JP4558269B2 - Digital camera - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital camera that performs automatic focus (hereinafter referred to as AF) control using a so-called hill-climbing method, and more particularly to a digital camera that is suitable for photographing a high-luminance subject in a low-luminance image.
[0002]
[Prior art]
In recent years, passive AF control using a CCD has become common for digital cameras. The passive AF control has advantages such as a lower manufacturing cost of the apparatus than the active AF control.
[0003]
In addition, regardless of whether it is a passive type or an active type, it is generally desired that the AF control shortens the time required for focusing and the accuracy of focusing.
[0004]
A conventional digital camera (for example, Patent Document 1) for solving these problems will be described below. FIG. 4 is a block diagram showing a configuration of a conventional digital camera.
[0005]
In FIG. 4, a focus lens 1 focuses an image that is an input optical signal, and a CCD 2 converts an image input from the focus lens 1 from an optical signal to an electrical signal. The luminance signal generating means 3 generates a luminance signal based on the electrical signal generated by the CCD 2, and the lens driving means 4 is composed of a motor or the like, and the focus lens 1 is connected to the optical axis of the focus lens 1. It is driven in the direction (arrow A direction or B direction).
[0006]
The low frequency filter 5 is a filter for acquiring a spatial frequency component of a predetermined band as low frequency evaluation data from the luminance signal generated by the luminance signal generating unit 3, and the high frequency filter 6 is generated by the luminance signal generating unit 3. This is a filter that acquires, as high-frequency evaluation data, a spatial frequency component in which the average value of the band is shifted to the high-frequency side from low-frequency evaluation data acquired by the low-frequency filter 5 from the luminance signal.
[0007]
Here, the characteristics of the low frequency filter 5 and the high frequency filter 6 will be described with reference to FIG. FIG. 5 is a characteristic diagram showing amplitude characteristics of the low-frequency filter 5 and the high-frequency filter 6. In FIG. 5, the horizontal axis represents the spatial frequency of the luminance signal, and the vertical axis represents the amplitude characteristic of the filter. As is apparent from FIG. 5, the low frequency filter 5 transmits even the low frequency component of the luminance signal, whereas the high frequency filter 6 transmits only the high frequency component of the luminance signal.
[0008]
Further, the evaluation data transmitted through the low frequency filter 5 or the high frequency filter 6 changes with the position of the focus lens to form a locus shown in FIG. Here, FIG. 7 is a schematic diagram showing a trajectory of evaluation data that passes through the low frequency filter 5 or the high frequency filter 6 when an image of normal brightness is captured, and the horizontal axis is the position of the focus lens. The vertical axis shows the strength of the evaluation data.
[0009]
Next, the arithmetic processing means 57 comprises a microcomputer or the like, and first controls the lens driving means 4 based on the low frequency evaluation data generated by the low frequency filter 5, and then the high frequency generated by the high frequency filter 6. The autofocus operation is controlled by controlling the lens driving means 4 based on the evaluation data.
[0010]
The operation of the digital camera configured as described above will be described with reference to FIGS. FIG. 6 is a flowchart showing an autofocus operation of a conventional digital camera.
[0011]
When an image input to the focus lens 1 is converted into an electrical signal by the CCD 2 and imaging is started (S51), the luminance signal generating means 3 generates a luminance signal from the electrical signal generated by the CCD 2 ( S52). Next, the low-frequency filter 5 generates low-frequency evaluation data from the luminance signal, and the arithmetic processing unit 57 controls the lens driving unit 4 based on the low-frequency evaluation data. The lens 1 is moved in the direction of arrow A or B (S53). As a result of the above operation, when the arithmetic processing unit 57 can detect the focal point (S54), the process proceeds to step S55. On the other hand, when the arithmetic processing unit 57 cannot detect the focal point (S54), the process proceeds to step S58. Migrate to
[0012]
In step S55, the high frequency filter 6 generates high frequency evaluation data from the luminance signal, the arithmetic processing means 57 controls the lens driving means 4 based on the high frequency evaluation data, and the lens driving means 4 controls the focus lens 1 based on the control. Is moved in the direction of arrow A or B. As a result of the operation in step S55, when the arithmetic processing unit 57 can detect the in-focus point (S56), the operation shifts to an operation such as image compression conversion for image recording (S57). On the other hand, when the arithmetic processing unit 57 cannot detect the in-focus point (S56), it is determined that the in-focus state is impossible and the imaging is stopped (S58).
[0013]
Next, using the conventional digital camera having the configuration shown in FIG. 4 and the operation shown in FIG. 6, an image of normal brightness is obtained from the state where the focus lens 1 is at the position C0 in FIG. The operation when starting imaging will be described with reference to FIGS. Here, the normal brightness means the brightness in the outdoors during the daytime or indoors when the lighting is turned on, and means to exclude dark situations such as outdoors at night.
[0014]
The CCD 2 picks up an image of normal brightness with the focus lens 1 at the position C0 in FIG. 7 (S51), and the luminance signal generation means 3 generates a luminance signal (S52), and the low frequency filter 5 generates low frequency evaluation data from the luminance signal (S53). When the focus lens 1 is moved in the direction of arrow A or B in the vicinity of the position C0, the arithmetic processing unit 57 detects that the low-frequency evaluation data increases by moving the focus lens 1 in the direction of arrow A. it can. Therefore, the arithmetic processing means 57 controls the lens driving means 4 to drive the focus lens 1 in the direction of arrow A ((2) in FIG. 7). Thereafter, the arithmetic processing means 57 can detect the position of the focus lens 1 ((3) in FIG. 7) in which the low-frequency evaluation data does not change even when the focus lens 1 is moved in the arrow A direction (S54).
[0015]
Next, the arithmetic processing means 57 receives the high frequency evaluation data from the high frequency filter 6 and detects that the high frequency evaluation data increases when the focus lens 1 is moved in the arrow A direction. Therefore, the arithmetic processing means 57 controls the lens driving means 4 to drive the focus lens 1 in the direction of arrow A ((4) in FIG. 7). Thereafter, the arithmetic processing means 57 can detect C1 as the position of the focus lens 1 in which the high-frequency evaluation data does not change even when the focus lens 1 is moved in the arrow A direction (S56).
[0016]
As described above, since the conventional digital camera performs the autofocus operation based on the high frequency evaluation data after performing the autofocus operation based on the low frequency evaluation data, the focus lens 1 is somewhat out of focus position. Even in this case, since the inclination of the loci of the low-frequency evaluation data is large, the autofocus operation can be started immediately, and finally the autofocus operation is performed based on the high-frequency evaluation data. It is possible to image.
[0017]
If the autofocus operation based on the high frequency evaluation data is performed immediately after the start of imaging without performing the autofocus operation based on the low frequency evaluation data, the imaging is started from a state where the focus lens 1 is somewhat out of focus. Since the inclination of the high-frequency evaluation data at the position of the focus lens 1 is small, it is not known whether the focus lens 1 should be moved in the arrow A direction or the B direction. As a result, the autofocus operation takes a long time. It will be necessary.
[0018]
[Patent Document 1]
Japanese Patent Laid-Open No. 63-157578
[Problems to be solved by the invention]
However, the above-described conventional configuration is effective when capturing an image of normal brightness, but has a problem when capturing an image of a dark night scene or the like as a whole. Hereinafter, this problem will be described.
[0020]
Here, the case where the image 20 shown in the schematic diagram 8 is captured will be considered. The image 20 shows a night highway. In FIG. 8, reference numeral 21 denotes a road surface on which an automobile runs, 22 denotes an illumination pole that provides illumination for night driving, and 23 a and b denote high-intensity light sources such as fluorescent lamps and halogen lamps. Therefore, the image 20 is an image in which the vicinity of the high-intensity light sources 23a and 23b is bright and the other portions are dark.
[0021]
As shown in the schematic diagram 9, the evaluation data generated from the luminance signal of the image 20 generated by the luminance signal generating means 3 is dark on the entire screen, and therefore low-frequency noise such as smear due to the influence of the high-intensity light source. The low-frequency evaluation data and the high-frequency evaluation data have a smoother trajectory than when an image with normal brightness is captured. In particular, the low-frequency evaluation data is easily affected by low-frequency noise, and does not show a mountain shape and is almost flat. If the shape of the low-frequency evaluation data is flat, the arithmetic processing means 7 determines the in-focus position by increasing or decreasing the evaluation data. Therefore, if the focus lens 1 is moved in either the arrow A direction or the B direction in FIG. Cannot judge whether it is good. Therefore, the arithmetic processing means 7 determines that it is impossible to detect the focal point, or switches the evaluation data to the high-frequency evaluation data to detect the focal point.
[0022]
As a result, the conventional digital camera has a problem that it is determined that autofocus is not possible when an entire dark image such as the image 20 is captured, or a long time is required until focusing.
[0023]
FIG. 9 is a schematic diagram showing a trajectory of evaluation data transmitted through the low-frequency filter 5 or the high-frequency filter 6 when an image having a dark image and a partially bright object is captured. It is the position of the focus lens, and the vertical axis indicates the strength of the evaluation data.
[0024]
The present invention solves the above-described conventional problems, and an object of the present invention is to provide a digital camera that can quickly focus on a high-luminance subject in a captured image even when the entire captured image is dark.
[0025]
[Means for Solving the Problems]
In order to achieve this object, a digital camera of the present invention includes a focus lens that focuses an image that is an input optical signal, and an imaging that converts the image input from the focus lens from an optical signal to an electrical signal. Element, luminance signal generating means for generating a luminance signal based on an electrical signal generated by the imaging element, and obtaining a spatial frequency component of a predetermined band as low frequency evaluation data from the luminance signal generated by the luminance signal generating means The spatial frequency component in which the average value of the band is shifted to the high frequency side from the low frequency evaluation data acquired by the low frequency filter is acquired as the high frequency evaluation data from the low frequency filter to be generated and the luminance signal generated by the luminance signal generation means. a high frequency filter, a lens driving unit that drives the focus lens, Contact night view mode at the user's operation is set Not, and if even in the automatic mode is not determined that the photographing night scenes, the after controlling the lens driving means on the basis of the low-frequency evaluation data, controls the lens driving means on the basis of the frequency evaluation data However, when the night view mode is set by the user's operation or when it is determined that the night view is taken by the automatic mode, the lens driving unit is not controlled based on the low frequency evaluation data. And an arithmetic processing means for controlling the lens driving means based only on the high-frequency evaluation data.
[0026]
With this configuration, it is possible to automatically detect whether a captured image has normal brightness or a high-luminance subject and the entire captured image is dark based on the luminance signal. Furthermore, in the case where a high-brightness subject exists and the captured image is dark as a whole, a suitable auto-focus operation is performed on such an image, so even in such a case, the high-brightness subject can be focused quickly. it can.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
[0028]
(Embodiment)
FIG. 1 is a block diagram showing a configuration of a digital camera according to an embodiment of the present invention. In FIG. 1, the same reference numerals are given to the same components as those in the prior art, and the description thereof is omitted.
[0029]
The digital camera in the embodiment of the present invention is different from the conventional digital camera in that the arithmetic processing unit 57 of the conventional digital camera uses the lens driving unit 4 based on the low frequency evaluation data generated by the low frequency filter 5. In contrast to controlling the lens driving unit 4 based on the high frequency evaluation data generated by the high frequency filter 6 after that, the arithmetic processing unit 7 is based on the luminance signal generated by the luminance signal generating unit 7. One of the low-frequency evaluation data generated by the low-frequency filter 5 and the high-frequency evaluation data generated by the high-frequency filter 6 is selected, and the lens driving means 4 is selected based on the selected low-frequency evaluation data or high-frequency evaluation data. The point is to control.
[0030]
The buffer 8 stores the intensity of the luminance signal generated by the luminance signal generating means 3. More specifically, the captured image is divided into a plurality of evaluation blocks, and the intensity of the luminance signal is accumulated and stored for each evaluation block. The operation means 9 is composed of a mode dial or the like, and instructs the arithmetic processing means 7 to either the automatic mode or the night view mode by a user operation. The CCD 2 is an example of the image sensor of the present invention.
[0031]
The operation of the digital camera according to the embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a flowchart showing the operation of the digital camera according to the embodiment of the present invention.
[0032]
Imaging is started by the CCD 2 converting an image, which is an optical signal input from the focus lens 1, into an electrical signal (S 1), and the luminance signal generation unit 3 generates a luminance signal from the electrical signal generated by the CCD 2. The buffer 8 generates an average value of intensity of luminance signals in one evaluation block (hereinafter referred to as level y (n). N is 1, 2,... N,. Is stored for each evaluation block, and an average value (hereinafter referred to as level Y) of luminance signals of all screens is stored (S2). Next, when the operation means 9 has instructed the automatic mode (S3), the process proceeds to step S4, and when the operation means 9 has instructed the night view mode, the process proceeds to step S9.
[0033]
Next, in step S4, the arithmetic processing means 7 obtains the level Y and the level y (1) from the buffer 8, and if the level y (1) is equal to or greater than the predetermined magnification of the level Y, the process proceeds to step S9. If it is less than the predetermined magnification, the process proceeds to step S5. In step S5, the arithmetic processing means 7 determines whether or not the comparative evaluation between the level y (n) and the level Y has been performed for all the evaluation blocks, and when all the evaluation blocks are not evaluated, For the next evaluation block (S6), the evaluation in step S4 is performed. As a result, until it is determined in step S4 that there is an evaluation block whose level y (n) is equal to or higher than the predetermined magnification of level Y, the evaluation block is updated (S6) and the evaluation is continued in step S4. On the other hand, when all the evaluation blocks have been evaluated in step S4, but no evaluation block satisfies the determination criterion in step S4, the process proceeds to step S7.
[0034]
Next, in step S7, the low-frequency filter 5 generates low-frequency evaluation data from the luminance signal, and the arithmetic processing unit 7 controls the lens driving unit 4 based on the low-frequency evaluation data. The means 4 moves the focus lens 1 in the direction of arrow A or B. As a result of the above operation, when the arithmetic processing unit 7 can detect the focal point (S8), the process proceeds to step S9. On the other hand, when the arithmetic processing unit 7 cannot detect the focal point (S8), the process proceeds to step S12. Migrate to
[0035]
In step S9, the high frequency filter 6 generates high frequency evaluation data from the luminance signal, the arithmetic processing means 7 controls the lens driving means 4 based on the high frequency evaluation data, and the lens driving means 4 controls the focus lens 1 by the control. Is moved in the direction of arrow A or B. As a result of the operation in step S9, when the arithmetic processing means 7 can detect the in-focus point (S10), the operation shifts to an operation such as image compression conversion for image recording (S11). On the other hand, when the arithmetic processing means 7 cannot detect the in-focus point (S10), it is determined that the in-focus state is impossible and the imaging is stopped (S12).
[0036]
As a result of the above operation, when the user operates the operation unit 9 to set the night scene mode (S3), or when the arithmetic processing unit 7 determines that the night scene is captured from the intensity of the measured luminance signal If (Yes in S4), the AF operation (S9) based on the high frequency evaluation data is performed immediately without performing the AF operation (S7) based on the low frequency evaluation data.
[0037]
FIG. 1 shows the operation when the image 20 shown in the schematic diagram 8 is captured in the automatic mode using the digital camera according to the embodiment of the present invention having the configuration shown in FIG. 1 and performing the operation shown in FIG. 1 to 3, 8 and 9 will be described. FIG. 3 is a schematic diagram in which an evaluation block 24 and an AF evaluation frame 25 are added to the image shown in FIG.
[0038]
When imaging of the image 20 is started (S1), the luminance signal generation unit 3 generates a luminance signal, and the buffer 8 stores the intensity of the luminance signal (S2). At this time, as shown in FIG. 3, the image 20 is divided into a plurality of evaluation blocks 24, and the buffer 8 has a level y (n) (n = 1, 2,... For each evaluation block 24. • 144) is stored.
[0039]
Next, when it is determined whether or not the night view mode is set (S3), since it is the automatic mode, the process proceeds to step S4. Then, the arithmetic processing means 7 calculates the level Y, which is the average value of the luminance signal intensity of the entire screen of the imaging screen 20, and the evaluation block which is the 27th in the image 20 and the first in the AF evaluation frame 25. The level y (27) that is the average value of the intensity of the luminance signal is compared. Then, since there is no bright subject in this evaluation block, the level y (27) becomes less than the predetermined magnification of level Y, and the process proceeds to step 5. Next, the process proceeds to determination of the evaluation block which is the 28th in the image 20 and the second in the AF evaluation frame 25 (S4). Since this evaluation block also does not include a high brightness subject, the process proceeds to step 5. To do. Next, the process proceeds to the determination of the 29th evaluation block in the image 20 and the 3rd evaluation block in the AF evaluation frame 25 (S4). Then, since the image 20 is a dark image except for the vicinity of the high-intensity light sources 23a and 23b, the value of the level Y is small. On the other hand, since this evaluation block includes the high-intensity light source 23a, the level y (29) When the value y is large and the level y (29) is greater than or equal to the predetermined magnification of level Y, the arithmetic processing means 7 determines to proceed to step S9. That is, the arithmetic processing means 7 determines that the image 20 is an image including a high-luminance subject although it is dark as a whole.
[0040]
Thereafter, the arithmetic processing means 7 changes the position of the focus lens 1 from the state in which the position of the focus lens 1 is C0 ((1) in FIG. 9) ((2) in FIG. 9). Then, it is detected that the high-frequency evaluation data increases when the focus lens 1 is in the vicinity of C1, and it is determined that the in-focus point can be detected by moving the focus lens 1 in the arrow A direction. Thereafter, the arithmetic processing means 7 performs an AF operation based on the high-frequency evaluation data ((3) in FIG. 9), and detects C2 as a focal point (S10). As a result, an image focused on the high-intensity light sources 23a and 23b can be taken. Finally, an operation such as compression conversion is started for recording the image 20 (S11).
[0041]
As described above, if the user sets the automatic mode, the digital camera according to the embodiment of the present invention automatically determines that the image 20 is an image that is dark as a whole and has a partially bright subject. The AF control can be performed using the high-frequency evaluation data suitable for the image 20.
[0042]
Note that if the image 20 does not have a high-luminance subject such as the high-intensity light source 23, the image 20 has no bright place anywhere, and a spot to be focused cannot be found. . The same applies to the case where a conventional digital camera is used.
[0043]
Next, an operation in the case where a captured image with normal brightness is captured in the automatic mode using the digital camera according to the embodiment of the present invention will be described with reference to FIGS.
[0044]
When imaging of such an image with normal brightness is started (S1), the luminance signal generation unit 3 generates a luminance signal, and the buffer 8 stores the intensity of the luminance signal (S2). Next, when it is determined whether or not the night view mode is set (S3), since it is the automatic mode, the process proceeds to step S4. Then, the arithmetic processing means 7 calculates the level Y that is the average value of the luminance signal intensity of the entire screen of the captured image and the level y that is the average value of the luminance signal intensity of the first evaluation block in the AF evaluation frame. Compare. Then, since the captured image is uniformly bright as a whole, the level y becomes less than the predetermined magnification of level Y, and the process proceeds to the evaluation in step S4 regarding the next evaluation block (S6). Subsequently, as a result of performing the evaluation in step S4 while updating the evaluation block, the evaluation in step S4 is performed for all the evaluation blocks. However, since the captured image is uniformly bright as a whole, the level y is level Y. An evaluation block with a predetermined magnification or higher is not found (S5), and the process proceeds to an AF operation (S7) using low-frequency evaluation data.
[0045]
In step S7, the low frequency filter 5 generates low frequency evaluation data from the luminance signal, and the arithmetic processing unit 7 controls the lens driving unit 4 based on the low frequency evaluation data. Here, the low-frequency evaluation data generated by the low-frequency filter 5 has a mountain shape as shown in FIG.
[0046]
Next, when the focus lens 1 is moved in the direction of arrow A or B in the vicinity of the position C0, the arithmetic processing means 7 moves the focus lens 1 in the direction of arrow A to increase the low frequency evaluation data. Can be detected. Therefore, the arithmetic processing means 7 controls the lens driving means 4 to drive the focus lens 1 in the direction of arrow A ((2) in FIG. 7). Thereafter, the arithmetic processing means 7 can detect the position of the focus lens 1 ((3) in FIG. 7) where the low-frequency evaluation data does not change even when the focus lens 1 is moved in the direction of arrow A (S8).
[0047]
Next, the arithmetic processing means 7 receives the high frequency evaluation data from the high frequency filter 6 and detects that the high frequency evaluation data increases when the focus lens 1 is moved in the arrow A direction. Therefore, the arithmetic processing means 7 controls the lens driving means 4 to drive the focus lens 1 in the direction of arrow A ((4) in FIG. 7). Thereafter, the arithmetic processing means 7 can detect C1 as the in-focus position of the focus lens 1 in which the high-frequency evaluation data does not change even when the focus lens 1 is moved in the arrow A direction (S10).
[0048]
As described above, the digital camera according to the embodiment of the present invention can quickly focus on a captured image with normal brightness.
[0049]
As described above, according to the embodiment of the present invention, the digital camera according to the embodiment of the present invention is generated by the low frequency filter 5 based on the luminance signal generated by the luminance signal generating means 3. Since it has arithmetic processing means 7 for selecting either the low frequency evaluation data or the high frequency evaluation data generated by the high frequency filter 6 and controlling the lens driving means 4 based on the selected low frequency evaluation data or high frequency evaluation data. Therefore, it is possible to automatically detect that it is a night view, and it is possible to quickly focus on a high brightness subject even in the night view.
[0050]
In the embodiment of the present invention, the predetermined magnification is used in the determination in step S4 in FIG. 2, but specifically, it is about 3 times, for example. However, the magnification may be different from three times. If the magnification is lowered, the frequency when “Yes” is determined in step S4 increases, and if the magnification is increased, the frequency when “No” is determined increases.
[0051]
In the embodiment of the present invention, the entire captured image is divided into 12 × 12 144 and the evaluation in step S4 shown in FIG. 2 is performed for each evaluation block. However, the number of divisions is not limited to 144, and the division is performed. You can increase the number.
[0052]
【The invention's effect】
As described above, the present invention provides an excellent effect that a high-intensity subject in a captured image can be focused quickly even when the entire captured image is dark.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a digital camera according to Embodiment 1 of the present invention. FIG. 2 is a flowchart showing operation of the digital camera according to Embodiment 1. FIG. 3 adds an evaluation block and an AF evaluation frame. Fig. 4 is a block diagram showing the configuration of a conventional digital camera. Fig. 5 is a characteristic diagram showing the spatial frequency characteristics of the amplitude characteristics of a low-frequency filter and a high-frequency filter. FIG. 7 is a schematic diagram showing high-frequency evaluation data and low-frequency evaluation data when an image of normal brightness is captured. FIG. 8 is a schematic diagram showing an image that is dark overall and has a high-luminance subject. 9] Schematic diagram showing high-frequency evaluation data and low-frequency evaluation data when an image having a high-luminance object that is dark overall is captured.
1 Focus lens 2 CCD
3 Luminance signal generating means 4 Lens driving means 5 Low frequency filter 6 High frequency filter 7 Arithmetic processing means 8 Buffer 9 Operating means

Claims (1)

A focus lens that focuses the image that is the input optical signal;
An image sensor for converting an image input from the focus lens from an optical signal to an electrical signal;
A luminance signal generating means for generating a luminance signal based on an electrical signal generated by the image sensor;
A low frequency filter for obtaining a spatial frequency component of a predetermined band as low frequency evaluation data from the luminance signal generated by the luminance signal generating means;
A high-frequency filter that acquires, as high-frequency evaluation data, a spatial frequency component in which the average value of the band is shifted to the high-frequency side from the low-frequency evaluation data acquired by the low-frequency filter from the luminance signal generated by the luminance signal generation unit;
Lens driving means for driving the focus lens;
When the night view mode is not set by the user's operation and it is not determined that the night view is taken even in the automatic mode, the high frequency is controlled after controlling the lens driving means based on the low frequency evaluation data. When the lens driving means is controlled based on the evaluation data and the night view mode is set by the user's operation, or when it is determined that the night view is shot in the automatic mode , the low frequency evaluation data is used to A digital camera comprising: arithmetic processing means for controlling the lens driving means based only on the high-frequency evaluation data without controlling the lens driving means.

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