JPH08317272A - Autofocus device - Google Patents

Abstract

PURPOSE: To perform the autofocus control of a television camera with high accuracy and inexpensively. CONSTITUTION: The evaluation value processing circuit in a vertical direction is composed by including a horizontal direction average value calculation filter 1 controlled by a timing generator 2, a digital high-pass filter 3 provided with a flip-flop 4 as a delay circuit, an absolute value processing circuit 5, an integration circuit 6 controlled by a frame control signal 7 and a horizontal synchronizing signal 8 further controlling the digital high-pass filter 3, the absolute value processing circuit 5 and the integration circuit 6. After a luminance signal Y is inputted in a horizontal direction average value calcultion filter 1, the average number of arbitrary number of picture element of a horizontal line is calculated, the signal is synchronized with the horizontal synchronizing signal 8 in the digital high-pass filter 3, a high frequency component is extracted and an absolute value processing is performed, the high frequency components of all the horizontal lines are integrated in the range controlled by the frame control signal 7 and the evaluation value for autofocus is calculated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for picking up an image by electric means such as a television camera, and more particularly to an autofocus apparatus for picking up an image.

[0002]

2. Description of the Related Art An example of a conventional autofocus apparatus for an image pickup apparatus using electric means represented by a television camera will be described with reference to FIGS.

Conventionally, there is an autofocus device having a structure in which an image signal obtained by a television camera is converted into a numerical value and counted, and then fed back to a focusing device of an image pickup lens for focusing. As shown in FIG.

In FIG. 3, a luminance signal Y is converted into digital data by an A / D converter 9 in synchronization with a sampling pulse 10, and a high frequency component is converted by a digital high pass filter 3 (hereinafter simply referred to as "HPF") shown in FIG. Is taken out, the absolute value is obtained in the absolute value processing circuit 5, the output is integrated over the entire evaluation area 21 of the screen 20 shown in FIG. 4, and the horizontal evaluation value for autofocus is calculated.

That is, this integration adds all the data in the horizontal line in the range set by the horizontal frame control signal 7H (reference 6H), and then sets it by the vertical frame control signal 7V. In the range thus defined, the horizontal synchronization signal 8 is synchronized in the vertical direction to obtain an evaluation value in the horizontal direction (reference numeral 6V).

Based on the evaluation value in the horizontal direction obtained by the above-described method, the lens is moved in the optical axis direction and stopped at a position where the evaluation value is maximum, that is, at a position where the focus coincides with the focus automatically. To adjust.

Since adjacent pixels input to the HPF 3 shown in FIG. 5 have no vertical difference in their positional relationship, the output of the HPF 3 of this system outputs a high frequency component only in the horizontal direction. As a result, the evaluation value is also an evaluation value of only the horizontal component.

However, the above-mentioned auto-focusing method has a drawback that the focusing accuracy is deteriorated with respect to an image such as a horizon that has little change in the horizontal direction, and that focusing is not performed in an extreme case.

Therefore, in order to solve this drawback, there is a conventional method of obtaining an evaluation value in the vertical direction and superimposing it on the above-mentioned autofocus as shown in FIG. That is, in the figure (a), the luminance signal Y is sampled by the A / D converter 9 at a frequency 4fsc which is four times the color subcarrier frequency fsc and converted into a digital signal, which is stored in the even field memory 13 and the odd field memory 14. The switch 11 is alternately switched by the even / odd switching signal, and the image data is stored for each field. Also, the even /
The odd switching signal causes the switch 12 to connect the memory other than the memory being read to the HPF3, read the image data from the other memory while storing the image data of one memory, and output the high frequency component in the vertical direction at the HPF3. Then, the absolute value processing circuit 5 obtains an absolute value, and all data is added (reference numeral 17) to continuously obtain evaluation values in the vertical direction. Here, writing and reading of the memory are controlled by the timing generator 2.

Next, referring to FIGS. 6B and 6C, writing and reading of image data in the memory will be further described. First, regarding writing, FIG.
As shown in (1), one field is captured according to the order of horizontal scanning. When the capture of one field is completed, the switch 11 is switched, the capture is started in the other one field memory, and at the same time, the switch 12 is switched for the image data just captured, and the image data is read in the vertical direction sequentially as shown in FIG. 6C. Is started. The image data read out in the vertical direction is input to the HPF 3 to obtain an evaluation value in the vertical direction.

Focus control is further applied based on the evaluation value in the vertical direction, but as described above, two field memories are required to obtain the evaluation value in the vertical direction. Was getting bigger and more expensive.

[0012]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a device for performing an autofocus operation with high precision even in an image captured by an image pickup device using electronic means such as a television camera and having little change in the horizontal direction. Is what you are trying to do.

[0013]

A horizontal frequency component of a specified image area of an image signal from a television camera is extracted, and an autofocus device for controlling the focus of the television camera on the basis of the extracted amount is used to extract the image signal of the image signal. Weighted addition is performed on a plurality of consecutive image data of each horizontal line in the specified image area, and the value obtained by weighted addition is used as a representative value of each horizontal line, and a high-pass filter is applied to the representative value, and the output value is evaluated. The above problem is solved by providing a vertical evaluation value calculation unit for calculating and adding a configuration for controlling focus based on the vertical evaluation value.

[0014]

The frequency component of the image in the vertical direction is extracted from the image data of each horizontal line in the specified image area of the image signal to focus the camera on the basis of the frequency component in the vertical direction even for an image having few frequency components in the horizontal direction. Control automatically.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIGS. The present embodiment relates to a vertical autofocus circuit configuration, and the horizontal one is the same as the conventional example, and a description thereof will be omitted.

The image luminance signal Y is input to the horizontal direction average value calculation filter 1, and based on the frame signal generated by the timing generator 2, an arbitrary value within the range regulated by the frame signal for each horizontal line of the screen. The average of the number of pixels (for example, 64 pixels) is calculated. The sequentially calculated average value of each horizontal line is input to the digital HPF 3 and a high frequency component is extracted in synchronization with the horizontal synchronizing signal 8. The absolute value of the high frequency component is obtained by the absolute value processing circuit 5, and the high frequency component of each horizontal line is integrated by the integrating circuit 6 within the range regulated by the frame control signal 7, and the high frequency components of all the horizontal lines in the frame are integrated. After is integrated, the vertical evaluation value is established. A flip-flop 4 is used as the delay circuit forming the HPF 3.

Focus control is performed based on the vertical evaluation value extracted as described above. The evaluation value is on the vertical center line of the evaluation area 21 of the screen 20 as shown in FIG. That is, since it is extracted only on the vertical direction evaluation value calculation line 22, focus control is not effective for an image with little change along the vertical direction evaluation value calculation line 22.

However, as described above, the present invention also uses the horizontal focus control shown in FIG. 3, and if the image has a frequency component in either the vertical direction or the horizontal direction, the focus control is performed. You can do it. Note that the evaluation value is calculated by prioritizing one of the vertical direction and the horizontal direction in advance, and only when the evaluation value is insufficient for use in focus control, the other evaluation value is calculated and the focus value is calculated. You may make it control.

[0019]

As described above, according to the present invention, even in an image captured by a television camera and having little change in the horizontal direction, the focus is automatically adjusted based on the evaluation value in the vertical direction extracted from the image components in the horizontal direction. be able to.

Since the circuit for extracting the evaluation value in the vertical direction from the image component in the horizontal direction is configured without using the image memory, an inexpensive autofocus device can be provided.

[Brief description of drawings]

FIG. 1 is a circuit block diagram for obtaining an evaluation value in a vertical direction for autofocus according to the present invention.

FIG. 2 is a diagram showing a screen portion for obtaining an evaluation value in a vertical direction according to the present invention.

FIG. 3 is a circuit block diagram for obtaining a horizontal evaluation value for conventional autofocus.

FIG. 4 is a diagram showing a conventional screen portion for obtaining an evaluation value in the horizontal direction.

FIG. 5 is a diagram showing a configuration of a digital high pass filter.

6A and 6B are diagrams for explaining a conventional autofocus method, in which FIG. 6A is a circuit block diagram for obtaining a vertical evaluation value for autofocus using a field memory, and FIG. The order of taking in the image data is shown, and (c) shows the order of reading the image data.

[Explanation of symbols]

 1 Horizontal direction average value calculation filter 2 Timing generator 3 Digital high pass filter 4 Flip-flop 5 Absolute value processing circuit 6 Integration circuit 7 Frame control signal 9 A / D converter 11, 12 switch 13 Even field memory 14 Odd field memory 15 1 Sampling clock Delay circuit 16 1H Delay circuit 20 Screen 21 Evaluation area 22 Vertical direction evaluation value calculation line

Claims (1)

[Claims] 1. An image pickup apparatus for picking up an image by electrical means, wherein a horizontal frequency component in a specific image area of an image signal from the image pickup apparatus is extracted, and the image pickup is performed based on the extracted horizontal frequency component. In an autofocus device for controlling the focus of the device, while performing a weighted addition of a plurality of continuous image data of each horizontal line in a specific image area of the image signal, the value obtained by the weighted addition as a representative value of each horizontal line An autofocus device characterized by applying a high-pass filter and further comprising a vertical evaluation value calculation unit for calculating an evaluation value from the output of the high-pass filter, and adding a configuration for controlling focus based on the evaluation value in the vertical direction. .