Method for editing input profiles, input profile editing device, program, and color conversion method

Abstract

To provide an input profile editing method which can make an image higher saturation by editing brightness and saturation.SOLUTION: An input file editing method comprises: an input profile acquisition step S1 of acquiring an input profile describing a correspondence between a hue value in a first color system depending on an instrument and a hue value in an L*a*b* color system as a second color system independent on the instrument; a brightness target value setting step S2 of setting a target value of the brightness correspondingly to the hue and saturation in an L*a*b* space; a brightness editing step S3 of converting an L* value according to the input profile in the direction of approaching the target value of the brightness; and a saturation editing step S4 of converting each of a* value and b* value in the hue value in which the L* value is edited in the direction of being apart from the center of an a*b* plane.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an input profile editing method, an input profile editing apparatus, a program, a color conversion method, and the like. Note that the input profile is also referred to as an input-side device profile. [Background Art]

[0002] Hereinafter, a description will be given of an example of a method for color-converting color values (RGB values, CMYK values, etc.) of an input image into L * a * b * values (hereinafter simply referred to as L * a * b * values).

[0003] The color values of an input image are converted into device-independent color values (L * a * b * values) by means of an input ICC profile, and then converted into color values dependent on an image output device by means of an output ICC profile, for example, CMYK values for a CMYK printer, or CMYKOr values for a CMYKOr printer.

[0004] An input ICC profile (hereinafter also simply referred to as an input profile) defines a color conversion method for converting color values of an input image into L * a * b * values. By changing the input ICC profile, the hue to be output can be changed.

[0005] Furthermore, an output ICC profile (hereinafter also simply referred to as an output profile) defines a color conversion method for converting color values in accordance with the characteristics of an image output device. When printing with a printer, output ICC profiles are prepared according to the printer model, the types of loaded ink colors, printing resolution, printing speed, and other factors.

[0006] Patent Document 1 describes how to reference an input ICC profile to obtain the RGB data of an input image. * a * b * The color value of the color system, in other words, L as a color value * a * b * When converting to a value, L corresponds to RGB data of chromatic colors. * a * b * Regarding the value, saturation C * Convert to increase the L corresponding to achromatic RGB data. * a * b * The document states that the values ​​should remain as they are, after being converted by the input ICC profile. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 5958725 [Overview of the project] [Problems that the invention aims to solve]

[0008] Patent Document 1 describes L corresponding to chromatic RGB data. * a * b * Among the values, a * Value and b * The color is converted to increase saturation by only changing the value. That is, L * The values ​​have not been changed.

[0009] However, brightness, that is, L * Depending on the value, a * Value and b * Changes in vividness due to fluctuations in the value may not be easily apparent. For example, in relatively bright areas or relatively dark areas. * Values ​​and b *Even if the values ​​are changed, the output image depends on the device that outputs the image, such as the printer's gamut, so it may be difficult to see any change in the vividness of the printed image.

[0010] Therefore, a technology is desired that takes brightness into consideration to make printed images more vivid. However, L * a * b * Because the number of grid points (hereinafter simply referred to as "points") contained in the color gamut of a color system is very large, for example, it is necessary to select from among them points that should be corrected and points that should not be corrected, and then correct, or convert, the points that should be corrected by an appropriate amount, and moreover, edited L * Associating a with a value * value, b * To properly convert values ​​and obtain images with increased vibrancy, the technique of editing input profiles, which are systematized according to the purpose, is necessary.

[0011] If editing is performed improperly, the desired effect may not be achieved. For example, it may inappropriately alter the shape of the gammart's outline, potentially negatively impacting the print image quality.

[0012] The above Patent Document 1 contains L * value, a * value, b * The text does not describe the input profile editing technique that allows for the simultaneous editing of three values—in other words, editing brightness and saturation to make the image more saturated—nor does it describe a solution to the above problem.

[0013] Note L * a * b * In a color space, saturation is a * b * It is expressed as the distance from the center on a plane. In other words, saturation is a * value, b * It can be expressed as the square root of the sum of the squares of the values, and therefore, a * , b *By editing each of the values, the saturation value, i.e., c * The value can be edited.

[0014] One objective of the present invention is to provide an input profile editing method that makes an image more saturated by editing its brightness and saturation.

[0015] Other objects of the present invention will become apparent to those skilled in the art by referring to the embodiments and best embodiments described below, as well as the accompanying drawings. [Means for solving the problem]

[0016] The following are examples of embodiments of the present invention to facilitate understanding of its outline.

[0017] In an embodiment according to the present invention, the method for editing an input profile includes color values ​​in a first color system that is dependent on the device and L as a second color system that is independent of the device. * a * b * An input profile acquisition step that obtains an input profile that describes the correspondence with color values ​​in the color system, and L * a * b * A brightness target value setting step that sets a brightness target value corresponding to the hue and saturation in space; a brightness editing step that converts the L value according to the input profile in a direction that approaches the brightness target value; and a according to the input profile * value, b * Each of the values ​​is a * b * This includes a saturation editing step that converts the saturation away from the center of the plane.

[0018] In an embodiment of the present invention, a target value is set in correspondence with hue and saturation to determine the target value when editing brightness, and the brightness is appropriately converted in a direction that approaches that target value, and in conjunction with this, a * value, b *By converting each value in a direction that increases saturation, it is possible to create an input profile editing method that makes the image more saturated.

[0019] Those skilled in the art will readily understand that the embodiments of the present invention illustrated can be further modified without departing from the spirit of the invention. [Brief explanation of the drawing]

[0020] [Figure 1] Figure 1 shows an example of the overall configuration of an image processing system, and an example of the display screen during the input profile editing process. [Figure 2] Figure 2 shows an example of the internal configuration of a host computer and an example of the configuration of a profile editing device. [Figure 3] Figure 3 shows an example of the steps involved in editing an input profile. [Figure 4] Figure 4 shows an example of hue editing processing. [Figure 5] Figure 5 shows an example of the procedure for editing brightness. [Figure 6] Figure 6 shows an example of the procedure for determining the brightness target value. [Figure 7] Figure 7 shows an example of the procedure for determining the amount of brightness conversion. [Figure 8] Figure 8 shows an example of a characteristic line representing the amount of brightness conversion, and an example of a correspondence table for determining the amount of brightness conversion. [Figure 9] Figure 9 shows an example of the saturation editing process. [Figure 10] Figure 10 shows an example of a characteristic line and a corresponding table used in the process of determining the amount of saturation conversion. [Figure 11] Figure 11 shows examples of point movement within the gammette and changes in the shape of the gammette's outline when the a* and b* values ​​are transformed based on the determined saturation conversion amount. [Figure 12] Figure 12 shows an example of a process that changes the lower and upper limits of brightness, i.e., the L* value. [Figure 13] Figure 13 is a flowchart showing an example of a color change method that includes multiple color conversion steps. [Modes for carrying out the invention]

[0021] The best embodiments described below are used to facilitate understanding of the present invention. Therefore, those skilled in the art should note that the present invention is not unduly limited by the embodiments described below.

[0022] Figure 1 shows an example of the overall configuration of an image processing system, and an example of the display screen during the input profile editing process.

[0023] As shown in Figure 1A-1, the computer system, or in other words, the image processing system 1, includes three holders 41, 44, and 46, a host computer 10 connected to each holder, a display unit 20 consisting of a liquid crystal display or the like connected to the host computer 10, and a keyboard 32 and a mouse 34 as an operation unit (input unit).

[0024] In the example shown in Figure 1, a scanner 39 is used as the input device. When the input image 38 is read by the scanner 39, device-dependent RGB data is obtained. This RGB data is supplied to the host computer 10. The input image 38 may also have RGB data obtained from drawing software.

[0025] A printer 50 is connected to the host computer 10 via communication line L1 as an output device. Note that the printer may sometimes be referred to as a printing device.

[0026] The host computer 10 is equipped with a CMM (Color Management Module) 18, which is a module that uniformly manages colors across different devices.

[0027] Furthermore, the memory 15 of the host computer 10 stores a program 17 for editing input profiles according to the present invention.

[0028] Furthermore, the first holder 41 is attached to the scanner 39 as an input device, and converts from the RGB color space to a device-independent color space, i.e., a profile connection space (PCS) as L * a * b * An input profile 42 is stored, which describes the correspondence when converting data to a color space.

[0029] In this embodiment, the input profile 42 can be edited to obtain an image with higher saturation, i.e., increased vividness. Details of the editing will be described later. The new input profile 43 created by the editing is saved separately from the original input profile 42, for example, in the folder 42.

[0030] Holder 44 contains L obtained by converting RGB data. * a * b * Data, in other words L * a * b * The color values ​​of the color system are stored here.

[0031] Note that RGB data L * a * b * The process of converting to data is performed by the CMM18. That is, when RGB data is supplied from the scanner 39, the CMM18 reads the input profile 42 from the holder 41, and refers to the input profile 42 to convert the RGB data to L * a * b * Convert to data. As described above, the converted L * a * b * The data is saved in folder 44.

[0032] The holder 46 holds an output profile 47 that is attached to the printer 50 serving as an output device, and in which the correspondence relationship for converting data from a profile connection space (PCS) to a color space dependent on the output device is described. Note that the output profile is also referred to as an output-side device profile.

[0033] When printing an image with the printer 50, the CMM 18 reads and refers to the output profile 47 held in the holder 46, and converts L * a * b * data into, for example, CMYK data or CMYKOr data.

[0034] When the host computer 10 operates in accordance with a program 17 for editing input profiles, the host computer 10 can function as an input profile editing device. Note that the input profile editing device can also be referred to as a profile editor, a color profile editor, a profile editing tool, or a color profile editing tool.

[0035] Functions as the input profile editing device include, for example, a hue editing function, a lightness editing function, a chroma editing function, a function for changing the upper and lower limits of lightness, and a function for obtaining the correspondence between RGB colorimetric values of an input image and edited L * a * b * color values to create a new input profile. Details of these will be described later. Note that the input profile editing device described below can also apply similar editing to device-dependent CMYK data.

[0036] A-2 in FIG. 1 shows a display example in input profile editing processing. In the example of A-2 in FIG. 1, a tag T1 that displays editing content on the display screen displays "chroma editing".

[0037] Furthermore, by selecting the contents of the three setting tags T2 to T4 located on the right side of the display screen using pull-down and pull-up menus, you can set values ​​such as hue interval, brightness grid interval, and saturation grid interval to your preferred values.

[0038] Furthermore, the display screen A-2 in Figure 1 shows a characteristic diagram and a correspondence table for saturation editing. Details of the characteristic diagram and correspondence table are explained in Figure 10. The correspondence table can also be referred to as a conversion table.

[0039] For example, the user can operate the mouse 34, which acts as an operating unit, to change the shape of the edited saturation characteristic line Q20 in the characteristic diagram. Alternatively, the user can input numerical values ​​from the keyboard 32, which also acts as an operating unit, to appropriately set the edited saturation value in the corresponding table.

[0040] Users can utilize various editing support functions when editing input profiles, which streamlines the editing process and reduces the burden on the user.

[0041] Next, refer to Figure 2. Figure 2 shows an example of the internal configuration of a host computer and an example of the configuration of a profile editing device. In Figure 2, parts common to Figure 1 are denoted by the same reference numerals.

[0042] The host computer 10 includes RAM 15 as memory in which a program 17 for editing input profiles is stored, a color management module (CMM) 18, a data interface 102, a storage unit 104 capable of storing data and files, a utility 106 as an interface for operation information, a control unit 110 consisting of at least one processor or the like that comprehensively controls each unit, and a display management interface 111.

[0043] Furthermore, the control unit 110 operates according to the program 17 for editing the input profile, thereby constructing the input profile editing device 11 as a functional block. This input profile editing device 11 has an input profile editing unit 113, which has a color editing processing unit 112.

[0044] The color editing processing unit 112 includes a hue value editing unit 114, a brightness editing unit 115, a saturation editing unit 117, a brightness upper and lower limit changing unit 119, an interpolation calculation unit 120, a function generation unit 122 that generates various functions or function variables necessary for editing, and input image data and the edited L * a * b * It includes a profile creation unit 123 that obtains the correspondence with color values ​​and creates a new input profile.

[0045] Each editorial unit 114-117, and the brightness upper / lower limit adjustment unit 119, can display the necessary images on the display unit 20 as appropriate via the display management interface 111.

[0046] Furthermore, each editing unit 114-117 and the brightness upper / lower limit changing unit 119 can use the calculation unit 121 as appropriate to obtain calculation data, and can also activate the function generation unit 122 to generate new functions or save the generated functions and variables.

[0047] The input profile editing unit 113 can receive support from CMM18 as needed.

[0048] Thus, the input profile editing device 11 has an input profile editing unit 113 that implements the input profile editing method of the present invention, which will be described later. The input profile editing device 11 also includes an information acquisition unit that acquires operation information input from the operation units 32 and 34, and an image output unit for displaying images on the display unit 20, but these are omitted in Figure 2.

[0049] By means of the input profile editing apparatus 11, L * a * b * L in the color space * value, a * value, b * of these three values can be converted. Therefore, in accordance with the input profile, L * a * b * one point in the color space can be converted to another point, and by acquiring and storing the correspondence between the point before conversion and the point after conversion, the input profile can be edited.

[0050] Accordingly, a new input profile that can, for example, make a printed image clearer can be easily created using an existing input profile.

[0051] Furthermore, the input profile editing apparatus 11 is realized by a computer operating in accordance with a program 17. Therefore, implementation is easy.

[0052] Next, refer to FIG. 3. FIG. 3 is a diagram showing an example procedure of input profile editing processing. Note that the procedure example shown in A-1 of FIG. 3 is an example, and the order of processing can be changed.

[0053] In the input profile editing processing shown in A-1 of FIG. 3, in step S1, RGB-L * a * b * or CMYK-L * a * b * a basic input profile indicating the correspondence of is acquired.

[0054] As previously shown in FIG. 1, the acquired input profile 42 is stored in a holder 41. Also, L * a * b * value data is held in a holder 44.

[0055] This process is performed by the input profile editing unit 113 shown in Figure 2. The input profile editing unit 113 appropriately refers to the image data etc. stored in the storage unit 104 shown in Figure 2, for example, L * a * b * The gamut (color range) in the color space can be detected and displayed on the display unit 20.

[0056] Now, refer to A-2 in Figure 3. In A-2 of Figure 3, L * a * b * The gamut 2 in the color space is shown. Point α in the RGB color system is converted to point β, which constitutes gamut 2.

[0057] Note L * a * b * In a color system, +a in the hue plane * Direction is red direction, -a * Direction is green direction, +b * Direction is yellow direction, -b * The direction is indicated by the blue line.

[0058] Gamut 2 is the hue plane, that is, a * b * When projected onto a plane, a chromaticity diagram like the one shown in Figure 3A-3 is obtained. The region 4 onto which the gamut 2 is projected, in other words, the outer shape of the two-dimensional gamut in the chromaticity diagram, is L * a * b * It changes according to the outline shape of the three-dimensional gamut in the color space.

[0059] Note L * a * b * In the color space, saturation C * is, a * b * It is expressed as the distance from the center on a plane. In other words, saturation C * is, a * value, b * It can be expressed as the square root of the sum of the squares of the values, and therefore, a* , b * By editing each of the values, the saturation value, i.e., c * The value can be edited.

[0060] Also, L * a * b * In a color space, h is b * It can be expressed as a counterclockwise hue angle θ with respect to the axis.

[0061] Let's return to A-1 in Figure 3 and continue the explanation. In step S2, the hue value is edited as needed. This process is not always performed. However, it is preferable to perform it in order to achieve high saturation in the output image. The hue value editing process is performed by the hue value editing unit 114 shown in Figure 2.

[0062] In step S3, the brightness is edited. The brightness editing process is performed by the brightness editing unit 115 shown in Figure 2.

[0063] In step S4, the saturation is edited. The saturation editing process is performed by the saturation editing unit 117 shown in Figure 2.

[0064] In step S5, the upper and lower limits of brightness are changed as needed. This process is not mandatory, but it is preferable to perform in order to ensure black gradation in the output image. This process is performed by the brightness upper and lower limit changing unit 119 shown in Figure 2.

[0065] In step S6, the edited RGB-L * a * b * or CMYK-L * a * b * Obtain the correspondence between them. In some cases, this can be used as an ICC profile.

[0066] Then, in step S7, the edited input profile, i.e., the new input profile, is saved in the holder 41 as the new input profile 43, as shown in Figure 1. These processes are carried out by the profile creation unit 123 shown in Figure 2.

[0067] The following describes editing in the order of hue, lightness, saturation, and upper / lower limits of lightness, but the editing order of these four indicators is not limited to this.

[0068] Next, refer to Figure 4. Figure 4 shows an example of hue editing processing. In step S2-1 of the hue editing process, the pre-edited L * a * b * The range of values ​​that will change the hue is determined.

[0069] The region where the hue is changed is preferably a region that appears duller than neighboring hues, even with similar saturation. For example, as shown in A-2 of Figure 4, the region RS between blue and purple, shown as an ellipse in the chromaticity diagram, can be designated as the region where the hue is changed.

[0070] For this region RS, L * a * b * It is preferable to change the hue value of the points, for example, towards light blue or towards magenta.

[0071] In step S2-2, the amount of change in the hue value is determined. One way to determine the amount of change in the hue value is, for example, as shown in A-4 of Figure 4, the original L * Depending on the value and the hue angle θ, the amount of hue change can be determined using the correspondence table. L not listed in the correspondence table * a * b * For the points, the amount of hue change may be determined by interpolation.

[0072] Furthermore, in areas with low saturation, i.e., the gray range, human vision is sensitive to changes in hue. If the hue is significantly altered in the gray range, the color perceived by a person may differ greatly from the original color.

[0073] Considering this point, as shown in A-3 of Figure 4, it is preferable to define a reference first saturation value c1 and to avoid changing the hue in the region below this saturation value c1.

[0074] Furthermore, for areas with a reference second saturation value c2 (>c1) or higher, the hue may be changed according to the specified amount in the correspondence table.

[0075] Furthermore, in the region between the first saturation value c1 and the second saturation value c2, the amount of change may be gradually increased as it approaches the second saturation value c2. Here, four points D1 to D4 are shown in the chromaticity diagram A-3 of Figure 4. Changes in hue are indicated by straight arrows. For point D1, where the saturation value is less than or equal to c1, the hue is not changed.

[0076] For points D2 and D4 in the region where the saturation is between c1 and c2, the change in saturation for point D3 is set to be larger because D2 and D3 approach c2 in that order. Also, for point D4 in the region where the saturation exceeds c2, a larger change is set than the change for points D2 and D3.

[0077] Thus, in the example in Figure 4, the unedited L follows input profile 42. * a * b * A hue conversion process is performed to convert the hue of points in a predetermined region that appear duller than neighboring hues, even if they have similar saturation, in a direction that reduces dullness.

[0078] This effectively enhances the saturation of dull-looking areas in the output image.

[0079] Next, refer to Figure 5. Figure 5 shows an example of the procedure for editing brightness.

[0080] In the brightness editing process, the brightness target value targetL is determined in step S3-1, and in step S3-2, L is adjusted to approach the target value targetL. * a * b * Determine the amount of value conversion, and based on the amount of conversion determined in step S3-3, L * Convert the value.

[0081] Next, refer to Figure 6. Figure 6 shows an example of the procedure for determining the brightness target value.

[0082] As shown in Figure 6A-1, in the process of determining the brightness target value targetL, the hue angle θ is set to 0 in step S10, and in step S11, it is determined whether θ is less than 360°. If the result is Y, the process proceeds to step S12; if the result is N, the process ends.

[0083] In step S12, L * a * b * The outline of the gamut is obtained when the gamut in space is cut by a hue plane at a hue angle θ.

[0084] As shown in Figure 6A-2, the shape of the outline 2 is determined by cutting the gamut 2 with the hue plane 3 at a hue angle θ.

[0085] As a result, as shown in Figure 6A-3, the brightness L * , saturation C * , and L by h, which is determined by the hue angle θ. * C * The shape of the outer boundary line 5 of gamut 2 in the h color space is determined.

[0086] In step S13, L is a highly saturated point within the region defined by the gamut's outline. * Set the value to the target value targetL at the hue angle θ.

[0087] Here, in Figure 6A-3, we focus on the shape of the outline 5 of the gamut 2, which indicates the color reproduction range of the color values ​​according to the input profile. The maximum C that can be reproduced * The value is cix. * The main purpose of editing the values ​​is to improve the color rendering of L * The goal is to obtain a value. Therefore, a preferred example is the maximum C. * L corresponding to the value * You may set the value to the target value, target L.

[0088] However, C corresponding to that target value targetL * If the value is outside the color reproduction range of the output profile, L * The value adjustments are not reflected in the output image, and the objective of increasing the saturation of dull-looking areas in the output image cannot be achieved.

[0089] Therefore, L * a * b * When converting the color values ​​of a color system according to an output profile and obtaining an output image based on the converted color values, in the brightness target value setting step, L * a * b * The L value of a single point with high saturation within the region specified by the outer boundary of the gamut, which is obtained by cutting a gamut that follows an output profile in space using a hue plane at a hue angle θ, may be set as the target brightness value at a hue angle θ.

[0090] In Figure 6A-4, the gamut outline 7, which follows the output profile, is shown as a dashed line. Within the region defined by this dashed outline 7, for example, L corresponds to the cox with the highest saturation value. * The value can be set to the target value, targetL.

[0091] This allows for good color reproduction within the range of the gamut that follows the output profile, in other words, within the range where the color reproduction of the printed image is possible. * A value is selected. Therefore, high saturation of the output image can be reliably achieved.

[0092] In another example, as shown in Figure 6A-4, in addition to the gamut outline 5 corresponding to the input profile, the gamut outline 7 corresponding to the output profile may also be considered when setting an appropriate target value targetL. Note that outline 7 is shown as a dashed line.

[0093] In the example of A-4 in Figure 6, the maximum C that can be reproduced in the input profile is shown. * L corresponding to the value cix * The value and the maximum C value that allows for color reproduction in the output profile. * L corresponding to the value cox * L * A range R is defined for setting values. For example, the user can set any L within that range R. * The value can be set. This increases the user's freedom in adjusting the colors and ensures that the output image has high saturation.

[0094] In step S14, θ is updated by adding 10° to the current value of θ, and the process returns to step S11. This process is then repeated until step S11 reaches N. Note that the update range for the value of θ may be greater than or less than 10°.

[0095] Next, refer to Figure 7. Figure 7 shows an example of the procedure for determining the amount of brightness conversion.

[0096] As shown in Figure 7A-1, in step S20, hue h and saturation C * Four brightness threshold values ​​are set accordingly: brightLmin, brightLmax, darkLmin, and darkLmax. Note that these threshold values ​​can also be referred to as reference values.

[0097] Here, brightLmin and brightLmax are L * The smallest L in the region to be edited to increase the value * The value, and the maximum L *These are the values. Also, darkLmin and darkLmax are L * The smallest L in the region to be edited to decrease the value * The value, and the maximum L * This is a value. Alternatively, a reference value may be obtained by interpolation based on multiple set values.

[0098] The four reference values ​​can be determined, for example, using the correspondence table shown in Figure 7A-2. The correspondence table includes saturation C * The above four reference values ​​are described when the hue angle θ is changed in 10° increments.

[0099] Figure 7A-3 shows examples of setting four reference values. Note that in Figure 6A-3, brightLmin, brightLmax, darkLmin, and darkLmax are abbreviated as bn, bx, dn, and dx respectively for space limitations.

[0100] When the hue angle θ = 10°, the region Z1 specified by the reference values ​​bn1 and bx1 is L * This is an editing area where the value is edited to increase. The area Z2, which is identified by the reference values ​​dn1 and dx1, is L * This is an editing area where you edit to decrease the value.

[0101] When setting reference values, it is preferable to keep the following points in mind. In other words, L * When editing values, the L of all color values * Changing the values ​​can cause the original color tendency to be lost and the color tones to change significantly, so to suppress this, L * It is preferable to leave some areas where the values ​​should not be changed.

[0102] For example, darkLmin(dn1) and brightLmax(bx1) are not made to be the same, but rather L is placed between them. * It is preferable to leave a gap area where the value is not changed. In the example of A-3 in Figure 7, targetL is set in that gap area.

[0103] In addition, in order not to inadvertently change the tendency of color values before editing and maintain the original tendency in the vicinity of black, it is preferable not to set brightLmin(bn1) to 0. In other words, between brightLmin(bn1) and L * value 0, it is preferable to provide a region where the L * value is not changed.

[0104] In addition, in order not to inadvertently change the tendency of color values before editing and maintain the original tendency in the vicinity of white, it is preferable not to set darkLmax to 100. In other words, between darkLmax(dx1) and L * value 100, it is preferable to provide a region where the L * value is not changed.

[0105] Returning to A-1 of FIG. 7, the description will be continued. In step S21, the L * value before editing is defined as Lin, and the L * value after editing is defined as Lout. Then, when brightLmin < Lin < brightLmax, editing is performed to increase Lout, and when darkLmin < Lin < darkLmax, editing is performed to decrease Lout. The editing can be implemented, for example, by using different functions representing the relationship between Lin and Lout, or by changing the variables of the function.

[0106] In A-4 of FIG. 7, the horizontal axis represents Lin, the vertical axis represents Lout, and the relationship between Lin and Lout is shown. A characteristic line Q0 shown by a solid line is a straight line with a slope of 1.

[0107] A characteristic line Q1 on the side where Lin is small, shown by a dashed curve, represents the conversion characteristic from Lin to Lout in the editing region Z1 where editing is performed to increase the brightness. Lin1 is converted to Lout1 (>Lin1).

[0108] A characteristic line Q2 on the side where Lin is larger, which is indicated by a broken curve, shows the conversion characteristic from Lin to Lout in an editing area Z2 to be edited so as to decrease lightness. Lin2 is converted into Lout2 (<Lin2).

[0109] It is preferable that the straight line of the characteristic line Q0 and the curves of the characteristic lines Q1 and Q2 are smoothly connected. Further, it is preferable that a region represented by each of the characteristic lines Q1 and Q2 is divided into a region that increases a change in Lout with respect to Lin and a region that decreases the change in Lout with respect to Lin, and a curve portion in the region that increases the change and a curve portion in the region that decreases the change are smoothly connected. These points will be described later.

[0110] In the example of A-5 in FIG. 7, L * by value editing, L * a * b * there is shown an example of how the position of a point in a space is changed, and an example of a change in an outer contour shape of a gamut accompanying the change. In A-5 of FIG. 7, an open circle indicates a point before L * value is edited, and a filled circle indicates a point after L * value is edited. A change in lightness is indicated by an arrow. Further, an amount of change in lightness is indicated by a length of the arrow.

[0111] In the example of A-5 in FIG. 7, an amount of change in lightness in a low-saturation region is set to be smaller than an amount of change in lightness in a high-saturation region. A change in lightness is easily visually recognized by a person in a low-saturation region. If L * value is greatly changed, there is a possibility that fine color changes cannot be reproduced. In consideration of this point, it is preferable to reduce the amount of change in lightness in a low-saturation region.

[0112] In the example of A-5 in FIG. 7, as points before L * editing, three points that have the same L * value and correspond to saturations c10, c20, and c30 are drawn. The relationship c10 < c20 < c30 is satisfied. L of each point *The changes in values ​​ΔL1, ΔL2, and ΔL3 are set such that the relationship ΔL1 < ΔL2 < ΔL3 holds true.

[0113] Next, refer to A-6 in Figure 7. In the example of A-6 in Figure 7, L * As the values ​​are edited, the shape of the gammette's outline changes. In the figure, 5-1 is L * The outline of the gamut before editing the values ​​is shown. Also, 5-2 is L * The outline of the gamut after editing the values ​​is shown. L * As a result of editing the values, the gamut has decreased compared to before the editing.

[0114] L * By editing the values, you can achieve effects such as reducing the amount of lighter areas and increasing the amount of darker areas, as well as reducing the amount of darker areas.

[0115] Next, refer to Figure 8. Figure 8 shows an example of a characteristic line representing the amount of brightness conversion, and an example of a correspondence table for determining the amount of brightness conversion.

[0116] Figure 8A-1 is a re-presentation of the correspondence table shown earlier in Figure 7A-4. As previously mentioned, it is preferable that the straight line of characteristic line Q0 and the curves of characteristic lines Q1 and Q2 are smoothly connected. Furthermore, it is preferable to divide the region represented by characteristic lines Q1 and Q2 into a region where the change in Lout with respect to Lin is large and a region where it is small, and to smoothly connect the curved portion in the region where the change is large and the curved portion in the region where the change is small.

[0117] Furthermore, the region where the change is large can be rephrased as the region where the slope of the characteristic curve showing the change is large, or in other words, the slope of the tangent line obtained by differentiating the characteristic curve is large. Conversely, the region where the change is small can be rephrased as the region where the slope of the characteristic curve showing the change is small, or in other words, the slope of the tangent line obtained by differentiating the characteristic curve is small.

[0118] For example, L *If values ​​are changed abruptly, for example, when printing a gradient image, the presence of areas in the image where the color values ​​change rapidly can cause the original color characteristics to be lost, resulting in a somewhat unnatural image.

[0119] Taking this point into consideration, L * When setting the amount of change in the value, it is preferable to avoid abrupt changes and aim for a gradual change overall. However, this does not exclude cases where there are regions of linear change in the middle of the change.

[0120] In Figure 8, A-2 is L * An enlarged view of the editing region Z1, where the value is increased, is shown. The region indicated by the characteristic line Q1 is divided into regions Z10 and Z12, where the slope of the characteristic line showing the change is increased, and region Z11, where the slope of the characteristic line is decreased. The range of region Z10 is determined by LinA and LinB, the range of region Z11 is determined by LinB and LinC, and the range of region Z12 is determined by LinC and LinD.

[0121] In Figure 8A-2, dashed ellipses are drawn at points corresponding to LinA to LinD on the characteristic curve Q1, which is shown as a dashed line, and each point is labeled with the signs K1 to K4.

[0122] Points K1 and K4 indicate the points where the straight line of characteristic line Q0 and the curve of characteristic line Q1 are connected. At these points, the straight line and the curve are smoothly connected, L * The changes in the values ​​are made less noticeable.

[0123] Furthermore, location K2 is the boundary between the above-mentioned regions Z10 and Z11, and location K3 is the boundary between the above-mentioned regions Z11 and Z12. In other words, these are the points that connect the curved parts in each region, and this point is also L * The changes in the values ​​are made less noticeable.

[0124] The smooth connection described above can be achieved, for example, by preparing multiple functions that define the shape of the characteristic curve and using them appropriately, or by using a common function but changing the variables as appropriate. As one example, one can consider changing the function in the region where the slope of the characteristic curve is large and the region where the slope is small.

[0125] Next, refer to A-3 in Figure 8. * An enlarged view of the editing region Z2, which decreases the value, is shown. The region indicated by the characteristic line Q2 is divided into regions Z20 and Z22, which reduce the slope of the characteristic line showing the change, and region Z21, which increases the slope of the characteristic line. The range of region Z20 is determined by LinD and LinE, the range of region Z21 is determined by LinE and LinF, and the range of region Z22 is determined by LinF and LinG.

[0126] In Figure 8A-3, dashed ellipses are drawn at points corresponding to LinD to LinG on the characteristic curve Q2, which is shown by a dashed line, and each point is labeled with the signs K5 to K8.

[0127] Each section K5 to K8 corresponds to sections K1 to K4 in A-2 of Figure 8. In A-3 of Figure 8, a smooth connection is also achieved at each section K5 to K8, L * The sharp changes in the values ​​are made less noticeable. The effect obtained is the same as in case A-2 in Figure 8.

[0128] One possible method for achieving smooth curves representing characteristic curves Q1 and Q2 is to prepare multiple functions to represent the curves and use them interchangeably, or to appropriately specify the value of at least one variable included in a common function.

[0129] Furthermore, the Lout value, which represents the brightness after editing, can be derived using a correspondence table like the one shown in Figure 8, A-4. This correspondence table can be implemented, for example, as a lookup table (LUT).

[0130] When using this correspondence table, hue and L *By specifying a value and Lin, Lout can be derived. However, this is just one example and is not the only way to do so.

[0131] As described above, the input profile editing method of the present invention uses color values ​​in a first color system that is dependent on the device and L as a second color system that is independent of the device. * a * b * An input profile acquisition step that obtains an input profile that describes the correspondence with color values ​​in the color system, and L * a * b * A brightness target value setting step sets a target brightness value corresponding to the hue and saturation in space, and a brightness editing step converts the L value according to the input profile in a direction that approaches the target brightness value, and L * a in color values ​​whose values ​​have been edited * value, b * Each of the values ​​is a * b * This includes a saturation editing step that converts the saturation away from the center of the plane.

[0132] This means L * a * b * L in color space * value, a * value, b * It is possible to convert the three values ​​of a value. Therefore, L follows the input profile. * a * b * It is possible to convert one point in a color space to another point. For example, the original RGB value and the L value after color conversion according to the present invention. * a * b * By obtaining a new correspondence with the values, a newly edited input profile can be obtained.

[0133] Therefore, it is possible to easily create new input profiles using existing input profiles, for example, to make printed images more vibrant.

[0134] In addition, in the brightness target value setting step, L * a * b * The L-axis, which is the point of highest saturation within the region defined by the outer boundary of the gamut when the gamut, which follows the input profile in space, is cut by a hue plane at a hue angle θ (where θ is an integer satisfying 0 ≤ θ < 360°), is defined as the point of highest saturation within that region. * The value may be set as the target brightness value at the hue angle θ.

[0135] This makes it possible to increase the saturation of L * Depending on the value, or in other words, the hue, an appropriate target brightness value can be set.

[0136] Also, L * a * b * When converting the color values ​​of a color system according to an output profile and obtaining an output image based on the converted color values, in the brightness target value setting step, L * a * b * When a gamut that follows an output profile in space is cut by a hue plane at a hue angle θ, the L of the point with the highest saturation within the region specified by the outline of the gamut is * The value may be set as the target brightness value at the hue angle θ.

[0137] This allows for good color reproduction within the range of the gamut that follows the output profile, in other words, within the range where the color reproduction of the printed image is possible. * A value is selected. Therefore, high saturation of the output image can be reliably achieved.

[0138] Also, L * a * b * When converting the color values ​​of a color system according to an output profile and obtaining an output image based on the converted color values, in the brightness target value setting step, L * a * b *The first L is the point with the highest saturation within the region defined by the outline of the first gamut when the first gamut, which follows the input profile in space, is cut by the hue plane at the hue angle θ. * Value and L * a * b * The second L is the point with the highest saturation within the region defined by the outline of the second gamut when the second gamut, which follows the output profile in space, is cut by the hue plane at the hue angle θ. * The value and the brightness range determined by (1st L * Value and the second L * Within the range (including the value), you may set a target brightness value at the hue angle θ.

[0139] This makes it possible to set an appropriate brightness target value within a brightness range determined by considering both the input and output profiles. Therefore, high saturation of the output image is reliably achieved. Furthermore, if, for example, the user is allowed to set an arbitrary value as the brightness target value within that brightness range, it also increases the user's freedom in color adjustment.

[0140] Also, in the brightness editing step, L * a * b * Within the region defined by the outer boundary of the gamut when the gamut following the input profile in space is cut by the hue plane at the hue angle θ, on the side of the gamut with a lightness lower than the target lightness value, L following the input profile * A first region is set in which the value is changed in the direction of increasing it, and L follows the input profile on the side where the brightness is higher than the target brightness value. * A second region is set in which the value is changed in the direction of decreasing, and in a third region with lower brightness than the first region, or a fourth region with higher brightness than the second region, L follows the input profile. * You may choose not to change the value.

[0141] This means L *A region where values are not changed remains, which suppresses a significant change in color tone caused by losing the tendency of original color values.

[0142] For example, in the vicinity of black or white, L * By providing a region where values are not changed, the tendency of color values before editing is not inadvertently changed, and the original tendency can be maintained.

[0143] Further, in the lightness editing step, before lightness editing, L * When there are regions having the same value but different chroma, the amount of change in lightness in a low-chroma region may be set to be smaller than the amount of change in lightness in a high-chroma region.

[0144] Accordingly, fine color changes can be reproduced even in a low-chroma region, that is, a gray region. In other words, humans can easily visually recognize changes in lightness in low-chroma regions. If L * values are changed greatly, there is a risk that fine color changes cannot be reproduced. The above problem is solved by setting the amount of change in lightness to be small in low-chroma regions.

[0145] Further, in the lightness editing step, L before lightness editing * a value Lin, and L after editing * A characteristic line indicating the relationship with an output value Lout is a curve in the first and second regions, and is a straight line in the third and fourth regions. At the first and second points corresponding to the lower limit and upper limit of the first region, and the third and fourth points corresponding to the lower limit and upper limit of the second region on the characteristic line, the curved portion and the straight portion are smoothly connected. The region represented by a curve in the characteristic line is divided into a region where a change of Lout with respect to Lin is increased and a region where the change is decreased, and the curved portion in the region where the change is increased and the curved portion in the region where the change is decreased may be smoothly connected.

[0146] Accordingly, L *This suppresses abrupt changes in values, resulting in a smoother overall change. Therefore, for example, when printing a gradient image, the presence of areas in the image where color values ​​change abruptly is suppressed. As a result, the color tendencies of the original image can be maintained, and a natural image without any unnaturalness can be reproduced.

[0147] Next, refer to Figure 9. Figure 9 shows an example of the procedure for saturation editing. As shown in A-1 of Figure 9, in the saturation editing process, in step S30, the boundary value between the area to be edited and the area not to be edited is determined. In step S31, the amount of conversion in the area to be edited is determined.

[0148] In step S32, based on the determined saturation conversion amount, a * Value and b * Convert the values ​​and edit the saturation. In other words, L * a in color values ​​whose values ​​have been edited * value, b * Each of the values ​​is a * b * This changes the saturation away from the center of the plane, or in other words, away from the position where the saturation is 0. This increases the saturation and makes the image more vivid.

[0149] In step S30, the boundary value between the area where saturation is edited and the area where it is not edited is L * It may remain constant regardless of the value. In Figure 9A-2, L * a * b * Within the region defined by the outer boundary line 5 of gamut 2, which is obtained by cutting the gamut according to the input profile in space using a hue plane at a hue angle θ, a region Z3 is set where the saturation value is not edited, and a region Z4 is set where the saturation is edited on the higher saturation side, based on the saturation boundary value c10. The saturation boundary value will be simply referred to as the boundary value below.

[0150] In Figure 9A-2, the boundary value c10 is constant regardless of the L value, so the boundary line determined by the boundary value c10 is represented by a straight line parallel to the L axis. In this case, since the boundary value c10 is fixed, setting the boundary value is simplified.

[0151] The area Z3, where saturation is not changed, corresponds to a low-saturation gray area. In gray areas, differences in saturation are easily noticeable, so the saturation is not edited. This prevents unnatural brightness correction and maintains the original image's color tendencies.

[0152] On the other hand, in areas Z4 that are not gray and have a relatively high level of saturation, saturation editing is performed. This makes the overall image more saturated, resulting in a more vibrant image.

[0153] In Figure 9A-3, the boundary value c10' is L * The boundary line, which changes depending on the value and is determined by the boundary value c10', is represented by a curve. Corresponding to the distribution of the gray area, the boundary value c10' is L * By setting it to be variable in accordance with the value, it is possible to more reliably suppress saturation editing in the gray area.

[0154] Next, refer to Figure 10. Figure 10 shows an example of a characteristic line used in the process of determining the amount of saturation conversion, and an example of a correspondence table.

[0155] Figure 10, A-1 shows the characteristic curve Q20 used to edit saturation. Similar to the example in Figure 9, A-2, it is preferable that this characteristic curve Q20, in other words, the saturation conversion curve, be a smooth curve.

[0156] This helps to suppress abrupt color changes. In other words, it prevents unnatural and sudden alterations to the color values ​​of the original image. This also contributes to maintaining the color tendencies of the original image.

[0157] Note that the straight characteristic line Q10 is a straight line that shows the relationship cout = cin. The characteristic line Q10 is applied in the region Z3 where the saturation is not edited. Note that cin is L * a after the value has been edited, and before the saturation has been edited. * Value and b * This is the saturation value derived from the value. `cout` is the saturation value after saturation editing.

[0158] It is preferable that the straight line of characteristic line Q10 and the curve of characteristic line Q20 are smoothly connected. In particular, in the low saturation range, changes in saturation are easily visible, so it is preferable to suppress abrupt changes in saturation to make changes in saturation less noticeable.

[0159] One possible method for achieving a smooth curve representing the characteristic curve Q20 is to prepare at least one function that represents the curve and use that function selectively, or to specify the value of at least one variable included in that function as appropriate.

[0160] Furthermore, the cout value, which represents the saturation after editing, can also be derived using a correspondence table as shown in Figure 10, A-2. This correspondence table can be implemented, for example, as a lookup table (LUT). When using this correspondence table, hue and L * By specifying a value and cin, cout can be derived. However, this is just one example and is not the only way to do so.

[0161] As explained above, in the saturation conversion step, L * a * b * When a gamut following an input profile in space is cut by a hue plane at a hue angle θ, a boundary value is set that indicates the boundary between an area on the low-saturation side where the saturation value is not edited and an area on the high-saturation side where the saturation is edited, within the region specified by the outer boundary of the gamut, a region on the low-saturation side where the saturation value is not edited, and a region on the high-saturation side where the saturation is edited. The amount of transformation for each point in the region where the saturation is edited is determined, and based on the determined amount of transformation, L * a in color values ​​whose values ​​have been edited * value, b *Each of the values may be converted.

[0162] In a low-saturation gray region, differences in saturation are easily noticeable. In consideration of this point, it is determined that saturation is not edited in the gray region.

[0163] Thereby, unnatural brightness correction is not performed, and the color tone tendency of the original image can be maintained. On the other hand, saturation editing is performed in regions with relatively high saturation other than the gray region. This allows the entire image to have increased saturation, and an image with enhanced vividness can be obtained.

[0164] Furthermore, the boundary value that defines the boundary between the region where saturation is edited and the region where saturation is not edited is L * is constant regardless of the value, and the boundary line defined by the boundary value may be represented by a straight line parallel to the L axis, or the boundary value is L * the boundary line defined by the boundary value, which changes according to the value, may be represented by a curve.

[0165] When the boundary line is a straight line, since the boundary value is fixed, setting of the boundary value is facilitated. In addition, when the boundary line is a curve, the boundary value is adjusted to L in accordance with the distribution of the gray region * By variably setting the boundary value in accordance with the value, it is possible to more reliably suppress saturation editing from being performed in the gray region.

[0166] Furthermore, in the process of determining the conversion amount for each point in the region where saturation is edited, the saturation value before saturation editing, that is, C * where cin is the value, and C after editing * the characteristic line indicating the relationship between cout, which is the value, is a straight line in the region where saturation is not edited, and is a curve in the region where saturation is edited; at the position of the characteristic line corresponding to the boundary value, the straight line and the curve may be smoothly connected.

[0167] Thereby, abrupt color changes can be suppressed. In other words, the color values of the original image are not unnaturally and abruptly changed. This also contributes to maintaining the color tendency of the original image.

[0168] Next, refer to Figure 11. Based on the determined saturation conversion amount, a * value, b * This figure shows examples of how points within a gammette move and how the shape of the gammette's outline changes when values ​​are transformed.

[0169] In the saturation editing process, as explained earlier in Figure 9A-1, the amount of conversion in the area to be edited for saturation is determined in step S31, and in step S32, based on the determined amount of conversion, a * Value and b * The value is converted, and the saturation value is changed. In other words, it follows the input profile. * value, b * Each of the values ​​is a * b * The color is shifted away from the center of the plane, or in other words, away from the position where the saturation is 0.

[0170] As a result, as shown in Figure 11A-1, L * a * b * When a gamut following an input profile in space is cut by a hue plane at a hue angle θ, within the region defined by the outer boundary line 5 of the gamut, the saturation of each point shifts towards higher saturation by the amount of saturation editing conversion, thereby changing the distribution of points within the region defined by the outer boundary line 5.

[0171] Note that in Figure 11A-1, the black circle is L * C after editing * The points before editing are shown. The gray circles indicate C. * The points after editing are shown.

[0172] The shape of the outline 5 of the gamut 2 changes by editing the brightness and saturation. An example of this change in outline 5 is shown in Figure 11A-2. Note that in Figure 11A-2, +C * Not only direction, but also -C * The outline of the gammat in terms of direction is also depicted.

[0173] In Figure 11A-2, the dashed outline 5-1 is L * This shows the outline of the gamut before editing.

[0174] The solid outline 5-2 is L * C after editing * The outline of the gamut before editing is shown. L * The editing alters the distribution of points within gamut 2, causing gamut 2 to shrink. Therefore, outline 5-2 is located inside outline 5-1.

[0175] The outline 5-3, shown by the dashed line, is L * Editing and C * The outline of the gamut after editing is shown. C * Through editing, the point within Gamat 2 is C * It moves left and right along the axis. As this point moves, Gamatt 2 moves to C * It is pushed outwards in the direction away from the center of the axis, and in the example of A-2 in Figure 11, the outer boundary line 5-3 is L * It is located outside the outer boundary line 5-1 before editing. That is, L * Through editing, Gamatt 2 was temporarily reduced in size, and then C * This edit expands upon Gamatt 2.

[0176] Thus, L * , C * Editing may not only change the distribution of points within gamut 2, but may also affect the shape of the outer boundary 5 and the size of gamut 2.

[0177] Considering this point, C * When editing, we differentiate between edits that contribute only to the distribution of points inside Gamat 2 and edits that contribute not only to the distribution of points inside Gamat 2 but also to the outer boundary of the Gamat, and by independently adjusting the content of each edit, we can control the distribution of points inside Gamat 2. * b * It is preferable to allow the distribution of points and the outline of gamut 2 to be adjusted separately.

[0178] For example, when editing saturation using a function that includes variables, it is possible to make the above adjustments by separating variables that contribute to both the interior and exterior of the gamut from variables that contribute only to the interior of the gamut, and by preparing two types of lookup tables (LUTs) to determine the values ​​of the variables and using them appropriately.

[0179] For example, when printing an image, the colors of the printed image depend on the characteristics of the output profile. However, if the high-saturation region of the gamut that follows the output profile is wider than the high-saturation region of the gamut that follows the input profile, and there is extra space in the printable high-saturation region, then C will be used to make effective use of that region. * The amount of change in the editing process may be increased to the above-mentioned printable high-saturation range. This can further improve the overall vibrancy of the image.

[0180] On the other hand, if the high-saturation region of the gamut following the output profile is narrower than the high-saturation region of the gamut following the input profile, then C * Even if you increase the amount of change, it will not be reflected in the printed image, so the C point that affects the outline * You may also choose to minimize the amount of change and maintain the saturation trend of the original image.

[0181] By implementing the adjustments described above, it becomes possible to edit saturation more flexibly depending on the situation. In other words, a saturation editing method is realized that takes into account the characteristics of output devices such as printers and fully utilizes the color reproduction performance of those output devices.

[0182] In Figure 11, A-3 shows the gamut as a * b * An example of how the gamut's outline shape changes before and after editing the color values ​​in the chromaticity diagram obtained by projecting onto a plane is shown. Outline 6-1, shown by the dashed line, is L * and C * This is the outline of the gamut before editing. Also, the outline 6-2 shown in solid line is L * and C *This is the outline of the gamut after editing. The edited outline 6-2 is located on the higher saturation side than the original outline 6-1, and the color gamut has also been expanded overall.

[0183] In this way, editing the color values ​​makes it possible to reproduce the entire image more vividly.

[0184] Next, refer to Figure 12. Brightness, i.e., L * This figure shows an example of a process for changing the lower and upper limits of a value.

[0185] In the present invention, as described above, L * The value can be edited. Using this editing function, in the example in Figure 12, L * The upper and lower limits are changed. This makes it easier to accurately reproduce the gradation near black in the original image, for example, in output images such as printed images.

[0186] When printing an image with a printer, the lower limit of the ink brightness value for the printed image is L * It is usually set to a value greater than the brightness equivalent to =0. For example, edited L * a * b * L in space * If the lower limit is set to 0, the black gradation from 0 to the lower limit brightness value of the ink will all be aggregated to the lower limit of the ink value in the printed image, making it impossible to reproduce the black gradation of the original image.

[0187] For example, in Figure 12, A-1, L is on the left side. * a * b * In space, L * Lin before editing, and L * A characteristic line Q30 is shown, illustrating the relationship with Lout after editing. Characteristic line Q30 is a straight line showing the relationship Lout = Lin. Additionally, the ink value gradation range is indicated by an arrow on the right.

[0188] In the example A-1 in Figure 12, L * a* b * In space, L * In printed images, gradations in the range of 0 to 2 are all consolidated at the lower limit of the ink value, P10, making it impossible to display black in multiple gradations.

[0189] Therefore, in Figure 12A-2, L * For editing, use characteristic line Q40 instead of characteristic line Q30.

[0190] The conversion characteristics of characteristic line Q40 can be expressed by the following formula, where Lwh is the upper limit of brightness and Lbk is the lower limit of brightness. Lout = (Lwh - Lbk) / 100 × Lin + Lbk For example, Lbk is set to 2 and Lwh is set to 98. From this point onward, image processing is performed with the upper brightness limit Lwh set to a brightness of 100 and the lower brightness limit Lbk set to a brightness of 0. In other words, the upper and lower brightness limits are changed.

[0191] According to example A-2 in Figure 12, Lin with a brightness in the range of 0 to 2 is converted to Lout in the range of 2 to 4. * A value in the range of 2 to 4 corresponds to the gradation range of ink values ​​P10 to P20 in a printed image. Therefore, colors near black in the original image can be displayed, for example, printed, using multiple gradations. In other words, as in the example A-1 in Figure 12, the compression of all image gradations near black by consolidating them into ink value gradation P10 is suppressed, thus improving the gradation of colors near black.

[0192] Thus, in the example of A-2 in Figure 12, L * a * b * After editing each value, further L * Raise the lower limit of the value, and L * Lower the upper limit of the value, L * You may also perform operations to change the lower and upper limits of the values. In the example above, the lower limit is increased from 0 to 2, and the upper limit is decreased from 100 to 98.

[0193] This allows the original image's near-black colors to be displayed in multiple shades, for example, for printing. For instance, it prevents the image's near-black shades from being compressed and consolidated into a single ink value, thus improving the gradation of colors near black.

[0194] (Content and effects of claim 16) Next, refer to Figure 13. Figure 13 is a flowchart showing an example procedure for a color change method that includes multiple color conversion steps. Although the above embodiment describes a method for editing an input profile, the present invention can also be understood as a color conversion method that includes multiple color conversion steps.

[0195] In step S40 of Figure 13, the color values ​​in the first color system, which are dependent on the input device, are converted to a second color system, which is independent of the input device, based on the input profile. * a * b * Convert to color values ​​in a color system. This step S40 may also be called the first color conversion step.

[0196] In step S41, L * a * b * In space, the brightness and saturation of the color values ​​according to the input profile are converted to other color values, for example, using the methods shown in Figures 4 to 11. This step S41 may also be called the second color conversion step.

[0197] Step S41 may include steps S41-1 for setting a target value for brightness, step S41-2 for editing brightness, and step S41-3 for editing saturation. Here, step S41-1 corresponds to step S3-1 in Figure 5, which was explained earlier. That is, step S41-1 is L * a * b * This is a brightness target value setting step, where a target value for brightness is set corresponding to the hue and saturation in the space. Furthermore, step S41-2 corresponds to steps S3-2 and S3-3 in Figure 5, which were explained earlier. That is, in step S41-2, L is adjusted so that it approaches the target value of brightness, targetL. * a * b * L * Determine the amount of value conversion, and based on the determined amount of conversion, L * Convert the value. This will perform brightness editing.

[0198] Furthermore, step S41-3 corresponds to the saturation editing process shown in A-1 of Figure 9, as explained earlier, i.e., steps S30-S32. In other words, in step S41-3, according to the input profile a * value, b * Each of the values ​​is a * b * The saturation is edited by transforming it in a direction away from the center of the plane.

[0199] Next, in step S42, the color values ​​after step S41 are converted to color values ​​in a third color system that depends on the output device, based on the output profile. This step S42 may also be called the third color conversion step.

[0200] Thus, according to the above series of color conversion processes, the color values ​​of the first color system, which depends on the input device, are converted to L as a second color system independent of the input device. * a * b * After converting to color values ​​in a color system, a target value is set for editing the brightness, corresponding to the hue and saturation, and the brightness is appropriately converted in a direction that approaches that target value, and in conjunction with this, a * value, b * Each value can be converted in a direction that increases saturation, and further converted into color values ​​of a third color system that depends on the output device. In other words, L * a * , b *A systematic series of methods is provided that appropriately convert each of the values ​​in conjunction, making it possible, for example, to reproduce, i.e., output a vividly colored input image as is.

[0201] As described above, the present invention provides an input profile editing method that makes an image more saturated by editing its brightness and saturation.

[0202] The present invention is not limited to the embodiments described above and can be modified in various ways. For example, the order in which each editing process is performed can be changed as appropriate.

[0203] The present invention is not limited to the exemplary embodiments described above, and those skilled in the art will be able to easily modify the exemplary embodiments described above to the extent included in the claims. [Explanation of Symbols]

[0204] 1...Computer system (image processing system), 2...Gamut (color gamut), 3...Cross-section of the gamut, 5...Outline of the gamut according to the input profile (outline of the gamut), 7...Outline of the gamut according to the output profile (outline of the gamut), 10...Host computer, 11...Input profile editing device (profile editor, color profile editor, profile editing tool, color profile editing tool), 20...Display unit, 15...Memory (RAM), 17...Program (program for input profile editing), 18...Color management module (CMM), 32...Keyboard, 34...Mouse, 38...Input image, 39...Scanner (input device), 41, 44, 46...Holder, 42...Input profile Ill, 50...Printer (output device), 102...Data interface, 104...Storage unit, 106...Utilities, 110...Control unit (processor, etc.), 111...Display management interface, 112...Color editing processing unit, 113...Input profile editing unit, 114...Hue value editing unit, 115...Brightness editing unit, 117...Saturation editing unit, 119...Brightness Upper and lower limit change section, 120... interpolation calculation section, 121... calculation section, 122... function generation section, 123... profile creation section, θ... hue angle, brightLmin(bn), brightLmax(bx), darkLmin(dn), darkLmax(dx)... reference value (threshold) for brightness, Q0, Q1, Q2, Q10, Q20, Q30... characteristic line (conversion line or conversion curve showing conversion characteristics).

Claims

1. An input profile acquisition step to obtain an input profile that describes the correspondence between color values ​​in a first color system that is dependent on the device and color values ​​in a second color system, the L*a*b* color system, which is independent of the device; A brightness target value setting step in which a brightness target value is set corresponding to the hue and saturation in L*a*b* space, A brightness editing step that converts the L* value according to the input profile in a direction that approaches the target brightness value, A saturation editing step that converts each of the a* and b* values ​​according to the input profile in a direction away from the center of the a*b* plane, Includes, In the brightness target value setting step, A method for editing an input profile, wherein the gamut following the input profile in L*a*b* space is cut by a hue plane at a hue angle θ (where θ is an integer satisfying 0 ≤ θ < 360°), and within the region specified by the outline of the gamut, the L* value with high saturation in that region is set as the target brightness value at the hue angle θ.

2. An input profile acquisition step that acquires an input profile describing the correspondence between color values ​​in a first color system that depends on the device and color values ​​in the L*a*b* color system, which is a second color system that does not depend on the device, A brightness target value setting step in which a brightness target value is set corresponding to the hue and saturation in L*a*b* space, A brightness editing step that converts the L* value according to the input profile in a direction that approaches the target brightness value, A saturation editing step that converts each of the a* and b* values ​​according to the input profile in a direction away from the center of the a*b* plane, Includes, When the color values ​​of the L*a*b* color system are color-converted according to the output profile, and an output image is obtained based on the color values ​​after color conversion, In the brightness target value setting step, The gamut conforming to the output profile in the L*a*b* space is cut by a hue plane at a hue angle θ (where θ is an integer satisfying 0 ≤ θ < 360°). The L* value with high saturation within the region specified by the outline of the gamut at this hue angle θ is set as the target brightness value at hue angle θ. How to edit the input profile.

3. An input profile acquisition step that acquires an input profile describing the correspondence between color values ​​in a first color system that depends on the device and color values ​​in the L*a*b* color system, which is a second color system that does not depend on the device, A brightness target value setting step in which a brightness target value is set corresponding to the hue and saturation in L*a*b* space, A brightness editing step that converts the L* value according to the input profile in a direction that approaches the target brightness value, A saturation editing step that converts each of the a* and b* values ​​according to the input profile in a direction away from the center of the a*b* plane, Includes, When the color values ​​of the L*a*b* color system are color-converted according to the output profile, and an output image is obtained based on the color values ​​after color conversion, In the brightness target value setting step, The first L* value of the point with the highest saturation within the region specified by the outline of the first gamut when the first gamut conforming to the input profile in L*a*b* space is cut by a hue plane at a hue angle θ (where θ is an integer satisfying 0 ≤ θ < 360°), The second L* value of the point with the highest saturation within the region specified by the outline of the second gamut when the second gamut, which conforms to the output profile in L*a*b* space, is cut by the hue plane at the hue angle θ, Within the brightness range determined by (including the first L* value and the second L* value), a target brightness value is set at the hue angle θ. How to edit the input profile.

4. In the brightness editing step described above, In the region defined by the outline of the gamut when the gamut conforming to the input profile in L*a*b* space is cut by a hue plane of hue angle θ (where θ is an integer satisfying 0 ≤ θ < 360°), A first region is set on the side of the brightness that is lower than the aforementioned brightness target value, in which the L* value according to the input profile is changed in a direction that increases. A second region is set where the brightness is higher than the aforementioned brightness target value, and the L* value according to the input profile is changed in a direction that decreases it. In a third region with lower brightness than the first region, or a fourth region with higher brightness than the second region, the L* value according to the input profile is not changed. A method for editing an input profile according to any one of claims 1 to 3.

5. In the brightness editing step described above, If there are areas with the same L* value but different saturation levels before brightness editing, set the brightness change in the low-saturation areas to be smaller than the brightness change in the high-saturation areas. A method for editing an input profile according to any one of claims 1 to 3.

6. In the brightness editing step described above, The characteristic curve showing the relationship between Lin, which is the L* value before brightness editing, and Lout, which is the L* value after editing, is: In the first and second regions, the curves are In the third and fourth regions mentioned above, the lines are straight. At the first and second points corresponding to the lower and upper limits of the first region of the characteristic curve, and at the third and fourth points corresponding to the lower and upper limits of the second region, the curved portion and the straight portion are smoothly connected. The region of the characteristic curve represented by the curve is divided into a region where the change in Lout with respect to Lin is increased and a region where it is decreased, and the portion of the curve in the region where the change is increased and the portion of the curve in the region where the change is decreased are smoothly connected. The method for editing an input profile according to claim 4.

7. In the aforementioned saturation editing step, In the region defined by the outline of the gamut when the gamut conforming to the input profile in L*a*b* space is cut by a hue plane of hue angle θ (where θ is an integer satisfying 0 ≤ θ < 360°), A boundary value is set to indicate the boundary between the area on the low-saturation side where the saturation value is not edited and the area on the high-saturation side where the saturation is edited. Determine the amount of transformation for each point in the area where the saturation is edited. Based on the determined conversion amount, the a* and b* values ​​in the color values ​​are converted. A method for editing an input profile according to any one of claims 1 to 3.

8. The aforementioned boundary value is constant regardless of the L* value, and the boundary line determined by the aforementioned boundary value is represented by a straight line parallel to the L axis. Or, The boundary value changes according to the L* value, and the boundary line determined by the boundary value is represented by a curve. The method for editing an input profile according to claim 7.

9. In the process of determining the amount of transformation for each point in the area where the saturation is edited, The characteristic line showing the relationship between the saturation value before saturation editing, i.e., the C* value cin, and the C* value after editing, cout, is: In the area where the saturation is not edited, it is a straight line. In the area where the saturation is edited, it is a curve. At the point on the characteristic curve corresponding to the boundary value, the straight line and the curve are smoothly connected. The method for editing an input profile according to claim 7.

10. When editing saturation, editing that contributes only to the distribution of points inside the gamut according to the input profile is handled separately from editing that contributes not only to the distribution of points inside the gamut but also to the outline of the gamut. By independently adjusting the content of each edit, the distribution of L*a*b* points inside the gamut and the outline of the gamut are adjusted separately. A method for editing an input profile according to any one of claims 1 to 3.

11. A hue conversion process is performed to convert the hue of points in a predetermined region, which appear duller than neighboring hues even with similar saturation, among the unedited L*a*b* values ​​according to the aforementioned input profile, in a direction that reduces dullness. A method for editing an input profile according to any one of claims 1 to 3.

12. Perform a process to change the lower and upper limits of the L* value, which involves raising the lower limit of the L* value and lowering the upper limit of the L* value. A method for editing an input profile according to any one of claims 1 to 3.

13. The device has an input profile editing unit that performs the input profile editing method described in any one of claims 1 to 3. Input profile editing device.

14. A program that causes a computer to function as an input profile editing device having an input profile editing unit as described in claim 13.

15. A first color conversion step that converts color values ​​in a first color system dependent on the input device to color values ​​in the L*a*b* color system, which is a second color system independent of the input device, based on the input profile. A second color conversion step that converts the brightness and saturation of color values ​​according to the input profile, A third color conversion step that converts the color values ​​after the second color conversion step has been performed into color values ​​in a third color system dependent on the output device, based on the output profile, Includes, The second color conversion step described above is: A brightness target value setting step in which a brightness target value is set corresponding to the hue and saturation in L*a*b* space, A brightness editing step that converts the L* value according to the input profile in a direction that approaches the target brightness value, A saturation editing step that converts each of the a* and b* values ​​according to the input profile in a direction away from the center of the a*b* plane, Includes, In the brightness target value setting step, The gamut conforming to the input profile in L*a*b* space is cut by a hue plane at a hue angle θ (where θ is an integer satisfying 0 ≤ θ < 360°). The L* value with high saturation within the region specified by the outline of the gamut at this hue angle θ is set as the target brightness value at hue angle θ. Color conversion method.

16. A first color conversion step of converting color values ​​in a first color system that depends on an input device to color values ​​in the L*a*b* color system, which is a second color system that does not depend on an input device, based on an input profile, A second color conversion step that converts the brightness and saturation of color values ​​according to the input profile, A third color conversion step that converts the color values ​​after the second color conversion step has been performed into color values ​​in a third color system dependent on the output device, based on the output profile, Includes, The second color conversion step described above is: A brightness target value setting step in which a brightness target value is set corresponding to the hue and saturation in L*a*b* space, A brightness editing step that converts the L* value according to the input profile in a direction that approaches the target brightness value, A saturation editing step that converts each of the a* and b* values ​​according to the input profile in a direction away from the center of the a*b* plane, Includes, In the brightness target value setting step, The gamut conforming to the output profile in the L*a*b* space is cut by a hue plane at a hue angle θ (where θ is an integer satisfying 0 ≤ θ < 360°). The L* value with high saturation within the region specified by the outline of the gamut at this hue angle θ is set as the target brightness value at hue angle θ. Color conversion method.

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