JP2001144986A - Image processing method, image processor and computer- readable recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology that can respond to strong needs of improving the image quality in response to the preference of users and of acquisition of a special image effect. SOLUTION: An image input section 106 inputs an image to be processed. A function acquisition section 104 acquires a function to convert an angle when each pixel of the image is represented by the angle in a hue space. An image conversion section 106 converts the hue of each pixel according to the function to generate a 2nd image. The function has a prescribed dead zone at which an input angle is outputted as it is so as to inhibit a change in the color in the zone.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an image processing technique. The present invention particularly relates to an image processing apparatus and an image processing method having a color conversion function of an image.

[0002]

2. Description of the Related Art In a computer such as a printer, a PC (personal computer), and various image processing or editing apparatuses, a technique for modifying the color of an image is known. JP-A-2-128869 discloses a color correction processing method having a color conversion function. This method adds a process called multiplexing at the same time as correcting the color from the spectral density data to the recording density data. Multiplexing is
While the hue of the input data makes one rotation in the angle space, the hue of the output data is rotated several times. This method can be applied to a device that converts, for example, RGB data into CMY data, and records, prints, or the like.

[0003]

The above-described color correction processing method aims to increase the processing efficiency. That is, by realizing the color correction from the spectral density data to the recording density data and the multiplexing process at the same time, it is possible to improve the past process of performing both separately.

[0004] However, in today's widespread use of digital cameras, color printers, and the like, there is a strong demand for users to improve the image quality as desired or to create their own images, and the above-described color correction processing method does not always meet the demands. Absent.

[0005] The present invention has been made in view of such a point, and an object of the present invention is to provide a technique for improving the subjective image quality of an image and applying a special effect to the image. This object is achieved by a combination of features described in the independent claims. The dependent claims define specific and useful aspects of the present invention.

[0006]

One embodiment of the present invention is an image processing apparatus. This apparatus is an image input unit that inputs an image, a function acquisition unit that determines a hue of the image, and acquires a conversion function that includes a predetermined immobile section, and a function acquisition unit that obtains a conversion function for each of the constituent units of the image according to the conversion function. A conversion unit configured to convert a hue to generate a second image.

When a function becomes an identity map for a certain section of the domain of the function, the section is called an "immobile section". In this device, by providing an immobile section, the other hues are converted to other hues while maintaining the hue of the section. Examples of the “image constituent unit” include a pixel and an image block that is subdivided to some extent.

The conversion function may be defined for a periodic hue space, and may be a continuous function in that space. As an example of the periodicity, there is a hue space indicated by an angle of 0 to 360 °. By adopting a continuous function,
Smooth color conversion is realized.

The immovable section may be determined in relation to the hue of the region of interest included in the image. For example, a person or its face may be used as a region of interest, and an immovable section may be defined around the hue of the skin. In that case, the skin color is not converted and other colors are converted. The image converter may convert hue while maintaining luminance.

[0010] The function acquiring section may acquire the conversion function with reference to a user's instruction. This image processing device may also have a preview control unit. The preview control unit generates a preview image of the second image to be obtained by the conversion function. This image processing device may also have a color designation unit. The color designating unit designates a color whose hue is to be changed or maintained by the conversion. For example, by selecting a point on the screen, the color of the point may be designated.

This image processing apparatus may further have an area designating section. The region designating unit designates a region in which the hue is to be changed or maintained by the conversion. The designation may be made with a boundary line surrounding the area. This image processing device may also have a function editing unit. The function editing unit edits the conversion function based on a user's instruction, such as correcting or newly creating the conversion function.

Another embodiment of the present invention is an image processing method. The method comprises the steps of: obtaining a conversion function defined for a hue of an image and including a predetermined immovable section; converting the hue for each constituent unit of the image according to the conversion function to generate a second image Performing the steps. A recording medium storing a program may be provided as a project that causes a computer to execute these steps.

The above summary of the invention does not list all the features required for the present invention, and naturally, a sub-combination of these features can also be an invention.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following embodiments do not limit the invention described in the claims, and all combinations of features described in the embodiments are solutions of the invention. It is not always necessary for the means.

Here, a color thermal printer will be described as an example of a system incorporating the image processing apparatus according to the embodiment. First, an outline of color thermal paper will be described as preliminary knowledge.

The color thermosensitive paper has, for example, a cyan, magenta, and yellow thermosensitive layer and a transparent protective layer formed in this order from the bottom on a support. The thermal energy to be applied to each heat-sensitive layer to develop a color is different, and the energy of the lowermost cyan heat-sensitive layer is usually the highest, and the energy of the uppermost yellow heat-sensitive layer is usually the lowest. Therefore, the heat energy can be adjusted so that each heat-sensitive layer can be colored sequentially.

The colors of the yellow and magenta heat-sensitive layers obtained after heating are fixed by different ultraviolet rays. For example,
The maximum absorption wavelengths of the yellow and magenta heat-sensitive layers are about 420 nm and about 365 nm, respectively. When the heat-sensitive layers are irradiated with ultraviolet light having an energy peak at the maximum absorption wavelength corresponding to each, the color is fixed. Fixing prevents the recorded thermosensitive layer from re-coloring during the recording of the next thermosensitive layer.

When printing yellow, magenta, and cyan, two heat energies, bias heat energy and gradation heat energy, are applied to each color.
The bias heat energy is slightly lower than the heat energy required for the heat-sensitive layer of each color to develop a color, and is applied to the color heat-sensitive paper prior to recording. The bias thermal energy is determined with reference to bias data described later. On the other hand, the gradation thermal energy is determined by the gradation level of the color to be recorded, and is applied after bias heating. The gradation heat energy is determined by image data described later.

FIG. 1 is a schematic configuration of a color thermal printer. The image processing apparatus according to the embodiment is realized mainly by the cooperation of the controller 12 of the printer 10 and the image processing program stored in the system memory 14, as shown in FIG.

The printer 10 has a controller 12 for controlling the entire apparatus. The controller 12 can be composed of, for example, a general-purpose microprocessor. System memory 14
Stores a control program of the printer 10, a system program, and other system information. System memory 1
4 may be composed of a DRAM, an SRAM, or the like.
It may be constituted by a nonvolatile memory such as a LASH memory or an EEPROM (electrically erasable and programmable memory). In this embodiment, the system memory 14 is provided with an LUT (lookup table) which the controller 12 refers to appropriately for controlling the thermal head 32.

The controller 12 sends and receives signals such as data, commands, and status necessary for processing to and from various parts of the printer 10 via the data bus 60 and the control bus 62. The controller 12 receives a print request and image data to be printed from an external device (not shown) such as a PC via a communication I / F unit 52 or a Centronics I / F connector (not shown). According to the print request, the controller 1
Numeral 2 controls thermal energy to be generated by the thermal head 32.

The external device control section 46 is an arbitrary storage device such as a memory card, a floppy disk, or a hard disk in which images are stored, or a PC having various I / O functions.
It controls an MCIA-compliant card or the like (hereinafter, collectively referred to as “external device”). The printer 10 may acquire image data to be printed from an external device.

The display unit 64 includes, for example, an LCD and its driver, and operates and sets the printer 10.
The input user's instructions and the like are displayed. Operation unit 6
Reference numeral 6 includes a menu button, a selection button, a numerical key, and the like for inputting a user's instruction to the printer 10. When a touch panel is used, the display unit 64 and the operation unit 66 are integrally formed.

The image memory 16 has a yellow (Y) image memory 16a, a magenta (M) image memory 16b, and a cyan (C) image memory 16c. Each image memory 16a-
16c stores corresponding color data. At the time of recording on the color thermal paper 30, image data of each color is read line by line from the image memory 16 and written to the image line memory 18.

The bias line memory 20 holds one line of bias data. The bias data is set for each heating element, for example, in order to correct a variation in resistance values of a large number of heating elements (described later).

The strobe circuit 24 generates a strobe pulse having a predetermined duty ratio in accordance with an instruction from the controller 12, and sends the generated strobe pulse to the head drive unit 26. The selector 22 first reads one line of bias data from the bias line memory 20 and sends it to the head drive unit 26.
Subsequently, one line of image data is read from the image line memory 18 and sent to the head drive unit 26.

The head drive unit 26 generates drive data due to heat generation corresponding to bias data and image data for each line. An AND operation is performed between the drive data and the above-described strobe pulse, and a drive pulse is output.
When the drive data is “1”, the drive pulse also becomes “1”,
A transistor provided for each heating element of the thermal head 32 is driven. As a result, each heating element generates heat.

The roller pair 36 is bidirectionally rotated by a pulse motor 48, and reciprocates the color thermosensitive paper 30 in the transport path. In addition, a transport path for the color thermal paper 30 is formed by a pair of rollers (not shown). A thermal head 32 is disposed on the upper surface of the transport path, and a platen roller 44 is provided on the lower surface of the transport path opposite to the thermal head 32.

The thermal head 32 has a heating element array 32a arranged linearly in the width direction of the color thermal paper. This array includes a number of heating elements. The thermal head 32 has a first position at which the heating element array 32a is pressed against the color thermal paper 30 on the platen roller 44, and a second position at which a space is provided between them. Thermal head 32
Prints an image for each color for each line while the color thermal paper 30 is being conveyed, and when the color thermal paper 30 reciprocates three times, a color image is completed. Note that a thermal head may be provided for each color, in which case a color image is completed by one reciprocation.

A yellow fixing section 40 and a magenta fixing section 42 are provided at the end of the conveying path when viewed from the roller pair 36. The yellow fixing unit 40 and the magenta fixing unit 42 respectively have ultraviolet lamps 40a and 42a that emit ultraviolet light having the above-described energy peak. The lamp driving unit 28 is configured such that at the time of yellow recording, only the ultraviolet lamp 40a for yellow is used.
When recording magenta, an ultraviolet lamp 42 for magenta is used.
Only b is turned on.

The yellow fixing section 40 is provided with an illuminance sensor 50 for measuring the intensity of ultraviolet rays. Illuminance sensor 5
The measurement signal of 0 is sent to the controller 12, where necessary illuminance correction is performed. Even when the order of lamination of the heat-sensitive layers is different, the coloring heat energy of the intermediate layer to be recorded next may be adjusted based on the irradiation amount of the ultraviolet ray for fixing the uppermost layer.

FIG. 2 shows a schematic configuration of the image processing apparatus 100 incorporated in the printer 10. Image processing device 100
When an image is displayed in brightness and chromaticity, the hue of the chromaticity is displayed in an angle, and the angle is converted to convert the hue. The objective is to improve the subjective quality of the image and special effects.

The image processing apparatus 100 includes an image input unit 102 for inputting image data from the image memory 16 and the like, a function obtaining unit 104 for obtaining a hue conversion function, and a conversion function for the input image. And an image conversion unit 106 that generates the second image. A plurality of conversion functions are registered in the function directory 108 in advance.
Selects and obtains available conversion functions as needed.

The preview control unit 118 converts the second image into a preview image format and sends it to the display unit 64 in FIG. The second image is sent to the external device control unit 46, the communication I / F unit 52, and the like, and is recorded and transmitted to the external device as needed.

The user-related function unit 110 is a function group for linking a user's instruction to hue conversion, and is provided as a part or extension of the operation unit 66 in FIG. This unit includes a color specifying unit 112 for specifying a color to be converted.
And a function editing unit 114 that edits a conversion function according to a user's instruction, and an area specifying unit 116 that specifies an area to be converted in color on the image. The color specifying unit 112 and the function editing unit 114 directly operate on the conversion function, while the area specifying unit 116 defines an image area on which the conversion function should operate. Note that information on the designation of a color or area or the conversion function being edited is appropriately sent to the display unit 64 and used by the user.

The image processing apparatus 100 refers to a conversion function when converting a hue. Hue domain of image data input to the conversion function (hereinafter represented by φi), and hue value range after conversion which is the output of the conversion function (hereinafter represented by φt)
Are both angles in the hue space. The feature of the conversion function in this embodiment is that a fixed point is a continuous section,
That is, it has an immovable section (hereinafter referred to as [φa, φb]). That is, the conversion function f is

F (φi) = φi: {φi} [φa, φb] is satisfied. If [φa, φb] is set near the flesh color, another hue can be converted while the hue of the flesh color remains unchanged. in this case,
A special effect of converting another color can be obtained without making the human skin an unnatural color.

Another feature of the conversion function is that it is a continuous function. If there is a discontinuous point, the hue after conversion at that point becomes discontinuous, which may cause unnaturalness. However, for the purpose of obtaining a special effect, a discontinuity may be intentionally generated. The hue space of the angle display is, for example, 0 to 360 ° or -1.
Since it has periodicity in the range of 80 to 180 °, the conversion function returns the same φt for φi at both ends of the range. That is, for the above two domains,
Respectively,

F (0) = f (360) + 360n where n is an integer or f (−180) = f (180) −180 + 360n where n is an integer.

Here, a function for linearly converting an angle other than [φa, φb] is specifically shown. First, φp = φb−φah = (360n + 360−φp) / (360−φp)
Here, n is a natural number. At this time, for φi> φb, φt = f (φi) = h (φi−φb) + φb (Formula 1) For φi <φa, φt = f (φi) = h (φi + 180) −180 + h (180−φb) ) + (Φb−180) (formula 2). This is the required conversion function.

It is assumed that the image data is represented by 8-bit luminance and color difference Y, Cr, Cb. The conversion equation between these parameters and RGB is generally Y = 0.2990R + 0.5870G + 0.1140B Cr = 0.5000R−0.4187G−0.0813B + 128 (Equation 3) Cb = −0.1687R−0.3313G−0.5000B + 128 (Equation 4) . Here, the term “128” of Cr and Cb is added for convenience of representing data with 8 bits of 0 to 255. Therefore, from Equations 3 and 4, as an example of the hue coordinate axes used in this embodiment,

Cr = Cr-128 (Equation 5) cb = Cb-128 (Equation 6), and the hue angle display φ (φi or φ
t) can be defined as φ = tan ⁻¹ (cr / cb) (Equation 7).

FIG. 3 shows a hue angle-displayed using cr and cb. In the drawing, M, B, C, G, Y, and R indicate approximate angles of magenta, blue, cyan, green, yellow, and red, respectively. Here, the range of -180 to 180 ° is set, and 90 to 180 °, in which the flesh color is definitely included, is set to the immovable section 1.
30. That is, φa = 90 and φb = 180. For simplicity, if n = 1 in equations 1 and 2, h = 7
/ 3, and the conversion function is an area other than the immobile area 130 (hereinafter referred to as “processing area 132”), that is, φi <90, φt = f (φi) = (φi + 180) · 7 / 3−180 (Equation 8) It's easy.

FIG. 4 shows this conversion function. As shown in the figure, φt = φ at 90 to 180 ° which is the immobile region 130.
i is protected. The image conversion unit 106 may perform hue conversion for each pixel of the image based on Expression 8.

FIG. 5 is a flowchart showing the processing performed by the image conversion unit 106. As shown in the figure, in order to change the input image data to the hue angle display, the preprocessing S1 is performed.
0, S12, and S14 are performed. First, luminance and color differences Y, Cr, and Cb are obtained for a pixel having image data (S10). Subsequently, the coordinates (cr, cb) in the hue space (FIG. 3) are obtained according to Equations 5 and 6 (S12).
Next, the input of the conversion function is obtained as φi according to Equation 7 (S14).

The processing of S16, S18, and S24 is as follows.
It is determined by the conversion function notified to the image conversion unit 106. In this example, φi is defined as −180 to 180 °, and the immobile section 130 is 90 to 180 °,
The distinction between the immobile section 130 and the processing section 132 is simply φi and 9
A comparison of 0 ° is sufficient (S16). If φi <90 ° (Y in S16), φt converted by Expression 8 is obtained (S18). Subsequently, coordinates (cr1, cb1) in the hue space corresponding to the φt are obtained (S20).
Thereafter, 128 is added to each of cr1 and cb1 to finally obtain the converted color differences CR and CB (S
22).

On the other hand, in the judgment of S16, φi ≧ 90 °
If (N in S16), since no conversion process is performed, c
r and cb are once saved to cr1 and cb1, respectively (S24). The process is passed to S22. As a result, CR = C
The non-conversion process of r, CB = Cb is realized. The image processing according to the embodiment is completed by performing the above series of processing for all the pixels.

Here, the luminance Y is kept as it is because a natural image is easily generated by changing only the hue. Experiments have also provided images that are so natural that it is not possible to see which part of the image has changed color. Of course, the conversion of the luminance Y can be performed at the same time, and the effect can be confirmed in a preview image described later.

The image processing apparatus 100 provides various functions for performing color conversion according to the user's preference. FIG.
Shows a procedure for specifying a color to be changed by the color specifying unit 112. Here, consider an image 140 in which two persons 142 and 144 are projected. The first person 142 is wearing yellow clothing 146 and the second person 144 is wearing blue clothing 148. The user points to a point P on the clothes of the second person 144 with a pointing device such as a mouse. Since the pixel at this point P is blue, the color designation unit 112 acquires “blue” as the conversion source color.

Subsequently, the color designation section 112 causes the display unit 64 to display the pallet 150 in order to determine the destination color. The palette 150 displays first to fourth color candidates. It is assumed that the user clicks red on the palette 150. Thus, the color of the conversion destination is acquired as “red”. The color designation unit 112 sends information of (conversion source, conversion destination) = (blue, red) to the function acquisition unit 104. Function acquisition unit 104
Searches for a conversion function from the function directory 108 using this information as a search condition and sends it to the image conversion unit 106.

FIG. 7 shows the obtained conversion function.
Since “blue” extends around −20 to −10 °, the range from −50 to 10 ° is converted to 110 ° that is “red” here. Thus, the clothes 148 of the second person 144
Changes from blue to red. The result of the color conversion is displayed on the display unit 64 via the preview control unit 118. In addition,
Here, the color of the pixel at the point P has been changed.
May be configured to confirm with the user whether to "change the designated color" or conversely, "change the color other than the designated color".

FIG. 8 shows another conversion function. In this example, the entire image is converted to red except for the area near the skin color. In other words, the face of the first person 142 and the face of the second person 144 can be reconstructed into an image as if the other parts were viewed with a red filter while leaving the original color. Color designation section 112
For example, the user may prepare an option such as "Remove flesh color" or "Whole red" and click on this.

The function editing unit 114 has an interface that allows the display unit 64 to display, for example, the conversion functions shown in FIGS. 7 and 8 and allows the graph itself to be directly edited. That is, a function of arbitrarily moving an arbitrary point on the graph in the manner of clicking and dragging is provided. The resulting image is displayed on display unit 64 via preview control unit 118.

FIG. 9 shows the operation of the area designating section 116.
When the color to be changed is designated as “blue” by the color designation unit 112, not only clothes but also colors with similar hues such as the sky are converted. Therefore, when it is really desired to change only the color of the clothes, the area specifying unit 116 is used.

The user draws a boundary 160 surrounding the second person 144 to be changed using the draw function provided by the area designating section 116. Subsequently, the area specifying unit 116
Prompts the user to select either "change color inside area" or "change color outside area". At this time, if the conversion function is that of FIG. 7 and the user selects “change color in area”, “blue” inside boundary line 160 changes to “red”.
And the intended purpose is achieved.

Although the embodiments have been described above, the technical scope of the present invention is not limited to these descriptions. It is understood by those skilled in the art that various changes or improvements can be made to these embodiments.

As a first modification, the embodiment is considered to be applied to a color thermal printer. However, this may naturally be another type of printer, an image-related device such as a digital camera other than the printer, or a widely used device. It may be a general computer. For example, the present invention can also be realized by implementing a program for performing the processing of the embodiment on a personal computer. This program can be provided on a recording medium such as a floppy disk.

As a second modification, FIG. 2 shows the function obtaining unit 104 and the image conversion unit 106 as separate components. However, they may be of an integrated configuration for performing the processing of FIG. 5 collectively, for example. .

As a third modification, in the embodiment, c
Although r and cb are color coordinates, they may be other color coordinates. For example, a uniform color space L ^* a ^* b ^* or L ^* u
^* V ^* .

As a fourth modification, in the embodiment, the skin color area is set as the immobile section, but this may be a section corresponding to another color. For example, leaving only red flowers,
A process of converting all other portions to blue can be considered.

As a fifth modification, when selecting or correcting a conversion function, a configuration may be employed in which the color distribution of an image to be processed is referred to. For example, in FIG. 7, the conversion function is −5.
It changes sharply at 0 ° and 10 ° (these points are simply called “change points”). Therefore, first, all the pixels of the image to be processed are converted into a histogram according to the hue, and a hue having a low appearance frequency is searched for. Subsequently, a conversion function is determined so that the hue angle becomes a change point. This makes the color change of the image obtained after the conversion more natural. Histogram conversion is performed by the image input unit 102 and others.
Modification of the conversion function is performed by the function acquisition unit 104 and the function editing unit 11
4 etc. may be performed.

As a sixth modification, a plurality of designations may be made by the color designation section 112 and the area designation section 116, respectively. For example, changing the color of one point and maintaining the color of another point, or changing the color of one point within a boundary line and maintaining the color of another point, etc. Multiple specification of specification is also possible.

As a seventh modification, the conversion function shown in FIG. 4 and the like may be registered in the three-dimensional LUT as numerical data in advance. In that case, the image conversion unit 106 can perform high-speed conversion processing by referring to the LUT and performing necessary interpolation.

As an eighth modification, the image conversion unit 106 performs color conversion on a pixel-by-pixel basis, but this may be performed on a block-by-block basis comprising a plurality of pixels. In that case, the average angle of the hue of the pixel may be calculated for each block, and a conversion function may be applied to the average angle. Thereafter, processing such as adding the difference between the hue angle of each pixel and the average angle to the hue of each pixel after conversion may be performed.

As described above, according to the embodiment and its modifications, it is possible to arbitrarily change, for example, dramatically, the color of the background or the like while leaving necessary colors by a relatively simple method.
In addition, at that time, an image with little discomfort desired by the user can be obtained relatively easily.

[0066]

According to the present invention, improvement of the subjective image quality of an image and special effect processing can be easily realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a color thermal printer according to an embodiment.

FIG. 2 is a configuration diagram of an image processing apparatus according to an embodiment.

FIG. 3 is a diagram showing a hue space used in the embodiment.

FIG. 4 is a diagram showing an example of a conversion function used in the embodiment.

FIG. 5 is a flowchart of a process in an image conversion unit according to the embodiment.

FIG. 6 is a diagram illustrating processing of a color designation unit according to the embodiment.

FIG. 7 is a diagram showing an example of a conversion function adopted in the embodiment.

FIG. 8 is a diagram illustrating an example of a conversion function adopted in the embodiment.

FIG. 9 is a diagram illustrating processing of an area specifying unit according to the embodiment.

[Explanation of symbols]

 Reference Signs List 10 printer 12 controller 14 system memory 16 image memory 64 display unit 66 operation unit 100 image processing device 102 image input unit 104 function acquisition unit 106 image conversion unit 108 function directory 112 color designation unit 114 function editing unit 116 region designation unit 118 preview unit 130 Fixed area 132 Processing area 160 Boundary

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) MA11 MA19 MA20 NA03 NA13 NA27 PA03

Claims (13)

[Claims] 1. An apparatus for processing an image, comprising: an image input unit that inputs the image; a function acquisition unit that determines a hue of the image and acquires a conversion function including a predetermined immovable section; An image conversion unit that converts a hue of each of the constituent units of the image according to the conversion function and generates a second image. 2. The image processing apparatus according to claim 1, wherein the conversion function is determined for a periodic hue space, and is a continuous function in the space. 3. The image processing apparatus according to claim 1, wherein the immobile section is determined in relation to a hue of a region of interest included in the image. 4. The image processing apparatus according to claim 3, wherein the attention area is an area occupied by a person in the image. 5. The function acquiring unit according to claim 1, wherein the function acquiring unit acquires the conversion function by referring to a user's instruction.
5. The image processing apparatus according to any one of claims 1 to 4. 6. The image processing apparatus according to claim 1, further comprising a preview control unit that generates a preview image of the second image to be obtained by the conversion function. 7. The image processing apparatus according to claim 1, further comprising a color specifying unit that specifies a color whose hue is to be changed or maintained by the conversion. 8. The image processing apparatus according to claim 1, further comprising an area specifying unit that specifies an area in which hue is to be changed or maintained by the conversion. 9. The image processing apparatus according to claim 8, wherein the area designating unit receives a user's instruction in the form of a boundary surrounding an area where the hue is to be changed or maintained. 10. The image processing apparatus according to claim 1, further comprising a function editing unit that edits the conversion function based on a user's instruction. 11. The image processing apparatus according to claim 1, wherein the image conversion unit converts the hue while maintaining luminance of the image. 12. A method for performing processing on an image, comprising: obtaining a conversion function defined for a hue of the image and including a predetermined immovable section; and for each constituent unit of the image according to the conversion function. Converting the hue to generate a second image. 13. A computer-readable recording medium, comprising: a step of acquiring a conversion function defined for a hue of an image and including a predetermined immovable section; and for each constituent unit of the image according to the conversion function. Converting the hue to generate a second image, and a program for causing a computer to execute the steps.