JPH1188760A - Automatic focusing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic focusing device which can precisely execute an automatic focusing operation regardless of image pickup conditions. SOLUTION: An integrating circuit 9b and a focusing detection circuit 10 output a selection signal S1 when the number of areas where the levels of luminance signal Y are below a reference value exceeds a prescribed rate in each of plural areas of a screen. Thus, a selector circuit 8 switches its input to a high pass filter 6b whose cut-off frequency is higher than a regular case so that the evaluation value of the area is not used for focusing. Accordingly only components higher than the signal Y are extracted, are gain-upped and are integrated in an integrating circuit 9a. The focusing detection circuit 10 outputs a control signal CL so as to make an integrated value S1n maximum, and to drive the focus lens of a lens block 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocusing device, and more particularly to an autofocusing device that detects an in-focus point by using a video signal obtained by imaging as an evaluation value having a maximum value at the in-focus point.

[0002]

2. Description of the Related Art In an auto-focusing device used for a video camera or a digital still camera, a video signal obtained from an image pickup device is used as an evaluation value having a maximum value at a focal point. A method has been developed.

This method has no parallax, and has many excellent features such as accurate focusing even when the depth of field is small or the subject is located at a distant place. I have. Moreover, according to this method, there is no need to provide a special sensor for autofocus,
It is extremely simple in function.

As an example of such a focus control method using a video signal, a control method called a so-called hill-climbing servo method is known. An automatic focusing apparatus using this method is disclosed in JP-A-63-215268 (H0
No. 4N 5/232), this will be briefly described here. First, a high-frequency component of a video signal obtained by imaging is detected as a focus evaluation value for each field, and this focus evaluation value is constantly compared with that obtained one field before, so that the focus evaluation value always takes a maximum value. As described above, the focus lens position is continuously vibrated minutely.

In the case of photographing a low-luminance subject, Japanese Patent Laid-Open No. Hei 5-21626 (H04N 5/232)
As disclosed in Japanese Unexamined Patent Publication, a method has been proposed in which the luminance of an object is detected from a video signal, and when the luminance is low, non-linear processing is performed to increase high-frequency level components, thereby increasing the accuracy of detecting the evaluation value.

However, in a state where there is a point light source in a dark place (such as a night scene), there is a problem that a malfunction of the autofocus operation may occur even if the latter method is used.
In this case, unless the high-pass filter (HPF) for extracting the high-frequency component is set to a cutoff frequency (fc) higher than that normally used, the focus position and the position at the local maximum value are not necessarily the entire evaluation value. It does not match. Also, using only such a high fc HPF results in a small evaluation value, resulting in reduced focusing accuracy, and is susceptible to noise even when nonlinear processing is performed.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an autofocus apparatus which can always perform an autofocus operation with high accuracy irrespective of imaging conditions.

[0008]

According to the first aspect of the present invention, there is provided an auto-focusing apparatus which uses a high-frequency component of a video signal obtained by imaging using a focus lens as an evaluation value having a maximum value at a focal point. Detecting means for detecting that there are many areas that become noise components in the automatic focusing of a plurality of areas based on the high-frequency component, and Normally, the integrated value of the high frequency band component in the high frequency component is output, and when the detection unit detects that there are many regions that become noise components, the higher frequency band component with the gain increased in the high frequency component is output. Integrated value output means for outputting an integrated value, and means for driving a focus lens such that the integrated value output by the integrated value output means is maximized. Configured to include a.

Therefore, the image is divided into a plurality of areas, and the integrated value output is performed under the imaging conditions in which it is determined that there are many areas that become noise components in the automatic focus adjustment based on the high frequency components of each area. The means determines that the evaluation value of the area that becomes a noise component is unnecessary for focusing and ignores it, and in other areas, extracts the higher frequency band component of the high frequency component than usual and increases the gain-up evaluation value. Integrate.

[0010] Therefore, under the imaging condition in which it is determined that there are many regions that become noise components in the automatic focusing of the focal point, the evaluation values of these noise component regions are ignored and the other regions have higher frequency bands of higher frequency bands. The high-frequency component is gained up and integrated, and the focus lens is driven so that the integrated value becomes maximum, so that a highly accurate focus position can be obtained.

According to a second aspect of the present invention, in the automatic focusing apparatus, the detecting means of the first aspect includes at least one of a first and a second detecting means. The first detecting means has first integrating means for integrating the high-frequency component for each of the plurality of areas, and the number of areas whose integrated value by the first integrating means is less than a predetermined reference is a predetermined ratio on the screen. Detect that it has been reached. Further, the second detecting means has second integrating means for integrating the high-frequency component for each of the plurality of areas for each field. In each of the plurality of areas, the displacement of the integrated value by the second integrating means between the fields is determined. It detects that there are many areas exceeding a predetermined value.

Therefore, when there are many regions that become noise components in the automatic focusing of the focal point, the number of regions in which the value obtained by integrating the high frequency components for each of the plurality of regions is less than a predetermined reference is a predetermined ratio on the screen. And at least one of the cases where the value obtained by integrating the high-frequency component for each of the plurality of regions for each field is large in many of the regions where the displacement between the fields exceeds a predetermined value in each of the plurality of regions.

Therefore, when the number of regions in which the integrated value of the high frequency component for each of the plurality of regions is less than the predetermined reference reaches a predetermined ratio on the screen, that is, when the point light source is located in a dark place such as a night scene. If the condition, or if there are many regions where the displacement between the fields of the integrated value of the high frequency component for each of the plurality of regions exceeds a predetermined value,
That is, when the imaging condition is such that many point light sources frequently blink in the screen, only the higher frequency band components of the high frequency components of the video signal are extracted and gain-up in each region, and the gain is increased in other regions. The focus value is integrated as an evaluation value and the focus lens is driven so that the integrated value becomes maximum, so that a highly accurate focus position can be obtained even under an imaging condition in which a malfunction is likely to occur.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a configuration diagram of an autofocus device according to an embodiment of the present invention. In FIG. 1, an autofocus device includes a lens block 1 including a focus lens, an image sensor 2, a preprocessing circuit 3, an A / D (analog / digital) converter 4, a signal processing circuit 5, and an HPF 6a.
6b, a gain-up circuit 7, a selector circuit 8, integrating circuits 9a and 9b, and a focus detection circuit 10. It should be noted that the cutoff frequency fc is
a <HPF 6b.

FIG. 2 is a block diagram of the focus detection circuit 10 of FIG. In FIG. 2, a focus detection circuit 10 is a comparison circuit 11
And 13, an integrating circuit 12, a local maximum value detecting circuit 14, and a signal generating circuit 15.

In operation, an image formed on the imaging surface of the imaging device 2 by the lens block 1 is photoelectrically converted by the imaging device 2 and provided to the preprocessing circuit 3 as a video signal. The pre-processing circuit 3 performs predetermined processing such as noise elimination and gain adjustment on the given video signal,
It is provided to the A / D converter 4.

The video signal digitized by the A / D converter 4 is processed by a signal processing circuit 5 to generate and output a luminance signal Y.

The luminance signal Y is supplied to each of the HPFs 6a and 6b and a plurality of predetermined areas of the screen.
To an integrating circuit 9b which outputs an integrated value S2n. The output of the HPF 6b is supplied to the gain-up circuit 7, and the output of the circuit 7 is selected by the selector circuit 8 as the output of the HPF 6a according to a selection signal SL described later.

It is to be noted that the luminance signal Y is changed to a cutoff frequency fc.
However, when a higher HPF is passed, the evaluation value becomes smaller, and it becomes difficult to determine a maximum value in a local maximum value detection circuit 14 described later. Therefore, here, after passing the luminance signal Y through the HPF 6b, a gain-up circuit 7, the gain is increased.

Normally, the selector circuit 8 selects and outputs the output from the HPF 6a. When the selection signal SF is given from the focus detection circuit 10, the selector circuit 8 selects the output of the gain-up circuit 7. The integrating circuit 9a integrates the output of the selector circuit 8 for each of a plurality of areas on the screen described above and outputs an integrated value S1n.

In FIG. 2, the focus detection circuit 10 compares the integrated value S2n of each area of the screen provided from the integrating circuit 9b with a certain reference value D1 in a comparing circuit 11 to obtain a value D1.
When the number of regions having the smaller integrated value S2n is integrated (counted) by the integrating circuit 12, when the comparing circuit 13 detects that the integrated number of regions exceeds a certain ratio value D2 with respect to the total number of regions. The selection signal SL is output. In other words, the comparison circuits 11 and 13 and the integration circuit 1
2, when it is determined that the image capturing condition is a night view with a point light source in a dark place, a selection signal SL is output, and the HPF 6 is output to the integrating circuit 9 a via the selector circuit 8.
b and a signal whose gain has been increased in a higher frequency band component of the luminance signal Y that has passed through the gain-up circuit 7.

The maximum value detection circuit 14 of the focus detection circuit 10 receives the integrated value S1n from the integration circuit 9a to detect a maximum value, and the signal generation circuit 15 generates a control signal CL corresponding to the detected maximum value. Then, it is given to the lens block 1. Accordingly, the focus lens of the lens block 1 is driven and adjusted by the control signal CL to a position where the integrated value S1n becomes a maximum value.

Therefore, for example, under the condition that a night scene is photographed, the integrated value S2n of the luminance signal Y is displayed on the screen.
Is determined as noise (or an unnecessary evaluation value of the focus detection unit), and is masked by the selector circuit 8 so as not to be integrated by the integration circuit 9a. Then, the focus detection circuit 10 outputs a control signal CL for controlling the focus lens of the lens block 1 so that the integrated value S1n takes the maximum value.

In addition to the above-described imaging conditions for night scenes, noise (in the case of an imaging condition where the evaluation value greatly changes between fields in each area of the screen, that is, an imaging condition in which there are many light sources that blink frequently, is not limited). An evaluation value for an area determined to be unnecessary evaluation value for focus detection) may not be integrated. FIG. 3 shows the configuration of FIG.
It is a block diagram added in order to determine that the evaluation value increases and decreases frequently between fields in each area of the screen. 3 is a block diagram of the signal processing circuit 5 shown in FIG.
The input signal Y is input and processed, and the processing result is selected as a selection signal SL
1 may be added to the selector circuit 8, or may be provided instead of the integrating circuit 9b, the comparing circuits 11 and 13 of the focus detection circuit 10, and the integrating circuit 12 in FIG.

In each area of the screen shown in FIG. 3, a block 20 for judging that the evaluation value frequently changes between fields is composed of a selector circuit 21, integration circuits 22 and 2.
3, including a difference circuit 24 and a comparison circuit 25. In operation, the selector circuit 21 switches the luminance signal Y by the switching signal FS switched in the field and outputs the luminance signal Y to the integrating circuits 22 and 23 alternately. In each of the integrating circuits 22 and 23, the integrated value of the luminance signal Y is calculated for each field for each of the plurality of regions of the screen, and is provided to the difference circuit 24. The difference circuit 24 calculates the difference of the integrated value for each area in the screen for each field. Comparison circuit 15
Inputs the result in the difference circuit 24, compares the difference obtained for each region with the difference reference value D3, and if the number of regions having a difference exceeding the reference value D3 is larger than the set value D4, the selection signal SL is output. Output.

In this embodiment, the selection signal SL is generated using the circuit shown in FIG. 2 or FIG. 3. However, the selection signal SL is supplied to the selector circuit 8 by an external signal, for example, by operating an external switch. You may give it.

The integrated value S2n of the integrating circuit 9b can be used as it is as data of the automatic exposure mechanism. In brief, if the integrated value S2n is small, the lens block 1 can be used to adjust the aperture so as to open, or the preprocessing circuit 3 can increase the gain to make the image brighter.

The integrating circuit and the focus detecting circuit may be constituted by software instead of being constituted by hardware.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an autofocus device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a focus detection circuit of FIG. 1;

FIG. 3 is a block diagram added in order to determine that the evaluation value frequently changes between fields in each area of the screen in the configuration of FIG. 1;

[Explanation of symbols]

 1 Lens Blocks 6a and 6b HPF 7 Gain Up Circuit 8 Selector Circuit 9a and 9b Integration Circuit 10 Focus Detection Circuit SL Selection Signal CL Control Signal The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (2)

[Claims] 1. An auto-focusing apparatus for performing automatic focusing of a focus by using a high-frequency component of a video signal obtained by imaging using a focus lens as an evaluation value having a maximum value at the focus. Detecting means for detecting that there are many areas that become noise components in the automatic focusing of the focus in a plurality of areas of the screen based on the high-frequency component; and for each of the plurality of areas, the high-frequency The integrated value for the high frequency band component in the component is output, and when the detection unit detects that there is a large area serving as the noise component, the integrated value for the higher frequency band component with the gain increased in the high frequency component Means for driving the focus lens such that the integrated value output by the integrated value output means is maximized. An autofocus device comprising a step and a step. 2. The detection device includes at least one of a first detection device and a second detection device. The first detection device includes a first integration device that integrates the high frequency component for each of the plurality of regions. Detecting that the number of the areas in which the integrated value by the first integrating means is less than a predetermined reference has reached a predetermined ratio on the screen; and wherein the second detecting means determines the high-frequency component for each field. A second integrating unit that integrates each of the plurality of regions, wherein detecting that there are many regions in each of the plurality of regions where the displacement of the integrated value by the second integrating unit exceeds a predetermined value between the fields. The autofocus device according to claim 1, wherein