JPH0328691B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus detection signal processing method used in optical equipment such as cameras.

2. Description of the Related Art Conventionally, as one method of a focus detection device for a camera, a method is known in which the pupil of a photographic lens is divided and a shift between two images formed is observed to determine the in-focus state. For example, US Pat. No. 4,185,191 discloses an apparatus in which a group of fly-eye lenses is arranged on a predetermined image formation plane of a camera photographing lens, and two images are generated shifted in accordance with the amount of defocus of the photographing lens.
In addition, so-called secondary imaging is performed in which the aerial image formed on the predetermined imaging surface is guided to the solid-state image sensor surface by two secondary imaging threads arranged in parallel, and the relative positional shift of each image is detected. The method is disclosed in Japanese Patent Application Laid-open No. 55-118019, Japanese Patent Application Laid-open No. 55-155331, etc. The latter secondary imaging method has the advantage that it does not require a special optical system, although the overall length becomes slightly larger.

To briefly explain the principle of focus detection using this secondary imaging method using Fig. 1, a field lens 2 is placed on the same optical axis as the photographing lens 1 that adjusts the focus, and two field lenses are placed behind it. Secondary imaging lenses 3a and 3b are arranged in parallel, and light receiving sensor arrays 4a and 4b are arranged behind them, respectively. Note that 5a and 5b are secondary imaging lenses 3a and 3
This is a diaphragm provided near b. The field lens 2 forms an image of the exit pupil of the photographic lens 1 approximately on the pupil plane of the two secondary imaging lenses 3a and 3b. As a result, the light beams incident on each of the secondary imaging lenses 3a and 3b correspond to the respective secondary imaging lenses 3a and 3b on the exit pupil plane of the photographing lens 1.
They are emitted from areas of equal area that do not overlap each other. Aerial images formed near the field lens 2 are secondary imaging lenses 3a and 3b.
When the images are re-formed on the surfaces of the sensor arrays 4a and 4b, the positions of the two re-formed images change based on the difference in the positions in the optical axis direction where the aerial images were formed.

FIG. 2 shows how this phenomenon occurs, with the sensor arrays 4a and 4b centered on the in-focus state shown in FIG. 2a, and in front and rear focus as shown in FIGS. The two images formed on the surface move in opposite directions on the sensor array 4a, 4b surface. The in-focus state can be determined by photoelectrically converting this image intensity distribution using sensor arrays 4a and 4b and detecting the amount of relative positional deviation between the two images using an electrical processing circuit.

For example, US Pat. No. 4,250,376 is known as a method for processing photoelectrically converted signals. This means that when the received light signals obtained by photoelectrically converting two secondary images are respectively a(i) and b(i) (where i=1 to N), in the above example, for an appropriate constant k, V = _NK 〓 ⁱ⁼¹ a(i)-b(i+k) | - _NK 〓 ⁱ⁼¹ a(i+k)-b(i) | ...(1) is calculated digitally using an analog calculation circuit. , the direction in which the photographic lens 1 is extended is determined by the positive or negative value of this V.

However, in the calculation processing method based on this formula (1),
At most, the direction in which the photographing lens 1 should be extended is determined. Therefore, in a focus detection device that determines the in-focus state from the amount of deviation between the two images, the relationship between the amount of deviation of the two images and the amount of defocus is approximately proportional.
A method is known in which the amount of extension of the photographic lens 1 is calculated by displacing one image relative to the other. This method has been known for a long time for baseline distance meter type focus detection devices. In addition, as the price of semiconductor integrated devices has declined, it has become possible to process a considerable amount of information inside cameras, so arithmetic processing methods using the above-mentioned principles are also available for TTL focus detection devices that require high precision. Some suggestions have been made. For example, JP-A-56-
In Publication No. 75707 and Publication No. 57-45510, b(i)
Then, the image represented by a(i) is expressed as a correlation amount that represents the degree of agreement between the two images relative to the image represented by a(i).
V in equation (1) is calculated by circuit processing. That ^{is ,} V(m) is set as The relative displacement amount m is within the range m ₁
The calculation is repeated for each integer value of ≦m≦m ₂ .
A graph plotting the value of V(m) against m is shown in FIG. When the two images match, V(m) should be 0, so in Figure 3,
This means that there is an image shift amount equivalent to 1.5 bits.

However, the above equation (2) includes nonlinear processing called absolute value calculation, which appears as an increase in calculation steps even in digital processing using a microcomputer or the like. Further, in this calculation process of calculating the difference between two signals, noise components are superimposed, which causes a reduction in noise resistance.

An object of the present invention is to improve the problems of the above-mentioned embodiments, and to provide a focus detection signal processing method that is comprised only of linear calculations and can easily and accurately determine the amount of extension of the photographic lens, that is, the amount of focus shift. The gist of the system is to detect a plurality of object images formed by passing through a plurality of different optical paths using a photoelectric conversion element array, and to detect changes in the optical system based on changes in the relative positions of the plurality of object images. A method for determining the in-focus state, in which each element of a plurality of photoelectric conversion element arrays that receive the respective subject images is associated with each other in a certain correspondence relationship, and the photoelectric outputs of the corresponding photoelectric conversion elements are compared. Then, the process of extracting the minimum or maximum output value and obtaining the added value is repeated while changing the correspondence of the photoelectric conversion elements by a fixed amount, and the magnitude of the added value with respect to the amount of change in the correspondence is calculated. The present invention is characterized in that the amount of deviation of the optical system with respect to the in-focus position is calculated based on the change in the angle.

The present invention will be explained in detail based on the embodiment shown in FIG. 4 and below.

The applicant ^has _{previously determined} that ^: Calculate V= _NK 〓 ⁱ⁼¹ max {a(i), b(i+k)}- _NK 〓 ⁱ⁼¹ max{a(i+k), b(i)}...(4), and shoot based on the sign of V. A method for determining the direction in which the lens 1 is extended has been proposed. However, here, min{x, y} represents the smaller of the two real numbers x, y, and max{x, y} represents the smaller of the two real numbers x, y.
It represents something large, and k is an appropriate constant, usually 1.

This example is a correlation value calculation method that calculates while displacing one image relative to the other image.
As shown in equations (3) and (4), the intensity distribution information a(i) and b(i) of the two images are made to correspond based on a certain relative relationship, and the set of binary values { a(j1),
b(j2)}, one of them is selected based on the result, and then added. For example, when using equation (3), V(m)= 〓 ⁱ min{a(i), b(i+k-m)}- 〓 ⁱ min{a(i+k), b(i-m)}... When calculating (5) for different m and using equation (4), V(m)= 〓 ⁱ max{a(i),b(i+k−m)}− 〓 ⁱ max{a(i+k ), b(i-m)} ...(6) are calculated for different m. The range of i to be summed is determined from the condition that each subscript i, i+k-m, l+k, i-m must fall within the closed interval [1, N]. V (m) calculated by formula (5)
The graph plotted against m is shown in Figure 4a.
A graph in which V(m) calculated by equation (6) is plotted against m is shown in FIG. 4b.

According to this embodiment, since non-linear calculations including absolute values etc. are not used, the signal processing circuit can be easily configured, the number of program steps during digital processing is reduced, and the accumulation of errors is also reduced compared to the conventional technology. The calculation accuracy improves.

In FIG. 4, m, where V(m) is 0, is not an integer value but a fractional number, but a detailed value can be obtained using an appropriate interpolation method.
The simplest interpolation method in this case is linear interpolation, and if there is a sign reversal between V(m ₀ ) and V(m ₀ +1), the image shift amount M ₀ including fractions is M ₀ It can be calculated by =m ₀ +|V(m ₀ )/V(m ₀ +1)−V(m ₀ )|.

The present invention can also be implemented as follows. ^In other words, _as a correlation amount representing ^the degree of coincidence _between the two images, i), b(i)} ...(8) can be used. In these equations (7) and (8), to calculate while displacing one image relative to the other, for example, when using equation (7), V(m)= 〓 ⁱ min {a(i), b(i-m)} ...(9) Also, when using formula (8), V(m)= 〓 ⁱ max{a(i), b(i-m)} It is sufficient to calculate V(m) defined by ...(10). Figure 5a shows a graph in which V(m) in equation (9) is plotted against relative displacement m, and Figure 5b shows a graph in which V(m) in equation (10) is plotted against m. show. in general,
V(m) in equation (9) becomes maximum when the two images coincide and are in focus, and V(m) in equation (10) becomes minimum when in focus.
In this embodiment as well, since m corresponding to the extreme point is usually not an integer, interpolation is required to obtain detailed values including fractions. The simplest interpolation method in this case is interpolation using a quadratic function.

Note that the method according to the present invention is not limited to a so-called TTL type focus detection device in which two images to be subjected to arithmetic processing are formed by light beams transmitted through a photographic lens. It goes without saying that the present invention can also be applied to a focus detection method or a distance measurement method using a shift between two images, such as a baseline distance type focus detection device.

As described above, the focus detection signal processing method according to the present invention compares the magnitude relationship of two photoelectric conversion output values that are matched as a signal processing method for focus detection using the shift of two images, and the result is Based on the above 2
This is to selectively add one of the output values. Therefore, the method according to the present invention consists only of linear calculations, and although the calculation time is quick and the configuration is easy, it has the advantage of being as accurate as the prior art and having less accumulation of errors.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the focus detection method using the secondary imaging method, Fig. 2 a, b, and c are explanatory diagrams of the principle of image shift, and Fig. 3 is the characteristic of the calculation output value according to the conventional example.
Fig. 4 and the following show an embodiment of the focus detection signal processing method according to the present invention, Fig. 4 a and b are calculation output characteristic diagrams thereof, and Fig. 5 a and b are calculation output characteristic diagrams according to another embodiment. be. Code 1 is a photographic lens, 2 is a field lens,
3a and 3b are secondary imaging lenses, and 4a and 4b are sensor arrays.

Claims (1)

[Claims] 1. A plurality of object images formed by passing through a plurality of different optical paths are detected by a photoelectric conversion element array, and the in-focus state of the optical system is determined from changes in the relative positions of the plurality of object images. A method of determining a photoelectric conversion element by associating each element of a plurality of photoelectric conversion element arrays that receive the respective subject images in a certain correspondence relationship, comparing the photoelectric outputs of the corresponding photoelectric conversion elements, and comparing the photoelectric outputs of the corresponding photoelectric conversion elements. Extracting the minimum or maximum output value and finding the added value is repeated while changing the correspondence of the photoelectric conversion elements by a certain amount, and the magnitude of the added value changes with respect to the amount of change in the correspondence. A method for processing a focus detection signal, characterized in that the amount of deviation of the optical system with respect to the in-focus position is calculated based on . 2. A pupil of an imaging optical system to be focused and detected is divided, and a plurality of subject images formed by imaging light beams emitted from each divided pupil area are detected by the photoelectric conversion element array. Range 1
The focus detection signal processing method described in .