Video camera

Abstract: A video camera wherein the number of times that an output signal from a swing sensor reaches or exceeds a threshold value is counted, and based on the resulting counted value, the video camera is judged as being in a photographing state or not, the recording operation being stopped if the video camera is judged to be not in a photographing state. When the counted value has reached a predetermined value, the operator of the video camera is notified of a faulty photographing condition. Furthermore, it is judged, based on the detection result of the swing sensor, whether the video camera is in a misrecording operation; if the video camera is judged to be in a misrecording operation, the recording operation is stopped, and then, the recording tape is rewound to the start position of the misrecording.

Description: The present invention relates to a video camera (a VTR provided with a camera) for recording an object captured by the camera. In the accompanying drawings Fig. 1 is a block diagram showing an essential configuration of a prior art video camera disclosed in Japanese Patent Unexamined Publication No.4-90273. A power switch 24 used to cut off power is connected to a power supply circuit 25. Supplied to a power cutoff circuit 27 are: a contact detection signal 32 from a contact detection circuit 31 that detects the opening, after the closure, of a contact switch provided on the grip of the video camera; a swing detection signal 29 from a swing detection circuit 30 that detects a swinging motion of the video camera; and a record ON signal 28 that is output during a recording operation. The power cutoff circuit 27 outputs a power cutoff signal 26 which is supplied to the power supply circuit 25. The operation of the above video camera will be described below. When the contact switch provided on the grip of the video camera is closed by the pressure of the hand holding the grip, the contact detection circuit 31 does not output the contact detection signal 32. The contact detection signal 32 is output and supplied to the power cutoff circuit 27 when the pressure is released from the contact switch. The swing detection circuit 30 detects a swinging motion of the video camera by means of an angular velocity sensor (not shown) built in the video camera, and upon detection of the swinging motion, supplies the swing detection signal 29 to the power cutoff circuit 27. The video camera has a construction such as shown in Fig. 2. When an operator is carrying the video camera VC by gripping a handle H in his hand, the video camera VC is lightly swung back and forth as he walks. This swinging motion is detected by the angular velocity sensor built in the video camera. When the video camera is in a recording operation, the record ON signal 28 that signifies that the video camera is recording is supplied to the power cutoff circuit 27. While the recording ON signal 28 is being supplied to the power cutoff circuit 27, if the application of the swing detection signal 29 continues for a predetermined length of time (for example, one minute), the power cutoff signal 26 is supplied to the power supply circuit 25 to cut off the power of the video camera VC. In recent years, video cameras have been drastically reduced both in size and weight, and video cameras without such a carrying handle as shown in Fig. 2 are a general trend. Furthermore, video cameras generally known as single-hand video movie cameras are so designed that, when not photographing, the operator carries the video camera with his hand placed on the grip which is usually used to hold the camera during photographing, or the video camera is carried in a shoulder bag or the like or on a shoulder strap attached to the camera. Thus, as the video camera becomes smaller and lighter, the method of carrying it has been changing. Since the video cameras that can be carried with the operator's hand placed on the grip are not provided with a carrying handle, no such signal as supplied from the contact detection circuit described above can be obtained to cut off power when the video camera is being carried. Furthermore, when the video camera is carried in a shoulder bag or the like, the swinging directions of the video camera are not determined, and the amount of its swinging movement is usually smaller than when it is carried with its grip held by hand, so that the level of the output signal of the angular velocity sensor becomes smaller. When it is carried on a shoulder strap, the swinging directions of the video camera are not determined, as in the above case; therefore, it is difficult to judge whether the video camera is being operated for photographing a scene or is just being carried. Accordingly, recent video cameras without a carrying handle have the problem that when the camera is carried around while being mistakenly left in a record mode, the recording operation is allowed to continue and mis-recording cannot be prevented. Another problem is that if the video camera is subjected to heavy shaking while photographing a scene, thus adversely affecting the quality of the captured image,the operator may not notice the adverse photographing condition and may continue the photographing operation as he is so absorbed in photographing the scene. There is the further problem that once mis-recording is done, the mis-recorded portions remain recorded on tape which, when replayed, reproduces a mis-recorded, jarring image here and there. DE-A-41 35 643 discloses a video camera in accordance with the precharacterising portion of claim 1 in which the number of transitions from a tilted state to a level state (as measured by a mercury tilt switch) within a predetermined period are measured and if a predetermined number is exceeded, recording is stopped on the assumption that camera shake is too bad for recording to be intentional. It is an object of the invention to provide a video camera that is capable of preventing mis-recording by stopping the recording operation when the video camera is carried around while being left in a record mode due to mis-operation on the side of the operator. It is another object of the invention to provide a video camera that can notify the operator of a faulty photographing condition when the photographing of a scene is continued while shaking the video camera. It is a further object of the invention to provide a video camera in which when mis-recording is done, the mis-recorded portions will not remain recorded on tape. According to the present invention, there is provided a video camera incorporating a swing sensor for detecting a swinging motion of the camera body and preventing an erroneous recording operation on the basis of an output signal from the swing sensor, comprising: comparing means for comparing the output signal of the swing sensor with a threshold value; counting means for counting the number of times that the output signal reaches or goes beyond the threshold value in a predetermined interval; judging means for judging whether the video camera is correctly in a photographing state or not on the basis of a counted value supplied from said counting means; and means for stopping the recording operation or notifying the camera operator when it is judged that the video camera is not correctly in a photographing state; characterised in that: said swing sensor is an angular velocity sensor for sending positive and negative angular velocities; and said judging means judges whether or not the camera is correctly in a photographing state by finding, for a plurality of consecutive previous intervals, the number of those intervals in which the number of times the threshold value was exceeded by the sensed positive or negative angular velocity exceeds a preset value. By "not correctly in a photographing state", is meant that the camera is just being carried, rather than used for photographing, or is being shaken too much to give a good picture even though the operator is trying to take a picture, which could result in mis-recording. For instance, when the photographing of a scene is continued while heavily shaking the video camera, if the captured image condition is bad, such condition is notified to the operator to alert him to the possibility of mis-recording; therefore the photographing of a scene can be readily stopped when the photographing condition has worsened. In one embodiment, when mis-recording is done under faulty photographing conditions, the recording tape is re-wound to the mis-recording start position; therefore, the mis-recorded portions of the object photographed under such faulty conditions will not remain recorded on the tape, thus recording only objects that have been intentionally photographed by the operator under proper photographing conditions. The invention will be further described by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a block diagram showing an essential configuration of a prior art video camera. Fig. 2 is a schematic perspective view of the prior art video camera. Fig. 3 is a schematic perspective view of a video camera according to the invention. Fig. 4 is a block diagram showing an essential configuration of one embodiment of the video camera according to the invention. Fig. 5 is a flowchart showing a control procedure for a microcomputer shown in Fig. 4. Fig. 6 is a diagram showing the waveform of an angular velocity signal when the video camera is not in a photographing state. Fig. 7 is a diagram for explaining the variation of a level difference counted value when the video camera is not in a photographing state. Fig. 8 is a diagram showing the waveform of an angular velocity signal when the video camera is in a photographing state. Fig. 9 is a diagram for explaining the variation of a level difference counted value when the video camera is in a photographing state. Fig. 10 is a diagram showing the waveform of an angular velocity signal when the video camera is in a tilting photographing state. Fig. 11 is a diagram for explaining the variation of a counted value of positive level difference for the angular velocity signal when the video camera is in a tilting photographing state. Fig. 12 is a diagram for explaining the variation of a counted value of negative level difference for the angular velocity signal when the video camera is in a tilting photographing state. Fig. 13 is a flowchart showing another control procedure for the microcomputer shown in Fig. 4. Fig. 14 is a block diagram of a circuit for compensating for variation in the angular velocity signal due to circuit elements. Fig. 15 is a block diagram of a circuit for compensating for variation in the angular velocity signal due to circuit elements. Fig. 16 is a block diagram showing an essential configuration of another embodiment of the video camera according to the invention. Fig. 17(a) is part of a flowchart showing a control procedure for a microcomputer shown in Fig. 16. Fig. 17(b) is part of a flowchart showing a control procedure for a microcomputer shown in Fig. 16. Fig. 17(c) is part of a flowchart showing a control procedure for a microcomputer shown in Fig. 16. Fig. 18 is a diagram showing the waveform of an angular velocity signal output from an angular velocity sensor in pitching directions. Fig. 19 is a diagram showing the waveform of an angular velocity signal output from an angular velocity sensor in yawing directions. Fig. 20 is a diagram for explaining a counted value of positive level difference for the angular velocity signal in pitching directions. Fig. 21 is a diagram for explaining a counted value of negative level difference for the angular velocity signal in pitching directions. Fig. 22 is a diagram for explaining a counted value of positive level difference for the angular velocity signal in yawing directions. Fig. 23 is a diagram for explaining a counted value of negative level difference for the angular velocity signal in pitching directions. Fig. 24 is a block diagram showing an essential configuration of a further embodiment of the video camera according to the invention. Fig. 25 is a block diagram showing an essential configuration of a still further embodiment of the video camera according to the invention. Fig. 26 is a flowchart showing a control procedure for a microcomputer shown in Fig. 25. Fig. 27 is a flowchart showing another control procedure for the microcomputer shown in Fig. 25. Fig. 28 is a flowchart showing still another control procedure for the microcomputer shown in Fig. 25. The preferred embodiments of the invention will be described in detail below with reference to the accompanying drawings. Fig. 3 is a schematic side view of a video camera according to the invention. At the front of the video camera VC is a lens LNS through which light from an object is admitted into the video camera VC. A viewfinder VF is provided on the right-hand side of the back of the video camera VC. Centrally placed on the right-hand side of the video camera VC is a grip G. The video camera VC contains a built-in angular velocity sensor (not shown) which acts as a swing sensor. Fig. 4 is a block diagram showing an essential configuration of the video camera according to a first embodiment of the invention. An angular velocity sensor 1 detects the swinging motion of the video camera in the arrow directions shown in Fig. 3, that is, in pitching directions. An output signal from the angular velocity sensor 1 is fed to a microcomputer 3 via an amplifier 2, and a control signal from the microcomputer 3 is supplied to a system microcomputer 4. The microcomputer 3 converts an analog signal output from the amplifier 2 into a digital signal, counts the number of signals greater than a predetermined angular velocity in a predetermined time, and determines whether the resulting counted value has exceeded a predetermined value. The system microcomputer 4 that controls the system of the video camera VC is supplied with signals from a key array 7 provided on the video camera for operation. A control signal from the system microcomputer 4 is supplied to a power supply circuit 11, a video processing circuit 5, and a character appending circuit 8. The light admitted through the lens LNS is converted by a camera circuit 10 into electrical signals. A video signal output from the camera circuit 10 is supplied to the video processing circuit 5, and a video signal output from the video processing circuit 5 is given to the character appending circuit 8 which appends character data to the video signal. A video signal output from the character appending circuit 8 is given to the viewfinder VF. The video signal output from the video processing circuit 5 is also supplied to a record/playback circuit 6 which records the video signal on a recording tape; the record/playback circuit 6 also plays back a video signal from the recording tape and supplies the playback video signal to the video processing circuit 5. The operation of the video camera of the above configuration will be described below with reference to the flowchart of Fig. 5 which shows a control procedures for the microcomputer 3. An angular velocity signal output from the angular velocity sensor 1 and amplified by the amplifier 2 is supplied to the microcomputer 3 where the signal is input to an analog/digital converter (not shown) internal to the microcomputer 3. The microcomputer 3 performs mathematical operations on the input angular velocity signal to determine whether the currently input angular velocity signal is one that has been generated from a photographing action. More specifically, when the angular velocity signal from the angular velocity sensor 1 is input to the microcomputer 3, the microcomputer 3 calculates a level difference VA between the input value and a reference value (S1). Next, "1" is counted if the calculated level difference V A is equal to or greater than a threshold value V TH , and "0" is counted if it is smaller than the threshold value V TH (S2). The "1" and "0" are counted at the sampling timing of the angular velocity signal on both the positive and negative sides of the signal (S3). It is then determined whether the number of times has reached a predetermined number of times, L, in a predetermined time (S4), and when the number of times, L, is reached, a counted value S is obtained for the L times (S5). As each counted value S is obtained for the L times, the counted value S is fed to a memory (not shown) internal to the microcomputer 3; each time it is fed to the memory, the counted value S is written at a different address R N in the memory (S6). For the past M times addresses R N at which the counted values S have been written, the number of addresses R N that are greater than a predetermined value GM is calculated to obtain an address number H (57). Next, the address number H is compared with an integer T for size (S8); if the address number H is greater than the integer T, it is determined that the condition does not represent a photographing action (S9), and if the address number H is not greater than the integer T, then it is determined that the condition represents a photographing action (S10). More specifically, when the video camera is being carried around, the video camera is heavily swinging back and forth, causing the angular velocity signal to go beyond the threshold value V TH on both the positive and negative sides of the signal as shown in Fig. 6. Accordingly, the counted value obtained by counting the angular velocity signal where it exceeds the threshold value V TH varies as shown in Fig. 7 which plots the counted value for the angular velocity signal shown in Fig. 6. On the other hand, the swinging motion of the video camera in a photographing state is smaller than that caused by a carrying action, so that the angular velocity signal stays inside of the threshold value V TH most of the time, as shown in Fig. 8. Accordingly, the counted value obtained by counting the angular velocity signal where it exceeds the threshold value V TH varies as shown in Fig. 9 which plots the counted value for the angular velocity signal shown in Fig. 8. Therefore, whether the video camera is in a photographing state or not can be accurately determined by counting the number of times that the counted value S for the angular velocity signal exceeding the threshold value V TH in a predetermined time has exceeded the predetermined value GM. Next, we will explain how the constants, i.e., the threshold value V TH , the number of times, L, the number, M, of past data items written in the memory, the predetermined value GM, and the integer T, are selected. Since the angular velocity signal during a photographing action is smaller than the angular velocity signal being output when the video camera is being carried around (see Fig. 8), the threshold value V TH is selected so that most of the angular velocity signal during a photographing action stays inside of the threshold value V TH . On the other hand, when the video camera is being carried around, the swinging of the video camera is mostly caused by the walking action of the operator; therefore, it is effective if the number of times, L, i.e. the time in which the angular velocity signal is counted, is selected equal to 1/2 of the swinging cycle of walking. As for the number, M, of past data items, a larger number would reduce the possibility of misjudgement, but would in turn require a longer time to judge whether the condition represents a photographing action or not. Therefore, when Sampling time x number of counts L = 1 second the number, M, of past data items is selected experimentally as Data number M = 5 to 10 The predetermined value GM and the integer T are determined experimentally, since the counted value S is greatly influenced by the gain of the amplifier 2 and the weight of the video camera. For example, when the sensitivity of the angular velocity sensor is 0.8 mv · DEG/sec., the gain of the amplifier 2 is x 120, the weight of the video camera is 600 g, and the sampling rate per second is 480, then the predetermined value GM = 100 to 200 and the integer T = 2 to 3 would be appropriate. The microcomputer 3 thus judges whether the video camera is in a photographing state or not, and supplies the signal representing the result of the judgement to the system microcomputer 4. When the signal given from the microcomputer 3 indicates that the video camera is operating in a record mode but is not in a photographing state, the system microcomputer 4 controls the power supply circuit 11 to cut off the power of the video camera to stop the recording operation. Thus, when the video camera is carried around while being left in a record mode, the recording operation automatically stops to prevent misrecording. In the above-described procedure, the absolute value of the amplitude of the angular velocity signal, that is, the angular velocity signal that gives an input value equal to or greater than the threshold value V TH , has been counted. However, when photographing a scene with the video camera being continuously tilted upward (tilting photographing), the angular velocity signal varies as shown in Fig. 10; therefore, with the above-described method of counting, it is difficult to distinguish the swinging motion of the video camera during a tilting photographing action from that of the video camera during a carrying action on the basis of the counted value of the angular velocity signal. That is, the angular velocity signal during a tilting photographing action stays above the threshold value V TH , as shown in Fig. 10, until the photographing action is completed. As a result, the counted values S taken at the sampling rate L for the angular velocity signal exceeding the threshold value V TH exceed the predetermined value GM on the positive side of the signal, as shown in Figs. 11 and 12 that are given in contrast with Fig. 10, thus making the tilting action indistinguishable from the carrying action. Therefore, in the case of a tilting photographing action, the microcomputer 3 performs mathematical operations on the input angular velocity signal in accordance with the flowchart of Fig. 13, which shows another control procedure for the microcomputer 3, to determine whether the currently input angular velocity signal is one that has been generated from a photographing action. When an angular velocity signal, such as shown in Fig. 10, is generated from a tilting photographing action and is input to the microcomputer 3, the microcomputer 3 calculates a level difference V A between the input value and the reference value (S20). It is then determined whether the calculated level difference V A is for the angular velocity signal on the positive side or the angular velocity signal on the negative side (S21). When the level difference V A is for the positive side signal, if the level difference V A is equal to or greater than the threshold value V TH , "1" is counted, and if it is smaller than the threshold value V TH , "0" is counted, while for the level difference -V A for the angular velocity signal on the negative side, "0" is counted (S22). On the other hand, when the level difference is determined as -V A which is for the angular velocity signal on the negative side, if the level difference -V A is equal to or greater than the threshold value V TH , "1" is counted, and if it is smaller than the threshold value V TH , "0" is counted, while for the level difference V A for the angular velocity signal on the positive side, "0" is counted (S23). The "1" and "0" are counted at the sampling timing of the angular velocity signal on the positive side and of the angular velocity signal on the negative side (S24). It is then determined whether the number of times has reached a predetermined number of times, L, in a predetermined time (S25), and when the number of counts is reached L times, a counted value S P is obtained for the L times of the angular velocity signal on the positive side, and a counted value S N obtained for the L times of the angular velocity signal on the negative side (S26). Each time the number of times reaches L, the counted values S P and S N are fed to a memory (not shown) in the microcomputer 3, and each counted value S P is written at a different designated address R PN and each counted value S N written at a different designated address R NN in the memory (S27). For the past M times addresses R PN , R NN at which the counted values S P , S N have been written, the numbers of addresses R PN , R NN that are greater than the predetermined value GM are calculated to obtain address numbers H P and H N , respectively (S28). Next, the address numbers H P and H N are respectively compared with the integer T for size (S29); if both of the address numbers H P and H N are greater than the integer T, it is determined that the condition does not represent a photographing action (S30), and if one or other of the address numbers H P and H N is not greater than the integer T, then it is determined that the condition represents a tilting photographing action (S31). More specifically, when the video camera is being carried around, the video camera is swinging repeatedly in both pitching directions, whereas during a tilting photographing action, the video camera is moved in one pitching direction only; based on this, it is judged whether the video camera is just being carried around or being operated in a tilting photographing state. The microcomputer 3 thus judges whether the video camera is in a tilting photographing state or not, and supplies the signal representing the result of the judgement to the system microcomputer 4. As previously described, when the signal given from the microcomputer 3 indicates that the video camera is operating in a record mode but is not in a tilting photographing state, the system microcomputer 4 controls the power supply circuit 11 to cut off the power of the video camera to stop the recording operation, thus preventing misrecording. When counting the angular velocity signal from the angular velocity sensor in the manner described above, the angular velocity signal at zero angular velocity is taken as the reference value. however, the voltage of the angular velocity signal is not always constant because of variations of circuit elements, etc. Fig. 14 is a block diagram of a circuit for compensating for voltage variations of the angular velocity signal. A reference voltage V ref is given to the angular velocity sensor 1. The angular velocity signal output from the angular velocity sensor 1 is applied via a coupling capacitor 13 to a non-inverting input terminal + of an operational amplifier 14. The reference voltage V ref is also applied via a biasing resistor 15 to the non-inverting input terminal + of the operational amplifier 14. The reference voltage V ref is applied to an inverting input terminal - of an operational amplifier 14 via a resistor 16 as well as to the output terminal of the operational amplifier 14 via a series circuit of registers 16 and 17. An output signal from the operational amplifier 14 is fed to the microcomputer 3. A control signal from the microcomputer 3 is given to an analog switch 18 which is connected in parallel with the biasing resistor 15 and which is opened and closed by the control signal. The output signal from the angular velocity sensor 1 is amplified by the amplification ratio determined by the resistors 16 and 17. When the angular velocity is zero, the output voltage of the operational amplifier 14 becomes equal to the reference voltage V ref in an ideal condition. In reality, however, the output voltage deviates from the reference voltage V ref because of the bias current, offset voltage, etc. of the operational amplifier 14. If the analog switch 18 is turned on and kept on for a few seconds after power on, the non-inverting input terminal + of the operational amplifier 14 is held at the reference voltage V ref , so that the operational amplifier 14 outputs a signal containing the error caused by the offset voltage of the operational amplifier at zero angular velocity, which signal is then input to the microcomputer 3. The microcomputer 3 performs operations using the input signal voltage as the reference voltage, to obtain an angular velocity signal corrected for variations of circuit elements. Variations of the angular velocity signal due to circuit elements can also be corrected using the circuit shown in Fig. 15. In the circuit shown, the output signal of the operational amplifier 14 is fed to the microcomputer 3 via a low pass filter 19; otherwise, the circuit configuration is identical to that of the circuit shown in Fig. 14, and the same component parts as those shown in Fig. 14 are designated by the same reference numerals. The output signal from the operational amplifier 14 branches into two lines, one directly coupled to the microcomputer 3 and the other coupled to the microcomputer 3 via the low pass filter 19. The cutoff frequency of the low pass filter is selected not to pass the frequency components of the swinging motion associated with a walking action. The microcomputer 3 performs operations using the signal passed through the low pass filter 19 as the reference value, to obtain an angular velocity signal corrected for voltage variations due to circuit elements. The video camera may be carried in a bag or a carrying case, or on a shoulder strap. In such cases, unlike cases where the video camera is carried with its grip held by hand, the swinging directions of the video camera cannot be determined. Therefore, an angular velocity sensor for detecting swinging movements in pitching directions and an angular velocity sensor for detecting swinging movements in yawing directions are incorporated in the video camera in order to distinguish the carrying action from the photographing action. Fig. 16 is a block diagram showing an essential configuration of the video camera incorporating the two angular velocity sensors. An output signal from the angular velocity sensor 1 for detecting swinging movements of the video camera in pitching directions is input to the microcomputer 3 via the amplifier 2, while an output signal from the angular velocity sensor 20 for detecting swinging movements of the video camera in yawing directions is input to the microcomputer 3 via an amplifier 21. A signal from the system microcomputer 4 is given to a buzzer 22 that is used to alert the operator during a photographing action. Otherwise, the configuration of the video camera is identical to that of the video camera shown in Fig. 4, and the same component parts as shown in Fig. 4 are designated by the same reference numerals. Next, the operation of the video camera of the above configuration will be described below with reference to the flowcharts shown in Figs. 17(a), (b) and (c). Suppose that an angular velocity signal, such as shown in Fig. 18, representing movements in pitching directions, is supplied to the microcomputer 3 from the angular velocity sensor 1, and an angular velocity signal, such as shown in Fig. 19, representing movements iii yawing directions, is supplied to the microcomputer 3 from the angular velocity sensor 20. Then, the microcomputer 3 calculates a level difference V PA between the reference value and the input value of the angular velocity signal in pitching directions, and a level difference V YA between the reference value and the input value of the angular velocity signal in yawing directions (S40). Next, it is determined whether the level difference V PA is for the angular velocity signal on the positive side or on the negative side (S41). If it is determined that the level difference V PA is for the positive side signal, then it is determined whether the level difference V YA is For the positive side or the negative side angular velocity signal (S42). If it is determined that the level difference V YA is for the positive side signal, then "1" is counted if the level difference V PA is equal to or greater than the threshold value V TH , and "0" is counted if it is smaller than the threshold value V TH . Also, if the level difference V YA is equal to or greater than the threshold value V TH , "1" is counted, and if it is smaller than the threshold value V TH , "0" is counted. Further, for the level difference V PBN for the negative side angular velocity signal in pitching directions and for the level difference V YBN for the negative side angular velocity signal in yawing directions, "0" is counted (S43). On the other hand, if it is determined that the level difference V YA is for the negative side angular velocity signal, then "1" is counted if the level difference V PA is equal to or greater than the threshold value V TH , and "0" is counted if it is smaller than the threshold value V TH . Also, if the level difference -V YA for the negative side angular velocity signal is equal to or greater than the threshold value V TH , "1" is counted, and if it is smaller than the threshold value V TH , "0" is counted. Further, for the level difference V PBN for the negative side angular velocity signal in pitching directions and for the level difference V BP for the positive side angular velocity signal in yawing directions, "0" is counted (S44). In step (S41), if it is determined that the level difference V PA is for the negative side angular velocity signal, then it is determined whether the level direction V YA in yawing directions is for the angular velocity signal on the positive side or on the negative side (S45). If it is determined that the level difference V YA is for the positive side signal, then "1" is counted if the level difference -V PA for the negative side angular velocity signal in pitching directions is equal to or greater than the threshold value V TH , and "0" is counted if it is smaller than the threshold value V TH . Also, if the level difference V YA in yawing directions is equal to or greater than the threshold value V TH , "1" is counted, and if it is smaller than the threshold value V TH , "0" is counted. Further, for the level difference V PBP for the positive side angular velocity signal in pitching directions and for the level difference V YBN on the negative side angular velocity signal in yawing directions, "0" is counted (S46). On the other hand, if it is determined that the level difference V YA is for the negative side angular velocity signal, then "1" is counted if the level difference -V PA for the negative side angular velocity signal is equal to or greater than the threshold value V TH , and "0" is counted if it is smaller than the threshold value V TH . Also, if the level difference -V YA for the negative side angular velocity signal in yawing directions is equal to or greater than the threshold value V TH , "1" is counted, and if it is smaller than the threshold value V TH , "0" is counted. Further, for the level difference V PBP for the positive side angular velocity signal in pitching directions and for the level difference V YBP for the positive side angular velocity signal in yawing directions, "0" is counted (S47). The "1" and "0" are counted at the sampling timing of the angular velocity signal, to obtain a counted value S PP for the positive angular velocity signal in pitching directions, a counted value S PN for the negative angular velocity signal, a counted value S YP for the positive angular velocity signal in yawing directions, and a counted value S YN for the negative angular velocity signal (S48). Each time the number of counts reaches L (S49), the respective counted values for the L times are obtained (S50). The thus obtained counted values for the angular velocity signals are as shown in Figs. 20 and 21, which are given in contrast with Fig. 18, for the angular velocity signal in pitching directions shown in Fig. 18, and as shown in Figs. 22 and 23, which are given in contrast with Fig. 19, for the angular velocity signal in yawing directions shown in Fig. 19. Each time the number of counts reaches L, the counted values S PP , S PN , S YP , and S YN are given to a memory (not shown) in the microcomputer 3; the counted values S PP , S PN , S YP , and S YN are written at respectively designated address R PPN , R PNN , R YPN , and R YNN (S51). For the past M times addresses R PPN , R PNN , R YPN , and R YNN at which the counted values have been written, the numbers of addresses that are greater than the predetermined value GM are calculated to obtain address numbers H PP , H PN , H YP , and H YN (S52). Next, the address numbers H PP and H PN are respectively compared with the integer T for size (S53). If both of the address numbers H PP and H PN in pitching directions are judged to be greater than the integer T, then it means that the video camera is swinging in both pitching directions, and therefore, it is determined that the condition represents movements associated with a carrying action, not a photographing action (S54). On the other hand, if one or other of the address numbers H PP and H PN is judged to be equal to or smaller than the integer T, the address numbers H YP and H YN in yawing directions are respectively compared with the integer T for size (S55). If both of the address numbers H YP and H YN are judged to be greater than the integer T, it means that the video camera is being repeatedly moved in yawing directions, and therefore, it is determined that the video camera is not in a photographing state (S54). On the other hand, if one or other of the address numbers H YP and H YN is judged to be equal to or smaller than the integer T, it means that the video camera is being moved in yawing directions but with no repetitiveness in the movement, and therefore, it is determined that the video camera is in a photographing state (S56). When it is determined that the video camera is not in a photographing state whereas it is left in a record mode, the system microcomputer 4 cuts off power to stop the recording operation to prevent misrecording, as previously described. Also, when the video camera is in a recording operation, if a signal indicating that the video camera is not in a photographing state is given to the system microcomputer 4, the system microcomputer 4 issues a signal to activate the buzzer 22 to notify the operator of a faulty recording condition. In the video camera of the above configuration, movements associated with a photographing action can be distinguished with certainty from other movements even in cases where the swinging directions of the video camera cannot be determined when it is being carried around. Therefore, a misrecording situation can be avoided without fail even if the video signal is carried around while being left in a record mode. In a photographing action under heavily shaking conditions, for example, when photographing a scene from a vehicle running on a rough road, the video camera may be subjected to shaking of the magnitude equivalent to that of the movements encountered when it is being carried around. In such photographing conditions, it may be erroneously judged that the video camera is not in a photographing state even if it is in a photographing state. In such cases, if a signal is given from the microcomputer 3 indicating that the video camera is not in a photographing state, the system microcomputer 4 ignores such a signal for a predetermined time after a certain key operation, and judges that the video camera is in a photographing state. Also, there are situations where the operator continues photographing a scene while heavily shaking his video camera unconsciously. Such situations occur, for example, when the operator is photographing different objects in short intervals of time or photographing an object while walking. In such photographing situations, the recorded image will often become fragmented and jarred. To avoid such a problem, the video camera is constructed to notify the operator of a faulty photographing condition when the video camera is subjected to heavy shaking while photographing a scene. This is done by calculating an angular velocity signal in pitching directions and an angular velocity signal in yawing directions by the microcomputer 3. In this case, the threshold value V TH with which each angular velocity signal is compared is set smaller than the threshold value V TH used to distinguish the carrying movements. Control is performed in accordance with the flowchart of Fig. 17 in the same manner as previously described. For the past M times, if both of the address numbers H PP and H PN , each representing the number of addresses greater than the predetermined value GM, are greater than the integer T (S53), it is judged that the photographing condition is bad. A signal representing the result of the judgement is input to the system microcomputer 4. When the video camera is in a record mode, if the result indicating a bad photographing condition is given from the microcomputer 3, then the system microcomputer 4 issues a signal to activate the buzzer 22 to notify the operator of the bad photographing condition. At the same time, the system microcomputer 4 issues a signal to the character appending circuit 8 to append a character or characters to the video signal so that a message indicating a faulty photographing condition is displayed on the image displayed in the viewfinder VF. Apart from the previously described carrying condition of the video camera, when the video camera is carried around in a bag, the amount of the swinging movement of the video camera may be reduced because of the weight of the bag, etc. In such situations, it is difficult to distinguish a carrying action. However, because of the darkness in the bag, the average value of the video signal produced by the video camera is reduced. Therefore, when the average value of tlie video signal is small, it is judged that the video camera is carried in a bag or a carrying case, and therefore that the video camera is not in a photographing state. More specifically, when the average value of the video signal is smaller than a predetermined value, the threshold value used when counting the output signal of the angular velocity sensor is decreased so that even the slightest movement can be judged whether it is a movement resulting from a photographing action or not. Fig. 24 is a block diagram showing an essential configuration of a video camera that is capable of making such distinction. The video signal output from the video processing circuit 5 is supplied to an average value calculating circuit 23 where the average value of the video signal is calculated. The average value calculating circuit 23 produces an average value signal which is input to the microcomputer 3. The configuration other than the average value calculating circuit 23 is identical to that of the video camera shown in Fig. 4, and the same component parts as those shown in Fig. 4 are designated by the same reference numerals. When the average value of the video signal is low, the microcomputer 3 decreases the threshold value V TH with which the input value of the angular velocity signal is to be compared. Also, when the video camera is carried in a bag or the like, the swinging period of the video camera becomes long. Therefore, the number of times, L, for counting the level difference V A is increased to lengthen the unit time of counting. This enables the carrying condition to be judged on the basis of the video signal. In situations where the operator photographs a scene while heavily shaking his video camera intentionally or where the operator photographs a scene from a vehicle running on a rough road, such situations may lead to the judgement that the video camera is not in a photographing state. To avoid such a problem, a delay time of predetermined length is provided from the time such judgement is made, until the power is cut off, and during the delay time period, a message is displayed to the effect that the power will be cut off to avoid misrecording. More specifically, when the system microcomputer 4 determines the condition as misrecording, a character signal indicating the misrecording condition is appended to the video signal supplied to the viewfinder VF from the character appending circuit 8. As a result, a misrecording message is displayed in the viewfinder VF to alert the operator. After such a message has been displayed for the predetermined length of time, the system microcomputer 4 controls the power supply circuit 11 to cut off the power. An LED may be built in the viewfinder VF to substitute for the misrecording message to alert the operator. When alerted, the operator can avoid getting the power cut off by performing a prescribed key operation, or by reducing the amount of the shaking motion and putting the video camera out of the erroneous recording condition, while the misrecording display is on. Fig. 25 is a block diagram showing the configuration of a video camera according to another embodiment of the invention. A rewind instruction signal RW is given to the record/playback circuit 6 from the system microcomputer 4. A rewind end signal WEN is given to the system microcomputer 4 from the record/playback circuit 6. A character display signal WW is given to the viewfinder VF from the system microcomputer 4. Otherwise, the configuration of the video camera is identical to that of the video camera shown in Fig. 4, and the same component parts as those shown in Fig. 4 are designated by the same reference numerals. The operation of the video camera of the above configuration will be described below with reference to the flowchart of Fig. 26 which shows a control procedure for the system microcomputer 4. When an angular velocity signal representing the photographing condition is given from the angular velocity sensor 1 to the microcomputer 3 via the amplifier 2, the microcomputer 3 judges whether the photographing condition is normal or not, and supplies the result of the judgement to the system microcomputer 4. The system microcomputer 4 then judges whether the video camera is in a misrecording condition (S60). If it is judged that the video camera is not in a misrecording condition, then it is determined that the video camera is in a normal photographing state based on the intention of the operator (S61), and the control operation is terminated. On the other hand, if it is judged that the video camera is in a misrecording condition, then it is determined that the video camera is not in a normal photographing state but in an abnormal photographing state not based on the intention of the operator (S62), and the recording operation is stopped under control of the system microcomputer 4 (S63). Next, the system microcomputer 4 gives a rewind instruction signal RW to the record/playback circuit 6 to rewind the recording tape by the amount equivalent to the time during which the misrecording was made, i.e. to the position where the misrecording started (S64). When the rewinding operation is completed, the record/playback circuit 6 gives a rewind end signal WEN to the system microcomputer 4. When the system microcomputer 4 determines that the rewinding operation has been completed (S65), the power supply circuit 11 is cut off (S66), and the control operation is terminated. Thus, in the event that an object is erroneously recorded without intention of the operator, the recording tape is automatically rewound so that the erroneously recorded portions will not remain recorded on the tape, thus recording only objects that have been intentionally photographed by the operator. Next, the operation of the video camera will be described with reference to the flowchart of Fig. 27 which shows another control procedure for the system microcomputer 4. As in the above-described procedure, when an angular velocity signal representing the photographing condition is given to the microcomputer 3 from the angular velocity sensor 1, the microcomputer 3 judges whether the photographing condition is normal or not, and supplies the result of the judgement to the system microcomputer 4. The system microcomputer 4 then judges whether the video camera is in a misrecording condition (S70). If it is judged that the video camera is not in a misrecording condition, then it is determined that the video camera is in a normal photographing state based on the intention of the operator (S71), and the control operation is terminated. On the other hand, if it is judged that the video camera is in a misrecording condition, then it is determined that the video camera is not in a normal photographing state but in an abnormal photographing state not based on the intention of the operator (S72), and the recording operation is stopped under control of the system microcomputer 4 (S73), which is followed by a predetermined wait time (S74). During the predetermined wait time, the system microcomputer 4 gives a character display signal WW to the viewfinder VF to display a notice in the viewfinder VF notifying that the recording operation is stopped or that the recording tape is being rewound because of misrecording (S75). Next, the system microcomputer 4 gives a rewind instruction signal RW to the record/playback circuit 6 to rewind the recording tape by the amount equivalent to the time during which the misrecording was made, i.e. to the position where the misrecording started (S76). The display remains on until the rewinding operation is completed. When the rewinding operation is completed, the record/playback circuit 6 gives a rewind end signal WEN to the system microcomputer 4. When the system microcomputer 4 determines that the rewinding operation has been completed (S77), the power supply circuit 11 is cut off under control of the system microcomputer 4 (S78), and the control operation is terminated. Thus, in the event of misrecording, the recording tape is rewound with a notice displayed in the viewfinder VF notifying that the recording operation has been stopped, so that the operator can avoid photographing during the rewinding of the recording tape. This also ensures recording only of objects that have been intentionally photographed by the operator under proper photographing conditions. The operation of the video camera will be further described below with reference to Fig. 28 which shows yet another control procedure for the system microcomputer 4. As in the above-described procedure, when an angular velocity signal representing the photographing condition is given to the microcomputer 3 from the angular velocity sensor 1, the microcomputer 3 judges whether the photographing condition is normal or not, and supplies the result of the judgement to the system microcomputer 4. The system microcomputer 4 then judges whether the video camera is in a misrecording condition (S80). If it is judged that the video camera is not in a misrecording condition, then it is determined that the video camera is in a normal photographing state based on the intention of the operator (S81), and the control operation is terminated. On the other hand, if it is judged that the video camera is in a misrecording condition, then it is determined that the video camera is not in a normal photographing state but in an abnormal photographing state not based on the intention of the operator (S82), and the recording operation is stopped under control of the system microcomputer 4 (S83) The above step is followed by a predetermined wait time (S84). During the predetermined wait time, the system microcomputer 4 gives a character display signal WW to the viewfinder VF to display a notice in the viewfinder VF notifying that the recording operation is stopped or that the recording tape is being rewound because of misrecording (S85). Next, it is judges whether any photographing operation has been performed during the wait time through the key array 7, etc. provided for photographing operation (S86). If it is determined that no photographing operation has been performed, the power supply circuit 11 is cut off under control of the system microcomputer 4 (S87), and the control operation is terminated. In this case, rewinding of the recording tape is not performed, so that the misrecorded portions will remain recorded on the recording tape. In other words, if no photographing operation is performed during the time that the record stop display is on, the misrecorded portions can be saved. On the other hand, if any photographing operation is performed during the predetermined time through the key array 7, etc., the recording tape is rewound by the amount equivalent to the time during which the misrecording was made, i.e., to the misrecording start position (S88). The record stop display remains on until the rewinding operation is completed. When the rewinding operation is completed, the record/playback circuit 6 gives a rewind end signal WEN to the system microcomputer 4. When the system microcomputer 4 determines that the rewinding operation has been completed (S89), the power supply circuit 11 is cut off under control of the system microcomputer 4 (S87), and the control operation is terminated. In this case, if a prescribed key is operated for a photographing operation during the time that the record stop display is on, the recording tape is rewound so that the misrecorded portions will not remain recorded on the recording tape. Thus, whether to save the misrecorded portions on the recording tape or not can be determined as desired by performing or not performing a key operation for photographing during the time that the record stop display is on. In this embodiment, the power supply circuit 11 is cut off after the rewinding of the recording tape has been completed. Alternatively, when the microcomputer 3 has determined that the photographing condition is abnormal, the power supply circuit 11 may be cut off under control of the microcomputer 3 to prevent misrecording, and after that, the power supply circuit 11 may be turned on by the operator performing a photographing operation, followed by the operation of the rewind key on the video camera body to rewind the recording tape to the misrecording start position so that the misrecorded portion will not remain recorded on the recording tape. Furthermore, in this embodiment, the record stop or tape rewind notice is displayed in the viewfinder VF, but alternatively, such notice may be displayed on the video camera body.

Claims: A video camera incorporating a swing sensor (1) for detecting a swinging motion of the camera body (VC) and preventing an erroneous recording operation on the basis of an output signal from the swing sensor (1), comprising: comparing means (4,S1) for comparing the output signal of the swing sensor (1) with a threshold value; counting means (4,S2) for counting the number of times (S) that the output signal reaches or goes beyond the threshold value in a predetermined interval (L); judging means (4,S9,S10) for judging whether the video camera is correctly in a photographing state or not on the basis of a counted value supplied from said counting means (4,S2); and means (4) for stopping the recording operation or notifying the camera operator when it is judged that the video camera is not correctly in a photographing state; characterised in that: said swing sensor (1) is an angular velocity sensor for sending positive and negative angular velocities; and said judging means (4,S9,S10) judges whether or not the camera is correctly in a photographing state by finding, for a plurality (M) of consecutive previous intervals (L), the number (H) of those intervals in which the number of times (S) the threshold value was exceeded by the sensed positive or negative angular velocity exceeds a preset value (Gm). A video camera according to claim 1, wherein said judging means (4,S9,S10) judges whether said number (H) of intervals exceeds a predetermined number (T). A video camera according to claim 1 or 2, wherein the angular velocity is taken relative to a reference value derived from the output voltage of the swing sensor when zero swinging motion is detected by the swing sensor (1). A video camera according to claim 2, wherein the angular velocity is taken relative to a reference value derived from a signal obtained by passing the output signal of the swing sensor (1) through a low pass filter (19). A video camera according to claim 1, 2, 3 or 4, wherein the swing sensor (1) includes a first swing sensor (1) for detecting a swinging motion in pitching directions and a second swing sensor (20) for detecting a swinging motion in yawing directions. A video camera according to any one of the preceding claims, further comprising: an operation key for inputting a control signal for controlling the operation of said judging means (4); and control means for controlling said judging means (4) in response to the operation of said operation key so that said judging mean (4) ignores the counted result of said counting means (4) for a predetermined length of time and judges that the video camera is in a photographing state. A video camera according to any one of the preceding claims, wherein when said judging means (4) has judged that the video camera is not correctly in a photographing state, said means (4) cuts off power. A video camera according to claim 7, further comprising: means for displaying a warning of imminent power off for a predetermined duration of time until said means (4) cuts off power after said judging means (4) has judged that the video camera is not correctly in a photographing state. A video camera according to any one of the preceding claims, further comprising: means for issuing a warning sound when said judging means (4) has judged that the video camera is not correctly in a photographing state. A video camera according to any one of the preceding claims, further comprising: means (23) for calculating an average value of the video signal produced during a photographing operation, wherein when the calculated average value is not greater than a predetermined value, the threshold value with which the output signal of the swing sensor (1) is compared by said comparing means (4) is decreased. A video camera according to any one of the preceding claims, further comprising: means (23) for calculating an average value of the video signal produced during a photographing operation, wherein when the calculated average value is not greater than a predetermined value, the time during which said counting means counts the output signal of the swing sensor is lengthened. A video camera according to any one of the preceding claims, further comprising: stopping means (S63,S73,S83) for stopping the recording operation, and rewinding means (S64,S76,S88) for rewinding a recording tape to the start position of incorrect photographing. A video camera according to claim 12, further comprising: means (S75,S85) for displaying information on the recording stop or the rewinding of the recording tape for a predetermined duration of time after the recording operation has been stopped by said stopping means (S63,S73,S83). A video camera according to claim 12 or 13, further comprising: means (S86) for disabling said rewinding means (S88) from rewinding the recording tape when a photographing operation has not been performed within a predetermined time after the recording operation ha been stopped by said stopping means (S83). A video camera according to claim 12, 13 or 14, further comprising: means (S86) for operating said rewinding means (S88) to rewind the recording tape when a photographing operation has been performed within a predetermined time after the recording operation has been stopped by said stopping means (S83).

Inventors: ISHIDA KOZO, NAKA MASAFUMI, ISHIDA, KOZO, NAKA, MASAFUMI, Ishida, Kozo, c/o Mitsubishi Denki K.K., Naka, Masafumi, c/o Mitsubishi Denki K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1993
Main classification: H04N3
IPC codes: H04N5, G11B31, G11B33