JPH0961702A - Range-finding system and autofocusing camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a range-finding system rapidly detecting the insufficient contrast of an image formed on a line sensor for range-finding, and an autofocusing camera provided therewith. SOLUTION: A photoelectric conversion element 33 constituting the line sensors 31 and 32 is provided with a latch part 33c outputting a latch signal when potential increased by charge accumulation reaches a specified value. Counters 34 and 35 count the number of the latch signals and measure the elapsed time from the time when the charge accumulation is started till the time when the latch signal is inputted. By comparing the time when the first latch signal is inputted in the counters 34 and 35 with the time when the last latch signal is inputted therein, the difference of brightness between the brightest part and the darkest part of the image on the line sensors 31 and 32 is detected so as to judge whether the contrast of the image is sufficient or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring system for detecting a distance from a position of a pair of images formed on a light receiving element to a distance measuring object and an autofocus camera using the distance measuring system. The present invention relates to the determination of the contrast of the image formed on the light receiving element.

[0002]

2. Description of the Related Art Conventionally, in autofocus cameras,
The light from the subject is guided to a pair of line sensors to form two images, and the distance to the subject is detected from the difference between the image positions to adjust the focus of the photographing lens. Specifically, the optical system for distance measurement guides the light from the subject to a pair of line sensors composed of photoelectric conversion elements to form an image, and the accumulated charge of the photoelectric conversion elements for each pixel between the two line sensors. A correlation calculation for comparison is performed to detect the distance between the two subject images. The distance between the two object images is determined depending on the geometric conditions of the distance measuring system such as the distance between the distance measuring optical system and the line sensor and the distance to the object. When the distance is obtained, the distance to the subject is calculated from the geometric condition of the distance measuring system. The focus is automatically adjusted for the subject by controlling the motor that adjusts the focus position of the taking lens according to the distance to the subject calculated in this way.

In automatic focus adjustment of a single-lens reflex camera, the light that has passed through the taking lens and is incident is guided to a pair of line sensors to form a pair of subject images. Normally, the distance between these two images should match the distance when focusing,
Drives the focus adjustment motor of the taking lens. in this case,
Automatic focus adjustment will be performed directly without calculating the distance to the subject, but if necessary, the distance to the subject can be calculated from the detected subject-to-image distance and the geometric conditions of the ranging system. Done.

The applicant of the present invention has disclosed a detailed method of distance measurement calculation in Japanese Patent Laid-Open Publication No. 59-126517.

[0005]

In order to calculate the distance to the subject by the above method, it is an essential condition that the pair of images formed on the line sensor have sufficient contrast. . When the contrast is low, that is, when there is not much difference in the accumulated charges of the photoelectric conversion elements of the line sensor, the image cannot be recognized, and it becomes impossible to obtain the object-image distance. In such a case, it becomes impossible to focus on the subject correctly, so it is necessary to determine in advance whether or not the contrast of the image on the line sensor is sufficient.

For this reason, conventionally, the contrast has been calculated when performing the correlation calculation. Specifically, the charge is accumulated by the photoelectric conversion element for a predetermined period, and the accumulated charge of each photoelectric conversion element is transferred as a potential to the distance measurement calculation device in order to perform the correlation calculation. The distance measurement calculation device obtains the difference value of the potentials of the adjacent photoelectric conversion elements for each line sensor and calculates the sum. The calculated sum is compared with a predetermined value, and when it is equal to or larger than the predetermined value, it is determined that the contrast is sufficient, and the correlation calculation is performed. On the other hand, when the calculated total is less than the predetermined value, it is determined that the contrast of the image is insufficient. In this case, the correlation calculation is not performed, and the camera user is warned by the display or sound, or the auxiliary light for distance measurement is emitted.

However, according to this method, the transfer of the photoelectric conversion element potential to the arithmetic unit, that is, the reading of the accumulated charge is always performed. For this reason, the time required to determine that the contrast is insufficient becomes long, and the time required to calculate the difference value and the sum is also added, so that the measure for dealing with the insufficient contrast tends to be delayed. For example, in a system in which the auxiliary light is automatically emitted when the contrast is insufficient, the emission of the auxiliary light is delayed.
In contrast, in the autofocus camera, the delay in detection of insufficient contrast causes a decrease in the followability of focus adjustment with respect to a moving subject, which causes a decrease in the function of automatic focus adjustment.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a distance measuring system for quickly detecting insufficient contrast of an image formed on a line sensor and an autofocus camera equipped with the distance measuring system.

[0009]

In order to achieve the above object, in the present invention, light from a distance measuring object is guided to a pair of photoelectric conversion element arrays, and each photoelectric conversion element array is photoelectrically converted and accumulated. In a distance measurement system that performs distance measurement by comparing charge distributions, it took at least one photoelectric conversion element array for a photoelectric conversion element whose accumulated charge reaches a predetermined amount first to reach the predetermined amount. Detecting a first time and a second time required for the accumulated charges of all photoelectric conversion elements to reach the predetermined amount, and obtaining a difference or ratio between the second time and the first time. Then, when the calculated value is equal to or larger than the predetermined value, the charge distributions for distance measurement are compared.

The accumulated charge of the photoelectric conversion element rises more quickly as the amount of received light increases. Therefore, the time required for the accumulated charges of the photoelectric conversion element to reach the predetermined amount represents the amount of received light, and the first time and the second time are respectively
It corresponds to the brightness of the brightest part and the darkest part in the photoelectric conversion element array. A small difference in the amount of received light between the brightest part and the darkest part means that the contrast of the image on the photoelectric conversion element array is small, and distance measurement is difficult.
By obtaining the difference or ratio between the second time and the first time, the degree of difference in brightness between the brightest part and the darkest part can be known, and when the difference or ratio is equal to or more than a predetermined value, sufficient contrast is obtained. There is a high possibility that there is a possibility that there will be a charge, and the distribution of the accumulated charges in each photoelectric conversion element array is compared. On the contrary, when the calculated value is less than the predetermined value, the distribution of the accumulated charges is not compared for distance measurement. This avoids wasteful calculation for distance measurement when the distance cannot be measured correctly due to insufficient contrast.

The detection of the second time and the first time, the calculation of the difference or the ratio, and the comparison with the predetermined value may be carried out for only one photoelectric conversion element array or both photoelectric conversion element arrays. May be. If both are performed, the reliability of the contrast determination becomes high.

Further, the distance from the object to be measured is guided to a pair of photoelectric conversion element arrays, and each photoelectric conversion element array performs photoelectric conversion for a predetermined period of time to compare the distribution of charges accumulated to perform the distance measurement. In the distance measuring system, for at least one of the photoelectric conversion element arrays, the time required for the photoelectric conversion element that the accumulated charge first reaches the predetermined amount to reach the predetermined amount is detected, and is detected as the predetermined time. The time difference or ratio is calculated, and the distance is measured when the calculated value is equal to or larger than a predetermined value.

In this case, the photoelectric conversion of the photoelectric conversion element array is stopped in a predetermined time. This predetermined time is set to such an extent that the photoelectric conversion element array can receive a sufficient amount of light under normal distance measuring conditions. The time detected here corresponds to the amount of received light of the brightest part, and this time becomes long when the light from the object to be measured is weak, and at this time, distance measurement becomes difficult. By obtaining the value of the difference or ratio between the predetermined time and the detected time, it is determined whether or not the photoelectric conversion element array receives the amount of light necessary for distance measurement. When the obtained value is equal to or larger than the predetermined value, it is when a sufficient amount of light is obtained, and in this case, the distribution of the accumulated charges in each photoelectric conversion element array is compared. On the contrary, when the calculated value is less than the predetermined value, it means that the amount of light is insufficient and the charge distributions are not compared. As a result, it is possible to avoid wasteful calculation for distance measurement when the distance cannot be correctly measured due to insufficient light amount.

Detecting the time, obtaining the difference or ratio with respect to the predetermined time, and comparing with the predetermined value may be performed for only one photoelectric conversion element array or for both photoelectric conversion element arrays. Good. If both are performed, the reliability of the contrast determination becomes high.

An autofocus camera is equipped with the above distance measuring system to measure the distance to a subject, and the focus of the photographing lens of the camera is automatically adjusted based on the distance measurement result. With this configuration of the camera, when the contrast of the subject is low or when the subject is totally dark, it is promptly detected that distance measurement is impossible or the result of distance measurement is unreliable.
Useless calculation for distance measurement can be avoided.

[0016]

FIG. 1 shows the configuration of an embodiment in which the distance measuring system of the present invention is applied to an autofocus camera. The camera body 1 includes a pair of left and right line sensors 31, 3
Distance measuring IC (AFIC) 3 having 2 and line sensor 3
A distance measuring optical system 2 composed of left and right lenses 21 and 22 for respectively focusing light from a subject on the lenses 1 and 32, a distance measuring device 4 including a microprocessor and connected to an AFIC 3, a photographing lens 5, and a photographing lens. A lens driving device 6 for changing the focal position of the lens 5 is provided. Each of the line sensors 31 and 32 is configured by arranging a plurality of photoelectric conversion elements in a line.

A film 7 is supplied behind the taking lens 5, and a shutter 9 is provided between the taking lens 5 and the film 7. The shutter 9 is driven by the exposure control device 8. The lens driving device 6 and the exposure control device 8 are controlled by the distance measurement calculation device 4.

Further, a warning device 1 which is connected to the distance measurement calculation device 4 and comprises an auxiliary light device 10 for emitting auxiliary light for distance measurement, and an LED which lights up when distance measurement is impossible and issues a warning to the user.
1 and two switches S1 and S2 which are interlocked with a shutter release button (not shown). The switch S1 is closed when the release button is pressed halfway, and the switch S2 is closed when the release button is further pressed. When the switch S1 is closed, the distance measurement calculation device 4 instructs the AFIC 3 to start photoelectric conversion by the line sensors 31 and 32, and starts distance measurement. When the switch S2 is closed, the distance measurement calculation device 4 instructs the exposure control device 8 to open and close the shutter 9, and photographing is performed.

After the AFIC 3 is caused to perform photoelectric conversion for a predetermined time, the distance measurement calculation unit 4 gives an instruction to stop the photoelectric conversion. After that, the potentials corresponding to the accumulated charges are read from the photoelectric conversion elements of the line sensors 31 and 32. The distance measurement calculation device 4 calculates the distance to the subject by performing a correlation calculation for comparing the potentials of the left and right line sensors for each pixel, and the photographing lens 5 via the lens driving device 6 according to the calculated distance.
Drive. A series of processes of photoelectric conversion, distance measurement calculation, and lens driving are constantly repeated while the switch S1 is closed, that is, while the release button is half pressed. As a result, the taking lens 5 is always in focus with respect to the subject regardless of the movement of the subject. When the release button is further pressed and the switch S2 is closed, the shutter 9 is opened by the exposure control device 8 and the subject light is imaged on the film 7, and a clear image of the subject is recorded on the film 7.

FIG. 2 shows the configurations of the AFIC 3 and the distance measurement calculation device 4. In the figure, solid arrows represent the flow of data to be processed, and dotted arrows represent the flow of control signals. AFI
In addition to the left and right line sensors 31 and 32, the C3 is provided with two counters 34 and 35 and a clock 36 that supplies a clock signal to these. The photoelectric conversion elements 33 constituting the left and right line sensors 31, 32 are respectively a light receiving section 33a, a storage section 33b and a latch section 33c.
Consisting of The light receiving section 33a converts the received light into an electric charge and outputs it to the storage section 33b. The accumulating portion 33b accumulates the electric charge given from the light receiving portion 33a as a potential. The latch unit 33c corresponds to each storage unit 33b so as to output a latch signal when the potential of each storage unit 33b rises and reaches a predetermined value, or when a command is received from the distance measurement calculation device 4. It is provided. 128 such photoelectric conversion elements 33 are arranged in the left and right line sensors 31 and 32.

The distance measuring device 4 is started by closing the switch S1 and starts the timer 41, the line sensors 31, 3
2. An integration start instruction circuit 42 for generating an integration start signal INT for instructing the start of photoelectric conversion and charge accumulation by 2 and an integration end instruction circuit 43 for generating an integration end signal TRM for instructing the end of photoelectric conversion and charge accumulation are provided. There is. The distance measurement calculation circuit 4 also performs a distance calculation unit 60 that performs various calculations for distance measurement, and the images formed on the line sensors 31 and 32 have sufficient contrast before the distance calculation calculation by the distance calculation unit 60. Contrast detection unit 50 for determining whether or not
It has. The configuration and operation of these will be described later.

When the shutter release button is half-depressed and the switch S1 is closed, the timer 41 starts the time counting operation and gives a signal for instructing the integration start instruction circuit 42 to generate a signal. Further, the timer 41 gives a signal to the integration end instruction circuit 43 to notify that the predetermined time TE has elapsed when the predetermined time TE has elapsed after the start of time counting.
The integration start instruction circuit 42 sends an integration start signal IN to the left and right line sensors 31 and 32 in response to a command signal from the timer 41.
Give T. The integration start signal INT is transmitted to the counter 34,
The counters 34 and 35 are also supplied to the clock 35.
The clocking based on the clock signal from 6 is started.

In response to the integration start signal INT, the accumulating portions 33b of all photoelectric conversion elements 33 are initialized to discharge the accumulated charges to zero the potential, and the light receiving portion 33a starts photoelectric conversion. The charges generated by the photoelectric conversion of the light receiving unit 33a are given to the storage unit 33b, and the storage unit 33b
The potential of b increases according to the amount of light received by the light receiving unit 33a. When the potential of the storage section 33b reaches a predetermined potential V0, the latch signal is output from the latch section 33c. The photoelectric conversion by the light receiving section 33a and the charge accumulation by the accumulating section 33b are continued even after the latch signal is output from the latch section 33c.

When a predetermined time TE has elapsed after the start of integration,
Based on the signal from the timer 41, the integration end instruction circuit 43 sends the integration end signal TRM to all the photoelectric conversion elements 33.
Given to. By this integration end signal TRM, the light receiving unit 33a of each photoelectric conversion element 33 stops photoelectric conversion, and the storage unit 33b holds the accumulated charges. Also, the latch unit 3
3c outputs a latch signal when it is not outputting a latch signal after receiving the integration start signal INT. Therefore, each photoelectric conversion element 33 outputs a latch signal either when the accumulated charge reaches a predetermined amount or when the integration is completed.

All photoelectric conversion elements 33 of the left line sensor 31
A latch signal from the photoelectric conversion elements 33 of the right line sensor 35 is input to the counter 35. These counters 34, 35
Starts timing simultaneously with the start of integration by the integration start signal INT, and when a latch signal is input, the elapsed time from the start of integration can be measured.

The counter 34 counts the number of latch signals input from the left line sensor 31, outputs the elapsed time TL1 up to that time to the contrast detection unit 50 when the latch signal is input for the first time, and outputs the 128th signal. When the latch signal, that is, the last latch signal is input, the elapsed time TL2 until then is output to the contrast detection unit 50. Similarly, the counter 35 counts the latch signals input from the right line sensor 32, and when the first and last latch signals are input, the respective elapsed times TR after the start of integration are counted.
1 and TR2 are output to the contrast detection unit 50.

The first elapsed times TL1 and TR1 output from the counters 34 and 35 are the left and right line sensors 3 respectively.
The time required for the accumulated charge of the brightest part of each of Nos. 1 and 32, that is, the photoelectric conversion element having the largest amount of received light to reach a predetermined amount is shown. The second elapsed times TL2 and TR2 are the time required for the accumulated charge of the darkest part of each of the left and right line sensors 31, 32, that is, the photoelectric conversion element having the smallest amount of received light, to reach the predetermined amount, that is, each line sensor. It represents the time required for the accumulated charges of all photoelectric conversion elements 31 and 32 to reach the predetermined amount, or the integration time TE. FIG. 4 shows the relationship between the image brightness and the first and second elapsed times.

The contrast detecting section 50 includes a first contrast calculating circuit 51 and a first distance measuring possibility determining circuit 52.
Consisting of The first contrast calculation circuit 51 includes four elapsed times TL1, TL2, TR from the counters 34, 35.
Given 1, TR2, two values PL and PR are calculated from equation (1) and equation (2). PL = log (TL2 / TL1) / log2 ≡ log ₂ (TL2 / TL1) (1) PR = log (TR2 / TR1) / log2 ≡ log ₂ (TR2 / TR1) (2)

The time required for the potential of the storage portion 33b of the photoelectric conversion element 33 to reach the predetermined value V0 is inversely proportional to the brightness of the image portion imaged on the photoelectric conversion element. Therefore, the larger TL2 / TL1 or TR2 / TR1 is, the larger the difference in brightness between the brightest part and the darkest part of the left and right sign sensors 31, 32 is. The value P obtained as the logarithm of the values of these ratios by the equations (1) and (2)
L and PR represent relative EV values of the brightest part and the darkest part, and each different value means that the brightness is doubled. When there is no difference in brightness between the brightest part and the darkest part, that is, when there is no contrast in the image, PL or P
The value of R becomes 0.

The first distance measurement availability determination circuit 52 determines the left and right line sensors 3 based on the above two values PL and PR.
It is determined whether or not the images formed at 1 and 32 have sufficient contrast for distance measurement. Specifically, PL
And PR are compared with a predetermined value P0, it is determined that distance measurement is possible when both PL and PR are P0 or more, and when either PL or PR is less than P0, distance measurement is impossible due to insufficient contrast. It is determined that

When it is determined that the distance measurement is impossible, the distance measurement possibility determination circuit 52 blinks the LED of the warning device 11 to notify the user that the contrast is insufficient, and restarts the timer 41. Signal RS to indicate
T is given to cause the line sensors 31 and 32 to perform photoelectric conversion and charge accumulation again. At this time, the distance measurement possibility determination circuit 5
2 makes the auxiliary light device 10 emit light. The left and right line sensors 31, 32 because the entire subject is dark due to insufficient light quantity
When the contrast image does not have sufficient contrast, the distance can be measured by illuminating the subject with the auxiliary light for distance measurement in this way. If the two values PL and PR do not become P0 or more even after performing the photoelectric conversion and the charge storage while emitting the auxiliary light, it is impossible to measure the distance to the user by turning on the LED of the warning device 11. Then, the lens driving device 6 is controlled so that the photographing lens 6 is focused at infinity.

The storage units 3 of all photoelectric conversion elements 33 are
When the potential of 3b does not reach the predetermined value V0 within the integration time TE, the second elapsed time TL2 or TR2 is set to the integration time T
Will represent E. At this time, the values of PL and PR do not represent the difference in brightness between the brightest part and the darkest part of the image. However, this is the case where the darkest part is so dark that it does not reach the predetermined potential V0 even if photoelectric conversion is performed for a predetermined integration time TE, and if the brightest part has a certain level of brightness, that is, TL1 or TR1. If is a small value below a certain level, there is sufficient contrast. Therefore, in this case as well, whether or not the distance measurement is possible can be determined by comparing PL and PR with the predetermined value P0.

Conversely, TL2 and TR2 are the integration time T
Since it cannot be a value larger than E, TL1 and TL2
When is larger than a certain level, it can be determined that the contrast is insufficient. Specifically, T0 = TE
Set a predetermined time T0 of / 2 ^P0, and set TL1 or TR1
Is larger than the predetermined value T0, it is determined that the contrast is insufficient. In this case, the first elapsed times TL1 and TR1 are directly applied from the counters 34 and 35 to the first distance measurement adequacy determination circuit 52 to determine the adequacy of distance measurement.

When at least one of the first elapsed times TL1 and TR1 exceeds the predetermined value T0, at least one of PL and PR becomes less than the predetermined value P0 even if the predetermined integration time TE photoelectric conversion is performed. TL1
It is meaningless to continue photoelectric conversion after detection of TR1 or TR1. Therefore, the photoelectric conversion may be ended when it is determined that the contrast is insufficient in this way. However, when both the first elapsed times TL1 and TR1 are equal to or less than the predetermined value T0, it is necessary to calculate PL and PR and compare them with the predetermined value P0 for the contrast determination.

The difference in brightness between the brightest part and the darkest part of the images of the left and right line sensors 31 and 32 is expressed by equations (1) and (2).
Instead of obtaining the ratio value by using the first contrast calculation circuit 51, the first contrast calculation circuit 51 calculates the difference in brightness between the brightest part and the darkest part from the equation (3) and the equation (4).
Alternatively, the difference may be obtained as the difference between the elapsed times. DL = TL2-TL1 (3) DR = TR2-TR1 (4)

At this time, the first distance measurement availability determination circuit 52
Compares the two values DL and DR with a predetermined value D0,
When DL and DR are both D0 or more, it is determined that distance measurement is possible. Also in this case, T0 '= TE-
A predetermined value T0 'which is D0 may be set, and when TL1 or TR1 exceeds the predetermined value T0', it may be determined that the contrast is insufficient, and the photoelectric conversion may be terminated at that time.

When it is determined that the images of the left and right line sensors 31 and 32 have sufficient contrast based on PL and PR or DL and DR, the distance measurement availability determination circuit 5
2 is a storage unit 32 for the left and right line sensors 31, 32.
A signal OUT that gives an instruction to output the potential of b is given. Each photoelectric conversion element 33 outputs the potential of the storage section 33b to the distance calculation section 60 in response to the signal OUT.

The distance calculation unit 60 includes AD converters 61 and 6
2, RAM 63, 64, difference conversion circuits 65, 66, RA
M67, 68, second contrast calculation circuit 69, second
The distance measurement availability determination circuit 70, the correlation calculation circuit 71, and the subject distance calculation circuit 72. The output potential from each photoelectric conversion element 33 of the left line sensor 31 is sequentially converted into a digital value by the AD converter 61, and the converted 128 pixel values VL _{1 to} VL ₁₂₈ are stored in the RAM 63. Similarly, the output potential from the photoelectric conversion element 33 of the right line sensor 32 is also sequentially converted into a digital value by the AD converter 62, and the converted VR pixel values VR _{1 to} VR ₁₂₈ are stored in the RAM 6.
Stored in 4.

The difference conversion circuit 65 reads out the pixel value of the RAM 63 and takes the difference every 4 pixels (AL _j = VL _{j + 4).}
-VL _j , j = 1,2, ..., 124), and their difference values AL _{1 to} AL ₁₂₄
Is stored in the RAM 67. The difference conversion circuit 66 is also R
The pixel value of AM64 is taken every 4 pixels (AR _j = V
R _{j + 4} −VR _j , j = 1,2, ..., 124), difference values AR _{1 to} AR
₁₂₄ is stored in the RAM 68. Obtaining the difference value in this way is called a filter process, and the sensitivity difference between the left and right line sensors 31 and 32 is removed by this process, and the reliability of the correlation calculation is improved.

The second contrast calculation circuit 69 calculates the contrast value C by performing the calculation of equation (5).

[0041]

[Equation 1]

The second distance measurement availability determination circuit 70 determines whether or not distance measurement is possible based on the calculated contrast value C. Specifically, the contrast value C is set to a predetermined value C0.
When the contrast value C is equal to or greater than the predetermined value C0, it is determined that distance measurement is possible, and the contrast value C is equal to the predetermined value C0.
When it is less than 0, the reliability of the correlation calculation is low due to insufficient contrast, and it is determined that distance measurement is impossible.

The second distance measurement availability determination circuit 70, when it is determined that the distance measurement is impossible, causes the first distance measurement availability determination circuit 52 described above.
Similarly, the LED of the warning device 11 is blinked to inform the user that the contrast is insufficient, and the signal RST for instructing the restart is given to the timer 41 to perform photoelectric conversion and charge accumulation by the line sensors 31 and 32. Let me try again. At this time, the distance measurement availability determination circuit 52 causes the auxiliary light device 10 to emit light to illuminate the subject. Even if the auxiliary light is turned on and photoelectric conversion and charge accumulation are performed again, if the calculated contrast value C is less than the predetermined value C0, the LED of the warning device 11 is continuously turned on and the user cannot measure the distance. Then, the lens driving device 6 is controlled so that the taking lens 5 is focused at infinity.

When it is determined that the distance measurement is possible, the second distance measurement availability determination circuit 70 instructs the correlation calculation circuit 71 to start the correlation calculation. The correlation calculation circuit 71 includes RAM 67 and RAM 68.
Equation (6) is calculated in order to obtain the correlation between the pixel values of. H (m, k) obtained here represents the degree of coincidence between the compared left and right images, and the smaller the value, the higher the degree of coincidence.

[0045]

[Equation 2]

Here, the pixels AL _{3 to} AL of the RAM 67 are
₁₂₂ blocks in 3 blocks of 40 pixels each (AL _{3 to} AL ₄₂ ),
Divide into (AL _{43 to} AL ₈₂ ), (AL _{83 to} AL ₁₂₂ ),
85 blocks (AR ₁ to AR ₄₀ ) to (AR ₈₅ to AR, each consisting of 40 pixels of RAM 68 and shifted by 1 pixel
₁₂₄ ). Calculated H (1,1) ~ H (3,85)
The value of 255 is given to the subject distance calculation circuit 72.

The subject distance calculation circuit 72 finds the smallest value H (m1, k1) among H (1,1) to H (3,85) given from the correlation calculation circuit 71. The m1 and k1 found here are the m1th of the three blocks in the RAM 67.
And the block starting from the k1 pixel of the RAM 68 is the best match. Next, this H (m1, k1) and H (m1, k1-1), H (m1, k1 +
1) is used for interpolation processing, and the maximum matching score H0 (m1, k
The value k0 of k that is 0) is calculated. In consideration of the arrangement pitch of the photoelectric conversion elements 33 and the installation intervals of the left and right line sensors 31 and 32, the first pixel number (40 · m1−37 = 3, 43 or 83) of the m1st block and k0 From the value, the distance between the parts of the images of the line sensors 31 and 32 that best match each other is calculated. The distance to the subject is calculated from the image distance thus calculated and the geometric conditions of the distance measuring system such as the distance between the distance measuring optical system 2 and the line sensors 31 and 32.

The subject distance calculation circuit 72 outputs the calculated subject distance to the lens driving device 6. The lens driving device 6 calculates the focal position of the photographing lens 5 corresponding to the given subject distance and sets the focal position of the photographing lens 5. In this way, autofocus is performed.

The flow of the above distance measurement processing is shown in the flowchart of FIG. The distance measurement process is started by pressing the shutter release button halfway (step # 100), and photoelectric conversion and charge accumulation are started by the integration start signal INT (# 105). As the photoelectric conversion progresses, the photoelectric conversion element 3
The first elapsed time TL1, TR1 when the potential of the brightest part reaches the predetermined potential V0 and the accumulated charge of 3 rises, and the second elapsed time when the potential of the darkest part reaches the predetermined potential V0. TL2 and TR2 are detected (# 110). When a predetermined integration time TE has elapsed, an integration end signal TRM is issued, and photoelectric conversion and charge accumulation are completed (# 11).
5). When the potential of the darkest portion has not reached the predetermined potential V0, the second elapsed times TL2 and TR2 are detected at this point (# 120).

Ratio P of second elapsed time to first elapsed time
The difference in brightness between the brightest part and the darkest part is detected by obtaining L, PR or the differences DL, DR (# 125). Next, the ratio values PL, PR or the difference values DL, DR are compared with a predetermined value P0 or D0 to determine whether or not the images of the two line sensors have sufficient contrast (#
130). If the contrast is insufficient even in one of the images of the two line sensors, it is determined whether or not auxiliary light is emitted in the charge accumulation (# 135). When the auxiliary light is not emitted, the user is warned that the contrast is insufficient (# 140), and the auxiliary light is emitted (# 14).
5), photoelectric conversion and charge accumulation are performed again (# 105). If it is determined in step # 135 that the auxiliary light is being emitted, the user is warned that distance measurement is impossible (# 15
0), focus the taking lens 5 to infinity (# 15
5). Then, the process returns to step # 105 to restart photoelectric conversion and charge accumulation.

When it is determined in step # 130 that the images of the two line sensors have a sufficient contrast, the electric potential of the photoelectric conversion elements of the line sensors 31, 32, that is, the pixel value, is measured by the distance calculating unit 60. To read (# 160). Next, the contrast is strictly calculated from the difference between the pixel values of the adjacent pixels (# 165). By comparing the calculated contrast value C with a predetermined value C0, it is determined whether or not reliable correlation calculation can be performed (# 17).
0). When the contrast value C is smaller than the predetermined value C0, it is determined that the contrast is insufficient and the reliability is lowered, and the process proceeds to step # 135 to perform the above-mentioned processing. When the contrast value C is equal to or more than the predetermined value C0, it is determined that the subject distance can be calculated with high reliability, and the correlation calculation of the images of the two line sensors is performed (# 175) to calculate the subject distance (# 180). ), The photographing lens 5 is driven so that the subject is in focus (# 185).

The processing after the reading of the potentials of the photoelectric conversion elements of the line sensors 31 and 32 is almost the same as the conventional method. However, in the present invention, prior to the reading of the potentials, the maximum of the images of the line sensors 31 and 32 is read. This is different from the conventional distance measuring system in that the difference in brightness between the bright part and the darkest part is determined. The detection of the first elapsed time TL1, TR1 and the second elapsed time TL2, TR2 is performed in parallel with photoelectric conversion and charge accumulation, and the image is detected before the charge accumulation is completed or at the latest immediately after the charge accumulation is completed. The determination of the difference in brightness between the brightest part and the darkest part of is completed. Therefore, when the contrast of the image is insufficient, it is possible to take appropriate measures immediately without performing the time-consuming reading of the potential of the photoelectric conversion element and the conventional contrast calculation or correlation calculation.

In the above embodiment, the left and right line sensors 31 and 32 detect the first elapsed time and the second elapsed time to determine the difference in brightness between the brightest part and the darkest part. Although the case has been described, the difference between the brightness of the brightest part and the brightness of the darkest part may be determined by detecting the first and second elapsed times for only one of the line sensors. In that case, it is not necessary to provide the latch portion 33c in the photoelectric conversion element 33 of the other line sensor, and one of the counters 34 and 35 is also unnecessary.
However, the reliability of the determination result is higher when the difference in brightness between the brightest part and the darkest part of both line sensors 31 and 32 is determined.

[0054]

According to the distance measuring system of the present invention, it is possible to quickly detect the difference in brightness between the brightest part and the darkest part of the object to be measured, and the distance can be measured before performing the strict contrast calculation. It is possible to judge whether it is possible or not. Therefore, when the object to be measured is in a state of insufficient contrast,
It is possible to avoid wasteful calculation of contrast and comparison of distribution of accumulated charges, promptly inform the user that the contrast is insufficient, and take appropriate measures such as emission of auxiliary light for distance measurement. Can be taken promptly.

In the distance measuring system according to the second aspect, it is possible to promptly judge whether or not the distance measuring object is bright enough to perform the distance measuring based on the brightness of the brightest part of the distance measuring object. You can Therefore, when the object to be measured is in a state of insufficient light quantity as a whole, it is possible to avoid wasteful calculation of contrast and comparison of the distribution of the accumulated charge, and to prevent the emission of auxiliary light for distance measurement. It becomes possible to take appropriate measures immediately. As a result, distance measurement processing can be performed quickly.

In the autofocus camera according to claim 3,
Insufficient contrast of the subject or insufficient overall brightness can be promptly detected. In such a state in which distance measurement is impossible or only reliable distance measurement can be performed, it is possible to wastefully perform various calculations or to wastefully drive the taking lens to adjust the focus position. Can be avoided. Therefore, the efficiency of the entire autofocus process is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an autofocus camera according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration and a signal flow of a ranging IC and a ranging calculation device.

FIG. 3 is a flowchart showing the flow of distance measurement processing.

FIG. 4 is a diagram showing a relationship between the image brightness of the line sensor and the time required for the potential of the photoelectric conversion element forming the line sensor to reach a predetermined potential.

[Explanation of symbols]

 1 Auto Focus Camera Main Body 2 Distance Measuring Optical System 3 Distance Measuring IC 4 Distance Measuring Calculator 5 Photographing Lens 6 Lens Driving Device 7 Film 8 Exposure Control Device 9 Shutter 10 Auxiliary Light Device 11 Warning Device 21, 22 Distance Measuring Lens 31 left line sensor 32 right line sensor 33 photoelectric conversion element 33a light receiving section 33b storage section 33c latch section 34, 35 counter 36 clock 41 timer 42 integration start instruction circuit 43 integration end instruction circuit 50 contrast detection section 51 first contrast calculation circuit 52 first distance measurement propriety determination circuit 60 distance calculation unit 61, 62 AD converter 63, 64 RAM 65, 66 difference conversion circuit 67, 68 RAM 69 second contrast calculation circuit 70 second distance measurement propriety determination circuit 71 Correlation calculation circuit 72 Subject distance calculation circuit S1, S2 Switch, TL1, TR1 first elapsed time (first time) TL2, TR2 second elapsed time (second time) TE integration time

Claims (3)

[Claims] 1. A distance measuring system for measuring a distance by guiding light from a distance measuring object to a pair of photoelectric conversion element arrays, and comparing distributions of charges accumulated by photoelectric conversion of each photoelectric conversion element array. , For at least one of the photoelectric conversion element rows, the first time required for the photoelectric conversion elements to reach the predetermined amount of accumulated charge first and the accumulated charge of all photoelectric conversion elements The second time required to reach the predetermined amount is detected, and the difference or ratio between the second time and the first time is calculated. When the calculated value is equal to or larger than the predetermined value, distance measurement is performed. Ranging system characterized by comparing the charge distribution for. 2. Distance measurement is performed by guiding light from a distance measurement target to a pair of photoelectric conversion element arrays, and comparing the distribution of charges accumulated by photoelectric conversion for a predetermined time by each photoelectric conversion element array. In the distance measuring system, at least one of the photoelectric conversion element arrays detects the time required for the photoelectric conversion element that first reaches the predetermined amount of accumulated charge to reach the predetermined amount, and detects the predetermined time. A distance measuring system characterized in that a time difference or ratio is obtained, and when the obtained value is equal to or larger than a predetermined value, charge distributions for distance measurement are compared. 3. The distance measuring system according to claim 1 or 2 is provided to measure the distance to a subject, and the focus of the photographing lens is automatically adjusted based on the distance measuring result. Autofocus camera.