JPH01277211A - Focus detector for camera - Google Patents

Abstract

PURPOSE:To detect the extent of deviation of an object image having a period ical pattern by detecting the infocus state based on the output signal of a photoe lectric conversion element train with a pattern light projected in the case of a high periodicity of the output signal of the photoelectric conversion element train. CONSTITUTION:The periodicity of an object pattern is discriminated; and when it is discriminated that the periodicity of the object is high, an auxiliary light emitting means is caused to emit light and the pattern light is projected to the object face. It is necessary that the distribution of the quantity of auxiliary light has a pattern, and for example, the auxiliary light having the distribution of the quantity of light shown in a figure (b) is projected to the periodic object shown in a figure (a) to obtain the distribution of luminance of the object shown in a figure (c), and the object is changed to an aperiodic object to change it to the state where the focus can be detected. Thus, the focus is automatically and accurately detected even for the periodic object.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the focus detection ability for a periodic pattern object in a pupil division image shift detection type focus detection device.

[Conventional technology]

Conventionally, as one type of camera focus adjustment device, the exit pupil of the photographic lens is divided into two by a focus detection optical system, and the two subject images formed by the light flux passing through each pupil area are converted into photoelectric converters. Receives light with an element array (for example, a CCD sensor array), detects the focal state of the photographing lens from its output,
A method is known in which a photographic lens is driven based on the detection result.

In FIG. 1, a field lens FLD is placed on the same optical axis as the photographing lens LNS whose focus is to be detected. Behind it, two frozen image lenses FCLA and FCLB are placed at symmetrical positions with respect to the optical axis. Placed.

Furthermore, sensor arrays SAA and SAB are arranged behind it. Apertures DIA and DIB are provided near the two frozen image lenses FCLA and FCLB. Field L Nonozu F
The LD forms an image of the exit pupil of the photographic lens LNS approximately on the pupil plane of two frozen image lenses FCLA and FCLB. As a result, the light beams incident on the two frozen imaging lenses FCLA and FCLB exit from regions of equal area that do not overlap each other and correspond to the respective secondary imaging lenses FCLA and FCLB on the exit pupil plane of the photographing lens LNS. It becomes what is given. When the aerial image formed near the field lens FLD is re-imaged onto the surfaces of the sensor arrays SAA and SAB by the two frozen image lenses FCLA and FCLB, based on the displacement of the aerial image position in the optical axis direction, The two images on the sensor arrays SAA and SAB will change their positions. Therefore, if the amount of displacement (shift) in the relative positions of the two images on the sensor array is detected,
The focal state of the photographic lens LNS can be known.

The focus state detection method described above may not work well depending on the subject conditions. The most typical example is a low-luminance subject. There is a practical limit to the photoelectric charge accumulation time of a photoelectric sensor, and if there is not enough light to generate a sufficient photocharge during that time, a signal cannot be formed. In such a case, even if the storage time is extended, the camera becomes extremely difficult to use, or the dark current increases and the effective S/N ratio does not improve.

Therefore, a focus detection auxiliary light is often installed in the camera to compensate for the lack of light intensity at low brightness times. The upper optical system in Fig. 1 is the auxiliary light projection system, and the light emitted by the LED of the light source illuminates the pattern chart CRT via the condenser lens CON, and the pattern of the CHT is projected onto the subject plane by the projection lens LEL. . If the photographing lens and the light projecting lens are separated as shown in FIG. 1, parallax will occur, but if light is projected from the photographing lens, ghosts will likely occur, so a separate light projecting system is usually provided outside the photographing system.

It is known that fill-in illumination is effective not only for low-brightness subjects but also for low-contrast subjects. When the contrast is low, there is no light-dark pattern to form the basis of calculations, and focus cannot be detected. In such a case, it is possible to forcibly give a brightness pattern to the subject by projecting a pattern onto the subject plane, and perform focus detection calculations using this as a foothold.

FIG. 2 shows a sensor array SAA having the configuration shown in FIG.

An example of photoelectric conversion output of two images formed on the SAB is shown.

The output of SAA is A (i), the output of SAB is B (i)
shall be. In addition, the number of pixels of the sensor is required to be at least 5,
Preferably, the number is several dozen or more. image signal A(i),
As a signal processing method for detecting the image shift amount PR from B(i), Japanese Patent Application Laid-Open Nos. 58-142306 and 5
No. 9-107313, Japanese Unexamined Patent Publication No. 101513/1980, Japanese Patent Application No. 160824/1984, etc. are disclosed by the present applicant.

The amount of image shift is determined by the method disclosed in these publications,
The method disclosed in the above-mentioned publication is to adjust the focus of the photographic lens based on this, thereby bringing the photographic lens into focus, for example, two image signals A(')+B(1)
+ 1=:1.2. ..., for N, V(m)=Σm
ax (A(i), B(i0km)11Σmax
IA(i+k), B(i-m)] (1) is calculated for an integer value m. The range of i to be summed is each subscript i,
-m for i+, i-m for i+ is a closed interval [i, N]
It is determined by the condition that one must go inside.

k is an integer constant, typically =1. Also, the range of m cannot be determined unconditionally depending on the purpose of detecting how large an image shift amount is, but it is usually N.
Defined by equation (1) where m is varied within N −-< m <-2
~ ~2 The correlation amount given above is just an example, and the following principle is exactly the same for other known correlation amounts.

As a correlation quantity equation other than equation (1), for example, Σmin [A
(i), B(i+ to -m)] ~ Σmin (A(i+
k), B(i-m)]Σl A(i) -B(-m to i+) l-Σl fA(i+k) -B(i-m)
lΣl A(i) B(i+−m) l ”−Σl
[A(i+k) −B(i−m) l” is adopted.

A typical result obtained by calculating the above equation (1) for each m is as shown in FIG. 3, where m where (m) is reversed in sign is the image shift amount expressed in units of pixel pitch. This value usually does not take an integer. v(mo) and V Cmo +1)
If there is a sign reversal between the two, the image shift amount M0 including fractions is Mo=m0+IV(mo)/[V(mo+t)
−V(mo)11 It can be calculated by (2).

In addition to the above-mentioned conventional example, the means for dividing the exit pupil of the photographic lens is as disclosed in USP 4185191.
A large number of units each having a microlens placed in front of the photoelectric sensor pair may be arranged in a straight line without any particular limitation.

[Problems to be Solved by the Invention] The focus detection device based on detecting the amount of image shift as described above has the characteristic that it malfunctions for periodic subject patterns such as those used in boat fishing. This defect arises directly from the principle of detecting the misalignment of two images.

For example, suppose that the subject image is a repeating pattern with a pitch P on the photoelectric sensor surface as shown in FIG. At this time, if you try to align the two images A (i) and B (i), even if you shift A (i) in the direction of arrow α, you will also shift B (i) in the direction of arrow β. However, the two images can be matched, and the amount of image shift cannot be uniquely defined (→-).

Furthermore, in addition to the above-mentioned α and β, there are shift points at which the two images coincide for each pitch of periodicity.

Due to the above-mentioned circumstances, it is impossible to detect the amount of image shift of an object having a periodic pattern using the conventional method, and therefore the amount of defocus of the photographic lens cannot be calculated, and the in-focus state of the photographic lens cannot be determined. Periodic patterns are surprisingly common in man-made structures (for example, window lattices, railings, blinds, checkered and striped clothing, arranged bookshelves, etc.), and there are many cases where they cannot be ignored as subjects for cameras.

[Means for solving problems]

The present invention has a means for calculating and determining the strength of periodicity of the brightness and darkness pattern of the subject surface using the output of a photoelectric conversion element array that receives the imaging light flux from the subject surface, and at least the strength of the periodicity is determined. When the predetermined standard is exceeded, the above-mentioned method is detected by detecting the in-focus state of the photographic lens using the output of the photoelectric conversion element array of the received imaging light beam when the auxiliary light emitting means emits light. It is a solution to a problem.

By using the focus detection method of the present invention, it becomes possible to detect focus on all periodic objects within a distance where auxiliary light emission is effective. Furthermore, since the present invention has a means for determining the strength of periodicity, it is possible to emit auxiliary light only where necessary, which is also advantageous from the point of view of energy efficiency. Furthermore, the periodicity determining means of the present invention is suitable for being configured with digital calculations,
It can be housed in the microprocessor that is standard in automatic focus detection cameras. Further, the present invention is even more effective when used in combination with a photoelectric conversion element having an external light removal function. In such a combination, periodic subject patterns that are harmful and useless to focus detection are canceled out,
Since only the projection pattern of the auxiliary light remains as an image signal for focus detection, a focus detection device with no room for malfunction can be obtained.

〔Example〕

Next, examples of the present invention will be described. FIG. 5 shows a pupil splitting type focus detection optical system using a secondary imaging separation optical system used in the focus detection apparatus according to the present invention.

The photographing lens of the camera and the like are omitted, and only the focus detection optical system is shown. In FIG. 5, a field mask having a distance measurement field aperture Z is placed near the field lens FLD, and a combination of the field mask and the field lens is placed near the intended imaging plane of a photographic lens (not shown). The image of the field of view Z is separated and formed onto the sensor array SAA by the lens FCLA, and onto the sensor array SAB by the lens FCLB. 2 sensor rows S
On both sides of AA and SAB, an AGC circuit for controlling the accumulation time of the sensor according to the amount of incident light and a readout circuit RD for sequentially outputting the data of each pixel to the outside are integrated on-chip. The operating principle of the sensor array may be any type, such as a CCD structure or a MOS structure, as long as it detects and outputs the light intensity distribution on a line.

FIG. 6 is a circuit diagram showing an embodiment of a camera equipped with an automatic focusing device according to the present invention.

In the figure, PRS is a camera control device that includes, for example, a CPU (central processing unit), ROM, and RAM.

It is a 1-chip microcomputer with an A/D conversion function. The PRS performs a series of camera operations such as an automatic exposure control function, an automatic focus adjustment function, and film winding/rewinding according to a camera sequence program stored in the ROM.

For this purpose, PRS uses communication signals So, Sr, 5CLK.
.

Using communication selection signals CLCM, C3DR, CDDR,
It communicates with the peripheral circuits inside the camera body and the control device inside the lens to control the operation of each circuit and lens.

SO is the data signal output from PRS, SI is PRS
The data signal input to 5CLK is the signal So, S
This is the synchronous clock of I.

LCM is a lens communication buffer circuit, and when the camera is in operation, it supplies power to the lens power supply terminal VL, and the selection signal CLCM from PRS is at a high potential level (hereinafter abbreviated as "H", and a low potential level is (abbreviated as “L”), it serves as a communication buffer between the camera and the lens.

When PRS sets CLCM to "H" and sends predetermined data from SO in synchronization with SCLK, LCM transmits 5CLK and S through the camera-lens communication contact.

The respective buffer signals LCK and DCL are output to the lens. At the same time, the buffer signal of the signal DLC from the lens is output to Sl, and PRS synchronizes with SCLK.
Enter the lens data from I.

SDR is a drive circuit for a line sensor device SNS for focus detection, which is composed of a COD or the like. The line sensor device SNS is configured as shown in FIG. 5, and includes integrated light receiving element arrays SAA and SAB, a signal processing circuit, and the like. Further, the drive circuit SDR is selected when the signal C3DR is H" and is controlled by the PRS using So, SI, and 5CLK. The signal CK is a clock for generating COD drive clocks Φl and Φ2. The signal INTEND is a signal that notifies the PRS that the storage operation has ended.

The output signal O8 of the SNS is the clock Φ1. It is a time-series image signal synchronized with Φ2, and after being amplified by the amplifier circuit in the SDR, it is output to the PRS as AO3. PRS is AO
3 is input from the analog input terminal, and in synchronization with CK, the internal A/D conversion function sequentially stores it as a digital signal at a predetermined address in the RAM.

The same (SNS output signal 5AGC is the AGC (automatic gain control: Auto Ga1n Co
ntrol) sensor output, is input to the SDR, and is used for SNS storage control.

SPC is a photometric sensor for exposure control that receives light from the subject through the photographic lens, and its output 5spc is input to the analog input terminal of PRS, and after A/D conversion,
Used for automatic exposure control according to a predetermined program.

AuT is an auxiliary light unit and communicates with the control device PRS via contacts. SAL is an auxiliary light emission signal,
When AL is at H level, the auxiliary light ALED is turned on.

DDR is a switch detection and display circuit, and the signal C
Selected when DDR is “H”, So, Sl.

Controlled from PRS using 5CLK. That is, PRS
Display member D of the camera based on the data sent from
It switches the SP display and notifies the PRS of the on/off status of various camera operating members through communication.

SWI and SW2 are switches that are linked to a release button (not shown), and when the release button is pressed in the first step, SW is activated.
1 is turned on, and then SW2 is turned on at the second stage of pressing. PRS performs photometry and automatic focus adjustment when SW1 is turned on, and exposure control and film winding are performed using SW2 as a trigger.

In addition, SW2 is a microcomputer called PRS.
Even when the program is running when SW1 is on, an interrupt is generated when SW2 is turned on.
Control can be immediately transferred to a predetermined interrupt program.

MTRI is for film feeding, MTR2 is for mirror up/
It is a motor for down and shutter spring charging,
Forward rotation and reverse rotation are controlled by respective drive circuits MDRI and MDR2. PRS to MDRI.

Signals MIF, MIR, M2F input to MDR2
.

M2R is a signal for motor control.

MCI and MG2 are magnets for starting the movement of the front and rear shutter curtains, respectively, and are energized by signals SMGI, 5MG2, and amplification transistors TRI and TR2, and shutter control is performed by PR3. In addition, switch detection and display circuit D
DR, motor drive circuit MDRI.

Since the MDR2 and shutter control are not directly related to the present invention, detailed explanations will be omitted.

A signal DCL input to the intra-lens control circuit LPR3 in synchronization with LCK is data of a command from the camera to the lens FLNS, and the operation of the lens in response to the command is determined in advance. LPR3 analyzes the command according to a predetermined procedure and performs focus adjustment, aperture control, and output DLC.
Outputs the operation status of each part of the lens (driving status of the focusing optical system, driving status of the aperture, etc.) and various parameters (open F number, focal length, coefficient of defocus amount vs. movement amount of the focusing optical system, etc.) I do.

In the embodiment, an example of a zoom lens is shown, and when a focus adjustment command is sent from the camera, the focus adjustment motor LTMR is driven by signals LMF and LMR according to the drive amount and direction sent at the same time. Then, the optical system is moved in the optical axis direction to adjust the focus.The amount of movement of the optical system is monitored by the pulse signal 5ENC of the encoder circuit ENC, and the L
Counting is done by a counter inside PR8, and when a predetermined movement is completed, LPR3 itself sets the signals LMF and LMR to "L".
to brake motor LMTR.

Therefore, once the focus adjustment command is sent from the camera, the camera control device PR3 does not need to be involved in lens driving at all until the lens driving is completed. Furthermore, the configuration is such that it is possible to send the contents of the counter to the camera if there is a request from the camera.

When an aperture control command is sent from the camera, a stepping motor DMTR, which is known for driving an aperture, is driven in accordance with the number of aperture stages sent at the same time. In addition,
Stepper motors are open-controlled and do not require an encoder to monitor operation.

Before explaining the operation shown in FIG. 6 above, the periodicity determination operation of the present invention will be explained.

First, a case will be described in which the periodicity of a subject pattern is determined from the result of a correlation calculation for focus detection.

Based on the above formula (1), two subject images A (i), B
When calculating the cross-correlation (differential form of
m) is obtained, and the zero cross point corresponding to the amount of defocus of the photographing lens can be determined. However, in a strongly periodic pattern as shown in Figure 4, when calculating V(m), Figure 7 (
a) (repetition appears, and multiple zero-crossing points appear. Assuming that V(m) is reversed in positive/negative between a certain ml and m1+1, △V (m,) = V(m H+1)
The magnitude of the absolute value of -V(m +) (3) 1△V(m,)l represents the reliability of that zero-crossing point as a two-image matching point, but 1△V
(m) There is a large difference in the value of l (this is a characteristic of the results of correlation calculations for periodic objects. In other words, ■ m: ml, m2, where the sign of V(m) is reversed...
There are multiple zero crossing points such as ■1△V(m
I) l=l△V(m2) I=-.

Although multiple zero-crossing points may occur even in normal non-periodic subjects, as shown in Figure 7(b), 1△V(
m+)I)I△V(m2)l and corresponds to the true two-image matching point, zero-crossing point m1, and other zero-crossing points are clearly distinguished from each other in terms of reliability.

From the above facts, for example, as one periodicity determination method, if the zero cross point showing the maximum 1△V(m)l is m, then 1△V(m)l > FX lΔV(m I ) +
The fact that there are L or more m satisfying (4) can be used as a condition for determining that the pattern is a periodic pattern.

Here, F is a positive constant satisfying O<F≦1, and L is a positive integer of 1 or more. In addition, when using this determination condition, the reliability factor 1ΔV(m 2 ) l of the zero crossing point may be divided by the contrast C of the subject for normalization.

Generally, C is C=MAX[A(il-MIN[A(+)]
(5a) N or C=, Σ l A(i) −A(i−1)
l (5b)! =2. Here, MAX[A(i)l is the image signal Al
+A2. ... Maximum value of AN, MIN (A(i)l means the minimum value of image signal A I + A2 + ...AN. B(i) may be used instead of A(+). , or C may be calculated by using both image signals together.

Another criterion is, for example, more simply V(m
) may be set by simply counting the number of zero-crossing points where the sign of A reliability threshold may be defined for the th zero crossing point.

The periodicity of the object pattern is determined by the method disclosed above, and if it is determined that the periodicity of the object is large, the auxiliary light emitting means is emitted to project the pattern onto the surface of the object. The light intensity distribution of the auxiliary light must have a pattern, for example, for a periodic subject as shown in Figure 8(a),
By projecting an auxiliary light with the light intensity distribution shown in Figure (b), making the subject's brightness distribution as shown in Figure (C), and changing the subject to aperiodic, it is possible to transition to a state where focus can be detected. .

Next, the flow of the focus detection apparatus according to the present invention shown in FIG. 6 will be explained.

When a power switch (not shown) is operated, power supply to the microcomputer PR5 is started, and execution of the sequence program stored in PR3 (tROM) is started.

FIG. 9(a) is a flow chart showing the overall flow of the above program.

When the execution of the program is started by the above operation, the state of the switch SW, which is turned on at the first stroke of the release button, is detected in step (002), and when the switch SW is off, the state of the switch SW, which is turned on at the first stroke of the release button, is detected, and when the switch SW is turned off, the state of the switch SW, which is turned on at the first stroke of the release button, is detected. All control flags set in the RAM in the PRS are cleared. Incidentally, the detection of this switch SW1 is made by setting the signal CDDR to H from the computer PR8 and outputting the signal CDDR from the computer PR8 to the circuit DDR.
is selected and transmitted to the SO multiplied signal DDR as a detection command for the switch SW1, the state of the switch SW1 is detected by the DDR, and the result is sent as an SI multiplied signal to PR3.
This will be done by informing. The above step (002),
(003) is executed repeatedly until switch SW1 is turned on or the power switch is turned off, and
When l is turned on, the process moves to step (004).

Step (004) means the "rAE control" subroutine. This rAE control subroutine performs photometry calculation processing, exposure control, and post-exposure shutter charging.
A series of camera operation controls such as film winding are performed.

Note that the "rAE control" subroutine is not directly related to the present invention, so a detailed explanation will be omitted, but an outline of the function of this subroutine is as follows.

While SWl is on, this "rAE control" subroutine is executed, and each time the camera mode setting, photometry and exposure control calculations and display are performed. When the switch SW2 is turned on by the second stroke of the release button (not shown), the release operation is started by the interrupt processing function of the microcomputer PR3, and the aperture or shutter speed is adjusted based on the exposure amount determined by the above exposure control calculation. After the exposure is completed, one frame of film is photographed by performing shutter charging and film feeding operations.

Now, when the "AE control" is completed in step (004), the "rAE control" subroutine of step (005) is executed.

FIG. 9(b) shows a flowchart of the "l'-AF control" subroutine.

First, in step (102), the state of the flag PRMV is detected. PRMV is a flag related to lens control as described later, and SW as described above.

Since all flags are cleared in step (003) while the switch is off, step (00
When the "rAF control" subroutine of 5) is called, the flag PRMV is also 0, so step (106) is executed.
Move to.

In step (106), the state of the flag AUXJF is detected. AUXJF is a flag related to auxiliary light control,
As mentioned above, it was cleared in step (003) and the flag AUXJF is also φ, so step (108)
Move to.

Step (108) is an "image signal input" subroutine, and by executing this subroutine, the A/D conversion signal of the image signal from the sensor device SNS is stored in a predetermined address on the RAM of the microcomputer PR3. Further, in step (10B), the level of the image signal and (5a
), (5b), etc. are calculated at the same time as the input, and low brightness or low contrast (C is small)
When it is determined that the flag LSIGFLG is set to 1.

In step (111), the state of the flag AUXMOD is detected. The flag AUXMOD is a flag indicating the auxiliary light mode. Control regarding the auxiliary light will be described later.

As mentioned above, all flags are cleared at (003) and flag AUXMOD is also 0, so step (
112). In step (112), the flag L
Detects the state of SIGFLG. LSIGFLG is a flag set in the "image signal input" subroutine of step (10B), and is set to l when the subject brightness is low or the contrast of the image signal is low. Here, the subject has sufficient brightness and contrast (L
The explanation will proceed assuming that SIGFLG is O). Flag LSI
Since GFLG is O, move to step (113),
Since the object brightness and contrast are sufficient, the auxiliary light mode flag AUXMOD is cleared.

Next, in step (114), a "focus detection" subroutine is executed.

In this subroutine, the focus of the photographing lens is calculated and detected from the image signal data stored in the RAM using equations (1) and (2), and if it is in focus, the focus flag JF is set to 1, If the focus cannot be detected due to low contrast even though the subject is illuminated with a fill-in light, set the focus detection failure flag AFNG to 1, and in either of the two conditions, stop the lens drive. The lens driving prohibition flag LMVDI is set to 1 and the process returns.

Further, when the contrast is high and the image is not in focus, the amount of defocus is determined. At this time, the flag LMVDI is O.
will be retained as is.

In the next step (115), periodicity is determined.

For example, for the zerox point ゛ for V(m) found using the equation (1), use equations (3) and (4) to determine whether there are multiple 1△V(m)l approximated at the zerox point. death,
That is, the reliability of a plurality of zero correlation points is determined, and if there are a plurality of points that are recognized as two-image matching, LSIGFLG is set to 1, and the process branches to step (131). If the subject is not a periodic subject, the process advances to step (116). The flag control related to the auxiliary light after step (131) is basically the same as that after step (121), which will be described later.

In the next step (116), a "display" subroutine is executed to display in-focus or inability to detect focus. This communicates predetermined data to the display circuit DDR and displays the display device D.
Although this operation is not directly related to the present invention, further explanation will be omitted.

Now, in the next step (117), the state of the flag LMVDI is detected. As mentioned above, when lens driving is not necessary, LMVDI is set to 1, so if the flag LMVDI is 1 in step (117), the "rAF control" subroutine is returned in step (11B). If LMVDI is 0, the process moves to step (119) to execute the lens drive subroutine "lens drive" to drive the lens in accordance with the calculated defocus amount.

When the "lens drive" subroutine (119) is finished,
At step (120), the lens drive execution flag PRMV is
After setting "rAF control" to 1, the "rAF control" subroutine is returned at step (130).

rAF control" subroutine, step (
002), and as long as the switch SW1 is on, the AE control and AF control subroutines are repeated.

Now, if "rAF control" in step (005) is called again (second time) in the main flow of FIG. 9(a), the state of the flag PRMV is detected in step (102).

If focusing or focus detection is not possible in the previous AF sub-control routine, the flag PRMV is not set to l, so the above flow from step (106) onwards should be executed again. If it has been done, PRMV is set to 1 in step (120), so the process moves to step (103).

In step (103), the lens is communicated with to detect the current driving status of the lens, and step (119) is performed from the lens side.
) When it is notified that the specified drive instructed in step (106) has been completed, the flag PRMV is set to 0 in step (105), and the flow from step (106) is executed. This determination is made by detecting the monitor signal 5ENC by the computer PR3, since the monitor signal 5ENC is sent from the encoder ENC while the lens is being driven. Further, if it is notified from the lens side that the lens is still being driven, the process moves to step (104) and returns to the AF sub-control subroutine.

Therefore, in the "rAF control" subroutine, a new focus detection operation and lens control are performed only when the lens is not being driven.

That is, in the normal mode, as long as the switch SW1 is on, the AE and AF control subroutines are narrowed down, and the AF
In the control subroutine, the defocus amount is detected based on the image signal, and if a predetermined condition is not met for the image signal or the calculated value, a focus detection failure display is displayed.If focus is determined, an in-focus display is displayed, and a non-focus display is performed. When the amount of defocus is determined in focus, the lens is driven by the amount of defocus to bring it into focus.

Next, operations related to the auxiliary light will be explained.

In the above AF control subroutine, the subject brightness is low.
Or if the contrast is low, step (10
8), and in the case of a periodic subject, step (115)
The flag LSIGGFLG is set to 1 in step (112), and the process moves to step (121) when the LSIGGFLG state is detected in step (112).

In step (121), the state of the auxiliary light unit AUT device member is detected, and if the unit AUT is not attached, the process moves to step (113), and the same normal operation as described above is performed. If the unit is installed, the process moves to step (122) and the auxiliary light mode flag AUX is set.
Set MOD to 1.

Note that if the auxiliary light unit AUT is built into the camera body, step (121) may be omitted.

Next, in step (123), the state of the flag AUXUSE is detected. AUXUSE is a flag that is set to l when the image signal manual J subroutine in step (108) is executed when the auxiliary light is actually emitted (with the flag AUXMOD set to 1). be. In the situation just described, since the auxiliary light mode is entered for the first time, the auxiliary light has not been emitted before then, and the process returns to step (124) 7-rAF control. That is, in this case, the image signal data input in step (108) is discarded, and in the next rAF control, an image signal is input in the auxiliary light projection state and used for focus detection.

Now, in step (122), AUXMOD becomes 1 for the first time.
When the rAF control J returns and the rAF control subroutine is called again as described above, the image signal input subroutine in step (108) returns the auxiliary light in the auxiliary light emission state. An image signal is input, and upon detection of the state of the auxiliary light mode flag AUXMOD in step (111), the process moves to step (121).

In addition, in the "image signal input" subroutine, the flag AUXM
Since OD is set to 1, when accumulating the image signal, SAL is set to H level and the auxiliary light ALED is turned on.

After steps (121) and (122), step (
In step 123), the state of the auxiliary light use flag AUXUSH is detected. The "image signal manual" subroutine has already been executed in step (108) in the auxiliary light emission state, and the AUX
USE is set to l, so step (114)
, and executes the "focus detection" subroutine. The subsequent steps are the same as normal AF control.

Further, when the periodicity of repetition is detected in step (115), steps (131), (132),
(134) is step (121) under the above-mentioned low contrast detection.

(122) and (123) are carried out and "rAF control" is returned, and then "rAF control" is called again, step (1
0B), (111), (121), (122), (12
Step (114) is executed via step (3). Therefore, even when it is determined that the repetition periodicity is high, the AF control operation under the auxiliary light projection is performed in the same way as when the contrast is low.

As mentioned above, when shooting under conditions of low brightness, low contrast, or periodic objects, and when the auxiliary light unit is attached, the camera enters auxiliary light mode and performs focus adjustment based on the detected image signal under the auxiliary light emission. However, if the focus is achieved while the auxiliary light is being emitted, the auxiliary light focus flag AUXJF is set to 1 in the "focus detection" subroutine of step (114).
In this case, in the flow of "rAF control", the state of AUXJF is detected in step (106), the process moves to step (107), and then the "rAF control" subroutine is returned. That is, when focusing is achieved in the auxiliary light projection state, the focus adjustment operation and lens drive will not be performed again until the switch SW is turned off.

FIG. 10 is an explanatory diagram showing another example of periodicity determination.

When there is a subject image signal A (i) or B (i) as shown in FIG. 10, its maximum value Amax and minimum value Am1n are determined, and the slice level SL is set between them.

SL=(Amax+Am1n)/2 (6
) If it is a periodic pattern, the magnitude relationship of the image signal A (i) with respect to the slice level changes periodically depending on i.

This phenomenon can be easily detected by focusing only on the sign of (A(i)-8L), and when the number of alternating positive and negative periodic reversals exceeds a predetermined number, the periodicity is detected. It is sufficient if it is determined that the subject pattern is strong.

Note that the slice level may be set as the average value of A (i) over the entire visual field (ΣA(i))/N. Furthermore, since a loose luminance distribution often exists superimposed on the periodic pattern of the subject, better discrimination can be achieved by setting the slice level as a local image signal average value and changing it together with i. That is, 5L(i)=Σ A(i+1ri/(2J+1)
(7) Let A=-J. However, J is an appropriate positive integer, and the smoothing width (
2J+1) is set to be sufficiently larger than the pitch of the periodic pattern in question.

The above method only detects the severe fluctuation of A (i), but does not detect the periodicity of the fluctuation. The gist of the present invention is that periodic determination signals may be output for a slightly larger set of image signals, including periodic objects, so this method can be used except in some cases where the auxiliary light is emitted for objects that do not require emitting light. Fully practical.

When determining periodicity directly from fluctuations in the image signal using the above equations (6), (7), etc., the determination can be made practically before the focus detection calculation, so that invalid calculations are reduced. That is, in the flowchart of FIG. 9, step (1)
08), the LS of step (112)
Until the IGFLG set state is detected, (6), (7
), etc., to determine the periodicity of the image signal, and when it is determined that the subject is a periodic object, the LS
Set IGFLG to 1.

from step (112) to step (121)
Create a flow that branches into At this time, the steps from step (115) to step (131) in FIG. 9(b) can be omitted.

Further, as another method for determining periodicity, a method using digital Fourier transform may be adopted. When the power spectrum of the digital Fourier transform of the image signal luminance distribution is calculated, a smooth power spectrum without very drastic fluctuations is obtained for an irrational subject, as shown in FIG. 11(a). In the figure, the horizontal axis is the spatial frequency, and fN is the Nightquist frequency. However, in the periodic pattern, a strong peak is seen at a specific spatial frequency as shown in FIG. Therefore, the ratio of the specific spectrum to the total power spectrum sum is determined, and if the ratio exceeds a certain value, it can be determined that the subject is a periodic subject. Specifically, the image signal A (
i), i=1.2. ...The power spectrum component of N is A(3), i=1.2. . . . When N is determined, if there is an i that satisfies γ+>R, it is considered to be a periodic subject. A more reliable operation can be achieved by adding a predetermined value of 0<R<1 to R, and determining that the periodicity is strong when the sum exceeds the threshold R.

Note that the power spectrum referred to in this embodiment is the sum of squares of Fourier sine transform and cosine transform.

In addition, equation (8) can be transformed using Parspal's theorem, so in the power spectrum for all i, the spectral components can be found simultaneously for all i, but the number of pixels N is not necessarily large and N = 2K (K integer ), it cannot be said that a high-speed conversion algorithm is advantageous. It is relatively easy to calculate the power spectrum for a small number of i, and it is also possible to roughly estimate i for which the spectrum should be calculated by calculation in real space. Note that the position of the subroutine in the flowchart does not change whether direct arithmetic judgment is performed or digital Fourier transform is performed from the image signal.

In all of the above embodiments, periodicity is determined using an image signal formed without auxiliary light emission, and auxiliary light with a pattern is projected onto a subject that is determined to have strong periodicity.
The assumption is that the sequence will form an image signal again. However, the present invention presents a method for converting a highly periodic subject brightness distribution into an aperiodic one by projecting auxiliary light with a light intensity distribution pattern onto the subject surface, and a means for determining the effectiveness of the method. It is something to do. For example, the present invention is also effective in a sequence that has an image signal when the auxiliary light is emitted and an image signal when the auxiliary light is not emitted, and selects the image signal.

〔Effect of the invention〕

As described above, according to the focus detection device of the present invention, accurate automatic focus detection can be performed even for periodic objects that cannot be detected using conventional image shift detection type focus detection methods. Furthermore, since the present invention is equipped with a pattern determining means that specifically responds only to periodic patterns, it is possible to minimize the emission of auxiliary light, which is advantageous in terms of power consumption. Furthermore, since the periodicity determining means can be configured with simple software, it can be operated on a microprocessor built into an autofocus camera, and can be easily implemented, resulting in great effects.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing the optical system of the automatic focus detection device, Figure 2
FIG. 3 is an explanatory diagram showing an image signal in a sensor, FIG. 3 is an explanatory diagram showing a correlation amount by a focus detection device, FIG. 4 is an explanatory diagram showing an image signal having synchronization, and FIG. 5 is an explanatory diagram showing a focus according to the present invention. FIG. 6 is a block diagram showing the optical system of the detection device; FIG. 6 is a circuit diagram showing an embodiment of the focus detection device according to the present invention; FIG. 7(a)
, (b) is an explanatory diagram for explaining the periodicity determination operation used in the focus detection device according to the present invention, and FIG.
), (b). (c) is an explanatory diagram showing image signal changes during auxiliary light projection; FIGS. 9(a) and (b) are explanatory diagrams explaining the operation of the focus detection device shown in FIG. 6; and FIG. FIGS. 11(a) and 11(b) are explanatory diagrams showing another example of determination. FIGS. 11(a) and 11(b) are explanatory diagrams showing another example of periodicity determination. AUT...Auxiliary light unit PR8...Microcomputer - Patent applicant Canon Co., Ltd. (b) (b) (C) CrND (α) (b,) δN

Claims (2)

[Claims] (1) For a camera that includes first and second photoelectric conversion element arrays that each receive an image from a subject, and that detects the focal state of the photographic lens based on the outputs of the first and second photoelectric conversion element arrays. In the focus detection device, there is provided an arithmetic circuit that calculates and determines the strength of periodicity of the output signal of the photoelectric conversion element array based on the output of the photoelectric conversion element array, and a calculation circuit that determines that the periodicity is strong in the output signal of the photoelectric conversion element array An auxiliary light drive circuit is provided to drive an auxiliary light source to perform pattern light projection, and when the periodicity of the output signal of the photoelectric conversion element array is strong, the auxiliary light drive circuit drives the auxiliary light source to perform pattern light projection. A camera focus detection device characterized by detecting a focus state. (2) The arithmetic circuit calculates the amount of correlation for each shift while shifting the relationship between each output signal of the first and second photoelectric conversion element rows, and the number showing the amount of correlation greater than a predetermined value is equal to or greater than the predetermined value. The focus detection device for a camera according to claim 1, which sometimes determines that periodicity is strong.