JP4341202B2 - Focus detection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a focus detection device that detects a focus adjustment state of an objective lens.
[0002]
[Prior art]
The pair of images having the parallax of the subject is guided onto the pair of image sensor arrays, and the relative shift amount of the pair of subject images is calculated based on the electrical output of the pair of image sensor arrays, thereby adjusting the focus of the objective lens. A phase difference detection type focus detection device that detects a state is known.
[0003]
A phase difference detection type focus detection apparatus will be described with reference to FIG. In FIG. 5, a band-pass filter 700, a field mask 200, a field lens 300, diaphragm apertures 401 and 402, and re-imaging lenses 501 and 502 constitute a focus detection optical system, and a pair of subject images is formed by these focus detection optical systems. Is imaged on the pair of image sensor arrays A and B. In some cases, the bandpass filter 700 is disposed behind the field mask 200. A region 101 on the objective lens 100 is a back-projected image of the stop aperture 401 by the field lens 300. Similarly, a region 102 on the objective lens 100 is a back-projected image of the stop aperture 402 by the field lens 300. The focus detection area is a portion where the image sensor arrays A and B are projected by the re-imaging lenses 501 and 502 and overlap in the vicinity of the planned focal plane 600.
[0004]
The light flux from the subject incident through the region 101 of the objective lens 100 forms an image on or before the planned focal plane 600 equivalent to the film surface, and then the bandpass filter 700, the opening of the field mask 200, the field lens 300, An image is formed on the image sensor array A through the aperture opening 401 and the re-imaging lens 501. Similarly, a light beam from a subject incident through the region 102 of the objective lens 100 forms an image on or before and after the planned focal plane 600, and then the bandpass filter 700, the opening of the field mask 200, the field lens 300, and the aperture opening. The image is formed on the image sensor array B through the unit 402 and the re-imaging lens 502.
[0005]
The pair of subject images formed on the pair of image sensor arrays A and B are separated from each other in a so-called front pin state in which the objective lens forms a sharp image of the subject before the planned focal plane 600, and conversely the planned focal plane. A pair of subject images on the pair of image sensor arrays A and B are close to each other in a so-called rear pin state in which the sharp image of the subject is connected after 600, and at the time of the so-called in-focus state in which the sharp image of the subject is just connected to the planned focal plane 600. Match relatively. Accordingly, the pair of subject images are photoelectrically converted by the image sensor arrays A and B to be converted into electric signals, and these signals are subjected to arithmetic processing to obtain the relative positions of the pair of subject images. Here, it is possible to detect the amount and direction away from the in-focus state, that is, the defocus amount.
[0006]
Next, a calculation processing method for obtaining the defocus amount will be described. Each of the image sensor arrays A and B is composed of a plurality of photoelectric conversion elements. As shown in FIGS. 6A and 6B, the signals a1.an and b1. Output. Then, the correlation calculation is performed while the pair of data strings (a1 to an) and (b1 to bn) are relatively shifted by L by predetermined data. Specifically, the correlation amount C (L) is calculated by the following equation.
[Expression 1]
C (L) = Σ | ai−bj |
Here, Σ represents a total operation of i = k to r, and j−i = L, L = −lmax,..., −2, −1, 0, 1, 2,.
[0007]
L is an integer corresponding to the shift amount of the data string as described above, and the first term k and the last term r may be changed depending on the shift amount L. A constant determined by the pitch width of the focus detection optical system and the photoelectric conversion elements of the image sensor arrays A and B shown in FIG. 5 as the shift amount that gives the minimum correlation amount in the correlation amount C (L) thus obtained. The defocus amount is multiplied by. However, the correlation amount C (L) is a discrete value as shown in FIG. 6C, and the minimum unit of the defocus amount that can be detected is limited by the pitch width of the photoelectric conversion elements of the image sensor arrays A and B. Will be.
[0008]
Therefore, a method has been proposed in which a minimum value Cex is newly calculated by performing an interpolation operation from a discrete correlation amount C (L), and fine focus detection is performed (see, for example, Japanese Patent Laid-Open No. 60-037513). ). As shown in FIG. 7, this focus detection method is a method of calculating based on a correlation value C (0) which is a minimum value and correlation amounts C (1) and C (-1) between shift amounts on both sides thereof. The shift amount Fm and the defocus amount DF that give Cex are obtained by the following equations.
[Expression 2]
DF = Kf * Fm,
Fm = L + DL / E,
DL = {C (-1) -C (1)} / 2
Cex = C (0) − | DL |,
E = MAX [{C (1) -C (0)}, {C (-1) -C (0)}]
Here, MAX {Ca, Cb} means that the larger one of Ca and Cb is selected, and Kf is the pitch width of the photoelectric conversion elements of the focus detection optical system and the image sensor arrays A and B shown in FIG. Is a constant determined by.
[0009]
It is necessary to determine whether the defocus amount obtained in this way truly indicates the defocus amount or due to fluctuations in the correlation amount due to noise or the like, and when the following conditions are satisfied, the defocus amount is Be trusted.
[Equation 3]
E> E1 and Cex / E <G1
Here, E1 and G1 are predetermined values. E is a value that depends on the contrast of the subject. The larger the value, the higher the contrast and the higher the reliability. Cex / E mainly depends on the degree of coincidence of images, and the closer to 0, the higher the reliability. become. Then, if it is determined that there is reliability, the objective lens is driven based on the defocus amount DF.
[0010]
As described above, whether or not focus detection is possible and the reliability of the detection result greatly depend on the contrast height which is the light luminance distribution of the subject. Therefore, it is necessary to optimally reflect the contrast of the subject in the image sensor output. For example, when focus detection is performed on a subject having a contrast as shown in FIG. 8A, it is desirable to obtain an image sensor output as shown in FIG. In FIG. 8, Vsat indicates the saturation voltage of the photoelectric conversion element. However, if the accumulation time is short, the contrast becomes low as shown in FIG. On the other hand, if the storage time is long, the contrast that should originally exist is lost as shown in FIG. Therefore, it is necessary to obtain an image output of an appropriate size, and for this purpose, charge accumulation must be performed with an appropriate accumulation time.
[0011]
In order to obtain this appropriate accumulation time, the accumulation time is calculated so that the peak value of the image sensor output in the next accumulation operation becomes an appropriate size based on the accumulation time in the previous accumulation operation and the image sensor output. There is a way to do it. For example, it is assumed that an image sensor output as shown in FIG. 8B is obtained, the accumulation time at that time is Tb, and the peak value is Vb. In such a case, in order to obtain an output having an appropriate magnitude as shown in FIG.
[Expression 4]
Tc = (Vc / Vb) * Tb
And it is sufficient. Here, Vc is a target peak value in the next accumulation operation. For this target peak value, Vsat is the output of the image sensor when a saturated state is created in advance, and Vc is calculated by the following equation and stored in the camera.
[Equation 5]
Vc = A * Vsat
Here, A is a positive real number less than 1, and the “appropriate size” of the image sensor output is determined by the size of A. When A is small, the contrast of the image sensor output is always low. On the other hand, when A is large, the image sensor output is saturated immediately even if the brightness of the subject changes slightly. This method of adjusting the image sensor output is called AGC (Auto Gain Control). There is also a method of adjusting the image sensor output based on the average value instead of the peak value.
[0012]
By the way, in recent years, a so-called multipoint ranging type focus detection apparatus that performs focus detection in a plurality of regions in a photographing screen has been used. For example, as shown in FIG. 4, this type of focus detection apparatus includes a plurality of focus detection areas in a shooting screen. Among these multiple focus detection areas, there is a method for selecting a focus detection area that captures a main subject, in other words, a focus detection calculation and a focus detection area to be a lens driving target based on the calculation result. There are a manual selection method by the photographer and a selection method automatically performed by the focus detection apparatus. In the case of the manual selection method by the photographer, the focus detection calculation is performed based on the image sensor output corresponding to the focus detection area selected by the photographer using the manual selection member, and the lens is driven based on the focus detection result. However, when the photographer switches the selected area, all of them are selected even when the focus detection area is manually selected in order to quickly execute the focus detection calculation and the lens driving based on the image sensor output of the newly selected area. It is desirable to perform the above-described AGC in the focus detection region.
[0013]
On the other hand, when the focus detection area is automatically selected by the focus detection device, the focus detection calculation is performed in all focus detection areas, and the focus detection area showing the closest defocus amount is selected from the calculation results. There is a known method (for example, see Japanese Patent Application Laid-Open No. 59-146028). However, in the case of automatic selection, if the number of focus detection areas is large, there is a drawback that the required time from the start of the automatic focus detection operation to the completion of automatic selection of the focus detection area becomes long. That is, immediately after the start of focus detection, the output of the “appropriate size” is difficult to obtain because the output of the image sensor does not converge to the “appropriate size” by AGC. Therefore, even though focus detection results are obtained in almost all focus detection areas, only one focus detection area becomes impossible to detect the focus, so that the focus detection area showing the closest defocus amount is selected. In other words, the image sensor charge accumulation and focus detection calculation must be performed again in all focus detection regions. If such an operation is repeated until calculation results are obtained in all the focus detection areas, the time required for completing the automatic selection of the focus detection areas becomes long.
[0014]
[Problems to be solved by the invention]
Therefore, in order to shorten the time from the start of the focus detection operation to the completion of the automatic selection of the focus detection region, the focus detection calculation is prohibited until all image sensor outputs are appropriately sized by AGC. It is possible. By doing so, useless focus detection calculation is not performed until all the image sensor outputs have appropriate sizes, and the time can be shortened accordingly.
[0015]
However, when using a destructive readout type image sensor such as a CCD, for example, when the AGC determines that all the image sensor outputs have an appropriate size, the accumulated charges of all the image sensors are read out. The same accumulated charge cannot be read again because it is not left. Therefore, it is necessary to store all image sensor outputs.
[0016]
However, storing all image sensor outputs requires a large-capacity memory, which is expensive. However, if memory is prepared for one focus detection area and the output data is overwritten for each calculation, the memory capacity can be reduced, but all image sensor outputs are appropriately sized by AGC. After the determination is made, the charge accumulation of the image sensor and the focus detection calculation have to be performed again in all focus detection areas, resulting in a poor response.
[0017]
An object of the present invention is to automatically select a region to be lens-driven from a plurality of focus detection regions in a short time based on a focus detection calculation result.
[0018]
[Means for Solving the Problems]
(1) The invention of claim 1 is provided corresponding to each of a plurality of focus detection areas of the object scene, and a plurality of destructions that repeatedly perform charge accumulation by accumulation control according to the luminance of the plurality of focus detection areas. Readout photoelectric conversion means, calculation means for calculating the focus adjustment state of the objective lens with respect to the plurality of focus detection areas based on outputs of the plurality of destructive readout photoelectric conversion means, and outputs of the plurality of photoelectric conversion means Determination means for determining whether or not the predetermined value is suitable for calculation by the calculation means; and outputs of the plurality of photoelectric conversion means And the next accumulation time for which the target output is obtained based on the accumulation time when the output is obtained, Predicting means for predicting whether or not the next output of the plurality of photoelectric conversion means by the charge accumulation will be a predetermined value suitable for the calculation by the calculation means, and the output of the plurality of photoelectric conversion means by the determination means Even if it is determined that the predetermined value is not suitable for the calculation by the calculation means, the output of the plurality of photoelectric conversion means by the next charge accumulation by the prediction means is a predetermined value suitable for the calculation by the calculation means. And a control unit that causes the calculation unit to calculate the focus adjustment state of the objective lens based on the outputs of the plurality of photoelectric conversion units by the next charge accumulation.
(2) In the focus detection apparatus according to a second aspect, each of the plurality of photoelectric conversion units includes a plurality of photoelectric conversion elements. light When the maximum output among the outputs of the plurality of photoelectric conversion elements included in each of the electricity conversion means is in the vicinity of a preset target value, the outputs of the plurality of photoelectric conversion means are predetermined values suitable for calculation by the calculation means. It is determined to be a value.
(3) In the focus detection device according to a third aspect, each of the plurality of photoelectric conversion units includes a plurality of photoelectric conversion elements, and the plurality of photoelectric conversion units included in each of the plurality of photoelectric conversion units by the determination unit. When the average output of the elements is in the vicinity of a preset target value, it is determined that the outputs of the plurality of photoelectric conversion means are predetermined values suitable for calculation by the calculation means.
(4) The focus detection device according to claim 4 is: Counting means for counting the number of times the charge accumulation is repeated without shifting to the calculation of the focus adjustment state based on the determination result of the determination means and the prediction result of the prediction means, and the control means When the number of counts reaches a predetermined number, the next charge accumulation of the photoelectric conversion means that outputs an output determined to be a predetermined value suitable for calculation by the calculation means among the plurality of photoelectric conversion means Based on the output, the calculation means calculates the focus adjustment state of the objective lens. It is what I did.
(5) The focus detection apparatus according to claim 5 is a counting unit that counts the number of times the charge accumulation is repeated without shifting to the calculation of the focus adjustment state based on the determination result of the determination unit and the prediction result of the prediction unit. When the number of counts of the counting means reaches a predetermined number by the control means, the plurality of photoelectric conversion means Selected based on at least one of the number of photoelectric conversion elements in which maximum output, contrast and overflow occur Based on the next output by the charge accumulation of the photoelectric conversion means, the calculation means calculates the focus adjustment state of the objective lens.
(6) The focus detection apparatus according to claim 6 is: When the illumination field is illuminated by the illumination unit at the time of focus detection, the counting number of the counting unit is reset to an initial value. It is what I did.
(7) The focus detection device according to claim 7 is: A region selection unit that selects a focus detection region for performing focus adjustment of the objective lens from the plurality of focus detection regions based on a calculation result by the calculation unit. It is what I did.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a configuration of a camera including a focus detection apparatus according to an embodiment. The light flux from the subject corresponding to the plurality of focus detection areas of the object scene passes through the objective lens 1 and the focus detection optical system 2, and the image sensors 31 to 3n (n = n = n) of the image sensor 3 corresponding to each focus detection area. 1, 2,... Each of the image sensors 31 to 3n is a destructive readout type image sensor composed of a plurality of charge storage type photoelectric conversion elements. In the destructive readout type image sensors 31 to 3n, when stored charges are read from the image sensor, The stored charge is lost. Each of the image sensors 31 to 3n accumulates electric charge according to the luminance distribution of the object scene in each focus detection area, and repeatedly outputs an electric signal corresponding to the accumulated electric charge. Each image sensor output of the image sensor group 3 is A / D converted by the A / D converter 4 and then sent to the calculator 5.
[0020]
The calculation unit 5 includes a peak detection unit 6, a preliminary accumulation necessity determination unit 7, a focus detection calculation unit 8, a focus detection area automatic selection unit 9, and an auxiliary light necessity determination unit 10. The peak detector 6 calculates a peak value for each of the image sensors 31 to 3n based on the output of each image sensor A / D converted by the A / D converter 4. The preliminary accumulation necessity determination unit 7 determines whether or not an accumulation operation (hereinafter referred to as preliminary accumulation) for the purpose of prohibiting the focus detection calculation and performing AGC is performed. Note that the storage operation for the purpose of performing the focus detection calculation with respect to the preliminary storage is referred to as main storage. The focus detection calculation unit 8 performs focus detection calculation based on the image sensor output A / D by the A / D conversion unit 4 and calculates the defocus amount of each focus detection region.
[0021]
The focus detection area automatic selection unit 9 automatically selects a focus detection area to be a lens driving target based on the calculation result by the focus detection calculation unit 8. The auxiliary light necessity determination unit 10 determines whether the auxiliary light is necessary based on the output of the image sensor and the control data. The counter 11 counts the number of determinations by the preliminary accumulation necessity determination unit 7, that is, the number of AGC operations. The image sensor drive control unit 12 drives and controls the image sensor group 3 based on the output of the calculation unit 5. The lens drive control unit 13 drives the motor 14 based on the defocus amount calculated by the calculation unit 5 to drive the objective lens 1 in focus. The auxiliary light drive control unit 15 drives the auxiliary light projecting unit 16 based on the determination result of the auxiliary light necessity determination unit 10 to emit auxiliary light.
[0022]
2 to 3 are flowcharts illustrating the focus detection operation according to the embodiment. The operation of the embodiment will be described with reference to these flowcharts. In this embodiment, an example in which AGC is performed based on the peak value of the image sensor output is shown. When a release button (not shown) of the camera is half-pressed, this focus detection operation is started.
[0023]
In step 1, the calculation unit 5 gives the initial value T = T0 of the accumulation time of each of the image sensors 31 to 3n to the image sensor drive control unit 12. T0 may be an appropriate predetermined value, or may be the shortest accumulation time so that the image sensor output is not saturated when the subject is bright. In addition, an optimal accumulation time may be calculated for each image sensor based on the photometry element output for exposure control. Next, in step 2, the arithmetic unit 5 sets the preliminary accumulation necessity flag of the preliminary accumulation necessity judgment unit 7 to 0, and sets the AGC count value of the counter 11 to 1.
[0024]
Here, when the preliminary accumulation necessity flag is 0, the next accumulation operation is the preliminary accumulation, and when it is 1, the next accumulation operation is the main accumulation. The AGC count value is obtained by counting the number of preliminary accumulation operations of the image sensors 31 to 3n from the start of the focus detection operation. It should be noted that “AGC is applied” means that the image sensor output has an appropriate magnitude as described above by AGC.
[0025]
As described above, when only one of the plurality of focus detection areas has an image sensor output of an appropriate size and it is difficult to apply AGC, the focus detection operation cannot be continued forever and the focus detection operation as a whole is slow. If the AGC count value reaches a predetermined number, the focus detection calculation is forcibly performed even if the output is not an appropriate size due to AGC in all the image sensors 31 to 3n. Transition.
[0026]
In step 3, the image sensor drive controller 12 performs the charge accumulation operation of the image sensors 31 to 3n based on the given accumulation time T. In subsequent step 4, the preliminary accumulation necessity determination unit 7 determines whether or not the preliminary accumulation necessity flag as a result of the previous accumulation operation is 0. If it is 0, the process proceeds to step 5. Since the preliminary accumulation necessity flag is set to 0 in step 2 for the first time, the process proceeds to step 5 as a matter of course. In step 5, A / D conversion is performed by the A / D conversion unit 4 in order from the image sensors 31 to 3 n that have completed the accumulation earlier, and the peak value is detected by the peak detection unit 6 after being input to the calculation unit 5.
[0027]
Next, in step 6, the preliminary accumulation necessity determination unit 7 determines whether the next accumulation operation is the preliminary accumulation or the main accumulation. For example, for all the image sensors 31 to 3n, when the output of the next accumulation operation by AGC is expected to be an appropriate level, or even if the accumulation operation is repeated further, it is not expected to become an appropriate size. In this case, or when the AGC count value of the counter 11 reaches a predetermined number of times set in advance, the next accumulation operation is set as the main accumulation.
[0028]
Whether or not the image sensor output has an appropriate magnitude by AGC, that is, whether or not AGC is applied is determined by the following equation.
[Formula 6]
| Vpeak−Vc | <B
Here, Vpeak is a peak value for each of the image sensors 31 to 3n, and Vc is a target peak value (AGC target value) for each of the image sensors 31 to 3n described above, that is, the “appropriate magnitude” described above. B is a determination reference value set in advance for determining whether or not the peak value Vpeak of each image sensor output is in the vicinity of the AGC target value Vc. Note that the determination reference value B may also be set for each of the image sensors 31 to 3n.
[0029]
If the image sensor output after the current accumulation operation has an appropriate magnitude and AGC is applied, the image sensor output will have an appropriate magnitude if the same accumulation time is used for the next accumulation operation. AGC should take. In addition, in the normal output range of the image sensor, the accumulation time and the output are proportional to each other. Therefore, even if the image sensor output after the current accumulation operation is lower than an appropriate size and AGC is not applied, the accumulation time is reduced. By extending, it can be expected that the output of the image sensor after the next accumulation operation becomes an appropriate magnitude and AGC is applied.
[0030]
FIG. 9 shows the relationship between the accumulation time and the peak value of the image sensor output under a certain uniform illuminance. The output a is the offset and noise level of the circuit, and is output even when the accumulation time is short and there is almost no accumulated charge. As the accumulation time increases, the output also increases. When the output exceeds b, the increase rate decreases rapidly and eventually saturates at the output c. If the image sensor output after the current accumulation operation is within the range of a to b shown in FIG. 9, the image sensor output after the next accumulation operation is controlled by controlling the charge accumulation with the accumulation time obtained by Equation 4. It is expected that AGC will take an appropriate size.
[0031]
Even if the subject is dark and the accumulation time in the current accumulation operation is the longest time, even if the output of the image sensor is lower than the appropriate size, the output of the image sensor is appropriate. It is determined that AGC is applied at the size. Even when the image sensor output is expected to be lower than an appropriate value even if the accumulation time after the next accumulation operation is the longest time, the image sensor will output properly in the next accumulation operation. It is determined that AGC is applied due to the size. Similarly, if the subject is too bright and the output becomes equal to or greater than the predetermined value even if the subject is controlled with the shortest accumulation time, it is similarly determined that the AGC is applied with an appropriate magnitude of the image sensor output.
[0032]
Here, the longest accumulation time is a value set arbitrarily. This longest accumulation time affects the responsiveness of the focus detection operation. On the other hand, the shortest accumulation time is a value set by the restrictions on the circuits of the image sensors 31 to 3n.
[0033]
By the way, since the luminance state of the subject is not always constant, the preliminary accumulation necessity determination flag is set to 1, that is, after determining that the next accumulation operation is the main accumulation for the purpose of focus detection calculation, It is possible that the output is lower than the appropriate magnitude and AGC is not applied. However, also in this case, it is not necessary to reset the preliminary accumulation necessity determination flag to 0 and return to the preliminary accumulation. If only one of the multiple focus detection areas has a sharp change in brightness, and the image sensor output corresponding to that area is not of an appropriate size and AGC is difficult to apply, focus detection is possible in other areas. In spite of this, it may not be possible to shift to the focus detection calculation indefinitely, and the focus detection operation may be delayed as a whole. .
[0034]
If it is determined in step 6 that the next storage operation is preliminary storage, the process proceeds to step 7, the AGC count value of the counter 11 is incremented, and then the process proceeds to step 9. In step 9, the calculation unit 5 calculates the next accumulation time based on the accumulation time and output of each of the image sensors 31 to 3n this time. On the other hand, if it is determined in step 6 that the next accumulation operation is the main accumulation, the process proceeds to step 8, the preliminary accumulation necessity flag is set to 1, and the process proceeds to step 9. The subsequent steps 10 to 12 will be described later.
[0035]
If the preliminary accumulation necessity flag is set to 1 in Step 4 after the accumulation operation in Step 3, that is, if it is determined that the next accumulation operation is the main accumulation for the purpose of focus detection calculation, Step 13 Proceed to In the initial stage, since the automatic selection area is undecided, it is necessary to read out the accumulated charges from all the image sensors 31 to 3n and perform focus detection calculation. If the automatic selection area is undecided in step 13, the process proceeds to step 14, where the image sensor drive control unit 12 reads out accumulated charges, that is, pixel data in order from the image sensors 31 to 3 n that have completed accumulation earlier.
[0036]
In step 15, the focus detection calculation unit 8 performs focus detection calculation. At the previous charge accumulation, the output of each of the image sensors 31 to 3n is determined to have an appropriate magnitude and AGC is applied, or at the next (here this time) charge accumulation to an appropriate magnitude. If it is predicted that AGC will be applied, the outputs of all the image sensors 31 to 3n should have an appropriate magnitude and AGC will be applied during the current charge accumulation. Therefore, in this case, the focus detection calculation is performed based on the outputs of all the image sensors 31 to 3n, and the focus adjustment state of the objective lens 1 can be obtained in all the focus detection regions.
[0037]
On the other hand, when the AGC count value of the counter 11 reaches a preset number of times, that is, when the number of AGC operations reaches the set number and is forcibly switched from the preliminary accumulation operation to the main accumulation operation, the image sensor array 31. In ˜3n, there are a mixture of output having an appropriate magnitude and AGC applied, and other output. In this case, there are the following methods for selecting the image sensors 31 to 3n that execute the focus detection calculation. The first selection method is an image sensor in which the output is determined to have an appropriate magnitude during the previous charge accumulation or AGC is applied, or the output becomes an appropriate magnitude during the next (current) charge accumulation and the AGC. This is a method of selecting an image sensor predicted to be subject to focus detection calculation. According to this method, the focus detection calculation is executed only in the focus detection region corresponding to the image sensor whose image sensor output is appropriate and AGC is applied, and the focus adjustment of the obtained objective lens 1 is performed. All states are reliable. The automatic selection area can be determined based on the highly reliable focus detection calculation result.
[0038]
The second selection method selects an image sensor that is a focus detection calculation target by a method different from the first selection method. In the second selection method, it is determined whether or not the following expression is satisfied with respect to the outputs of all the image sensors 31 to 3n. This output is an output obtained by the next accumulation after the AGC count value of the counter 11 reaches the set number of times.
[Expression 7]
(Α · Vpeak + β · C) ≧ K1
and,
(Number of OV elements) ≤ K2
Here, Vpeak is a peak value for each of the image sensors 31 to 3n, and C is a contrast value for each of the image sensors 31 to 3n. The contrast value C is obtained, for example, from the maximum value of output differences between adjacent photoelectric conversion elements, the sum of absolute values of output differences, or the like. The number of OV elements is the number of overflowing elements among the plurality of photoelectric conversion elements included in each of the image sensors 31 to 3n. α, β, K1, and K2 are predetermined values. That is, in the second selection method, for each of the image sensors 31 to 3n, the output peak value Vpeak and the contrast value C are weighted by the predetermined values α and β and added, and the value is equal to or larger than the predetermined value K1 set in advance. In addition, it is determined whether or not the number of overflow elements is equal to or less than a predetermined value K2, and focus detection calculation is performed on the output of the image sensor that satisfies this selection condition, and in a focus detection region corresponding to the image sensor that satisfies the selection condition Get the focus adjustment state of the objective lens.
[0039]
In the first selection method in which only the image sensor having an appropriate size and the AGC is applied to the focus detection calculation target, the maximum value (peak value) Vpeak of each image sensor output is obtained by the above-described Expression 6. Judgment is made based only on this. On the other hand, in the second selection method, the determination is made based on the maximum value Vpeak and the contrast value C of each image sensor output. In other words, the determination is performed in consideration of not only the maximum value Vpeak of each image sensor output but also the contrast value C. Therefore, even if the maximum value is low, if the contrast is high, the image sensor becomes a focus detection calculation target. The focus adjustment state of the objective lens 1 is obtained in the focus detection region corresponding to, and the calculation result is sufficiently reliable. That is, according to the second selection method, there is a high probability that the focus adjustment state of the objective lens 1 is obtained even in a focus detection region that is not a focus detection calculation target in the first selection method. As a result, there is a high probability that an area that captures the main subject intended by the photographer can be determined as an automatic selection area from among many focus detection areas. In addition, according to the second selection method, the determination is performed in consideration of the number of photoelectric conversion elements in which overflow has occurred, so that a focus detection area that captures a high-luminance subject such as the sun is automatically set. It can prevent becoming a selection area. In the second selection method, the image sensor may be selected based on at least one of the maximum output Vpeak of the image sensor, the contrast value C, and the number of photoelectric conversion elements in which overflow has occurred. .
[0040]
In step 16, it is confirmed whether or not the charge reading and focus detection calculation of all the image sensors 31 to 3 n are completed. If not completed, the process returns to step 14 to repeat the charge reading and focus detection calculation. When the charge readout and focus detection calculation for all the image sensors 31 to 3n are completed, the process proceeds to step 17.
[0041]
In step 17, the focus detection area automatic selection unit 9 selects one of the focus detection calculation results of all the image sensors 31 to 3n, and sets the focus detection area corresponding to the calculation result as the automatic selection area. . When this focus detection area is automatically selected, for example, the area where the calculation result closest to the camera may be selected, or the area where the calculation result closest to the current focus adjustment state is selected. May be. Next, in step 18, the lens drive control unit 13 drives the motor 14 based on the focus detection calculation result of the automatic selection region input from the calculation unit 5 to drive the objective lens 1.
[0042]
When the preliminary accumulation necessity flag is set to 1 and the automatic selection area is determined in this way, the process proceeds from step 13 to step 19 after the next accumulation operation. In step 19, the arithmetic unit 5 first requests reading of the image sensor output in the automatic selection area. The image sensor drive control unit 12 reads out pixel data of the image sensor that has been requested to be read out. In subsequent step 20, the focus detection calculation unit 8 performs focus detection calculation based on the read pixel data.
[0043]
In step 21, the focus detection area automatic selection unit 9 determines whether or not the automatic selection area captures the same subject as in the previous focus detection operation. Based on the results of previous focus detection operations, it is possible to determine whether the main subject is stationary with respect to the camera, how fast it is moving, and how fast it is driving the lens. . Therefore, if the defocus amount obtained during the current focus detection operation is close to the defocus amount predicted from the result of the focus detection operation up to the previous time, the auto-selection area will be the same subject as during the previous focus detection operation. Judge that it is captured.
[0044]
However, if the defocus amount predicted from the previous focus detection result and the current calculation result are significantly different, it is considered that the subject captured until the previous time has been removed from the automatic selection region. In this case, the focus detection area automatic selection unit 9 requests the image sensor drive control unit 12 to read out charges from the image sensors corresponding to the other focus detection areas, and returns to step 19.
[0045]
The image sensor drive control unit 12 reads an image sensor output corresponding to the requested focus detection area. When the main subject is removed from the previous automatic selection area, the charge detection of the corresponding image sensor and focus detection calculation are performed for all remaining focus detection areas, and then predicted from the previous focus detection results. The focus detection area indicating the defocus amount closest to the defocus amount to be set may be reset as a new automatic selection area. Alternatively, charge reading and focus detection calculation are performed in a predetermined order with respect to the remaining focus detection areas, and subsequent reading is performed when a defocus amount close to the defocus amount predicted from the focus detection results up to the previous time is obtained. The focus detection calculation may be stopped and the focus detection area may be reset to the automatic selection area.
[0046]
If the automatic selection area is continued or reselected in step 21 and there is no other image sensor read request, the process proceeds to step 22. In step 22, the lens is driven based on the focus detection calculation result of the automatic selection area. In subsequent step 23, the peak value of the non-reading image sensor is detected in preparation for the next AGC, and the process returns to step 9. In step 9, the calculation unit 5 calculates the next accumulation time for each of the image sensors 31 to 3n based on the peak value and the accumulation time during the previous accumulation operation.
[0047]
By the way, when it is determined that the subject has low brightness and the auxiliary light for focus detection is turned on before the automatic selection area is determined and immediately before the AGC count value reaches the predetermined value, the image sensor is turned on before the lighting. Even in an image sensor having an appropriate output and AGC applied, the output is naturally lower than the appropriate size after the focus detection auxiliary light is turned on, and AGC is not applied. When the AGC count value reaches the predetermined number in this state, the focus detection calculation is performed with the output being lower than an appropriate level in most of the image sensors 31 to 3n and no AGC being applied. Also, the possibility of obtaining a reliable focus detection result is reduced.
[0048]
In order to avoid such inconvenience, in step 10, the auxiliary light necessity determination unit 10 predicts the luminance of the subject based on the accumulation time and output of the image sensors 31 to 3n, and based on a predetermined criterion luminance. If it is dark, it is determined that the auxiliary light needs to be turned on. In response to this determination, when the auxiliary light is switched from the off state to the on state, the process proceeds from step 11 to step 12, and the counter 11 receives the reset signal from the auxiliary light necessity determination unit 10 and resets the AGC count value to 1. To do. Then, during the next accumulation operation, the auxiliary light driving control unit 15 drives the auxiliary light projecting unit 16 to project auxiliary light.
[0049]
In the above-described embodiment, the case where AGC is applied according to the peak values of the image sensors 31 to 3n has been described. However, when the AGC is applied based on the average value, the peak detection unit 6 is replaced with the average value detection unit 6.
[0050]
According to the above-described embodiment, it is determined whether the output peak value of each of the image sensors 31 to 3n is appropriate and AGC is applied, or the output peak of each of the image sensors 31 to 3n. Based on the value, when it is predicted that the output of each of the next image sensors 31 to 3n will have an appropriate magnitude and AGC will be applied, the objective is based on the output of each of the image sensors 31 to 3n after the next charge accumulation. A calculation of the focus adjustment state of the lens 1 is executed, and a focus detection region for performing focus adjustment of the objective lens 1, that is, a focus detection calculation result is selected from a plurality of focus detection regions based on the focus detection calculation result. I made it. In other words, based on the current image sensor output, it is predicted whether or not AGC will be applied when the output becomes an appropriate magnitude at the next charge accumulation, and for the image sensor that is expected to be subjected to AGC at the next charge accumulation. Thus, even if the output of the image sensor at the time of current charge accumulation is lower than an appropriate size and AGC is not applied, the focus detection calculation is executed based on the output after the next charge accumulation of the image sensor.
[0051]
Therefore, according to the first embodiment described above, the focus detection calculation is executed based on the output after the next charge accumulation after all the image sensor outputs become appropriate and AGC is applied. It is possible to shift to the focus detection calculation earlier than the focus detection method by one charge accumulation operation. That is, the transition from the charge accumulation operation of the plurality of image sensors 31 to 3n to the focus detection calculation operation based on the image sensor output is performed quickly and smoothly. As a result, based on the focus detection calculation result from the plurality of focus detection regions. Thus, it is possible to automatically select a region where the lens should be driven in a short time. Therefore, when the image sensor output of any focus detection area does not have an appropriate size and AGC is not applied as in the prior art, the focus detection calculation operation based on the image sensor output cannot be performed, and the focus detection area is automatically detected. The problem that selection takes time can be solved.
[0052]
Of course, all image sensor outputs are once stored in the memory, and when it is determined that all of these outputs are of an appropriate size and AGC is applied, the focus detection calculation is performed quickly. Yes, but a large amount of memory is required to store all image sensor outputs. According to the embodiment described above, such a large-capacity memory is not necessary.
[0053]
The correspondence between the constituent elements of the claims and the constituent elements of the embodiment is as follows. That is, the charge storage type photoelectric conversion means is constituted by, for example, image sensors 31 to 3n. In addition, the determination unit, the prediction unit, the calculation unit, and the region selection unit are configured by the calculation unit 5, for example. Further, the counting means is constituted by a counter 11. In addition, as long as the characteristic function of this invention is not impaired, each component is not limited to the said structure.
[0054]
【The invention's effect】
As described above, according to the present invention, the transition from the charge accumulation operation of the plurality of destructive readout photoelectric conversion means to the focus detection calculation operation based on the output of the photoelectric conversion means is performed quickly and smoothly. Based on the focus detection calculation result, it is possible to automatically select a region where the lens should be driven from the focus detection region in a short time. Therefore, unlike the conventional case, when the output of the photoelectric conversion means in any focus detection region does not have an appropriate size and AGC is not applied, it is not possible to shift to the focus detection calculation based on the output of the photoelectric conversion means. The problem that it takes time to automatically select a region can be solved.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a camera including a focus detection apparatus according to an embodiment.
FIG. 2 is a flowchart illustrating a focus detection operation according to an embodiment.
FIG. 3 is a flowchart illustrating the focus detection operation of the embodiment following FIG. 2;
FIG. 4 is a diagram illustrating an arrangement of a plurality of focus detection areas on a photographing screen.
FIG. 5 is a diagram showing a phase difference detection type focus detection optical system and an image sensor array;
FIG. 6 is a diagram for explaining correlation calculation of a phase difference detection type focus detection apparatus;
FIG. 7 is a diagram for explaining correlation calculation of a phase difference detection type focus detection apparatus;
FIG. 8 is a diagram for explaining AGC;
FIG. 9 is a diagram illustrating a relationship between an accumulation time of an image sensor and an output.
[Explanation of symbols]
1 Objective lens
2 Focus detection optical system
3 Image sensors
4 A / D converter
5 Calculation unit
6 Peak detector
7 Preliminary accumulation necessity judgment section
8 Focus detection calculator
9 Focus detection area automatic selection part
10 Auxiliary light necessity determination unit
11 Counter
12 Image sensor drive controller
13 Lens drive controller
14 Motor
15 Auxiliary light drive controller
16 Auxiliary light projector
31-3n image sensor

Claims (7)

A plurality of destructive readout photoelectric conversion means provided corresponding to each of a plurality of focus detection areas of the object scene, and repeatedly performing charge accumulation by accumulation control according to the luminance of the plurality of focus detection areas;
Arithmetic means for calculating a focus adjustment state of the objective lens with respect to the plurality of focus detection areas based on outputs of the plurality of destructive readout photoelectric conversion means;
Determination means for determining whether or not the outputs of the plurality of photoelectric conversion means are predetermined values suitable for calculation by the calculation means;
By determining the next accumulation time for obtaining the target output based on the outputs of the plurality of photoelectric conversion means and the accumulation time when the output is obtained, the plurality of photoelectric conversion means by the next charge accumulation Predicting means for predicting whether or not the output will be a predetermined value suitable for calculation by the calculating means;
Even if it is determined by the determination means that the outputs of the plurality of photoelectric conversion means are not predetermined values suitable for the calculation by the calculation means, the plurality of photoelectric conversion means by the next charge accumulation by the prediction means Is predicted to be a predetermined value suitable for calculation by the calculation means, the focus adjustment state of the objective lens based on the outputs of the plurality of photoelectric conversion means by the next charge accumulation by the calculation means And a control means for executing the above calculation. The focus detection apparatus according to claim 1,
Each of the plurality of photoelectric conversion means is composed of a plurality of photoelectric conversion elements,
The determination means, may become a target value near the maximum output preset of the outputs of the plurality of photoelectric conversion elements included in each of the plurality of photoelectric conversion means, an output of said plurality of photoelectric conversion means It is determined that the value is a predetermined value suitable for calculation by the calculation means. The focus detection apparatus according to claim 1.
Each of the plurality of photoelectric conversion means is composed of a plurality of photoelectric conversion elements,
When the average output of the plurality of photoelectric conversion elements included in each of the plurality of photoelectric conversion units is in the vicinity of a preset target value, the determination unit calculates the output of the plurality of photoelectric conversion units by the calculation unit. It is determined that the predetermined value is suitable for the focus detection device. In the focus detection apparatus according to any one of claims 1 to 3,
A counting unit that counts the number of times the charge accumulation is repeated without shifting to the calculation of the focus adjustment state based on the determination result of the determination unit and the prediction result of the prediction unit;
When the number of counts of the counting unit reaches a predetermined number, the control unit outputs a photoelectric output that is determined to be a predetermined value suitable for calculation by the calculation unit among the plurality of photoelectric conversion units. A focus detection apparatus , wherein the calculation means calculates the focus adjustment state of the objective lens based on the next output from the charge accumulation of the conversion means . In the focus detection apparatus according to any one of claims 1 to 4,
A counting unit that counts the number of times the charge accumulation is repeated without shifting to the calculation of the focus adjustment state based on the determination result of the determination unit and the prediction result of the prediction unit;
The control means, when the number of counts of the counting means reaches a predetermined number, at least one of the maximum output of the plurality of photoelectric conversion means, the number of photoelectric conversion elements in which contrast and overflow have occurred. A focus detection apparatus that causes the calculation means to calculate the focus adjustment state of the objective lens based on the next output by the charge accumulation of the photoelectric conversion means selected based on In the focus detection apparatus according to claim 4 or 5 ,
A focus detection apparatus that resets the number of counts of the counting means to an initial value when illumination of the object field is performed by the illumination means during focus detection. In the focus detection apparatus according to any one of claims 1 to 6 ,
A focus detection apparatus comprising: area selection means for selecting a focus detection area for performing focus adjustment of the objective lens from among the plurality of focus detection areas based on a calculation result by the calculation means .

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