JPH06281855A - Focusing information detecting device - Google Patents

Abstract

PURPOSE:To detect focusing information from one image information with high accuracy and at a high speed by forming image information on the surface of an image pickup means, and deriving appropriately a self-correlation of the image information by a luminous flux passing through a prescribed opening part on the pupil surface of a photographic lens. CONSTITUTION:Image information from an object to be photographed, passing through a photographing optical system 11, forms an image on an image pickup element 12. The image information converted to an electric signal therein is subjected to sample holding by a sample holding circuit 13, and thereafter, becomes an RGB signal in a color separation/gamma converting circuit 14. Also, a green signal output from the color separation/gamma converting circuit 14 is converted to digital data in an A/D converter 16, an autocorrelation function is calculated in a correlation arithmetic circuit 17, and based on its result, focusing information, that is, distance information of the object to be photographed is derived in a focusing information detecting part 18. Based on the distance information of the object to be photographed, derived by this focusing information detecting part 18, a lens driving circuit 19 moves a focusing lens of the photographing optical system 11 to a focused position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-focus information detecting device, and more particularly, to forming an image information of an object on a surface of an image pickup means by a photographing optical system and obtaining an autocorrelation of an output signal from the image pickup means. The present invention relates to a focus information detecting device suitable for, for example, a video camera, which detects focus information and performs a focus operation of the photographing optical system.

[0002]

2. Description of the Related Art Conventionally, various light-receiving type focus information detecting devices have been proposed which detect focus information by using image information based on a light flux passing through a photographing optical system (photographing lens).

Of these, in a focus information detecting device for forming image information on the surface of an image pickup means (image pickup element) by a photographing optical system and detecting a focus shift from an output signal (image information) from the image pickup means, A distance measuring frame is set near the center of the shooting area, and a frequency component having a relatively high frequency is separated from the data in the distance measuring frame by a band pass filter and taken out.

While moving the imaging position of the photographing lens in the optical axis direction, the change in the separated high frequency components is measured, and the position where the maximum value is detected is detected as the in-focus position. .

[0005]

In a conventional apparatus for detecting focusing information of a photographing lens by obtaining a high frequency component of an output signal from the photographing means, a relative positional relationship between the photographing lens and the photographing means is determined. It is necessary to change variously and use a plurality of image information obtained at this time.

Therefore, it takes a lot of time to obtain the focus information, and it is difficult to obtain the instantaneous focus information (distance measurement information).

According to the present invention, a light beam which has passed through a predetermined opening on the pupil surface of a photographing lens forms image information on the surface of an image pickup means, and an autocorrelation of the image information is appropriately obtained to obtain the image pickup lens. An object of the present invention is to provide a focus information detection device suitable for, for example, a video camera, which can detect focus information from one image information with high accuracy and at high speed without performing relative movement with the image pickup means. And

[0008]

In the focusing information detecting apparatus of the present invention, a shading member having a plurality of openings is detachably arranged in the optical path of the photographing optical system, and the photographing optical system and the shading member are separated from each other. Image information is formed on the surface of the image pickup means by the light flux passing through the aperture, and the third or higher order autocorrelation of the output signal from the image pickup means is calculated by the calculation means. It is characterized by seeking focus information.

In particular, the calculating means obtains the autocorrelation between pixels arranged in a similar shape to the openings on the image pickup surface of the image pickup means according to the shapes and the arrangements of the plurality of openings of the light shielding member. That the calculation means obtains the autocorrelation after applying the prefilter to the output signal from the image pickup means, and the calculation means has the characteristics of the prefilter according to the interval of the pixels of the autocorrelation calculation. It is characterized by switching the.

[0010]

Embodiment 1 FIG. 1 is a block diagram of the essential parts of Embodiment 1 of the present invention.

In the figure, reference numeral 11 is a photographing optical system, and a light-shielding plate having a plurality of openings is provided in the optical path so that it can be inserted and removed. Reference numeral 12 denotes an image pickup means (image pickup element), which converts the image information formed by the photographing optical system 11 into an electric signal.

Reference numeral 13 is a sample hold circuit, 14 is a color separation and γ conversion circuit, 15 is a matrix circuit for obtaining luminance and color difference outputs, 16 is an A / D conversion circuit for converting an analog signal into a digital signal, 17 Is a computing means,
It is composed of a correlation calculation processing block for performing an autocorrelation calculation.

Reference numeral 18 is a focus information detection block for detecting focus information based on the result of correlation calculation, 19 is a lens drive circuit, and 20 is a clock generator for supplying a clock to each block.

In FIG. 1, image information from a subject that has passed through the taking optical system 11 is imaged on the image pickup device 12.

The image information converted into the electric signal is sampled and held by the sample and hold circuit 13, and then becomes an RGB signal in the color separation and γ conversion circuit 14. The RGB output is converted into a luminance signal and a color difference signal by the matrix circuit 15 and output.

On the other hand, the green signal (G signal) output from the color separation / γ conversion circuit 14 is converted into digital data by the A / D converter 16, and the autocorrelation function is calculated by the correlation calculation circuit 17, and the result is obtained. Based on the above, the focus information detecting unit 18 obtains the focus information, that is, the distance information of the subject.

Based on the object distance information obtained by the focus information detector 18, the lens drive circuit 19 causes the photographing optical system 11 to operate.
Move the focusing lens of to the in-focus position.

In the present embodiment, the focusing operation of the photographing optical system 11 is performed by the above-mentioned operation.

Next, the photographing optical system 11 in the present embodiment,
The operation and processing of the correlation calculation circuit 17 and the focus information detection unit 18 will be described.

FIG. 2 is a schematic view of the essential parts showing the relationship between the projection optical system 11 and the image pickup device (sensor) 12 according to the present invention. In the figure, 1 is a taking lens, 2 is a plurality of openings 2a, 2
A light-shielding plate having b and 2c, 3 is the position of the sensor in the rear focus state, 4 is the position of the sensor in the focus state, and 5 is the position of the sensor in the front focus state.

The light shielding plate 2 has three openings 2a, 2b and 2c.
The light passing through each opening forms an image on the sensor. When the sensor is at position 3, the light passing through the opening 2a is in the area 3a, and the light passing through the opening 2b is in the area 3b.
Then, the light passing through the opening 2c forms an image on the region 3c.

When the sensor is in the in-focus position, the three light beams form an image at one point. When the sensor is at the position 5, the light passing through the opening 2a is imaged in the area 5a, the light passing through the opening 2b is imaged in the area 5b, and the light passing through the opening 2c is imaged in the area 5c.

FIG. 3 shows the state of image information on each image plane of FIG.

In FIG. 3, reference numerals 3, 4, and 5 respectively represent images of the sensors provided at the positions 3, 4, and 5 in FIG. As is clear from FIG. 3, the images of the light passing through the openings 2a, 2b, 2c are in point symmetry at positions 3 and 5.

Therefore, in the present embodiment, if the orientation of the pixel on the sensor is the same as that of the light shielding plate 2, it is determined that the state is the rear pin state, and if it is rotated by 180 degrees, the front pin state is determined.

Next, the correlation calculation unit 1 as the calculation means of FIG.
The signal processing of No. 7 will be described with reference to FIG.

FIG. 4A is a view showing the shape of the light shielding plate 30,
FIG. 4B is a diagram showing a positional relationship between the openings a, b, c of the light shielding plate 30, and FIG. 4C is a diagram showing a positional relationship of pixels on the image sensor 12 for performing calculation.

As shown in FIG. 4A, the light shielding plate 30 has three holes (openings) a, b and c. The positional relationship among the three openings a, b, c is as shown in FIG. 4 (B), for example.

As shown in FIG. 4B, when writing a square in the horizontal and vertical directions, the three openings are arranged in the horizontal direction from left to right in the order of b, a, and c. Further, in the vertical direction, c, b, and a are arranged at equal intervals from the top. Here, the horizontal and vertical pitches are equal.

When the openings a, b, and c have such a positional relationship, the image for the point light source has a similar shape to that of the rear focus when viewed from the object side when the object is rear-focused. In the case of the front focus, the image is similar to this and rotated 180 degrees when viewed from the subject side.

Since a general image can be regarded as an infinite superimposition of point light sources having different brightnesses, the images on the sensor also have images similar in shape to the openings a, b, c of the light shielding plate 30. Will be things.

Therefore, the correlation between the pixels in this positional relationship becomes strong except in the in-focus state. Further, the size of the blurred image changes in proportion to the magnitude of the focus shift while maintaining the similar relationship with the openings a, b, and c.

Therefore, in order to obtain the correlation between the image of the opening b and the image of the opening c with reference to the image of the opening a, the following calculation may be performed.

As shown in FIG. 4C, when the coordinate of the pixel in the horizontal direction is represented by i and the pixel in the vertical direction is represented by coordinate j, the opening b is formed at the reference point x (i, j). The corresponding image is on the line of arrow 31, and the image corresponding to the opening C is on the line of arrow 32. (In the case of the rear pin, the arrow is in front of the arrow, and in the case of the front pin, it is behind the arrow.) Therefore, the autocorrelation calculation is performed on the pixel on the extension line of the arrow 31 and on the extension line of the arrow 32 with respect to the reference pixel. Only the pixels need to be calculated.

[0035]

[Equation 1] Equation (1) shows the autocorrelation calculation formula. FIG. 5 shows the autocorrelation C (n, m) calculated based on the equation (1).

FIG. 5 shows the correlation of the blurred image with respect to the point light source, and FIG. 5A shows the blurred image at the time of the rear focus, and FIG.
5B is a calculation result of the correlation for the image of FIG.
FIG. 5 (C) is a blurred image at the time of front focus, and FIG. 5 (D) is FIG.
It is the calculation result of the correlation about the image of (C). Figure 5
The peak 51 appearing at the center in (B) and (D) is m =
The origin is 0 and n = 0, and appears regardless of the amount of deviation. In addition to the central peak, a peak 52 appears in the negative regions of both n and m in FIG. 5B, and a peak 53 appears in the positive regions of both n and m in FIG. 5D.

As described above, the areas where peaks appear are different between the front pin and the rear pin.

Further, the distances of the peaks 52 and 53 from the origin are
It corresponds to the amount of out-of-focus. Further, if the shape of the blur, that is, the shape of the opening is known in advance, the relationship between n and m is determined in one way, so it is possible to express the correlation by either one of the variables.

In this case, since it is known that a peak occurs on the line of m = n, it is sufficient to perform the calculation only on the line of m = n.

FIG. 6 shows values on the line of m = n.

In FIG. 6, FIG. 6 (A) corresponds to FIG. 5 (B),
FIG. 6B corresponds to FIG. 5D. Peak 51,
The numbers 52 and 53 correspond to each other.

Although the case of the point light source has been described with reference to FIGS. 5 and 6, the case other than the point light source will be described with reference to FIG.

FIG. 7A shows a state in which the image is in focus, and FIG.
FIG. 7B is an image of the rear pin state, and FIG. 7D is an image of the front pin state. 7C and 7E show the results of correlation obtained for the images of FIGS. 7B and 7D in the same manner as in FIG.

In FIG. 7C, two peaks 72 and 73 are generated in addition to the peak 71 at the origin. See also FIG.
Also in (E), two peaks 74 and 75 are generated in addition to the peak 71 at the origin.

In the case of FIG. 7C, the peak 7 on the negative side of n is 7
2 is higher than the peak 73.

On the contrary, in the case of FIG. 7E, the peak 75 on the positive side of n is higher than the peak 74.

As described above, even in the case other than the point light source, it is possible to know the focus shift amount and the direction by obtaining the maximum point other than the origin.

The focus information detecting unit 18 of FIG. 1 obtains the peak position of the autocorrelation function thus obtained excluding the origin, and obtains the value of the variable n at the maximum peak. Since the value of n is proportional to the amount of focus deviation, the amount of movement of the lens required for focusing is determined from this value and the data is sent to the lens drive circuit 19.

Then, the lens driving circuit 19 drives the focusing lens to perform the focusing operation.

Next, a second embodiment of the present invention will be described.
The main part of the constituent requirements is substantially the same as that shown in FIG.

The present embodiment is different from the first embodiment shown in FIG. 1 in the calculation processing method performed by the correlation calculation circuit 18.

In the correlation calculation circuit 18 of this embodiment, the autocorrelation is obtained after the image signal is passed through the prefilter (digital filter).

Next, the features of this embodiment will be described with reference to FIGS.

FIG. 8 shows the coefficients of the digital filter Q. When the light shielding member 30 shown in FIG. 4A is used, the output signal from the image pickup device 12 is subjected to the digital filter Q shown in FIG. 8 and then the same correlation calculation as in the first embodiment is performed.

Here, the output signal of the image sensor 12 is x
(T), the signal y (t) after being subjected to the digital filter Q
Since this digital filter Q is a high pass filter, y (t) has a positive value and a negative value. Since the correlation calculation only needs to be performed for signals having the same polarity, only the signals having the same sign of y (t) have the same polarity. If y (t) is negative, the calculation result If the absolute value is used, the correlation peak becomes clearer.

FIG. 9 shows the result of the calculation thus obtained. The image data used for the calculation is the same as in FIG. 9A is obtained from FIG. 7B, that is, the data of the state of the rear pin, and FIG. 9B is obtained from FIG. 7D, that is, the data of the state of the front pin.

FIGS. 9A and 9B and FIGS. 7C and 7E.
As can be seen from the comparison between and, by using the digital filter shown in FIG. 8, the peak of the correlation calculation result becomes sharp and the peak can be easily discriminated.

In the case of FIG. 7C, there are three peaks, the first peak 71 having the largest correlation, the second peak 72 having the next largest correlation, and the third peak 73 having the third largest correlation. The determination was made as to whether it is the front pinning or the rear pinning depending on which of the second and third peaks is larger. In the case of FIG. 9A, the first peak 91 and the second peak 92 are determined.
, But the third peak does not appear clearly. Therefore, the determination of the front pin and the rear pin becomes easy.

The same applies to the case of FIG. 7E, where the second and third peaks of the three peaks 71, 74, and 75 are compared, while the case of FIG. 9B. The first peak 91 and the second peak 95 remarkably appear, and the third peak does not appear clearly. Therefore, since the peak 95 is on the plus side, it can be easily determined that it is the front pin. Further, since a peak appears sharply by using the filter as in this embodiment, even if there is a correlation peak near the origin, the correlation peak can be detected.

Next, a third embodiment of the present invention will be described.

The main part of the constituent elements is substantially the same as that shown in FIG. In this embodiment, the calculation processing method performed by the correlation calculation unit 18 is different from that of the first embodiment shown in FIG. Similar to the second embodiment, the correlation calculator 18 of the present embodiment obtains the autocorrelation of the image signal by using the digital filter.

Next, the features of this embodiment will be described with reference to FIGS.

In this embodiment, the digital filter used in the second embodiment is improved. In the present embodiment, the coefficient matrix of the digital filter is "4" at the center, the coefficient at positions shifted by n pixels in the horizontal and vertical directions from the center is "-1", and the others are "0".

FIG. 10 shows the coefficients when n = 1, n = 2, and n = 3. T is a matrix when n = 1, U is n = 2, and V is n = 3. Similarly, when n is 4 or more, the coefficient at the position shifted by n pixels is "-1". When n = 0, five coefficients are overlapped and 4 −1 −1 −1 −1 −1 = 0, so all the coefficients are “0”. The value of n is the same as the variable n for the correlation calculation used in the first embodiment, and the digital filter also changes according to the variable of the correlation calculation.

When the correlation calculation is performed after applying the digital filter of this embodiment, the results shown in FIGS. 11 and 12 are obtained.

FIGS. 11A and 11B are respectively shown in FIGS.
It is the result of processing the data of (C). Calculation result when no filter is used FIG. 5 (B),
Compared with (D), in the case of FIGS.
The peak 51 at = 0 disappears. The maximum value is taken at position 52 in FIG. 5 (B) and position 5 in FIG. 5 (D).
The positions 111 and 112 correspond to 3. Since the peak near the origin disappears in this way, it becomes easy to detect the peak of the correlation generated by the focus shift.

FIGS. 12A and 12B are respectively FIG. 7B and
It is a result of processing the data of (D) with n = m. Correlation data obtained from the data of FIGS. 7 (B) and (D) When compared with FIGS. 7 (C), (E), FIGS. 9 (A), and (B), n in FIGS. Since the peak does not occur at = 0, the maximum value of each position is 121
And the position 122 can be detected as the peak of the correlation.

As described above, according to the present embodiment, it is possible to remove the influence of the correlation that strongly appears near the origin in the correlation calculation, so that it is possible to easily detect the focus shift.

[0069]

As described above, according to the present invention, image information is formed on the surface of the image pickup means by the light flux passing through the predetermined opening on the pupil plane of the photographing lens, and the autocorrelation of the image information is calculated. By appropriately obtaining the focus information, it is possible to detect the focus information from one image information with high accuracy and at high speed without performing relative movement between the taking lens and the image pickup means. For example, it is suitable for a video camera. A focus information detection device can be achieved.

Particularly, according to the present invention, it becomes possible to detect the in-focus position only from the information of one screen at a certain moment.
It is not necessary to move the taking lens or the image pickup element to detect the focus information, and it is possible to achieve the focus information detection device having the effect that the speed of the focus information detection can be increased.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of a first embodiment of the present invention.

FIG. 2 is a schematic view of a main part of the taking optical system shown in FIG.

FIG. 3 is an explanatory diagram of the image information of FIG. 1.

FIG. 4 is a schematic diagram showing a correlation calculation method according to the present invention.

FIG. 5 is an explanatory diagram of a calculation result by a correlation calculation according to the present invention.

FIG. 6 is an explanatory diagram of a calculation result by a correlation calculation according to the present invention.

FIG. 7 is an explanatory diagram of a calculation result by a correlation calculation according to the present invention.

FIG. 8 is an explanatory diagram of a digital filter according to a second embodiment of the present invention.

FIG. 9 is an explanatory diagram of a result of a correlation calculation according to the second embodiment of the present invention.

FIG. 10 is an explanatory diagram of a digital filter according to a third embodiment of the present invention.

FIG. 11 is an explanatory diagram of a result of a correlation calculation according to the third embodiment of the present invention.

FIG. 12 is an explanatory diagram of a result of a correlation calculation according to the third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photographing lens 2 Light-shielding plates 2a, 2b, 2c Opening 11 Photographing optical system 12 Imaging means 13 Sample and hold circuit 14 Color separation, γ conversion circuit 15 Matrix circuit 16 A / D converter 17 Correlation calculation circuit 18 Focusing information detector 19 Lens drive circuit 30 Light shield

Claims (4)

[Claims] 1. A light-shielding member having a plurality of openings is removably arranged in the optical path of a photographing optical system, and image information is picked up by a light flux passing through the photographing optical system and the opening of the light-shielding member. Focus information detection, which is formed on the above, obtains the third or higher order autocorrelation of the output signal from the image pickup means by the operation means, and obtains the focus information of the photographing optical system from the operation result. apparatus. 2. The calculation means obtains an autocorrelation between pixels arranged in a similar shape to the openings on the image pickup surface of the image pickup means in accordance with the shapes and the arrangements of the plurality of openings of the light shielding member. The focus information detecting device according to claim 1, wherein 3. The focusing information detecting apparatus according to claim 2, wherein the arithmetic means obtains the autocorrelation after pre-filtering the output signal from the image pickup means. 4. The focus information detecting device according to claim 3, wherein the calculation means switches the characteristics of the pre-filter in accordance with the pixel interval of the autocorrelation calculation.