Image forming apparatus, image forming system, and image forming method

Abstract

To increase the accuracy of color conversion.SOLUTION: An image forming apparatus comprises: a first image input unit that receives input of a first image being an image indicating a color to be a target; a second image input unit that receives input of a second image being an image formed by an image forming unit to be adjusted; a determination unit that determines the types of objects; and a generation unit that compares the first image and the second image with each other, and generates a color conversion parameter for every type of the object based on the correspondence relationship between chromaticity values.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, an image forming system, and an image forming method.

Background Art

[0002] In order to cause an image forming apparatus to perform image formation so as to reproduce a target color, a technique for creating a color conversion table is known.

[0003] Specifically, first, for creating a color conversion table, the image forming apparatus prints a target print showing a target color. Further, the image forming apparatus to be adjusted prints a reference print showing a reference color. These prints are read, and image data showing the target print and image data showing the reference print are acquired. Using these image data, chromaticity values are associated to create a color conversion table. In this way, a technique for achieving both high-definition image reproduction and reliability is known (see, for example, Patent Document 1).

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventional techniques do not consider so-called object information. Therefore, it may be difficult to change the corresponding color for each object. Therefore, conventional techniques have a problem of low color conversion accuracy.

[0005] An object of the present invention is to improve the accuracy of color conversion.

Means for Solving the Problems

[0006] In order to solve the above problems, an image forming apparatus according to an aspect of the present invention includes: a first image input unit that inputs a first image, which is an image showing a target color; a second image input unit that inputs a second image, which is an image formed by an image forming unit to be adjusted; A determination unit that determines the type of object, A generation unit that compares the first image and the second image and generates color conversion parameters for each object based on the correspondence relationship of chromaticity values characterized by comprising.

Advantages of the Invention

[0007] According to the present invention, the accuracy of color conversion can be improved.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0009] Hereinafter, specific examples will be described with reference to the accompanying drawings. Note that the embodiments are not limited to the specific examples described below.

[0010] [First Embodiment]

[0011] [Example of Image Forming Apparatus] FIG. 1 is a diagram showing an example of an image forming apparatus. For example, the image forming apparatus is a MultiFunction Peripheral (hereinafter referred to as "MFP100") as shown in the figure.

[0012] As shown in the figure, the MFP 100 may include a post-processing device or the like.

[0013] FIG. 2 is a diagram showing an example of the hardware configuration of an image forming apparatus. For example, the MFP 100 has a hardware configuration including an arithmetic unit 101, a storage device 102, a printer engine 103, a scanner 104, an input device 105, a control device 106, and the like.

[0014] The arithmetic unit 101 is, for example, an electronic circuit such as a Central Processing Unit (CPU) or an Application Specific Integrated Circuit (ASIC).

[0015] The storage device 102 is, for example, a memory or the like.

[0016] The printer engine 103 is a device that performs processes such as exposure, development, charging, cleaning, fixing, and transfer, and forms an image on a sheet or the like, and a device that controls each device.

[0017] The scanner 104 is a device that reads an image described on a sheet using an optical sensor or the like.

[0018] The input device 105 is a device that inputs data from peripheral devices or a network.

[0019] The control device 106 is a device that controls the operation of each device.

[0020] Note that the image forming apparatus is not limited to the MFP 100. That is, the image forming apparatus may be a combination of a reading device such as a scanner that reads an image formed on a sheet or the like, an image processing apparatus having an arithmetic unit that processes an image, and an image forming apparatus that forms an image on a sheet or the like. For example, each device may be different devices connected by a network or the like.

[0021] [Overall processing example] FIG. 3 is a diagram showing an overall processing example of the first embodiment. Hereinafter, the target color, that is, the image indicating the color to be output to the image forming apparatus after adjustment is referred to as "first image IMG1". Also, the image formed by the image forming unit to be adjusted is referred to as "second image IMG2". That is, the second image is an image showing the "current situation" of what color will be formed when the image forming apparatus to be adjusted performs image formation aiming at the first image IMG1 in the state before adjustment.

[0022] In step S0301, the image forming apparatus inputs the first image IMG1. For example, when reproducing the color of a printed matter printed by a separately adjusted printer, the first image IMG1 is input when the printed matter is read by a scanner.

[0023] In step S0302, the image forming apparatus inputs the second image IMG2. For example, the image forming apparatus inputs data indicating the second image IMG2. That is, in the first embodiment, the second image IMG2 is an image before being formed.

[0024] In step S0303, the image forming apparatus determines the object included in the second image IMG2. It is desirable that the determination of the object be performed at the time of rasterization (sometimes referred to as "RIP", etc.) as in step S0303. When the object is determined at such a timing, the image forming apparatus can accurately associate the signal value of the second image IMG2 with the object of each pixel and acquire it.

[0025] In step S0304, the image forming apparatus rasterizes the second image IMG2. That is, by rasterization, the image forming apparatus converts the second image IMG2 into a raster image.

[0026] Note that the result of determining the object may be embedded in the image data as additional information, or may be in another file or the like.

[0027] In step S0305, the image forming apparatus performs image alignment. For example, the alignment is realized by pattern matching or the phase-only correlation method, etc. Alternatively, the alignment may include a process of performing geometric transformation such as affine transformation.

[0028] In step S0306, the image forming apparatus acquires chromaticity values. Specifically, the image forming apparatus first determines a region of interest in the data indicating the first image IMG1 and the data indicating the second image IMG2. Next, the image forming apparatus acquires the chromaticity values of the region of interest.

[0029] The chromaticity values are shown for each region of interest in a first color space for handling the first image IMG1 and a second color space for handling the second image IMG2 based on the respective data. Note that the same color space may be used for the first color space and the second color space.

[0030] The region of interest is, for example, in pixel units or the like. On the other hand, for the region of interest, a certain range such as "5×5" may be set, and in the region of interest, statistical values such as an average value may be calculated to obtain the chromaticity values.

[0031] In step S0307, the image forming apparatus determines the correspondence relationship of the chromaticity values for each object. That is, based on the determination result of the object, the image forming apparatus determines the correspondence relationship of what chromaticity values in the second image IMG2 are associated with the chromaticity values shown in the first image IMG1.

[0032] In step S0308, the image forming apparatus generates color conversion parameters. For example, the color conversion parameters are in the form of an ICC profile or the like. Therefore, when the color conversion parameters are determined, it is set for what colors should be associated with the input image for image formation.

[0033] Note that the overall process does not have to be in the illustrated order. For example, the input procedures for the first image and the second image may not be in parallel but may be performed in order.

[0034] The image forming apparatus preferably determines whether there are differences in the correspondence relationship depending on the type of object. Then, the image forming apparatus switches the method of generating the color conversion parameters according to the determination result of the difference.

[0035] For example, in the overall process, the image forming apparatus first determines the correspondence relationship of chromaticity values for at least one object. Specifically, color conversion parameters for converting chromaticity values in the first color space to chromaticity values in the second color space are generated. Then, the image forming apparatus performs color conversion on objects of a different type from the generated table using the same color conversion parameters. In this way, the image forming apparatus performs the same color conversion among different types of objects. As a result, the image forming apparatus compares the chromaticity values of each object shown in the second image IMG2 with the chromaticity values that are the result of the color conversion. The chromaticity values can be compared using an index such as the ΔE00 color difference (International Commission on Illumination (CIE) 2000, CIE No. 15:2004, hereinafter referred to as the "ΔE00 color difference").

[0036] Then, when the result is within a certain threshold value with the same color conversion even for different types of objects, the image forming apparatus determines that there is no difference in the correspondence relationship depending on the type of object.

[0037] The threshold value is a value set in advance. Specifically, when using the ΔE00 color difference for the comparison of chromaticity values, the threshold value is set like "3.2". Therefore, when it can be converted to a value within "3.2" or less, the image forming apparatus determines that there is no difference in the correspondence relationship depending on the type of object.

[0038] However, a value other than "3.2" may be set for the threshold value. For example, in a printer with high stability, that is, an image forming apparatus that can form an image with a stable color, the threshold value may be set low.

[0039] That is, when the stability is high and the reproducibility of the colors to be formed is high, the image forming apparatus can form an image by reproducing the same colors even when performing image formation multiple times. In such a case, it is desirable to set the threshold value low.

[0040] On the other hand, for a printer with low stability, it is desirable to set the threshold value high. In this way, when the threshold value is set in consideration of the stability of the image forming apparatus, etc., the difference in the correspondence relationship can be accurately determined.

[0041] Also, if there is a bias in the colors included in the object, the image forming apparatus may have difficulty accurately determining whether there is a difference in the correspondence relationship. For example, the image forming apparatus calculates the Euclidean distance between the chromaticity values in the first color space corresponding to the type of object of interest and the chromaticity values in the first color space corresponding to a type different from the object of interest. Then, if the minimum value of the Euclidean distance is equal to or greater than a certain value, it is determined that it is difficult to determine whether there is a difference in the correspondence relationship.

[0042] In this way, when it is difficult to determine whether there is a difference in the correspondence relationship, the image forming apparatus may use the correspondence relationship for the case where it is difficult to accurately determine whether there is a difference in the correspondence relationship. Specifically, in advance, a target color of red (R, G, B) = (255, 0, 0) is defined as (L, a, b) = (53, 80, 67). Then, when the first image IMG1 and the second image IMG2 do not contain colors close to red (R, G, B) = (255, 0, 0), this correspondence relationship is added to generate color conversion parameters. By doing so, even when the number of colors used for the object is small, the image forming apparatus can generate general-purpose color conversion parameters.

[0043] Also, when it is difficult to determine whether there are differences in the correspondence relationship, the color conversion parameters may be generated by adding the color of the hue existing only in a predetermined object. That is, in the correspondence relationship, the image forming apparatus may generate color conversion parameters by adding the missing color. Specifically, when creating the color conversion parameters of a character object with image data that includes red data in a photo object but does not include a color close to red in the character object, the color conversion parameters can be created by adding the target color of red in the photo object. In this way, by adding the missing color, highly accurate color conversion can be performed across the entire color space.

[0044] [Regarding the object] Objects are classified into types such as, for example, characters, charts, photos, lines, or graphics. Therefore, the object information indicates what type each object is. For example, the object information is set in advance or in an operation system (OS).

[0045] Specifically, the image forming apparatus first generates color conversion parameters for a photo object based on the comparison between the first image IMG1 and the second image IMG2. Then, the image forming apparatus also performs image formation on objects other than photos using the color conversion parameters generated for photos.

[0046] In this way, when an image close to the target color can be formed even using color conversion parameters for objects of different types, the image forming apparatus may determine that there is no difference in the correspondence relationship between the objects. In this way, between objects with no difference in the correspondence relationship, a common color conversion parameter can be used, that is, there is no need to switch the color conversion parameters.

[0047] [Second Embodiment] The overall process of the second embodiment is different from that of the first embodiment. Hereinafter, the description will focus on the differences from the first embodiment.

[0048] FIG. 4 is a diagram showing an overall processing example of the second embodiment.

[0049] In step S0401, the image forming apparatus inputs a second image IMG2.

[0050] In step S0402, the image forming apparatus performs image processing. For example, when forming the second image IMG2, the image forming apparatus performs so-called pre-processing such as rasterization, color conversion, or gradation processing on the data representing the second image IMG2.

[0051] In step S0403, the image forming apparatus outputs the second image IMG2. That is, the image forming apparatus forms the second image IMG2 on paper or the like based on the pre-processed data in step S0402.

[0052] In step S0404, the image forming apparatus reads and inputs the first image IMG1 and the second image IMG2. For example, the image forming apparatus reads a printed matter on which the first image IMG1 and the second image IMG2 are formed and inputs the first image IMG1 and the second image IMG2.

[0053] In step S0405, the image forming apparatus performs image alignment. For example, step S0405 is the same process as step S0305.

[0054] In step S0406, the image forming apparatus acquires a chromaticity value and object information. The image processing in step S0402 switches color conversion parameters for each object. Then, in step S0406, the image forming apparatus acquires object information from the second image IMG2.

[0055] In step S0407, the image forming apparatus determines a correspondence relationship. For example, step S0407 is the same process as step S0307.

[0056] In step S0408, the image forming apparatus generates color conversion parameters. For example, step S0408 is the same process as step S0308.

[0057] In steps S0401 to S0404, the image forming apparatus inputs the second image IMG2 once, performs preprocessing and image formation, and then inputs it again by reading.

[0058] Note that in step S0402, the color conversion parameters may be switched so that the output range is different for each object.

[0059] Hereinafter, the case where two objects are included in the image will be described as an example. And, among the two objects, one object performs color conversion with the hue angle ranging from 0° to 180°. On the other hand, among the two objects, the other object performs color conversion with the hue angle ranging from 180° to 360°. In this example, the image forming apparatus generates color conversion parameters so that color conversion is performed so that the hue angles are different for each object.

[0060] Therefore, when image formation is performed using such color conversion parameters, since the objects have different phases, the image forming apparatus can perform image formation so that the objects have different colors. In this way, when the objects are formed with different colors, since the colors are different, it is easy to determine the objects from the second image IMG2.

[0061] Note that the range of the hue angle is set in advance for the object, for example. Also, the output range may be set outside the range of the hue angle. For example, the output range may be set by lightness or the like.

[0062] In this way, the image forming apparatus may generate color conversion parameters so that the output range for each object, that is, the range where the results of color conversion do not overlap.

[0063] Alternatively, the image may be divided into a plurality of images, and only one object may be output on each page, etc.

[0064] [Functional configuration example] FIG. 5 is a diagram showing a functional configuration example. For example, the image forming apparatus includes a first image input unit 100F1, a second image input unit 100F2, a determination unit 100F3, a generation unit 100F4, and the like.

[0065] The first image input unit 100F1 performs a first image input procedure for inputting the first image IMG1. For example, the first image input unit 100F1 is realized by a scanner 104, an input device 105, or the like.

[0066] The second image input unit 100F2 performs a second image input procedure for inputting the second image IMG2. For example, the second image input unit 100F2 is realized by a scanner 104, an input device 105, or the like.

[0067] The determination unit 100F3 performs a determination procedure for determining the type of the object. For example, the determination unit 100F3 is realized by an arithmetic unit 101 or the like.

[0068] The generation unit 100F4 performs a generation procedure for comparing the first image IMG1 and the second image IMG2 and generating color conversion parameters based on the correspondence relationship of chromaticity values for each object. For example, the generation unit 100F4 is realized by an arithmetic unit 101 or the like.

[0069] An image forming apparatus such as a printer may change the processing or the like for each object included in the image. On the other hand, if the color conversion parameters are generated without considering the type of the object in the correspondence relationship between the target color, that is, the first image IMG1, and the color that the image forming unit to be adjusted currently forms, that is, the second image IMG2, the images will be formed to have the same color even if the objects are different, and the accuracy of color conversion will deteriorate.

[0070] Therefore, the image forming apparatus first determines the objects included in the image. In this way, the image forming apparatus considers the type of object and the like when generating the color conversion parameters. By doing so, since the image forming apparatus uses different color conversion parameters for each object, the accuracy of color conversion can be improved.

[0071] Note that the image forming apparatus is not limited to the illustrated functional configuration. For example, the image forming apparatus may further include an image forming unit. That is, the image forming unit performs image formation based on the color conversion parameters generated by the generation unit 100F4.

[0072] [Examples of effects] FIG. 6 is a diagram showing an example of making different colors for each object. Hereinafter, the case under the conditions as illustrated will be described as an example.

[0073] FIG. 6(A) is a diagram showing an example of data indicating a printing target. For example, it is assumed that the data having the content shown in FIG. 6(A) is input to the image forming apparatus to perform image formation.

[0074] FIG. 6(B) is a diagram showing an example of a printing result. That is, FIG. 6(B) is an example of the case where image formation is performed by inputting the data shown in FIG. 6(A).

[0075] As shown in the figure, the data includes different types of objects, an object of characters (hereinafter referred to as "first object OB1") and an object of a photograph (hereinafter referred to as "second object OB2").

[0076] For example, on the data, the color is specified by RGB values. Hereinafter, as shown in FIG. 6(A), it is assumed that the same RGB value of "(R, G, B) = (255, 0, 0)" is set for both the first object OB1 and the second object OB2 on the data. Therefore, both the first object OB1 and the second object OB2 are "red" on the data.

[0077] On the other hand, assume that the result of image formation aims to have different colors for the first object OB1 and the second object OB2. Specifically, as shown in FIG. 6(B), the first object OB1 has a color of "(L, a, b) = (54, 71, 60)". On the other hand, the second object OB2 has a color of "(L, a, b) = (60, 68, 58)". In this way, although the same color is specified in terms of data depending on the type of object, image formation may be set to be performed so that different colors are obtained by changing the processing according to the type of object. In the first image IMG1, the first object OB1 is "red", while the second object OB2 is "orange".

[0078] In such a case, in order to indicate how to set the color, the image forming apparatus forms the first image IMG1 on a sheet or the like. Therefore, when the first image IMG1 is read, the image forming apparatus can grasp the target color.

[0079] On the other hand, the color conversion parameters, that is, how the image forming apparatus currently performs image formation, can be grasped by reading the second image IMG2 formed based on the data shown in FIG. 6(A). For example, if the type of object is not considered, the following results will occur.

[0080] FIG. 7 is a diagram showing an example when the object is not considered. As shown in FIG. 7(A), the same data as in FIG. 6(A) is input to an image forming apparatus that does not consider the object, and image formation is performed.

[0081] If the object is not considered, for example, the result as shown in FIG. 7(B) will be obtained. Comparing with FIG. 6(B), both the first object OB1 and the second object OB2 have a color of "(L, a, b) = (58, 69, 59)". That is, as shown in FIG. 6(B), even though the first object OB1 and the second object OB2 are aimed to have different colors, if the object is not considered, the same color conversion parameters are used for processing, so the result as shown in FIG. 7(B) may occur.

[0082] Therefore, when comparing the first image IMG1 and the second image IMG2, the image forming apparatus can grasp the correspondence relationship such as changing the color by an object or the like.

[0083] When generating color conversion parameters in consideration of an object, the following results can be obtained.

[0084] FIG. 8 is a diagram showing an example when an object is considered. When compared with FIG. 7, FIG. 8 is the same in that the same data as in FIG. 7(A) is used as shown in FIG. 8(A). On the other hand, as shown in FIG. 8(B), when an object is considered, the first object OB1 has a color of "(L, a, b) = (54, 71, 60)". On the other hand, the second object OB2 has a color of "(L, a, b) = (60, 68, 58)".

[0085] That is, the result shown in FIG. 8(B) is consistent with the result shown in FIG. 6(B), and the image has been formed as intended. In this way, the image forming apparatus can improve the accuracy of color conversion when considering an object.

[0086] Also, the determination as to whether there are differences in the correspondence relationship is performed by forming an image of the first object OB1 and the second object OB2 with the same color conversion parameters in the example shown in FIG. 6. First, the image forming apparatus generates color conversion parameters for the first object OB1, that is, an object of characters. Hereinafter, the color conversion parameters for the object of characters are referred to as "first color conversion parameters".

[0087] The first color conversion parameters are generated from the correspondence relationships in FIGS. 6(A) and 6(B).

[0088] Then, the image forming apparatus applies the first color conversion parameter to the formation of an image of an object other than characters, i.e., the second object OB2, to determine whether there is a difference in the correspondence relationship. In this way, even if a color conversion parameter for another object is applied, if the color conversion is an error that falls within the threshold value or less, the image forming apparatus determines that there is no difference in the correspondence relationship.

[0089] When determining as described above, the image forming apparatus can determine whether there is a difference in the color correspondence relationship for each object.

[0090] And, when there is a difference in the correspondence relationship, the image forming apparatus generates different color conversion parameters for each object. Specifically, when there is a difference in the correspondence relationship, the image forming apparatus generates a color conversion parameter for the second object OB2 (hereinafter referred to as the "second color conversion parameter") separately from the first color conversion parameter. In this way, when there is a switch between the first color conversion parameter and the second color conversion parameter, the image forming apparatus can form images of the first object OB1 and the second object OB2 in different colors.

[0091] When there is no difference in the correspondence relationship, the image forming apparatus generates a common color conversion parameter among different objects. Specifically, when there is no difference in the correspondence relationship, the image forming apparatus commonly uses the first color conversion parameter for both the first object OB1 and the second object OB2. By doing so, the number of color conversion parameters can be reduced.

[0092] Also, by making the color conversion parameters common and not switching them, fluctuations in the in-plane color can be reduced.

[0093] [Other Embodiments] The image forming method described above may be realized by a program such as firmware for example. That is, the image forming method is a method executed by a computer, in which an arithmetic unit, a storage device, an input device, an output device, and a control device cooperate to operate based on the program. Further, the program may be written in a storage device or a storage medium etc. and distributed, or distributed through a telecommunication line etc.

[0094] The image forming apparatus described above does not have to be a single device. That is, each device may be an image forming system etc. constituted by a plurality of devices. For example, the image forming system may be a combination of a scanner, an information processing device, and a printer connected via a network etc.

[0095] The image forming apparatus may be, for example, a commercial printing machine (such as a large electrophotographic printer or an inkjet printer etc.).

[0096] The recording medium is, for example, paper (also referred to as "plain paper" etc.). However, the recording medium may be coated paper, label paper etc. other than paper, overhead projector sheets, films, or flexible thin plates etc. Further, the recording medium may be roll paper etc.

[0097] Specifically, the recording medium is a recording medium such as paper, film, or cloth etc.

[0098] Thus, the material of the recording medium is paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, or a combination thereof etc.

[0099] Note that the present invention is not limited to each of the embodiments exemplified above, and various modifications are possible without departing from the technical gist, and all of the technical matters included in the technical idea described in the claims are the subject of the present invention.

[0100] The above embodiments show preferred examples. However, those skilled in the art can realize various modifications from the disclosed content. Such modifications are also included in the technical scope described in the claims.

Explanation of Signs

[0101] 100 : MFP 100F1 : First Image Input Unit 100F2 : Second Image Input Unit 100F3 : Determination Unit 100F4 : Generation Unit 101 : Arithmetic Unit 102 : Storage Device 103 : Printer Engine 104 : Scanner 105 : Input Device 106 : Control Device IMG1 : First Image IMG2 : Second Image OB1 : First Object OB2 : Second Object

Prior Art Documents

Patent Documents

[0102]

Patent Document 1

Claims

1. A first image input unit that inputs a first image which is an image indicating a target color; A second image input unit that inputs a second image which is an image formed by an image forming unit to be adjusted; A determination unit that determines the type of object; A generation unit that compares the first image and the second image, and generates color conversion parameters for converting chromaticity values in a first color space to chromaticity values in a second color space based on the correspondence relationship of chromaticity values of the object in the first image and the object in the second image for each type of object; Comprising: The generation unit: When there are differences in the correspondence relationship depending on the type of object, generates the color conversion parameters to be different for each type of object; When there are no differences in the correspondence relationship depending on the type of object, generates the color conversion parameters common to different types of objects. An image forming apparatus.

2. The determination unit: Determines when rasterizing the second image. The image forming apparatus according to Claim 1.

3. Whether there are differences in the correspondence relationship: Is determined by applying the color conversion parameters generated for forming a first object among the objects to a second object different from the first object. The image forming apparatus according to Claim 1.

4. The second image: Has different output ranges for each object. The image forming apparatus according to any one of Claims 1 to 3.

5. The generation unit: When it is difficult to determine whether there are differences in the correspondence relationship: Adds the lacking colors and generates the color conversion parameters. The image forming apparatus according to any one of Claims 1 to 4.

6. A first image input unit that inputs a first image which is an image indicating a target color; A second image input unit that inputs a second image which is an image formed by an image forming unit to be adjusted; A determination unit that determines the type of object; A generation unit that compares the first image and the second image, and generates color conversion parameters for converting chromaticity values in a first color space to chromaticity values in a second color space based on the correspondence relationship of chromaticity values of the object in the first image and the object in the second image for each object; Comprising: The generation unit: When there are differences in the correspondence relationship depending on the type of object, generates the color conversion parameters to be different for each type of object; When there is no difference in the correspondence relationship according to the type of the object, generate the color conversion parameters common to different types of the object Image forming system.

7. An image forming method performed by an image forming apparatus, comprising: a first image input step of inputting a first image which is an image indicating a target color; a second image input step of inputting a second image which is an image formed by an image forming unit to be adjusted; a determination step of determining the type of an object; a generation step of comparing the first image and the second image, and generating color conversion parameters for converting a chromaticity value in a first color space to a chromaticity value in a second color space based on a correspondence relationship between the chromaticity values of the object in the first image and the object in the second image for each object; and in the generation step, when there is a difference in the correspondence relationship according to the type of the object, generate the color conversion parameters to be different for each type of the object; when there is no difference in the correspondence relationship according to the type of the object, generate the color conversion parameters common to different types of the object Image forming method.

Images