Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Applications No. 2008-302740, filed Nov. 27, 2008; and No. 2009-241497, filed Oct. 20, 2009, the entire contents of both of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a projection apparatus, a projection method, and a program which are suitable for a projector apparatus or the like. 
     2. Description of the Related Art 
     Various projector apparatuses have been commercially available which use a scheme called a field sequential scheme to enable color images in a plurality of colors to be visually perceived by switching the images at a high speed to consecutively project the images. 
     In particular, for projector apparatuses of this kind which use LEDs as a light source, a technique can be used which simultaneously lights LEDs in a plurality of colors, R (red), G (green), and B (blue), which serve as a light source, in order to ensure a sufficient quantity of light. 
       FIG. 5  illustrates the emission luminance of each of the color LEDs obtained when one image frame is divided into three fields to project the respective RGB color images.  FIG. 5(A)  shows timings (fields) when for example, an LCD panel or a micromirror element forming optical images forms color images. 
     For example, in the R field, a red LED-R shown in  FIG. 5(B)  can emit light at a high current value. At the same time, a green LED-G shown in  FIG. 5(C)  and a blue LED-B shown in  FIG. 5(D)  can emit light at a preset low current value. The resulting mixed light forms a red optical image. 
       FIG. 6  is a CIExy chromaticity diagram illustrating a comparison of a chromaticity set when such multicolor LEDs as described above are simultaneously driven to emit light, with a chromaticity set when a single-color LED is lit. In  FIG. 6 , a horseshoe shape indicates a human visible region V. Furthermore, dashed lines and circles at vertex positions show the range of the chromaticity set by the single-color LED. On the other hand, solid lines and triangles at vertex positions show the range of the chromaticity set by the multicolor LEDs. 
     LEDs have a property wherein not only luminance but also chromaticity varies with the value of a supplied current. Thus, when the apparatus actually operates, if LEDs in three colors are made to emit light, for example, in an R field of one frame, the resulting mixed light has an unexpected chromaticity owing to the above-described property. 
     If the chromaticity of the light source varies in at least one of the R, G, and B fields, the chromaticity in one frame as a whole may also vary. This prevents projection from being achieved at the correct chromaticity. 
     As described above, an object of the present invention is to provide a projection apparatus, a projection method, and a program which enable the chromaticity of light source light according to the field sequential scheme to be accurately maintained at a set content. 
     BRIEF SUMMARY OF THE INVENTION 
     A preferred embodiment of the present invention includes: 
     a plurality of light sources individually emitting light in a plurality of colors; 
     a projection section using light from the light sources to generate images corresponding to respective plural color components of the light source light for each period, to sequentially project the images; 
     a measurement section measuring a brightness of the light sources for each of the plurality of colors at a term at which the projection section projects an image of each of the plural color components; 
     an average brightness calculation section calculating, at each image projection term for the same color component, an average brightness of the brightness measured by the measurement section at the image projection term; and 
     a light source control section adjusting the brightness of the light sources so that an average chromaticity based on the average brightness calculated by the average brightness calculation section and indicating the brightness is equal or approximate to a target chromaticity. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a block diagram showing the general configuration of a functional circuit in a projector apparatus according to the present embodiment; 
         FIG. 2  is a timing chart showing how the light emission of light sources according to the present driven; 
         FIG. 3  is a flowchart showing how the light emission of the light sources according to the present embodiment, particularly for an R field, is driven; 
         FIG. 4A  to  FIG. 4E  are diagrams illustrating the transition state of light emission and chromaticity determination for the R field according to the present embodiment; 
         FIG. 5  is schematic diagram illustrating the emission luminance obtained when a data projector apparatus using LEDs as a light source according to the present embodiment simultaneously makes LEDs in a plurality of colors emit light; and 
         FIG. 6  is a CIExy chromaticity diagram illustrating a chromaticity set when the multicolor LEDs according to the present embodiment are simultaneously made to emit light and a chromaticity set when a single-color LED is made to emit light. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The best mode for carrying out the present invention will be described below with reference to the drawings. However, the embodiment described below involves various limitations that are technically preferred for carrying out the present invention. However, the limitations are not intended to limit the scope of the present invention to the following embodiment and illustrated examples. 
     An embodiment of the present invention will be described with reference to the drawings. 
       FIG. 1  is a block diagram showing the general functional configuration of an electronic circuit included in a data projector apparatus  10  according to the embodiment. 
     An I/O connector section  11  includes, for example, a pin jack (RCA) type video input terminal, a D-sub  15  type RGB input terminal, and a USB (Universal Serial Bus) connector. 
     Image signals according to various standards input through the I/O connector section  11  are input, via an I/O interface (I/F)  12  and a system bus SB, to an image conversion section  13 , generally called a scaler. The image conversion section  13 , integrally converts the input image signals into a predetermined format suitable for projection. The image conversion section  13  appropriately stores the image signals in a video RAM  14  that is a buffer memory for display and then feeds the image signals to a projection image processing section  15 . 
     At this time, data such as symbols which indicates operational statuses for OSD (On Screen Display) is superimposed on the image signals by the video RAM  14 . The processed image signals are fed to the projection image processing section  15 . 
     The projection image processing section  15  drives a micromirror element  16 , which is a spatial optical modulating element (SOM), so that the micromirror element  16  provides display, using faster time division driving in which a frame rate according to a predetermined format, for example, 60 [frames/sec.], the number of color components resulting from division, and the number of display gray levels are multiplied together, according to the fed image signals. 
     The micromirror element  16  performs a quick on/off operation on the inclination of each of a plurality of arrayed micromirrors which, for example, correspond to XGA (1,024×768 dots). The micromirror element  16  then forms reflected light from the micromirrors into an optical image. 
     On the other hand, an LED array  17  is used as a light source for the present data projector apparatus  10 . In the LED array  17 , a large number of LEDs emitting light in colors R, G, and B are regularly mixed together in an array form. Light with each color component emitted in a time division manner is condensed by a pyramidal housing  18  in which a reflection mirror is stuck to the entire inner surface of the housing. An integrator  19  then forms the light into a flux with an even luminance distribution. A mirror  20  then totally reflects the flux. The micromirror element  16  is thus irradiated with the reflected flux. 
     An optical image formed by reflected light from the micromirror element  16  is projected and displayed on a screen (not shown in the drawings) serving as a projection target, via a projection lens unit  21 . 
     In the LED array  17 , an R driver  22 , a G driver  23 , and a B driver  24  drivingly controls LED groups with corresponding colors so that light in the primary colors R, G, and B is emitted in a time division manner. 
     The R driver  22 , the G driver  23 , and the B driver  24  drive the LED groups with the respective color components forming the LED array  17 , at timings and driving currents based on a control signal from a projection light processing section  25 . 
     The projection light processing section  25  controls the light emission timings and the driving currents for the R driver  22 , the G driver  23 , and the B driver  24  according to image data provided by the projection image processing section  15 . Moreover, the projection light processing section  25  receives detection signals from illuminance sensors  26 R,  26 G, and  26 B detecting the brightness of the respective colors of an optical image formed by the micromirror element  16 . The projection light processing section  25  includes a chromaticity storage section  25   a  storing the brightness detected by the illuminance sensors  26 R,  26 G, and  26 B and the current light emission current values of the LEDs, as information indicative of chromaticity. 
     CPU  27  controls all the operations of the above-described circuits. CPU  27  is connected to a main memory  28  and a program memory  29 . The main memory  28  is composed of DRAM and functions as a work memory. The program memory  29  is composed of an electrically rewritable nonvolatile memory storing operation programs, various routine data, and the like. CPU  27  uses the main memory  28  and the program memory  29  to perform control operations in the data projector apparatus  10 . 
     CPU  27  described above performs various projection operations according to key operation signals from an operation section  30 . The operation section  30  includes a key operation section provided in the main body of the data projector apparatus  10 , and a laser light receiving section receiving infrared light from a remote controller (not shown in the drawings) dedicated to the data projector apparatus  10 . Key operation signals based on keys operated by a user directly or via the remote controller are output directly to CPU  27 . 
     CPU  27  is further connected to an audio processing section  31  and a radio LAN interface (I/F)  32  via the above-described system bus SB. 
     The audio processing section  31  includes a sound source circuit such as a PCM sound source. The audio processing circuit  31  converts audio data provided for a projection operation into analog data and drives a speaker section  33  to amplify the data and emit a corresponding sound. Alternatively, the audio processing section  31  generates a beep sound or the like as required. 
     The radio LAN interface  32  transmits and receives data, via a radio LAN antenna  34 , to and from a plurality of external devices including a personal computer, for example, using a radio wave in a 2.4 [GHz] band according to the IEEE 802.11 b/g standard. 
     Now, the operation of the above-described embodiment will be described. 
     In the present embodiment, the data projector  1  divides one frame shown in  FIG. 2  into three subframes; a first subframe, a second subframe, and a third subframe. Then, the data projector  1  sequentially and repeatedly projects color images in the R, G, and B fields, respectively, in each subframe. 
       FIG. 2(A)  shows timings at which the above-described micromirror element  16  enables optical images to be formed by the color images in the R, G, and B fields. Furthermore,  FIG. 2(B) to 2(D)  show current driving values for the LED array  17  lit in synchronism with the above-described R, G, and B fields. 
     For example, in the B field of each subframe, the projector  1  makes the red LED-R emit light at a high current value as shown in  FIG. 2(B) . In addition, the projector  1  allows the green LED-G shown in  FIG. 2(C)  and the blue LED-B shown in  FIG. 2(D)  to emit light at respective low current values. As a result, a red optical image is formed using the resulting mixed light in R, G, and B. 
     Further, in the G field and the B field, the LEDs in the three colors are simultaneously made to emit light as required, to form a green optical image and a blue optical image using the resulting mixed light. 
       FIG. 3  shows how processing is executed to adjust the chromaticity in each subframe of each frame, particularly in the R field. In the processing, basically, the operation programs stored in the program memory  29  are expanded and stored in the main memory  28  so that CPU  27  executes the operation programs. Then, under the control of CPU  27 , the projection light processing section  25  drivingly controls the R driver  22 , the G driver  23 , and the B driver  24 . 
     Similar operations are also performed on the G field and the B field. However, for simplification of description, only the operation on the R field will be described. 
     First, CPU  27  waits for a timing for lighting in the R field (step S 01 ). Then, upon determining that the timing has been reached, CPU  27  determines whether or not current values required to enable the R, G, and B LEDs, respectively, of the LED array  17  to emit light are stored in the chromaticity storage section  25   a  of the projection light processing section  25  (step S 02 ). In other words, the projection light processing section  25  determines whether or riot the timing corresponds to light emission in the R field of the second or third subframe of the image frame. 
     Here, if the light emission current values are riot stored in the chromaticity storage section  25   a  yet, CPU  27  determines that the light emission timing corresponds to the R field in the first subframe. Then, CPU  27  stores the initial light emission current values for the LEDs based on a preset target chromaticity in the chromaticity storage section  25   a  (step S 103 ). Thereafter, a variable (n) indicating the number of subframes is set to an initial value “1” (step S 104 ). 
     Then, CPU  27  reads the light emission current values for the color LEDs of the LED array  17  stored in the chromaticity storage section  25   a . Then, in the nth subframe corresponding to the current variable (n) (that is, here, the first subframe), CPU  27  uses the R driver  22 , the G driver  23 , and the B driver  24  to drive the LED array  17  at the read light emission current values so that the LED array  17  emits light (step S 105 ). 
     According to light emission from the LED array  17 , CPU  27  makes the illuminance sensors  26 R,  26 G, and  26 B measure the brightness of the respective color components of the light source light (step S 106 ). Based on the measured brightness of the respective colors, CPU  27  calculates the total chromaticity in the R field of the first subframe. Then, based on the differential value between the calculated total chromaticity and the target chromaticity, CPU  27  calculates a chromaticity for lighting in the R field of the next subframe (step S 107 ). 
       FIG. 4A  shows an example of the relationship between the chromaticity r 1  measured in the R field of the subframe and the target chromaticity OC. A dashed line in  FIG. 4A  shows an error range ER attributed to the characteristics and possible age deterioration of the LEDs forming the LED array  17 . 
     That is, the dashed line in  FIG. 4A  shows the range of errors between the target chromaticity OC and the actual chromaticity r 1  obtained when the LEDs actually lit at the light emission current values for the LEDs set such that the total chromaticity of the LEDs is equal to the target chromaticity.  FIG. 4A  shows that the actual measured chromaticity r 1  falls within the error range ER. 
     Based on the measurement results, as shown in  FIG. 4B , CPU  27  calculates a position with which the measured chromaticity r 1  has a point-symmetrical relationship with respect to the target chromaticity OC on the chromaticity space, to be a target chromaticity O(r 2 ) for light emission in the R field of the next subframe. 
     If light can actually be emitted at the above-described target chromaticity O(r 2 ) in the R field of the second subframe, an average chromaticity obtained by calculating an average of the total chromaticity in the R fields of the first and second subframes can be determined to be the target chromaticity OC. That is, by thus setting the chromaticity at which light is emitted in the R field of the second subframe, the error between the measured chromaticity in the R field of the first subframe and the target chromaticity OC can be offset. 
     On the other hand, even if light fails to be emitted at the target chromaticity O(r 2 ) in the R field of the second subframe, the average chromaticity in the fields of the first and second subframes can be reliably made closer to the target chromaticity OC. 
     To achieve this, CPU  27  calculates such light emission current values for the color LEDs as enable the target chromaticity O(r 2 ) calculated in the above-described step S 101  to be achieved (step S 108 ). CPU  27  then newly stores the calculated fight emission current values for the color LEDs in the chromaticity storage section  25   a  (step S 109 ). 
     Then, CPU  27  re-sets the value of the variable (n), indicating the subframes, by adding one (“+1”) to the value (step S 110 ). Upon determining that the re-set value of the variable (n) does not exceed the number N of subframes in one frame as a whole (here, N is “3”) (step S 111 ), CPU  27  returns to the processing starting with the above-described step S 101 . 
     In step S 101 , CPU  27  determines whether or not the timing for the R field of the second subframe of the frame is reached. In the subsequent step S 102 , since the light emission current values for the LEDs are stored in the chromaticity storage section  25   a , CPU  27  reads, from the chromaticity storage section  25   a , the light emission current values for the LEDs newly stored in the chromaticity storage section  25   a  in the above-described step S 109 . CPU  27  uses the R driver  22 , the G driver  23 , and the B driver  24  to drive the LED array  17  at the read light emission current values so that the LED array  17  emits light. 
     In addition, in step S 106 , CPU  27  makes the illuminance sensors  26 R,  260 , and  263  measure the brightness of the respective color components of the light source light. Then, in step S 107 , based on the measured brightness of the color components, CPU  27  calculates the total chromaticity in the R field of the second subframe. 
     Subsequently, based on the calculated total chromaticity in the second frame, CPU  27  calculates the average chromaticity in the R fields of the first and second subframes. Then, based on the differential value between the average chromaticity for the first and second frames and the target chromaticity, CPU  27  calculates a chromaticity for lighting in the R field of the next subframe. 
       FIG. 4C  shows an example of the relationship between the above-described target chromaticity O(r 2 ) and the total chromaticity r 2  actually measured in the R field of the second subframe. As shown by a dashed line in  FIG. 4C , the actual measured chromaticity r 2  falls within the error range E 2 , based on the target chromaticity O(r 2 ) and attributed to the characteristics and possible age deterioration of the LEDs forming the LED array  17 . 
     In connection with the measurement results, as shown in  FIG. 4D , the middle point between the measured chromaticity r 1  and the measured chromaticity r 2  on the chromaticity space is defined as a chromaticity M( 1 ,  2 ) corresponding to the sum of the above-described two measurement results. Then, based on the differential value between the above-described target chromaticity OC and the chromaticity M( 1 ,  2 ) corresponding to the average chromaticity obtained by the actual lighting in the R fields of the first and second subframes, CPU  27  calculates a target chromaticity O(r 3 ) for light emission from the R field of the next third subframe, as shown in  FIG. 4E . 
     Here, the target chromaticity O(r 3 ) is set at an object position such that when the distance to the above-described middle point M( 1 ,  2 ) corresponding to the sum of the two chromaticities, between which the target chromaticity is positioned, is defined to be 1, the distance from the target chromaticity OC to the object position is “2”. 
     If light can actually be emitted at the above-described target chromaticity O(r 3 ) in the R field of the third subframe, the average chromaticity obtained by calculating an average of the total chromaticity in the R fields of the first to third subframes can be determined to be the target chromaticity OC. 
     That is, setting the chromaticity at which light is emitted in the R field of the third frame as described above allows offsetting of the error from the target chromaticity OC and the average chromaticity in the R fields of the first and second subframes. 
     On the other hand, even if light cannot actually be emitted at the above-described target chromaticity O(r 3 ) in the R field of the third subframe, since the target chromaticity for the third subframe is set as described above with the error range ER of the LEDs taken into account, the average chromaticity for the R fields in one frame can be reliably made closer to the target chromaticity OC. 
     Then, CPU  27  calculates such light emission current values for the color LEDs as enable the target chromaticity O(r 3 ) calculated in the above-described step S 107  to be achieved (step  108 ). CPU  27  then newly stores the calculated light emission current values for the color LEDs in the chromaticity storage section  25   a  (step S 109 ). 
     Then, CPU  27  re-sets the value of the variable (n), indicating the subframes, by adding one (“+1”) to the value (step S 110 ). Upon determining that the re-set value of the variable (n) does not exceed the number N of subframes in one frame as a whole, here, the value does not exceed “3” (step S 111 ), CPU  27  returns to the processing starting with the above-described step S 101 . 
     In step S 101 , CPU  27  determines whether or not the timing for the R field of the third subframe of the frame is reached. In the subsequent step S 102 , CPU  27  determines that light emission current values for the LEDs are stored in the chromaticity storage section  25   a . CPU  27  then proceeds to step S 105 . In step S 105 , CPU  27  reads the light emission current values for the LEDs newly stored in step S 109 , from the chromaticity storage section  25   a . CPU  27  then uses the R driver  22 , the G driver  23 , and the B driver  24  to drive the LED array  17  at the read light emission current values so that the LED array  17  emits light. 
     In addition, in step S 106 , CPU  27  makes the illuminance sensors  26 R,  26 G, and  26 B measure the brightness of the respective color components of the light source light. Then, in step S 107 , based on the measured bright of the color components, CPU  27  calculates the total chromaticity in the R field of the third subframe. Based on the calculated total chromaticity in the third frame, CPU  27  calculates the average chromaticity in the R fields of the first to third subframes. Then, based on the differential value between the average chromaticity for the first and second frames and the target chromaticity, CPU  27  calculates a chromaticity in the R field of the next subframe. 
     Then, CPU  27  calculates such light emission current values for the color LEDs as enable the calculated target chromaticity to be achieved (step S 108 ). CPU  27  then newly stores the calculated light emission current values for the color LEDs in the chromaticity storage section  25   a  (step S 109 ). 
     Then, CPU  27  re-sets the value of the variable (n), indicating the subframes, to “4” by adding one (“+1”) to the value (step S 110 ). In the subsequent step S 111 , upon determining that the re-set value “4” of the variable (n) exceeds the number “3” of subframes in one frame as a whole (step S 111 ), CPU  27  sets the variable (n) to the initial value “1” (step S 112 ). CPU  27  returns to the processing starting with the above-described step S 101  again. 
     Thus, a red optical image is formed using red light the chromaticity of which has been adjusted based on the plurality of R fields in one image frame. The optical image is then projected. 
     Similar operations are performed on each of the G and B fields as described above. As a result, the LED array  17  is driven so as to emit light at the chromaticity correctly adjusted in all of the R, G, and B fields. Thus, a projection operation is performed. 
     Furthermore, predetermined values for the target chromaticity for the R, G, and B fields, respectively, are stored before shipment. Alternatively, the values may be changed as needed. That is, a plurality of selectable projection modes such as a luminance mode and a chromaticity mode are prepared for the projector apparatus  10 . Then, if for example, the luminance mode is selected, the quantity of light emission in all the fields other than a particular one is increased. For example, in the R field, the quantity of light emission from LED-G and LED-B, that is, all the LEDs other than LED-R to be originally lit is increased. The total chromaticity for the LEDs for which the quantity of light emission has been adjusted is thus set to be a new target chromaticity. 
     If the target chromaticity is thus changed, the light emission current values for the LEDs stored in the chromaticity storage section  25   a  are reset. The processing shown in  FIG. 3  is then executed again based on the new target chromaticity. 
     As described above, the present embodiment enables the chromaticity of the light source light according to the field-sequential scheme to be accurately maintained at the set content. 
     In addition, the above-described embodiment utilizes the content stored in the chromaticity storage section  25   a  for the subsequent frames. This allows convergence of a variation in the luminance of the individual LEDs forming the LED array  17  which variation is caused by a variation in temperature, age deterioration, or the like. As a result, the chromaticity of the light source light can be more accurately maintained. 
     Although not shown in the above-described embodiment, when for each subframe, a target chromaticity for the next subframe is calculated, a specific, limited adjustment range may be set based on the target luminance to be achieved for the entire frame. 
     In this case, by limiting the range of a variation in chromaticity between the adjacent subframes to a given value, the luminance of the light source can be prevented from varying significantly. Thus, since human eyes are more sensitive to a variation in brightness than to colors, projected images can be prevented from being degraded. 
     Furthermore, in the above-described embodiment, unless the target chromaticity is changed, the light emission current values for the LEDs are sequentially adjusted so that the average chromaticity from the first subframe is set to be the target chromaticity. However, an increase in the period over which the average chromaticity is calculated may prevent the average chromaticity from being perceived depending on the human (user&#39;s) color identification ability. Thus, even though the LED current values are adjusted so that the average chromaticity is set to be the target chromaticity, a chromaticity different from the target chromaticity may be perceived. 
     To solve this problem, it is possible to reset the light emission current values for the LEDs newly stored in the chromaticity storage section  25   a  in every predetermined period (for example, every frame). That is, the processing shown in  FIG. 3  described above is re-executed every predetermined period. The predetermined time is preferably set based on the human (user&#39;s) color identification ability. 
     In this case, the light emission current values for the LEDs adjusted during the first, above-described predetermined period may be used during the next predetermined period without change. Thus, unless the target chromaticity itself is changed, the light emission current values for the LEDs adjusted during the first predetermined period can be used for the subsequent light emission. As a result, the processing can be simplified, with the chromaticity of the light source light maintained at the appropriate value. 
     Furthermore, in the above-described embodiment, as shown in  FIG. 1 , the illuminance sensors  26 R,  26 G, and  26 B are arranged near the LED light source in order to measure the luminance of the LED light source. However, the present invention is not limited to this configuration. The illuminance sensors may be arranged near and over a regular optical path from the LED light source in order to measure leakage light from the regular optical path. Alternatively, part of the light over the regular optical path may be reflected to the sensor side as light to be measured. Moreover, the illuminance sensors may be arranged in front of the projector in order to measure the illuminance of irradiation light projected on the screen. In any way, it is only necessary to measure the brightness of light emitted by the LED light source in each color. 
     Additionally, in the above-described embodiment, in each of the R, G, and B fields, the R, G, and B LEDs forming the LED array  17  simultaneously emit light. However, the present invention is not limited to this configuration. The present invention is also applicable to the case where in each field, only the LED with the corresponding color emits light. 
     Moreover, in the above-described embodiment, LEDs are used as light emitting elements for a light source. However, the present invention is not limited to this configuration. The present invention is also effective for a projection apparatus according to the field-sequential scheme which uses a different light source, for example, a light source irradiating a phosphor with laser light to excite light source light in R, G, and B. 
     Furthermore, in the above-described embodiment, as shown in  FIG. 2 , one frame is divided into three subframes; first to third subframes. However, the present invention is not limited to this configuration. One frame may be divided into any number of subframes provided that the number is at least two. That is, as described above, an increase in the number of subframes allows the error range of the LED light source to be adjustably reduced. 
     Moreover, in the above-described embodiment, even though currents with values adjusted for the target chromaticity are passed, the error range ER results from the characteristics and possible aged deterioration of the LEDs forming the LED array  17 . However, obviously, the error range ER does not have a fixed value and varies depending on the individual differences among the LEDs, and the situation and environment in which the LEDs are used. Thus, for example, the measurement error range may be corrected every given period, or different measurement error values may be set for the respective LEDs. 
     Furthermore, the present invention is not limited to the above-described embodiments. In practice, many variations may be made to the embodiments without departing from the spirit of the present invention. Additionally, the functions executed in the above-described embodiments may be appropriately combined together if at all possible. The above-described embodiments include various stages. A plurality of the disclosed compositions may be appropriately combined together to allow various inventions to be extracted. For example, if the present invention is still effective after some of the components shown in the embodiments have been removed, the configuration resulting from the removal of these components can be extracted as an invention. 
     Furthermore, the present invention is not limited to the above-described embodiments. The embodiments can be freely changed or modified without departing from the spirit of the present invention. 
     Various typical embodiments have been shown and described. However, the present invention is not limited to the embodiments. Therefore, the scope of the present invention is limited only by the claims.

Technology Category: g