JP2002300468A - Imaging device and method for controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device capable of controlling exposure for realizing the optimal exposure in a backlight scene and a tunnel scene or the like. SOLUTION: This imaging device is provided with an imaging control unit (control means) 103 for dividing an imaging screen into a plurality of areas, and for performing imaging operation, based on the exposure information to be obtained by operating preliminarily weighting to a luminance value to be obtained from each area; and an AE control unit (correction means) 104 for correcting the weighting, when the rate of the luminance value of a prescribed area among those areas to the luminance value of the other area is larger than a prescribed rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus and a control method thereof.

[0002]

2. Description of the Related Art In a conventional imaging apparatus, a center-weighted photometry system is used to calculate a luminance value of an imaged screen by dividing the screen into a plurality of parts and calculating the divided luminance values using weights with emphasis on a central part. Various photometric methods are used, such as an average photometric method in which the entire screen is calculated using uniform weights.

[0003]

However, in the photometric method using such means, the brightness of the screen is always calculated using a predetermined weight regardless of the scene to be photographed. In some cases, an image different from the user's intention was taken.

[0004] For example, such typical examples include a backlight scene and a tunnel scene. When the main subject is at the center of the screen and its surroundings are bright due to backlight, or when the main subject is in front of a dark background such as a tunnel, etc. Although the weight of the brightness is increased, it is greatly affected by the brightness information of the background area.In a backlight scene, the main subject is below the user's intention, and in a tunnel scene, the main subject is In some cases, the image may be overshot than intended.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an image pickup apparatus capable of performing exposure control so as to obtain an appropriate exposure even in a backlight scene, a tunnel scene, and the like, and an image pickup apparatus therefor. It is an object to provide a control method.

[0006]

An imaging apparatus and a control method thereof according to the present invention are configured as follows.

(1) In an imaging apparatus, an imaging screen is divided into a plurality of areas, and an imaging operation is performed based on exposure information obtained by performing a predetermined weighting on a luminance value obtained from each area. A control unit; and a correction unit configured to correct the weighting when a ratio between a luminance value of a predetermined area and a luminance value of another area among the plurality of areas is larger than a predetermined ratio.

(2) In an image pickup apparatus, an image pickup screen is divided into a plurality of areas, and an image pickup operation is performed based on exposure information obtained by performing a predetermined weighting on a luminance value obtained from each area. The image processing apparatus further includes a control unit, and a correction unit that corrects the weight when a difference between a luminance value of a predetermined area and a luminance value of another area among the plurality of areas is larger than a predetermined value.

(3) In the imaging device according to (1) or (2), the predetermined area is set based on a focus position on the imaging screen.

(4) In the control method of the image pickup apparatus, the image pickup screen is divided into a plurality of areas, and image pickup is performed based on exposure information obtained by performing predetermined weighting on luminance values obtained from each area. Controlling the operation and, when the ratio between the luminance value of the predetermined area and the luminance value of the other area is larger than the predetermined ratio, among the plurality of areas, corrects the weighting and sets the luminance obtained from each of the areas. The imaging operation is controlled based on exposure information obtained by performing the corrected weighting on the value.

(5) In the control method of the image pickup apparatus, the image pickup screen is divided into a plurality of areas, and image pickup is performed based on exposure information obtained by performing predetermined weighting on a luminance value obtained from each area. Controlling the operation and, when the ratio between the luminance value of the predetermined area and the luminance value of the other area is larger than a predetermined value, among the plurality of areas, correcting the weighting, and obtaining the luminance obtained from each of the areas. The imaging operation is controlled based on exposure information obtained by performing the corrected weighting on the value.

[0012]

(First Embodiment) FIG. 1 is a block diagram showing a schematic configuration of a digital camera according to a first embodiment. In FIG. 1, reference numeral 101 denotes an imaging unit. The imaging unit 101 includes a lens system, an aperture, a shutter, an electronic shutter, a CCD,
An image projected on the CCD by the lens system including an A / D converter is output as a digital signal.

When the shutter is released, the AF control unit 102 detects focus. Focusing data is subjected to lens focusing control by the imaging control unit 103. Next, in the imaging unit 101, image data is photographed in the focused state.

The AE control unit 104 calculates the brightness of the image based on the image data sent from the imaging unit 101, and calculates the appropriate exposure information.

FIG. 2 is a block diagram showing the configuration of the AE control unit 104. The processing in the AE control unit 104 will be described below with reference to FIG. In the figure, reference numeral 201 denotes an area luminance value calculation unit,
The CD signal data is divided into 36 × 6 areas divided into 6 rows and 6 columns with respect to the imaging screen, and the average luminance values Y (I, J) (I = 0 to 5, J = 0 to 5) are calculated. Further, based on the luminance value Y (I, J) for each area, a luminance value Yc of a central portion serving as a main subject area is calculated by the following equation (1) in the main subject luminance value calculation unit 202.

Yc = (Y (2,2) + Y (2,3) + Y (3,2) + Y (3,3)) / 4 Equation (1) These Y (I, J) and Yc data are area The weight is sent to the weight determination unit 203. The area weight determination unit 203 prepares weight coefficients W (I, J) (I = 0 to 5, J = 0 to 5) for each of the divided areas shown in FIG.
Correction coefficients H (I, J) and Y (I, J) for each area shown in FIG.
And the magnitude of Yc, the weight Weight (I, J) for each area according to the scene is obtained by the following equation.

When Y (I, J) ≧ Yc × α, Weight (I, J) = W (I, J) × H (I, J) Equation (2) Y (I, J) ≦ Yc × α Case Weight (I, J) = W (I, J) × H (I, J) Expression (3) In other cases Weight (I, J) = W (I, J) Expression (4) where α = 2 area The data of the weights Weight (I, J) and Y (I, J) for each area obtained by the weight determination unit 203 are sent to the exposure control correction value determination unit 204, and the exposure control correction value is calculated by the following equation (5). Delta is required.

Delta = Log ₂ (Σ (Y (I, J) × Weight (I, J)) / Σ (Weight (I, J)) / Yref) Equation (5) where Yref is a screen target luminance value. This will be described with an actual example. It is assumed that a luminance value Y (I, J) for each area as shown in FIG. 8 has been obtained. First, the main subject luminance value is Yc = 60 from the above equation (1). Here, from the above equation (2), Y (I, J) is Yc × 2 = 1.
If Y (I, J) is Y from the above equation (3)
Correction coefficient H (I, J) to a value smaller than c / 2 = 30
, And Weight (I, J) as shown in FIG.
Is required. As a result, the degree of importance of the main subject is increased, so that the main subject is corrected so as to have more appropriate exposure.

The exposure control correction value obtained by the AE control unit 104 shown in FIG. 1 is sent to the imaging control unit 103, and the aperture value Av, shutter speed value Tv, CCD sensitivity value S at the time of main exposure are obtained.
v is determined, and the aperture, shutter speed, and CCD sensitivity of the imaging unit 101 are controlled.

When the respective values are set, the image pickup unit 101
Then, the main exposure is performed, and the final image digital signal is sent to the image processing unit 105. The final image digital signal is subjected to image processing such as color processing and luminance processing, edge emphasis processing, gamma processing, and JPEG conversion processing in the image processing unit 105, and is further sent to the data writing unit 106, where it is sent to the storage medium. Data writing is performed.

In this embodiment, the ratio between the luminance value of the main subject and the luminance value of each area is used as in the above equations (2) and (3) to determine the expression for determining the weight for each area. However, the determination may be made using the luminance difference as in the following equations (6) and (7).

When | Y (I, J) −Yc | ≧ β (where β is a constant) Weight (I, J) = W (I, J) × H (I, J) Equation (6) Weight (I, J) = W (I, J) Equation (7) where | A | is the absolute value of A.

As described above, in the present embodiment, the exposure screen obtained by dividing the imaged screen into 36 areas of 6 in the vertical and 6 in the horizontal, and applying a predetermined weight to the luminance value obtained from each area. An imaging control unit (control means) 103 that performs an imaging operation based on information; and a case where a ratio between a luminance value of a predetermined area and a luminance value of another area among the 36 areas is larger than a predetermined ratio. Since the AE control unit (correction unit) 104 for correcting the weight is provided, it is possible to perform exposure control so that an appropriate exposure is obtained even in a backlight scene, a tunnel scene, or the like.

In this embodiment, the area is divided into 36 areas of 6 in the vertical direction and 6 in the horizontal direction. However, the present invention is not limited to this number. N × M (N, M
Is an arbitrary constant), or any shape as long as the main subject and other areas can be separated.

(Embodiment 2) The basic configuration is the same as that of Embodiment 1, and the same figure is used for the description.

The image pickup unit 101 shown in FIG.
A shutter, an electronic shutter, a CCD, an A / D converter, and the like are included, and an image projected on the CCD by a lens system is output as a digital signal. When the shutter is released, the AF control unit 102 performs focus detection. In this case, the distance of the subject at the position of the image shown in FIG. 5 is measured, and the focus control of the focusing data is performed by the imaging control unit 103 so that the subject at the closest position is focused.

Next, in the image pickup unit 101, image data is photographed in the focused state. AE controller 10
In step 4, the brightness of the screen is calculated based on the image data sent from the imaging unit 101, and the proper exposure information is calculated.

The CCD data signal sent from the image pickup unit 101 is divided into 36 × 6 (36 × 6) areas by dividing the screen into six rows and six columns by the area luminance value calculation unit 201, and the average luminance of each area is calculated. Value Y (I, J) (I = 0 to 5, J =
0 to 5) are calculated. Further, the luminance value Y for each area
On the basis of (I, J), the main subject luminance value calculation unit 202 calculates the luminance value of the central portion serving as the main subject area by the following equation.

When the focus is on the position A in FIG. 5, Yc = (Y (1,2) + Y (2,2) + Y (1,3) + Y (2,3)) / 4 Equation (8) When the focus is on the position B in FIG. 5 Yc = (Y (2,2) + Y (3,2) + Y (2,3) + Y (3,3)) / 4 Equation (9) When the focus is on the position of A, Yc = (Y (3,2) + Y (4,2) + Y (3,3) + Y (4,3)) / 4 Equation (10) These Y (I, J) and Yc data are sent to the area weight determination unit 203. In the area weight determination unit 203, the focus prepared in advance as shown in FIG. 6 is changed into a weight coefficient W for each of the divided areas corresponding to the adjusted position in FIG.
A (I, J), WB (I, J), WC (I, J) (I =
0, 5 and J = 0 to 5), and the correction coefficient HA (I, I) for each area corresponding to the focused position shown in FIG.
J), HB (I, J), HC (I, J), Y (I, J)
And the magnitude of Yc, the weight Weight (I, J) for each area according to the scene is obtained by the following equation.

When the focus is on the position A in FIG. 5, when Y (I, J) ≧ Yc × α, Weight (I, J) = WA (I, J) × HA (I, J) Equation ( 11) When Y (I, J) ≦ Yc / α Weight (I, J) = WA (I, J) × HA (I, J) Equation (12) In Other Cases, Weight (I, J) = WA ( I, J) Equation (13) where α = 2 When focusing on the position of B in FIG. 5 When Y (I, J) ≧ Yc × α Weight (I, J) = WB (I, J) × HB (I, J) Equation (14) When Y (I, J) ≦ Yc / α Weight (I, J) = WB (I, J) × HB (I, J) Equation (15) Weight (I, J) = WB (I, J) Equation (16) When focusing on the position of C in FIG. 5 Y (I, J) ≧ Yc × α Case Weight (I, J) = WC (I, J) × HC (I, J) Formula (17) When Y (I, J) ≦ Yc / α Weight (I, J) = WC (I, J) × HC (I, J) Expression (18) In other cases Weight (I, J) = WC (I, J) Expression (19) We for each area obtained by the area weight determination unit 203
The data of light (I, J) and Y (I, J) are sent to the exposure control correction value determination unit 204, and the exposure control correction value Delta is calculated by the following equation (20).

Delta = Log ₂ (Σ (Y (I, J) × Weight (I, J)) / Σ (Weight (I, J)) / Yref) Expression (20) where Yref is a screen target luminance value. The exposure control correction value obtained by the AE control unit 104 is sent to the imaging control unit 103, and the aperture value Av, shutter speed value Tv, and CCD sensitivity value Sv at the time of main exposure are determined. Shutter speed, CCD
Control the sensitivity.

When the respective values are set, the image pickup unit 101
Then, the main exposure is performed, and the final image digital signal is sent to the image processing unit 105. The final image digital signal is subjected to image processing such as color processing and luminance processing, edge emphasis processing, gamma processing, and JPEG conversion processing in the image processing unit 105, and is further sent to the data writing unit 106, where it is sent to the storage medium. Data writing is performed.

[0033]

As described above, according to the present invention,
There is an effect that exposure control can be performed so that proper exposure is obtained even in a backlight scene, a tunnel scene, and the like.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of first and second embodiments.

FIG. 2 is a block diagram illustrating a configuration of an AE control unit in FIG. 1;

FIG. 3 is a diagram illustrating a weight coefficient for each area prepared in advance according to the first embodiment;

FIG. 4 is a diagram illustrating weight correction coefficients prepared for each area according to the first embodiment;

FIG. 5 is a diagram illustrating a focus position according to the second embodiment.

FIG. 6 is a diagram illustrating a weight coefficient for each area according to a focused position according to the second embodiment;

FIG. 7 is a diagram illustrating a correction coefficient for each area according to a focused position according to the second embodiment.

FIG. 8 is a diagram showing an example of luminance for each area.

FIG. 9 is a diagram showing an example of weights for each area.

[Explanation of symbols]

 Reference Signs List 101 imaging unit 102 AF control unit 103 imaging control unit (control unit) 104 AE control unit (correction unit) 105 image processing unit 106 data writing unit 201 area brightness value calculation unit 202 main subject brightness value calculation unit 203 area weight determination unit 204 Exposure control correction value determination unit

Claims (5)

[Claims] A control unit configured to divide an imaging screen into a plurality of areas and perform an imaging operation based on exposure information obtained by performing a predetermined weighting on a luminance value obtained from each area; An image pickup apparatus comprising: a correcting unit that corrects the weighting when a ratio between a luminance value of a predetermined area and a luminance value of another area is larger than a predetermined ratio. 2. A control unit that divides an imaging screen into a plurality of areas and performs an imaging operation based on exposure information obtained by performing a predetermined weighting on a luminance value obtained from each area; When the difference between the luminance value of the predetermined area and the luminance value of the other area is larger than the predetermined value,
An imaging device comprising: a correction unit configured to correct the weighting. 3. The imaging apparatus according to claim 1, wherein the predetermined area is set based on a focus position on the imaging screen. 4. An imaging operation is controlled based on exposure information obtained by dividing an imaging screen into a plurality of areas and performing a predetermined weighting on a luminance value obtained from each area. Of the areas, when the ratio between the luminance value of a predetermined area and the luminance value of another area is larger than a predetermined ratio, the weighting is corrected, and the corrected luminance value is obtained for the luminance value obtained from each area. A method for controlling an imaging apparatus, comprising: controlling an imaging operation based on exposure information obtained by performing weighting. 5. An imaging screen is divided into a plurality of areas, and an imaging operation is controlled based on exposure information obtained by performing predetermined weighting on a luminance value obtained from each area, and Of the areas, when the ratio between the luminance value of the predetermined area and the luminance value of the other area is larger than a predetermined value, the weighting is corrected, and the corrected luminance value is obtained for the luminance value obtained from each area. A method for controlling an imaging apparatus, comprising: controlling an imaging operation based on exposure information obtained by performing weighting.