JP2003259199A - Camera signal processor and exposure range expanding method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform exposure control through which a dynamic range wider than a shutter range and an exposure control range by AGC can be obtained. <P>SOLUTION: In addition to the shutter range and the exposure control range by AGC, a low-luminance expansion control range and a high-luminance expansion control range are set. In the low-luminance expansion control range, the exposure control range is expanded by dividing a clock of a frame rate by 2 after increasing an AGC gain value to a specified value while maximizing a shutter accumulation time in a low-luminance area and gradually increasing the AGC gain value after lowering the AGC gain value by a specified value. In the high-luminance expansion control range, when the shutter accumulation time is minimum and the quantity of light is further suppressed, the exposure control range is expanded by halving the accumulation time by doubling the clock and gradually lowering the AGC gain value after increasing the AGC gain value by a specified time. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera signal processing apparatus having a function of varying a frame rate of an image signal output from an image pickup means and an exposure range expanding method thereof.

[0002]

2. Description of the Related Art Conventionally, in various camera systems using, for example, a CCD image sensor or a CMOS image sensor, an image pickup signal from the image sensor is input through an analog front end to determine the brightness of the image pickup signal. There is provided a camera signal processing device that controls exposure of an image sensor and the like. By the way, in the conventional camera system, the frame rate of the image pickup signal is generally fixed and controlled, and the exposure control can be performed only within the normal shutter range and AGC range. Therefore, if the image pickup signal has high brightness, it will be saturated beyond the shutter range, and if the image pickup signal has low brightness (low illuminance), there is no choice but to increase the gain amplifier, resulting in a noisy image. It was

FIG. 5 is an explanatory diagram showing the relationship between the dynamic range, the AGC amount, and the shutter accumulation time in the exposure control in the conventional method. FIG. 5A shows (a) AG.
AG in C control range and (b) shutter control range
The change in the C amount and the shutter accumulation time is shown in FIG.
7 shows a change in dynamic range due to a combined gain of GC control and shutter control. In this system, the shutter storage time is controlled to 44 dB, and the AGC amount is controlled to 3
Exposure control for 6 dB can be performed. Hereinafter, operations in the (a) AGC control range and the (b) shutter control range shown in FIG. 5 will be described.

(A) AGC control range The control by the AGC is mainly performed in the low luminance (low illuminance) region side, and the AGC gain value is increased when more light quantity is required when the shutter accumulation time is maximum. As a result, the signal amount is amplified. The AGC gain value is AGCMIN
From (minimum AGC gain value) to AGCMAX (AGC
Control within the range of maximum gain value). (B) Shutter control range The control by the shutter is mainly performed on the high brightness area side, and the signal amount is suppressed by shortening the shutter accumulation time when the light amount is too much. Shutter accumulation time is SHTM
Control is performed in the range from AX (maximum shutter accumulation time) to SHTMIN (minimum shutter accumulation time). Then, a combination of the gain amounts by such AGC control and shutter control becomes the dynamic range in the conventional method,
In this example, control is possible only up to the range of 36 dB + 44 dB = 80 dB.

[0005]

As described above, in the conventional system, since the frame rate of the image pickup signal is fixed and controlled, the exposure control can be performed only within the normal shutter range and AGC range. However, there was a problem that a sufficient dynamic range could not be obtained.

Therefore, an object of the present invention is to provide a camera signal processing apparatus and an exposure range expanding method capable of performing exposure control capable of obtaining a dynamic range exceeding a control range by a shutter range and AGC.

[0007]

In order to achieve the above object, the present invention is provided in a camera system having an image pickup means with a shutter function and a gain control means for performing gain control of an image pickup signal by the image pickup means. In a camera signal processing device for controlling exposure of a camera system by controlling a shutter period of the image pickup means and a gain amount of the gain control means, a frame rate switching means for switching a frame rate of image output, and a shutter in the image pickup means. There is an exposure control means for performing exposure control by controlling a time and a gain value in the gain control means, and the exposure control means controls the brightness range that cannot be controlled by a change in the shutter time and the gain value. Control by switching the frame rate by the frame rate switching means By Rukoto, characterized in that to extend the exposure range.

Further, the present invention is provided in a camera system having an image pickup means with a shutter function and a gain control means for performing gain control of an image pickup signal by the image pickup means,
In a method of expanding an exposure range of a camera signal processing apparatus for controlling exposure of a camera system by controlling a shutter period of the image pickup means and a gain amount of the gain control means, a shutter time in the image pickup means and a gain control means When exposure control is performed by controlling the gain value, the exposure range is expanded by switching the frame rate of image output to a brightness range that cannot be controlled by the change of the shutter time and the gain value.

In the camera signal processing apparatus of the present invention, the exposure range is expanded by controlling the frame rate switching means by switching the frame rate to a brightness range that cannot be controlled by the change of the shutter time and the gain value. It is possible to obtain a dynamic range beyond the control range of the shutter range and AGC. Further, in the exposure range extending method for the camera signal processing device of the present invention, the exposure range is controlled by controlling the frame rate switching by the frame rate switching means for the brightness range that cannot be controlled by the change of the shutter time and the gain value. Due to the expansion, it is possible to obtain a dynamic range that is more than the control range of the shutter range and AGC.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a camera signal processing apparatus and an exposure range expanding method thereof according to the present invention will be described below. The camera signal processing device according to the present embodiment controls the master clock frequency dividing circuit by the microcomputer and the extended control program in addition to the conventional shutter range and exposure control by AGC.
The frame rate of the image pickup signal is automatically changed to extend the dynamic range in exposure control.

That is, in the camera signal processing apparatus of this example, in addition to the conventional exposure control range by the shutter range and AGC, a low-luminance extension control range and a high-luminance extension control range are provided. In the low-brightness extended control range, the AGC is performed in the low-brightness region with the shutter accumulation time maximized.
The exposure control range is expanded by increasing the gain value to a predetermined value, dividing the frame rate clock by 1/2, decreasing the AGC gain value by a predetermined value, and then gradually increasing the AGC gain value. To do. In the high brightness extended control range,
In the high-brightness region, the shutter accumulation time is the minimum, and the accumulation time is halved by doubling the clock.
After increasing the AGC gain value by a predetermined value, the exposure control range is expanded by gradually decreasing the AGC gain value.

A specific example according to this embodiment will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a camera system provided with a camera signal processing device according to this embodiment. As shown, the camera system includes a CMOS image sensor 100, an analog front end (AFE) 200, and a camera signal processing circuit 300. CMOS image sensor 10
Reference numeral 0 is an example of an image pickup unit having an electronic shutter function for picking up an image of a subject. Analog front end (AFE) 20
Reference numeral 0 denotes a circuit that performs qualitative processing on the analog image pickup signal from the CMOS image sensor 100 in the preceding stage of the camera signal processing circuit 300. Particularly, in this example, the image pickup is performed based on the control from the camera signal processing circuit 300. Performs processing to adjust the analog gain value of the signal.

The camera signal processing circuit 300 performs various kinds of signal processing on the image pickup signal and outputs the image pickup signal to the pixel output section in the subsequent stage, and has a function of controlling the entire camera system according to the present embodiment. That is, the camera signal processing circuit 300 includes a master clock frequency divider 310, an image signal processing section 320A, and a brightness detecting section (OPD) 320B.
DSP (Digital Signal Processor) 320 including
A microcomputer 330, a RAM 340,
It has a ROM 350 and is connected to an external master clock generator 410 and a non-volatile memory 420.

The master clock divider 310 divides the master clock from the master clock generator 410 based on an instruction from the microcomputer 330, and divides the cycle of the master clock by ½ or 1 /.
4, 1/8, ... Divide twice. Image signal processing unit 320
A is for performing image processing such as primary color separation, white balance, and gamma correction. The brightness OPD 320B inputs the brightness signal from the image signal processing unit 320A and calculates the integrated value of the brightness signal for one frame. The microcomputer 330 controls the entire system, adjusts the shutter value and the AGC gain value according to the signal amount (OPD value) received from the brightness OPD 320B, the CMOS image sensor 100, and the AF.
The control signal is transferred to the E200.

The RAM 340 is the microcomputer 3
Reference numeral 30 provides a work area for processing various programs, and in this example, it is used to store variable data used in automatic exposure control. ROM350 is
It stores various programs for controlling the microcomputer 330 and fixed data. Particularly, in this example, initial values used for automatic exposure control and their control programs are stored. The master clock generator 410 generates a master clock which is the basis of various operations in this system. The non-volatile memory 420 stores data that should not be erased even when the power is turned off, and is composed of, for example, an EEPROM. Particularly, in this example, a parameter that is an expanded range of the dynamic range is stored.

Next, the exposure control of the camera system according to this embodiment will be described. FIG. 2 is an explanatory diagram showing the relationship between the dynamic range, the AGC amount, and the shutter accumulation time in the exposure control of this embodiment.
(A) AGC control range, (b) low luminance (low illuminance) extended control range, (c) shutter control range, and (d) high luminance extended control range AGC amount and shutter accumulation time change FIG. 5B shows the change in the dynamic range due to the combined gain of AGC control and shutter control. In this system, it is assumed that the entire system operates with a clock that is 1/4 times the master clock, and the master clock divider 310 can control the clock up to 1/16 times. Further, similarly to the above-mentioned conventional example (FIG. 5), by controlling the shutter accumulation time, 44 dB, AGC
Exposure control of 36 dB can be performed by controlling the amount.

(A) AGC control range The AGC control range of this example is similar to the operation of the AGC control range of the above-mentioned conventional example (FIG. 5A), but will be described later (b).
Even if the low-brightness extension control is performed, if a light amount larger than that is required, the signal amount is amplified by linearly increasing the AGC gain value. The AGC gain value is AGC
From MIN (minimum AGC gain value) to AGCMAX
Control is performed within the range of (maximum AGC gain value).

(B) Low-brightness extended control range This range is the AGC control range of the above-mentioned conventional example (see FIG. 5).
(A)) is extended, and in the low brightness region,
When the shutter accumulation time is maximum and more light quantity is required, the AGC gain value is increased in the same manner as the AGC control. Then, when the gain value reaches 6 dB, the clock is divided into 1/2, and the AGC gain value is lowered by 6 dB. As a result, the amount of signal is doubled by dividing the clock, but the amount of signal is halved due to the decrease in the gain value, so that the amount of signal does not change. That is, it is possible to extend the dynamic range of the low luminance area without using the AGC gain. In the example shown in FIG. 2, since the master clock can be controlled by the clock divider 310 up to 1/16 times, the clock can be divided twice, that is, 1/4 → 1/8 → 1/16, and thus 6 dB. The dynamic range on the low luminance side can be expanded to the range of x2 = 12 dB. The more detailed operation will be described later with reference to FIG.

(C) Shutter control range The shutter control range of this example is similar to the operation of the shutter control range of the above-mentioned conventional example (FIG. 5 (b)), and when there is too much light on the high brightness area side. The signal amount is suppressed by gradually shortening the shutter accumulation time. The shutter accumulation time is from SHTMAX (maximum shutter accumulation time) to SHTM
Control is performed in the range of IN (shutter accumulation time minimum).

(D) High-brightness extended control range This range is the shutter control range of the above-mentioned conventional example (see FIG. 5).
(B)) is extended, and in the high brightness area,
When the shutter accumulation time is the minimum and it is desired to further reduce the light amount, the accumulation time can be reduced to half by doubling the clock. Here, since the storage time is halved, the signal amount becomes 1/2 times that of the previous frame, which causes a difference from the signal amount of the previous frame. The difference increases the AGC gain value by 6 dB, Interpolation is performed by doubling the signal amount. After that, the AGC gain value used for the interpolation is reduced, and when it becomes the minimum value, the same operation is performed again to expand the dynamic range of the high luminance region.

In the example of FIG. 2, since the system clock is 1/4 times the master clock, 1/4 → 1/2 → 1/1
Since the clock can be doubled twice, the dynamic range on the high luminance side can be expanded to a range of 6 dB × 2 = 12 dB. Note that more detailed operations will be described later with reference to FIG. A combination of the above ranges (a) to (d) is the dynamic range according to the present embodiment, and in this example, 36 dB + 44 dB + 12 dB + 12 dB = 104.
It is possible to control up to the range of dB.

Next, the details of the low-brightness extended control range shown in FIG. 2B will be described. FIG. 3 is an explanatory diagram showing a dynamic range expansion method on the low brightness area side. (I) Exposure Control by Shutter Since a large amount of signal needs to be secured in the low brightness region, a larger amount of signal can be obtained by gradually increasing the shutter accumulation time. FIG. 3 (i) shows that the shutter accumulation time is gradually increased,
The shutter accumulation time is gradually increased to t1, t2, and t3 for each shutter start synchronization signal (V-Sync). (Ii) Exposure control by AGC When the shutter accumulation time is maximized and if a further signal amount is required, the AGC gain value is increased to obtain a larger signal amount. Figure 3 (i
i) shows that the AGC gain value is gradually increased, and the synchronization signal (V-Syn) for activating the shutter is shown.
The AGC gain value gradually increases to g1, g2, and g3 for each c).

(Iii) The clock is halved when the AGC gain value is 6 dB. In FIG. 3 (iii), the clock is halved when the AGC gain value is 6 dB. AGC gain value is 6d
The signal amount at the time of becoming B is twice the signal amount when the AGC gain is not applied. If the clock is halved and the AGC gain value is lowered by 6 dB,
Since the storage time is doubled by dividing the clock, the signal amount is twice that of the previous frame, but the signal amount is halved because the gain value is reduced by 6 dB. That is, AG
The signal amount is the same as that of the previous frame, which has used the C gain value of 6 dB, and a connection with no discomfort can be realized.

After that, when it is desired to secure a further signal amount, the dynamic range on the low luminance side can be expanded by repeating the processes of (ii) and (iii). Also, by operating in this way,
Since the dynamic range can be expanded with almost no use of the AGC gain, it is possible to suppress noise, which has been a problem in the conventional method. The extension range of the dynamic range in the low luminance region according to the method of this example is determined by the set value of the master clock frequency divider 310. Further, since this set value is stored in the non-volatile memory 420, the user can arbitrarily determine to what extent the low-brightness region is extended within the settable range of the master clock frequency divider 310. It can be designated by key input (not shown).

Next, the details of the high-brightness extended control range shown in FIG. 2D will be described. FIG. 4 is an explanatory diagram showing a dynamic range expansion method on the high brightness area side. The shutter speed is 1H at the fastest (horizontal synchronization period)
It is assumed that the system expires in time. (I) (ii) Exposure control by shutter As shown in FIGS. 4 (i) and (ii), the amount of light is too large in the high-luminance region of the shutter, so that the amount of signal is suppressed by gradually reducing the shutter accumulation time. Go. Then, the accumulation time becomes the minimum when the shutter is released at the time of 1H.

(Iii) Double the clock when the storage time is the minimum When the shutter storage time is the minimum (t0), if you want to further reduce the light quantity, double the clock to increase the storage time. Is half, the time for 1H is also halved, and the signal amount can be halved. However, if this is left as it is, there will be a difference from the signal amount of the previous frame, so the difference in the signal amount is interpolated with an AGC gain value of 6 dB and the signal amounts are made equal, so that there is no discomfort Has been realized.

After that, if it is desired to further suppress the signal amount, the AGC gain value used for interpolation is gradually reduced, and when the AGC gain value of 6 dB is exhausted, the process of (iii) is performed again. This makes it possible to extend the dynamic range on the high brightness side. The extension range of the dynamic range in the high-luminance region by this method is determined by the set value of the master clock frequency divider 310, similarly to the exposure control in the low-luminance region. Also,
Since this set value is stored in the non-volatile memory 420, the user arbitrarily inputs a key input (not shown) as to how high the brightness is to be expanded within the settable range of the master clock frequency divider 310. It is possible to specify by such as.

As described above, in the camera signal processing apparatus of this example, the master clock frequency divider 310 variably controls the frame rate to extend the dynamic range, and the illuminance range which cannot be controlled by the conventional method. It is possible to control the exposure. In particular, as a method of varying the frame rate, the clock frequency is multiplied by 2 (2 ⁰ ,
2 ^-1 , 2 ^-2 , 2 ^-3 , ...), the image format of the digital output (the leading bit position of the effective pixel, etc.) does not change.

The camera system in which the camera signal processing device according to the present invention is mounted is not limited to a system for a specific purpose, and various types from a digital camera for personal use to a high-end model for professional use. It is widely applicable to various forms. Further, the image pickup means is not limited to the above-mentioned CMOS image sensor, and may be, for example, a CCD.
An image sensor may be used. The present invention also includes an exposure range extension control program for performing the above-described processing, and further, a floppy disk or a CD storing this exposure range extension control program.
A storage medium such as a ROM is also included in the present invention.

[0030]

As described above, according to the camera signal processing apparatus of the present invention, the luminance range that cannot be controlled by the change of the shutter time and the gain value is controlled by the frame rate switching means for switching the frame rate. As a result, since the exposure range is expanded, it is possible to obtain a dynamic range that is more than the control range of the shutter range and AGC. Further, according to the exposure range extending method of the camera signal processing apparatus of the present invention, the exposure range is controlled by switching the frame rate by the frame rate switching means for the brightness range which cannot be controlled by the change of the shutter time and the gain value. Since the range is expanded, it is possible to obtain a dynamic range that is more than the control range of the shutter range and AGC.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a camera system provided with a camera signal processing device according to an embodiment.

2 is an explanatory diagram showing a relationship between a dynamic range, an AGC amount, and a shutter accumulation time in exposure control of the camera system shown in FIG.

FIG. 3 is an explanatory diagram showing a dynamic range extension method on the low luminance region side of the camera system shown in FIG.

FIG. 4 is an explanatory diagram showing a dynamic range extension method on the high luminance region side of the camera system shown in FIG.

FIG. 5 is an explanatory diagram showing a relationship between a dynamic range, an AGC amount, and a shutter accumulation time in exposure control in the conventional method.

[Explanation of symbols]

100 ... CMOS image sensor, 200 ... Analog front end (AFE), 300 ... Camera signal processing circuit, 310 ... Master clock divider, 320 ...
... DSP, 320A ... image signal processing unit, 320B ...
Luminance detector (OPD), 330 ... Microcomputer, 340 ... RAM, 350 ... ROM, 410 ...
Master clock generator 420: Non-volatile memory.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsumi Kato             134, Kobe-cho, Hodogaya-ku, Yokohama-shi, Kanagawa               Sony LSI Design Stock Association             In-house F-term (reference) 2H002 CC00 CC01 JA07 JA08 ZA02                       ZA03                 5C022 AB17 AB20 AC42 AC52 AC69                 5C024 AX01 CX43 CX54 DX04 GY31                       GZ32 HX18 HX58 HX59

Claims (13)

[Claims] 1. A camera system provided with an image pickup means having a shutter function and a gain control means for performing gain control of an image pickup signal by the image pickup means, wherein a shutter period of the image pickup means and a gain amount of the gain control means are set. In the camera signal processing device that controls the exposure of the camera system by controlling, by controlling the frame rate switching unit that switches the frame rate of the image output, the shutter time in the image capturing unit, and the gain value in the gain control unit. An exposure control unit for performing exposure control, wherein the exposure control unit controls a brightness range that cannot be controlled by a change in the shutter time and a gain value by controlling a frame rate by the frame rate switching unit. , Extend the exposure range, A camera signal processing apparatus according to. 2. The camera signal processing device according to claim 1, wherein the frame rate switching means is a frequency dividing circuit for dividing a master clock. 3. The camera signal processing apparatus according to claim 1, wherein the exposure control means is a microcomputer that executes an exposure range expansion control program. 4. The exposure control means reads out a frame rate switching value preset in a nonvolatile memory and causes the frame rate switching means to switch the frame rate.
The described camera signal processing device. 5. The camera signal processing apparatus according to claim 4, further comprising means for arbitrarily setting the switching value of the frame rate in the non-volatile memory. 6. The exposure control means, when performing the exposure control by switching the frame rate, interpolates the stepwise change of the exposure amount due to the switching of the frame rate by controlling the gain amount. Item 1. The camera signal processing device according to item 1. 7. A camera system provided with an image pickup means having a shutter function and a gain control means for performing gain control of an image pickup signal by the image pickup means, wherein a shutter period of the image pickup means and a gain amount of the gain control means are set. In the exposure range expanding method of the camera signal processing device for controlling the exposure of the camera system by controlling, when performing the exposure control by controlling the shutter time in the image pickup unit and the gain value in the gain control unit,
An exposure range expansion method for a camera signal processing device, wherein the exposure range is expanded by switching a frame rate of image output in a brightness range that cannot be controlled by a change in the shutter time and the gain value. 8. The method for expanding an exposure range of a camera signal processing apparatus according to claim 7, wherein the frame rate switching is performed by dividing a master clock. 9. The exposure range expansion method for a camera signal processing apparatus according to claim 7, wherein the exposure range expansion control program is executed by a microcomputer that executes the exposure range expansion control program. 10. The exposure range extending method for a camera signal processing apparatus according to claim 7, wherein a frame rate switching value set in advance in a non-volatile memory is read and the frame rate switching is executed. 11. The camera according to claim 7, wherein when the exposure control is performed by switching the frame rate, a stepwise change in the exposure amount due to the switching of the frame rate is interpolated by controlling the gain amount. A method for extending an exposure range of a signal processing device. 12. A camera system having an image pickup means with a shutter function and a gain control means for performing gain control of an image pickup signal by the image pickup means, wherein a shutter period of the image pickup means and a gain amount of the gain control means are controlled. Thereby, in the exposure range expansion control program executed by the computer that controls the exposure of the camera system, when the computer controls the shutter time in the image pickup unit and the gain value in the gain control unit to perform the exposure control, An exposure range expansion control program for executing a step of expanding an exposure range by switching a frame rate of image output to a brightness range that cannot be controlled by a change in the shutter time and the gain value. 13. A camera system having an image pickup means with a shutter function, and a gain control means for performing gain control of an image pickup signal by the image pickup means, wherein a shutter period of the image pickup means and a gain amount of the gain control means are controlled. Thus, in the computer-readable storage medium storing the exposure range extension control program executed by the computer that controls the exposure of the camera system, the computer controls the shutter time in the image pickup unit and the gain value in the gain control unit. When performing exposure control, an exposure range extension control program for executing the step of extending the exposure range by switching the frame rate of image output for a luminance range that cannot be controlled by the change of the shutter time and the gain value is stored. , A storage medium characterized by .