JPH0276480A - Auto focus device - Google Patents

Abstract

PURPOSE:To focus onto a subject to be mainly photographed by a photographer by removing high luminance information at the time of processing a signal even when a small high luminance subject is present at the place except the subject to be photographed. CONSTITUTION:A video signal is given to a video signal processing type, HPF2 and a high luminance part detecting circuit 3. At the HPF 2, a higher component is extracted from a video signal and sent to a high luminance part removing circuit 4. At the circuit 3, the high luminance part during the video signal is detected and this is sent to the circuit 4 as a gate signal. At the circuit 4, a signal from the HPF 2 is gated by a gate signal from the circuit 3 and the signal excluding the high luminance part of the video signal is sent to a detecting averaging circuit 5. Thus, at a part in the picture to be photographed, even if the high luminance part such as reflection of a metal is present, this is removed by the circuit 4. The output of the circuit 5 is given through a sampling circuit 6, a maximal value deciding circuit 7, etc., to a motor driving circuit 9 and the focusing is executed.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention extracts high-frequency components in a video signal by a high-frequency component extraction means, and adjusts a lens system so that the extracted high-frequency components have a maximum value. The present invention relates to an autofocus device that performs focus adjustment through control, and is used, for example, in a video camera.

(Prior Art) Conventionally, an autofocus device has been proposed that utilizes the fact that the high frequency component of a video signal becomes maximum when the image is in focus (at the time of in-focus point).

The electrical configuration of this device is shown in FIG.

In the figure, 11 is a bypass filter that extracts high-frequency components in the video signal, 12 is a detection averaging circuit that detects and averages the extracted high-frequency components, and 13 is a sampling circuit that performs sampling every certain period T. , 14 is a previous value holding circuit, 15 is a local maximum value determining circuit, and 16 is a focusing motor drive circuit.

In other words, the high-frequency components in the video signal are filtered through the bypass filter 1.
1, and the extracted high-frequency components are detected and averaged by a detection and averaging circuit 12 to be used as a focus information signal. This focus information signal has more high-frequency components (the more it is in focus), so focus adjustment can be performed by finding the maximum value of this focus information signal.To find the maximum value of this focus information signal, the focus information signal is sampled by the sampling circuit 13 at every period T and sequentially held in the previous value holding circuit 14.Then, the next sampled pulse train and the previous pulse string held in this previous value holding circuit 14 are is determined by the maximum value determination circuit 15, and the motor drive circuit 16 is driven until the maximum value is determined to rotate the focusing motor forward or reverse.

(Problem to be Solved by the Invention) However, in such conventional autofocus devices, when there is not much change in brightness within the screen, it is difficult to perform sufficient focus adjustment by finding the maximum value of the high frequency component. However, if there is a high-brightness object (such as a metal reflection) in a small part of the screen that is far away from the main subject you want to photograph, the high-brightness will be There was a problem in that the subject part was in focus, and the screen as a whole became out of focus, with the part that was originally intended to be out of focus.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned circumstances, and the present invention extracts high-frequency components in a video signal by a high-frequency component extracting means, and extracts high-frequency components from a video signal so that the extracted high-frequency components have a maximum value. In an autofocus device that performs focus adjustment by controlling a lens system, there is provided a high-brightness part detection means for detecting a high-brightness part in a video signal, and a high-brightness output from the high-brightness part detection means is used as a gate signal to detect the high-brightness part. and high-luminance removal means for removing the high-frequency components of the high-luminance portions from the area component extraction means.

(Function) The high-brightness portion in the video signal is detected by the high-brightness portion detection means, and the detected high-brightness output is used as a gate signal to detect the high-brightness portion of the high-brightness portion from the high-brightness component extraction means by the high-brightness removal means. Remove ingredients. Then, the focusing lens is controlled based on the maximum value of the high frequency component of the signal excluding the high brightness portion. As a result, even if there is a high-brightness object far away from the part of the screen that you want to focus on, the object will not be in focus, but the part you want to focus on will be in focus.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic block diagram showing the electrical configuration of an autofocus device of the present invention.

In the figure, 1 is a signal line that sends a video signal captured by an image sensor (not shown) such as a CCD, and the signal line 1 connects to a video signal processing system (not shown) and extracts high frequency components from the video signal. and a high-brightness part detection circuit 3 which detects high-brightness parts in a video signal. The output of the bypass filter 2 is given to the high brightness part removal circuit 4, and the output of the high brightness part detection circuit 3 is given to the high brightness part removal circuit 4 as a gate signal. The output of the high brightness part removal circuit 4 is given to a detection averaging circuit 5, and the detected and averaged signal is given to a sampling circuit 6. The signal sampled every period T by the sampling circuit 6 is given to a maximum value determination circuit 7 and a previous value holding circuit 8. When the previous value holding circuit 8 receives the next signal from the sampling circuit 6, it sends the previous signal from the sampling circuit 6, which has been held until then, to the maximum value determining circuit 7. The maximum value determination circuit 7 compares the signal from the sampling circuit 6 with the signal from the previous value holding circuit 8 to determine the maximum value.
A signal based on this determination result is sent to the motor drive circuit 9 for focus control.

Next, the operation of the autofocus device having the above configuration will be explained.

A video signal captured by the image sensor is provided to a video signal processing system, a bypass filter 2, and a high brightness portion detection circuit 3 through a signal line 1. The bypass filter 2 extracts high-frequency components from the video signal and sends them to the high-brightness removal circuit 4.
Send to. Further, the high-brightness portion detection circuit 3 detects a high-brightness portion in the video signal, and sends this detection signal to the high-brightness portion removal circuit 4 as a gate signal. The high-brightness part removal circuit 4 gates the signal from the bypass filter 2 using the gate signal from the high-brightness part detection circuit 3, and sends the signal from which the high-brightness part of the video signal has been removed to the detection averaging circuit 5.

As a result, even if there is a high-brightness part such as metal reflection in a part of the screen to be photographed, the information of this high-brightness part is removed by the high-brightness part removal circuit 4.

The signal applied to the detection and averaging circuit 5 is detected and averaged here and then sent to the sampling circuit 6. The signal sent to the sampling circuit 6 is a signal that reaches a maximum when the focus is focused. The sampling circuit 6 samples the signal from the detection and averaging circuit 5 at certain regular intervals T, and sends the sampling signal to the maximum value determination circuit 7 and the previous value holding circuit 8.

When the previous value holding circuit 8 receives the sampling signal from the sampling circuit 6, it sends the previous sampling signal held until then to the maximum value determination circuit 7.

The local maximum value determining circuit 7 compares the signal directly input from the sampling circuit 6 with the signal input from the previous value holding circuit 8 to determine the local maximum value. In other words, if the high-frequency component of the signal input from the sampling circuit 6 is greater than the high-frequency component of the signal input from the previous value holding circuit 8, it is determined that the value is not the maximum value because it is not yet in focus. When this ratio is reversed, that is, when the high frequency component of the signal input from the sampling circuit 6 becomes smaller than the high frequency component of the signal input from the previous value holding circuit 8, it is determined that the value is the maximum value. Then, the motor drive circuit 9 is driven and controlled until the maximum value is determined, and the focus motor is rotated forward or reverse to perform focus adjustment.

(Effects of the Invention) As explained above, according to the autofocus device of the present invention, it is possible to take pictures of areas other than the subject that the photographer mainly wants to photograph (
Even if there is a high-brightness object such as a small metal reflective object in front or behind the camera, this high-brightness information can be removed during signal processing, allowing the photographer to focus on the subject he/she wants to photograph. .

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing the electrical configuration of an autofocus device of the present invention, and FIG. 2 is a schematic block diagram showing the electrical configuration of a conventional autofocus device. 1...Signal 1 2...Bypass filter 3...High brightness area detection circuit 4...High brightness area removal circuit 5...Detection averaging circuit 6...Sampling circuit 7...Local maximum value Judgment circuit 8... Previous value holding circuit 9.
・・Motor drive circuit

Claims (1)

[Scope of Claims] 1) An autofocus device that extracts high-frequency components from a video signal using high-frequency component extracting means, and performs focus adjustment by controlling a lens system so that the extracted high-frequency components have a maximum value. A high-brightness part detection means for detecting a high-brightness part in a video signal;
An autofocus device comprising: a high-brightness removing means for removing a high-frequency component of a high-brightness portion from the high-brightness component extracting means using a high-brightness output from the high-brightness portion detection means as a gate signal.