JP2663493B2 - Focus detection device - Google Patents

Description

The present invention relates to a focus detection device using a line sensor including a plurality of photoelectric conversion elements such as a CCD.

2. Description of the Related Art A focus detection device using a line sensor of a photoelectric conversion element including a plurality of photoelectric conversion elements such as a CCD is currently realized by an automatic focus adjustment device of a single-lens reflex camera.

FIG. 20 shows an example of such a conventional focus detection device.

That is, the focus detection device is a line sensor including an optical unit 110 disposed after the objective lens 100 and a plurality of photoelectric conversion elements that receive subject light processed by the optical unit 110.
120, an accumulation time control means 130 for controlling the line sensor 120, an A / D converter 140 for processing the output of the line sensor 120, a memory 150 for storing the output of the A / D converter 140, and a storage for the memory 150. And an arithmetic means 160 for performing an arithmetic operation based on this.

Then, the optical image from the objective lens 100 is projected onto the line sensor 120 by the optical means 110, and the focus adjustment state of the objective lens 100 is detected based on the state of the projected optical image.

In the operation of this focus detection device, the line sensor 120 performs accumulation for a certain time under the control of the accumulation time control means 130.

The A / D converter 140 converts the output of the line sensor 120 into a predetermined N-bit digital value.

The N-bit digital value is stored in the memory 150.

The calculation means 160 calculates the focus adjustment state of the objective lens 100 based on the N-bit digital value stored in the memory 150.

It is performed in such a manner.

Here, the accumulation time of the line sensor 120 is set by the accumulation time control means 130 to a short time when the luminance of the subject is high, and to a long time when the luminance of the subject is low, and the output of the line sensor 120 is set to A / D. The resolution is controlled so as not to overflow the N-bit dynamic range, which is the resolution capability of the converter 140, or to fall within an appropriate level without becoming a very low level.

In the prior art, the A / D converter 140 generally uses an 8-bit A / D converter, and the memory 150 generally uses the same 8-bit.

[Problem to be Solved by the Invention] However, in the conventional technique based on the above-mentioned 8 bits, the limit comes earlier if only the accumulation time corresponds to the luminance of the subject, and there is a limit in performing more advanced shooting.

For example, the brightness of a subject in a photograph is higher than Ev20 for a high object and about Ev1 for a low object.
If it took 400ms, the storage time for an Ev20 subject would be 4
00 ms ÷ 2 ¹⁹ ≒ 760 ns, but control of such a short accumulation is very difficult in terms of circuitry.

Therefore, it is conceivable to insert a variable gain amplifier between the line sensor 120 and the A / D converter 140 in FIG. 1 to reduce the output of the line sensor to cope with the problem. However, there is a problem in that a camera which is limited to the above is disadvantageous in terms of implementation and is not realistic.

The present invention has been made in view of the above-described conventional problems, and provides a focus detection device that can perform focus detection even on a high-luminance subject without increasing the circuit scale. It is an object.

Means for Solving the Problems The gist of the present invention to achieve the above object is to project a light image of a subject by a line sensor including a plurality of photoelectric conversion elements and an objective lens onto the line sensor. An A / D converter for converting a plurality of outputs of the line sensor into an M-bit digital value; and an N-bit digital value smaller than M bits from the M-bit digital value output by the A / D converter. A memory for storing the N-bit digital value extracted by the data processing means, and a calculation for calculating the focus state of the objective lens based on the plurality of N-bit digital values in the memory Means, the data processing means,
A focus detection apparatus characterized in that a range for extracting an N-bit digital value from an M-bit digital value is made variable.

[Operation] The major flow of the focus adjustment operation is as follows.

The optical image of the object by the objective lens is projected onto the line sensor by the optical means, and the line sensor outputs a plurality of outputs from the plurality of photoelectric conversion elements to the A / D converter while controlling the accumulation time by the accumulation time control means, The A / D converter converts this output into an M-bit digital value.

The output of the A / D converter is processed by data processing means into an N-bit digital signal, a plurality of digital values of this signal are stored in a memory, and a calculating means operates the objective lens based on the plurality of digital values in the memory. The focus adjustment state is detected.

In the above flow, the data processing means operates as follows.

If the accumulation time of the line sensor is shorter than the predetermined accumulation time due to the high luminance of the subject, the A / D converter processes information up to a digit exceeding N bits.

Therefore, the data processing means extracts N bits from the M-bit digital value output from the A / D converter, and the memory stores the N-bit digital value.

As described above, the focus detection device in which the N-bit digital value and the calculating means perform the focus detection calculation based on the output of the line sensor, processes M bits larger than N bits to convert the analog output of the line sensor into a digital value. A / D
By using the converter, the dynamic range is 2 ^(MN) times as large as that when using the N-bit A / D converter.

Therefore, if the shortest accumulation time is the same, N bits
It is possible to raise the subject brightness (MN) steps that can detect focus compared to when the A / D converter is used, and since the focus detection calculation uses N-bit data, the same memory area and calculation scale as the conventional one can be used. I'm done.

Hereinafter, various embodiments of the present invention will be described with reference to the drawings.

1 to 15 are views for explaining a first embodiment of the present invention.

In the first embodiment, the calculation means performs focus detection calculation with an 8-bit digital value based on the output of the line sensor, and a 10-bit A / D converter is used.

That is, as shown in FIG. 1, the focus detection device includes an optical unit 110 disposed after the objective lens 100, and an optical unit 110.
A line sensor 120 including a plurality of photoelectric conversion elements that receive the subject light processed by 110; an accumulation time control unit 130 that controls the line sensor 120; and an A / A that converts the output of the line sensor 120 into a 10-bit digital value. D converter 1
40, a data processing means 170 for processing the 10-bit output of the A / D converter 140, and 8 data processed by the data processing means 170.
Memory 150 for storing a plurality of bit-valued digital values
Operation means 160 for performing an operation based on the storage of the memory 150
It is composed of

The accumulation time control means 130 is a line sensor 1 converted to a digital value by the 10-bit A / D converter 140.
The value indicating the maximum value among the outputs of the photoelectric conversion elements is
The accumulation time of the line sensor 120 is controlled so that the value becomes 1/8 with respect to the 10-bit dynamic range, that is, it becomes 128 with respect to 1023 in a decimal number.

The data processing means 170 takes in a 10-bit digital value, detects the brightness of the subject, and
It has a function of shifting the digit of the bit digital value in the lower direction and extracting the lower 8 bits of the 10-bit digital value.

Specifically, when it is detected that the brightness of the subject is not too high, the shift to the shift 0 mode as shown in FIGS. 3 to 5 is performed, and the output of the line sensor 120 becomes 1 as shown in FIG.
When it is determined that the dynamic range of 0 bits falls within the lower 8 bits, that is, converted to a decimal number and falls within 255 with respect to 1023, no digit shift is performed in the lower direction, as shown in FIG. The lower 8 bits are extracted and stored in the memory 150 as an 8-bit output as shown in FIG.

When it is detected that the subject brightness is high, FIGS.
The shift 1 mode shown in FIG.
Even if the accumulation time is a predetermined minimum time within the controllable time of the accumulation time control means 130, as shown in FIG. If it does not fit in and goes to the next higher bit, that is, if it is converted to a decimal number and it does not fit in 255 for 1023, but it is determined to fit in 511, the 10-bit data is transferred once in the lower direction By extracting the lower 8 bits by shifting the digit, that is, by extracting the 8 bits of the portion shown in FIG. 6, the memory 150 is output as an 8-bit output as shown in FIG.
Is to be stored.

Further, when it is detected that the subject brightness is high, FIGS.
The shift 2 mode shown in FIG.
As shown in FIG. 10, the output of the line sensor when the accumulation time becomes the shortest time does not fit in the lower 8 bits of the 10-bit dynamic range but extends to the upper 2 bits which are two higher. In other words, convert to decimal
If it does not fit in 1023 but does not fit in 511, but it is determined to fit in 1023, it shifts the 10-bit data two times in the lower direction and extracts the lower 8 bits. The bits are extracted and stored in the memory 150 as an 8-bit output as shown in FIG.

As shown in FIG. 2, when the shift mode is switched, the ranges of the shift 0 mode and the shift 1 mode, and the shift 1 mode and the shift 2 mode are set so as to overlap around 255 bits and 512 bits.

This is to prevent the shift mode from frequently switching when the processing value fluctuates near the boundary, and to provide hysteresis so as to perform stable data processing. The example in which the focus detection device is configured by hardware has been described above. Next, an example in which the focus detection device is configured by a microcomputer will be described.

Next, the accumulation time control means 130, the A / D converter 140, the data processing means 170, and the memory of the focus detection device shown in FIG.
The data processing means 170 operates as shown in the flowcharts of FIGS. 12 to 15. (The operation of the components other than the data processing means 170 is already performed by a known method.) In these flowcharts, the FLG (the flag setting unit 170e in FIG. 1) performs a number of downward shifts on the 10-bit digital value. FLG =
When 0, no lower shift is performed (shift 0 mode), and F
When LG = 1, the lower shift is performed once (shift 1 mode), and when FLG = 2, the lower shift is performed twice (shift 2 mode).

DATA (10) (data storage register 170a in FIG. 1) is 10
The output of the line sensor 120, which is converted into a 10-bit digital value by the A / D converter 140,
The maximum value of ATA (10) is MAX (10) (maximum value memory 170d in FIG. 1).

Ts is the accumulation time of the line sensor 120 this time, and this T
The storage time control means 130 of FIG. 1 controls the storage time of the line sensor 120 based on s.

 PEAK is a predetermined value described later.

The operation is started from step 1 in FIG. 12 by half-pressing a release switch of a camera not shown in FIG. Initially, initial setting is performed, FLG = 0, PEAK = 128, Ts = T
Int is set (steps 2 and 3). Tint is the first accumulation time, and may be set based on the output of the luminance monitor of the subject provided in the line sensor 120 in FIG. 2, or may be an appropriate time.

Subsequently, MAX (10) is set to 0 (step 4), and accumulation of the line sensor 120 is started by the accumulation time control means 130 (step 5). When the accumulation is completed, the output of each pixel is output in time series from the line sensor 120.

The output of each pixel is first converted to a 10-bit digital value DATA (10) by the 10-bit A / D converter 140 (step
6, 7), and then the comparison of the DATA (10) with the MAX (10) (comparing process by the comparing unit 170b in FIG. 1) is performed (step 8), and the DATA (10) is compared with the MAX (10). ) Is large, DATA (10) is stored as MAX (10) (stored in the maximum value memory 170d in FIG. 1) (step 9).

Next, it is determined whether or not FLG is 0 (step 10),
If it is determined to be 0, the process proceeds to step 14, where the lower 8 bits of DATA (10) are extracted and stored in the memory 150. If it is determined in step 10 that FLG is not 0, the process proceeds to step 11 where data (10) is shifted once in the lower direction (shifting once in the lower direction halves the data by half). To do that).

Next, it is determined whether or not FLG is 1 (step 1).
2) If it is determined that FLG = 1, the process proceeds to step 14, and in step 11, the data DATA (1
The lower 8 bits of (0) are extracted and stored in the memory 150.

If it is determined in step 12 that FLG is not 1, FLG =
2 and go to step 13. Step 13
In step (1), the data (10) is shifted one more time in the lower direction, and then the process proceeds to step 14, where the lower 8 bits of the data (10) are extracted and stored in the memory 150.

DATA (10) that is a 10-bit digital value in step 14
Is changed to 8-bit data and stored in the memory 150. When the process is completed, the process proceeds to step 15 where DATA (10) processed in step 14 is output at the end of the pixel output of the line sensor 120 generated in time series. It is determined whether or not the data is data.

If it is determined that DATA (10) is not the last data, the process returns to step 6, where A / D conversion, data lower-direction shift, and memory storage are performed on the next pixel output in the same manner as described above. Such an operation is performed. DATA in step 15
If it is determined that (10) is the last data, it means that the data of all the pixels of the line sensor 120 has been stored in the memory 150, and the operation such as A / D conversion is terminated.
Proceed to.

At this point, the maximum value among the plurality of pixels of the line sensor 120 is stored as MAX (10), and in the step 22 described later, the next accumulation time Ts of the line sensor 120 is determined based on this MAX (10). Is calculated. Subsequently, looking at the value of FLG, when FLG = 0, it goes to the shift 0 mode starting from step 30 shown in FIG. 13, and when FLG = 1, it goes to the shift 1 mode starting from step 42 shown in FIG. In other cases, branching is made to the shift 2 mode starting from step 49 shown in FIG.

The subsequent operation will be described first in the case of the shift 0 mode shown in FIG.

If FLG = 0 is determined in step 16 of FIG. 12, the process proceeds to step 30 of FIG. 13, and in step 31, MAX (1) is determined in order to determine whether or not the MAX (10) is within the lower 8 bits.
If it is determined whether MAX (10) is smaller than 256 by checking whether (0) is smaller than 256 or not, the process proceeds to step 32 and then MAX (10)
Is greater than or equal to 100.

If it is determined in step 32 that MAX (10) is greater than 100, the focus detection calculation based on the output of the line sensor 120 stored in the memory 150 is performed by the calculation means 160 (step 3).
4) If it is determined to be 100 or less, focus detection is not performed. The reason why the focus detection calculation is not performed when MAX (10) is 100 or less is that accurate focus detection cannot be performed if the output of the line sensor 120 is too small.

If it is determined in step 32 that MAX (10) is 100 or less, the process proceeds to step 33, where the current accumulation time Ts is set to the longest accumulation time Tm.
Determines whether it is equal to ax. Here, Ts = Tmax means that even if the accumulation time is the longest, the output of the line sensor 120 is small and focus detection calculation cannot be performed. Therefore, if Ts = Tmax is determined, a detection impossible warning is issued ( In step 39), the process jumps to step 21 in FIG. 12 to perform accumulation again (step 41).

If it is determined in step 33 that Ts is not equal to Tmax, there is a possibility that the output of the line sensor 120 will be obtained so that focus detection can be performed by performing the next accumulation using Ts calculated in step 22 in FIG. Therefore, the process jumps to step 21 in FIG. 12 to perform the next accumulation without issuing an undetectable warning (step 41).

If it is determined in step 31 that MAX (10) is 256 or more, it means that the output of the line sensor 120 has overflowed the 8-bit dynamic range. Then, it is determined whether or not the current accumulation time Ts is equal to the shortest accumulation time Tmin (the shortest accumulation time that can be controlled by the circuit as described later).

If it is determined that Ts ≠ Tmin, step 22 in FIG.
If the next accumulation is performed by using the Ts calculated in step (1), there is a possibility that the output of the line sensor 120 that enables focus detection may be obtained. Therefore, the process jumps to step 21 in FIG. 12 to perform the next accumulation (step 41). .

If it is determined in step 35 that Ts = Tmin, the focus is not detected in the shift 0 mode in which the lower 8 bits are extracted without performing the lower shift on the 10-bit data. Make changes.

First, in step 36, it is determined whether or not MAX (10) is greater than or equal to 512. If it is determined that MAX (10) is smaller than 512, one downward shift is performed next time on 10-bit data. Assuming that the focus detection becomes possible by adopting the shift 1 mode, FLG = 1 is set (step 4).
0), and jump to step 21 in FIG. 12 to perform the next accumulation (step 41).

If MAX (10) is determined to be 512 or more in step 36, FLG = 2 because focus detection is impossible even in the shift 1 mode.
And the shift 2 mode is adopted (step 37).

Subsequently, in step 38, it is determined whether or not MAX (10) is equal to 1023. If MAX (10) is 1023, the data of the line sensor 120 is a 10-bit dynamic even if the accumulation time is the shortest. Since it indicates that the range has overflowed, an undetectable warning is issued (step 39), and the process jumps to step 21 in FIG. 12 to perform the next accumulation (step 41).

If it is determined in step 38 that MAX (10) is not equal to 1023, there is a possibility that the output of the line sensor 120 that can detect the focus in the next accumulation may be obtained. Jump to step 21 in FIG.

Steps 31, 32, 35, and 36 in the shift 0 mode correspond to the calculation possible / impossible determination section 170f in FIG.

Next, the operation in the shift 1 mode will be described with reference to FIG.

If it is determined in step 18 in FIG. 12 that FLG = 1, the process jumps to step 42 in FIG. 14, and in step 43, MAX (10) becomes 512
It is determined whether or not this is the case.

If MAX (10) is determined to be 512 or more in step 43
Since it means that the data obtained by shifting the 10-bit data once in the lower direction and extracting the lower 8 bits is not within the dynamic range of 8 bits, FLG = 2 is set to adopt the shift 2 mode ( Step 46) Jump to Step 21 in FIG. 12 (Step 48) to perform the next accumulation.

When it is determined in step 43 that MAX (10) is smaller than 512, the process proceeds to step 44, where it is determined whether MAX (10) is larger than 200. When MAX (10) is determined to be larger than 200, The calculation means 160 performs a focus detection calculation based on the output of the line sensor 120 stored in the memory 150 (step 45).

If MAX (10) is 200 or less in step 44, the focus detection calculation is not performed and FLG = 0 is set in step 47, and the process jumps to step 21 in FIG. 12 to perform the next accumulation.

Here, the reason why focus detection is not performed when MAX (10) is 200 or less is that if focus detection calculation is performed with very small data, accuracy deteriorates. In such a case, it is better to set to shift 0 mode. = 0 is set and the next accumulation is performed.

Steps 43 and 44 in the shift 1 mode correspond to the calculation possible / impossible determination section 170f in FIG.

Next, the operation in the shift 2 mode will be described with reference to FIG.

If it is determined in step 18 in FIG. 12 that FLG is not 1, the process jumps to step 49 in FIG.
0) is 1023 or not, and when it is 1023, the output of the line sensor 120 has overflowed the 10-bit dynamic range and focus detection is impossible, so a detection impossible warning is issued. (Step 57) Jump to Step 21 in FIG. 12 (Step 56) to perform the next accumulation.

If it is determined in step 50 that MAX (10) is not equal to 1023, the output of the line sensor 120 is within the 10-bit dynamic range, so the 10-bit data is shifted twice in the lower direction to lower 8 bits. Is also within the 8-bit dynamic range, and if it is determined in step 51 that MAX (10) is greater than 400, the focus detection calculation is performed by the calculation means 160 (step 5).
2).

Here, when MAX (10) is 400 or less, the reason why focus detection calculation is not performed is that the dynamic range of 10 bits or less is 400 or less. The lower 8 bits are extracted by shifting the 10-bit data twice in the lower direction. In this case, it is less than 100, and if the focus detection calculation is performed with too small data, high-precision detection cannot be performed. In such a case, it is better to use the shift 1 mode or the shift 0 mode. .

Therefore, if it is determined in step 51 that MAX (10) is 400 or less, FLG = 1 is set (step 53), and the flow advances to step 54. If MAX (10) is determined to be larger than 200 in step 54, 12Jump to step 21 (step 56)
The next accumulation is performed, and if it is determined in step 54 that MAX (10) is 200 or less, the shift 0 mode is adopted and the FLG
= 0 (step 55) to execute the next accumulation.
Jump to step 21 in FIG. 12 (step 56).

Steps 50 and 51 in the shift 2 mode correspond to the calculation possible / impossible determination section 170f in FIG.

As described above, in each mode shown in FIGS. 13 to 15, when the data of the line sensor 120 obtained last time is not suitable for the focus detection calculation, the data of the line sensor 120 suitable for the focus detection calculation is obtained. Re-accumulation is performed as needed.

That is, when it is determined that the data of the line sensor 120 is not suitable for the focus detection calculation in the shift 0 mode, the shift 1 mode, and the shift 2 mode, respectively, FIG. 13, step 41, FIG. 14, step 48, and FIG. By the operation in step 56, the process jumps to step 21 in FIG.

In step 21 of FIG. 12, first, as the time Ts of the accumulation of the line sensor 120 to be performed, the next accumulation time is determined in step 22 based on the maximum value MAX (10) of the output of the line sensor 120 obtained by the previous accumulation. Ts is calculated.

Ts is calculated so that MAX (10) becomes the predetermined value PEAK at the next accumulation, and in this embodiment, the predetermined value PEAK is set to 128.
Therefore, Ts is obtained by the following equation.

Here, when the brightness of the subject is very low, Ts obtained by the equation (1) becomes a very long time. However, if the accumulation time is too long, the response becomes poor or occurs at each pixel of the licensor. For a reason such as an increase in the dark current component, a predetermined maximum time Tmax is determined, and (1)
When Ts calculated by the equation exceeds the above Tmax, Ts =
Tmax is set (steps 23 and 24).

On the contrary, when the subject is very bright, it can be obtained by the formula (1).
Although Ts is a very short time, it is impossible to control the accumulation time too short due to problems such as the minimum effective time of the microcomputer for the delay time of each element constituting the circuit.
Therefore, a predetermined controllable minimum time Tmin is determined, and when Ts obtained by the equation (1) is smaller than Tmin, Ts = Tmin is set (steps 25 and 26).

Then, the process proceeds to step 4. In step 4 and subsequent steps, operations such as data shift and memory storage are performed as described above.

Referring to FIG. 2 earlier, when the shift mode is switched by each operation, the shift 0 mode, the shift 1 mode, and the shift 1 mode are changed.
It is explained that the range of the mode and the shift 2 mode are overlapped to provide hysteresis, but the width of this hysteresis is determined by the steps 44 and 44 in FIG. 14 and the steps 51 and 54 in FIG.
Determined by the numerical value to be compared with MAX (10), 255 ~ 140, respectively
Values of about 511-280, 255-140 are desirable.

In the first embodiment described above, only the shift 0 mode is normally used, and when the accumulation time reaches a predetermined minimum time Tmin, the maximum
The shift mode was switched according to the value of (10). However, when the accumulation time is short, the influence of noise and the afterimage of the photoelectric element constituting the line sensor 120 increases, so that the S / N ratio deteriorates in the shift 0 mode using only 1/4 of the 10-bit dynamic range. The accuracy of the focus detection calculation may be reduced.

Therefore, a second embodiment in which the shift mode is switched when the accumulation time becomes equal to or shorter than a predetermined accumulation time longer than the shortest time Tmin will be described below.

The block configuration of the second embodiment is the same as that of the first embodiment shown in FIG.

As shown in FIG. 16, the switching of the shift mode by the accumulation time Ts is Tmin = 10 μs, Ta = 30 μ, and Tb = 90 μs. As described above, the overlap between the shift 0 mode and the shift 1 mode, that is, Ta and Tb The hysteresis is provided by appropriately taking a time interval between the shift modes so as not to become unstable at the boundary where the shift mode is switched.

The operation of the microcomputer when the focus detection device of the second embodiment is constituted by a microcomputer will be described with reference to FIG. 12 of the first embodiment and further with reference to the flowcharts of FIGS.

First, steps 1 to 26 in FIG. 12 are the same as those in the above-described first embodiment, and will not be described.

Next, the operation in the shift 0 mode will be described with reference to FIG.

If FLG = 0 is determined in step 16 in FIG. 12, the process proceeds to step 30 in FIG. 17, and in step 58, MAX (1) is determined in order to determine whether or not the MAX (10) is within the lower 8 bits.
If MAX (10) is determined to be smaller than 256 by checking whether (0) is smaller than 256 or not, the process proceeds to step 59 and then MAX (10)
Is greater than or equal to 100.

If it is determined in step 59 that MAX (10) is greater than 100, in step 62, the current accumulation time Ts is set to the predetermined accumulation time Ta.
(Ta> Tmin) is determined, and if Ts <Ta is not determined, the line sensor 1 stored in the memory 150 is determined.
The focus detection calculation based on the output of 20 is performed by the calculation means 160 (step 63).

If it is determined in step 62 that Ts <Ta, as described above, it is determined that the shift 0 mode is inappropriate for focus detection due to noise, afterimages, and the like, and the flow proceeds to step 65 described below without performing focus detection calculation.

If it is determined in step 59 that MAX (10) is 100 or less, the flow proceeds to step 60 without performing the focus detection calculation. Here MA
The reason why the focus detection calculation is not performed when X (10) is 100 or less is
This is because if the output of the line sensor 120 is too small, accurate focus detection cannot be performed.

In step 60, the current accumulation time Ts is the longest accumulation time.
It is determined whether it is equal to Tmax. Here, Ts = Tmax means that even if the accumulation time is the longest, the output of the line sensor 120 is small and focus detection calculation cannot be performed. Therefore, if Ts = Tmax is determined, a detection impossible warning is issued ( Step 61), and jump to step 21 in FIG. 12 to store again (step 66).

If it is determined in step 60 that Ts is not equal to Tmax, the output of the line sensor 120 can be obtained such that the focus can be detected by performing the next accumulation using Ts as calculated in step 22 in FIG. Therefore, the process jumps to step 21 in FIG. 12 to perform the next accumulation without issuing an undetectable warning (step 66).

If it is determined in step 58 that MAX (10) is 256 or more, it means that the output of the line sensor 120 has overflowed the 8-bit dynamic range, and the flow advances to step 64 without performing the focus detection calculation. It is determined whether the current accumulation time Ts is shorter than a predetermined accumulation time Ta (Ta> Tmin).

Here, if it is determined that Ts <Ta is not satisfied, there is a possibility that an output of the line sensor 120 that enables focus detection if the next accumulation is performed using Ts calculated in step 22 in FIG. The process jumps to step 21 in FIG. 12 to perform the next accumulation (step 66).

If it is determined in step 64 or 62 that Ts <Ta, it is determined that focus detection is impossible or inappropriate in the shift 0 mode in which the lower 8 bits are extracted without performing the lower shift on the 10-bit data. FLG = 1 and PEAK = 256 are set so as to switch to the shift 1 mode from the next time (step 65).
Jump to 21 (step 66).

The reason why PEAK256 is set in step 65 is that PEAK = 128 in the shift 0 mode and that the value of 256 is doubled in the shift 1 mode.

Next, the operation in the shift 1 mode will be described with reference to FIG.

If it is determined in step 18 in FIG. 12 that FLG = 1, the process jumps to step 42 in FIG. 18, and in step 67, MAX (10) becomes 5
It is determined whether it is 12 or more.

If it is determined in step 67 that MAX (10) is smaller than 512, the process proceeds to step 68, where Ts is equal to a predetermined accumulation time Tb (Tb> Ta).
> Tmin). Ts in step 68
When it is determined that Tb is greater than Tb, it is determined that the effects of the above-described noise and afterimages can be ignored, and FLG is used to return to the shift 0 mode.
= 0, PEAK = 128 (step 69), and jump to step 21 in FIG. 12 to perform the next accumulation.

If it is determined in step 68 that Ts> Tb, then step
Go to 70 and determine if it is greater than MAX (10) 200,
When it is determined that (10) is larger than 200, the calculation means 160 performs a focus detection calculation based on the output of the line sensor 120 stored in the memory 150 (step 71).

If MAX (10) is 200 or less in step 70, the focus detection calculation is not performed, and the process jumps to step 21 in FIG. 12 to perform the next accumulation.

If it is determined in step 67 that MAX (10) is 512 or more, the 10-bit data is shifted once to the right to
Since it means that the data from which the bits have been extracted are not within the dynamic range of 8 bits, the flow proceeds to step 72 without performing the focus detection calculation.

In step 72, it is determined whether or not Ts is equal to the shortest time Tmin. When it is determined that Ts = Tmin, FLG = 2 is set to switch to the shift 2 mode, and the flow proceeds to step 74 to perform the next accumulation. When it is determined in step 72 that Ts is not equal to Tmin, it means that Ts <Tmin. In this case, the process proceeds to step 74 without switching the shift mode, and the next accumulation is performed.

Next, the operation in the shift 2 mode will be described with reference to FIG.

If it is determined in step 18 of FIG. 12 that FLG is not 1, jump to step 49 of FIG.
0) is 1023 or not, and when it is 1023, the output of the line sensor 120 has overflowed the 10-bit dynamic range and focus detection is impossible, so a detection impossible warning is issued. (Step 80) Jump to Step 21 in FIG. 12 (Step 78) to perform the next accumulation.

If it is determined in step 75 that MAX (10) is not equal to 1023, since the output of the line sensor 120 is within the dynamic range of 10 bits, the 10-bit data is shifted twice in the lower direction to lower 8 bits. Is also within the 8-bit dynamic range, and if it is determined in step 76 that MAX (10) is greater than 400, the focus detection calculation is performed by the calculation means 160 (step 7).
9).

Here, when MAX (10) is 400 or less, the reason why focus detection calculation is not performed is that the dynamic range of 10 bits or less is 400 or less. The lower 8 bits are extracted by shifting the 10-bit data twice in the lower direction. In this case, the data is less than 100, and if the focus detection calculation is performed with too small data, it is not possible to perform high-precision detection. In such a case, it is better to use the shift 1 mode.

Therefore, if it is determined in step 76 that MAX (10) is 400 or less, FLG = 1 is set (step 77), and the flow advances to step 78 to perform the next accumulation.

As described above, in the above-described embodiment, an 8-bit digital value is extracted from a 10-bit digital value. Therefore, only one byte of memory is required for one digital value, and the number of pixels of the line sensor is 200 pixels. Even so, the required memory area is 200 bytes, which is the same as in the case of the conventional focus detection device.

If the digital value of 10 bits is to be stored in the memory, a memory area of 2 bytes is required for one digital value.
If it is 00 pixels, a memory area of 400 bytes is required.

In the first and second embodiments described above, the shift 0 mode in which the rightward shift is not performed is normally used, and the mode is switched between the shift 1 mode and the shift 2 mode as the subject luminance increases. The shift mode may be switched such that the shift 2 mode is used when the subject brightness is high, and the shift 0 mode is used when the subject brightness is low.

In this embodiment, the shift mode for the sensor output obtained by the next accumulation is set based on the value indicating the maximum value of the previous sensor accumulation time and the sensor output at that time. A method of predicting and setting an optimal shift mode based on the output of a monitor photodiode installed in the vicinity may be used.

[Effects of the Invention] According to the focus detection device of the present invention, the circuit that performs data processing makes the range in which the N-bit digital value is extracted from the M-bit digital value output from the A / D converter variable. Therefore, reliable focus detection can be performed even on a high-luminance subject without increasing the circuit scale. In addition, the operation scale memory capacity can be about the same as the conventional one.

[Brief description of the drawings]

1 to 15 show a first embodiment of the present invention. FIG. 1 is a block diagram showing the configuration of a focus detection device, and FIG. 2 is a diagram showing the maximum value of the output of an A / D converter at the time of mode switching. 3 to 5 are explanatory diagrams showing the digital output of the A / D converter, the output of the line sensor, and the output to the memory in the shift 0 mode in order, and FIGS. 6 to 8. 9 also shows the shift 1 mode, FIGS. 9 to 11 show the same shift 2 mode, FIGS. 12 to 15 show flowcharts showing the operation, FIGS. 16 to 19 show the second embodiment, FIG. 16 is a diagram showing a reference value of the accumulation time at the time of mode switching, FIGS. 17 to 19 are flowcharts showing the operation, and FIG. 100 objective lens 110 optical means 120 line sensor 130 storage time control means 140 A / D converter 150 memory 160 arithmetic means 170 data processing means

Claims (3)

(57) [Claims] 1. A line sensor comprising a plurality of photoelectric conversion elements, an optical unit for projecting a light image of a subject by an objective lens onto the line sensor, and converting a plurality of outputs of the line sensor into M-bit digital values. An A / D converter, an N-bit digital value extracted from the M-bit digital value output from the A / D converter, and an N-bit digital value extracted from the M-bit digital value. And a calculating means for calculating a focus state of the objective lens based on a plurality of N-bit digital values in the memory, wherein the data processing means converts the M-bit digital value into N-bit digital values. A focus detection device, wherein a range for extracting a digital value is made variable. 2. The focus detection device according to claim 1, wherein the range to be extracted is based on an output value of the A / D converter. 3. The method according to claim 1, wherein the extracting of the N-bit digital value from the M-bit digital value in the data processing means is performed by the A / D converter.
3. The focus detection device according to claim 2, wherein the M-bit data is shifted to the lower side by a predetermined number of times in accordance with the output value of the converter, and the lower N bits of the shifted M bits are extracted.