JP2003023568A - Exposure control device and exposure control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exposure control device and an exposure control method, capable of obtaining a target exposure amount in a short time and enabling exposure control with superior response performance, even when the quantity of incident light amount into an imaging device is large, and to provide a program capable of realizing the same. SOLUTION: The luminance detected from an photographing signal outputted from an imaging element is integrated by an integrator, and an exposure time or sensitivity of the imaging element is adjusted, so that the integrated value is a prescribed target control value. The target control value is set at 50% of the maximum integrated value which can be detected by an integrator. If the quantity of incident light is so large that an integrated value is at the maximum integrated value to become a saturated state during control, the target control value is changed from initial value (50%) to 25%. Thereafter, at the releasing of the saturated state, the target control value is changed back to the initial value (50%). Since an exposure control width is widened, when the integrated value is in a saturated state, this state is released in an early stage and the target exposure amount can be obtained in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure control device, an exposure control method, and a program capable of realizing the same.

[0002]

2. Description of the Related Art Conventionally, in various image pickup apparatuses such as digital cameras using image pickup elements such as CCDs, the exposure amount at the time of image pickup is controlled as follows, for example. FIG. 3 is a diagram showing a main part of a digital camera or the like, in which an image pickup signal output by the image pickup device 1 by photoelectric conversion is amplified by an AGC (automatic gain control) circuit 2 and is digital signal by an A / D converter 3. Is converted into a signal, and the signal processing circuit 4 performs various kinds of signal processing. Here, the exposure amount is controlled by adding brightness data corresponding to the incident light amount of the image sensor 1 output from the signal processing circuit 4 by the integrator 5 and sequentially detecting the exposure amount by the addition result (integral value). Based on the detection result, the control unit 6 including the CPU, ROM, RAM and other peripheral circuits is
Is performed by controlling the exposure time in the image sensor 1 corresponding to the shutter speed, and controlling the analog gain in the AGC circuit 2 corresponding to the sensitivity of the image sensor 1.

In the actual exposure control, a predetermined value (target value) such as 50% of the maximum integral value detectable by the integrator 5 is set as a control target, and the integrator 5 is set.
The exposure control value such as the exposure time and the analog gain is adjusted based on the ratio of the integral value to the target value so that the integral value of is the target value. For example, when the control is started immediately after the power is turned on, as shown in FIG.
When the integrated value of the first time is smaller than the target value (underexposure), the exposure control value is set to perform exposure next brighter, and conversely, as shown in FIG. When the integrated value is larger than the target value (overexposure), the exposure control value is set so that the next dark exposure is performed, so that the target exposure amount can be obtained.

[0004]

However, in the conventional exposure control described above, for example, as shown in FIG.
When the first control operation is performed, overexposure occurs, the amount of light incident on the image sensor is large, and the integrated value of the integrator 5 reaches three times the maximum integrated value. It becomes saturated. Therefore, the integrated value is determined to be the maximum integrated value at the time of detecting the exposure amount associated with the second control operation, and the integrated value does not saturate at the time of detecting the third exposure amount. The integrated value will finally converge to the target value at the time of the fourth detection. That is, when the integrated value of the integrator 5 becomes saturated at the beginning of exposure control or during the control,
There is a problem that the accurate exposure amount cannot be detected until the exposure control operation is repeated a plurality of times, and the time for the integrated value to converge to the target value, that is, the time until the control target exposure amount is obtained becomes long. there were.

The present invention has been made in view of the above-mentioned conventional problems, and it is possible to obtain a target exposure amount in a short time even when the amount of light incident on the image pickup device is large, and the exposure is highly responsive. It is an object of the present invention to provide a controllable exposure control device, an exposure control method, and a program capable of realizing the same.

[0006]

In order to solve the above-mentioned problems, according to the invention of claim 1, the exposure amount of the image pickup device is detected from the image pickup signal output from the image pickup device, and based on the detection result. In an exposure control device that controls the exposure amount of the image sensor to a predetermined control target, the exposure control by the exposure control in which the degree of decrease in the exposure amount is performed before the final control toward the control target is performed. The change means for changing the exposure control to be larger than the degree of decrease in the amount is provided.

In such a configuration, before the final control toward the control target is performed, the degree of decrease in the exposure amount becomes larger than the degree of decrease in the exposure amount due to the exposure control toward the control target. During the control, the saturated state in which the detected exposure amount exceeds the maximum value is eliminated early.

According to the invention of claim 2, the exposure amount of the image pickup device is detected from the image pickup signal output from the image pickup device, and the exposure amount of the image pickup device is set to a predetermined control target based on the detection result. In the exposure control apparatus that controls the control target, before the final control for the control target is performed, the exposure control device is provided with a changing unit that changes the control target to a smaller temporary control target.

In such a configuration, when the exposure is overexposed, the exposure control width before the exposure amount is finally controlled by the control target is widened, so that the exposure amount detected during the control is detected. The saturated state in which the value exceeds the maximum value is resolved early.

Further, in the invention of claim 3, the changing means changes the control target to the temporary control target when the detection result is equal to or more than the maximum detectable exposure amount. And

In such a configuration, the exposure control width is not unnecessarily widened before the exposure amount is finally controlled to the control target, and useless exposure control is prevented.

Further, in the invention of claim 4, the changing means changes the temporary control target to the control target when the detection result becomes less than the maximum detectable exposure amount. And

In such a configuration, the state in which the exposure control range is widened is not wastefully maintained before the exposure amount is finally controlled to the control target, and wasteful exposure control is prevented.

According to a fifth aspect of the invention, the exposure amount of the image pickup device is detected from the image pickup signal output from the image pickup device, and the exposure amount of the image pickup device is set to a predetermined control target based on the detection result. In the exposure control method of controlling the control target, the control target is changed to a tentative control target smaller than the control target before the final control toward the control target is performed.

According to this method, when the exposure is overexposed, the exposure control width before the exposure amount is finally controlled by the control target is expanded, so that the detected exposure is detected during the control. Saturation in which the quantity exceeds its maximum value is resolved early.

Further, in the invention of claim 6, the exposure amount of the image pickup device is detected from the image pickup signal output from the image pickup device, and the exposure amount of the image pickup device is set to a predetermined control target based on the detection result. A program for causing a computer of an exposure control device to control the control target to function as a changing unit for changing the control target to a tentative control target smaller than the control target before performing final control toward the control target. .

By using such a program, the present invention can be easily implemented in an exposure control device equipped with a computer.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. In the present embodiment, the RO that constitutes the control unit 6 in the configuration shown in FIG.
In M, a control program for causing the CPU to perform control relating to exposure control (exposure control) and functioning as a changing unit of the present invention, and two types of target values used when the control program is executed, that is, the first Parameters such as the target value (T1) and the second target value (T2) are stored. Where the first
The target value (T1) of is a control target of the present invention used with a final control target value in exposure control described later,
The second target value (T2) is a temporary control target value used in the exposure control described later and a temporary control target of the present invention, and in the present embodiment, the first target value (T1). Is the maximum integrated value 50 that can be detected by the integrator 5.
% Value is recorded and the second target value (T2)
The value of 25% of the maximum integrated value is recorded in.

The above control program and the two types of target values are not necessarily stored in the ROM, and may be, for example, a removable flash memory or the like of a digital camera which has a rewritable recording content. It may be recorded in another recording medium.

Next, the exposure control operation based on the control program by the control unit 6 will be described with reference to the flowchart of FIG.

The control unit 6 starts its operation when the power is turned on, and first sets an initial value to an exposure control value such as the exposure time of the image pickup device 1 and the analog gain of the AGC circuit 2, and the control target of the exposure amount (exposure amount). A first target value is set as the value (step S1). Thereafter, exposure is performed by the image sensor 1 (step S2), the integrated value is read from the integrator 5 (step S3), and it is determined whether the read integrated value is the first target value (T1) ( Step S
4) If the integrated value is not the first target value, it is further determined whether it is the maximum integrated value in the integrator 5 (step S5). At this time, if the integrated value is not the maximum integrated value (NO in step S5), the first target value is maintained as the control target value (step S6),
The exposure control value to be set next is calculated based on the ratio of the integrated value at that time to the control target value (step S7).
That is, the exposure control value to be set next is EN, the current exposure control value is E, the first target value (control target value at that time) is T1, and the current integrated value is I. E: I = EN The exposure control value to be set next is calculated from both equations: T1.EN = E.times.T1 / I. Then, the calculation result (EN) is set as a new exposure control value (step S8), and the process returns to step S2.

Here, when the first exposure control operation is performed, if the integrated value (I) read from the integrator 5 is underexposure smaller than the control target value (T1 in this case), it becomes brighter. By setting the exposure value as the exposure control value (EN) to be set next, the final control target value (T1) is obtained as the integrated value (I) at the time of the second exposure control. (See FIG. 4 (a)).
Further, at the time of performing the first exposure control operation, when the integral value (I) read from the integrator 5 is larger than the control target value (however, it is less than the maximum integral value) overexposure, a value for dark exposure Exposure control value (E
N) is set as the final control target value (T1) as the integrated value (I) at the time of the second exposure control.
Is obtained (see FIG. 4B). That is,
A target exposure amount can be obtained. The operation is the same as the conventional one. Also, after the target exposure amount is obtained (YES in step S4), the process returns to step S2.

On the other hand, when the integrated value read from the integrator 5 is equal to or larger than the maximum integrated value at the beginning of the exposure control, that is, during overexposure when the integrator 5 is in the saturated state (NO in step S4, step S5 in step S5). YES), after changing the control target value to the second target value that is a temporary control target value that is smaller than the first target value that is the initial value (final control target value) (step S9), then The exposure control value to be set to is calculated based on the ratio of the integrated value at that time to the control target value (step S10). That is, the exposure control value to be set next is EN, the current exposure control value is E, the second target value (control target value at that time) is T2, and the current integration value is I. E: I = EN The exposure control value to be set next is calculated from both equations: T2.EN = E.times.T2 / I. Then, the calculation result (EN) is set as a new exposure control value (step S11), and the process returns to step S2.

Here, the second target value (T2) is smaller than the first target value (1/2 in this embodiment).
2), the difference between the current exposure control value (E) and the calculation result (EN) in step S10 is larger than that when the first target value is set as the control target value, and The control value adjustment range, that is, the exposure amount control range is wide. Therefore, in the first exposure control operation, the value for dark exposure is set as the exposure control value (EN) to be set next, but the degree of decrease in the exposure control value at that time becomes large.

As a result, when the exposure amount in the image pickup device 1 reaches, for example, an amount corresponding to three times the maximum integral value of the integrator 5, as shown in FIG. The exposure amount is controlled so that the integrated value (I) is less than the maximum integrated value. Therefore, in that case, when the exposure is performed immediately after returning to step S2, the saturation state of the integrator 5 has already been resolved (step S2), and after the integrated value of the integrator 5 is read (step S3), the step Both the determination results of S4 and step S5 are NO, and after the control target value is returned to the first target value T1 (initial value) in step S6, the processes of step S7 and step S8 described above (second exposure control Operation) is performed. Therefore, 3
The final control target value (T1) can be obtained as the integral value (I) at the time of the second exposure control, that is, earlier than in the conventional case. Therefore, the target exposure amount can be obtained in a short time, and the exposure can be controlled with good responsiveness. As a result, a state in which shooting can be performed in a short time can be secured.

The operation described above is the same not only immediately after the power is turned on, but also during the subsequent exposure control. For example, after the target exposure amount is obtained, the light amount of the subject changes abruptly. Thus, even when the integrated value of the integrator 5 becomes saturated, the above-mentioned step S
The processing of 9 to S11 will be performed at any time.

Further, in the present embodiment, when the integrator 5 is in a saturated state in which the integral value read from the integrator 5 is equal to or larger than the maximum integral value during the exposure control (step S5 is YE).
S), the control target value is changed to the second target value. Therefore, before the final exposure amount is finally obtained, for example, the exposure control width does not unnecessarily widen during the second control operation, and it is possible to prevent the useless exposure control operation from being performed. Therefore, exposure control with better response can be performed.

In the present embodiment, the case where the second target value (T2) is set to 1/2 of the first target value (T1) has been described.
2) may be a value that satisfies at least the relationship of T2 <T1. Further, the second target value (T2) does not have to be a fixed value, and further, for example, when performing control to change the first target value (T1), the second target value (T1) of the first target value (T1) The second target value (T2) may be changed according to the change.

Further, in the present embodiment, when the integrated value read out from the integrator 5 becomes a saturated state equal to or larger than the maximum integrated value, the control target value is changed to the second target value to reduce the exposure amount. Although the exposure control value having a large degree is set, the exposure amount of the exposure amount is not changed when the control target value is changed and set, but when the integrated value read from the integrator 5 becomes a saturated state of the maximum integrated value or more. It is also possible to directly set a predetermined exposure control value having a large degree of decrease.

[0030]

As described above, according to the first aspect of the invention, before the final control toward the control target is performed, the degree of decrease in the exposure amount is determined by the exposure control toward the control target. When the control is performed, the saturation state in which the detected exposure amount exceeds the maximum value is eliminated early during the control. Therefore,
Even when the amount of light incident on the image sensor is large, it is possible to obtain a target exposure amount in a short time, and it is possible to perform exposure control with good responsiveness. it can.

According to the second and fifth aspects of the present invention, when the exposure is overexposed, the exposure control width before the exposure amount is finally controlled to the control target is widened, and the control is performed. In the middle of the process, the saturation state in which the detected exposure amount exceeds the maximum value is eliminated early. Therefore, even when the amount of light incident on the image sensor is large,
The target exposure amount can be obtained in a short time, and the exposure can be controlled with good response. As a result, it is possible to secure a state in which shooting can be performed in a short time.

According to the third aspect of the invention, the exposure control width does not unnecessarily widen before the exposure amount is finally controlled to the control target, and the useless exposure control is prevented. Therefore, more responsive exposure control is possible.

Further, according to the invention of claim 4, the state in which the exposure control width is widened is not wastefully maintained before the exposure amount is finally controlled to the control target, and wasteful exposure control is prevented. I was made to do it. This also enables more responsive exposure control.

According to the invention of claim 6, the present invention can be easily implemented in an exposure control device equipped with a computer.

[Brief description of drawings]

FIG. 1 is a flowchart showing an exposure control operation by a control unit showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing control contents at the time of overexposure in which a detected value of an exposure amount is saturated at the beginning of control in the same embodiment.

FIG. 3 is a block diagram showing a configuration of an exposure control device common to the embodiment and a conventional technique.

4A and 4B are explanatory diagrams showing the control contents at the time of exposure common to the embodiment and the conventional technique, FIG. 4A is an explanatory diagram showing the control contents at the time of underexposure, and FIG. It is explanatory drawing which shows the control content at the time.

FIG. 5 is an explanatory diagram showing the control content at the time of overexposure in which the detected value of the exposure amount is saturated at the beginning of control in the conventional technique.

[Explanation of symbols]

1 Image sensor 2 AGC circuit 3 A / D converter 4 Signal processing circuit 5 integrator 6 control unit 7 Timing generator

Claims (6)

[Claims] 1. An exposure control apparatus for detecting an exposure amount of an image pickup device from an image pickup signal output from the image pickup device and controlling the exposure amount of the image pickup device to a predetermined control target based on the detection result. Before performing the final control toward the target, a change means is provided for changing to an exposure control in which the degree of decrease in the exposure amount is larger than the degree of decrease in the exposure amount due to the exposure control toward the control target. Exposure control device. 2. An exposure control apparatus for detecting an exposure amount of an image pickup device from an image pickup signal output from the image pickup device and controlling the exposure amount of the image pickup device to a predetermined control target based on the detection result. An exposure control apparatus comprising: a changing unit that changes the control target to a smaller number of temporary control targets before performing final control toward the target. 3. The exposure according to claim 2, wherein the changing unit changes the control target to the temporary control target when the detection result is equal to or more than the maximum detectable exposure amount. Control device. 4. The changing means changes the temporary control target to the control target when the detection result becomes less than the maximum detectable exposure amount. Exposure control device. 5. An exposure control method for detecting an exposure amount of an image sensor from an image signal output from the image sensor and controlling the exposure amount of the image sensor to a predetermined control target based on the detection result. An exposure control method, characterized in that the control target is changed to a smaller number of temporary control targets before the final control toward the target is performed. 6. A computer included in an exposure control device, which detects an exposure amount of the image pickup device from an image pickup signal output from the image pickup device and controls the exposure amount of the image pickup device to a predetermined control target based on the detection result. A program for causing the control target to function as a changing unit that changes the control target to a smaller number of temporary control targets before performing final control toward the control target.