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. 14 of the accompanying drawings shows an example based on JP-A-1143485 upon which the precharacterising portion of appended claim 1 is based, of an imaging apparatus such as a color video camera, etc comprising a predecessor automatic white-balance controlling apparatus, which is a lightly-modified apparatus based on the technical concept disclosed in Japanese Patent Publication JP-A-55 136 204 (43872/1979.). In FIG. 14, the apparatus includes a lens 1, an imaging element 2, and a color separating circuit 3. The lens 1 receives an optical image in a 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. 14 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. 15 shows an example of the operation of the microcomputer 12. As shown in FIG. 15, 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 signnal 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 for 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. 26 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. 27 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 a automatic gain controller 116 between the imaging element 102 and the color separating circuit 103 such as disclosed in JP-A-213194. 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. Firstly, 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 breakes, thereby for example the blue sky would appear inclined to white, and the skin of a Japanese would appear white. Secondly, the output value of the comparing circuit would be unstable, if noise were introduced to its input. Namely, the white-balance oscillates. Thirdly, the white-balance tends to be unstable when there is too short a distance to the object. When the distance to the object is long, the objects can usually be within the visual field. Therefore, the integration of the color difference signal can be executed based on the many objects, providing stable white-balance control. However, when the distance to the object is short, the number of objects that fall within the visual field becomes too small, namely only one or the like, thereby the polarity of the output of the comparing circuit tends to reverse. As a result, the white-balance control tends to be unstable. Fourthly, with the use of a zooming lens if the zooming ratio is on the tele-side, the white-balance control would tend to be unstable. This is because; when the zooming ratio is on the wide side and a number of objects can be within the visual field, the integration of the color difference signal can be executed on the basis of the various objects. However, in this case the number of objects to be within the visual field is small, one or the like, thereby the output of the comparing circuit can reverse frequently. 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 it the lightness is insufficient, the output polarity of the comparing circuit would tend to reverse due to the noise. It is therefore the first object of this invention to prevent the divergence of the white-balance control; the second object of this invention is to prevent the vibration generated when controlling the white-balance; the third object of this invention is to cope with the cases when the zooming ratio is on the tele side and when the lightness of the object is insufficient. According to this invention, there is provided an automatic white-balance controlling apparatus for controlling the white-balance of an image formed from three color signals comprising: (a) an integrating means for respectively integrating, over a predetermined period, the values of two types of color difference signal; (b) a comparing means for comparing each of the two integrated values obtained from the integrating means for the predetermined period to a reference value representing an achromatic color so as to produce respective comparison results; (c) a command means for outputting a gain command based on the comparison results of the comparing means; (d) an adjusting means for adjusting the levels of at least two of said color signals in accordance with the gain command from the command means; characterised in that said command means is arranged for: storing, for each of the color difference signals, the comparison results for a series in time of at least two of said predetermined periods; judging, for each of the color difference signals, if the stored comparison results for a respective color difference signal are completely in accordance with each other; and only when the comparison results for a color difference signal are in accordance, executing, for each predetermined period, an up-down count for that color difference signal, the count being incremented or decremented according to the respective comparison results and the gain command providing a command based on the running total of the up-down counting. In such an arrangement, when the up-down counting is performed after comparing the integrated color values, the effects of vibrations hardly affect the gain commanding operation and so the color signal controlling operation, and thus the white-balance control, is stabilized. In this arrangement, apparatus which can meet a variety of requirements can be realized. For instance, if the distance to the object is detected and the number of time-series storing times is set in accordance with the detected distance, a stable white-balance control can be achieved irrespective of the distance to the object. Further, if the zooming position of the lens is detected and the number of time-series storing times is set in accordance with the detected zooming position, a stable white-balance control can be achieved irrespective of the distance to the object. Furthermore, if the number of time-series storing times is set in accordance with the controlling level of the imaging signal (signal obtained by imaging and being the base for the color signal generation), a stable white-balance control can be achieved irrespective of the lightness of the object. Still further, if the high-frequency component of the brightness signal is extracted from the three-color signals and the number of time-series storing times is set in accordance with the amount of the high-frequency component, a stable white-balance control can be achieved irrespective of the amount of the high-frequency component. In addition, a significantly vibration-proof apparatus can be realized in application of the second composition. For example, the compared result at the time point preceding the compared result being stored in time-series is stored by the command means. The command means makes judgment after executing the up-down counting. This judgment is whether the compared result being stored in time-series has changed or not in view of the compared result of the preceding time points. If it is changed, the command means increases the number of time-series storing times, while decreases the same if it is not changed. In this manner, the affect of the temporary fluctuation of the color difference signal on the white-balance control is eliminated, thereby preventing the introduction of noises etc.. 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 the composition of a color imaging apparatus which includes 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 according to the first embodiment of this invention; FIG. 3 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, said color imaging apparatus comprising a distance detecting apparatus; FIG. 4 is a flow diagram showing the operation of the microcomputer according to the second embodiment of this invention; FIG. 5 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, said color imaging apparatus comprising a zooming position detecting circuit; FIG. 6 is a flow diagram showing the operation of the microcomputer according to the third embodiment of this invention; FIG. 7 is a block diagram showing the composition of a color imaging apparatus including an automatic white-balance controlling apparatus according to the fourth embodiment of this invention; FIG. 8 is a flow diagram showing the operation of the microcomputer according to the fourth embodiment of this invention; FIG. 9 is a timing diagram showing the outputs of the D/A converter and the comparing circuit in the fourth embodiment of this invention; FIG. 9 is a timing diagram showing the outputs of the D/A converter and the comparing circuit in the fourth embodiment of this invention; FIG. 10 is a block diagram showing a composition of a color imaging apparatus including an automatic white-balance controlling apparatus according to the fifth embodiment of this invention, said color imaging apparatus comprising an AGC (auto gain controller); FIG. 11 is a flow diagram showing the operation of the microcomputer according to the fifth embodiment of this invention; FIG. 12 is a block diagram showing the composition of a color imaging apparatus including an automatic white balance controlling apparatus according to the sixth embodiment of this invention; FIG. 13 is a flow diagram showing the operation of a microcomputer in an automatic white-balance controlling apparatus according to the sixth embodiment of this invention; FIG. 14 is a block diagram showing a composition of a color imaging apparatus including a conventional automatic white-balance controlling apparatus; FIG. 15 is a flow diagram showing the operation of the conventional microcomputer in FIG. 14; FIG. 16 is a flow diagram showing another operation of the conventional microcomputer in FIG. 15; FIG. 17 is a block diagram showing the composition of the apparatus of FIG. 14 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 212, 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 212 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 212, thereby enabling automatic white-balance control. The microcomputer 312 of this embodiment performs functions as shown in FIG. 2. The operation shown in FIG. 2 starts with an initial setting of RchUDC and BchUDC (S301). Thereafter, the microcomputer 312 shifts to the normal operation and repeats the operation described hereinafter. In the normal operation, the step S308 is executed. In this step S308, RchUDC and BchUDC are output. Namely, RchUDC and BchUDC are dealt directly as RchOUT and BchOUT respectively. After the step S308, the step S328 is executed. In the step S328, the parameter I of the iteration is set to 1. Subsequently, RchCOMP is substituted for the variable R (I) (S329), and BchCOMP is substituted for the variable B (I) (S330). Further, I is increased (S331), and it is judged if a clock pulse is input (S309). Upon input of the clock pulse, the microcomputer 312 judges if I has become N+1 (S332) where N is a predetermined integer. If these conditions are not satisfied, namely if the substitutions of RchCOMP and BchCOMP for the R(I) and B(I) with respect to I being 1 - N have not been completed, the operation returns to the step S329. If the conditions are satisfied, namely if the substitions are completed, the operation shifts to the next step S333. In the step S333, it is judged if all of values of R(I) up to R(N) being stored are equal. If they are equal, the step s334 is executed, and if not, it is shifted to step S335. In this case, the state where all of R(I) up to R(N) being stored are equal signifies that the value of RchCOMP has not been changed during the latest period where the N number of clock pulses are generated. More specifically, it is not a state where RchCOMP is temporarily changed, but a state where uniform tendency continuously appears during a period in which at least N number of clock pulses have been generated. Accordingly, noises contained in RchCOMP can be eliminated, except such strong noises that would continue for a period longer than that during which N number of clock pulses are generated. But such strong noises rarely appear, and even if they do appear they can be eliminated by the operations of other parts. Therefore, in the step S334, judgment is made as is whether the value of RchCOMP is H or L , and the up-down counting is executed depending on the judged result. But since all of R (I) are the same, the judgment in the step S334 can be executed by any of N number of R(I). If the value is judged as being H, step S303 concerning the decrement of RchUDC is executed, while if it is judged as being L, step S304 concerning the increment of RchUDC is executed. In both cases, thereafter, it is shifted to step S335. In the step S335, it is judged if all the N number of B(I) being stored are the same. As a result of this judgment, if they are judged as being the same, the step S336 is executed, and if not, the sequence returns to the step S308. In this case, the state where all N number of B(I) being stored are equal signifies that the value of BchCOMP has not been changed during the latest period where N number of the clock pulses are generated. More specifically, it is not a state where BchCOMP is temporarily changed, but a state where a uniform tendency continuously appears during a period in which at least N number of clock pulses are generated. Accordingly, noises contained in RchCOMP can be eliminated, except such strong noises that would continue for a period longer than that during which N number of clock pulses are generated. But such strong noises rarely appear, and even if they do appear they can be eliminated by the operations of other parts. In the step S336, it is judged if the value of BchCOMP is the H or L, and the up-down counting is executed in accordance with the judged result. But since all of the B(I) are the same, any one of the B(I) can be used for the judgment. If the value is judged as being the H, the step S306 for the increment of BchUDC is executed, and if it is judged as L , the step S307 for the decrement of RchUDC is executed. In both cases, thereafter the operation is returned to the step S308. When the microcomputer 312 operates in such a manner as mentioned above, the up-down counting with respect to RchUDC or BchUDC would not be executed unless RchCOMP or BchCOMP is constant for N clock periods. Accordingly, the fluctuation of RchCOMP or BchCOMP for a short time will be eliminated from the white-balance controlling operation, thereby reducing the so-called controlling vibration. Namely, more stable operation is realized. II. SECOND EMBODIMENT FIG. 3 shows a color imaging apparatus comprising an automatic white-balance controlling circuit according to the second embodiment of this invention. The composition of the apparatus in FIG. 3 is substantially the same as that of the first embodiment, except for the composition of the microcomputer 412 and the addition of a distance detecting device in the vicinity of the lens 401. Namely, the composition of the microcomputer 412 is such as executing the operation represented in FIG. 4, not FIG. 2. And the distance detecting device 416 measures the distance from the lens 401 to the object. In FIG. 4, the operation starts with the initial setting of RchUDC and BchUDC (S401). Thereafter, the microcomputer 412 shifts to the normal operation to execute the following processes. In the normal operation, firstly a step S408 is executed. In the step S408, RchUDC and BchUDC are output, in the same manner as the step S308 in the second embodiment. Next, in advance of the execution of a step S428, being the similar operation to the step S328, steps S437 and S438 being the characteristic steps of this embodiment are executed. Namely, the microcomputer 412 receives the distance data from the lens 401 to the object sent from the distance detecting device 416 (S437), and determines the value N from the received distance (S437). Then, the steps S429, S430, S431, S409, S432, S433, S434, S403, S404, S435, S436, S406, S407, corresponding to the steps in the second embodiment, S329, S330, S331, S309, S332, S333, S334, S303, S304, S335, S336, S306, S307, respectively, are executed. Accordingly, in this embodiment, the same function is generated as in the first embodiment, thereby providing similar effects. In addition, since the value of N is changed in accordance with the distance from the object to the lens, any unstability of the white-balance controlling due to the distance can be prevented. For instance, if the distance is small, it is expected that RchCOMP, BchCOMP frequently change in accordance with the state change of the object. But in this case, if the operation of the apparatus in FIG. 4 is designed to set the N to a relatively large value, the undesirable influences of the frequent change can be eliminated and a stable white-balance controlling is realized. Also, any method to determined the N, e.g. by using a change table or by executing a linear transformation can be adopted. Further, for detecting the distance from the lens to the object, such methods as detecting the focus position of the lens 401, or using a separate distance detecting apparatus, can be adopted. III. THIRD EMBODIMENT FIG. 5 shows an example of a color imaging apparatus comprising an automatic white-balance controlling circuit according to the third embodiment of this invention. The composition of the apparatus in FIG. 5 is substantially the same as that of the second embodiment, except for the composition of the microcomputer 512 and a zoom position detecting device 516 provided the in vicinity of the lens 501. Namely, the microcomputer 512 is designed to execute the operation represented in FIG. 6, not FIG. 4, and the zoom position detecting apparatus 516 measures the zooming position of the lens 501. The differences of the operation shown in FIG. 6 from those in FIG. 4 lie in the steps S537 and S538, and other corresponding operations are the same. In the step S537, the microcomputer 512 receives the zooming position data of the lens 501, and in the step 5538 the microcomputer 512 determines the value N from the received zooming position. Accordingly, in this embodiment, substantially the same operation as in the first embodiment is executed to provide substantially the same effects. In addition, since the value of N is changed in accordance with the zooming position, no instability of the white-balance controlling could occur irrespective of whether the zooming position is tele-side or wide-side. For instance, by setting the N to be larger in the case of tele-side and to be smaller in the case of wide-side respectively, the undesirable influence of the change of RchCOMP and BchCOMP generated with a frequency in accordance with the zooming position on the stability of the white-balance controlling can be prevented. Thus, a stable white-balance controlling operation can be attained, eliminating the effects of the frequent changes. IV. FOURTH EMBODIMENT FIG. 7 shows an embodiment of the color imaging apparatus comprising an automatic white-balance controlling apparatus according to the fourth embodiment of this invention. Although the basic composition of the shown apparatus is substantially the same as that in FIG. 1, the differences lie in the microcomputer 712 being composed of hard logic and operating differently from the microcomputer 212 in FIG. 1. The microcomputer 712 comprises: a N-times memory 719 for memorizing RchCOMP in number of N in accordance with the clock pulses; a N-times memory 720 for memorizing BchCOMP in number of N in accordance with the clock pulses; a N-times data memory 721 for judging the concordance of the contents in the N-times memory 720; a judging section 723 for judging the direction of the counting (increment or decrement); a N-value determining section 724 for determining the N value; an output value determining section 725 for outputting RchUDC being the result of the up-down counting with regard to RchCOMP; an output value determining section 726 for outputting BchUDC being the result of the up-down counting with regard to BchCOMP. Next, the operation of the microcomputer 712 will now be described. FIG. 8 shows the flow of this operation. Steps constituting the operations in FIG. 8 correspond to those in FIG. 2. For example, as the step S701 corresponds to the step S301 in FIG. 2, the steps in both cases having the same of lower two digits operate in the same manner. But the difference of this embodiment from the first embodiment lie in steps S746-S749 which will be described hereinafter. Firstly, the up-down counting with respect to RchUDC and BchUDC are executed in the step 5746. In the step S746, it is judged if R(0) and RchUDC, and B(0) and BchUDC are the same respectively. Since the cases where RchCOMP and BchCOMP are unstable are eliminated in the steps S733 and S735, RchUDC and BchUDC become equal to the R(1) and B(1) respectively. In consequence, in the step S746, the R(1) is substituted for RchUDC, and the B(1) is substituted for BchUDC. In the step S746, if it is judged that both of the equations are effective, Nsmall is substituted for N (S747), while if it is judged as not effective, Nlarge is substituted for N (S748). After the steps S747 or S748, R(1) is substituted for R(0) while B(0) is substituted for B(O) (S749), and thereafter the operation is shifted to the step S708. A predetermined initial value is-already set for R(0) and B(0) in the step S701. The significance of the above-mentioned operation can be described as follows: As clearly understood from the operation in the step S749, the R(0) and B(0) stand for RchCOMP and BchCOMP after the execution of the up-down counting with regard to RchCOMP and BchCOMP at the last time. Accordingly, the operation in the step S746 is for judging if the RchCOMP or the BchCOMP have changed from the viewpoint of preceding up-down counting with regard to BchCOMP. Namely, the N is set to a smaller value when RchCOMP or BchCOMP is expected to change in a relatively short term, while the N is set to a larger value when that is not expected to change for a long term. By setting the value of N as mentioned-above, the deviations of RchCOMP or BchCOMP arising in a short term due to e.g. noises can be eliminated to provide a more stable white-balance controlling. Of course, the same effects as obtained by the first embodiment can be rendered in this embodiment. FIGS 9 and 9B show examples of the operation where Nsmall = 2, Nlarge = 4. In the case of FIG. 9, the average voltage of the R-Y signal for one screen is significantly lower than the reference voltage, requiring an to increase in the R signal level. In FIG. 16A, only RchCOMP and RchUDC are shown. In such a case, the value of RchCOMP would be L for a long term. Since the condition R(0) = R(1) becomes effective during a period τ1 where the value of the RchCOMP does not change, a step S747 will be executed if the condition B(0) = B(1) is effective. As a result, it is set to N = 2. During this period, RchUDC will be changed every two cycles of the clock pulses. In the next period τ2, since the value of RchCOMP is changed, the condition R(0) = R(1) becomes ineffective and a step S748 is executed. Then, the value of N is changed to N = 4. As a result, during the period τ3 until the execution of the next step S746, the clock pulses will continue for a term of four cycles of the clock pulses. During the period τ3, once the value of RchCOMP is changed, and after the starting of the period, the value H of RchCOMP when receiving the fourth clock pulse is different from the value L at receiving the first clock pulse. Accordingly, since the conditional formula of the step S746 can not be satisfied, a step S748 is executed. Namely, the successive period τ4 will also be a period corresponding to four clock pulses. During the period τ4, once the value of RchCOMP is changed, and after the starting of the period, the value L of RchCOMP when receiving the fourth clock pulse is different from the value H when receiving the first clock pulse. Accordingly, since the conditional formula of the step S746 can not be satisfied, a step S748 is executed. Namely, the successive period τ 5 will also be a period corresponding to four clock pulses. During the period 5, if the values of both RchCOMP and BchCOMP have not been changed, the step S747 is executed to set the value of N to N = 2. Thus, the controlling vibrations caused by other factors than the color temperature change, for example, can be eliminated. Next, the case of FIG. 9 will now be described. This is a case where the average value of the R-Y signal for one screen has significantly changed due to the change of the color temperature of the object. In this case, the value of N is changed from 2 to 4 reflecting the change, and thereafter changed from 4 to 2 reflecting the termination of the change. Thus, according to this embodiment, controlling vibrations caused by noises etc. can be prevented so as to provide a more stable white-balance controlling operation. Namely, the color difference signal would scarcely vary by any factors other than the color temperature difference of the illumninating light of the object. V. FIFTH EMBODIMENT FIG. 10 shows a color imaging apparatus comprising an automatic white-balance controlling circuit according to the fifth embodiment of this invention. Although the composition is substantially the same as in the first embodiment, the differences lie in a microcomputer 812, an automatic gain controlling circuit 816 coupled between a imaging element 812 and the color separating circuit 803, and an AID converting circuit 827 coupled between the automatic gain controlling circuit 816 and the microcomputer 812. Namely, the composition of the microcomputer 812 is aimed at executing the operation represented in FIG. 11 and not in FIG. 2, and the imaging signal output from the imaging element 802 is gain-controlled by the automatic gain controlling circuit 816 and the gain data is supplied to the A/D converting circuit 827. FIG. 11 shows an operating flow of the microcomputer 812. The steps shown in FIG. 11 correspond to those in FIG. 2. Namely, the steps having the same lower two digits perform the same function. The difference of this embodiment from the second embodiment lies in that the N is set in accordance with the gain controlling voltage which is the gain of the automatic gain controlling circuit 816. Specifically, after the execution of the step S808, the microcomputer 812 receives the gain controlling voltage (S850), and sets N in accordance with the received result (S851). In this manner, a stable white-balance control can be achieved by preventing the controlling vibrations even when the lightness of the object is insufficient and the gain of the automatic gain controlling circuit 816 is high, namely, RchCOMP and BchCOMP tend to be unstable. Further, if the lightness of the object is sufficient, a response property for quickly following the change of the lightness of the light source for illuminating the object can be obtained. VI. SIXTH EMBODIMENT FIG. 12 shows a color imaging apparatus comprising an automatic white-balance controlling circuit according to the sixth 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 FIG. 13, not FIG. 2. Further, in this embodiement 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; a integrating circuit 931 for integrating the output of the wave-detecting circuit 930 and supplying the integrated data to the microcomputer 912. FIG. 23 shows an operation of the automatic white-balance controlling apparatus according to the sixth embodiment of this invention, particularly the flow of the microcomputer. In this embodiment, an amount of the high-frequency component is input after the outputs of the RchUDC and the BchUDC (S1052), and the value of N is determined in accordance with this amount (S1054). Accordingly, the white-balance controlling speed can be highly assured by decreasing the value of N when the amount of the high-frequency component is large, while it is reduced by increasing the same when the amount is small. This concept is based on the fact that the amount of the high-frequency component is typically large when the color temperature is high, requiring a high-speed white-balance controlling operation. Accordingly, in this embodiment, it is possible to perform the white-balance controlling operation in accordance with the change of the object so as to prevent the deviation of the white-balance control.

Claims: An automatic white-balance controlling apparatus for controlling the white-balance of an image formed from three color signals (R,G,B) comprising: (a) an integrating means (208,209) for respectively integrating, over a predetermined period, the values of two types of color difference signal (R-Y;B-Y); (b) a comparing means (210,211) for comparing each of the two integrated values obtained from the integrating means (208,209) for the predetermined period to a reference value (Vref) representing an achromatic color so as to produce respective comparison results; (c) a command means for outputting a gain command based on the comparison results of the comparing means (210,211); (d) an adjusting means (204,205) for adjusting the levels of at least two of said color signals (R,G,B) in accordance with the gain command from the command means; characterised in that said command means (312, 712) is arranged for: storing, for each of the color difference signals, the comparison results for a series in time of at least two of said predetermined periods; judging, for each of the color difference signals, if the stored comparison results for a respective color difference signal are completely in accordance with each other; and only when the comparison results for a color difference signal are in accordance over said at least two of said predetermined periods, executing, for each predetermined period, an up-down count for that color difference signal (R-Y,B-Y), the count being incremented or decremented according to the respective comparison results and the gain command providing a command based on the running total of the up-down counting. An automatic white-balance controlling apparatus according to claim 1, wherein said apparatus further comprises a distance detecting means (416) for detecting the distance from an object to a lens (401) of an associated optical system providing the three color signals (R,G,B) forming an image of said object, and the number of said predetermined periods for which comparison results are stored in said command means (412) is set in accordance with the detected distance. An automatic white-balance controlling apparatus according to claim 1, wherein said apparatus further comprises a zooming position detecting means (516) for detecting the zooming position of a lens (501) of an associated optical system providing the three color signals (R,G,B), and the number of said predetermined periods for which comparison results are stored in the command means (512) are set depending on the zooming position. An automatic white-balance controlling apparatus according to claim 1, 2 or 3, wherein said command means (712) comprises means for: storing (719,720) a new comparison result for the predetermined period following the comparison results previously stored for the time series; judging (723) if the new comparison result has any change relative to the previous comparison results; and increasing the number of said predetermined periods for which comparison results are stored when there is any change, while decreasing it when unchanged. An automatic white-color balance controlling apparatus according to any preceding claim, wherein said apparatus further comprises a level controlling means (816) capable of variably adjusting the level of a signal from which the three color signals (R,G,B) originate, and the number of predetermined periods in time series of the command means is set with reference to said level controlling means. An automatic white-color balance controlling apparatus according to any preceding claim, wherein said apparatus further comprises a high-frequency component extracting means (929) for extracting the high-frequency component of the brightness signal from the three color signals (R,G,B), and the number of predetermined periods in time series of said command means (912) is set by reference 5 to said extracting means (929). An automatic white-balance controlling apparatus according to any preceding claim wherein the number of predetermined periods in time series of said command means is determined so as to substantially prevent the effects of noise present in the color signals on the judging result, over a long period of time. 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, c/o Mitsubishi Denki K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1991
Main classification: H04N9
IPC codes: H04N9