text: 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 . fig1 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 . in the present embodiment , the data projector 1 divides one frame shown in fig2 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 . fig2 ( 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 , fig2 ( 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 fig2 ( b ) . in addition , the projector 1 allows the green led - g shown in fig2 ( c ) and the blue led - b shown in fig2 ( 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 . fig3 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 ). fig4 a 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 fig4 a 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 fig4 a 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 . fig4 a shows that the actual measured chromaticity r 1 falls within the error range er . based on the measurement results , as shown in fig4 b , 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 . fig4 c 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 fig4 c , 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 fig4 d , 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 fig4 e . 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 fig3 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 fig3 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 fig1 , 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 fig2 , 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 .