JP3296687B2 - Auto focus video camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing apparatus for a video camera which performs automatic focus adjustment based on an image signal obtained from an image sensor.

[0002]

2. Description of the Related Art In recent years, in a video camera that creates a video signal using an image sensor, a method of performing a focusing operation based on a high-frequency component in the video signal has been awarded.

[0003] Referring to FIG. 2, this auto-focusing device will be described. The incident light incident through the lens 1 forms an image on the imaging surface of the CCD 2 and is photoelectrically converted. The processing is executed, and the captured video signal is output and input to the high-pass filter (HPF) 4 and the sync separation circuit 5.

The HPF 4 extracts only high-frequency components of a predetermined frequency (for example, 600 kHz) or more from the picked-up video signal, and inputs the high-frequency components to an A / D converter 8 via a gate circuit 6 to convert the digital signals into digital signals. The value is converted to a value and output to the subsequent integration circuit 9, that is, a digital integrator.

The sync separation circuit 5 separates the vertical and horizontal sync signals, and these sync signals are input to a focus area setting circuit 7. The focus area setting circuit 7 sets the H level only during a period corresponding to the focus area set on the screen based on the two synchronization signals and the oscillation output of the predetermined frequency.
A focus area signal which becomes a level is output to the gate circuit 6.

The gate circuit 6 receives the focus area signal, and permits only the high-frequency component of the image signal in the focus area to be input to the A / D converter 8.

The integrating circuit 9 is connected to the HP via the gate circuit 6.
A digital integrator for adding the F4 output over one field period to calculate the sum of one field period;
The integrated value for one field period is output as a focus evaluation value for each field.

The focus evaluation value output for each field is output to a microcomputer (microcomputer) 10. Information indicating the current lens position is input to the microcomputer 10 as lens position information from a focus motor 11 for moving the lens 1 in the optical axis direction. This lens position information is calculated based on the amount of rotation of the focus motor 11 in one direction from the initial position. That is, when the lens 1 starts the focusing operation from the initial position, the motor 1
When 1 rotates in the positive direction and the lens rotates toward infinity, the rotation amount of the motor 11 is added to the initial value corresponding to the initial position, and when the lens rotates in the reverse direction and rotates in the near point direction. Is derived by subtracting the rotation amount of the motor 11.

Further, a command for instructing the rotation direction is given from the microcomputer 10 to the focus motor 11, and the rotation direction is controlled, and the movement direction of the lens 1 is changed by the change in the rotation direction.

Here, the processing of the hill-climbing focusing operation in the microcomputer 10 will be described with reference to the flowchart of FIG. Step S1 is a step for confirming the set state of the AF completion flag which is set only when the hill-climbing control is completed and the lens is stopped at the in-focus position. Move to S2. In addition, as shown in FIG. 4, the focus evaluation value becomes the maximum value at the in-focus position, and has a mountain shape with respect to a change in the lens position.

The flag CL is a flag that is set to a clear state when it is recognized that the lens 1 has gone too far from the in-focus position, and is set during a normal hill-climbing in-focus operation.
Move to step S3.

In step S3, the input latest focus evaluation value V is compared with the maximum evaluation value MAX so far. If it is determined that the latest evaluation value is larger, the lens 1 is checked in step S4. Updates the value of the maximum evaluation value MAX with the latest evaluation value assuming that the user is climbing a mountain. Step S
In step 5, the current lens position at the time when the latest evaluation value is input is stored in the lens position memory ML.

Next, assuming that the in-focus position exists in the current moving direction, the lens moving direction is maintained as it is in step 6 and the hill-climbing control should be continued, and the flag CL is determined in step S7. Is set to complete the focusing operation process.

By the above-described series of hill-climbing focusing operations, FIG.
As shown by arrow Y1, the lens gradually approaches the in-focus position P while moving in the direction in which the focus evaluation value increases.

On the other hand, if it is determined in step S3 that the latest focus evaluation value is lower than the maximum evaluation value MAX, is the focus evaluation value dropped to a threshold width u or more that can confirm that the in-focus position has been exceeded too much? It is determined in step 8 whether or not a slight drop within the threshold width u may be caused by noise or the like. Therefore, the hill-climbing operation is continued. If it has reached, the process proceeds to step S9, in which the rotation direction of the motor 11 is reversed so that the lens movement direction is reversed.
A flag C is used to indicate that the focus position has been exceeded by 0.
L is cleared, and the lens is moved in the direction of arrow Y2 in FIG.

Accordingly, in the subsequent focusing operation processing, the process proceeds from step S2 to step S11, where the current lens position is compared with the lens position having the maximum evaluation value stored in the lens position memory ML. It is determined whether the lens has returned to the position where the focus evaluation value reaches the maximum evaluation value MAX. If the lens has not returned, the lens movement in the direction of the arrow Y2 is continued.
At 12, the driving of the focus motor 11 is stopped to stop the lens 1, and at step S13, an AF completion flag is set. This stops the lens at the in-focus position,
This means that the focusing operation has been completed, and in the subsequent focusing operation processing, the series of hill-climbing focusing operations from step S1 is not executed.

Incidentally, such an autofocus device has the following problems. That is, the high-frequency component level of the video signal depends not only on the shift of the focus from the in-focus point but also on the brightness of the subject present in the focus area. Therefore, when there is not much change in luminance in the focus area, the maximum value of the focus evaluation value can be reliably detected. In some cases, the high-luminance subject has a large amount of high-frequency components, so that the subject is in focus. Become.

When the high-luminance portion is extremely large, H
There have been various problems that the PF output is saturated and the reliability of the obtained focus evaluation value is reduced.

An example of a measure for preventing the influence of the high luminance portion is disclosed in Japanese Patent Application Laid-Open No. 2-76480.
That is, when shooting a subject image in which a high-brightness subject exceeding a predetermined threshold is included in the focus area of the imaging screen, the high-brightness subject is detected from the video signal and the high-frequency range obtained from the high-brightness subject is detected. By adopting a configuration in which the component is excluded from the calculation of the focus evaluation value, the influence on the focusing operation of a high-luminance subject is eliminated.

[0020]

As described above, in the method of eliminating a high-brightness portion, when the brightness level exceeds a threshold value regardless of the area of the high-brightness portion, the system is unconditionally prevented from participating in the focus evaluation value. Therefore, a phenomenon occurs in which the focusing operation becomes unstable depending on the size of the high luminance portion.

Hereinafter, this phenomenon will be specifically described. FIG.
Shows a shooting screen in a focus area set at the center of the shooting screen, and shows a case where the sun, which is a high-brightness portion G having a relatively small area, exists in addition to the main subject Z. FIG. 6 illustrates the relationship between the time lapse and the focus evaluation value when the hill-climbing focusing operation is performed while gradually displacing the lens in the focusing position direction.

As is apparent from FIG. 6, the focus evaluation value includes not only a true peak which is the in-focus position of the main subject, but also a pseudo peak whose focus evaluation value becomes a peak due to the luminance of the high luminance portion. Exists.

When a hill-climbing focusing operation is started at time to on such an imaged screen, it is determined that the luminance level of the high-luminance portion does not exceed the threshold value at the beginning, and the high-frequency component of the main subject is determined. Then, the hill-climbing focusing operation is performed along the focus evaluation value obtained by adding the influence of the luminance level of the high luminance portion to the above.

By the way, in the photographing state as shown in FIG. 5, the main subject is in a backlight state of the sun, and the main subject is darkened as it is. Therefore, in a normal video camera, in order to raise the brightness of the main subject to an optimum value, a so-called backlight correction operation of raising the brightness of the entire shooting screen by an auto iris device is gradually executed, and accordingly, the brightness of the high brightness portion also increases. Lifted gradually, as a result, at time t1
If it is determined that the luminance level of the high-luminance portion exceeds the threshold value and the luminance is determined to be high, the focus evaluation value due to the influence of the luminance of the high-luminance portion is removed.
At time t1 as shown in FIG.

A similar drop occurs when the area of the high luminance portion in the focus area is large as shown in FIG. That is, the change of the focus evaluation value accompanying the hill-climbing focusing operation in the photographing state of FIG. 7 is as shown in FIG. As is clear from FIG. 8, similar to FIG. 6, the focus evaluation value includes a true peak and a pseudo peak due to a high luminance portion.
Since the area of the high-brightness portion is large, the addition to the focus evaluation value by the brightness of the high-brightness portion and the size of the pseudo peak are also shown in FIG.
It is larger than.

If it is determined that the luminance of this image is high at time t1 and the high-frequency component of this portion is removed, the focus evaluation value suddenly increases to △ x2 at time t1 as shown in FIG. The amount of the drop is much larger than Δx1 in FIG.

Therefore, in the hill-climbing focusing operation as described above, the timing at which the lens moves too far to the in-focus position and reverses the lens movement is determined at the time when it is confirmed that the focus evaluation value has fallen by the threshold width u. Because of the setting, the sudden drop in the focus evaluation value due to the elimination of the high-luminance portion is erroneously recognized as a drop after passing through the focus position, and a malfunction occurs in which the movement of the lens is reversed at time t1. In particular, this tendency becomes stronger as the area of the high-luminance portion increases.

[0028]

According to the present invention, there is provided an image pickup means for outputting an image pickup signal obtained by photoelectrically converting incident light incident through a lens by an image pickup device, and a plurality of small areas constituting a focus area. And a high-frequency level detecting means for detecting a high-frequency component level of the imaging signal in each of the small areas, and a value corresponding to an area of a high-luminance subject having a luminance exceeding a threshold, which is present in the plurality of small areas, A high-luminance area calculation means for calculating for each small area, and a value corresponding to the area of the high-luminance subject such that the weighting amount decreases as the area of the high-luminance subject increases for each of the small areas. Weighting means for determining a weighting amount for each of the small areas, and weighting a high-frequency component level for each of the small areas with the weighting amount, and adding the high-frequency component levels after the weighting processing. A focus evaluation value calculating means for outputting as a focus evaluation value, the focus evaluation value; and a focus control means for controlling a distance between said lens so that the maximum value the imaging element.

[0029]

Since the present invention is constructed as described above, when a high-luminance subject other than the main subject exists in the focus area, the focus evaluation when removing the influence of the luminance of the high-luminance subject on the focus evaluation value is removed. A sharp drop in value is prevented.

[0030]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the present embodiment.
In FIG. 1, the same parts as those in FIG.

In this embodiment, as shown in FIG. 9, the focus area set at the center of the screen is further composed of first to fourth areas A1, A2, A3 and A4. It is explained that there is.

When a high-luminance portion exists in the focus area, the luminance level of a position corresponding to the high-luminance portion in the video signal obtained from the image pickup device becomes large. Then, a high luminance detection signal which becomes H level at the position of the high luminance portion is output. The specific detection operation of the high luminance portion detection circuit 21 compares the video signal level with a predetermined threshold, and sets the high luminance detection signal to the H level only when the video signal level is higher.

The focus area setting circuit 20 includes first to fourth areas A1, A2, A3, and A4, which form a focus area based on a synchronization signal and a clock having a predetermined frequency.
The first to fourth area setting signals which become H level in A4 are output to the selection circuits 23 and 24 at the subsequent stage.

The high frequency component of the video signal output from the HPF 4 is sampled by the A / D converter 22 at a predetermined sampling cycle, converted into a digital value, and output to the selection circuit 23.

The high-brightness detection signal output from the high-brightness portion detection circuit 21 is sampled at a predetermined sampling cycle by the A / D converter 25, converted into a digital value, and output to the selection circuit 24. You.

The selection circuits 23 and 24 receive the first to fourth area setting signals output from the focus area setting circuit 20, and selectively output the input digital data to one of the subsequent integration circuits. In the period corresponding to the first area A1, the first area setting signal becomes H level, the selection circuit 23 switches to the fixed contact 23b, outputs the output of the A / D converter 22 to the integration circuit 31, and selects The circuit 24 switches to the fixed contact 24b and outputs the output of the A / D converter 25 to the integrating circuit 35.

Similarly, during the period corresponding to the second area A2, the second area setting signal becomes H level, and the selection circuit 2
3 switches to the fixed contact 23c and outputs the output of the A / D converter 22 to the integrating circuit 32.
4c and outputs the output of the A / D converter 25 to the integrating circuit 3
6 during the period corresponding to the third area A3.
The area setting signal becomes H level, the selection circuit 23 switches to the fixed contact 23d and outputs the output of the A / D converter 22 to the integrating circuit 33, and the selection circuit 24 switches to the fixed contact 24d and outputs the A / D converter 25. Is output to the integrating circuit 37, and in the period corresponding to the fourth area A4, the fourth area setting signal becomes H level, and the selection circuit 23
e, and outputs the output of the A / D converter 22 to the integrating circuit 34.
The selection circuit 24 switches to the fixed contact 24e and outputs the output of the A / D converter 25 to the integrating circuit 38.

In a period that does not correspond to any of the first to fourth areas, that is, in a period that corresponds to outside the focus area, the selection circuits 23 and 24 are respectively connected to the fixed contacts 23.
a, 24a, and each A / D converted value is not supplied to any of the integrating circuits.

Each of the integrating circuits 31,..., 38 is a digital integrator for digitally integrating the input digital value over one field period.
The integrated values V1, V2, V3, and V4 output from 1, 32, 33, and 34 for each field correspond to the focus evaluation values for the first to fourth areas, respectively.
7, 38, the integrated value H1 output for each field,
H2, H3, and H4 correspond to the area values of the high luminance portions of the first to fourth areas, respectively. The focus evaluation value and the high luminance area value of each area thus obtained are supplied to the microcomputer 40.

The microcomputer 40 calculates the focus evaluation value of the entire focus area after weighting the focus evaluation value of each area with the weight of each area set based on the area value of the high luminance portion of each area. .

Next, the calculation of the weighting amount for each area by the microcomputer 40 and the calculation of the focus evaluation value based on the weighting amount will be described with reference to the flowchart of FIG. A series of steps constituting step S100 indicate a weighting amount calculation process, and step S50 sets a variable j to an initial value 1 as an initial setting of the weighting amount calculation process.

Step S51 is a step for judging whether or not the area of the high-luminance portion of each area exceeds the first reference value m. For the area not exceeding the first reference value m, the weighting amount Wj is determined in step S52. Is fixed to 1 and conversely
If it exceeds the reference value m, it is determined in a step S53 whether or not the flag F is set.

Since the flag F is cleared unless it is set in step S58, which will be described later, the process normally proceeds to step S54 to calculate the weight. In this step S54, a new weight is calculated by subtracting a value obtained by multiplying the reciprocal of the area value of the high-luminance portion by a constant k from the weight before one field.

When this calculation is completed, it is determined in step S55 whether or not the area value of the high luminance portion exceeds the second reference value n. If not, the weighting amount W is determined in step S56.
It is determined whether or not j is less than the first convergence value of 0.5. If the value is less than 0.5, the weighting amount Wj is fixed to the first convergence value in step S57, and then the flag F is set in step S58.
Is set. If it exceeds, steps S57 and S58
Jumps to step S61.

On the other hand, if it is determined in step S55 that the area value of the high luminance portion exceeds the second reference value n, then in step S59 the weighting amount Wj is set to 0, which is the second convergence value.
It is determined whether or not it is less than or equal to 0. If it is less than 0, the weight amount Wj is fixed to the second convergence value in step S60. If it exceeds, steps S60 and S58 are skipped and the routine goes to step S61.

Steps S61 and S62 are processes for performing the above-described series of weighting amount setting operations for all of the first to fourth areas. When the weighting amounts of the four areas are determined, the focus of the subsequent stage is determined. Evaluation value calculation processing routine S63
Execute In this routine, the focus evaluation value of each area is weighted by the weighting amount determined as described above with respect to the focus evaluation value of each area according to Expression 1, and then the focus evaluation values of all four areas are added to obtain the focus evaluation value of all the focus areas. The value V is calculated.

[0047]

V = W1 × V1 + W2 × V2 + W3 × V3 + W4 × V4 Based on the focus evaluation value thus calculated, a hill-climbing focusing operation similar to the conventional example is executed in the hill-climbing focusing routine S64.

Next, the calculation of the focus evaluation value when a high luminance portion exists in the focus area will be described specifically.
Now, as shown in FIG. 11, a high-luminance portion G having a relatively small area exists only in the second area A2.
2 is larger than the first reference value m and smaller than the second reference value n, the weighting amounts W1, W of the first, third, and fourth areas
3, W4 is always fixed to 1 in step S52,
The weighting amount W2 of the second area A2 is a value obtained by subtracting (k × 1 / H2) from the value one field before in step S54, and the weighting amount W2 is the first convergence value of 0. This operation is repeated until it is determined that the value becomes equal to or less than 5, and the value decreases by (k × 1 / H2).
If it becomes 5 or less, it is fixed to 0.5 in step S57,
At the same time, the flag F is set in step S58. Therefore, after the next field, a series of processes is skipped from step S53 to step S61, and as a result, the weighting amount W2 is fixed at 0.5.

FIG. 12 shows the lapse of time and the change in the weighting amount of each area in this case. As is clear from this figure, the second area A where the high luminance portion exists
2, only the weighting amount W2 of the other area is reduced with respect to the weighting amount of the other area. As a result, it becomes possible to remove the pseudo peak, and the initial weighting amount is reduced from 1 to the first convergence value. Although the time required for a certain 0.5 is relatively short, as is clear from FIG. 6, when the area of the high luminance portion is small, the reduction amount of the focus evaluation value caused by removing the high luminance portion is small. So it doesn't matter. In FIG. 12, time t1 indicates the point in time when it is recognized that the luminance level of the high luminance portion has exceeded the threshold.

On the other hand, as shown in FIG.
When the area of the high luminance portion existing in the area is large and the area H2 is larger than the second reference value n, the weighting amounts W1, W3, and W4 of the first, third, and fourth areas are determined in the same manner as in the above-described case in step S52. Is always fixed at 1, but the weighting amount W2 of the second area A2 is a value obtained by subtracting (k × 1 / H2) from the value one field before in step S54, and the weighting amount is determined in step S59. This operation is repeated until it is determined that W2 has become equal to or less than the second convergence value of 0, and is reduced by (k × 1 / H2).
If the value finally becomes 0 or less by the calculation in step S54, it is fixed to 0 in step S60, and at the same time, in step S5
At 8, the flag F is set. Therefore, after the next field, a series of processes jumps from step S53 to step S61, and as a result, the weighting amount W2 is fixed to the second convergence value 0.

FIG. 14 shows such a lapse of time and a change in the weight of each area. As is clear from FIG. 12, as in FIG. 12, only the weighting amount W2 of the second area A2 where the high-luminance object is present is reduced with respect to the weighting amounts of the other areas. The value is set smaller than in the case of FIG. This is because the pseudo peak cannot be removed unless the weight of the second area A2 is reduced significantly as compared with FIG. 12 by the large area of the high luminance portion.

Further, as is apparent from FIG. 8, since the focus evaluation value is largely reduced by removing the high luminance portion, if the weight W2 is instantaneously set to 0, the focus evaluation value drops sharply and malfunctions occur. Cause. Therefore, the change of the weight must be performed over a long time,
To realize this, the absolute value of the slope of the decreasing line of the weight amount W2 is set to a value corresponding to (k × 1 / H2), and this value is set so as to be inversely proportional to the area value H2. The change in the amount of weight can be made more gradual.

FIG. 15 is a diagram showing a change in the focus evaluation value of the hill-climbing focusing operation using the focus evaluation value after the weighting process when the high luminance portion occupies a large area in the focus area. As shown by the solid line in FIG. 15, the focus evaluation value does not drop sharply and is not influenced by the high luminance portion. You will be heading for the peak. Note that the chain line in FIG. 15 indicates a drop in the evaluation value in the conventional example in FIG.

In the above embodiment, the CCD 2 is fixed to move the lens 1 in the optical axis direction. Alternatively, the lens may be fixed to move the CCD in the optical axis direction. Needless to say, a piezoelectric element can be used instead of the focus motor.

Further, in the above embodiment, the convergence values of the weighting amounts of the areas where the high luminance portion exists are set to two types of 0.5 and 0, but the reference value for distinguishing the area of the high luminance portion is set as the reference value. If a plurality of values other than the first and second reference values m and n are set, a plurality of convergence values can be set, and it goes without saying that finer control becomes possible.

The constant k at the time of calculating the weighting amount is set in advance to an optimum value by an experiment. At the start of focusing, the flag F is cleared, and the weighting amounts W1 to W4 are all set to 1 which is the initial value. It is assumed that

In the above embodiment, the video signal obtained from the imaging circuit is converted into a digital value after passing through the HPF. However, the video signal from the imaging circuit is directly converted into a digital value, and then the digital HPF is converted. It is needless to say that the present invention can also be used for a so-called digital video camera that passes through the camera.

[0058]

As described above, according to the present invention, when a high-luminance subject other than the main subject exists in the focus area, when the influence of the luminance of the high-luminance subject on the focus evaluation value is removed, Since a sharp drop in the focus evaluation value is prevented, a stable focusing operation can be realized without causing a malfunction in the focusing operation.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a block diagram of a conventional example of the present invention.

FIG. 3 is a flowchart illustrating a processing routine of a hill-climbing focusing operation.

FIG. 4 is a diagram illustrating a relationship between a lens position and a focus evaluation value.

FIG. 5 is a diagram illustrating a screen in a focus area where a high-luminance subject having a small area exists.

FIG. 6 is a diagram illustrating a conventional example when a high-luminance subject having a small area exists in a focus area.

FIG. 7 is a diagram illustrating a screen in a focus area where a high-luminance subject having a large area exists.

FIG. 8 is a diagram illustrating a conventional example when a high-luminance subject having a large area exists in a focus area.

FIG. 9 is a diagram illustrating a configuration of a focus area according to an embodiment of the present invention.

FIG. 10 is a flowchart of an autofocus process according to one embodiment of the present invention.

FIG. 11 is a diagram illustrating a screen in a focus area where a high-luminance subject having a small area exists according to an embodiment of the present invention.

FIG. 12 is a diagram illustrating a relationship between weighting amounts over time when a high-luminance subject having a small area is present in a focus area according to an embodiment of the present invention.

FIG. 13 is a diagram illustrating a screen in a focus area where a high-luminance subject having a large area exists according to an embodiment of the present invention.

FIG. 14 is a diagram illustrating a relationship between weights over time when a high-luminance subject having a large area exists in a focus area according to an embodiment of the present invention.

FIG. 15 is a diagram illustrating the relationship between the passage of time and the focus evaluation value according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 lens 3 imaging circuit A1 first area A2 second area A3 third area A4 fourth area 31 integrating circuit 32 integrating circuit 33 integrating circuit 34 integrating circuit 40 microcomputer 11 focus motor

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 5/232

Claims (1)

(57) [Claims] 1. An image pickup means for outputting an image signal obtained by photoelectrically converting incident light incident through a lens by an image sensor, and a high-frequency component of an image signal in a plurality of small areas constituting a focus area. A high-frequency level detecting means for detecting a level for each of the small areas; and a high-luminance area for calculating, for each of the small areas, a value corresponding to an area of a high-luminance subject existing in the small area, wherein the luminance exceeds a threshold value. Calculating means for increasing the area of a high-luminance subject for each of the small areas;
Weighting amount determining means for determining a weighting amount for each of the small areas according to a value corresponding to the area of the high-luminance subject so that the weighting amount decreases accordingly; A focus evaluation value calculating means for performing weighting processing on the area component levels, adding each of the high frequency component levels after the weighting processing , and outputting the result as a focus evaluation value; and the lens and the imaging device so that the focus evaluation value becomes a maximum value. An autofocus video camera comprising: a focus control unit that controls a distance between elements.