JPH055729Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to an autofocus mechanism for automatically focusing on a subject in a video camera.

<Prior art> As an autofocus mechanism for a video camera,
There is a method of detecting a focus position by focusing on high frequency components included in a video signal from an image pickup device such as an image pickup tube or a solid-state image pickup device. In this method, the frequency components of the video signal include only low frequency components in the out-of-focus state, but as it comes into focus, that is, as it gets closer to focus, the frequency components of the video signal increase. It takes advantage of the characteristic that appears.

However, in this type of autofocus mechanism, when focusing, it is difficult to determine which direction the focus lens should initially move to get closer to the in-focus position. cannot be determined. For this reason, conventionally,
Rotate the focus ring in one direction randomly to move the focus lens, thereby
When the high frequency component of the video signal increases, it is assumed that the direction is in focus and the focus ring continues to rotate.On the other hand, when the high frequency component decreases, it is assumed that the direction is opposite to the focus direction and the focus ring is rotated again. I'm trying to rotate it in the opposite direction.

In this way, the conventional autofocus mechanism
During the initial movement of the focus lens, the lens may move in the opposite direction to the focusing direction, resulting in an unsightly out-of-focus image and the disadvantage that it takes a long time to achieve focusing.

<Purpose of the invention> The present invention has been made in view of the above points, and aims to prevent malfunctions such as movement of the focus lens in the opposite direction to the focusing direction during the initial movement, and to achieve smooth focusing. The purpose of the present invention is to provide an autofocus mechanism capable of focusing.

<Structure of the invention> In order to achieve the above-mentioned object, the present invention includes a driving means for angularly displacing the imaging surface of the imaging device around an axis perpendicular to the optical axis of the lens system, and a driving means for angularly displacing the imaging surface of the imaging device around an axis perpendicular to the optical axis of the lens system; first and second level detection means for respectively detecting the levels of high frequency components of video signals corresponding to two first and second horizontal scanning lines on both sides of the image pickup surface with the axis line as a boundary; a focusing direction detecting means for detecting a focusing direction based on a change in detection levels of both the level detecting means before and after the angular displacement; and a maximum value detecting means for detecting a maximum value of the detection levels of the both of the level detecting means. The focus motor is driven and controlled based on the outputs of the focusing direction detecting means and the maximum value detecting means.

According to the above configuration, since the focusing direction is detected based on the level change of the high frequency component of the video signal corresponding to the first and second horizontal scanning lines before and after angularly displacing the imaging plane, the initial movement as in the conventional case is detected. If the focus lens is driven in a direction opposite to the focusing direction during operation, this can be prevented.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of an embodiment of the present invention. In the figure, 1 is a focus lens, and 2 is a solid-state image sensor. As shown in FIG. 2, the imaging surface A of the solid-state image sensor 2 is moved in a direction perpendicular to the optical axis 4 of the lens system including the focus lens 1, that is, perpendicular to the plane of the paper, as shown in FIG. It can be angularly displaced around the axis 5.

Here, the basic principle of the autofocus mechanism of the present invention will be explained. In the present invention, the solid-state image sensor 2
Detection of the focusing direction based on a change in the high frequency component of the video signal by angularly displacing the imaging surface A of the image pickup surface A and the resulting focusing are performed as follows.

That is, as shown in FIG. 3, the upper and lower two first,
Consider second horizontal scanning lines h1 and h2. This first,
The second horizontal scanning lines h1 and h2 are spaced apart from each other and are selected at positions where the subject can be photographed well.

First, assume that in an out-of-focus state, the imaging plane A is not angularly displaced, as shown by the solid line in FIG. 2, that is, it is perpendicular to the optical axis 4. Assume that the subject is, for example, a white bar-shaped object as shown by the outline in FIG. 3, and the remaining part is black as shown by the hatching. At this time, the video signals corresponding to the first and second scanning lines h1 and h2 are out of focus, so there are few high frequency components, and as shown in FIG. The fall will be gradual. However, in Fig. 4, H is the horizontal synchronization signal, and T1 and T2 are the third
In the figure, T3 corresponds to the black part and the white part.

Next, the imaging surface A is angularly displaced and tilted by the driving means 3 as shown by the imaginary line in FIG. Now, suppose that due to this angular displacement, the upper part of the imaging surface A approaches the focus, and the lower part moves away from the focus. In other words, it is assumed that the subject is in a front-focus state where the focus is on the front. At this time, in the frequency component of the video signal corresponding to the first scanning line h1, the high frequency component increases as it approaches the in-focus position, and the rising and falling of the waveform as shown in FIG. It becomes steep. On the other hand, the high frequency component of the video signal corresponding to the second scanning line H2 decreases as it moves away from the in-focus position, and the waveform of the video signal becomes as shown in FIG. 4C.

Therefore, the focusing direction can be detected by detecting changes in the high frequency components of the video signals corresponding to the first and second horizontal scanning lines h1 and h2 before and after angularly displacing the imaging plane A.

Now, assuming that the front focus state is detected as described above, next, the focus lens 1 is moved in the focusing direction while the imaging surface A remains tilted. Then, since the imaging plane A is tilted, the position of the first horizontal scanning line h1 at the top reaches the in-focus position, and the high frequency component of the video signal becomes maximum. This maximum position is detected and the imaging plane A is returned from the tilted state to the original state perpendicular to the optical axis 4. At the time of this return, the position of the first horizontal scanning line h1 returns to the direction opposite to the focusing direction, so the high frequency component of the video signal corresponding to the first horizontal scanning line h1 changes from the maximum value. Although it decreases once, the high frequency component increases again as the focus lens 1 approaches the in-focus position. When the high frequency component of the video signal reaches its maximum value again with the imaging plane A being vertical, this is determined to be the in-focus position, and the focus lens 1 is stopped and focused.

Referring again to FIG. 1, the autofocus mechanism of this embodiment focuses on the first and second horizontal scanning lines h1 and h2 of the video signal provided from the solid-state image sensor 2 via the signal processing circuit 6. The first and second level detection means 7 and 8 respectively detect the level of the high frequency component of the video signal corresponding to Focusing direction detection means 9 for detecting the focusing direction based on changes in components
, a maximum value detection means 10 that detects the maximum value of the detection levels of both the level detection means 7 and 8, and a focus motor 11 and a drive means based on the outputs of the focusing direction detection means 9 and the maximum value detection means 10. 3
and a control means 12 for controlling.

The first level detection means 7 includes a first sampling circuit 13 that extracts only the video signal corresponding to the first horizontal scanning line h1 from among the video signals from the signal processing circuit 6.
and a first high-pass filter 14 that separates high frequency components from the video signal from this extraction circuit 13.
and a first level detection circuit 15 that detects the level of the high frequency component from the first high pass filter 14.
It consists of Similarly to the first level detection means 7, the second level detection means 8 also has a second extraction circuit 16 for extracting the video signal corresponding to the second horizontal scanning line h2.
, a second high-pass filter 17 , and a second level detection circuit 18 .

Each level detecting means 7, 8 detects each horizontal scanning line h.
Detection outputs corresponding to high frequency components included in the video signals corresponding to 1 and h2 are respectively provided to the focusing direction detection means 9.

The focusing direction detecting means 9 detects the focusing direction according to the above-mentioned principle based on the change in the detection level of both the level detecting means 7 and 8 before and after the angular displacement of the imaging surface A of the solid-state image sensor 2. , provides a corresponding output to the control means 12.

The maximum value detection means 10 determines whether or not the focus lens 1 has been driven to reach the in-focus position, that is,
This is to detect whether the high frequency component of the video signal has reached its maximum value.

The control means 12 drives the focus motor 11 in the focusing direction based on the output from the focus direction detection means 9, and based on the output from the maximum value detection means 10,
The drive of the focus motor 11 is stopped. Further, the control means 12 controls the drive means 3 to angularly displace the imaging surface A of the solid-state image sensor 2.

The focusing direction detection means 9, the maximum value detection means 10, and the control means 12 are realized by a microcomputer or the like.

FIG. 5 is a flowchart illustrating the operation of the autofocus mechanism when the above configuration is implemented by a microcomputer. It should be noted that since this operation description is based on the case where the microcomputer is used, the functions corresponding to each of the means 9, 10, and 12 are realized by the following steps.

First, in an initial state in which the solid-state image sensor 2 is perpendicular to the optical axis 4, detection data H1 and H2 of the first and second horizontal scanning lines h1 and h2 by the first and second detection means 7 and 8 are taken in, respectively ( Step n1).
Next, the solid-state image sensor 2 is moved to a second position by the driving means 3.
Angular displacement is made to the state shown by the imaginary line in the figure (step n2). The first and second horizontal scanning lines h in this state
Detection data H1' and H2' corresponding to H1 and h2 are taken in, respectively (step n3).

Next, detection data H corresponding to the first scanning line h1
1' is larger than the initial detection data H1 (step n4). When it is determined that the focus is large, it is determined that the focus is in the front and the drive of the focus motor 11 in the focusing direction is started (step n7). Next, detection data H corresponding to the first horizontal scanning line h1
1' is taken in (step n8). This captured detection data is compared with the previously captured data to determine whether it is the maximum value (step n9).

When it is determined that the position of the first horizontal scanning line h1 has reached the in-focus position, the imaging plane A is returned to the original state perpendicular to the optical axis 4 (step n10). Next, in this vertical state, the detection data H1' corresponding to the first horizontal scanning line h1 is taken in (step n11). Determine again whether this detected data is the maximum value (step
n12). When it is determined that the value is the maximum value, it is assumed that the focus is in focus, and the drive of the focus motor 11 is stopped (step n13), and the process ends.

At step n4, the detection data H1' corresponding to the first horizontal scanning line h1 becomes the initial detection data H1.
If it is determined that the detected data H2' is not larger than the initial detected data H2, it is determined whether the detected data H2' corresponding to the second horizontal scanning line h2 is larger than the initial detected data H2 (step n5). When it is determined that the detection data H2' corresponding to the second horizontal scanning line h2 is larger than the initial detection data H2, it is determined that the focus is on the rear, and the drive of the focus motor 11 in the direction opposite to step n7 is started (step n7). n14). Next, detection data H2' corresponding to the second horizontal scanning line h2 is taken in (step n15). This captured detection data is compared with the previously captured data to determine whether it is the maximum value (step n16).

When it is determined that the second horizontal scanning line h2 has reached the in-focus position, the imaging plane A is returned to its original state perpendicular to the optical axis 4 (step n17). Next, in this vertical state, detection data H2' corresponding to the second horizontal scanning line h2 is taken in (step n18). Determine again whether this detected data is the maximum value (step
n19). When it is determined that the value is the maximum value, it is assumed that the focus is in focus, and the driving of the focus motor 11 is stopped (step n20), and the process ends.

At step n5, the detection data H2' corresponding to the second horizontal scanning line h2 is changed to the initial detection data H2.
If it is determined that it is not larger than that, it is assumed that the image is already in focus, and the imaging plane A is returned to its original state (step n6), and the process ends.

<Effects of the invention> As described above, according to the invention, there is provided a driving means for angularly displacing the imaging surface of the imaging device around an axis perpendicular to the optical axis of the lens system, and a drive means for angularly displacing the imaging surface of the imaging device around an axis perpendicular to the optical axis of the lens system; , a first detecting level of a high frequency component of a video signal corresponding to two first and second horizontal scanning lines on both sides of the imaging surface with the axis line as a boundary;
a second level detecting means; and a focusing direction detecting means for detecting a focusing direction based on changes in detection levels of both the level detecting means before and after the angular displacement;
and maximum value detection means for detecting the maximum value of the detection levels of both the level detection means, and drive control of the focus motor is performed based on the outputs of the focusing direction detection means and the maximum value detection means. This prevents the problem of driving the focus lens in the opposite direction to the focusing direction during the initial movement as in the conventional case, and enables smooth focusing operation.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an embodiment of the present invention;
The figure is a side view showing the positional relationship between the focus lens and the image sensor in Fig. 1, and Fig. 3 is a view showing the imaging surface.
FIG. 4 is a waveform diagram showing a video signal, and FIG. 5 is a flow chart for explaining the operation of FIG. 2...Image sensor, 3...Driving means, 7, 8...
First and second level detection means, 9... Focusing direction detection means, 10... Maximum value detection means, 11... Focus motor, A... Imaging surface.

Claims (1)

[Claims for Utility Model Registration] Driving means for angularly displacing the imaging surface of an imaging device around an axis perpendicular to the optical axis of a lens system; first and second level detection means for respectively detecting the levels of high frequency components of video signals corresponding to two first and second horizontal scanning lines on both sides of the boundary; and both level detection means before and after the angular displacement. a focusing direction detecting means for detecting a focusing direction based on a change in a detection level of the focusing direction detecting means; and a maximum value detecting means for detecting a maximum value of the detection levels of both the level detecting means, the focusing direction detecting means and An autofocus mechanism for a video camera, characterized in that drive control of a focus motor is performed based on the output of a maximum value detection means.