JPH11305108A - Digital camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely focus a lens on an object having high luminance under low illuminance. SOLUTION: First of all, the illuminance of the object is discriminated at a prescribed lens position and the high luminance component thereof is detected. Next, the AF lens 12 is moved by each prescribed amount at a time. At the respective lens positions, the contrast component and the low luminance component of the object are calculated. Then, the data of the respective lens positions and the contrast component and the low luminance component obtained at the lens positions are mutually related and held by a table 40c. Besides, the maximum lens position where the contrast component becomes the maximum and the minimum lens position where the low luminance component becomes the minimum are detected. When the illuminance is low, the high luminance component exists and deviation amount between the maximum lens position and the minimum lens position is large, the minimum lens position is decided as the focusing position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital camera, and more particularly, to a digital camera for determining, for example, a focus position of a focus lens.

[0002]

2. Description of the Related Art As a conventional digital camera of this type, a focus evaluation value (AF evaluation value) is obtained at each lens position.
Was calculated, and the lens position having the maximum value was determined as the in-focus position. Such a method of detecting the focus position utilizes the fact that the AF evaluation value usually changes in a mountain shape, and the peak of the mountain indicates the focus position. Note that the AF evaluation value is obtained by integrating the contrast component of the subject over one screen.

[0003]

However, when an image of a point light source under low illuminance is photographed in such a conventional technique, the AF evaluation value changes not in a peak but in a valley. In other words, when the focus is adjusted to the point light source, the point light source shines small and sharp as shown in FIG. 15A, but when the focus deviates from the point light source, the point light source shines large and dull as shown in FIG. 15B. . Therefore, the AF evaluation value obtained by integrating the contrast component over one screen becomes minimum at the in-focus position, and increases as the focus shifts. That is, the characteristic of the AF evaluation value changes in a valley shape as shown in FIG. Therefore, in the related art, focusing may not be performed depending on the situation of the subject.

[0004] Therefore, a main object of the present invention is to provide a digital camera capable of accurately adjusting the focus regardless of the situation of a subject.

[0005]

According to a first aspect of the present invention, there is provided a digital camera for determining an in-focus position of a focus lens based on a camera signal of a subject photographed through a focus lens, wherein the illuminance of the subject is determined based on the camera signal. A digital camera characterized by comprising: means, a high-brightness detecting means for detecting a high-brightness component of a camera signal, and a determining means for determining a focus position based on a result of illuminance determination and the high-brightness component.

According to a second aspect of the present invention, in a digital camera for determining a focus position by moving a focus lens by a predetermined amount, a detecting means for detecting a minimum lens position at which a low luminance component of a camera signal is minimized, and a minimum lens A digital camera including a determination unit that determines a position as a focus position.

[0007]

First, the illuminance of a subject is determined at a predetermined lens position, and a high luminance component of the subject is detected. Next, the focus lens is moved by a predetermined amount by the motor drive circuit, and the contrast component and the low luminance component of the subject are calculated at each lens position. Each lens position data and the contrast component and the low luminance component obtained at the lens position are held in a table in association with each other, and the maximum lens position where the contrast component is maximum and the minimum lens position where the low luminance component is minimum are detected. You. If there is a high luminance component at low illuminance and the amount of deviation between the maximum lens position and the minimum lens position is large, the minimum lens position is determined as the focus position.

When an image of a subject in which a point light source exists under low illuminance is taken, the calculated low luminance component has a characteristic that it becomes minimum at the in-focus position and becomes large as the focus shifts. That is, the low luminance component changes like a valley with respect to the lens position. Therefore, if the shift amount is larger than the predetermined value, the minimum lens position is determined as the focus position.

[0009]

According to the first aspect of the invention, the focus position is determined based on the illuminance determination result and the high luminance detection result, so that the focus can be accurately adjusted regardless of the situation of the subject. According to the second aspect, the minimum lens position at which the low luminance component of the subject is minimized is determined as the focus position, so that the focus can be accurately adjusted regardless of the situation of the subject.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0011]

Referring to FIG. 1, a digital camera 10 of this embodiment includes an AF lens 12,
The light image of the subject incident from the CCD imager 2 is
It is irradiated to 0. As shown in FIG. 2, a plurality of light receiving sections 20a are formed in the CCD imager 20.
On the front surface of Oa, a complementary color filter 20d in which Ye, Cy, Mg and G are arranged in a mosaic pattern as shown in FIG. 3 is mounted. Each light receiving unit 20a constitutes each pixel of the CCD imager 20, and one of Ye, Cy, Mg, and G is
It is arranged corresponding to each light receiving section 20a. The illuminated light image is supplied to the light receiving section 20a of the CCD imager 20 via the complementary color filter 20d, and is photoelectrically converted.

The CCD imager 20 will be described in more detail. As shown in FIG.
Are a plurality of light receiving units 20a corresponding to each pixel, and light receiving units 2a
0a, a plurality of vertical transfer registers 20b for vertically transferring the charges which have been photoelectrically converted and accumulated, and a horizontal transfer register arranged at the end of the vertical transfer registers 20b for transferring the charges transferred by the vertical transfer registers 20b in the horizontal direction. A timing generator 22 including a transfer register 20c;
It is driven by a timing signal output from. Here, the timing signal includes a read pulse for reading out charges from the light receiving unit 20a to the vertical transfer register 20b, a vertical transfer pulse for vertically transferring the charges in the vertical transfer register 20b line by line, and a charge in the horizontal transfer register 20c. Is a horizontal transfer pulse for transferring pixel by pixel in the horizontal direction,
During the non-exposure period, that is, the non-charge accumulation period,
For example, there is a sweeping pulse for sweeping the charge generated at a into an overflow drain (not shown).

The timing generator 22 controls the output period of the sweep-out pulse in accordance with the shutter speed instruction signal output from the microcomputer 40. As a result, the charge accumulation period is controlled, and a desired exposure period (shutter speed) is obtained. The technique of controlling the exposure period by the output period of the sweep-out pulse is well known as an electronic shutter function.

In the camera mode, the CCD imager 2
The pixel signal output from 0, that is, the camera signal is A / D
The converter 24 converts the digital data into pixel data, that is, camera data. The camera data is written into the RAM 26 by the memory control circuit 28 that operates according to the timing signal from the timing generator 22. The camera data stored in the RAM 26 is thereafter read by the memory control circuit 28 and input to the arithmetic circuit 30.

The arithmetic circuit 30 receives the input Ye, Cy,
Based on the respective camera data of Mg and G, luminance data (Y data) and color difference data RY and BY
Is calculated. The arithmetic circuit 30 inputs the calculated color difference data to a white balance adjustment circuit (not shown),
The data is input to the integrator 36. The integrator 36 integrates the input Y data every frame period (1/30 second) and calculates a luminance evaluation value Ya to be evaluated for exposure adjustment.

The microcomputer 40 calculates an optimum exposure period based on the luminance evaluation value Ya input from the integrator 36. If this optimal exposure period is shorter than 1/30 second, this optimal exposure period is the exposure period at the time of main exposure, that is, at the time of capturing a recorded image. On the other hand, if the optimum exposure period is longer than 1/30 second, the microcomputer 40 sets the exposure period in the main exposure to 1/30 second.
The exposure time is set to 30 seconds, and the insufficient exposure is compensated by a strobe (not shown). The microcomputer 40 also determines the illuminance of the subject from the calculated optimal exposure period. That is, the optimal exposure period is 1
If it is / 10 seconds or more, it is determined that the illuminance is low.

When the exposure period at the time of the main exposure is determined and the illuminance of the subject is determined, focus control is executed. Specifically, first, the AF lens 12 is moved by a predetermined amount by the motor drive circuit 18 and pre-exposure is performed at each lens position for a period corresponding to the illuminance of the subject. Optimal exposure period is 1
If it is shorter than / 30 seconds, this optimal exposure period is the pre-exposure period. On the other hand, the optimal exposure period is 1/30 second or more.
If less than 10 seconds (3 frame periods), the pre-exposure period is set to 1/30 seconds. Also, the optimal exposure period is 1 /
If it is 10 seconds or more, the pre-exposure period is set to 1/15 second (two frame periods).

That is, if the optimal exposure period is not shorter than 1/10 second even if it is 1/30 second or longer, the subject can be appropriately evaluated with a pre-exposure of about 1/30 second. For this reason, the pre-exposure is 1 / the maximum exposure period during the main exposure.
Performed for only 30 seconds. However, the optimal exposure period is 1/10
When the exposure time is increased to seconds, the subject cannot be sufficiently evaluated by the pre-exposure of about 1/30 seconds, and the accuracy of the AF control is reduced. For this reason, the pre-exposure period is set to 1/15 second, which is twice (an integral multiple) of 1/30 second.

At the time of focus control, the arithmetic circuit 30 inputs the calculated Y data to the high-level extraction circuit 32 and the low-level extraction circuit 34. The high-level extraction circuit 32 extracts a high-level component of luminance. Specifically, the Y data is 10 bits, of which the upper 3 bits are extracted by the high-level extraction circuit 32. The extracted high level component is divided by the integrator 38 into 1/30 seconds or 1/15 seconds.
Integrated every second. In other words, if the set pre-exposure period is 1/30 second or less, the high frequency component is integrated for each screen, and if the set pre-exposure period is 1/15 second,
The high frequency component is integrated for each of two screens. The integration data output from the integrator 38 is input to the microcomputer 40 as a high brightness evaluation value (high brightness component). If the pre-exposure period during the focus control is shorter than one frame period, the excess charge is swept away by the sweep-out pulse. Therefore, there is no particular problem even if the integration period of the integrator 38 at this time is set to one frame period.

The low level extraction circuit 40 extracts a low level component of luminance, that is, lower 4 bits of Y data. Then, the extracted low-level component is integrated by the integrator 39 for each screen or every two screens, and a low luminance evaluation value (low luminance component) is obtained. This low luminance evaluation value is also input to the microcomputer 40. Arithmetic circuit 3 during focus control
The Y data calculated by 0 is also input to the gate circuit 42. Since the focus needs to be adjusted to the main subject, the gate circuit 42 extracts only the Y data at the center of the screen where the main subject is considered to be located, and inputs the Y data to the high-pass filter (HPF) 44. High pass filter 4
At 4, the high-frequency component of the luminance data is extracted, and the integration circuit 4
Numeral 6 integrates this high-frequency component every one or two screens.
The integration data output from the integration circuit 46 is input to the microcomputer 40 as an AF evaluation value (contrast component).

Such processing is executed at different lens positions, and a plurality of high luminance evaluation values, a plurality of low luminance evaluation values, and a plurality of AF evaluation values are input to the microcomputer 40. The microcomputer 40 detects the maximum AF evaluation value and the minimum low luminance evaluation value from the input AF evaluation value and the low luminance evaluation value, and further detects a lens position (maximum lens position) and a lens position corresponding to the maximum AF evaluation value. A lens position (minimum lens position) corresponding to the minimum low luminance evaluation value is detected. Then, one of the lens positions is determined as the focus position according to the illuminance determined at the time of calculating the optimal exposure period, the high luminance evaluation value at the minimum lens position, and the amount of deviation between the maximum lens position and the minimum lens position.

More specifically, a high luminance evaluation value having a low illuminance and greater than a predetermined value is detected, and if the shift amount is larger than a predetermined value, the minimum lens position is determined as the focus position. On the other hand, if any one of the illuminance, the high luminance evaluation value, and the shift amount does not satisfy the above condition, the maximum lens position is determined as the focus position. in this way,
The reason why the minimum lens position is determined as the in-focus position under a predetermined condition is as follows. When a subject in which a point light source is present under low illuminance is photographed, the calculated low luminance component becomes minimum at the in-focus position and becomes larger as the focus is shifted. That is, when the focus is adjusted to the point light source, the point light source shines small and sharp as shown in FIG. 15A, but when the focus deviates from the point light source, the point light source shines large and dull as shown in FIG. 15B. Therefore, the AF evaluation value obtained by integrating the contrast component over one screen becomes minimum at the in-focus position, and increases as the focus shifts. As a result, the characteristic of the AF evaluation value changes in a valley shape as shown in FIG. 17A, and the maximum lens position is far away from the in-focus position. Incidentally, when a typical subject as shown in FIG. 14 is photographed, the AF evaluation value changes to a mountain as shown in FIG. 16, and the maximum lens position coincides with the in-focus position. As described above, the characteristics of the AF evaluation value vary greatly depending on the subject.

On the other hand, the low luminance evaluation value changes in a valley-like manner with respect to the lens position irrespective of the condition of the subject. The reason why the low luminance evaluation value changes in a valley shape is as follows.
When a subject having a striped pattern as shown in FIG. 13A is photographed, the brightness changes sharply as shown in FIG. 13B if the subject is in focus. It changes slowly as shown in FIG. That is, the luminance signal shown in FIG. 13B is a perfect rectangular wave, whereas the luminance signal shown in FIG. 13C has a parabolic waveform. For this reason, the low-level component of the luminance becomes lowest at the in-focus position, and becomes larger as the focus is lost. The same applies to the low luminance evaluation value obtained by integrating the low level component, and as a result, the low luminance evaluation value changes to a valley with respect to the lens position. Further, FIG. 16 (B) showing the characteristics of the low luminance evaluation value when photographing the subject shown in FIG. 14 and FIG. 17 (B) showing the characteristics of the low luminance evaluation value when photographing the subject shown in FIG. As can be seen, the low luminance evaluation value changes like a valley irrespective of the situation of the subject.

In a typical subject as shown in FIG. 14, the maximum lens position and the minimum lens position almost coincide as can be seen from FIGS. 16A and 16B.
As shown in FIGS. 17A and 17B, the maximum lens position and the minimum lens position of a subject having a point light source under low illuminance as shown in FIG. As described above, since the focus cannot be adjusted from the AF evaluation value for some subjects, the lens position determined as the focus position is changed according to the conditions. That is,
If the illuminance is low, a high brightness evaluation value greater than a predetermined value or more is detected, and if the shift amount is larger than a predetermined value, the minimum lens position is determined to be the in-focus position, and any one of these conditions is satisfied. If not, the maximum lens position is set as the focus position.

When the release button 48 is half-pressed, the microcomputer 40 starts the processing of the flowcharts shown in FIGS.
Determine the position of. First, the microcomputer 40 executes step S1.
And the exposure period is initialized in step S3. The initial exposure period is 1/250 second. Next, the microcomputer 40 gives a shutter speed instruction signal for setting the exposure period, that is, the shutter speed to 1/250 second, to the timing generator 22 in step S5, and executes the pre-exposure at this shutter speed. Thus, the above-described luminance evaluation value Ya is calculated.

The microcomputer 40 fetches the luminance evaluation value Ya output from the computing unit 38 based on the pre-exposure in step S5 in step S7, and calculates an optimum exposure period in step S9. Specifically, the brightness evaluation value Ya is compared with a target evaluation value Yt obtained in an optimal exposure state, and an exposure period in which the brightness evaluation value Ya matches the target evaluation value Yt is calculated. For example, if the luminance evaluation value Ya is "50" and the target evaluation value Yt is "100", the current luminance is only half of the optimum state. Therefore, the optimal exposure time is 1/125 second.

In step S10, the exposure period at the time of main exposure, that is, when the release button 54 is completely pressed, is determined depending on whether the optimum exposure period calculated in this way is 1/30 second or more. That is, when the release button 54 is fully depressed to obtain the recorded image data, the exposure period is usually set not to exceed 1/30 second, that is, one frame period, in consideration of camera shake. Therefore, when the calculated optimal exposure period exceeds 1/30 second, the exposure period at the time of the main exposure is set to 1/30 second. If the optimal exposure period is 1/30 second or less, the optimal exposure period is equal to the exposure period for the main exposure.

The microcomputer 40 also initializes the count value of the counter 40a in step S11, that is, sets the count value (CNT) to "1", and then proceeds to step S13.
Then, the illuminance of the subject is determined. Whether the illuminance is low or not depends on whether the optimal exposure period calculated in step S9 is 1/10.
Judge by whether it is longer than seconds. And 1 /
If a sufficient level of the AF evaluation value cannot be obtained unless exposure is performed for 10 seconds or more, it is determined that the illuminance is low, and step S15 is performed.
Proceed to. On the other hand, if the optimum exposure period is less than 1/10 second, it is determined that the illuminance is sufficient and the process proceeds to step S17. In step S15, the flag 40b is set, but in step S17, the flag 40b is reset. That is,
The flag 40b is set when the subject has low illuminance.

The microcomputer 40 determines whether or not the flag 40b has been set in step S19. If "YES", the pre-exposure period during the AF control is set to 1/15 second in step S25, and the process proceeds to step S27. On the other hand, if “NO” in the step S19, it is determined whether or not the optimal exposure period is longer than 1/30 second in a step S21. If "NO" here, directly to step S2
7, but if “YES”, A is determined in the step S23.
The exposure period at the time of the F control is set to 1/30 second, and the process proceeds to step S27. That is, if the optimal exposure period is longer than 1/30 second, the pre-exposure period during AF control is 1/30 second, but if the optimal exposure period is 1/30 second or less, the optimal exposure period is This is a pre-exposure period during control.

When the calculation of the main exposure period and the determination of the illuminance are completed, the microcomputer 40 executes the AF control. First, in step S27, the AF lens 12 is moved to the position shown in FIG.
And at the initial position shown in FIG.
29, the position data L ₍₁₎ of the initial position is counted
11 is stored in the table 40c shown in FIG. 11. The microcomputer 40 subsequently detects the beginning of the next one frame period according to the timing signal from the timing generator 22. The beginning of the one frame period is detected. Then, "YES" is determined in the step S31, and the step S31 is performed.
At 32, pre-exposure of the subject according to the exposure time set in the processing of steps S19 to S25 is started.

Thereafter, the flag 40b is set in step S33.
Judge whether it is set, and if "NO",
The process proceeds to step S37, but if "YES",
In step S35, it is determined that the beginning of one frame has been detected.
After waiting for the start, the process proceeds to step S37. That is, the flag
When 40b is set, pre-exposure is performed for 2 frames.
The flag 40b is reset because it is performed over a period.
Step one frame period later than the case where
Proceed to S37. Then, in step S37, the next one frame
After the start of the program period is detected, the AF
The lens 12 is moved by a predetermined amount. Step S
41, the position data L of the AF lens 12 ₍₂₎Count
The data is written into the table 40c in association with the value “2”. this
Steps S39 and S41 are shown in FIG.
Or during the period shown in FIG.

In step S42, the microcomputer 40 starts pre-exposure in the same manner as in step S32.
To determine whether the beginning of one frame period has been detected. If "YES" here, A is determined in a step S45.
AF of subject image exposed before F lens 12 moves
The evaluation value, the high luminance evaluation value, and the low luminance evaluation value are fetched.
Then, in step S47, the AF evaluation value AF _(CNT) ,
The high-luminance evaluation value YH _(CNT) and the low-luminance evaluation value YL _(CNT) are written in the table 40c in association with the current count value. Subsequently, in step S49, it is determined whether or not the flag 40b has been set. If "NO", the process directly proceeds to step S5.
3. If “YES”, the process proceeds to step S5 via the process of step S51, that is, one frame period later.
Proceed to 3.

In step S53, the microcomputer 40 sets the AF
The lens 12 is moved by a predetermined amount, and then, in step S55
The position data L _{(CNT + 2)} of the AF lens 12 after the movement in the table 40 is associated with the current count value + 2 count value.
c. Then, in step S57, the counter 40
a is incremented, and in a step S59, it is determined whether or not the current count value exceeds a predetermined value A (= 6). If “NO” here, AF evaluation values at all lens positions,
The process returns to step S42 assuming that the acquisition of the high luminance evaluation value and the low luminance evaluation value has not been completed. If “YES”, it is determined that all the AF evaluation value, the high luminance evaluation value, and the low luminance evaluation value have been obtained. Proceed to step S61.

As described above, in steps S11 to S59, the AF lens 12 moves by a predetermined amount,
At each position, the AF evaluation value, the high luminance evaluation value, and the low luminance evaluation value are captured. It takes one frame period to calculate each evaluation value. In each of FIGS. 10 and 11, the subject exposed before the movement is delayed by one frame after the AF lens 12 moves to the next position. An AF evaluation value, a high luminance evaluation value, and a low luminance evaluation value of the image are obtained. AF
Since there is such a difference between the movement timing of the lens 12 and the timing of taking in each evaluation value, the count value associated with each evaluation value in step S47 and the count value associated with lens position data in step S55 are different from each other. Note that FIG.
And the numbers shown in FIG. 11 indicate the lens positions.

The microcomputer 40 performs the processing from step S61 onward.
The maximum lens position and the minimum lens position are detected with reference to the table 40c, and one of them is determined as the focus position. Then, the AF lens 12 is moved to the in-focus position. First, in step S61, the count value of the counter 40a is set to an initial value (= 1), and in step S63, the maximum AF evaluation value AF _MAX and the minimum low luminance evaluation value Y _LMIN are set to temporary values (= 0). . Subsequently, in a step S65, it is determined whether or not the AF evaluation value AF _(CNT) of the current count value is larger than the maximum AF evaluation value AF _MAX . Where "N
If "O", the process directly proceeds to step S71, but "YES".
If the maximum AF evaluation value AF _MAX and updates the current AF evaluation value AF _(CNT) in step S67, the maximum lens position data L _S1 in step S69 that the current lens position data L _(CNT).

In step S71, it is determined whether the low luminance evaluation value Y _{L (CNT)} of the current count value is smaller than the minimum low luminance evaluation value Y _LMIN . If “NO”, the process directly proceeds to step S77, and if “YES”, the process proceeds to step S77.
At 73, the minimum low luminance evaluation value Y _{LM IN} is _replaced with the current low luminance evaluation value Y.
_The minimum lens position data L _S2 is updated as the current lens position data L _(CNT) in step S75.

Then, the count value is incremented in a step S77, and it is determined whether or not the count value exceeds a predetermined value A in a step S79. If "NO" here, the process returns to the step S65 and the above-mentioned processing is repeated. On the other hand, if “YES” is determined in the step S79, the microcomputer 4
If it is 0, the process proceeds to step S81. At step S81, it reads the high luminance evaluation value Y _H corresponding to the minimum lens position L _S2 from the table 40c, in step S83 the high luminance evaluation value Y _H is whether greater than a predetermined value B and the flag 40b is set to decide. If any one of the conditions is not satisfied, the microcomputer 40 determines the maximum lens position L _S1 as the focus position, and moves the AF lens 12 to the first lens position L _S1 in step S91. In contrast, high luminance evaluation value Y _H is it is set large and the flag 40b than the predetermined value C, the step S85
Is used to calculate the amount of deviation between the maximum lens position data L _S1 and the minimum lens position data L _S2 . Next, it is determined in step S87 whether the amount of deviation is greater than a predetermined value C. Here, if the shift amount is equal to or less than the predetermined value C, the maximum lens position L
_S1 is determined as the focus position, and the process proceeds to step S91. Then, the AF lens 12 is moved to the maximum lens position L _S1 and the process ends.

On the other hand, if the deviation is larger than the predetermined value C, the microcomputer 40 determines "YES" in a step S87. That is, the minimum lens position L _S2 is determined as the focus position. Therefore, in step S89, the maximum lens position data L _S1 is updated with the minimum lens position data L _S2 ,
In step S91, the updated maximum lens position L _{S1 is set} to A.
The F lens 12 is moved.

According to this embodiment, the focus position is determined on the basis of the high luminance evaluation value and the illuminance at the minimum lens position and the amount of deviation between the maximum lens position and the minimum lens position. The focus can be adjusted accurately. Also, it is determined whether or not the subject has low illuminance based on the optimal exposure period. If the illuminance is low, the exposure period during AF control is set to 1/15 second (= 2 frame periods). , The AF evaluation value, the high luminance evaluation value, and the low luminance evaluation value can be accurately calculated.

In this embodiment, when all of the high luminance evaluation value and illuminance at the minimum lens position and the amount of deviation between the maximum lens position and the minimum lens position satisfy predetermined conditions, the minimum lens position is changed to the in-focus position. However, instead of the minimum lens position, the center position of the moving range of the AF lens 12 may be determined as the focus position. In this case, it is necessary to process step S89 'shown in FIG. 9 instead of step S89 shown in FIG. The lens position determined as the focus position when the above condition is satisfied is
In addition to the center position, an infinite position is also conceivable.

In this embodiment, all the pixel signals are read from the CCD imager 20.
If the number of pixels of the D imager 20 is large, unnecessary lines may be thinned out. That is, if the number of pixels is 1
When the number of pixels is 200,000, only two lines out of eight continuous lines may be read. As the lines to be read, the first Mg, G, Mg, G... Line and the fourth Ye, Cy, Ye, Cy.

Further, in this embodiment, the exposure period for generating the recording image data is set to 1/30 second or less, that is, one frame period or less. However, the recording image data is generated based on the image signal for one field. When generating data, it is better to set the exposure period to 1/60 second or less, that is, one field period or less. Further, in this embodiment, the gate circuit 42 is provided only in the preceding stage of the HPF 44, and only the AF evaluation value is calculated from the luminance signal in the focus area. However, the preceding stage of the high level extracting circuit 32 and the low level extracting circuit 34 is used. Alternatively, it is preferable to provide a gate circuit also in the preceding stage of the integration circuits 38 and 39, and calculate the high luminance evaluation value and the low luminance evaluation value from the luminance signal in the focus area.

In this embodiment, the high level component and the low level component of the Y data output from the arithmetic circuit 30 are extracted. However, the Y data is weighted for so-called center-weighted photometry, and the weighting is performed. High-level components and low-level components of the extracted Y data may be extracted.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is an illustrative view showing a CCD imager;

FIG. 3 is an illustrative view showing a complementary color filter;

FIG. 4 is a flowchart showing a part of the operation of the embodiment in FIG. 1;

FIG. 5 is a flowchart showing another portion of the operation of the embodiment in FIG. 1;

FIG. 6 is a flowchart showing another portion of the operation of the embodiment in FIG. 1;

FIG. 7 is a flowchart showing yet another portion of the operation of the embodiment in FIG. 1;

FIG. 8 is a flowchart showing another portion of the operation of the embodiment in FIG. 1;

FIG. 9 is a flowchart showing a part of the operation of another embodiment of the present invention.

FIG. 10 is an illustrative view showing one portion of an operation of the embodiment in FIG. 1;

FIG. 11 is an illustrative view showing another portion of the operation of the embodiment in FIG. 1;

FIG. 12 is an illustrative view showing a table;

13A is an illustrative view showing one example of a subject image; FIG. 13B is a waveform diagram showing one example of a luminance signal;
(C) is a waveform chart showing another example of the luminance signal.

FIG. 14 is an illustrative view showing one example of a subject;

FIG. 15 is an illustrative view showing another example of the subject;

16A is a graph illustrating an example of a relationship between an AF lens position and an AF evaluation value, and FIG. 16B is a graph illustrating an example of a relationship between an AF lens position and a low luminance evaluation value.

17A is a graph showing another example of the relationship between the AF lens position and the AF evaluation value, and FIG. 17B is a graph showing another example of the relationship between the AF lens position and the low luminance evaluation value. It is.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Digital camera 12 ... AF lens 18 ... Motor control circuit 20 ... CCD imager 30 ... Calculation circuit 32 ... High level extraction circuit 34 ... Low level extraction circuit 36,38,39,46 ... Integrator 40 ... Microcomputer 42 ... Gate circuit 44… High-pass filter

Claims (12)

[Claims] 1. A digital camera that determines a focus position of a focus lens based on a camera signal of a subject photographed through a focus lens, a determining unit that determines illuminance of the subject based on the camera signal, and high brightness of the camera signal. A digital camera, comprising: high luminance detecting means for detecting a component; and deciding means for determining the in-focus position based on a result of the illuminance determination and the high luminance component. 2. The high-luminance detecting means extracts high-level components of a luminance signal included in the camera signal, and integrates the high-level components for a predetermined screen to convert the high-luminance components. 2. The digital camera according to claim 1, further comprising a high-level integrating means for calculating. 3. The digital camera according to claim 1, wherein said determining means determines a specific lens position as said in-focus position when the illuminance is low and said high luminance component is larger than a predetermined value. A moving means for moving the focus lens by a predetermined amount; and a minimum lens position detecting means for detecting a minimum lens position at which a low luminance component of the camera signal is minimized. The digital camera according to claim 3, wherein the digital camera is at a minimum lens position. 5. A moving means for moving the focus lens by a predetermined amount, a maximum lens position detecting means for detecting a maximum lens position at which a contrast component of the camera signal is maximum, and a means for detecting a low luminance component of the camera signal. A minimum lens position detecting means for detecting a minimum lens position, and a shift amount detecting means for detecting a shift amount between the maximum lens position and the minimum lens position. 2. The in-focus position is determined based on the shift amount.
Or the digital camera according to 2. 6. The maximum lens position detecting means includes high frequency extracting means for extracting a high frequency component of a luminance signal included in the camera signal, and integrating the high frequency component for a predetermined screen to reduce the contrast component. Including high-frequency integration means for calculating
The digital camera according to claim 5. 7. A low-level extracting means for extracting a low-level component of a luminance signal included in the camera signal, and a minimum-lens position detecting means, wherein the low-luminance component is integrated by a predetermined screen. The digital camera according to claim 5, further comprising a low-level integrating means for calculating the following. 8. The apparatus according to claim 5, wherein said determination means determines a specific lens position as said in-focus position when all of said determination result, said high luminance component and said shift amount satisfy predetermined conditions. A digital camera according to claim 1. 9. The digital camera according to claim 8, wherein said specific lens position is said minimum lens position. 10. The method according to claim 1, wherein the determining unit determines the maximum lens position as the in-focus position unless at least one of the determination result, the high luminance component, and the shift amount satisfies the predetermined condition. 10. The digital camera according to 8 or 9. 11. The method according to claim 8, wherein said predetermined condition is that at high illuminance, said high luminance component is larger than a first predetermined value and said shift amount is larger than a second predetermined value. Digital camera as described. 12. A digital camera for determining a focus position by moving a focus lens by a predetermined amount at a time, detecting means for detecting a minimum lens position at which a low luminance component of a camera signal is minimized, and detecting the minimum lens position. A digital camera, comprising: determining means for determining a focus position.