Automatic white-balance controlling apparatus

Abstract: An automatic white-balance controlling apparatus for controlling the white-balance of an imaged screen, by controlling the color signal level in accordance with the up-down counting result in a microcomputer. A limited area is established within a VB-VR plane, and the level adjusting operation of the color signals corresponding to the area is limeted so as to render a stable white-balance adjusted operation. Judged from data in time series, the accuracy of the white-balance controlling operation can be assured executing somewhat redundant processing.

Description: This invention relates to an apparatus for automatically controlling the white-balance of a color video camera. A color imaging system typically comprises a white-balance controlling apparatus for displaying an object on the screen in colors as close as possible to those viewed through the human eye. A human eye identifies a white color object as it is , when the color temperature of light illuminating the object is within a predetermined range, irrespective of the fluctuation. The color of an object captured by the color imaging system, however, originally tends to blue proportionally to the increase of the light color temperature, while it tends to redden proportionally to its decrease. This means that the colors recognized by the color imaging system and by the human eye differ mutually depending on the color temperature of the illumination light. A white-balance controlling apparatus has been used to adjust such a difference and to give correct levels of both colors. This apparatus acts to correct color data obtained by imaging an object in accordance with the color temperature of an illumination light. FIG. 12 of the accompanying drawings shows an example of an imaging apparatus such as color video cameras, etc. comprising a prior art automatic white-balance controlling apparatus, which is a lightly-modified apparatus based on the technical concept disclosed in JP-A-54 438 72 or JP-A-63 109 686 or US-A-4 750 032 and on which the pre-characterising part of claim 1 is based. In FIG. 12 the apparatus includes a lens 1, an imaging element 2, and a color separating circuit 3. The lens 1 receives an optical image in an imaging apparatus such as color video camera etc.. The color separating circuit 3 separates the signal obtained by photoelectrical conversion into three color signals of R. G. and B. These three color signals are supplied to the processing circuit 6 in the following manner respectively: the signal of R (hereinafter called the R signal, and similarly for the other two signals), through a gain control circuit (hereinafter called as GC); the G signal, directly; the B signal, through GC5. The processing circuit 6 generates a brightness signal (hereinafter referred to as Y signal) and a color difference signal from the R signal, G signal, and B signal. There are two types of color difference signal. These are, R-Y signal representing the level difference between the R signal and the Y signal, and B-Y signal representing the level difference between the B signal and the Y signal. These Y, R-Y, and B-Y signals are encoded by an encoder 7 and output therefrom as a color video signal. Aforementioned are a composition of signals generally not relevant to the white-balance control, which is performed by adjusting the levels of the R signal and the B signal by GC4 and GC5. GC4 and GC5 are circuits which adjust the level of the R signal or the B signal with a gain variable in accordance with the gain control signal. The gain control signal is generated by the following composition. Namely, the composition hereinafter described performs negative return control for the GC4 and the GC5 on the basis of the detected result of the integrated value of the R-Y signal and the B-Y signal, and is called an automatic white-balance controlling apparatus. FIG. 12 shows integrator circuits 8 and 9. The integrator circuit 8 integrates R-Y signal while the integrator circuit 9 integrates B-Y signal. The integrated values of the R-Y signal and the B-Y signal obtained in the integrated circuits 8 and 9 respectively are supplied to the non-inverse input terminal of the comparators 10 or 11. The inverse input terminals of the comparators 10 and 11 receives a reference voltage Vref from a reference voltage generator 15. The comparator 10 and 11 compare the integrated values of the R-Y signal and the B-Y signal to the reference voltage Vref and output a signal representing the compared result (hereinafter, the signals output from the comparators 10 and 11 are called RchCOMP and BchCOMP respectively). RchCOMP and BchCOMP are supplied to the microcomputer 12, which generates RchOUT and BchOUT based on RchCOMP and BchCOMP and outputs them in accordance with the clock pulse. RchOUT and BchOUT correspond to either the R signal or the B signal of the gain control signal, and are generated in accordance with a predetermined algorithm. The microcomputer 12 outputs one coupled is a D/A converters 13 and 14, where the former and the latter convert respectively RchOUT and BchOUT into analog gain controlling signal. A gain controlling signal for RchOUT is supplied to GC4 for controlling the R signal level, while a gain controlling signal for BchOUT is supplied to GC5 for controlling the B signal level. However, GC4 and GC5 increasingly changes the gains for the values of the gain controlling signals linearly. This control is performed such that the R-Y signal and the B-Y signal become zero when an achromatic color is imaged. The reason why such a control is possible is that; when a scene is imaged, if the R-Y signal in respect of the entire scene is integrated, the conditions become the same as in the case when an achromatic color is imaged, and if the B-Y signal in respect of the entire scene is integrated, the conditions again become the same as in the case when an achromatic color is imaged. Such adjustment would assure a certain white balance irrespective of the change of the light source for illuminating the object. Comprising such a composition, the operation of an automatic white-balance controlling apparatus has been dependent on the operation of the microcomputer 12. FIG. 13 shows an example of the operation of the microcomputer 12. As shown in FIG. 13 immediately after the starting of the operation, the initializations of RchOUT, BchOUT, RchUDC, BchUDC are carried out (S1). These RchUDC and BchUDC are original values for RchOUT and BchOUT respectively, and can be obtained by the following reversible calculation. Upon completion of the step S1, a calculation loop is entered as shown in the drawing. In this loop, firstly it is judged whether the H value or the L value should be selected from the comparing circuit 10 (S2). The case where RchCOMP from the comparing circuit 10 is the H value represents that the integrated value of R-Y signal is above the reference value Vref. The reference value Vref is set in accordance with the value of the color difference signal (near the 0V). Therefore, the case where RchCOMP from the comparing circuit 10 is the H value results from the average value of the R-Y signal for one screen being higher than the average value of R-Y signal in the case where an achromatic (white) color object is imaged. Meanwhile, on the contrary, the case where RchCOMP from the comparing circuit 10 is the L value results from the average value of the R-Y signal for one screen being lower than an average value of R-Y signal in the case where an achromatic (white) color object is imaged. After step S2, a decrement of RchUDC is executed when it is H value (S3), while RchUDC increment is executed when it is the L value (S4). Next, it is judged whether the H or L value is selected from the comparing circuit 11 (S5). In the same manner as step S2, the case where BchCOMP from the comparing circuit 11 is the H value results from the average voltage of B-Y signal for one screen being higher than the average voltage of B-Y signal of the case where an achromatic (white) object is imaged. On the contrary, the case where BchCOMP from the comparing circuit 11 is the L value results from the average voltage of B-Y signal for one screen being lower than the average voltage of B-Y signal of the case where an achromatic (white) object is imaged. In step S5, an increment of BchUDC increment is executed when it is judged as the H value (S6), and a decrement of BchUDC is executed when it is judged as the L value (S7). Thereafter, RchOUT and BchOUT are output (S8). RchOUT and BchOUT are generated based on the values of RchUDC and BchUDC. Most simply, RchUDC and BchUDC themselves are used as they are. After step S8, clock pulse-input waiting is executed (S9), and the loop returns to step S2 upon receiving the input. Thus, RchUDC and BchUDC are obtained from the information representing the level of the average voltage for one screen and on the basis of the comparison with the reference voltage Vref. Based on these values fcr RchUDC and BchUDC, the level adjustment for the R signal and B signal is carried out. As a result, it is possible to exercise control such that R-Y signal and B-Y signal are zero when an achromatic object is imaged as mentioned above. FIG. 14 shows another example of the operation of the microcomputer 12 where RchUDC and BchUDC are dealt as RchOUT and BchOUT respectively. Accordingly, unlike the case shown in FIG. 25, no initialization of RchOUT and BchOUT is performed in step S1', while RchUDC and BchUDC are output in step S8' after step S9. FIG. 15 shows another example of an imaging apparatus for a color video camera etc.. This apparatus also comprises a similar conventional automatic white-balance controlling apparatus but different in having an automatic gain controller 116 between the imaging element 102 and the color separating circuit 103. In this composition, it is possible to stabilize the white-balance adjustment by controlling the input level of the color separating circuit 103. However, several disadvantages have arisen in such conventional automatic white-balance controlling apparatus. For instance, when green colored objects occupy a majority of the visual imaging field and therefore green is the major color in the screen, the GC for the R signal and the GC for the B signal cause the GC circuits to enter an excessively gained state. In consequence, the image of a white object, which should be seen in white color in the screen, would be colored in magenta. Namely, the white-balance breaks, thereby for example the blue sky would appear inclined to white, and the skin of a Japanese would appear white. Also, the output value of the comparing circuit would be unstable, if noise were introduced to its input. Namely, the white balance oscillates. Further, the white-balance would tend to be unstable when the lightness of the object is insufficient. Namely, if the object has sufficient lightness and the level of the signal from the imaging element is large enough to ignore the noise, the white-balance controlling operation would stabilize. But if the lightness is insufficient, the output polarity of the comparing circuit would tend to reverse due to the noise. It is therefore an object of this invention to improve the white-balance control. According to the present invention there is provided an automatic white-balance controlling apparatus for controlling the white balance of input image signals, comprising: an integrating means for integrating two types of color difference signals in screen units respectively; a comparing means for comparing each of the integrated values obtained from the integrating means to a reference value representing an achromatic color; a command means for: repeatedly incrementing or decrementing respective counts for each color difference signal at each screen based on the output of the comparing means setting a gain value for each of said two color difference signals based on the respective counts; and an adjusting means for adjusting the levels of the color difference signals in accordance with the gain values, characterised in that the command means is adapted: to establish a limited area in a two-dimensional space defined by coordinates representing said respective count; to compare the position defined by said counts with said limited area; and if said position lies outside said limited area to reset one or both of the counts to their previous values before said increment or decrement to bring said position inside said limited area before setting such gain values on the basis of the counts. By setting the limiting area appropriately, the divergence of the white-balance control toward the magenta or green colors can be prevented. Further, it is possible to switch the operation in accordance with a selected mode, which includes a following mode and a storing mode. The command means sets the limiting area as a first limiting area when the following mode is selected, and sets the limiting area as a second limiting area when the storing mode is selected. The first limiting area is contained within the second limiting area and assures the proper response to the illuminating light when there is a change of object. When the selected mode is the storing mode, the command means executes the increment or decrement of the counts only when the trigger is generated. Here, the trigger acts to command the maintaining of a controlled white-balance state. Thus, real-time white-balance controlling in the following mode can be assured, and the vibration and instability of the white-balance in the storing mode can be reduced. Further, more noise-free and stable white-balance control can be achieved by monitoring the high-frequency component of the brightness signal. For instance, firstly, the high-frequency component of the brightness signal is extracted from the three-color signals by the high-frequency component extracting means. Next, the command means sets a wide limiting area when the amount of the high-frequency component is large and a narrow limiting area when the same is small. This is because, generally, the amount of the high-frequency component is small when the whole screen is in a single color, like a blue sky, while the same is large when the color temperature is high and the whole screen is blue. Thus, a white-balance control in accordance with the color temperature can be realised. The present invention will be further described by way of non-limitative example with reference to the accompanying drawings, in which:- FIG. 1 is a block diagram showing a color imaging apparatus including an automatic white-balance controlling apparatus according to the first embodiment of this invention; FIG. 2 is a flow diagram showing the operation of the microcomputer in the first embodiment; FIG. 3 is a graphic diagram showing VB-VR space in the first embodiment where the limiting area is represented by a hexagon; FIG. 4 is a block diagram showing the composition of a color imaging apparatus including an automatic white-balance controlling apparatus according to the second embodiment of this invention; FIG. 5 is a flow diagram showing an operation of the microcomputer according to the second embodiment of this invention; FIG. 6 is a flow diagram showing an up-down counting routine among the operations of the microcomputer according to the second embodiment of this invention; FIG. 7 is a graphic diagram showing VB-VR space in the second embodiment of this invention where two limiting areas are represented; FIG. 8 is a block diagram showing the composition of a color imaging apparatus including an automatic white-balance controlling apparatus according to the third embodiment of this invention; FIG. 9 is a flow diagram showing the operation of the microcomputer according to the third embodiment of this invention; FIG. 10 is a flow diagram showing an up-down counting routine among the operations of the microcomputer according to the third embodiment of this invention; FIG. 11 is a graphic diagram showing VB-VR space in the third embodiment of this invention, where the wide-narrow switching operation of the limiting area is represented; FIG. 12 is a block diagram showing a composition of a color imaging apparatus including a conventional automatic white-balance controlling apparatus; FIG. 13 is a flow diagram showing the operation of the conventional microcomputer in FIG. 12; FIG. 14 is a flow diagram showing another operation of the conventional microcomputer in FIG. 13; FIG. 15 is a bock diagram showing the composition of the apparatus of FIG. 12 to which AGC is added. I. First Embodiment: FIG. 1 shows an example of a color imaging apparatus including an automatic white-balance controlling apparatus according to the first embodiment of this invention. Firstly, the basic composition of this apparatus will be described. The lens 201, a representative component of the optical system, receives light beams from a imaging object and supplies them to the imaging element 202. The imaging element 202 receives the light beams from the lens 201 (representing the target image and known as a light image), photoelectrically converts and outputs them as an imaging signal. The imaging signal, having a level corresponding to the property of the imaging element 202, is subject to the level control by a not-shown amplifier because of signal weakness, and is then supplied to a color separator 203. The color separator 203 separates three color signals from the imaged signal. These three color signals are referred to as R (red) signal, G (green) signal, and B (blue) signal. The R, G, and B signals are supplied to a processor 206. The processor 206 generates a brightness signal (Y signal) and color difference signals (R-Y signal and B-Y signal). The Y, R-Y, and B-Y signals are supplied to the encoder 207. The encoder 207 encodes the Y, R-Y, and B-Y signals to provide and output color video signals. The above-mentioned composition covers all of the functions of the color imaging apparatus except the white-balance controlling operation. The automatic white-balance controlling apparatus in this embodiment comprises integrators 208, 209, comparators 210, 211, microcomputer 312, D/A converters 213, 214, reference voltage generator 215, and GCs (gain controllers) 204, 205. The integrators 208, 209 integrate the R-Y signal and the B-Y signal respectively for a predetermined period. The comparators 210, 211 compare the integrated result from the integrators 208, 209 respectively with a reference voltage Vref. The reference voltage Vref is supplied from the reference voltage generator 215 to the inversion input terminals of the comparators 210, 211, and its value is equivalent to an integrated value of one screen of R-Y signal or B-Y signal when an achromatic color object is imaged. Since the integrated results of the integrator 208, 209 are supplied to the non-inversion input terminals of the integrators 208, 209 respectively, the outputs of the comparators 210, 211 are H values when the integrated results are higher than the reference voltage Vref and L values when they are lower than the reference voltage Vref. The microcomputer 312 receives the outputs from the comparing circuits 210, 211 (hereinafter referred to as RchCOMP, BchCOMP respectively), executes up-down counting, and outputs RchOUT, BchOUT in accordance with the clock pulses. These RchOUT, BchOUT are values generated on the basis of the results of the up-down counting (hereinafter referred as RchUDC, BchUDC). RchOUT, BchOUT are then converted into analog gain controlling signals, which are supplied to the GC 204, 205 to set the amplifying gain therein. The GC 204, 205 amplifies the R signal and B signal respectively in accordance with the gains set by the gain controlling signal. Therefore, the levels of the R signal and B signal are controlled in accordance with the operation of the microcomputer 312, thereby enabling automatic white-balance control. Thus, the operation of the microcomputer 212 plays an important role in determining the white-balance controlling operation in this invention. FIG. 2 shows the operation of the microcomputer 312 of this embodiment, while FIG. 3 represents the basic concept embodied by the operation of FIG. 2. The operation of the microcomputer 312 is now described along with the flow diagram of FIG. 2 in view of FIG. 3. Firstly, the microcomputer 312 initially sets RchOUT, BchOUT, RchUDC and BchOUT (S 201). Thereafter, it returns to the routine operation and does not repeat the operation noted above. In the normal operation, firstly the step 210 is executed. Step S210 includes Steps S 202 - 204. The step S 202 judges if RchCOMP value obtained from the comparing circuit 210 is L or H. The step S 203 is executed When the value is judged as being H, while the step S 204 is executed when it is judged as being L. In the step S203 RchUDC is decremented by one, while in the step S204 RchUDC is incremented by one. Namely, in the step S210, the up-down counting is executed in accordance with the value of RchCOMP, and the executed result is stored in RchUDC. Next, the step S211 is executed. In the step S211, it is judged if the two-dimensional coordinates value (RchUDC, BchUDC) is on the border or outside of the border of the limiting area. Here, the term limiting area signifies a closed area formed above the VB-VR two-dimensional space, which is represented as a hexagonal area in FIG. 3. VB represents the level of the B signal, and VR represents the level of the R signal. These are of the same dimension as RchUDC, BchUDC, RchOUT, and BchOUT. The limiting area is set by the microcomputer 312. For example, the limiting area shown in FIG. 3 is set as satisfying all of the following conditions: VRL ≤ VR ≤ VRH VBL ≤ VB ≤ VBH VR -α ≤ VB ≤ VR +α In general, coordinates (VB, VR) of a normal object are located in an area of VB - VR two-dimensional space. The limiting area should be set to have coordinates (VB, VR) of a normal object therein, and to have that outside thereof when a green object different from the normal object occupies a majority of the screen. This is because in the latter case, the coordinates (VB, VR) represent an obviously different position from that in the former case. According to the setting of FIG. 3, it is possible to make a suitable limiting area by adjusting VBR, VBL and α. The judgment of the step S211 is equivalent to judging if the coordinates (RchUDC, BchUDC) pertain to the limiting area upon completion of the up-down counting on the basis of only RchCOMP. Namely, it is a judgment of whether or not the coordinates get out of the limiting area when RchUDC is changed by the up-down counting operation in step S210. If it is judged as not getting out thereof, step S212 is executed, and if it is judged as getting out thereof, step S213 is executed. The step S212 includes steps S214 - S216. In the step S214, it is judged if the value BchCOMP obtained from the comparing circuit 211 is H or L. If the value is H, step S215 is executed. If the value is L, step S216 is executed. In the step S215, BchUDC is incremented by one, while in the step S216, BchUDC is decremented by one. After passing these steps, the sequence is shifted to the operation in step S217. Accordingly, in the step 212 an up-down count is executed on the basis of BchCOMP. Step S217 is a similar judging step to the step S211. But since the up-down counting based on BchCOMP is already executed in the preceding step S212, the meaning of judgment is different. Namely, the coordinates, (RchUDC, BchUDC) to be judged if they pertain to the limiting area, are the coordinates provided after executing the up-down count based on both RchCOMP and BchCOMP. In the step S217, when the coordinates (RchUDC, BchUDC) are judged to be on the border or out of the border of the limiting area, step S218 is executed. In the step S218, the contents of RchUDC are substituted for RchOUT, while the contents of BchOUT are substituted for BchUDC. Thereafter, in step S208, RchOUT and BchOUT are output to the D/A converter 213 or 214, and the sequence returns to step S210 thereby the same cycle will be repeated. In step S217, when the coordinates (RchUDC, BchUDC) are judged not to be on the border or outside of the border of the limiting area, step S219 is executed. In this step S219, the contents of RchUDC are substituted for RchOUT, while the contents of BchUDC are substituted for BchOUT. Thereafter, shifting to the step S208 is executed, and the same operation as after step S218 is repeated. On the contrary, in step S211, when the coordinates (RchUDC, BchUDC) are judged to be on the border or outside of the border of the limiting area, the step S213 is executed. The step S213 includes steps S220 - S222 having the same contents as those of steps S214 - S216. Namely, the step S213 executes the up-down counting in accordance with the value of BchCOMP, and stores the counted result in BchUDC. After performing step S213, step S223 is executed. In the same manner as step S217, in step S223, it is judged if the coordinates (RchUDC, BchUDC) after the up-down counting based on both RchCOMP and BchCOMP pertain to the limiting area or not. After the execution of the step S223, step S224 or S225 is executed. When the judged result in the step S223 is "on or out of the border", it is shifted to the step S224, while if the result is "within the border", it is shifted to the step S225. In the step S224, it is judged if the coordinates (RchOUT, BchUDC) are on or out of the border or not. If the judged result is affirmative, step S226 is executed, while if the judged result is negative, step S227 is executed. In the step S226 RchOUT is substituted for RchUDC, and BchOUT is substituted for BchUDC. In the step S227, RchOUT is substituted for RchUDC, and BchUDC is substituted for BchOUT. Thereafter, step S208 is executed. In step S225, RchUDC is substituted for RchOUT, and BchUDC is substituted for BchOUT. Thereafter, step S208 is executed. The microcomputer 312 performs the above-mentioned operations. Next, prevention of a white-balance deviation effect will be now described in view of a specific embodiment. Firstly, as a first specific embodiment, a change A shown by a solid line in FIG. 3 will be considered. This change A is based on the assumption of a conventional operation as shown in FIG. 25, and is equivalent to the case where both BchCOMP and RchCOMP are H values. In addition, just before this change A, the coordinates (RchOUT, BchOUT) pertain to the limiting area, and after the change A they come out thereof to the upper side. In this embodiment, under these circumstances, the change of the coordinates (RchOUT, BchOUT) is not as shown in the solid line, but as shown in a dashed line Namely, in such a case, firstly in step S210 the branching to the step S203 and the decrement of RchUDC are executed, and in the step S211 it is judged as not being "on or out of the border". As a result, the step S212 is executed. In the step S212, when the judgment for BchCOMP is executed (S214), the step S215 for the increment of BchUDC is executed since BchCOMP is H value. In the step 217 which will be executed immediately thereafter, the coordinates (RchUDC, BchUDC) represent a point after a change as shown in the solid line is generated since BchUDC is already increased in the step S210. Accordingly, the coordinates (RchUDC, BchUDC) at this time will be out of the limiting area, thus, the step S218 will be executed. In the step S218, as mentioned before, the values of RchOUT, BchOUT will be set. In the same manner as imaging a normal object, when the coordinates (RchUDC, BchUDC) before or after the change are both within the limiting area, the coordinates (RchUDC, BchUDC) can be substituted directly to the coordinates (RchOUT, BchOUT) and be output (S208). Namely, since it is necessary to output RchOUT and BchOUT in the step S208, these RchOUT and BchOUT must be set to values reflecting the result of the up-down counting by the step S218 (the same is true in the steps S226, S227, and S225). In this case, however, under the circumstances according to the change A, RchUDC having passed the up-down counting operation in the step S210 is substituted for RchUDC so as to reflecting the result of the up-down counting on the RchOUT. On the contrary, the result of the up-down counting in the step S212 does not reflect on the BchOUT. In other words, no substituting operation for BchOUT is executed. Accordingly, BchOUT output from the microcomputer 312 in the step S208 will be either one of the values having been initially set in the step S201 or the value obtained after executing the operation of the step S208. The substituting operation of BchOUT for BchUDC in the step S218 acts to store the value necessary to execute the steps following to S210 in accordance with the input of the clock pulses. In this manner, under the circumstances according to the change A, the result of the up-down counting operation reflects only on the RchOUT, and not on the BchOUT. Namely, the calculating operation of the result of the up-down counting for BchOUT is canceled. Accordingly, the change would be as shown in dashed line, thereby assuring the white-balance controlling operation to be carried out within the limiting area. As a result, it is possible to prevent the white object in the screen from being tinged with magenta or green. As a second specific embodiment, the change B shown in FIG. 3 will now be considered. In this change, the value of RchCOMP is the L while BchCOMP is H. And, even when the result of the up-down counting is reflected on both of RchUDC and BchUDC values , these are held within the limiting area. Under these circumstances, the step S204 is firstly executed in the step S210, the judgment in the step S211 is "within the limiting area", the step S215 is executed in the step S212, and the judgment in the step S217 is "within the limiting area". Accordingly, the step S219 is executed, and any of the up-down counting results of RchUDC and BchUDC would be reflected in RchOUT and BchOUT being the values to be output. As a result, a change as shown in the solid line would occur. As a third specific embodiment, the change C shown in FIG. 3 will now be considered. In this change, the value of RchCOMP is L while BchCOMP is H. If the result of the up-down counting is reflected in RchOUT and BchOUT being the values to be output, deviations from the limiting area would occur in both of the directions VB, VR. Under these circumstances, the process flow would be as: S202 - S204 - S211 - S220 - S221-S223 - S224 - S226. In consequence, the up-down counting result would not be reflected in the RchOUT and BchOUT being the values, to be output. As a result, the same RchOUT and BchOUT as the preceding output values would be also output this time. As a fourth specific embodiment, the change D shown in FIG. 3 will now be considered. The change D represents the situation where both RchCOMP and BchCOMP are the L values, and where if the result of the up-down counting is reflected in RchOUT and BchOUT being the values to be output, it would be deviated from the limiting area. Under these circumstances, the process flow would be as: S202 - S204 - S211 - S220 - S223 - S225 - S224 - S227. Accordingly, the up-down counting result with respect to BchUDC would reflect only in BchOUT among values of RchOUT and BchOUT, while in view of the effect on RchOUT, the up-down counting result with respect to RchUDC is cancelled. As a fifth specific embodiment, the change E shown in FIG. 3 will now be considered. The change E represents a situation where the value of RchCOMP is L while BchCOMP is H, and if the up-down counting result is reflected in RchOUT, BchOUT being the values to be output, it would appear changing within the limiting area. Under these circumstances, the process flow would be as: S202 - S204 - S211 - S220 - S221-S223 - S225. Accordingly, the up-down counting result would reflect in both RchOUT and BchOUT being the values to be output, while the up-down counting result with respect to RchUDC, BchUDC is not cancelled. Thus, according to this embodiment, the microcomputer 312 judges whether the coordinates e.g. (RchUDC, BchUDC) pertain to the limiting area or not, and sets the output values RchOUT and BchOUT depending on the judged result. In consequence, any white-balance deviation can be prevented. It is also possible to compose the microcomputer 312, besides being a single processor, by hard logic such as an up-down counting circuit, etc. Further, the configuration of the limiting area and the setting condition formulas are at the designer's free will, on the condition that there is no possibility of coloring with magenta or green. Specifically, it is preferable to select such configurations as parallelogram, circle, ellipse, etc.. Of course, even if the details in FIG. 2 are different from the shown embodiment, they pertain to the technical scope of this invention. II SECOND EMBODIMENT Fig. 4 shows a color imaging apparatus comprising an automatic white-balance controlling circuit according to the second embodiment of this invention. The composition of this apparatus is almost the same as that in the first embodiment, but the differences lie in the microcomputer 612, and in that a selecting switch 617 and a trigger signal generating switch 618 are coupled to the microcomputer 612. Namely, the microcomputer 612 operates as represented in FIGS. 5 and 6. not FIG. 2. In this embodiment, the microcomputer 612, after the initial setting of RchUDC, BchUDC. RchOUT, and BchOUT (S601), receives the state data of the selecting switch 617 (S639). The operation of the microcomputer 612 shifts to the step S640 in the case of following mode being selected, while it shifts to the step S641 in the case of storing mode. The first closed area and the second closed area are set as a limiting area in the steps S640 and S641 respectively. The first and the second closed areas signify closed areas on the VB-VR plane as shown in FIG. 7 , being hexagonal as in the limiting area in FIG. 3. The first closed area belongs to the second closed area. Accordingly, if the operation as shown in FIG. 2 is executed with the first closed area as the limiting area, the GC control for the white-balance control would be allowed for a broader scope than when the same is executed with the second closed area as the limiting area. In the case of the first closed area being set as the limiting area, step S642 is executed. In this step S642, the up-down counting routine as shown in FIG. 7 is executed. Its detailed operation will be described later, though the basic contents of the step S642 are substantially the same as those in FIG. 2. After the step S642, the microcomputer 612 outputs RchOUT and BchOUT (S608), thereby controlling the GC gain. Thereafter, it is returned to the step S639. In case of the second area being set as the limiting area, a step S643 is executed. In this step S643, the state data of the trigger signal generating switch 618 is read and judged. Namely, the trigger signal generating switch 618 generates a trigger signal under predetermined conditions, and the microcomputer 612 executes a step S644 in the case of a trigger signal generation and executes a step S645 in the case of no trigger signal generation. In step S644, substantially the same up-down counting routine as in the step S642 is executed. After step S644, a judgment as to whether the convergence is made or not is executed (S646), and the sequence progresses to the step S645 if the judged result is affirmative while it returns to the step S644 if the result is negative. The step S645 has the same contents as the step S608, and thereafter the microcomputer returns to the step S639. Next, the up-down counting routine shown in FIG. 6 will now be described. This routine is executed in the steps S642 and S644. Firstly, the microcomputer 612 executes the steps S602 - S604. In the step S602, it is judged if the value of RchCOMP is H or L. If it is judged as being the H, RchUDC is decremented by one (S603), and if it is judged as being the L, RchUDC is incremented by one (S604). Secondly, the step S611 is executed. In the step S611, it is judged if the coordinates (RchUDC, BchUDC) are on or out of the border of the limiting area. In this case, the first or second closed areas are established in the preceding steps S640 or S641. In the step S611, it is judged if the coordinates deviate from the limiting area at the stage where only the up-down counting based on RchCOMP is executed. If the deviation is confirmed by the judgment, the step S620 is executed, while if it is not confirmed, the step S614 is executed. In the step S614, it is judged if the value of BchCOMP is H or L. If it is judged as being the H, the step S615 where BchUDC is incremented by one is executed, while if it is judged as being the L, the step S616 is executed where BchUDC is decremented by one. The next step S617 is operatively the same as the step S611. But since the up-down counting based on BchCOMP is already executed in the preceding steps, the significance of the judgment is different. Namely, in the step S617, the coordinates (RchUDC, BchUDC) to be judged to see if they pertain to the limiting area are the coordinates after the execution of the up-down counting based on both RchCOMP and BchCOMP. In the step S617, if it is judged as "on or outside of the border", the step S618 is executed. In this step S618, the contents of RchUDC are substituted for RchOUT, while the contents of BchOUT are substituted for BchUDC. Thereafter, RchOUT and BchOUT are output in the step S608, and then the microcomputer returns to the main routine. If it is judged as "not on or out of the border of the limiting area", the step S619 is executed. In this step S619, the contents of RchUDC are substituted for RchOUT, while the contents of BchUDC are substituted for BchOUT. Thereafter, it returns to the step S608, thereby operating in the same manner as after the execution of the step S618. On the contrary, in the step S608, if it is judged as being "on or outside of the border", the steps S620 and S621 or S622 are executed. Namely, the up-down counting is executed in accordance with the value of BchCOMP, and the counted result is stored in BchUDC. Next, the step S623 is executed. In the step S623, as in the step S617, it is judged if the coordinates (RchUDC, BchUDC) after the up-down counting operation based on both RchCOMP and BchCOMP pertain to the limiting area. After the execution of the step S623, steps S624 and S625 are executed. The step S624 is executed when the judged result in the step S623 is "on or outside of the border", while the step S625 is executed when the judged result is "not on or out of the border". In the step S624, it is judged if the coordinates (RchOUT, BchUDC) are on or out of the border of the limiting area. A step S626 is executed in the case of the judged result being affirmative, while a step S627 is executed in the case of the judged result being negative. In the step S626, RchOUT is substituted for RchUDC, while BchOUT is substituted for BchUDC. In the step S627, RchOUT is substituted for RchUDC, while BchUDC is substituted for BchOUT. After these operations, a step S608 is executed. In the step S625, RchUDC is substituted for RchOUT, while BchUDC is substituted for BchOUT. After these operations, a step S608 is executed. The microcomputer 612 operates as mentioned above. This embodiment also provides the same effects as in the first embodiment. Namely, in this embodiment, the microcomputer 612 judges if the coordinates (RchUDC, BchUDC) and the like pertain to the limiting area, and the output values RchOUT and BchOUT are set depending on the judged result, thereby preventing the deviation of the white-balance. For example, when the changes shown by arrows A-E in FIG. 7 are considered, if the limiting area is the first closed area, the following steps will be executed depending on the changes as in the first embodiment: the step S618 in case of the change A; the step S619 in case of the change B; the step S626 in case of the change C; the step S627 in case of the change D; and the step S625 in case of the change E. But in this embodiment, the limiting area can alternatively be set to the second area, being broader than the first area. In this case, any of the changes A-E can be allowed, namely the step S625 is executed in any case. Thus, according to this embodiment, two types of operation, the following mode operation and the storing mode operation can be selectively executed by appropriately switching. The following mode would be suitable for a dynamic imaging since an automatic white-balance controlling operation by a relatively broad limiting area (second closed area) in accordance with the changes of the object, lightness and position of the light source for illuminating the object is executed. In the storing mode, more stable image with less white-balance deviation can be achieved since the relatively narrow limiting area (first closed area) is used. III. THIRD EMBODIMENT FIG. 8 shows a color imaging apparatus comprising an automatic whitebalance controlling circuit according to the third embodiment of this invention. Although the composition of the apparatus in this embodiment is almost the same as that in the first embodiment, several changes and modifications are made. For example, firstly, a microcomputer 912 is aimed at executing the operation represented in FIGS. 9 and 10, not FIG. 2. Further, in this embodiment the following components are newly provided: a matrix circuit 928 for generating brightness signals by receiving the color signals R, G, B and matrixing them: a band-pass-filter 929 for extracting the high-frequency component from the brightness signal; a wave detecting circuit 930 for wave-detecting the high-frequency component 930; an integrating circuit 931 for integrating the output of the wave-detecting circuit 930 and supplying the integrated data to the microcomputer 912. The operation of the microcomputer 912 shown in FIG. 9 starts with receiving the output value of the integrating circuit 931 (S952), This output value stands for the amount of the high-frequency component extracted by the band-pass-filter 929. In the successive step S953, a limiting area is set in accordance with the amount of the high-frequency component, and subsequently the up-down counting (S954) and the outputting of RchOUT and BchOUT (S908) are executed. In this embodiment, the term "limiting area" signifies the same concept as described in the first embodiment referring to FIG. 3. But the differences of this embodiment from the first embodiment lie in setting the limiting area variably and in performing this variable setting in accordance with the amount of the high-frequency component. For example, as shown in FIG. 11, the limiting area is set to be broader when the amount of the high-frequency component is large, while it is set to be narrower when the same is small. Thus, the deviation of the white-balance controlling can be reduced, providing an image with more natural colors. This is because the amount of the high-frequency is generally small when the object is nearly all one color, such as blue sky, while it is large when the color temperature is high and the whole object is blue. Accordingly, if the limiting area is set narrower to limit the width of the white-balance controlling when the amount of the high-frequency component is small, the deviation of the white-balance control toward the magenta and green directions can be reduced. This embodiment has enabled such operations. The contents of the step S954 i.e. the up-down counting would be as shown in FIG. 10 substantially the same as the operation represented by FIG. 2. Namely, the steps having the same lower two digits are the same in operation. Further, in this embodiment, for extracting the amount of the high-frequency component, other means than the matrix and the filter, e.g. such a high-frequency component extracting means as included in a TTL type automatic focusing apparatus can be used. In this case, the change of the limiting area is preferably carried out at the completion of the focusing operation. Thus, the apparatus of this embodiment can be composed at a low cost by transferring components from apparatuses of other fields.

Claims: An automatic white-balance controlling apparatus for controlling the white balance of input image signals, comprising: an integrating means (208,209) for integrating over a predetermined period two types of color difference signals (R-Y, B-Y) respectively; a comparing means (210,211) for comparing each of the integrated values obtained from the integrating means (208,209) to a reference value representing an achromatic color; a command means (312) for: repeatedly incrementing or decrementing respective counts (R ch UDC, B ch UDC) for each color difference signal (R-Y, B-Y) at each predetermined period based on the output of the comparing means (210,211) setting a gain value (R ch OUT, B ch OUT) for each of said two color difference signals (R-Y, B-Y) based on the respective counts; and an adjusting means (204,205) for adjusting the levels of the color difference signals (R-Y, B-Y) in accordance with the gain values (R ch OUT, B ch OUT), characterised in that the command means (312) is adapted: to establish a limited area in a two-dimensional space defined by coordinates representing said respective count (R ch UDC, B ch UDC); to compare the position defined by said counts (R ch UDC, B ch UDC) with said limited area; and if said position lies outside said limited area to reset one or both of the counts (R ch UDC, B ch UDC) to their previous values before said increment or decrement to bring said position inside said limited area before setting such gain values (R ch OUT, B ch OUT) on the basis of the counts (R ch UDC, B ch UDC). An automatic white-balance controlling apparatus according to claim 1, wherein when incrementing or decrementing said counts (R ch UDC, B ch UDC) and comparing said incremented or decremented counts ((R ch UDC, B ch UDC) with said limited area said command means (312) is adapted to: first increment or decrement a first one of said counts (R ch UDC) and: (a) if said first increment or decrement brings said position outside the limited area to increment or decrement the second of said counts (B ch UDC), and if said position is brought back within the limited area to use both said incremented or decremented counts, without reset, to set said gain values (R ch OUT, B ch OUT), whereas if said position is not brought back within said limited area, to reset said first count to its previous value before the first increment or decrement operation, and if said position is brought back within the limited area using said reset first count (R ch UDC) and incremented or decremented second count (B ch UDC) to set said gain values (R ch OUT, B ch OUT), and if said position is not brought back within the limited area resetting also the second count to its previous value before its increment or decrement, and using both said reset counts (R ch UDC, B ch UDC) to set said gain values (R ch OUT, B ch OUT); or (b) if said first increment or decrement does not bring said position outside said limited area, to increment or decrement the second of the counts (B ch UDC), and if said increment or decrement of the second of the counts (B ch UDC) brings said position outside the limited area to reset the second of said counts (B ch UDC) to its previous value before increment or decrement and to set the gain values (R ch OUT, B ch OUT) on the basis of the incremented or decremented first count (R ch UDC) and the reset second count (B ch UDC); but otherwise to set said gain values (R ch OUT, B ch OUT) on the basis of both increment or decremented counts (R ch UDC, B ch UDC). An automatic white-balance controlling apparatus according to claim 1 or 2, wherein said limited area is defined as lying between maximum and minimum values of each of said counts and such that said first count is within a predetermined range (α) above or below said second count. An automatic white-balance controlling apparatus according to claim 1, 2 or 3, wherein said limited area is hexagonal, a parallelogram, a circle or an ellipse when defined in an orthogonal two-dimensional coordinate space. An automatic white-balance controlling apparatus according to claim 1, 2, 3 or 4, wherein said two-dimensional area is set to remove magenta or green coloring of image signals representing a white image. An automatic white-balance controlling apparatus according to any one of the preceding claims, wherein said apparatus further comprises: a means (617) for selecting either a chasing mode or a storing mode; a means (618) for generating a trigger signal in response to predetermined conditions; and wherein said command means (612) sets the limited area as a first limited area when the chasing mode is selected, and sets the limited area as a second limited area when the storing mode is selected, the first limited area being within the second limited area; and wherein in said storing mode (312) said command means increments or decrements said counts (R ch UDC, B ch UDC) only when the trigger signal is generated, otherwise using non incremented or decremented values of the counts to set said gain values (R ch OUT, B ch OUT). An automatic white-balance controlling apparatus according to any one of the preceding claims, wherein said apparatus further comprises a high-frequency component extracting means (930) for extracting the high-frequency component of a brightness signal from three color signals of said input image signals, and said command means (312) sets the limited area to be larger when the high-frequency component quantity is large and sets the limited area to be smaller when the high-frequency component quantity is small. A video camera including a white-color balance controlling apparatus according to any one of the preceding claims.

Inventors: SUGIURA HIROAKI, SUGIURA, HIROAKI, Sugiura, Hiroaki, Mitsubishi Denki K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1991
Main classification: H04N9
IPC codes: H04N9