JP2002094879A - Exposure control device of digital camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exposure control device of a digital camera which can realize rapidly optimum exposure control with simple constitution, without changing the gradation feature. SOLUTION: An output signal of an imaging element 3 is divided into m×n. A target window and a desired value are obtained from the luminance distribution of an object and luminance signal data of each of the regions of the whole image, a large window of the central image and a small window of the central image. The luminance level of the target window is controlled to be equal to the desired value by an exposure control means with an electronic shutter of the imaging element 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital camera equipped with an automatic exposure device for automatically controlling an image of a subject to be photographed to an optimum exposure.

[0002]

2. Description of the Related Art Conventionally, an automatic exposure control device is provided in a video camera, a digital camera, and the like in order to obtain an optimum exposure level according to a subject image to be photographed. In a video camera, for example, a method of performing exposure control by keeping the average value level of a video signal in one field constant is used. Further, a proposal has been made to input a luminance distribution in an imaging screen to a neural network unit, and to correct backlight or excessive forward light based on the output. However, these circuits have a large circuit scale, and it is necessary to change the gradation characteristics by the output from the neural network unit.

[0003]

Generally, in such a system, it is possible to obtain optimum exposure control with considerable accuracy. However, there is a problem in that changing the gradation characteristic by the output of the neural network circuit requires a large circuit scale and complicated control. Also, it is not suitable for a digital camera that captures a still image because it is necessary to shorten the processing time until shooting. SUMMARY OF THE INVENTION It is an object of the present invention to provide an exposure control device for a digital camera that can realize optimal exposure control at high speed with a simple configuration without changing the gradation characteristic.

[0004]

In order to achieve the above object, according to the first aspect of the present invention, a captured image is divided into m × n to obtain m × n luminance signal data. Means for calculating luminance signal data of a large window and a small window at the entire screen and the center from the m × n luminance signal data, and means for determining a distribution pattern of the m × n luminance signal data. In a digital camera with
Means for comparing the distribution pattern of the m × n pieces of luminance signal data with the luminance signal data of the large window and the small window at the center of the entire screen and calculating a target value that provides an optimal exposure level; And means for controlling the exposure so that the luminance data of the exposure data coincide with each other.

According to a second aspect of the present invention, there is provided a means for dividing a taken image into m × n to obtain m × n luminance signal data, In a digital camera having means for calculating luminance signal data of a large window and a small window, and means for determining a distribution pattern of the m × n luminance signal data, a distribution of the m × n luminance signal data is provided. Means for comparing the pattern with the luminance signal data of the large window and the small window in the center of the entire screen and the central window, and calculating a target value that provides an optimal exposure level; and controlling the exposure so that the central large window luminance data matches the target value. Means for performing the operation.

According to a third aspect of the present invention, there is provided means for dividing a taken image into m × n to obtain m × n luminance signal data, In a digital camera having means for calculating luminance signal data of a large window and a small window, and means for determining a distribution pattern of the m × n luminance signal data, a distribution of the m × n luminance signal data is provided. Means for comparing the pattern with the luminance signal data of the large window and the small window at the center of the entire screen, and calculating a target value that provides an optimum exposure level; and controlling the exposure so that the central small window luminance data matches the target value. Characterized in that it comprises means for performing

According to a fourth aspect of the present invention, there is provided means for dividing a captured image into m × n to obtain m × n luminance signal data, In a digital camera having means for calculating luminance signal data of a large window and a small window, and means for determining a distribution pattern of the m × n luminance signal data, a distribution of the m × n luminance signal data is provided. Means for comparing the pattern with the luminance signal data of the large window and the small window at the center of the entire screen and calculating a target value that provides an optimum exposure level; and performing exposure so that the window luminance data selected to the target value coincides with the target value. It is characterized by having means for controlling.

According to the above construction, it is possible to obtain an optimum exposure level for a subject to be photographed.
According to the configuration, the optimal exposure control can be performed by the average photometry of the entire screen. According to the configuration of claim 2, the optimal exposure control can be performed by the central average photometry. According to the configuration of claim 3,
Optimal exposure control can be performed by spot metering. According to the configuration of claim 4, optimal exposure control can be performed by using the selected window.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing the configuration of an embodiment of the present invention. In the figure, the same parts are denoted by the same reference numerals. In the figure, reference numeral 1 denotes a lens, 2 denotes an aperture unit for controlling the amount of light, 3 denotes an image sensor for converting light into an electric signal, and 4 denotes noise reduction of a video signal output from the image sensor by a double correlation sampling process. A CDS circuit for performing the operation, an AD converter for converting an analog signal into a digital signal, a digital clamp circuit for subtracting a black level from a digitized video signal,
Is a gamma correction circuit for performing nonlinear processing, 8 is an SRAM memory for storing data, 9 is a color signal generation circuit block, 1
0 is a luminance signal generation block, 11 is an outline emphasis block,
Reference numeral 12 denotes an output processing circuit that outputs a luminance signal and a color signal to a memory, 13 denotes a region division circuit of an exposure detection block, 14 denotes a luminance signal data generation circuit of the divided region, and 15 denotes a CPU that controls each unit. Here, the present invention provides a unit for converting an image signal output from the image sensor 3 into a luminance signal, a unit for dividing a luminance signal in one field into m × n, and a unit for dividing the luminance signal into m × n. Means for outputting the luminance signal data of the area, means for calculating the average luminance data S0 of the entire screen from the luminance signal data of each divided area, and the average luminance signal data S1 of the large window at the center of the screen
Means for calculating the average luminance signal data S2 of the small window at the center of the screen, and means for calculating and determining the distribution pattern of the average luminance data of each of the divided areas. , Full screen brightness average data S
0, means for comparing the screen center large window luminance average data S1 and the screen center small window luminance average data S2.

Next, the operation in such a configuration will be described. FIG. 1 shows a first embodiment of the present invention. In the figure, a subject image input from a lens 1 is converted into an electric signal by an image sensor 3 and converted into digital data by an AD converter 5 through a CDS circuit 4. You. The digitized video signal passes through the clamp circuit 6 and the gamma correction circuit 7, and the data for one screen is stored in the SDRAM 8. S
One screen of digital image data stored in the DRAM 8 is sequentially read out, and a color signal generation circuit block 9 and a luminance signal generation block 10 generate a luminance signal and a color signal. The luminance signal is subjected to an outline emphasis process in an outline emphasis block 11.

As exposure control data, luminance signal data generated by the luminance signal generation block 10 is input to the luminance data generation circuit 14 via the area dividing circuit 13.
The luminance data generation circuit 14 integrates the luminance signal data for each area, and calculates the SDR from the data of the area where the integration has been completed.
The data is stored in AM8. As a result, luminance signal data of each area divided for exposure control can be obtained. The CPU 15 reads out the obtained data for exposure control, and controls the electronic shutter speed of the image pickup device 3 and the aperture unit 2 so as to obtain an optimal exposure level. FIG. 3 shows screen division in the embodiment of the present invention. The screen is divided into 36 6 × 6 screens. FIG.
5 shows a large window at the center of the screen, and FIG. 6 shows a small window at the center of the screen.

FIG. 2 shows a schematic flow chart of the present invention. The present invention will be described with reference to FIG. The CPU 15 reads out the exposure control luminance data divided into the respective areas from the SDRAM 8. In this embodiment, the screen is divided into 6 × 6 = 36. The brightness data calculated for exposure control is W
1 to W36. The luminance average data S0 of the entire screen, the luminance average data S1 of the large window at the center of the screen, and the luminance average data S2 of the small window at the center of the screen are calculated using the 36 read data. The calculation formula is as follows.

[0014]

(Equation 1)

Next, the luminance distribution of the captured image is calculated using the data of W1 to W36. In this embodiment, the luminance data is data from 0 to 255. The area from 0 to 255 is divided into eight areas from Y_LEV_CNT_0 to Y_LEV_CNT_7, and it is calculated at which luminance level the 36 pieces of data W1 to W36 are located. 7 and 8 show graphs of the luminance distribution according to the present embodiment.

After calculating the luminance distribution, the distribution pattern is determined. Pattern determination is performed based on luminance distribution data.
In the pattern determination, the first and second areas of the eight divided luminance areas are obtained and set as primary patterns. 7 shows the primary pattern 34 and FIG. 8 shows the primary pattern 26. Find out if the secondary pattern assumed from the obtained primary pattern applies. The secondary pattern analyzes shooting data under all conditions and classifies the data into 20 exposure control patterns. A pattern that does not correspond to any pattern is provided, and is classified into a total of 21 exposure control patterns. Based on the determined exposure control pattern, a target window having an optimal exposure level is obtained. When the target windows are classified into the above-described representative 20 exposure control patterns, a full-screen window is selected. When the exposure control pattern does not correspond to the representative 20 exposure control patterns, the large window at the center of the screen is selected. Next, an optimal exposure target value is obtained from the luminance distribution pattern. The exposure target value of the target window previously obtained is obtained from the exposure control pattern, the obtained luminance data of the target window, the luminance data S0 of the entire screen, and the small window data S2 at the center of the screen. First, a condition determination of “S0 ≧ 2 × S2” is performed. Classification is made when this condition is satisfied and when this condition is not satisfied. When satisfied, CASE_1; when not satisfied, CASE_2. For example, in FIG. 7, it is assumed that the pattern is classified as the exposure control pattern 20 as a result of performing the secondary pattern determination. At this time, it is assumed that the luminance data S0 of the entire screen is 128 and S2 is 120. At this time, it is CASE_2. Also, as shown in FIG. 8, if S0 is 148 and S2 is 68, CA
SE_1. Thus, even with the same exposure control pattern 20, unless the target value is changed according to the values of CASE_1, CASE_2, and S0, optimal exposure control cannot be performed. The conditions for calculating the target value of the exposure control 20 are shown in the following table.

[0017]

[Table 1]

At this time, the AE described in the condition or the target value
Values such as _TGT_1 are set as follows.

[0019]

[Table 2]

In the case of FIG. 7, since CASE_2, S0 = 128, the range is AE_TGT_3 to AE_TGT_5, and the target value is AE_TGT_5 (1
30). In the case of FIG. 8, since CASE_1 and S0 = 148, the range is AE_TGT_5 to AE_TGT_7, and the target value is AE_TGT_5 (1
30). As described above, the determination table is provided for each exposure control pattern, and an optimum target value is determined based on each exposure control pattern.

Determining a target window and a target value,
The difference between the target value and the luminance data of the target window is obtained, the shutter speed is calculated according to the difference, and the electronic shutter of the CCD is controlled, so that the exposure control is performed so that the luminance data of the target window becomes the target value. .

If the brightness data of the target window falls within a certain specified value with respect to the target value by the exposure level determination, the exposure determination is OK. Here, it is desirable that a certain specified value is converted into an exposure level to be within 0.2 EV.

[0023]

As described above, according to the configuration of the present invention, since the circuit scale is not increased and complicated control is not required, optimal exposure control according to the subject can be performed at high speed. Will be possible. Further, by comparing the luminance data of the entire screen with the small window data at the center of the screen, it is possible to easily perform backlight determination.

[Brief description of the drawings]

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

FIG. 2 is a flowchart illustrating an exposure control process according to the present invention.

FIG. 3 is a diagram showing an embodiment of screen division according to the present invention.

FIG. 4 is a diagram showing the entire screen of the present invention.

FIG. 5 is a diagram showing a large window at the center of the screen according to the present invention.

FIG. 6 is a view showing a small window at the center of the screen according to the present invention.

FIG. 7 is a diagram showing a luminance distribution of a screen according to the present invention.

FIG. 8 is a diagram showing a luminance distribution of a screen according to the present invention.

[Description of Signs] 1 lens 2 aperture unit 3 image sensor 4 CDS 5 AD converter 6 digital clamp circuit 7 gamma correction circuit 8 SDRAM 9 color signal generation block 10 luminance signal generation block 12 output processing circuit 13 area division circuit 14 luminance data Generation circuit 15 Central processing unit

Claims (4)

[Claims] 1. A means for dividing a taken image into m × n to obtain m × n luminance signal data, and a method for dividing a whole screen and a central large window and a small window from the m × n luminance signal data. In a digital camera having means for calculating luminance signal data and means for determining a distribution pattern of the m × n luminance signal data, the distribution pattern of the m × n luminance signal data, the whole screen, and the center Means for comparing the luminance signal data of the large window and the small window with each other to calculate a target value at which an optimum exposure level is obtained, and means for controlling exposure such that the luminance data of the entire screen matches the target value. An exposure control device for a digital camera. Means for dividing a captured image into m.times.n to obtain m.times.n pieces of luminance signal data; and obtaining a full screen, a central large window and a small window from said m.times.n luminance signal data. In a digital camera having means for calculating luminance signal data and means for determining a distribution pattern of the m × n luminance signal data, the distribution pattern of the m × n luminance signal data, the whole screen, and the center Means for comparing the luminance signal data of the large window and the small window with each other to calculate a target value at which the optimal exposure level is obtained, and means for controlling the exposure such that the central large window luminance data matches the target value. An exposure control device for a digital camera. 3. A means for dividing a taken image into m.times.n to obtain m.times.n pieces of luminance signal data, and means for dividing a whole screen, a central large window and a small window from said m.times.n pieces of luminance signal data. In a digital camera having means for calculating luminance signal data and means for determining a distribution pattern of the m × n luminance signal data, the distribution pattern of the m × n luminance signal data, the whole screen, and the center Means for comparing the luminance signal data of the large window and the small window with each other to calculate a target value that provides an optimum exposure level, and means for controlling the exposure such that the central small window luminance data matches the target value. An exposure control device for digital cameras. 4. A means for dividing a captured image into m.times.n to obtain m.times.n luminance signal data, and means for obtaining a full screen, a central large window and a small window from said m.times.n luminance signal data. In a digital camera having means for calculating luminance signal data and means for determining a distribution pattern of the m × n luminance signal data, the distribution pattern of the m × n luminance signal data, the whole screen, and the center Means for comparing the luminance signal data of the large window and the small window with each other to calculate a target value at which the optimal exposure level is obtained, and means for controlling the exposure so that the selected window luminance data matches the target value. An exposure control device for a digital camera.