JP2005070663A - Video camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the failure that the advance to a state (an out-of-focus state) deviating from an exact focusing position gives rise to a false peak and the occurrence of a problem leading to a malfunction of AF with a subject having saturated luminance. <P>SOLUTION: The video camera equipped with a function to perform autofocus operation by extracting a high-frequency component of an area 200 by an evaluation value generating means from the video signal obtained by an imaging element to generate an evaluation value and controlling the position of a focusing lens so as to maximize the evaluation value is set with a weighting coefficient in the area 200 in such a manner that the value of the weighting coefficient decreases by one each respectively in one line as the value of the weighting coefficient advances toward the peripheral part of a screen in upper and lower weighting areas 201 and 203. As a result, even if part of the saturated luminance portion intrudes into the weighting region 201 or 203 of the area 200, the ratio of addition in a perpendicular direction is reduced by the above setting of the weighting coefficient and therefore the occurrence of the false peak can be suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a video camera, and more particularly to a video camera including an autofocus (AF) device that drives and controls a focus lens so that an evaluation value is maximized.

  For video cameras that output subject images as video signals, the camera automatically recognizes the position of the subject and automatically adjusts the focus (focus) of the camera lens to the just-focused state for the recognized subject. Conventionally, an autofocus device is mounted (see, for example, Patent Document 1).

  FIG. 4 shows a block diagram of an example of a conventional video camera. In the figure, light from a subject (not shown) is converged by an objective lens 1 and a focus lens 2 and received by focusing on a light receiving surface of a charge transfer element (CCD) 3 which is a solid-state image sensor. After being converted and further converted into a video signal, it is supplied to the A / D converter 4 and converted into a digital signal to become image data, and predetermined signal processing is performed by the signal processing circuit 5.

  The image data output from the signal processing circuit 5 is converted into an analog video signal by the D / A converter 6 and supplied to the monitor 9 for image display, while being supplied to the evaluation value generation circuit 7, where High-frequency components are extracted, and evaluation value data obtained by integrating the high-frequency components existing in a predetermined setting area in the screen is generated.

  Here, it is well known that in order to detect whether or not the image is in focus, it may be determined whether the contrast of the video signal obtained by imaging is high or low. That is, when the contrast is high, the focus is on, and when the contrast is low, the focus is off. Therefore, the microcomputer 8 determines the level of contrast by a predetermined algorithm based on the evaluation value data, and focuses so that the evaluation value is maximized, that is, the contrast is maximized. AF can be realized by moving and adjusting the lens 2.

Japanese Patent Laid-Open No. 10-213840

  By the way, normally, when the AF control is operating correctly, the evaluation value decreases when the state shifts from the just focus position (blurred state). However, when the subject has saturation luminance, the evaluation value rises conversely, that is, a so-called false mountain may occur when the subject shifts from the just-focused position (blurred state). In such a case, simply searching for the peak of the evaluation value while moving the focus lens 2 cannot reach the just-focus position, resulting in a problem of AF malfunction.

  The present invention has been made in view of the above points, and an object thereof is to provide a video camera capable of suppressing the occurrence of so-called false mountains and performing an accurate autofocus operation without malfunction.

In order to achieve the above object, the present invention provides a focus lens for focusing incoming imaging light, an imaging device for converting imaging light obtained through the focus lens into an electrical signal, and processing the electrical signal And signal processing means for obtaining a video signal, and by extracting the high-frequency component of the focus detection area from the video signal and controlling the position of the focus lens so that the value of the extracted high-frequency component is maximized, autofocusing In a video camera with a function to perform the operation,
The evaluation value generating means for obtaining the maximum value of the high-frequency component is the maximum weighting for the high-frequency component located at the edge in the focus detection area and the extraction means for extracting the high-frequency component in the focus detection area of the video signal. , Weighting coefficient generating means for generating weighting coefficients whose weights are sequentially decreased from the edge to the outside, and weighting addition for adding the high frequency components extracted by the extracting means in accordance with the weighting coefficients from the weighting coefficient generating means The position of the focus lens is driven and controlled using the addition result obtained by the weighted addition means as an evaluation value.

  In this invention, the high-frequency component of the focus detection area of the video signal obtained by imaging is the largest weighting related to the high-frequency component located at the edge in the focus detection area, and as it goes outward from the edge, Since the addition result obtained by adding according to the weighting factors that become smaller in weight is used as the evaluation value, the saturation luminance portion of the video signal of the subject having the saturation luminance portion in the immediate vicinity of the focus detection area is blurred. Even if it enters the specific region, the change due to the blur portion of the saturated luminance portion can be suppressed by reducing the value of the weighting coefficient.

  According to the present invention, even if the saturated luminance portion of the subject has a saturated luminance portion in the immediate vicinity of the specific region and the saturated luminance portion blurs into the specific region, the change due to the blur portion of the saturated luminance portion is changed. Since the weighting coefficient value is reduced, the evaluation value can be created as accurately as possible even if a part of the saturated luminance portion enters the specific area. Occurrence can be suppressed, and as a result, the accuracy of autofocus control for moving the focus lens so as to maximize the evaluation value can be improved as compared with the conventional case.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a main part of a video camera according to the present invention. The basic block configuration of the present embodiment is the same as the block diagram of FIG. 4, but the present embodiment is characterized in that the evaluation value generation circuit 7 has the configuration shown in FIG.

  In FIG. 1, a luminance signal in a video signal that has been subjected to predetermined signal processing by a signal processing circuit (5 in FIG. 4) is a high-pass filter (HPF) that selects a high-frequency component (for example, a frequency higher than 1 MHz). 101, the signal is detected by the rectifier 102, and then supplied to the peak value storage unit 104 through the gate circuit 103 that passes through only a specific region generated by the area generation unit 107. Here, in the area limited by the area generation unit 107 The peak value in the horizontal interval at is stored. The specific area is a part of the monitor screen and is a focus detection area for extracting a high frequency component for AF control.

  In the present embodiment, the area information of the focus detection area generated by the area generation unit 107 is supplied to the weighting coefficient generation unit 108, and the vertical addition unit 105 at each of the upper and lower portions in the area as shown in FIG. Generates a weighting coefficient (to be described later) that changes the rate of addition, and supplies it to the vertical adder 105. The horizontal peak value stored in the horizontal peak value storage unit 104 is added according to the weighting factor in the vertical direction of the screen in the vertical addition unit 105, and the addition result is stored in the output memory 106 as an AF evaluation value. The evaluation value stored in the output memory 106 is processed by the microcomputer 8 in FIG. 4 and used for automatic focus adjustment of the focus lens 2.

  Next, the weighting coefficient will be described with reference to FIG. As shown in FIG. 2A, when the area 200 in the screen is divided into a normal area 202 having a relatively wide width at the center and weighting areas 201 and 203 having relatively narrow widths above and below the normal area 202, Then, “value 16” is set as shown in FIG. 2C, and the weighting areas 201 and 203 are set so that the value of the weighting coefficient is decreased by one for each line as it goes to the periphery of the screen. Also, as shown in FIG. 2B, the weighting coefficient is set to 0 as shown in FIG. 2C in the low level portion of the vertical area pulse.

  The weighting coefficient generator 108 in FIG. 1 generates a weighting coefficient that changes the value shown in FIG. In the vertical adder 105, a value obtained by dividing the weighting coefficient from the weighting coefficient generator 108 by “16” is set as an addition coefficient. That is, since the weighting coefficient is “16” in the normal area 201, the horizontal peak value is added as it is, but in the weighting areas 201 and 203, for example, when the weighting coefficient is “8”, it is divided by “16”. 0.5 "is used as an addition coefficient, and the horizontal peak value of the line is added by a half value.

  Next, the false mountain generation mechanism and the operation of the embodiment of FIG. 1 will be described with reference to FIG. As shown in FIG. 3A, when the saturated luminance portion 210 exists outside the area 200, it is naturally outside the area 200, so that it is obtained by adding the horizontal peak value in the vertical direction in the vertical adder 105. It is not reflected in the AF evaluation value.

  However, in the blurred state, the saturated luminance portion spreads away from the central portion so that ripples spread as indicated by 212 in FIG. When a part of the saturated luminance portion 212 enters the area 200 as shown in FIG. 3C, the luminance value is originally large, so the luminance value of the portion that has entered the area 200 is large to some extent even if it is blurred. The horizontal peak value will move here. In FIG. 3C, the white circle is the original peak value, but the horizontal peak value is moved to the left black circle.

  As a result, the evaluation value is calculated to be larger than the original value. As a result, as shown in the graph of FIG. 3D showing the relationship between the lens position and the evaluation value, there is a false mountain as indicated by II other than the just focus position I, which causes malfunction in AF control. give.

  However, according to the present embodiment, even if a part of the saturated luminance portion 212 enters the area 200 as shown in FIG. In FIG. 3B, the weighting coefficient that gradually decreases as it goes to the periphery of the area as shown in FIG. The horizontal peak value in a part of the saturated luminance portion 212 is a value near the original peak value indicated by a white circle in FIG. As a result, the occurrence of false mountains is suppressed, and it is easy to find the position of the just-focus mountain with respect to the AF control that moves the focus lens 2 so as to maximize the evaluation value, and the AF can be performed with high performance. .

  The present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the weighting process for the vertical area portion has been described. However, the weighting process for the horizontal area portion can be similarly performed. . It is also possible to perform weighting processing on both the vertical area portion and the horizontal area portion at the same time.

It is a block diagram of one Embodiment of the principal part of the video camera which becomes this invention. It is explanatory drawing of the weighting coefficient generate | occur | produced in the weighting coefficient generation | occurrence | production part in FIG. It is explanatory drawing about a false mountain generation mechanism and an effect | action of embodiment of FIG. It is a block diagram of an example of the conventional video camera.

Explanation of symbols

2 Focus lens 7 Evaluation value generation circuit 101 High pass filter (HPF)
DESCRIPTION OF SYMBOLS 102 Rectifier 103 Gate circuit 104 Horizontal peak value preservation | save part 105 Vertical addition part 106 Output memory 107 Area production | generation part 108 Weighting coefficient generation part 200 Area 201, 203 Weighting area 202 Normal area 211 Weighting coefficient

Claims (1)

A focus lens for focusing incoming imaging light, an imaging device for converting the imaging light obtained through the focus lens into an electrical signal, and a video signal obtained by processing the electrical signal A signal processing unit, and a function of extracting a high-frequency component of a focus detection region from the video signal, and performing an auto-focus operation by controlling the position of the focus lens so that the value of the extracted high-frequency component is maximized In a video camera
The evaluation value generating means for obtaining the maximum value of the high frequency component is:
Extracting means for extracting a high frequency component of the focus detection region of the video signal;
Weighting coefficient generating means for generating a weighting coefficient in which the weighting related to the high-frequency component located at the edge in the focus detection region is maximum, and the weighting sequentially decreases as going from the edge to the outside;
Weighting addition means for adding the high-frequency component extracted by the extraction means in accordance with the weighting coefficient from the weighting coefficient generation means, and the addition result obtained by the weighting addition means as the evaluation value A video camera characterized by controlling the position of a focus lens.

Images