing on the print medium based on a luminance value range being a range of a luminance value set in the luminance value range setting step. The printing step includes performing printing of the ink layer N times when the thickly-piled portion is formed. A luminance value of a darkest portion in the grayscale image data is minimum. The luminance value range not including a maximum luminance value being a maximum value among luminance values of the predetermined gradations but including a luminance value being a second largest after the maximum luminance value is set as a maximum luminance value range, and the luminance value range including a luminance value of 0 is set as a minimum luminance value range. A luminance value of a darkest portion in the grayscale image data is included in the minimum luminance value range. When the thickly-piled portion is formed in the printing step, in a portion in which a luminance value is included in the M-th luminance value range from the minimum luminance value range toward the maximum luminance value range in the grayscale image data, printing of the ink layers of (N−M+1) layers from an M-th printing of the ink layer to an N-th printing of the ink layer is performed, and in a portion in which a luminance value is the maximum luminance value in the grayscale image data, printing of the ink layer is not performed. The luminance value range setting step includes adjusting a division position of a luminance value of the predetermined gradations while checking the histogram displayed on a display that is predetermined.

In the print method of the present disclosure, in the luminance value range setting step, the division position of the luminance value of the predetermined gradations is adjusted while the histogram displayed on the display that is predetermined is checked. Therefore, in the present disclosure, it is possible to set the division position of the luminance value of the predetermined gradations to be divided into N so that the unevenness of the surface of the uneven portion can be made clear regardless of whether there is a bias or there is no bias in the histogram of the luminance values of the grayscale image data in which the thickness of the thickly-piled portion is represented with the grayscale of the predetermined gradations. Therefore, when printing is performed in the print method of the present disclosure, it is possible to make the unevenness of the surface of the uneven portion clear and express the unevenness feeling of the surface of the uneven portion regardless of whether there is a bias or there is no bias in the histogram of the luminance values of the grayscale image data.

In the present disclosure, in the luminance value range setting step, for example, when the frequency in a specific range of the histogram increases, the number of divisions of the luminance value of the predetermined gradations in the specific range is increased.

In the present disclosure, in the luminance value range setting step, it is preferable that the division position of the luminance value of the predetermined gradations can be set to any position. With this configuration, it is possible to set the division position of the luminance value of the predetermined gradations which is to be divided into N so that the unevenness of the surface of the uneven portion can be made clearer.

In the present disclosure, in the luminance value range setting step, an image corresponding to the ink layer on which printing is to be performed for the M-th time in the thickly-piled portion is preferably displayable on the display. With this configuration, in the luminance value range setting step, the division position of the luminance value of the predetermined gradations can be adjusted while the image corresponding to each ink layer in the thickly-piled portion is checked on the display. Therefore, it is possible to set the division position of the luminance value of the predetermined gradations which is to be divided into N so that the unevenness of the surface of the uneven portion can be made clearer.

In the present disclosure, for example, the thickly-piled portion is formed by stacking ink layers made of a cured clear ink. The uneven portion includes a color ink layer made of a cured color ink and the thickly-piled portion. The thickly-piled portion is formed on the color ink layer, or the color ink layer is formed on the thickly-piled portion. In addition, in the present disclosure, the thickly-piled portion may be formed by stacking ink layers made of a cured color ink. The uneven portion may include a color ink layer made of a cured color ink, a white ink layer made of a cured white ink, and the thickly-piled portion. The white ink layer may be formed on the thickly-piled portion, and the color ink layer is formed on the white ink layer.

As described above, in the present disclosure, in a print method for printing an uneven portion having unevenness on a surface on a print medium, it is possible to make the unevenness of the surface of the uneven portion clear and express the unevenness feeling of the surface of the uneven portion regardless of whether there is a bias or there is no bias in a histogram of luminance values of grayscale image data in which the thickness of a thickly-piled portion being a portion for giving a thickness to the uneven portion is represented by a grayscale of predetermined gradations.

