JP4118079B2 - Camera autofocus device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an autofocus device in a consumer camera such as a digital camera or a video camera, and in particular, a video signal type autofocus device that performs an autofocus operation (automatic focus operation) using a change in luminance signal. It is about.
[0002]
[Prior art]
In video signal systems that perform autofocus operations using changes in luminance signals, paying attention to the fact that the amount of high-frequency components in the luminance signal corresponds to the degree of focus, the amount of high-frequency components is always maximized. In this way, the position of the lens is adjusted by an AF motor, and an optical system for focus adjustment is unnecessary, which is suitable for downsizing and cost reduction of the camera.
[0003]
FIG. 9 is a configuration diagram of a main part of a camera using the above video signal system. In FIG. 9, 1 is a single focus lens (hereinafter referred to as a lens 1) as a focus lens, 2 is a shielding plate interlocked with the lens 1, 3 is a photointerrupter unit for detecting the passage of the shielding plate 2, 4 is an AF motor, A lens driving mechanism section composed of gears and the like, 5 is a motor driving driver for driving and controlling the AF motor of the lens driving mechanism section 4, 6 is a CCD (charge coupled divice), 7 is an AGC circuit (automatic gain control circuit), 8 Is an A / D converter (analog / digital converter), 9 is a DSP (digital signal processor), 9a is an AE data calculator, 9b is an AF data calculator, 10 is a DSP, 11 is a microcomputer, and 12 is a timing generator. is there.
[0004]
In the configuration shown in FIG. 9, the optical image from the lens 1 is formed on the CCD 6 and converted into an electric signal, and then the signal level is amplified by the AGC circuit 7 and converted into a digital video signal by the A / D converter 8. And input to the DSP 9. The DSP 9 performs preprocessing of video (image) processing according to the signal contents, and the AE data calculation unit 9a calculates a luminance value obtained by dividing the image into multiple parts for AE control, and an AF data calculation unit 9b. In, AF data indicating the degree of focus is calculated from the high frequency component of the luminance signal of the video signal. The video signal output from the DSP 9 is subjected to appropriate video processing such as image compression in the DSP 10 for image processing, and is output to a recording medium or an output terminal (not shown). The microcomputer 11 converts and acquires an AE (auto exposure) value from the output of the AE data calculation unit 9a, and acquires AF data from the AF data calculation unit 9b. Then, the microcomputer 11 passes the lens 1 through the motor drive driver 5 and the lens drive mechanism unit 4 so that the value of the AF data is maximized (that is, the amount of the high frequency component of the luminance signal is maximized). Move. Further, the microcomputer 11 supplies a predetermined vertical synchronizing signal (VD), horizontal synchronizing signal (HD), and clock to the CCD 6 via the timing generator 12 while referring to the AE value so that proper exposure can be achieved. Controls the timing of the electronic shutter.
[0005]
Further, when the lens reference position (focus reference position) is initialized, such as when the power is turned on, the lens 1 is driven in the direction of the photo interrupter unit 3, and the shielding plate 2 that moves in conjunction with the lens movement is the photo interrupter unit 3. The reference position of the lens 1 is detected by passing through. Subsequently, the microcomputer 11 manages the lens position (the position of the lens 1) as a relative position from the reference position, and moves the lens 1 by an AF motor such as a stepping motor.
[0006]
When all the areas to be focused are scanned when autofocusing is performed, and the image has a certain level of contrast, the relationship between the lens position and the high-frequency component of the luminance signal is, for example, a graph as shown in FIG. Become. In the example of FIG. 3, the point A has the highest high frequency component, so this position is set as the focus position, and the lens 1 is moved to the point A to perform shooting. On the other hand, when all the areas to be focused are scanned when autofocusing is performed, when the contrast of the image is low, the relationship between the lens position and the high frequency component of the luminance signal is, for example, a graph as shown in FIG. . As shown in FIG. 4, when the amount of change in the high-frequency component is equal to or smaller than a predetermined value, the in-focus position cannot be determined, so that the lens is fixed at the predetermined position as a focus failure (for example, with a focal length of 2 m). Fixed in position).
[0007]
By the way, when an impact is applied to the lens 1 by hitting the camera or the like, the lens 1 may cause an abnormal movement due to the gear of the lens 1 and the AF motor flying. In such a case, since the microcomputer 11 grasps the lens position based on the lens movement command amount (AF motor rotation amount) from the reference position, even if the lens 1 moves without a command from the microcomputer 11, this is used. It cannot be detected (that is, the abnormal movement of the lens 1 cannot be detected on the microcomputer 11 side). Therefore, after causing the lens 1 to move abnormally, a lens scan for detecting the in-focus position is performed in a region different from the original lens position. The relationship between the lens position and the high-frequency component of the luminance signal is, for example, As shown in FIG. 5, there may be a measurement result with almost no change in high-frequency components. Therefore, in such a case, since the change of the high frequency component is equal to or less than a predetermined value, the image is low as described above, so that the lens is placed at a fixed position. Will be filmed.
[0008]
[Problems to be solved by the invention]
As described above, in a digital camera that manages the lens position as a relative position from the focus reference position and performs an autofocus operation, even if the lens moves abnormally due to impact or the like, it cannot be detected, so the lens is abnormal. After the movement is caused, an accurate focus cannot be obtained, so that an out-of-focus image is taken. Furthermore, the reference position is usually checked mostly when the power is turned on, so that the focus cannot be maintained until the power is turned off / on. During this time, the user continues to take images that are out of focus. Become.
[0009]
In JP-A-6-125493 and JP-A-6-303487, a low-contrast image is recognized without lens scanning by looking at the difference level between the maximum value and the minimum value of the luminance signal. , A method for setting the focus to a fixed position as a focus failure without lens scanning is disclosed, but in the prior arts of these publications, the detection of abnormal lens movement due to impact or the like is considered. Is not paid.
[0010]
The present invention has been made in view of the above points. The object of the present invention is to manage the lens position as a relative position from the focus reference position and perform an autofocus operation. An object of the present invention is to realize an autofocus device for a camera that can discriminate abnormal movement and can automatically perform recovery when the lens moves abnormally.
[0011]
[Means for Solving the Problems]
The present invention, in order to achieve the above object, using a single focus lens as a focusing lens, in that you measure the focus reference position of the focus lens prior to an auto focus operation, the focus based on the lens position of full Okasurenzu It is managed as a relative position from the position, it scans over the entire area where the focus lens is focused, and the focus lens is moved to the position where the value of the high frequency component of the luminance signal is the maximum, so that the autofocus operation is performed In a camera autofocus device, the amount of change, which is a change width of a high-frequency component of a luminance signal for acquiring AF data indicating the degree of focus, which is sampled as the focus lens moves during autofocus operation, and an image From the luminance composition histogram of the To infer the presence or absence of abnormal movement of the autofocus lens, it is determined that the small changes in the high frequency component of the luminance signal when the change amount is a variation of the high frequency component of the luminance signal is below a predetermined value, the high frequency component of the luminance signal However, if the brightness difference is greater than or equal to a predetermined value, it is determined that the movement is abnormal, and if it is determined that the movement is abnormal, control is performed so that the focus reference position of the autofocus lens is measured again. Control is performed so that the autofocus operation is performed after the position is measured again, thereby avoiding focusing failure due to abnormal lens movement.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0013]
FIG. 1 is a configuration diagram of a main part of a camera according to an embodiment of the present invention. In FIG. 1, 1 is a lens (single focus lens as a focus lens), 2 is a shielding plate that works in conjunction with the lens 1, 3 is a photointerrupter unit that detects passage of the shielding plate 2, and 4 is constituted by an AF motor, a gear, or the like. The lens driving mechanism unit 5 is a motor driving driver for driving and controlling the AF motor of the lens driving mechanism unit 4, 6 is a CCD, 7 is an AGC circuit, 8 is an A / D converter, 9 is a DSP, and 9a is AE data calculation. , 9b is an AF data calculation unit, 9c is a maximum / minimum luminance value measurement unit, 10 is a DSP, 11 is a microcomputer, and 12 is a timing generator.
[0014]
In this embodiment, a maximum / minimum luminance value measuring unit 9c for measuring the maximum value and the minimum value of the luminance signal of the image is added to the DSP 9 in the conventional configuration shown in FIG. The brightness value measuring unit 9c measures the maximum brightness value, the minimum brightness value, and the brightness difference of the image. The other components of this embodiment are the same as those in FIG. 9 described above, and the description thereof is omitted to avoid duplication.
[0015]
When all the areas to be focused are scanned when autofocusing is performed, if there is a certain level of contrast in the image, the lens position, the high-frequency component of the luminance signal, and the difference between the maximum luminance and the minimum luminance of the image The relationship is as shown in the graph of FIG. 6, for example. As described above, the high frequency component of the luminance signal becomes the largest at the time of focusing. In general, the luminance difference is large at any lens position and becomes larger at the time of focusing, but the change is small.
[0016]
On the other hand, when all the areas to be focused are scanned when autofocusing is performed, when the contrast of the image is low, the relationship between the lens position, the high frequency component of the luminance signal, and the difference between the maximum luminance and the minimum luminance of the image For example, as shown in the graph of FIG. In this case, the high frequency component of the luminance signal is generally small, and the luminance difference is also small over the entire area.
[0017]
On the other hand, when the entire region to be focused for autofocusing is scanned after the lens causes an abnormal movement due to impact or the like as described above, the lens position and the high-frequency component of the luminance signal The relationship between the maximum luminance and the minimum luminance difference of the image is, for example, as shown in the graph shown in FIG. In this case, the high-frequency component of the luminance signal hardly changes, and the luminance difference is large at any lens position. Therefore, although the change of the high frequency component is small, it can be estimated that the lens causes an abnormal movement when the luminance difference is a predetermined value or more. Therefore, in this embodiment, although the change in the high-frequency component is small, if the luminance difference is equal to or greater than a predetermined value, the microcomputer 11 determines that an abnormal movement of the lens 1 has occurred, and the lens 1 described above. The reference position re-detection operation is executed.
[0018]
FIG. 2 shows a processing flow of the autofocus operation of the present embodiment. First, when the user presses the shutter halfway, the autofocus operation is started (step S1). By auto-focusing, scanning is performed over the entire area where the lens is focused, and at this time, the high-frequency component and luminance difference of the luminance signal are sequentially stored during scanning, and the high-frequency component and luminance difference of the luminance signal are stored throughout the entire area where the lens is focused. (Step S2). Next, in step S3, it is determined whether or not the amount of change in the high-frequency component of the luminance signal is greater than a predetermined value. If the amount of change in the high-frequency component is large, the process proceeds to step S4 and the highest frequency component is detected. A large position is set as a focus position. If the amount of change in the high frequency component is small, the process proceeds to step S5, where the amount of luminance difference is observed to determine whether the luminance difference is smaller than a predetermined value over the entire area. Advances to step S6, and the lens is fixed at a certain focal length as an image having a small contrast. On the other hand, when the amount of luminance difference is seen and it is larger than a predetermined value, the process proceeds to step S7, and the reference position of the lens is initialized as occurrence of abnormal lens movement.
[0019]
【The invention's effect】
As described above, according to the present invention, in a configuration in which the lens position is managed as a relative position from the focus reference position and the autofocus operation is performed, the abnormal movement of the lens due to an impact or the like is determined, and the lens abnormality is detected. Since the return at the time of movement is automatically performed, it is possible to avoid the situation of continuously taking an out-of-focus image until the power is turned off / on as in the conventional case, which greatly improves convenience for the user.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a main configuration of a camera according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a process flow of an autofocus operation in an embodiment of the present invention.
FIG. 3 is a graph showing a relationship between a lens position and a high frequency component of a luminance component in a general subject.
FIG. 4 is a graph showing a relationship between a lens position and a high frequency component of a luminance signal in a subject with low contrast.
FIG. 5 is a graph showing a relationship between a lens position and a high-frequency component of a luminance signal after occurrence of abnormal lens movement.
FIG. 6 is a graph showing a relationship between a lens position, a high-frequency component of a luminance signal, and a luminance difference in a general subject.
FIG. 7 is a graph showing a relationship between a lens position, a high frequency component of a luminance signal, and a luminance difference in a subject with low contrast.
FIG. 8 is a graph showing a relationship between a lens position, a high frequency component of a luminance signal, and a luminance difference after occurrence of abnormal lens movement.
FIG. 9 is an explanatory diagram showing a main configuration of a conventional camera.
[Explanation of symbols]
1 lens (single focus lens as focus lens)
2 Shield plate 3 Photo interrupter unit 4 Lens drive mechanism unit 5 Motor drive driver 6 CCD
7 AGC circuit 8 A / D converter 9 DSP
9a AE data calculation unit 9b AF data calculation unit 9c maximum / minimum luminance value measurement unit 10 DSP
11 Microcomputer 12 Timing generator

Claims (1)

Using the single focus lens as a focusing lens, in that you measure the focus reference position of the focus lens prior to an auto focus operation, it manages the lens position of full Okasurenzu relative position from the focus reference position, the focus lens In the autofocus device of the camera that scans over the entire area to be focused and moves the focus lens to the position where the value of the high frequency component of the luminance signal is maximum ,
From the amount of change, which is the change width of the high-frequency component of the luminance signal for acquiring AF data indicating the degree of focus, sampled with the movement of the focus lens during the autofocus operation, and the luminance configuration histogram of the image, Estimate the presence or absence of abnormal movement of the autofocus lens due to impact, etc. , and if the amount of change, which is the change width of the high-frequency component of the luminance signal, is less than or equal to a predetermined value, determine that the change in the high-frequency component of the luminance signal is small of but a change in the high frequency component is small, is determined as abnormal movement when the luminance difference is greater than a predetermined value, when it is determined that the abnormal movement, the focus reference position of the auto-focus lens is controlled to re-measure the camera o of which is characterized in that the means for controlling to perform the autofocus operation after the re-measured focus reference position, having Autofocus system.

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