Patent Publication Number: US-2020296340-A1

Title: Color conversion method, color conversion device, and display device

Description:
The present application is based on, and claims priority from JP Application Serial Number 2019-045705, filed Mar. 13, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a color conversion method, a color conversion device, and a display device. 
     2. Related Art 
     In the past, there has been known a color conversion device for converting color signals such as RGB signals input from the outside using a three-dimensional look-up table (hereinafter also referred to as 3D-LUT). 
     A user needs to change some of the colors in accordance with convenience in some cases when the user checked an image projected by a display device such as a projector. It requires a large amount of processing for entirely changing the 3D-LUT large in data amount to change some of the colors. Therefore, there has been demanded a method of converting some of the colors of an output image with a simple method. 
     SUMMARY 
     According to an aspect of the present disclosure, there is provided a color conversion method. The color conversion method may include the steps of taking a color required to be changed as a designated color out of input colors included in a display image to be displayed using an input image signal, taking a conversion color to be designated as an output color after changing the designated color, and performing color conversion of the designated color into the conversion color out of the input colors to output an output image signal for displaying the display image using the input image signal on which the color conversion was performed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a function of a projector as an example of a display device. 
         FIG. 2  is a block diagram particularly showing a configuration of a simple color gamut conversion circuit. 
         FIG. 3  is a flowchart showing a color conversion method to be performed by the simple color gamut conversion circuit. 
         FIG. 4  is an explanatory diagram schematically showing a selection screen for a designated color. 
         FIG. 5  is an explanatory diagram schematically showing a selection screen for a conversion color. 
         FIG. 6  is an explanatory diagram schematically showing a color conversion process in a three-dimensional color space. 
         FIG. 7  is an explanatory diagram showing a correspondence relationship of a conversion from an input image signal to an output image signal. 
         FIG. 8  is an explanatory diagram schematically showing a display image in a state on which a color conversion process has been performed. 
         FIG. 9  is a flowchart showing a color conversion method according to a second embodiment. 
         FIG. 10  is an explanatory diagram showing a correspondence relationship of a conversion in the second embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     A. First Embodiment 
       FIG. 1  is a block diagram showing a function of a projector  100  as an example of a display device. The projector  100  is coupled to an image supply device not shown, and projects a display image to form the display image on a screen SC using input image data input from the image supply device. The projector  100  is provided with a control device  50  which is constituted by a memory and a CPU, and performs overall control of the whole of the projector  100 , a color conversion device  30  for processing the input image data under the control by the control device  50 , and a projection device  20  for projecting the display image on the screen SC. In the present embodiment, a function of each section of the control device  50  is realized by a processor of the control device  50  executing a computer program. A function of each section of the color conversion device  30  is realized by a hardware circuit such as an FPGA (field-programmable gate array). Further, it is possible to realize some of the functions of the control device  50  with a hardware circuit, and it is possible to realize some of the functions of the color conversion device  30  with the processor. 
     The projection device  20  is provided with a light source section  21 , a light modulation section  22  for modulating the light emitted by the light source section  21 , and a projection optical system  23  for collecting and diffusing the light modulated by the light modulation section  22  to project the light on the screen SC. The light source section  21  is provided with a light source consisting of a xenon lamp, a super-high pressure mercury lamp, an LED, or the like. The light source section  21  is provided with a drive circuit for supplying the light source with a drive current in accordance with the control by the control device  50  to put ON/OFF the light source. Further, the light source section  21  is provided with a reflector for guiding the light emitted by the light source to the light modulation section  22 , and a lens group not shown for enhancing the optical characteristics of the projection light. It is possible for the light source section  21  to be provided with a polarization plate, a dimming element for reducing an amount of the light emitted by the light source on a path to the light modulation section  22 , and so on. 
     The light modulation section  22  is provided with a liquid crystal panel or a digital mirror device (DMD), and modulates the light emitted by the light source section  21 . For example, the light modulation section  22  is provided with three transmissive liquid crystal panels corresponding respectively to the colors of RGB, and these transmissive liquid crystal panels are driven by a light modulation section drive circuit  38  described later. Besides the configuration provided with the three transmissive liquid crystal panels, the light modulation section  22  can be provided with, for example, a configuration of being provided with three DMD, or a configuration in which a single transmissive liquid crystal panel or a single DMD, and a color wheel combined with each other. The projection optical system  23  is provided with a prism for combining the three colors of R, G and B of modulated light modulated by the light modulation section  22 , a lens group for imaging the projection image combined by the prism on the screen SC, and so on. 
     In the present embodiment, the input image data is input from a personal computer as the image supply device to the projector  100 . The input image data can be input from external equipment such as an image player or a digital camera, or can also be read out from a storage device provided to the projector  100 . The image signal input to the projector  100  can also be image data of a moving image besides image data of a still image. 
     The color conversion device  30  performs the conversion from the designated color to the conversion color in accordance with the designated color designated by the user and the conversion color out of the input image data input from the image supply device, and outputs the result as an image control signal for driving the light modulation section  22 . The color conversion device  30  is provided with a simple color gamut conversion circuit  32  and the light modulation section drive circuit  38 . The input image data input to the color conversion device  30  is input to the simple color gamut conversion circuit  32  as the image signal via an image input interface not shown. The image input interface can be provided with a connector to be coupled to the image supply device and an interface circuit, or it is also possible to provide the connector and the interface circuit instead of the image input interface. Further, the image input interface can be provided with a configuration capable of inputting an analog image signal, or it is also possible for the image input interface to be provided with an A/D converter for converting the analog image signal into a digital image data and so on to output the digital image data thus converted to a signal processing section. It is also possible to provide the signal processing section for performing a variety of types of image processing such as a resolution conversion process, a frame rate conversion process, a 3D image conversion process, a distortion correction process, and a zooming process disposed between the image input interface and the simple color gamut conversion circuit  32 . 
     The simple color gamut conversion circuit  32  performs a process of performing a color conversion from the designated color included in the input image signal to the conversion color. The input image signal to be input to the simple color gamut conversion circuit  32  is an RGB input image signal constituted by respective image signal components of R (red), G (green), and B (blue) in the present embodiment. The input image signal can be, for example, a YUV image signal constituted by Y (a luminance signal), U (a first color-difference signal), and V (a second color-difference signal), or can also be a YCbCr image signal or a YPbPr image signal. It is also possible to provide, for example, a color adjustment circuit between the image input interface and the simple color gamut conversion circuit  32 , the color adjustment circuit performing a conversion into an HLS image signal consisting of H (hue), S (saturation), and L (luminance) components to perform a color adjustment. 
     The simple color gamut conversion circuit  32  outputs the image signal on which the color conversion process has been performed to the light modulation section drive circuit  38 . In the present embodiment, the image signal output to the light modulation section drive circuit  38  includes the respective image signal components of R, G, and B. The light modulation section drive circuit  38  drives the light modulation section  22  based on the image signal input from the simple color gamut conversion circuit  32 . More specifically, the light modulation section drive circuit  38  drives the liquid crystal display panels of the light modulation section  22  based on the image control signal input, and thus draws the images on the liquid crystal display panels. The projection device  20  functions as a display section for projecting the display image on the screen SC in accordance with the images drawn on the liquid crystal display panels. 
     Then, a configuration of simple color gamut conversion circuit  32  will be described using  FIG. 2 .  FIG. 2  is a block diagram particularly showing a configuration of the simple color gamut conversion circuit  32 . The simple color gamut conversion circuit  32  is provided with a color comparison circuit  33  and an interpolation circuit  34 . The input image signal input from the image supply device via the image input interface is input to the color comparison circuit  33  and the interpolation circuit  34 . 
     The color comparison circuit  33  determines whether or not the designated color is included in the input image signal by comparing an RGB value of the designated color and RGB values corresponding to the colors included in the input image signal to each other. The designated color represents a color a change of which is requested by an instruction of the user out of the input colors included in the display image to be displayed using the input image signal by the projector  100 . The display image can also be an image to be displayed by a variety of devices for displaying an image based on the image signal such as a personal computer, a printer, or a liquid crystal monitor besides the projector  100 . In the present embodiment, the designated color is arbitrarily selected by the user of the personal computer as the image supply device to be coupled to the projector  100 . The designated color is input to the color comparison circuit  33  as the RGB value via the control device  50 . When the color comparison circuit  33  has detected the RGB value of the designated color in the input image signal, the color comparison circuit  33  outputs an ON signal for changing the RGB value of the designated color to the interpolation circuit  34 . 
     The interpolation circuit  34  converts only the designated color out of the colors included in the input image signal into the conversion color. The conversion color is a color to be designated as an output color after changing the designated color, and is arbitrarily selected by the user of the personal computer as the image supply device, and is input to the interpolation circuit  34  as the RGB value via the control device  50  similarly to the designated color in the present embodiment. The interpolation circuit  34  detects the RGB value of the designated color based on the ON signal input from the color comparison circuit  33 , and then converts only the RGB value corresponding to the designated color out of the input image signal into the RGB value corresponding to the conversion color. The RGB values corresponding to other colors than the designated color out of the input image signal are output to the light modulation section drive circuit  38  while being kept at the RGB values as input. 
     Then, the details of the color conversion method to be performed by the simple color gamut conversion circuit  32  will be described using  FIG. 3  through  FIG. 8 .  FIG. 3  is a flowchart showing the color conversion method to be performed by the simple color gamut conversion circuit  32  of the color conversion device  30 . The present flow starts in response to the control device  50  receiving the instruction of changing the designated color in accordance with, for example, an operation of the projector  100  by the user. 
     In the step S 10 , the control device  50  displays a selection screen for the designated color as the display image of the projector  100 .  FIG. 4  is an explanatory diagram schematically showing the selection screen for the designated color. In the present embodiment, an adjustment screen  60   a  is an image obtained by the control device  50  adding an image  70  and a cursor Pt to the display image projected on the screen SC by the projector  100  based on the arbitrary input image data input from the personal computer. It is possible for the user to select a color on the display image as the designated color while visually recognizing the color on the display image using the adjustment screen  60   a . The user operates the cursor Pt via the control device  50  with the operation of the personal computer or the projector  100  to move the cursor Pt to a desired color on the adjustment screen  60   a  to select the designated color. In the example shown in  FIG. 4 , it is assumed that the color C 1  in the adjustment screen  60   a  is selected. Hereinafter, the color C 1  is also referred to as the designated color C 1 . In the step S 20 , the RGB signal corresponding to the designated color C 1  thus selected is input to the color comparison circuit  33  via the control device  50 , and the color comparison circuit  33  detects the designated color C 1 . The color comparison circuit  33  outputs the ON signal corresponding to the designated color C 1  thus detected to the interpolation circuit  34 . 
     In the step S 30 , the control device  50  having received the input of the designated color displays the selection screen for the conversion color as the display image of the projector  100 .  FIG. 5  is an explanatory diagram schematically showing the selection screen for the conversion color. A conversion color selection screen  62  is a display image including a hue circle MC, an image  72 , and the cursor Pt. The conversion color selection screen  62  is projected on the screen SC by the projector  100  as the adjustment screen including the selection screen for the conversion color. It is possible for the user to select a color on the display image as the conversion color while visually recognizing the color on the display image using the conversion color selection screen  62 . The user operates the cursor Pt to move the cursor Pt to a desired color in the hue circle MC on the conversion color selection screen  62  to select the conversion color. The hue circle MC can have a simple configuration of displaying only colors which can be changed. It is possible for the conversion color selection screen  62  to use index colors using a color pallet instead of the hue circle MC, or to display a plurality of colors using an arbitrary method. In the example shown in  FIG. 5 , it is assumed that the color C 2  in the hue circle MC in the conversion color selection screen  62  is selected. Hereinafter, the color C 2  is also referred to as the conversion color C 2 . In the step S 40 , by inputting the RGB signal corresponding to the conversion color C 2  thus selected to the interpolation circuit  34  via the control device  50 , the interpolation circuit  34  detects the conversion color C 2 . 
     In the step S 50 , the interpolation circuit  34  having received the ON signal corresponding to the designated color C 1  and the conversion color C 2  performs a process for setting the conversion color C 2  in a grid-point group. Here, a process of setting the conversion color C 2  in the grid-point group performed by the simple color gamut conversion circuit  32  will be described using  FIG. 6  and  FIG. 7 .  FIG. 6  is an explanatory diagram schematically showing a color conversion process with the simple color gamut conversion circuit  32  in a three-dimensional color space. As shown in  FIG. 6 , the designated color C 1  is changed to the RGB value represented in the three-dimensional color space to thereby be converted into the conversion color C 2 . 
       FIG. 7  is an explanatory diagram showing a correspondence relationship of a conversion from the input image signal to the output image signal. In  FIG. 7 , there is only shown the color conversion in the R value in the three-dimensional color space shown in  FIG. 6  for the sake of convenience of explanation. The horizontal axis in the drawing represents the R value of the input image signal expressed in the grayscale from 0 through 255, and the vertical axis represents the R value of the output image signal expressed in the grayscale from 0 through 255. The correspondence relationship shown in  FIG. 7  is a so-called conversion map for converting the input image signal into the output image signal, and is stored in the memory of the control device  50 . The color conversion process performed in each of the G value and the B value other than the R value is substantially the same as the color conversion process performed in the R value, and therefore, the description thereof will be omitted. 
     In the present embodiment, in the color conversion process by the interpolation circuit  34 , there is used a plurality of grid-points discretized in the color space. The grid-pints are discretized into pixel values by 32 gray levels such as 0, 32, 64, . . . , 255 out of the R value in the 256 gray levels expressed by 0 through 255 shown in  FIG. 7 . The grid-points are not limited to the values by 32 gray levels, but can arbitrarily be set to values by 2 gray levels, 16 gray levels, 64 gray levels and so on. Among the plurality of grid-points, the grid-points representing the corresponding relationship in the R value of the output image signal with respect to the R value of the input image signal are also referred to as the grid-point group. In other words, the grid-point group defines an output color with respect to an input color.  FIG. 7  shows a grid-point group LG conceptually representing the grid-point group. The interpolation circuit  34  performs the color conversion process in three dimensions based on the RGB value based on the grid-point group LG developed in a reticular pattern in the three-dimensional color space represented by the RGB value. 
     The grid-point group LG on a straight line shown in  FIG. 7  represents the state of initial setting of the correspondence relationship of the R value of the output image signal with respect to the R value of the input image signal, and shows the correspondence relationship in which the R value of the input image signal and the R value of the output image signal correspond to each other in a one-to-one basis. The grid-point group LG is rewritten by the simple color gamut conversion circuit  32 , and is reset to the initial setting, for example, every start-up of the projector  100 . 
     The interpolation circuit  34  sets the R value included in the designated color C 1  as the R value of the input image signal, and sets the R value included in the conversion color C 2  as the R value of the output image signal. In the example shown in  FIG. 7 , the R value of the designated color C 1  is assumed as an input pixel value R 1  ( 150  in the drawing). It is assumed that the input pixel value R 1  is not included in the grid-points of the grid-point group LG. On the other hand, the R value of the conversion color C 2  is assumed as an output pixel value R 3  ( 224  in the drawing), and it is assumed that the output pixel value R 3  is the R value of the grid-point in the three-dimensional color space. 
     In the present embodiment, since the input pixel value R 1  of the designated color C 1  thus obtained is not included in the grid-points on the grid-point group LG, the interpolation circuit  34  approximates the input pixel value R 1  to the grid-point to be the nearest neighbor out of the grid-points included in the grid-point group LG. More specifically, the interpolation circuit  34  approximates the input pixel value R 1  to an input pixel value R 2  as the grid-point to be the nearest neighbor of the input pixel value R 1  using a nearest neighbor interpolation also cal led a nearest neighbor method. In contrast, when the pixel value of the designated color thus obtained is included in the grid-points on the grid-point group LG, the interpolation circuit  34  uses that pixel value. 
     Then, the interpolation circuit  34  replaces a grid-point La having the input pixel value R 2  thus approximated as the input image signal with a grid-point Lb having an output pixel value R 3  corresponding to the conversion color C 2  as the output image signal out of the grid-point group LG. It should be noted that the grid-point Lb is a grid-point corresponding to the conversion color C 2 , and is designated as another grid-point not included in the grid-point group LG. Thus, when the input color having the input pixel value R 2  is included in the input image signal, for example, there is performed the color conversion to the output image signal including the output color having the output pixel value R 3  corresponding to the conversion color C 2 . Further, in the present embodiment, even when the R value of the input image signal is not included in the grid-points of the grid-point group LG as in the case of the designated color C 1 , the approximation to the input pixel value R 2  as the grid-point on the grid-point group LG is performed using the nearest neighbor interpolation to perform the conversion into the output pixel value R 3  corresponding to the conversion color C 2 . In other words, the input color included in the color gamut in the vicinity of the grid-point La is converted into the conversion color C 2 . It is also possible to convert only the input color of the grid-point La into the conversion color C 2 . As described above, in the step S 50 , the interpolation circuit  34  rewrites the grid-point La to be the nearest neighbor of the designated color C 1  out of the grid-point group LG so as to become the grid-point Lb corresponding to the conversion color C 2 , and then stores the grid-point group LG thus rewritten in the memory of the control device  50 . 
     In the step S 60 , the interpolation circuit  34  converts the RGB value of the input image signal thus input into the RGB value corresponding to the output image signal to output the result to the light modulation section drive circuit  38  with reference to the grid-point group LG thus rewritten.  FIG. 8  is an explanatory diagram schematically showing the display image in the state in which the color conversion process from the designated color C 1  into the conversion color C 2  is performed. As shown in  FIG. 8 , there is output the display image  60   b  in which the color conversion from the designated color C 1  into the conversion color C 2  is performed using the grid-point group LG thus rewritten. 
     As described hereinabove, according to the color conversion method in the present embodiment, by rewriting only a part of the correspondence relationship between the input image signal and the output image signal, only the arbitrary designated color C 1  included in the display image is changed to the arbitrary conversion color C 2 . Therefore, it is possible for the user to arbitrarily convert some of the colors of the display image with a simple method without performing a process of a large amount of data such as rewriting of the entire conversion map. 
     According to the color conversion method related to the present embodiment, there is used the grid-point group LG determined in advance in the discretized state as the correspondence relationship between the input and output values of the image signal value. Thus, it is possible to constitute the correspondence relationship between the input image signal and the output image signal with a smaller amount of data, and at the same time, it is possible to simplify the process necessary for the color conversion. 
     B. Second Embodiment 
       FIG. 9  is a flowchart showing a color conversion method according to a second embodiment to be performed by the simple color gamut conversion circuit  32 . The color conversion method according to the second embodiment is different in the point that the step S 60   b  is provided instead of the step S 60  in the color conversion method according to the first embodiment, and the rest of the configuration is substantially the same as that in the first embodiment. In the step S 60   b , the interpolation circuit  34  further performs the color conversion process with the linear interpolation using the reference values Rf 1 , Rf 2 . 
       FIG. 10  is an explanatory diagram showing a correspondence relationship of a color conversion from the input image signal to the output image signal in the second embodiment. The interpolation circuit  34  performs a process of setting the conversion color C 2  in the grid-point group LG similarly to the first embodiment, and at the same time, sets the reference values Rf 1 , Rf 2  shown in  FIG. 10 . More specifically, the second nearest grid-point to the input pixel value R 2  which is the nearest neighbor of the input pixel value R 1  of the designated color C 1  is set by the interpolation circuit  34  as the reference value Rf 1 , and the grid-point located on the opposite side to the reference value Rf 1  with respect to the input pixel value R 2  to be the nearest neighbor is set by the interpolation circuit  34  as the reference value Rf 2 . In other words, the grid-points located at the anterior position and the posterior position with respect to the input pixel value R 2  to be the nearest neighbor of the designated color C 1  out of the grid-point group LG are set by the interpolation circuit  34  as the respective reference values Rf 1 , Rf 2 . 
     In the present embodiment, when the input color including the R value which is not included in the grid-point group LG in the vicinity of the input pixel value R 2  is input as the input image signal, the interpolation circuit  34  performs the color conversion process using the linear interpolation. More specifically, the color conversion with the linear interpolation using the output pixel value R 3  of the conversion color C 2  and the reference value Rf 1  is performed on the R value between the input pixel value R 2  as the grid-point to be the nearest neighbor of the designated color C 1  and the reference value Rf 1 , namely the designated color C 1  including the R value not included in the grid-point group LG. The correspondence relationship of the color conversion represented by the interpolation process is conceptually shown in  FIG. 10  as a straight line L 1 . In the example shown in  FIG. 10 , the input image signal including the input pixel value R 1  is converted into an output pixel value R 4  included in the straight line L 1  by the interpolation process of the interpolation circuit  34 . The color C 3  including the output pixel value R 4  is also referred to as an interpolation conversion color C 3 . Similarly, the color conversion process with the linear interpolation using the output pixel value R 3  and the reference value Rf 2  is preformed by the interpolation circuit  34  on the input color including the R value not included in the grid-point group LG between the input pixel value R 2  and the reference value Rf 2 . Similarly to the straight line L 1 , a straight line L 2  conceptually represents the correspondence relationship due to the linear interpolation using the reference value Rf 2  and the input pixel value R 2 . As described above, even when there is input the input image signal including the R value not included in the grid-point group LG from the reference value Rf 1  through the reference value Rf 2 , the interpolation circuit  34  performs the color conversion process of performing the conversion into the color on the straight lines L 1 , L 2  with the interpolation process. 
     According to the color conversion method related to the present embodiment, there is performed the process of performing the color conversion on the color in the vicinity of the designated color C 1  not included in the grid-points of the grid-point group LG with an interpolation calculation using the grid-point group LG to be the neighbor of the designated color C 1  as the reference value Rf 1 . Thus, it is possible to perform the color conversion on the input color not included in the grid-point group LG with the simple method. For example, even when performing the color conversion on a gradation image including the designated color C 1  not included in the grid-point group LG, it is possible to express the gradation with the display image on which the color conversion has been performed. 
     C. Other Embodiments 
     (C1) Although the RGB value on the grid-point is used for the color conversion process by the interpolation circuit  34  of the simple color gamut conversion circuit  32  in the embodiments described above, the RGB value on the grid-point is not a limitation, and it is also possible to perform the color conversion process using any of the RGB values expressed in, for example, 0 through 255 gray levels. Even in such a configuration, it is possible to simply convert only the designated color into the conversion color by rewriting a part of the correspondence relationship between the input image signal and the output image signal. 
     (C2) Although there is shown the example of selecting the conversion color C 2  having the R value included in the grid-point in the three-dimensional color space in the selection of the conversion color C 2  by the user in each of the embodiments described above, it is also possible to select a color having the R value other than the grid-points in the three-dimensional color space as the conversion color C 2 . In this case, the color in which the R value not included in the grid-point is approximated to the R value on the grid-point to be the nearest neighbor of the R value not included in the grid-point can be set as the conversion color. It is also possible to adopt a configuration in which only the colors on the grid-points are selected as the conversion color from the color pallet constituted by the colors set only by the RGB values on the grid-points in the three-dimensional color space. 
     D. Other Aspects 
     The present disclosure is not limited to the embodiments described above, but can be implemented in a variety of aspects within the scope or the spirit of the present disclosure. For example, the present disclosure can also be implemented in the following aspects. The technical features in each of the embodiments described above corresponding to the technical features in each of the aspects described below can arbitrarily be replaced or combined in order to solve a part or the whole of the problem of the present disclosure, or to achieve some or all of the advantages of the present disclosure. Further, the technical feature can arbitrarily be eliminated unless described in the present specification as an essential element. 
     (1) According to an aspect of the present disclosure, there is provided a color conversion method. The color conversion method may include the steps of taking a color required to be changed as a designated color out of input colors included in a display image to be displayed using an input image signal, taking a conversion color to be designated as an output color after changing the designated color, and performing color conversion of the designated color into the conversion color out of the input colors to output an output image signal for displaying the display image using the input image signal on which the color conversion was performed. According to the color conversion method of this aspect, the color conversion into the conversion color is performed only on the designated color using the input image signal. Therefore, it is possible to arbitrarily convert some of the colors of the display image with a simple method without performing a process of a large amount of data such as rewriting of the entire conversion map. 
     (2) In the color conversion method according to the above aspect, there may further be included the steps of performing the color conversion using a grid-point group determined in advance out of a plurality of grid-points defining an output color corresponding to the input color, approximating the designated color to a grid-point nearest neighbor of the designated color out of the grid-points included in the grid-point group, making the conversion color correspond to another grid-point not included in the grid-point group, and constituting the grid-point group by the another grid-point instead of the nearest neighbor grid-point approximated. According to the color conversion method of this aspect, since the color conversion from the designated color to the conversion color is performed using the input image signal using the grid-point determined in advance, the correspondence relationship of the conversion from the input image signal to the output image signal can be constituted with a small amount of data, and at the same time, the process necessary for the color conversion can be simplified. 
     (3) In the color conversion method according to the above aspect, there may further be included the steps of setting a second nearest grid-point to the nearest neighbor grid-point of the designated color as a reference value with respect to the designated color out of the grid-point group, and converting the designated color into an interpolation conversion color as the conversion color, the interpolation conversion color including a pixel value obtained by performing interpolation using a pixel value of the conversion color and the reference value, when taking a color including a pixel value between the nearest neighbor grid-point of the designated color and the reference value as the designated color. According to the color conversion method of this aspect, the color conversion is performed on the color in the vicinity of the designated color not corresponding to the grid-point group with interpolation calculation using the grid-point group in the vicinity of the designated color as the reference value. Thus, it is possible to perform the color conversion on the input color not included in the grid-point group with the simple method. For example, even when performing the color conversion on a gradation image including the designated color not included in the grid-point group, it is possible to express the gradation with the display image on which the color conversion has been performed. 
     (4) In the color conversion method according to the above aspect, there may further be included the steps of displaying an adjustment screen including a selection screen for the designated color, and taking the designated color selected from the adjustment screen. According to the color conversion method of this aspect, it is possible for the user to select a color on the display image as the designated color while visually recognizing the color on the display image using the adjustment screen. 
     (5) In the color conversion method according to the above aspect, there may further be included the steps of displaying an adjustment screen including a selection screen for the conversion color, and taking the conversion color selected from the adjustment screen. According to the color conversion method of this aspect, it is possible for the user to select a color on the display image as the conversion color while visually recognizing the color on the display image using the adjustment screen. 
     (6) According to another aspect of the present disclosure, there is provided a display device. The display device includes a color conversion device including a color comparison circuit and an interpolation circuit, the color comparison circuit taking a color required to be changed as a designated color out of input colors included in a display image to be displayed using an input image signal, the interpolation circuit taking a conversion color designated as an output color after changing the designated color, performing color conversion of the designated color out of the input colors into the conversion color, and outputting an output image signal for displaying the display image using the input image signal on which the color conversion was performed, a control device configured to input the designated color and the conversion color to the color conversion device, and a projection device including a light modulation section and a projection optical system, the light modulation section modulating light emitted from a light source in accordance with the output image signal output from the color conversion device, the projection optical system collecting, diffusing, and then projecting the light modulated by the light modulation section. 
     The present disclosure can be put into practice in a variety of aspects other than the color conversion method and the display device. The present disclosure can be realized in the aspects of, for example, a color conversion device of performing the color conversion method according to the present disclosure, a method of controlling a color conversion device, a method of controlling a display device, a computer program for realizing the control method, and a non-temporary recording medium on which the computer program is recorded.