Abstract:
An image sensing apparatus according to the invention includes two image sensing portions, a signal processing portion, a first analog switch for applying one of the outputs of the two image sensing portions to the signal processing portion, a digital/analog converter for converting the digital amounts of first and second white balance control signals for the image sensing portions into analog amounts, second analog switches for selecting one of the first and second white balance control signals from the digital/analog converter and applying the selected one to the signal processing portion, and a control portion 11 for controlling the digital/analog converter 12 and the first and second analog switches.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to image sensing apparatuses, and more specifically, to an auto white balance circuit for use in an image sensing apparatus such as a video camera. 
     2. Description of the Background Art 
     When one desires to obtain two image frames at a time using a conventional video camera, one possible method is to select the outputs of two independent video cameras 15, 16 as shown in FIG. 7 and to record them by a VTR 18. 
     According to such a method, however, though white balance is stable with the video cameras being independent, a large system will be necessary to accommodate the two video cameras, which is disadvantageous in terms of cost or portability. Constructing a video camera to have two image sensing portions, one signal processing portion, and a switch portion for switching between the image sensing portions as disclosed in Japanese Patent Laying-Open No. 2-143683 provides a less costly image sensing apparatus. However in this case, when the image sensing portions are switched from one to the other, or when an image obtained from one image sensing portion is entered into a part of an image obtained from the image sensing portion by switching the switch at a high speed a number of times, white balance is gradually disordered, resulting in difficulty in viewing of a reproduced image. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to improve the quality of a reproduced image in an image sensing apparatus having two image sensing portions and one signal processing portion. 
     Another object of the invention is to achieve appropriate white balance in an image sensing apparatus having two image sensing portions and one signal processing portion. 
     A further object of the invention is to conduct quick white balance control in an image sensing apparatus having two image sensing portions and one signal processing portion. 
     In order to achieve the above-stated objects, an image sensing apparatus in accordance with the invention includes a first image sensing portion for sensing the image of an object and outputting a first signal, a second image sensing portion for sensing the image of an object and outputting a second signal, a signal processing device for subjecting the input signal to a prescribed processing for output, a first switch for selecting one of the output first signal and second signal and applying the selected one to the signal processing device, a control signal generation device for generating a first control signal for the signal processing device to conduct a prescribed processing to the first signal and a second control signal for the signal processing device to conduct a prescribed processing to the second signal, a second switch for selecting one of the generated first control signal and second control signal and applying the selected one to the signal processing device, and a controller for controlling the first switch so that the switch selects one of the first signal and the second signal, and controlling the second switch so that the switch selects the first control signal or the second control signal corresponding to the selected first signal or second signal. 
     Thus constructed image sensing apparatus conducts a prescribed processing to a signal output from the switched image sensing portion based on a corresponding control signal, and the quality of a reproduced image is therefore improved. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a system block diagram showing a construction of an image sensing apparatus in accordance with a first embodiment of the invention; 
     FIG. 2 is a system block diagram showing a construction of an image sensing apparatus in accordance with a second embodiment of the invention; 
     FIG. 3 is a flow chart for use in illustration of the content of control executed by the microcomputer shown in FIG. 2; 
     FIG. 4 is a system block diagram showing a construction of an image sensing apparatus in accordance with a third embodiment of the invention; 
     FIG. 5 is a representation showing a control function for an image sensing portion A for use in white balance control executed by the microcomputer shown in FIG. 4; 
     FIG. 6 is a representation showing a control function for an image sensing portion B for use in white balance control executed by the microcomputer shown in FIG. 4; and 
     FIG. 7 is a diagram showing arrangement of two conventional video cameras disposed in parallel. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the invention is illustrated as a block circuit in FIG. 1. In FIG. 1, one of an output signal from an image sensing portion A formed of an image sensing lens 1, a CCD (Charge Coupled Device) 2, and a CDS (Correlating Double Sampling)·AGC (Auto Gain Control) circuit 3, and an output signal from an image sensing portion B formed of an image sensing lens 4, a CCD 5, and a CDS·AGC circuit 6 is selected by an analog switch 7 and input into a signal processing portion 8. 
     In the signal processing portion 8, the signal selected from the image sensing portions A or B is divided into chrominance signal components RGB, from which color difference signals R-Y and B-Y are formed and input into an encoder 9. In the encoder 9, a luminance signal and a chrominance signal are produced and then mixed to form a video signal which is output to a succeeding stage circuit (not shown). 
     In an auto white balance circuit of signal processing type, the RGB signals formed in the signal processing portion 8 are converted into DC voltages in an integrated circuit 10, and input to a microcomputer 11a. The microcomputer 11a subjects each of the converted RGB signals to an A/D conversion, and supplies to a D/A converter 12 white balance control data of a signal level satisfying R=G=B. When the microcomputer 11a selects the image sensing portion A, controlling the switch 7 by its switch control, only a signal from the image sensing portion A is input to the signal processing portion 8. Therefore, only RGB signals from the image sensing portion A are input to the microcomputer 11a through the integrated circuit 10. Based on the RGB signals, the microcomputer 11a decides white balance control values Rcont·A and Bcont·A for the image sensing portion A, and transmits these control values to the D/A converter 12 using three lines, CLK, DATA, and LD. The D/A converter 12 conducts D/A conversion based on the incoming data and generates DC voltages. The DC voltages are supplied to the Rcont and Bcont terminals of the signal processing portion 8 through analog switches 13 and 14. 
     Meanwhile, a signal from the image sensing portion B is stopped by the function of the analog switch 7 and not input to the signal processing portion 8, but white balance control values Rcont·B and Bcont·B for the image sensing portion B are preferably estimated by a proportion calculation based on white balance control values Rcont·A and Bcont·A to the image sensing portion A. 
     The estimated Rcont·B and Bcont·B are, as is the case with the Rcont·A and Bcont·A, transmitted to the D/A converter 12 using three lines, CLK, DATA, and LD from the microcomputer 11a, and converted into DC voltages at the D/A converter 12 for input to the analog switches 13 and 14. At that time, with the analog switches 13 and 14 being set to pass Rcont·A and Bcont·A, Rcont·B and Bcont·B are not applied to the signal processing portion 8. 
     When the microcomputer 11a receives as a switching signal an instruction of switching between the image sensing portions A and B from an external portion (operation key), the microcomputer 11a does not have to make a control to the D/A converter 12, but simply switches the analog switches 7, 13 and 14 by inverting switch control. This is because Rcont·B and Bcont·B from the D/A converter are immediately applied to signal processing circuit 8 through the switches 13 and 14. Thereafter, the RGB signals from the image sensing portion B are input into the microcomputer 11a from the signal processing circuit 8 through the integrated circuit 10 with a delay of the time constant of the integrated circuit 10, and the white balance control values Rcont·B and Bcont·B for the image sensing portion B are determined based on the signals. Then, based on the determined control values Rcont·B and Bcont·B the microcomputer 11a estimates white balance control values Rcont·A and Bcont·A for the image sensing portion A. 
     A high speed control operation of the microcomputer 11a to the switches 7, 13, and 14 permits composing outputs from the image sensing portions A and B. For example, suppose that a part of a picture frame from the image sensing portion A is placed in a picture frame from the image sensing portion B. In this case, if the area of the image sensing portion A is wide enough as compared to the area of the image sensing portion B, RGB signals input to the microcomputer can be considered as signals from the image sensing portion A. 
     As described, the Rcont·A and Bcont·A are determined, the Rcont·B and Bcont·B are estimated, and the respective control values are transmitted to the D/A converter 12. The output of D/A converter 12 is selected by the analog switches 13 and 14 for input to the signal processing portion 8. A high speed switch control by the microcomputer 11a permits the control voltages Rcont·A and Bcont·A to be applied to the portion corresponding to the picture frame of the image sensing portion A, and control voltages Rcont·B nd Bcont·B to be applied to the portion corresponding to the picture frame of the image sensing portion B, thereby achieving stable white balance. 
     A description of a second embodiment of the invention follows in conjunction with FIG. 2. The same reference characters as FIG. 1 denote the same or corresponding portions in FIG. 2. In this embodiment, white balance operation is achieved by an interruption of a vertical pulse VD in synchronization with a vertical synchronizing signal. White balance is set to work only in response to a completion of a certain number of interruptions of the vertical pulse VD, not for every interruption of the vertical pulse VD. For this purpose, a VD counter is provided in a microcomputer 11b in a programming manner. However, for a fixed period immediately after switching of the image sensing portions, white balance operation is conducted even with a smaller number of interruptions of the vertical pulse VD as compared to an usual state. This means time until initiation of the white balance operation is reduced when switching between the image sensing portions. 
     As illustrated by a flow chart in FIG. 3, when an interruption of the vertical pulse VD is made, the VD counter is decremented by 1 in step #5, and a determination whether or not the count value is 0 is made in step #10. If the count value is not 0, the interruption routine is completed (step #50), and if the count value is 0, the operation proceeds to step #15, and white balance operation as described above is conducted. 
     After the auto white balance operation is completed, a determination whether or not a switching signal is externally input from other microcomputers, switches, or the like to the microcomputer 11b is made in step #20. Then, if the switching signal is input, the microcomputer 11b proceeds to step #35, controls the analog switches 7, 13, 14 by its switch control, and switches between the outputs of the image sensing portions A, B and D/A converter 12. Then, in step #45, the value of the VD counter is set to a value for high speed operation, for example, 4VD, thus completing the interruption routine. Thus, the auto white balance operation is conducted at a high speed. 
     If in the above-stated step #20 there is not any switching signal, a determination whether or not white balance operation is presently going on at a high speed is made in the next step #25 and if the high speed operation is going on, a determination whether or not a fixed time period has elapsed is conducted (step #40), and if the fixed time has not yet elapsed, the high speed operation is continued (step #45). If the white balance operation is not going on at a high speed, or it is going on at a high speed but the fixed time period has already run out, the value of the VD counter is set to a value for usual operation 12VD, for example, in step #30, thus completing the interruption routine. Thus, after the elapsed time of 12VD counting value, the auto white balance operation will be resumed. 
     In the above-described operation, after a switching signal from an external portion (for example a key) is input and the image sensing portions are switched from one to the other, time until initiation of the auto white balance operation is reduced by the fixed time period. 
     A description of a third embodiment of the invention follows in conjunction with a block diagram shown in FIG. 4. In FIG. 4, one of an output signal from an image sensing portion A formed of an image sensing lens 1, a CCD 2, and a CDS·AGC circuit 3, and an output signal from an image sensing portion B formed of an image sensing lens 4, a CCD 5, and a CDS·AGC circuit 6 is selected by an analog switch 7 and input to a signal processing portion 8. 
     At the signal processing portion 8, the signal from the image sensing portion is divided into chrominance signal components RGB, from which color difference signals R-Y and B-Y are formed to be input to an encoder 9. At the encoder 9, a luminance signal and a chrominance signal are produced and mixed to form a video signal to be output to a circuit of a succeeding stage (not shown). 
     In an auto white balance circuit of a signal processing type, the RGB signals formed in the signal processing portion 8 are converted into DC voltages at an integrated circuit 10, and input into a microcomputer 11c. The microcomputer 11c subjects them to an A/D conversion, and increases control signals Rcont, Bcont (Rcont and Bcont are DC voltages) to satisfy R=G=B. This operation is called white balance operation. 
     Generally, a control function is decided from control values Rcont and Bcont indoors which are stored in the microcomputer or an external EEPROM 20 at the time of manufacture and control values Rcont and Bcont outdoors (in some cases, in addition to these values, control values Rcont and Bcont under two or three kinds of fluorescent light), and based on the function, the Rcont and Bcont are controlled (see fa in FIG. 5 and fb in FIG. 6). 
     Now, assume that the microcomputer 11c sets the analog switch 7 to select the output of the image sensing portion A by the function of the switch control output signal. At that time, only the signal of the image sensing portion A is input to the signal processing portion 8, and the white balance of the image sensing portion A is made by an auto white balance operation. Now, suppose that the control value of the image sensing portion A in an auto white balance operation resides at point X in FIG. 5. At that time, the following calculation is conducted for estimating the control value of the image sensing portion B to some extent. 
     In FIG. 5, assume that the difference between the control value Rcont outdoors and the control value Rcont indoors is Ra, the difference between the control value Rcont at point X representing the control value at present and the control value Rcont indoors is Rx, while in FIG. 6, the difference between the control value Rcont outdoors of the image sensing portion B and the control value Rcont indoors is Rb, and the difference between the control value Rcont at point Y to be estimated and the control value Rcont indoors is Ry. Assuming that a proportional relation is established between these values, let R=(Rx×Rb)/Ra hold. Similarly, let the control value Bcont at point Y be represented as By=(Bx×Bb) /Ba. Thus, if point X representing the control values of one image sensing portion changes, point Y representing the control values of the other image sensing portion is estimated following the change. 
     When a switching is made from the image sensing portion A to the image sensing portion B, the microcomputer 11c switches its switch control for the analog switch 7, and switches the control values from the Rcont and Bcont to the control values at point Y which has been estimated from the control values of point X. Similarly, when a switching is made from the image sensing portion B to the image sensing portion A, point X is estimated from point Y and the control values are switched accordingly. 
     When the image sensing portions are switched by the above-stated operation, the control values which have been previously estimated are output, and a substantially white balance match state is achieved. 
     As in the foregoing, according to the invention, the moment the image sensing portions are switched from one to the other, white balance is substantially established, and stable white balance is provided when two picture frames are mixed into one. 
     According to the invention, when objects under different conditions are image-sensed by the two image sensing portions, white balance shift created by a switching operation can quickly be corrected, and white balance follows a switching between picture frames with an improved accuracy. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.