How to print color images in monochrome

Abstract

To provide a monotonization printing method of a color image which can correctly convert a color image that is arbitrarily input into a monotone image in a color tone desired by a user.SOLUTION: A monotonization printing method of a color image includes a color image L*a*b* value acquisition step of acquiring a color image L*a*b* value in a standard color space by converting a value of a color space (RGB value or CMYK value) in each coloring unit with an input ICC profile for a color image being a monotonization object, and performs printing as a monotone image in a desired single color tone by using the color image L*a*b* value. After the color image L*a*b* value acquisition step, the method includes a desired color tone L*a*b* value acquisition step of converting the color image L*a*b* value into a desired color tone L*a*b* value in a desired single color tone, and performs printing by converting the desired color tone L*a*b* value into an ink value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for printing a monotone color image, particularly a method for printing a monotone color image by monotoneizing a color image with a desired hue.

Background Art

[0002] When a color image is printed in monotone, the color image becomes a monotone image composed of shades and brightness in a single-color color scheme. In particular, an image printed only with achromatic colors such as black, white, and gray is called a grayscale image.

[0003] So far, as a method for printing a monotone color image, data for monotoneizing a color image has been created using existing image editing software, and printing has been performed based on this data. In addition, Patent Document 1 discloses a device for creating a profile capable of reproducing stable gray.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In methods using image editing software, monochrome conversion was achieved by changing the color values ​​(RGB or CMYK values) within the color space of the color image (RGB or CMYK space). However, color images that had been monochromeized by image editing software were further color-converted by the input and output ICC profiles before printing, resulting in situations where the monochrome conversion did not achieve the desired color. In other words, even if the image was monochromeized to the desired color using image editing software, the subsequent color conversion by the input and output ICC profiles could result in the printed image being a color that deviated from the desired color.

[0006] Furthermore, the profile creation device described in Patent Document 1 is a device for creating a profile that stabilizes the reproduction of colors in the gray area, and is not a device for creating a profile for converting a color image to monochrome.

[0007] This invention has been made in view of the above problems, and its purpose is to provide a method for printing color images in monochrome, which can accurately convert any input color image into a monochrome image of a hue desired by the user. [Means for solving the problem]

[0008] To achieve the above objective, the monochrome printing method for a color image described in claim 1 is: A method for monochromeizing a color image includes a step of obtaining a color image L*a*b* value by converting the color space values ​​(RGB values ​​or CMYK values) for each color unit of a color image to be monochromeized using an input ICC profile to obtain a color image L*a*b* value in a standard color space, and printing the image as a monochrome image of a desired single hue using the color image L*a*b* value, The process includes, after the color image L*a*b* value acquisition process, a desired hue L*a*b* value acquisition process which converts the color image L*a*b* value into a desired hue L*a*b* value of a single desired hue, The method is characterized by converting the desired hue L*a*b* value into an ink value and printing it.

[0009] In this configuration, for the color image to be converted to monochrome, the L*a*b* values ​​of the color image in the standard color space are first obtained for each color unit using the input ICC profile. Obtaining the L*a*b* values ​​of the color image based on this standard color space provides the basic information necessary for stable monochrome conversion. Then, for the hue to be converted to monochrome, the desired hue L*a*b* value for that hue in the standard color space is obtained.

[0010] In other words, since the lightness and chromaticity information for each color unit is obtained based on the desired hue L*a*b* value in the standard color space, it becomes possible to create a monochrome image based on differences in lightness and chromaticity under the desired hue, regardless of the printer. Therefore, it becomes possible to create a monochrome image that suppresses deviations from the desired hue, unlike conventional methods. [Effects of the Invention]

[0011] The present invention provides a monochrome printing method for color images that suppresses variations in accuracy caused by printers and deviations from the desired hue, as seen in conventional methods. [Brief explanation of the drawing]

[0012] [Figure 1] This is a flowchart (monochrome image) of one embodiment of the monochrome printing method for color images of the present invention. [Figure 2] This is an explanatory diagram of the desired hue L*a*b* values ​​(monochrome image). [Figure 3] This is an explanatory diagram of the desired hue L*a*b* values ​​(monochrome image). [Figure 4] This is an explanatory diagram showing the curve representing hue and maximum saturation. [Figure 5] This is an explanatory diagram showing the curve representing hue and maximum saturation. [Figure 6] This is an explanatory diagram of the desired hue L*a*b* values ​​(monochrome image, where the curve representing hue is a straight line). [Figure 7]Flow chart (grayscale image) of an embodiment of the method for printing a grayscale color image according to the present invention. [Figure 8] Explanatory drawing of the desired hue L*a*b* value (grayscale image).

Embodiments for Carrying Out the Invention

[0013] In the present embodiment, an image composed of shades and brightness in a single-color color scheme is referred to as a monochrome image, and an image composed only of achromatic colors is referred to as a grayscale image.

[0014] Embodiments of the method for printing a monochrome color image according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a flow chart of the method for printing a monochrome color image.

[0015] First, a color image to be monochromed is acquired (step S1). For example, when a color image created with image editing software or the like is incorporated, the RGB values or CMYK values of the input color image are obtained. Next, an input ICC profile for converting these data into a standard color space is selected (step S2). Based on the selected input ICC profile, the RGB values or CMYK values of the input color image are converted into L*a*b* values in the standard color space (step S3, L*a*b* value acquisition step). This conversion is performed, for example, on a computer by processing software incorporated in the computer.

[0016] Here, the input ICC profile converts RGB values or CMYK values into L*a*b* values in the standard color space (A2B conversion), and defines a color conversion method for changing the color tone of a printed image. The user can select an input ICC profile for converting to a desired color tone from among a plurality of input ICC profiles, and convert the RGB values or CMYK values of the input color image into L*a*b* values in the standard color space. When the input image is in raster format, this conversion is performed for the number of pixels of the input image. When the input image is in vector format, this conversion is performed for the number of colors of the lines of the figures constituting the vector image and the colors filling the interiors of the figures. The raster format is a format representing an image as a set of pixels, and photos and the like correspond to raster format images. On the other hand, the vector format is a format representing an image with geometric information such as points, straight lines, curves, and surfaces, and figures created with the "Shape" function in PowerPoint and figures created with Illustrator correspond to vector format images. In this specification, the pixels of the input image, the colors of the lines of the figures constituting the vector image, and the colors filling the interiors of the figures are used as the coloring units of the color image.

[0017] Next, a setting of a desired hue (step S4, desired hue setting step) is performed. This setting operation is performed by displaying the standard color space, that is, the L*a*b* coordinate space, on a display unit (for example, a monitor screen) on a computer. At this time, the color gamut of the input ICC profile may be displayed on the monitor screen. As described above, a program for the setting operation is incorporated in the computer, and the user can perform the setting while viewing the standard color space on the monitor screen.

[0018] Here, as shown in FIG. 2, the L*a*b* coordinates of the standard color space are three-dimensional coordinates of the a* axis, the b* axis, and the L* axis. The L* axis represents lightness (from 0 to 100). The a* axis and the b* axis indicate the direction of color, where +a* indicates the red direction (from 0 to 127), -a* indicates the green direction (from -128 to 0), +b* indicates the yellow direction (from 0 to 127), and -b* indicates the blue direction (from -128 to 0). The hue is indicated by the ratio of the a* value and the b* value, and the angle θ representing the hue in the standard color space is θ = tan ―1It is defined as (b* / a*). Also, the saturation c* is (a*·a*+b*·b*). 1 / 2 This is represented by the following formula: L* represents lightness, a* and b* represent chromaticity, and the hue is determined by the ratio of a* to b*.

[0019] Setting a desired hue is equivalent to setting the angle θ representing the hue on the L*a*b* coordinate system, which is equivalent to setting a single curve 32 as shown in Figure 2. Figure 3 is a top view of the a*-b* plane. In other words, setting the hue is equivalent to setting the angle θ representing the hue. On this curve representing the hue, the ratio of the a* value to the b* value remains unchanged (the values ​​of a* and b* change), while the value of the lightness L* is different.

[0020] If you want to increase the redness of the hue represented by curve 32, you can, for example, select curve 32' which is located further in the +a* direction. In this way, the user can choose the desired hue.

[0021] The start and end points of curve 32 are located on the L* axis (saturation c* = zero) or near the L* axis where saturation c* is 20 or less. By setting the saturation of the brightest parts to zero or near zero, the possibility of ink being injected into areas that were white in the original color image is eliminated. Furthermore, by setting the saturation of the darkest parts to zero or near zero, the possibility of losing the dark tones of the original color image when the saturation range of the dark parts in the printer's color reproduction range (gamut) is narrow is eliminated. Figure 2 shows an example where the end point is on the L* axis.

[0022] In this embodiment, the saturation c* is set to 20 or less in the vicinity of the L* axis, but more preferably it is 15 or less, and even more preferably 10 or less.

[0023] Furthermore, the curve 32 is preferably semi-circular, as shown in Figure 4, or parabolic, as shown in Figure 5. This ensures that the curve 32 (32') changes monotonically in the L*a*b* space, preventing abrupt changes in saturation and brightness based on the a* and b* values, resulting in a very natural-looking monochrome image. Note that the point on the c* axis, which represents saturation, that is furthest from the L* axis of the curve 32 represents the maximum saturation c*max.

[0024] Next, set the maximum saturation (Step S5, Maximum Saturation Setting Process). The maximum saturation is (a*·a*+b*·b*). 1 / 2 This is the maximum value and corresponds to c*max of the curve shown in Figures 4 and 5. When setting curve 32 (32') on the computer's display screen, the user can also set the maximum saturation c*max at the same time. This allows for obtaining a monochrome image with rich variations in saturation.

[0025] Next, in the desired hue L*a*b* value acquisition step 6, the desired hue L*a*b* value corresponding to the L*a*b* value for each coloring unit of the color image is obtained. This is obtained as follows: For the multiple L*a*b* values ​​obtained in the previous L*a*b* value acquisition step (step S3), the intersection point B is found between the plane 30 parallel to the a*-b* plane containing a certain L*a*b* value (point A in Figure 2) and the curve 32 shown in the L*a*b* space shown in Figure 2 (intersection point B' in the case of curve 32'). This intersection point is the desired hue L*a*b* value corresponding to a specific L*a*b* value. However, the color difference from intersection point B is (L*·L*+a*·a*+b*·b*). 1 / 2 The desired hue L*a*b* value may be a point that is 10 or less away from the intersection point B. In this case, it is even more preferable to choose a point that is 5 or less away from the intersection point B as the desired hue L*a*b* value. The process of determining the desired hue L*a*b* value is performed for all L*a*b* values. In this way, the desired hue L*a*b* value of the desired monochrome image on the desired hue corresponding to all L*a*b* values ​​is obtained. Note that this process is performed on a computer by installing software programmed to determine the desired hue L*a*b* value into the computer.

[0026] Next, the desired hue L*a*b* value obtained in the desired hue L*a*b* value acquisition step is converted into an ink value using the output ICC profile (step S7, ink value conversion step). In other words, the input color image is made printable on the printer with the hue set by the user. Then, by printing in the printing step (step S8), the desired monochrome image can be obtained (step S9).

[0027] Here, the output ICC profile converts the L*a*b* values ​​of the standard color space into ink values ​​(B2A conversion), and defines a color conversion method for outputting printed images according to the characteristics of the printer. Ink value is, for example, a value that indicates how much ink is used during printing. For example, when using a printer equipped with four CMYK inks, the output ICC profile converts the desired hue L*a*b* value into the amount of each CMYK ink used. Users can select the output ICC profile according to the type of ink used for printing, the print resolution, and the print speed. Alternatively, the output ICC profile may be automatically determined according to the print mode.

[0028] In the above example, a curve representing the desired hue was set in the desired hue setting step, but as shown in Figure 6, a straight line 36 near the L* axis representing the desired hue may also be set. For example, a straight line parallel to the L* axis may be set where the saturation c* is greater than 0 and less than or equal to 20. In the straight line 36 of Figure 6, since both the a* and b* saturation values ​​are positive, a warm-toned monochrome image is obtained. If a cool-toned monochrome image is to be obtained, a straight line can be set in the region where both the a* and b* values ​​are negative, such as straight line 36'. Note that when a straight line parallel to the L* axis is set in the desired hue setting step, the maximum saturation setting step (step S5) that was performed when a curve was set in the desired hue setting step is not necessary. However, the straight line 36 may have a curved portion where the start and end points are close to the L* axis, as shown in the curve 32 of Figure 2. In this case, the maximum saturation setting step (step S5) may be performed.

[0029] Next, we will explain the method for printing grayscale images. Figure 7 is a flowchart of the grayscale printing method for color images. The steps of acquiring the color image to be grayscaled (step S1), selecting an input ICC profile to convert the RGB or CMYK values ​​of the input color image to the standard color space (step S2), and converting the RGB or CMYK values ​​of the input color image to L*a*b* values ​​in the standard color space based on the selected input ICC profile (step S3, L*a*b* value acquisition step) are the same as in the case of monochrome images.

[0030] Next, in the desired gray L*a*b* value acquisition step (Step 4), the desired gray L*a*b* value corresponding to the L*a*b* value for each coloring unit of the color image is obtained. This is obtained as follows: For the multiple L*a*b* values ​​obtained in the previous L*a*b* value acquisition step (Step S3), the intersection point F between the plane 40 parallel to the a*-b* plane containing a certain L*a*b* value (point E in Figure 8) and the L* axis 42 is determined in the L*a*b* space shown in Figure 8. This intersection point is the desired gray L*a*b* value corresponding to a certain L*a*b* value. However, the color difference (L*·L*+a*·a*+b*·b*) is obtained from the intersection point F. 1 / 2 The desired gray L*a*b* value may be a point that is 10 or less away from the intersection point F. In this case, it is even more preferable to use a point that is 5 or less away from the intersection point F as the desired gray L*a*b* value. This process is performed for all L*a*b* values. In this way, the desired gray L*a*b* value corresponding to all L*a*b* values ​​is obtained. Note that this process is performed on a computer by installing software programmed to find the desired gray L*a*b* value in this way into the computer.

[0031] Next, the desired gray L*a*b* values ​​obtained in the desired gray L*a*b* value acquisition step are converted into ink values ​​using the output ICC profile (step S5, ink value conversion step). In other words, the desired grayscale image is made printable by the printer. Then, the desired grayscale image can be obtained by printing in the printing step (step S6) (step S7).

[0032] According to the present invention's method for printing color images in monochrome, the RGB or CMYK values ​​of the input color image are converted to L*a*b* values ​​in the L*a*b* space using an input ICC profile. Based on the converted L*a*b* values, the desired hue L*a*b* value at the desired hue desired by the user is determined. Therefore, it is possible to provide a monochrome image that suppresses variations in accuracy due to the printer and deviations from the desired hue, as seen in conventional methods.

[0033] Furthermore, in obtaining the desired hue L*a*b* value, the L* value of the color image L*a*b* value is maintained within a predetermined range while converting the color image L*a*b* value to the desired hue L*a*b* value of a single desired hue, thereby making it possible to uniquely determine the desired hue L*a*b* value.

[0034] Furthermore, in obtaining the desired hue L*a*b* value, information on the intensity of saturation for each coloring unit is added without changing the desired hue, so a monochrome image with rich variations in saturation at the desired hue can be obtained.

[0035] Furthermore, in obtaining the desired hue L*a*b* values, the intensity of saturation for each coloring unit changes monotonically with respect to the L* value. As a result, the saturation and brightness do not change abruptly with respect to the a* and b* values, and a very natural-looking monochrome image is obtained.

[0036] Furthermore, in obtaining the desired hue L*a*b* values, the saturation strength for each coloring unit was kept constant for at least some L* values, resulting in a monochrome image with constant saturation.

[0037] Furthermore, by selecting the input ICC profile when acquiring the L*a*b* values ​​of a color image, it is possible to convert the input color image to the desired color tone.

[0038] Furthermore, in a grayscale printing method for a color image, the method includes a step to obtain a color image L*a*b* value by converting the color space values ​​(RGB or CMYK values) for each coloring unit of the color image to be grayscaled using an input ICC profile, and printing the desired grayscale image using the color image L*a*b* value. In this method, after the color image L*a*b* value acquisition step, the method includes a step to obtain a desired gray L*a*b* value by setting the a* and b* values ​​of the color image L*a*b* value to zero, and then converting the desired gray L*a*b* value to an ink value for printing. This makes it possible to provide a grayscale image that suppresses variations in accuracy due to the printer and deviations from the desired gray color, as in conventional methods.

[0039] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, the curve 32 representing the desired hue is semicircular or parabolic, but it is not limited to these and can be set in any other way. [Explanation of Symbols]

[0040] L* Coordinate representing lightness in the standard color space a*, b* Coordinates representing the whiteness in the standard color space. c* saturation θ is the angle on the *-b* plane representing hue. A point with a specific L*a*b* value obtained in the A, C, EL*a*b* value acquisition process B, B', D, D' Desired hue L*a*b* values ​​corresponding to points A and C above F Desired gray L*a*b* value corresponding to point E above

Claims

1. A method for monochromeizing a color image includes a step of obtaining a color image L*a*b* value by converting the color space value (RGB value or CMYK value) for each color unit of a color image to be monochromeized using an input ICC profile to obtain a color image L*a*b* value in a standard color space, and printing the image as a monochrome image of a desired single hue using the color image L*a*b* value, The process of setting the maximum saturation, The process includes, after the color image L*a*b* value acquisition step, a desired hue L*a*b* value acquisition step which converts the color image L*a*b* value to a desired hue L*a*b* value of a single hue for which monochrome conversion is desired, In obtaining the desired hue L*a*b* value, the point furthest from the L* axis passes through the maximum saturation, and the point at the intersection of the curve representing the desired hue and a plane parallel to the a*-b* plane containing the color image L*a*b* value is obtained as the desired hue L*a*b* value, where the color difference is 10 or less. A method for printing a color image in monochrome, characterized by converting the desired hue L*a*b* value into an ink value and printing it.

2. The method for printing a color image in monochrome according to Claim 1, characterized in that the saturation of the curve changes monotonically with respect to the L* value.

3. A method for monochromeizing a color image includes a step of obtaining a color image L*a*b* value by converting the color space value (RGB value or CMYK value) for each color unit of a color image to be monochromeized using an input ICC profile to obtain a color image L*a*b* value in a standard color space, and printing the image as a monochrome image of a desired single hue using the color image L*a*b* value, The process includes, after the color image L*a*b* value acquisition step, a desired hue L*a*b* value acquisition step in which the color image L*a*b* value is converted to a desired hue L*a*b* value of a single hue for which monochrome conversion is desired, In obtaining the desired hue L*a*b* values, points with a color difference of 10 or less are obtained as the desired hue L*a*b* values ​​from the intersection of a straight line representing the desired hue, which has a saturation greater than 0 for at least some of the L* values, is parallel to the L* axis and has a saturation of 20 or less, and is parallel to the a*-b* plane containing the color image L*a*b* values. A method for printing a color image in monochrome, characterized by obtaining the desired hue L*a*b* value and converting it to an ink value for printing.

4. The method for printing a color image in monochrome according to any one of claims 1 to 3, characterized in that the input ICC profile is selected when acquiring the L*a*b* values ​​of the color image.

Images