JP2005012397A - Imaging apparatus and control method of its image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus which can certainly stabilize the quality of an image acquired by an imaging operation during zoom operation, and to provide a control method of its image. <P>SOLUTION: The imaging apparatus latches the control target value of exposure control or white balance control calculated by a target value calculation unit 32 based on an imaged image to a latch register 33. A frame synchronizing signal is frequency divided by a frequency divider 34 to 1/N frequency division by a predetermined frequency demultiplying number N in response to a zoom state signal indicating the moving speed of a zoom lens, and output to the latch register 33. A control target value calculated and latched at each frame is outputted at each N frame as a control output, and the controlling frequency of the exposure control or the white balance control during the zoom operation is reduced in response to the zoom speed. The follow-up properties of the control during the zoom operation are delayed rather than that during the zoom stopping, and hence the stability of the control during the zoom operation is secured. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image pickup apparatus such as a digital camera having a zoom function, and an image control method suitable for use in an image pickup apparatus having a zoom function.
[0002]
[Prior art]
Conventionally, in an imaging apparatus such as a digital camera or a digital video camera, automatic exposure control (AE) and auto white balance control (AWB) are generally performed. These controls are generally feedback control that acquires a brightness component and a color component from a captured image and controls the amount of the brightness component and the ratio of the color component of the next image to be captured based on the brightness component and the color component.
[0003]
At present, many digital cameras and the like have a zoom function. However, for example, the drive control of a zoom lens, and automatic exposure control and auto white balance control are generally performed independently. is there.
[0004]
Therefore, in a digital camera equipped with a zoom function, the zoom lens is driven from the tele side to the wide side or from the wide side to the tele side during zoom operation, that is, while the angle of view continuously changes, If an image that affects exposure or white balance is included in the image, the automatic exposure control and auto white balance control will become unstable due to frequent changes in the brightness and color components of the sequentially captured image. There was a possibility.
[0005]
On the other hand, as a related technology, when the zoom lens position is wide, the white balance adjustment interval is shortened. When the zoom lens position is tele, the white balance adjustment interval is lengthened to adjust the white balance according to the zoom magnification. The method of performing is described in Patent Document 1 below.
[0006]
[Patent Document 1]
JP-A-4-245888
[Problems to be solved by the invention]
However, although the above method can satisfactorily perform white balance adjustment at a certain zoom magnification, stability cannot be ensured in auto white balance control during zoom operation. That is, the quality of an image captured during the zoom operation cannot be reliably stabilized.
[0008]
The present invention has been made in view of such a conventional problem, and provides an imaging apparatus capable of reliably stabilizing the quality of an image acquired by an imaging operation during a zoom operation, and an image control method thereof. With the goal.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, in the invention of claim 1, in an imaging apparatus having a zoom function, image control means for performing feedback control on an image to be captured based on a predetermined image component included in the captured image; Detecting means for detecting the operation state of the zoom function, and when the detecting means detects that the zoom operation is being performed, the tracking speed of the feedback control for the image captured by the image control means is being stopped. And delay means for delaying the time.
[0010]
In such a configuration, during zoom operation, the follow-up speed of feedback control with respect to the image to be captured becomes slower than that during stop of the zoom operation, so that a change in the angle of view during zoom operation causes a predetermined amount in the captured image. Even if the image component frequently changes, stable feedback control is performed.
[0011]
In the invention according to claim 2, the delay means delays the follow-up speed in accordance with a change speed of the angle of view during the zoom operation.
[0012]
In such a configuration, even when the change speed of the angle of view fluctuates during the zoom operation, the degree of feedback control delay at that time is appropriate.
[0013]
According to a third aspect of the present invention, the delay means delays the follow-up speed during the zoom operation more than when the zoom operation is stopped by reducing the operation frequency of the feedback control in the image control means. did.
[0014]
Even in such a configuration, stable feedback control is performed even if a predetermined image component frequently changes in the captured image as the angle of view changes during the zoom operation.
[0015]
According to a fourth aspect of the present invention, the delay unit delays the follow-up speed during the zoom operation compared to when the zoom operation is stopped by reducing the amount of control performed once by the image control unit. did.
[0016]
Even in such a configuration, stable feedback control is performed even if a predetermined image component frequently changes in the captured image as the angle of view changes during the zoom operation.
[0017]
In the invention of claim 5, the delay means gives a hysteresis to a control amount by the image control means.
[0018]
In such a configuration, the control amount at the time of feedback control during the zoom operation is more appropriate.
[0019]
In the invention of claim 6, the image control means includes an exposure control means for controlling exposure based on a brightness component of a captured image.
[0020]
In such a configuration, stable exposure control is performed even if the brightness component frequently changes in the captured image as the angle of view changes during the zoom operation.
[0021]
In the invention of claim 7, the image control means includes white balance control means for controlling white balance based on a color component of a captured image.
[0022]
In such a configuration, stable white balance control is performed even if the color component frequently changes in the captured image as the angle of view changes during the zoom operation. According to an eighth aspect of the present invention, there is provided an image control method for an image pickup apparatus having a zoom function, wherein feedback control is performed on an image to be picked up based on a predetermined image component included in the picked-up image, and zoom is performed. During the operation, the feedback control follow-up speed is made slower than when the zoom operation is stopped.
[0023]
According to this method, stable feedback control is performed even if a predetermined image component frequently changes in a captured image as the angle of view changes during the zoom operation.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram showing an electrical configuration of a digital camera according to the present invention. In this digital camera, a subject image is imaged through a lens 1, a zoom lens 2, and a diaphragm 3 on a photosensitive portion provided with a color filter with a Bayer arrangement of a CCD 4.
The CCD 4 is driven by a TG (Timing Generator) 20 and outputs a signal corresponding to the accumulated charge level of each pixel. This signal is sampled by a CDS (Correlated Double Sampling) circuit 5 using a signal synchronized with the timing from the TG 20 that drives the CCD 4, input to an AGC (Auto Gain Control) amplifier 6, and multiplied by a predetermined gain. The AD converter 7 converts it into digital data, for example, with 10 bits. This digital data is clamped to a predetermined black level by the digital clamp circuit 8 and stored as Bayer pixel data in the memory 10 (DRAM or the like) by DMA transfer via the memory bus interface 9.
[0025]
When the amount of pixel data on the memory 10 becomes usable in an image processing block unit (for example, 8 × 8 pixel unit) or more, DMA transfer is started, and the pixel data is transferred from the memory 10 via the memory bus interface 9 to the Bayer input buffer 11. Are transferred in units of image processing blocks. The pixel data for each image processing block is set with white balance (WB) by the RGB weighting unit 12 and then multiplied by a coefficient of a predetermined gamma correction curve by the gamma correction processing unit 13 to obtain a Y (luminance signal) generation unit 14, C A luminance signal Y and a color signal C are generated by each process of the (color signal) generation unit 15. Thereafter, various image processing processes (edge enhancement, color tone adjustment, etc.) are performed by the image processing processing unit 16 and stored in the memory 10 via the memory bus interface 9. At the same time, the luminance signal Y and the color signal C stored in the memory 10 are displayed on the display device 18 via the display data processing unit 17 controlled by the system control device 24.
[0026]
The system control device 24 includes a CPU, a ROM, and a RAM. The system control device 24 is operated by a program stored in the ROM, and controls the entire system while detecting the state of the key input device 23 operated by the user. When the state of the zoom operation is detected from the key input device 23, the system control device 24 controls the zoom drive unit 25 according to the moving direction (tele side or wide side) and the moving amount, and the zoom lens 2 is moved. The angle of view of the subject is changed by moving it. At this time, the zoom drive unit 25 is detection means of the present invention, and detects the moving speed of the zoom lens 2 in accordance with the zoom operation, that is, the zoom speed, and uses it as a zoom state signal and the AE control processing unit 19 and the AWB control processing. Output to the unit 22.
[0027]
On the other hand, the luminance signal Y output from the Y generation unit 14 described above is input to the AE control processing unit 19. The AE control processing unit 19 is an exposure control unit (image control unit) according to the present invention, and sends a control signal corresponding to the level of the input luminance signal Y to the aperture driving unit 21, the TG 20, and the AGC amplifier 6, respectively, and the subject image. If the aperture is dark, the aperture 3 is opened, and the exposure time of the CCD 4 is increased as much as possible. Further, if a sufficient output image level (integration level of the low-frequency luminance signal) cannot be obtained even in this state, the AGC amplifier Automatic exposure control (AE) for increasing the gain of 6 is performed. The color signal C output from the C generation unit 15 is input to the AWB control processing unit 22. The AWB control processing unit 22 is a white balance control unit (image control unit) according to the present invention, which sends a control signal corresponding to the color signal C to the RGB weighting unit 12 and performs auto white by adjusting (weighting) each component of RGB. Balance control (AWB) is performed.
[0028]
FIG. 2 is a diagram showing a circuit configuration of a part common to the AE control processing unit 19 and the AWB control processing unit 22, and both the processing units 19 and 22 are respectively an evaluation value extraction unit 31 and a target value calculation. 32, a latch register 33, and a frequency divider 34. The frequency divider 34 is synchronized with an image frame sent from the TG 20 that drives the CCD 4, and sent from the zoom drive unit 25. The zoom state signal (zoom speed) is input. In this embodiment, the latch register 33 and the frequency divider 34 function as delay means of the present invention.
[0029]
In the AE control processing unit 19 and the AWB control processing unit 22, the evaluation value extraction unit 31 performs evaluation values (components that reflect brightness in AE) from an image component input (luminance signal Y in AE and color signal C in AWB), In AWB, a component that reflects color deviation) is extracted, and based on this, a target value calculation unit 32 calculates a control target value (the aperture value, exposure time, and AGC gain in AE, and the RGB gain in AWB). The The calculated control target value is latched in the latch register 33, and is output to each unit described above every time a frame synchronization signal is input via the frequency divider 34. Accordingly, the above-described automatic exposure control and auto white balance control are performed, and the brightness and hue of the monitor image displayed on the display device 18 are automatically adjusted.
[0030]
On the other hand, the frequency divider 34 divides the frame synchronization signal by 1 / N at a predetermined frequency N in accordance with the zoom state signal, outputs it to the latch register 33, and controls the above-described control temporarily stored in the latch register 33. Control output of target value. In the present embodiment, the relationship between the zoom speed and frequency division number N in the frequency divider 34 is “1” when the zoom speed is zero, that is, when the zoom is stopped, and thereafter “2” to “ "5" is set to change in 5 steps.
[0031]
Thus, while zooming is stopped, control of AE and AWB is performed for each frame, while during zoom operation, the control interval is extended in frame units, and the control interval becomes longer in proportion to the zoom speed. . That is, thinning control is performed to reduce the control frequency during feedback control in proportion to the zoom speed.
[0032]
Therefore, since the tracking of AE and AWB with respect to changes in the subject is slow during zoom operation, even if the brightness and color components in the frame change frequently during zoom operation, stable automatic exposure is not affected by the change. Control and stable auto white balance control are performed. As a result, even during the zoom operation, the brightness and hue of the monitor image displayed on the display device 18 can be reliably controlled to be in a favorable state, and the brightness and hue of the monitor image are not satisfactory during the zoom operation. Natural fluctuations can be prevented.
[0033]
In this embodiment, the above-described thinning control is performed for both the automatic exposure control and the auto white balance control. However, the thinning control is performed for one of the controls, and the control for each frame is performed for the other control. It does not matter even if it is made to do.
[0034]
Further, the relationship between the zoom speed and the number of frequency divisions N in the frequency divider 34, that is, the control frequency may be set to a control frequency other than those described above, and further, these may be set by automatic exposure control and auto white balance control. You may make it differ.
[0035]
(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the present embodiment, in the digital camera shown in FIG. 1, the AE control processing unit 19 and the AWB control processing unit 22 have the common circuit configuration shown in FIG.
[0036]
That is, in the present embodiment, unlike the first embodiment, the first to third latch registers 41 to 43 are connected in series at the subsequent stage of the target value calculation unit 32, and their outputs are the first ones. The first to third reducers 44 to 46 are input to the adder 47, added there, and then output to the above-described units. The first to third latch registers 41 to 43, The delay means of the present invention is realized by the first to third reducers 44 to 46 and the adder 47.
[0037]
In the present embodiment, when the frame synchronization signal described above is input to each of the first to third latch registers 41 to 43, the target value calculation unit 32 calculates the first latch register 41. The current control target value (the control target value in the current frame) is output, the previous control target value is output from the second latch register 42, and the previous control target value is output from the third latch register 43. Each control target value is individually input to the first to third reducers 44 to 46. In the first to third reducers 44 to 46, the reduction magnifications different from each other according to the zoom state signal described above are individually multiplied, and the respective control target values after reduction are added in the adder 47, and after the addition, The value is output as an expenditure control target value.
[0038]
That is, the control target values in the current frame and the past two frames are respectively E (t), E (t-1), and E (t-2).
And the reduction ratios for these are K0, K1, and K2, respectively.
Then,
Control output = K0 * E (t) + K1 * E (t-1) + K2 * E (t-2)
Thus, damping is applied to the control target value in the current frame using the control target value in the past frame.
[0039]
In the present embodiment, the relationship between the zoom speed and the reduction magnification in the first to third reducers (multipliers) 44 to 46 is as follows.
When the zoom speed is zero, that is, when the zoom is stopped,
(K0, K1, K2) = (1, 0, 0)
After that, depending on the zoom speed,
(K0, K1, K2) = (0.8, 0.15, 0.05)
(K0, K1, K2) = (0.7, 0.2, 0.1)
(K0, K1, K2) = (0.6, 0.27, 0.13)
(K0, K1, K2) = (0.5, 0.2, 0.1)
It is set to change in five stages.
[0040]
Thus, during zoom stop, normal control by AE and AWB is performed, while during zoom operation, the degree of change in control is reduced in proportion to the zoom speed, and there is hysteresis in the reduction degree. Damping control is performed. That is, during the zoom operation, the amount of control during one control operation is reduced, so that the tracking of the AE and AWB with respect to changes in the subject is delayed.
[0041]
Therefore, during zoom operation, as in the first embodiment, even if the brightness and color components in the frame change frequently, stable automatic exposure control and stable auto white balance control are not affected by the change. Is done. As a result, even during the zoom operation, the brightness and hue of the monitor image displayed on the display device 18 can be reliably controlled to be in a favorable state, and the brightness and hue of the monitor image are not satisfactory during the zoom operation. Natural fluctuations can be prevented.
[0042]
In this embodiment, the above-described damping control is performed for both the automatic exposure control and the auto white balance control. However, the damping control is performed for one of the controls, and the control without damping is performed for the other control. It does not matter even if it is made to do.
[0043]
Further, the relationship between the zoom speed and the reduction magnification in the first to third multipliers 44 to 46, that is, the degree of reduction of the control amount and the strength of the hysteresis may be set to a degree other than those described above. These may be made different between automatic exposure control and auto white balance control.
[0044]
Further, in the present embodiment, during damping control during zoom operation, the control target value of the previous time and the previous time is reflected (having hysteresis) in the control amount at that time. Only the control target value may be reflected. In that case, the third latch register 43 and the third reducer 46 described above may be eliminated. Furthermore, the control amount may be reduced according to the zoom speed without giving hysteresis. In that case, the second and third latch registers 42 and 43, the second and third reducers 45 and 46, and the adder 47 may be eliminated. Even in such a case, it is possible to prevent frequent changes in brightness and hue of the monitor image displayed on the display device 18 during the zoom operation. However, as in this embodiment, reflecting the control target value for a certain period in the past in the control amount at that time increases the control amount for the automatic exposure control and auto white balance control at that time during the zoom operation. Since it can be made appropriate, the stability of control according to the change speed of the angle of view during the zoom operation can be further ensured.
[0045]
In addition to the embodiment described above, with regard to automatic exposure control and auto white balance control during zoom operation, the thinning control described in the first embodiment is adopted for one control, and the other control is used. You may make it employ | adopt the damping control demonstrated in 2nd Embodiment. Even in this case, the details of each control can be changed as appropriate as described above.
[0046]
Further, although the digital camera provided with the optical zoom capable of adjusting the angle of view by moving the zoom lens 2 has been described, the present invention is a zoom function realized by cutting out pixels on the CCD 4 or the memory 10, that is, a so-called so-called zoom function. The present invention can also be applied to a digital camera equipped with a digital (electronic) zoom, and even in that case, thinning control and damping control similar to the first or second embodiment for automatic exposure control and auto white balance control during zoom operation By adopting, it is possible to obtain the same effect as that of the above-described embodiment.
[0047]
In addition, although automatic exposure control and auto white balance control have been shown as examples of feedback control for an image to be captured, feedback to the next image to be captured based on a predetermined image component included in the captured image is also possible. In the control, the follow-up speed of the feedback control may be delayed during the zoom operation than during the zoom stop. Even in such a case, since the stability of the control operation can be ensured during the zoom operation, the image quality corresponding to the control content during the zoom operation can be stabilized.
[0048]
Furthermore, the present invention is not limited to a digital camera and can be applied to other imaging devices such as a digital video camera as long as it has a zoom function.
[0049]
【The invention's effect】
As described above, according to the first, third, fourth, and eighth aspects of the present invention, even when a predetermined image component frequently changes in a captured image due to a change in the angle of view during the zoom operation, stable feedback is achieved. Control was done. Therefore, the quality of the image acquired by the imaging operation during the zoom operation can be stabilized.
[0050]
Further, in the invention of claim 2, even when the change speed of the angle of view fluctuates during the zoom operation, the feedback control delay time at that time is appropriate. Therefore, the quality of the image acquired by the imaging operation during the zoom operation can be stabilized more reliably.
[0051]
In the invention of claim 5, when the feedback control follow-up speed during the zoom operation is delayed by reducing the control amount of the feedback control for the image to be picked up once, at the time of the feedback control at that time during the zoom operation The control amount was made more appropriate. Therefore, the quality of the image acquired by the imaging operation during the zoom operation can be more reliably stabilized.
[0052]
According to the sixth aspect of the present invention, stable exposure control is performed even if the brightness component frequently changes in the captured image as the angle of view changes during the zoom operation. Therefore, it is possible to stably control the brightness of the image acquired by the imaging operation during the zoom operation.
[0053]
According to the invention of claim 7, stable white balance control is performed even if the color component frequently changes in the captured image as the angle of view changes during the zoom operation. . Therefore, it is possible to stably control the hue of the image acquired by the imaging operation during the zoom operation.
[Brief description of the drawings]
FIG. 1 is a block diagram of a digital camera showing embodiments of the present invention.
FIG. 2 is a block diagram showing a circuit configuration common to an AE control processing unit and an AWB control processing unit in the first embodiment.
FIG. 3 is a block diagram showing a circuit configuration common to an AE control processing unit and an AWB control processing unit in the second embodiment.
[Explanation of symbols]
2 Zoom lens 4 CCD
19 AE control processing unit 22 AWB control processing unit 25 Zoom drive unit 31 Evaluation value extraction unit 32 Target value calculation unit 33 Latch register 34 Frequency dividers 41 to 43 First to third latch registers 44 to 46 First to third Reducer 47 Adder

Claims (8)

In an imaging device having a zoom function,
Image control means for performing feedback control on an image captured based on a predetermined image component included in the captured image;
Detection means for detecting the operating state of the zoom function;
A delay means for delaying a follow-up speed of feedback control for an image picked up by the image control means when the detection means detects that the zoom operation is being performed, compared to when the zoom operation is stopped; An imaging device. The imaging apparatus according to claim 1, wherein the delay unit delays the follow-up speed according to a change speed of a field angle during a zoom operation. 3. The imaging apparatus according to claim 1, wherein the delay unit delays the follow-up speed during the zoom operation than when the zoom operation is stopped by reducing an operation frequency of feedback control in the image control unit. . 3. The imaging apparatus according to claim 1, wherein the delay unit delays the follow-up speed during the zoom operation more than when the zoom operation is stopped by reducing a control amount of one time by the image control unit. . The imaging apparatus according to claim 4, wherein the delay unit gives hysteresis to a control amount by the image control unit. The imaging apparatus according to claim 1, wherein the image control unit includes an exposure control unit that controls exposure based on a brightness component of a captured image. The imaging apparatus according to claim 1, wherein the image control unit includes a white balance control unit that controls white balance based on a color component of a captured image. An image control method in an imaging apparatus having a zoom function,
An image control method, wherein feedback control is performed on an image to be captured based on a predetermined image component included in the captured image, and the follow-up speed of feedback control is delayed during zoom operation than when zoom operation is stopped.

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