JP3430647B2 - Auto focus circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing type auto-focus circuit for detecting a middle to high frequency component of a video signal and performing focus control. 2. Description of the Related Art An image processing type autofocus circuit which detects the level of a middle-high frequency component of a captured luminance signal and controls the position of a lens so that the level of the middle-high frequency component of the luminance signal is maximized. It has been known. [0003] That is, FIG. 2A shows a state of an image pickup signal when out of focus, and FIG. 3A shows a state of an image pickup signal when in focus. As shown in FIG. 2A,
When out of focus, the edge of the captured luminance signal is blurred. When the high-frequency component of such a signal is extracted by a high-pass filter, its output becomes small as shown in FIG. 2B. On the other hand, when focused, as shown in FIG. 3A, the edge of the captured luminance signal becomes clear. When the high-frequency components of such a signal are extracted by a high-pass filter, the output increases as shown in FIG. 3B. Accordingly, if the level of a high-frequency component of a captured luminance signal is detected and the position of the lens is controlled so that the level of the high-frequency component is maximized, the lens can be positioned at the in-focus position. . FIG. 4 shows an example of a conventional video camera. As described above, this conventional video camera is provided with an autofocus circuit that detects a high-frequency component level of an image pickup signal and obtains a focus position. In FIG. 4, reference numeral 101 denotes a CCD image pickup device. A lens 10 is provided on the light receiving surface of the CCD image sensor 101.
2. The subject image light is formed through the iris 103. The lens 102 is moved by a focus motor 104
It is possible to move. The focus motor 104 has
A drive signal is supplied from the controller 105 via the driver 106. The opening and closing of the iris 103 is controlled by the controller 105. The subject image light is photoelectrically converted by the CCD image pickup device 101. The output of the CCD image sensor 101 is supplied to the sample hold and AGC circuit 107. The output of the sample hold and AGC circuit 107 is supplied to the A / D converter 108. A / D converter 108
Then, the imaging signal is digitized. The output of the A / D converter 108 is supplied to the camera signal processing circuit 109. In the camera signal processing circuit 109, a luminance signal and a chroma signal are formed, and processes such as gamma correction, aperture correction, and white balance adjustment are performed. The output of the camera signal processing circuit 108 is supplied to the next processing circuit, and the luminance signal from the camera signal processing circuit 109 is supplied to the optical detection circuit 110. The optical detection circuit 110 includes a high-pass filter 111, a rectifier circuit 112, a gate circuit 113, and a peak detection circuit 114 for obtaining an evaluation value for auto-focusing.
7 for automatic exposure. [0010] The luminance signal from the camera signal circuit 109 is supplied to a high-pass filter 111 and also to a rectifier circuit 115. In the high-pass filter 111,
The high frequency component of the luminance signal is extracted. The output of the high-pass filter 111 is supplied to the rectifier circuit 112. The output of the rectifier circuit 112 is supplied to the gate circuit 113. The gate circuit 113 sets a distance measurement frame for performing focus adjustment. The output of the gate circuit 113 is supplied to the peak detection circuit 114. The peak detection circuit 114 detects the peak level of the high-frequency component of the luminance signal in the ranging frame. From the output of the peak detection circuit 114, the evaluation value S1
0 is obtained. This evaluation value S10 is
Supplied to The controller 105 includes a peak detection circuit 1
The maximum value of the evaluation values from 14 is detected. That is, while moving the lens 102, the evaluation value from the peak detection circuit 114 is determined, and the lens 1 whose evaluation value reaches a peak is determined.
The position of 02 is the focus position. With such control,
Auto focus control is performed. A luminance signal from the camera signal circuit 109 is supplied to a detection circuit 117 via a gate circuit 116.
Supplied to From the output of the detection circuit 117, a luminance signal level is detected. The output of the detection circuit 117 is supplied to the controller 105. The controller 105 controls the opening degree of the iris 103 and A so that the luminance signal level becomes a predetermined value.
The gain of the GC circuit 107 is set. With such control, automatic exposure control is performed. As described above, the conventional image processing type autofocus circuit detects a high-frequency component level of a captured luminance signal and uses it as an evaluation value. However, the high frequency component level of the luminance signal contains a noise component. Due to the influence of this noise component, the DC level of the evaluation value changes. For this reason, in a conventional image processing type autofocus circuit, for example, AG
When the noise level fluctuates due to the fluctuation of the C gain,
A malfunction may occur. FIG. 5 shows the relationship between the lens position and the evaluation value. In FIG. 5, the horizontal axis indicates the position of the focus lens, and the vertical axis indicates the evaluation value. When the lens 1 is positioned at L1, the evaluation value becomes maximum. The position at which this evaluation value is the maximum is the focus position. In FIG. 5, A1 is a curve of the evaluation value when bright,
A2 is a curve of the evaluation value when dark. As shown in FIG. 5, the DC level B2 of the evaluation value curve A2 when dark is larger than the DC level B1 of the evaluation value curve A1 when bright. This is because when dark, the gain of the AGC circuit 107 is increased by the automatic exposure control. When the gain of the AGC circuit 107 increases, the noise component increases, and this noise appears as a DC component of the evaluation value. Therefore, for example, if the amount of light in the surroundings is changed while the same subject is being photographed, the focused state may come and go. That is, FIG. 6 shows how the evaluation value changes when the amount of light around the same subject changes. In FIG. 6, the horizontal axis represents time, and the vertical axis represents AGC gain and evaluation value. As shown in FIG. 6, when the amount of ambient light changes with time T, the amount of ambient light changes, as shown by a curve C1, as shown by a curve C1.
The AGC gain changes. When the AGC gain changes in this way, the DC level of the evaluation value changes, and the evaluation value changes as shown by the curve D1. The change D1 in the evaluation value has a peak P1. At the peak P1, it may be determined that the lens has reached the in-focus position. Accordingly, an object of the present invention is to provide an auto-focusing circuit of an image processing system, which is not affected by a change in the DC level of an evaluation value, and in which an erroneous operation due to a change in ambient light quantity or the like is improved. To provide. According to the present invention, there is provided a lens whose position can be controlled, lens driving means for moving the lens,
Imaging means for forming an image of a subject through a lens;
Peak detection of the middle and high frequency components of the luminance signal from the imaging means
A peak detection means, and a middle and high frequency component of a luminance signal from the imaging means.
Mean detection means for finding the average value of minutes, and peak detection means
Multiply the output of the average value detection means by a predetermined coefficient from the output of
This is an auto-focusing circuit that includes an arithmetic unit that subtracts the calculated value to form an evaluation value, and a control unit that controls the position of the lens so that the evaluation value is maximized, thereby controlling the lens to the in-focus position. The peak detection circuit detects the peak value of the high frequency component of the luminance signal in the image signal, and the integration circuit detects the average value of the high frequency line segment of the luminance signal. Integration circuit 15
The DC level is obtained by multiplying the average value of the high-frequency line segment of the luminance signal from by a predetermined coefficient, and this DC level is subtracted from the peak detection value of the luminance signal to obtain an evaluation value. Focus control of the lens is performed based on this evaluation value. As a result, the evaluation value is not affected by a change in the DC level, and a malfunction due to a change in the amount of light in the surroundings does not occur. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a CCD image sensor.
A lens 2 and an iris 3 are provided on the light receiving surface of the CCD image pickup device 1.
, The subject image light is formed. The lens 2 is movable by a focus motor 4. A drive signal is supplied from the controller 5 to the focus motor 4 via the driver 6. The opening and closing of the iris 3 is controlled by the controller 5. The subject image light is photoelectrically converted by the CCD image pickup device 1. The output of the CCD image sensor 1 is supplied to a sample hold and AGC circuit 7. The output of the sample hold and AGC circuit 7 is supplied to the A / D converter 8. The image signal is digitized by the A / D converter 8. The output of the A / D converter 8 is supplied to the camera signal processing circuit 9. In the camera signal processing circuit 9, a luminance signal and a chroma signal are formed, and gamma correction, aperture correction,
Processing such as white balance adjustment is performed. The output of the camera signal processing circuit 9 is supplied to the next stage circuit, and the luminance signal from the camera signal processing circuit 9 is supplied to the optical detection circuit 10. The optical detection circuit 10 includes a high-pass filter 1
1, rectifier circuit 12, gate circuit 13, peak detection circuit 1
4, a circuit for obtaining an evaluation value for autofocus comprising an integrating circuit 15 and an arithmetic circuit 16; and a circuit for automatic exposure comprising a gate circuit 22 and a detection circuit 23. The luminance signal from the camera signal circuit 9 is
While being supplied to the high-pass filter 11, the rectifier circuit 2
1 is supplied. The high-pass filter 11 extracts a high-frequency component of the luminance signal. The output of the high-pass filter 11 is supplied to the rectifier circuit 12. The output of the rectifier circuit 12 is supplied to the gate circuit 13. The gate circuit 13 sets a distance measurement frame for performing focus adjustment. The output of the gate circuit 13 is supplied to the peak detection circuit 14 and also to the integration circuit 15. The peak detection circuit 14 detects the peak level of the high frequency component of the luminance signal in the distance measuring frame. The output Sa of the peak detection circuit 14 is supplied to the arithmetic circuit 16.
The integration circuit 15 obtains the average value of the high frequency component of the luminance signal. This average value Sb is supplied to the arithmetic circuit 16. The arithmetic circuit 16 subtracts the DC level from the high frequency level of the luminance signal from the peak detection circuit 14 to form an evaluation value S1. That is, the peak detection value Sa of the high frequency component of the luminance signal is obtained from the peak detection circuit 14. This peak detection value Sa includes a DC component Sn generated by detecting the noise with a peak. The average amplitude Sb of the high frequency component of the luminance signal is obtained from the integration circuit 15. DC value Sn generated by peak detection of random noise,
The average amplitude Sb is statistically correlated with the average amplitude Sb.
N times (N is obtained by actual measurement according to the system)
Then, the DC value Sn generated by peak detection of the noise can be estimated. Therefore, the operation circuit 16 performs the operation of S1 = Sa−N × Sb. Thus, the evaluation value S1 from which unnecessary DC components have been removed is obtained. This evaluation value S1 is supplied to the controller 5. The controller 5 detects the lens position at which the evaluation value S1 becomes maximum. That is, while the lens 2 is slightly vibrated, the evaluation value S1 from the arithmetic circuit 16 is determined, and the position of the lens 2 at which the evaluation value S1 reaches a peak is detected. The lens position at which the evaluation value S1 becomes the maximum is defined as the focus position. By such control, auto focus control is performed. The luminance signal from the camera signal circuit 9 is supplied to a rectifier 21, and the output of the rectifier 21 is supplied to a peak detector 23 via a gate 22. From the output of the peak detection circuit 23, a luminance signal level is detected. The output of the peak detection circuit 23 is supplied to the controller 5. The controller 5 sets the opening of the iris 3 and the gain of the AGC circuit 7 so that the luminance signal level becomes a predetermined value. With such control, automatic exposure control is performed. As described above, in one embodiment of the present invention, the evaluation value S1 of the auto focus is obtained by subtracting the DC value N × Sb of the high frequency component of the luminance signal from the high frequency component level Sa of the luminance signal. Like that. Therefore, the evaluation value is not affected by the fluctuation of the DC component. The arithmetic circuit 16 may be provided with dedicated hardware, or may be configured to perform an arithmetic operation by software. In the above-described embodiment, the high-pass filter 11 is used to extract the high-frequency component of the luminance signal. However, the high-pass component is extracted from the middle frequency of the luminance signal by the band-pass filter. You may do it. According to the present invention, the peak detection circuit detects the peak value of the high frequency component of the luminance signal in the image signal, and the integration circuit 15 averages the high frequency line segment of the luminance signal. Is detected, a DC level is obtained by multiplying the average value of the high frequency line segment of the luminance signal from the integration circuit 15 by a predetermined coefficient, and this DC level is subtracted from the peak detection value of the luminance signal to obtain an evaluation value. Focus control of the lens is performed based on this evaluation value. As a result, the evaluation value is not affected by a change in the DC level, and a malfunction due to a change in the amount of light in the surroundings does not occur.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment of the present invention. FIG. 2 is a waveform diagram used for describing autofocus of an image processing method. FIG. 3 is a waveform diagram used for describing autofocus of an image processing method. FIG. 4 is a block diagram used for describing a conventional autofocus circuit. FIG. 5 is a graph used to explain a conventional autofocus circuit. FIG. 6 is a graph used to explain a conventional autofocus circuit. [Description of Signs] 1 CCD imaging device 2 Lens 11 High-pass filter 14 Peak detection circuit 15 Integration circuit 16 Operation circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 7/28 G02B 7/08 G03B 13/36 H04N 5/232

Claims (1)

(57) [Claims 1] A lens whose position is controllable, lens driving means for moving the lens, imaging means for forming an image of a subject through the lens, Peak detection of middle and high frequency components of luminance signal from imaging means
And an average value of the middle and high frequency components of the luminance signal from the imaging means.
Average value detection means, and the output of the peak detection means
Subtract a value obtained by multiplying the output by a predetermined coefficient to form an evaluation value.
An autofocus circuit comprising: a calculating means for controlling the position of the lens so that the evaluation value is maximized; and a control means for controlling the lens to a focus position.