Patent Publication Number: US-2016232651-A1

Title: Signal adjustment apparatus, display apparatus, and signal adjustment method

Description:
The entire disclosure of Japanese Patent Application No. 2015-021911, filed Feb. 6, 2015 is expressly incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a signal adjustment apparatus that adjusts an image signal, a display apparatus, and a signal adjustment method. 
     2. Related Art 
     There is a known image display apparatus of related art that converts an inputted image signal into a signal in an HLS color space in which a color is expressed by a hue component, a luminance component, and a saturation component (see JP-A-2010-232773, for example). The thus converted image signal allows adjustment of the hue component, the luminance component, and the saturation component on a component basis. 
     To adjust the hue component, the luminance component, and the saturation component, it is conceivable to adjust the luminance on a hue basis. When the luminance is changed for a certain hue in the same manner over a range from a low saturation region to a high saturation region, however, the adjustment could cause an excessive change in the hue in the low saturation region due to the characteristics of the HLS color space. The excessive change undesirably amplifies noise contained in an image before the adjustment, possibly resulting in a decrease in image quality due to the adjustment. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a signal adjustment apparatus, a display apparatus and a signal adjustment method capable of suppressing, in the process of performing luminance adjustment on an image signal on a hue basis, an effect of noise by performing intended, appropriate adjustment. 
     A signal adjustment apparatus according to an aspect of the invention includes an adjustment section that performs luminance adjustment on an input image signal containing elements formed of luminance, saturation, and hue in accordance with an adjustment value on a hue basis, and the adjustment section sets, for at least one hue, the amount of adjustment of the luminance in a low saturation area where the saturation is low to be smaller than the amount of adjustment of the luminance in an area where the saturation is higher than in the low saturation area. 
     According to the aspect of the invention, an effect of noise in the case where luminance adjustment is performed on an input image signal on a hue basis can be suppressed. 
     In the aspect of the invention, in the signal adjustment apparatus described above, the adjustment section may have a correction value used to correct an adjustment value used to adjust the luminance in the low saturation area and correct the adjustment value by using the correction value to determine a luminance adjustment value that specifies the amount of adjustment of the luminance. 
     According to the aspect of the invention with this configuration, a color in a low saturation area can also be appropriately adjusted on the basis of an inputted adjustment value. 
     In the aspect of the invention, in the signal adjustment apparatus described above, the adjustment section may include a subtraction circuit that corrects the adjustment value by using the correction value. 
     According to the aspect of the invention with this configuration, the subtraction circuit, which corrects the adjustment value, can quickly produce an adjustment value suitable for the low saturation area, whereby delay in processing can be suppressed. 
     In the aspect of the invention, the signal adjustment apparatus described above may further include an adjustment LUT created on the basis of an input value and a correction LUT containing the correction value, and the hue of the input image signal may be applied to the adjustment LUT to determine the adjustment value used to adjust the luminance, the saturation of the input image signal may be applied to the correction LUT to determine the correction value, and the correction value may be applied to the adjustment value used to adjust the luminance to determine the luminance adjustment value. 
     According to the aspect of the invention with this configuration, the computation using the adjustment LUT and the correction LUT allows quick generation of an appropriate adjustment value, and the signal adjustment with a small amount of delay in processing allows suppression of an effect of noise, whereby a high-quality image signal can be outputted. 
     In the aspect of the invention, in the signal adjustment apparatus described above, the adjustment section may include a luminance adjustment section to which a hue signal, a luminance signal, and a saturation signal that form the input image signal are inputted, and the luminance adjustment section may include an adjustment value setting section that applies the hue of the input image signal to the adjustment LUT to determine the adjustment value used to adjust the luminance, a correction value setting section that applies the saturation of the input image signal to the correction LUT to determine the correction value, a subtraction circuit that subtracts the correction value determined by the correction value setting section from the adjustment value determined by the adjustment value setting section to produce the luminance adjustment value, and a multiplication circuit that multiplies the luminance signal by the luminance adjustment value produced by the subtraction circuit. 
     According to the aspect of the invention with this configuration, appropriate adjustment can be made on the basis of the hue signal, the luminance signal, and the saturation signal that form the input image signal to suppress an effect of noise. 
     In the aspect of the invention, the signal adjustment apparatus described above may further include a conversion section that is connected to a signal input section to which an image signal is inputted and performs polar coordinate conversion on the image signal inputted to the signal input section, the polar coordinate conversion converting the image signal into the input image signal containing the elements formed of the luminance, the saturation, and the hue in a polar coordinate system. 
     According to the aspect of the invention with this configuration, luminance adjustment can be performed on a hue basis not only on an image signal in a polar coordinate system but also on an input image signal in any other color space. 
     In the aspect of the invention, in the signal adjustment apparatus described above, a YUV-color-space or RGB-color-space image signal inputted to the signal input section may be converted into an input image signal containing the elements formed of the luminance, the saturation, and the hue in a polar coordinate system, and the input image signal may be adjusted in accordance with the adjustment value, converted into a YUV-color-space or RGB-color-space image signal, and outputted. 
     According to the aspect of the invention with this configuration, luminance adjustment on a hue basis in a polar coordinate color space can be performed on a YUV-color-space or RGB-color-space image signal, and the adjusted image signal can be outputted in the form of a YUV-color-space or RGB-color-space image signal. 
     In the aspect of the invention, in the signal adjustment apparatus described above, adjustment values used to adjust the luminance, the saturation, and the hue may be allowed to be inputted for each of six colors, R, G, B, C, M, and Y, and six-axis adjustment in which the luminance, the saturation, and the hue of the six colors, R, G, B, C, M, and Y, are adjusted on the basis of the inputted adjustment values may be performed. 
     According to the aspect of the invention with this configuration, an effect of noise in the six-axis adjustment can be suppressed, whereby a high-quality image signal can be outputted. 
     A display apparatus according to another aspect of the invention includes a signal input section to which an image signal to be processed is inputted, a control section that sets an adjustment value used to adjust the image signal, an adjustment section that performs luminance adjustment on an input image signal containing elements formed of luminance, saturation, and hue on a hue basis in accordance with the adjustment value set by the control section, and a display section that displays an image on the basis of the image signal adjusted by the adjustment section, and the adjustment section sets, for at least one hue, the amount of adjustment of the luminance in a low saturation area where the saturation is low to be smaller than the amount of adjustment of the luminance in an area where the saturation is higher than in the low saturation area. 
     According to the aspect of the invention, an effect of noise in the case where luminance adjustment is performed on an input image signal on a hue basis can be suppressed, whereby a high-quality image can be displayed. 
     A signal adjustment method according to still another aspect of the invention includes performing luminance adjustment on an input image signal containing elements formed of luminance, saturation, and hue on a hue basis and setting, in the adjustment, for at least one hue, the amount of adjustment of the luminance in a low saturation area where the saturation is low to be smaller than the amount of adjustment of the luminance in an area where the saturation is higher than in the low saturation area. 
     According to the aspect of the invention, an effect of noise in the case where luminance adjustment is performed on an input image signal on a hue basis can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a functional block diagram of a projector according to an embodiment. 
         FIG. 2  is a functional block diagram of an adjustment circuit provided in the projector. 
         FIGS. 3A to 3C  describe action of the projector. 
         FIG. 4  is a flowchart showing action of the projector. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     An embodiment to which the invention is applied will be described below with reference to the drawings. 
       FIG. 1  is a functional block diagram of a projector  1  according to an embodiment to which the invention is applied. 
     The projector  1  (display apparatus) is connected to an image supply apparatus (not shown) and projects an image on a screen SC on the basis of input image data D 1  outputted by the image supply apparatus. 
     The projector  1  includes a control unit  10 , which controls each portion of the projector  1 , an image processing unit  30  (signal adjustment apparatus), which processes the input image data D 1  under the control of the control unit  10 , and a projection unit  20  (display section), which project an image on the screen SC. 
     The projection unit  20  includes a light source section  21 , a light modulator  22 , which modulates light outputted by the light source section  21 , and a projection system  23 , which causes the light modulated by the light modulator  22  to converge and diverge to project the modulated light on the screen SC. 
     The light source section  21  includes a light source formed of a xenon lamp, an ultrahigh-pressure mercury lamp, an LED, or any other light source. The light source section  21  includes a drive circuit (not shown) that supplies the light source with drive current and turns on/off the light source under the control of the control unit  10 . The light source section  21  may further include a reflector that guides light emitted from the light source to the light modulator  22 , a lens group (not shown) for enhancing optical characteristics of projection light, a polarizer, a light control element that is disposed on the path to the light modulator  22  and attenuates the light emitted from the light source, and other components. 
     The light modulator  22  includes a liquid crystal panel or a digital mirror device (DMD) and modulates the light outputted by the light source section  21 . For example, the light modulator  22  includes three transmissive liquid crystal panels corresponding to colors R, G, and B, and the transmissive liquid crystal panels are driven by a light modulator drive circuit  36 , which will be described later. The light modulator  22  may, instead of including three transmissive liquid crystal panels, for example, include three DMDs or a combination of one transmissive liquid crystal panel or DMD and a color wheel. 
     The projection system  23  includes a prism that combines RGB three-color light fluxes modulated by the light modulator  22 , a lens group that brings a combined projection image from the prism into focus on the screen SC, and other components. 
     An operation panel  11 , which is disposed on the upper surface or the rear surface of a main body of the projector  1 , is connected to the control unit  10 . The operation panel  11  has a plurality of operation parts, produces an operation signal corresponding to operation performed on any of the operation parts, and outputs the operation signal to the control unit  10 . A remote control light receiving section  12  is further connected to the control unit  10 . The remote control light receiving section  12  receives an infrared light signal transmitted by a remote control  15 , produces an operation signal corresponding to operation performed on the remote control  15 , and outputs the operation signal to the control unit  10 . The remote control  15  has a variety of keys that allow a user to operate the projector  1  and transmits an infrared light signal corresponding to operation performed on any of the keys. The remote control  15  has, for example, a power key that issues an instruction to power on/off the projector  1 , numeral keys corresponding to numerals, and arrow keys or a cross-shaped key that specifies a direction. 
     The projector  1  receives an input in the form of digital image data from a storage device (not shown) built in the projector  1  or the external image supply apparatus (not shown), such as a personal computer and a variety of image players. The image signal inputted to the projector  1  may be formed of image data on a still image or image data on motion images (video images). The present embodiment will be described with reference to a case where image data on motion images is inputted by way of example. The input image data may be typical video data or stereoscopic video data. 
     The stereoscopic (3D) video data may be formatted by using a frame sequential method in which an image frame for the left eye (left image frame) and an image frame for the right eye (right image frame) are alternately inputted or a side-by-side method. 
     The image processing unit  30  processes the input image data D 1  inputted from the built-in storage device or the external image supply apparatus. The image processing unit  30  includes an image input interface (I/F)  31 , to which the input image data D 1  is inputted, and a plurality of processing sections that process the input image data D 1 . Specifically, the image processing unit  30  includes a processing section  32 , conversion circuits  33  (conversion section) and  35 , an adjustment circuit  34  (adjustment section), a light modulator drive circuit  36 , and an LUT (lookup table) storage section  39 . 
     The input image data D 1  inputted to the image input I/F  31  is image data stored in the storage device (not shown) built in the projector  1  or image data outputted by the image supply apparatus (not shown) external to the projector  1 . The image input I/F  31  may include a connector and an interface circuit connected to the image supply apparatus, or the projector  1  may be provided with a connector and an interface circuit separate from the image input I/F  31 . Further, the image input I/F  31  may be configured to be capable of receiving an input in the form of an analog image signal. In this case, the image input I/F  31  may include an A/D converter or any other component that converts the analog image signal to digital image data and output the converted digital image data to the processing section  32 . 
     The image input I/F  31  outputs the input image data D 1  to the processing section  32 . The processing section  32  performs a variety of types of image processing on the input image data D 1 . Specific examples of the image processing performed by the processing section  32  may include discrimination between a 3D (stereoscopic) image and a 2D (planar) image, resolution conversion, frame rate conversion, 3D image conversion, distortion correction, and zooming. A plurality of the types of image processing described above can be performed in combination with each other, and a result of the processing may be outputted to the control unit  10 . The resolution conversion is the process of converting the resolution of the input image data D 1  in accordance with the drawing resolution of the light modulator  22 . The frame rate conversion is the process of converting the frame rate of the input image data D 1  in such a way that the converted frame rate adapts to processing burden on and other factors of the image processing unit  30 . The 3D image conversion is the process of converting 3D video data in the side-by-side format or the top-and-bottom format into video data in the frame-sequential format. The distortion correction is the process of deforming an image in such a way that trapezoidal distortion or pincushion distortion of an image projected on the screen SC is compensated. The zooming is the process of enlarging or reducing a specific range or the entirety of a frame of the input image data D 1  at a specified enlargement or reduction factor. The processing section  32  may omit the image processing described above. 
     The processing section  32  produces an image signal based on the processed image data and outputs the image signal to the conversion circuit  33 . The signal outputted by the processing section  32  to the conversion circuit  33  is called hereinafter an image signal S 1 . In the present embodiment, the image signal S 1  is an image signal in a three-dimensional color space and particularly contains an R (red) image signal, a G (green) image signal, and a B (blue) image signal by way of example. The image signal S 1  may instead, for example, be an image signal in the YUV color space formed of Y (luminance signal), U (first color difference signal), and V (second color difference signal), an image signal in the YCbCr color space, or an image signal in the YPbPr color space. 
     The conversion circuit  33  converts the image signal S 1  outputted by the processing section  32  into an image signal in a color space of a polar coordinate system and outputs an input image signal S 2 , which is to be processed by the adjustment circuit  34 , to the adjustment circuit  34 . In the present embodiment, the conversion circuit  33  converts the RGB color space to the HLS color space formed of H (hue), S (saturation), and L (luminance). In this case, the input image signal S 2  contains a hue input signal H_IN, a saturation input signal S_IN, and a luminance input signal L_IN. 
     The adjustment circuit  34  adjusts the input image signal S 2  in terms of the hue, saturation, and luminance and outputs an output image signal S 3  having undergone the adjustment to the conversion circuit  35 . The output image signal S 3  contains a hue output signal H_OUT, a saturation output signal S_OUT, and a luminance output signal L_OUT. 
     The conversion circuit  35  converts the output image signal S 3  inputted by the adjustment circuit  34  into an image signal in a three-dimensional color space and outputs an image signal S 4  having undergone the conversion to the light modulator drive circuit  36 . In the present embodiment, the conversion circuit  35  converts the HLS color space into the RGB color space, and the image signal S 4  contains an R image signal, a G image signal, and a B image signal. 
     The light modulator drive circuit  36  drives the light modulator  22  on the basis of the image signal S 4  inputted from the conversion circuit  35 . For example, when the light modulator  22  includes liquid crystal display panels, the light modulator drive circuit  36  drives the liquid crystal display panels on the basis of the image signal S 4  to draw an image in each of the liquid crystal display panels. 
     The LUT storage section  39  is connected to the adjustment circuit  34 . The adjustment circuit  34  uses an LUT (lookup table) stored in the LUT storage section  39  to adjust the input image signal S 2 . The LUT storage section  39  has a storage area where a plurality of LUTs are stored, and the adjustment circuit  34  reads a necessary LUT from the LUT storage section  39 . The LUT storage section  39  is provided by using a storage area of a ROM (not shown) provided in the control unit  10 , a semiconductor storage device (not shown) connected to the control unit  10 , or a ROM (not shown) or a flash memory (not shown) provided in the image processing unit  30 . The LUT storage section  39  can instead be provided in a RAM (not shown), and in this case, when the projector  1  is started, an LUT is read from the ROM (not shown) to the LUT storage section  39 . 
       FIG. 2  shows the configuration of the adjustment circuit  34  in detail. 
     The adjustment circuit  34  includes a hue adjustment circuit  41 , which adjusts the hue of the input image signal S 2 , a saturation adjustment circuit  42 , which adjusts the saturation of the input image signal S 2 , and a luminance adjustment circuit  45  (luminance adjustment section), which adjusts the luminance of the input image signal S 2 . 
     The hue adjustment circuit  41  obtains, from a hue adjustment LUT  41   a , an output value corresponding to the value of the hue input signal H_IN and outputs the output value as the hue output signal H_OUT. The hue adjustment LUT  41   a  is an LUT that stores values of the hue output signal H_OUT corresponding to values of the hue input signal H_IN. The projector  1  according to the present embodiment allows six-axis adjustment in which the hue, the saturation, and the luminance of C (cyan), G (green), Y (yellow), R (red), M (magenta), and B (blue) are adjusted. To this end, the hue adjustment LUT  41   a  shown in  FIG. 2  by way of example contains hue adjustment values (output values) corresponding to the colors described above, C, G, Y, R, M, and B. 
     The hue adjustment LUT  41   a  is not limited to a table containing hue output signals H_OUT for all hue input signals H_IN and may contain values of the hue output signal H_OUT that correspond to a few representative hue input signals H_IN. When the value of a non-representative hue input signal H_IN is in question, the hue adjustment circuit  41  may perform interpolation on values contained in the hue adjustment LUT  41   a  and determine a hue output signal H_OUT corresponding to the non-representative hue input signal H_IN. 
     The hue adjustment LUT  41   a  shown in  FIG. 2  by way of example is an LUT which performs linear conversion of the hue input signal H_IN and to which two characteristics labeled with reference characters A 1  and A 2  are added. Reference character A 1  corresponds to a setting that changes the hue of R to a value close to the hue of Y, and reference character A 2  corresponds to a setting that changes the hue of C to a value close to the hue of G. The hue adjustment circuit  41 , which uses the hue adjustment LUT  41   a , adjusts hue values of the hue input signal H_IN that are in the vicinity of R to values close to the hue of Y and further adjusts hue values of the hue input signal H_IN that are in the vicinity of C to values close to the hue of G. 
     The hue adjustment LUT  41   a , a saturation gain setting LUT  43   a , and a luminance gain setting LUT  46   a , which are used by the adjustment circuit  34 , are created by the control unit  10  in accordance with operation performed on the operation panel  11  or the remote control  15  in an LUT creation process ( FIG. 4 ), which will be described later. For example, the setting related to the characteristic labeled with each of reference characters A 1  and A 2  in the hue adjustment LUT  41   a  is specified by operation performed on the operation panel  11  or the remote control  15 . The hue adjustment can therefore be performed in accordance with preference of the user who operates the projector  1 . 
     The saturation adjustment circuit  42  includes a saturation gain setting section  43 , which determines a saturation gain value (GAIN) by using the saturation gain LUT  43   a , and a multiplication circuit  44 , which multiplies the saturation input signal S_IN by the gain value determined by the saturation gain setting section  43 . 
     The saturation gain setting LUT  43   a  is an LUT used to set the saturation gain on a hue basis. Specifically, the saturation gain setting LUT  43   a  contains saturation gain values corresponding to values of the hue input signal H_IN. The saturation gain setting LUT  43   a  shown in  FIG. 2  by way of example contains two characteristics labeled with reference characters A 3  and A 4 . Reference character A 3  represents that the gain value is smaller than 1× magnification, and reference character A 4  represents that the gain value is greater than 1× magnification. That is, reference character A 3  corresponds to a setting that lowers the gain value for the saturation of R, and reference character A 4  corresponds to a setting that increases the gain value for the saturation of C. The characteristics labeled with reference characters A 3  and A 4  correspond to those labeled with reference characters A 1  and A 2  in the hue adjustment LUT  41   a .  FIG. 2  is presented only by way of example, and the gain values provided in the saturation gain setting LUT  43   a  are not limited to those within the range from 0× to 2× magnification shown in  FIG. 2 . 
     The hue input signal H_IN and the saturation input signal S_IN are inputted to the saturation adjustment circuit  42 , and the hue input signal H_IN is inputted to the saturation gain setting section  43 . The saturation gain setting section acquires the gain value (GAIN) for the saturation corresponding to the hue input signal H_IN from the saturation gain setting LUT  43   a  and outputs the gain value to the multiplication circuit  44 . 
     The gain value outputted by the saturation gain setting section  43  and the saturation input signal S_IN are inputted to the multiplication circuit  44 . The multiplication circuit  44  multiplies the saturation input signal S_IN by the gain value and outputs the result of the multiplication as the saturation output signal S_OUT. The saturation adjustment circuit  42  thus amplifies or attenuates the saturation input signal S_IN by using the saturation gain setting LUT  43   a  and outputs the result of the amplification or attenuation. 
     The luminance adjustment circuit  45  includes a luminance gain setting section  46  (adjustment value setting section), a saturation correction value setting section  47  (correction value setting section), a subtraction circuit  48 , and a multiplication circuit  49 . The hue input signal H_IN, the saturation input signal S_IN, and the luminance input signal L_IN are inputted to the luminance adjustment circuit  45 . 
     The hue input signal H_IN is inputted to the luminance gain setting section  46 . The luminance gain setting section  46  determines a gain value for the luminance corresponding to the hue input signal H_IN by using the luminance gain adjustment LUT  46   a  (adjustment LUT). 
     The luminance gain setting LUT  46   a  is an LUT used to set the luminance gain on a hue basis. Specifically, the luminance gain setting LUT  46   a  contains gain values for the luminance corresponding to values of the hue input signal H_IN. The luminance gain setting LUT  46   a  shown in  FIG. 2  by way of example contains two characteristics labeled with reference characters A 5  and A 6 . Reference character A 5  represents that the gain value is smaller than 1× magnification, and reference character A 6  represents that the gain value is greater than 1× magnification. That is, reference character A 5  corresponds to a setting that lowers the gain value for the luminance of R, and reference character A 6  corresponds to a setting that increases the gain value for the luminance of C. The characteristics labeled with reference characters A 5  and A 6  correspond to those labeled with reference characters A 1  and A 2  in the hue adjustment LUT  41   a  and those labeled with reference characters A 3  and A 4  in the saturation gain setting LUT  43   a . The luminance gain setting section  46  acquires again value corresponding to the hue input signal H_IN from the luminance gain setting LUT  46   a  and outputs the gain value (GAIN) to the subtraction circuit  48 .  FIG. 2  is presented only by way of example, and the gain values provided in the luminance gain setting LUT  46   a  are not limited to those within the range from 0× to 2× magnification shown in  FIG. 2 . 
     The saturation correction value setting section  47  determines a correction value used to correct the gain value outputted by the luminance gain setting section  46  by using a saturation correction value LUT  47   a  (correction LUT) and outputs the correction value. The saturation correction value LUT  47   a  is an LUT that stores correction values used to correct luminance gain values in relation to the value of the saturation input signal S_IN. 
     The saturation correction value LUT  47   a  has correction values greater than 0 in the area where the value of the saturation input signal S_IN is smaller than a threshold TH (low saturation area), and in the area where the value of the saturation input signal S_IN is greater than or equal to the threshold TH, correction values corresponding to the saturation input signal S_IN are 0, as shown in  FIG. 2 . In the low saturation area, the smaller the value of the saturation input signal S_IN, the greater the correction value. In the saturation correction value LUT  47   a  shown in  FIG. 2  by way of example, the correction value has a minimum of 0 (when the saturation input signal S_IN is greater than or equal to the threshold TH), and the correction value has a maximum of 1 (when the saturation input signal S_IN is 0). 
     The saturation correction value setting section  47  outputs a correction value corresponding to the saturation input signal S_IN to the subtraction circuit  48 . 
     The subtraction circuit  48  subtracts the correction value inputted by the saturation correction value setting section  47  from the gain value inputted by the luminance gain setting section  46  and outputs the gain value having undergone the subtraction (GAIN2: luminance correction value) to the multiplication circuit  49 . 
     The gain value having undergone the subtraction (GAIN2) and outputted by the subtraction circuit  48  and the luminance input signal L_IN are inputted to the multiplication circuit  49 . The multiplication circuit  49  multiplies the luminance input signal L_IN by the gain value (GAIN2) and outputs the value resulting from the multiplication as the luminance output signal L_OUT. 
     Creation of the hue adjustment LUT  41   a , the saturation gain setting LUT  43   a , and the luminance gain setting LUT  46   a , which are used by the adjustment circuit  34 , will be described. 
       FIGS. 3A to 3C  describe action of the projector  1 .  FIG. 3A  is a diagrammatic view showing the color space of the polar coordinate system processed by the adjustment circuit  34 .  FIG. 3B  shows an example of an adjustment screen  1   a  projected by the projector  1 .  FIG. 3C  shows an example of an adjustment screen  1   b  projected by the projector  1 .  FIG. 4  is a flowchart showing action of the projector  1  and particularly shows the process of creating LUTs. 
     The image processing unit  30  instructs the conversion circuit  33  to cause it to convert the input image data D 1  into an image signal in the color space of the polar coordinate system. The luminance, the saturation, and the hue in the converted color space can be expressed, for example, as shown in  FIG. 3A . In  FIG. 3A , the saturation R and the hue φ are shown in the U-V plane, and an angle θ (not shown) with respect to the Y axis, which is perpendicular to the plane of view, represents the luminance. Further, in  FIG. 3A , reference character LA denotes the low saturation area where the value of the saturation input signal S_IN is smaller than the threshold TH. 
     In the projector  1 , the six-axis adjustment can be performed in response to operation on the operation panel  11  or the remote control  15 . The six-axis adjustment is shown in  FIG. 4 . 
     The control unit  10  of the projector  1 , when it detects an instruction from the operation panel  11  or the remote control  15  to start the six-axis adjustment (step ST 1 ), displays the adjustment screen  1   a  and further displays the adjustment screen  1   b  (step ST 2 ). At this point, the control unit  10  detects input operation performed on the operation panel  11  or the remote control  15  (step ST 3 ) and acquires data corresponding to the input operation (step ST 4 ). The control unit  10  evaluates whether or not an instruction representing an end of the input has been inputted to the operation panel  11  or the remote control  15  (step ST 5 ). When a result of the evaluation shows that the instruction has not been inputted, the control unit  10  returns to step ST 3 . When a result of the evaluation shows that the instruction representing an end of the input has been inputted, the control unit  10  proceeds to step ST 6 . 
     In step ST 2 , the projection unit  20  displays the adjustment screen  1   a  shown in  FIG. 3B . The adjustment screen  1   a  allows the user to perform input operation of adjusting the hue, the saturation, and the luminance for each of R, G, B, C, M, and Y. When any of R, G, B, C, M, and Y is selected in the adjustment screen  1   a  as a color to be adjusted, the control unit  10  instructs the projection unit  20  to cause it to further project the adjustment screen  1   b  shown in  FIG. 3C .  FIG. 3C  shows the adjustment screen  1   b  for R by way of example. In the adjustment screen  1   b  is drawn a cursor that specifies the direction and the amount of the adjustment of each of the hue, the saturation, and the luminance of the color to be adjusted. For example, the hue of the color R can be adjusted in the direction in which it approaches the hue of M or in the direction in which it approaches the hue of Y. 
     When operation of moving any of the cursors in the adjustment screen  1   b  is performed on the operation panel  11  or the remote control  15 , the control unit  10  acquires the direction and the amount of movement of the cursor in the adjustment screen  1   b  in step ST 4 . 
     In step ST 6 , the control unit  10  creates the hue adjustment LUT  41   a , the saturation gain setting LUT  43   a , and the luminance gain setting LUT  46   a  on the basis of the data acquired in step ST 4 . 
     The control unit  10  then outputs the created LUTs (hue adjustment LUT  41   a , saturation gain setting LUT  43   a , and luminance gain setting LUT  46   a ) to the image processing unit  30 , instructs the LUT storage section  39  to cause it to store the LUTs (step ST 7 ), and terminates the procedure. 
     On the basis of inputted data on any one of the elements, the hue, the saturation, and the luminance, the control unit  10  creates LUTs corresponding to the other elements as required. For example, the control unit  10  creates the hue adjustment LUT  41   a , which is used to adjust the hue, in correspondence with input data on adjustment of the hue of the color R and further creates the saturation gain setting LUT  43   a  and the luminance gain setting LUT  46   a  in correspondence with the adjustment of that hue. 
     The adjustment circuit  34  can use the thus created hue adjustment LUT  41   a , saturation gain setting LUT  43   a , and luminance gain setting LUT  46   a  to perform the HLS six-axis adjustment as shown in  FIG. 2 , whereby the user can adjust displayed colors as desired. However, the hue of a low-saturation color, when the color is adjusted by the adjustment circuit  34 , greatly changes in some cases. 
     In the low saturation area LA shown in  FIG. 3A , where the saturation R is small, a change in the hue φ sharply changes the tone of a color. That is, when the luminance of a color in the low saturation area LA is adjusted on a hue basis, the change in the luminance produces a very large change in the tone of the color. 
     For example, consider a case where adjustment is made on a color P produced by adding a small amount of green to an achromatic color (gray) and a color Q produced by adding a small amount of violet to an achromatic color. It is assumed that the colors P and Q before adjustment are colors that are close to achromatic colors and do not allow a viewer to sense a large difference in color tone. Adjustment is made on the colors P and Q by applying the saturation gain setting LUT  43   a  in which the gain for the green is set at 1.2× magnification and the gain for the violet is set at 0.8× magnification. As a result, the color P is adjusted to a color P′ clearly different from the achromatic color because the luminance of the green increases. In contrast, the color Q is adjusted to a color Q′ closer to the achromatic color because the luminance of the violet decreases. Since the color Q has almost no green component, the application of the saturation gain setting LUT  43   a  causes almost no change in the green component. In this example, adjusting the colors P and Q, which are close to achromatic colors, by using the same saturation gain setting LUT  43   a  causes the colors P′ and Q′ after the adjustment to greatly differ from each other in terms of color tone. 
     As shown in this example, when a color that belongs to the low saturation area LA is adjusted by using the saturation gain setting LUT  43   a , a slight difference in color tone is amplified. Therefore, if noise is added to a color that belongs to the low saturation area LA, effect of the noise greatly changes the color tone after adjustment, possibly resulting in a decrease in the quality of an image after the adjustment. 
     In the projector  1  according to the present embodiment, the luminance adjustment circuit  45 , which adjusts the luminance in the adjustment circuit  34 , is provided with the saturation correction value setting section  47 . In a low saturation area, that is, an area where the saturation is nearly zero, the saturation correction value setting section  47  outputs a correction value that attenuates the gain value outputted by the luminance gain setting section  46 . As a result, the subtraction circuit  48  subtracts the correction value from the gain value from the luminance gain setting section  46  in the low saturation area, and the multiplication circuit  49  adjusts the luminance input signal L_IN by using the gain value having undergone the subtraction (GAIN2). Further, the saturation correction value LUT  47   a  is so configured to reduce the correction value in an area where the saturation is greater than or equal to the threshold TH, as shown in  FIG. 2  by way of example. Therefore, in the case of a color that does not belong to the low saturation area, the luminance input signal L_IN is adjusted in accordance with the luminance gain setting LUT  46   a , whereby the user can make intended adjustment. As a result, the projector  1  can prevent any excessive change in color tone in a low saturation area for suppression of an effect of noise and can adjust the luminance by a large amount in an area where the saturation is greater than in the low saturation area (high saturation area) without any change in the luminance gain setting LUT  46   a.    
     Further, according to the configuration described above, in the process of creating the luminance gain setting LUT  46   a , it is not necessary to distinguish between a low saturation area and the other area. The action and configuration of the projector  1  can therefore be achieved without any complication thereof, whereby convenience in the user&#39;s adjustment of an image is not compromised. Further, to reduce an effect of noise in a low saturation area, the saturation correction value LUT  47   a  does not need to be changed in correspondence with the content of the luminance gain setting LUT  46   a . The saturation correction value LUT  47   a  may, of course, be changed, but a sufficiently advantageous effect can be provided even when the projector  1  is configured to use a fixed saturation correction value LUT  47   a . Therefore, in the process of creating the luminance gain setting LUT  46   a , there is no concern about an increase in processing burden on the control unit  10  as compared with a case where no saturation correction value LUT  47   a  is used, whereby an efficient process can be carried out. 
     The luminance adjustment circuit  45  only needs to allow the subtraction circuit  48  to correct, for at least one hue, the gain value outputted by the luminance gain setting section  46  by using the correction value from the saturation correction value setting section  47 . Instead, the correction is not necessarily made for a specific hue, and the gain value from the luminance gain setting section  46  may be corrected by using the correction value from the saturation correction value setting section  47  for any hue. 
     As described above, the image processing unit  30  of the projector  1  according to the embodiment of the invention includes the adjustment circuit  34 , which performs luminance adjustment on an input image signal containing elements formed of the luminance, the saturation, and the hue on a hue basis in accordance with an adjustment value in the luminance gain setting LUT  46   a , which is created based on the input, and the adjustment circuit  34  sets, for at least one hue, the amount of adjustment (GAIN2) of the luminance in a low saturation area where the saturation is low to be smaller than the amount of adjustment (GAIN2) of the luminance in an area where the saturation is higher than in the low saturation area. As a result, when luminance adjustment is performed on an input image signal on a hue basis, an effect of noise can be suppressed. 
     The adjustment circuit  34 , which has the saturation correction value LUT  47   a  containing correction values used to correct adjustment values used to adjust the luminance in a low saturation area and corrects an adjustment value in the luminance gain setting LUT  46   a  by using a correction value to determine an adjustment value used to adjust the luminance, can adjust the luminance to a value suitable for the low saturation area. 
     The adjustment circuit  34 , which includes the subtraction circuit  48 , can quickly produce an adjustment value suitable for the low saturation area and can hence suppress delay in processing. 
     The image processing unit  30  has the luminance gain setting LUT  46   a  and the saturation correction value LUT  47   a  containing correction values. The adjustment circuit  34  applies the hue of an input image signal to the luminance gain setting LUT  46   a  to determine an adjustment value (gain value) used to adjust the luminance, applies the saturation of the input image signal to the saturation correction value LUT  47   a  to determine a correction value, and applies the correction value to the adjustment value used to adjust the luminance to determine an adjustment value used to adjust the input image signal. The computation using the LUTs described above allows quick generation of an appropriate adjustment value, and the signal adjustment with a small amount of delay in processing allows suppression of an effect of noise, whereby a high-quality image signal can be outputted. 
     The adjustment circuit  34  further includes the luminance adjustment circuit  45 , to which the hue input signal H_IN, which is a hue signal in an input image signal, the luminance input signal L_IN, which is a luminance signal in the input image signal, and the saturation input signal S_IN, which is a saturation signal in the input image signal, are inputted. The luminance adjustment circuit  45  includes the luminance gain setting section  46 , which applies the hue input signal H_IN to the luminance gain setting LUT  46   a  to determine a gain value for the luminance. The luminance adjustment circuit  45  further includes the saturation correction value setting section  47 , which applies the saturation input signal S_IN to the saturation correction value LUT  47   a  to determine a correction value. The luminance adjustment circuit  45  still further includes the subtraction circuit  48 , which subtracts the correction value determined by the saturation correction value setting section  47  from the gain value determined by the luminance gain setting section  46 , and the multiplication circuit  49 , which multiplies the luminance input signal L_IN by the gain value having undergone the subtraction performed by the subtraction circuit  48 . The luminance can therefore be appropriately adjusted for each hue on the basis of the hue input signal H_IN, the luminance input signal L_IN, and the saturation input signal S_IN. 
     The image processing unit  30  further includes the conversion circuit  33 , which is connected to the image input I/F  31  (signal input section) through which the input image data D 1  is inputted and performs polar coordinate conversion on an image signal inputted through the image input I/F  31 , the polar coordinate conversion converting the image signal into the input image signal containing the elements formed of the luminance, the saturation, and the hue in apolar coordinate system. Therefore, luminance adjustment can be performed on a hue basis not only on an image signal in a polar coordinate system but also on an input image signal in any other color space. 
     The image processing unit  30  converts an YUV-color-space or RGB-color-space image signal inputted through the image input I/F  31  into an input image signal containing elements formed of the luminance, the saturation, and the hue in a polar coordinate system, adjusts the input image signal in accordance with an adjustment value, converts the adjusted input image signal into a YUV-color-space or RGB-color-space image signal, and outputs the converted image signal. Therefore, luminance adjustment on a hue basis in a polar coordinate color space can be performed on a YUV-color-space or RGB-color-space image signal, and the adjusted image signal can be outputted in the form of a YUV-color-space or RGB-color-space image signal. 
     Further, the projector  1  is configured to be capable of receiving inputs of adjustment values used to adjust the luminance, the saturation, and the hue for each of the six colors, R, G, B, C, M, and Y and performs the six-axis adjustment, in which the luminance, the saturation, and the hue of the six colors, R, G, B, C, M, and Y, on the basis of the inputted adjustment values. An effect of noise in the case where the six-axis adjustment is performed can therefore be suppressed, whereby a high-quality image signal can be outputted. 
     The embodiment described above is only an example of a specific aspect to which the invention is applied and is not intended to limit the invention, and the invention is also applicable in the form of an aspect different from the embodiment described above. For example, the image processing performed by the image processing unit  30  provided in the projector  1  is not limited to resolution conversion, zooming, color correction, intermediate frame generation, and the like, and the image processing unit  30  may perform other types of image processing. Further, each of the circuits that form the image processing unit  30  in  FIG. 1  and the adjustment circuit  34  shown in  FIG. 2  may be achieved by using an IC (integrated circuit) or an SoC (system-on-a-chip) or may be achieved by using software executed by a CPU or an MPU.  FIGS. 1 and 2  are therefore not intended to limit the physical implementation of the image processing unit  30 . 
     Further, the display apparatus according to the embodiment of the invention is not limited to the projector  1 , which projects an image on the screen SC as described above, and a display system according to an embodiment of the invention may also include a variety of other display apparatus, such as a liquid crystal monitor or a liquid crystal television that displays an image on a liquid crystal display panel, a monitor apparatus or a television receiver that displays an image on a PDP (plasma display panel), a monitor apparatus or a television receiver that displays an image on an organic EL display panel, for example, called an OLED (organic light-emitting diode) and OEL (organic electro-luminescence), or other self-luminous display apparatus. In this case, the liquid crystal display panel, the plasma display panel, and the organic EL display panel correspond to the display section. Further, individual hardware corresponding to each of the functional portions of the projector  1  shown in  FIG. 1  is not necessarily implemented, and a single processor that executes a program can, of course, achieve the functions of the plurality of functional portions except for the image processing unit  30 .