JP3346839B2 - Digital still video camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital still video camera for recording or recording image information in the form of an electric signal by converting the brightness of a subject into an electric signal by a solid-state image pickup device. Related to exposure control of a camera.

[0002]

2. Description of the Related Art Conventionally, as a method for optimizing exposure even in a backlight in a video camera or a silver halide camera, an output in a central photometric area and an output in a surrounding photometric area are focused on a subject at the center of a screen. There is known a method of determining a correction amount based on an exposure amount. As another method, a method is known in which a scene is determined by multi-pattern photometry in which a plurality of photometry areas are provided on a screen, and exposure of a main subject is controlled.

[0003]

However, in the former method, since the emphasis is placed on the subject being located at the center of the screen, the exposure is appropriately controlled for a scene where the subject is not located at the center of the screen. Can not do. In addition, the latter method can solve this problem.However, the method of dividing the screen, that is, the method of dividing the photometric area, affects the scene determination. Become complicated.

The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide a digital still video camera capable of appropriately controlling exposure of a scene in which a subject is not located at the center of a screen without discriminating the scene. Aim.

[0005]

In order to achieve the above object, a first means is to record or record / reproduce image information in the form of an electric signal by converting the brightness of a subject into an electric signal by a solid-state image sensor. In a digital still video camera, part or all of a screen imaged by the solid-state imaging device is divided into a plurality of blocks, and the average value of the luminance signal of all blocks and the average value of the luminance signal of each block are compared. Comparison means; and exposure control means for controlling exposure by judging whether the light is backlight or normal light based on the comparison result of the comparison means , wherein the exposure control means
The average value of the luminance signal is lower than the average value of the luminance signals of all the blocks.
Calculate the number of blocks lower than the fixed value
If it is larger than the value, it is judged as backlight, and if it is smaller, it is judged as normal.
And controlling the exposure .

[0006]

The second means is characterized in that in the first means, when the exposure control means determines that the light is normal, the exposure is controlled based on luminance signals of all blocks.

The third means is based on the luminance signal in a block which is lower than the average value of the luminance signals of all the blocks by a predetermined value or more when the exposure control means in the first or second means determines that the image is backlit. It is characterized by controlling the exposure.

[0009]

[0010]

According to the first means, exposure is controlled by judging whether the light is backlight or normal light based on the number of blocks whose average value of the luminance signals of the blocks is lower than the average value of the luminance signals of all the blocks by a predetermined value or more. Therefore, it is possible to appropriately control exposure for a scene where the subject is not located at the center of the screen without discriminating the scene.

In the second means, when it is determined that the light is normal, the exposure is controlled based on the luminance signals of all the blocks. Therefore, the exposure is controlled based on the luminance signal used in determining whether the light is backlight or normal light, so that exposure in normal light can be appropriately controlled.

In the third means, when it is determined that the subject is backlit, exposure is controlled based on a luminance signal of a block which is lower than an average value of luminance signals of all blocks by a predetermined value or more. Therefore, since the exposure is controlled based on the luminance signal used in determining whether the light is backlight or normal light, exposure at the time of backlight can be appropriately controlled.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a digital still video camera according to the present invention, FIG. 2 is an explanatory diagram showing a divided block of a screen in the camera of FIG. 1, and FIG. 3 is a luminance signal of a pixel in each block of FIG. FIG. 4 is an explanatory diagram showing
FIG. 5 is an explanatory diagram showing an example of a subject, and FIG. 5 is an explanatory diagram showing a distribution of a luminance signal at the time of backlight in the screen of FIG.

First, as a solid-state imaging device used in a digital still video camera, a CCD device in which photoelectric conversion elements are generally arranged two-dimensionally is often used. Will be explained.
The CCD camera unit 11 shown in FIG. 1 includes a two-dimensional CCD and peripheral circuits, and exposure is controlled by a control signal (correction amount CV) from a correction amount generation circuit 17 to convert the brightness of the subject into an electric signal.

Here, in the case of a black and white camera, the luminance signal can be used as it is for exposure control as shown by a broken line, but in the case of a color camera, red (R), green (G), Since the luminance signals of the three colors of blue (B) are output independently and cannot be used for exposure control as they are, they are mixed and divided into a luminance signal and a color difference signal conforming to the NTSC system by the image signal processing unit 12. It is converted to a video signal.

A two-dimensional CCD generally comprises several hundreds to several hundreds of tens to hundreds of thousands of photoelectric conversion elements (pixels), and an image signal is in the form of P × Q pixels as shown in FIG. As shown in FIG. 3, they are output serially in time. On the other hand, in the present embodiment, the number of blocks used for exposure control is appropriately several to several tens, but the luminance signal of a pixel serially output in time is converted into a signal m shown in FIG.
× n blocks B (i, j) (i = 1 to m, j = 1 to
Every n) are collected and integrated or averaged. The signal distribution circuit 13 averages the luminance signal of each block B (i, j) and the luminance signal of all blocks based on the timing signal from the timing generation circuit 14 and compares the signals.

The signal distribution circuit 13 will be described in detail. The luminance signal for each pixel of each block B (i, j) is sampled by a sampling circuit 131 (i, j), and the integrating circuit 132 (i, j) is By averaging the values sampled by each sampling circuit 131 (i, j) by adjusting the integration constant, the average value of the luminance signal for each pixel in each block B (i, j) (hereinafter referred to as block Y (i, j) is calculated.

Further, the luminance signal for each pixel in all the blocks of m × n is sampled by the sampling circuit 131 (Σ), and the integrating circuit 132 (Σ) outputs the average value (hereinafter, referred to as the luminance signal) for each pixel in all the blocks. Y (Σ) is calculated, and the Σ brightness signal is multiplied by a multiplier (× 1).
/ 2 ^A ) is multiplied by a coefficient (× 1/2 ^A ).

Next, each of the comparators 133 (i, j) respectively outputs the block luminance signal Y (i, j) averaged by the integration circuit 132 (i, j) and the multiplier (× 1/2 ^A ). The outputs are compared, and the average luminance of each block is set to be A (EV value) higher than the average luminance of all blocks by the adder 15.
, That is, the number of blocks N that satisfies Y (Σ) ≧ Y (i, j) × 2 ^A (1) is calculated. Next, the comparator 16 compares the number of blocks with the number of blocks B set in the setting unit 16 ′, and outputs a comparison result of high for backlight and low for forward light to the exposure correction amount generation circuit 17. Output.

The exposure correction amount generation circuit 17 receives all the block luminance signals Y (i, j) Y (Σ) from the distribution circuit 13 in the case of normal light, based on the judgment signal from the comparator 16, In the case of backlight, only the block luminance signal Y ′ (i, j) corresponding to the equation (1) is accepted, the correction amount CV is calculated, and the correction amount CV is output to the CCD camera unit 11. An example of a method of calculating the exposure correction amount CV will be described.
When the exposure correction amount from the target to the appropriate target value T of the CCD is expressed by an EV value, CV = −log ₂ (T / RY) Further, as a certain luminance signal RY, RY = ΣY ′ (i, j) / N × BW is used when the light is in front, and when the light is backlit. Here, NW and BW are weights at the time of forward light and at the time of backlight, respectively, and Y ′ (i, j) is Y (i, j) satisfying the expression (1), and N represents the number thereof. .

FIG. 4 shows, as an example, a case where an object indicated by oblique lines is located on the right side of the center of the screen in an m × n block. FIG. 5 shows the distribution of luminance signals of m × n blocks when the screen is backlit.
This indicates that N blocks lower by (EV value) correspond to a part of the subject at the time of backlight.

Next, a second embodiment will be described. FIG. 6 is a block diagram showing a digital still video camera according to the second embodiment. FIG. 7 is a flowchart for explaining the operation of the exposure control section shown in FIG. It is composed of circuits.

The CCD camera unit 1 and the video signal processing unit 2 shown in FIG. 6 are the same as the circuit shown in FIG. 1, and the luminance signal obtained from the video signal processing unit 2 is converted into a digital signal by the A / D converter 3. Is converted. The luminance signal for one screen converted by the A / D converter 3 is stored in the frame memory 4,
Next, the screen dividing unit 5 divides the image into a plurality of blocks B (i, j) (i = 1 to m, j = 1 to n) as shown in FIG. ) Is performed based on the calculation shown in FIG. The CPU 7 controls the exposure of the CCD camera unit 1 via the CCD camera control unit 9 based on the calculation result of the exposure control unit 6. The image stored in the frame memory 4 can be stored in, for example, a removable memory card 8.

Next, the operation of the exposure controller 6 will be described with reference to FIG. First, an average value Y (Σ) of luminance signals for each pixel in all m × n blocks is calculated (step S).
1) Then, the number of blocks N whose average luminance Y (i, j) of each block is lower than the average luminance Y (Σ) of all blocks by A (EV value), that is, It is determined (step S2).

Next, it is determined whether or not the number of blocks N is equal to or greater than a specified value B to determine whether the light is backlight or normal light (step S3). If N> B, the blocks satisfying the equation (1) are determined. The correction amount CV at the time of backlight is obtained from the luminance signal Y '(i, j) (step S4). On the other hand, when N> B is not satisfied, the correction amount CV at the time of direct light is obtained from the Σ luminance signal Y (Σ) of all blocks. Is obtained (step S5). Then, the exposure of the CCD camera unit 1 is controlled based on the correction amount CV (step S6).

Therefore, according to the above embodiment, whether the light is direct light or back light is determined by comparing the average luminance Y (i, j) of each block with the average luminance Y (Σ) of all blocks. Can be determined only by a simple comparison as to whether the scene is forward light or back light, so that exposure can be appropriately controlled for a scene where the subject is not located at the center of the screen without performing scene determination.

[0027]

[0028]

According to the first aspect of the present invention, it is determined whether backlight is normal or backlight based on the number of blocks in which the average value of the luminance signals of the blocks is lower than the average value of the luminance signals of all the blocks by a predetermined value or more. Since the control is performed, exposure can be appropriately controlled for a scene where the subject is not located at the center of the screen without discriminating the scene.

According to the second aspect of the present invention, when it is determined that the light is normal, the exposure is controlled based on the luminance signals of all the blocks. Therefore, the exposure is controlled based on the luminance signal used in determining whether the light is backlight or normal light. Thus, the exposure is controlled, so that the exposure at the time of direct light can be appropriately controlled.

According to the third aspect of the present invention, when the backlight is determined, the exposure is controlled based on the luminance signal of the block lower than the average value of the luminance signals of all the blocks by a predetermined value or more.
Exposure is controlled based on the luminance signal used in determining whether the light is backlight or normal light. Therefore, exposure at the time of backlight can be appropriately controlled.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a digital still video camera according to the present invention.

FIG. 2 is an explanatory diagram showing divided blocks of a screen in the camera of FIG.

FIG. 3 is an explanatory diagram showing a luminance signal of a pixel in each block of FIG. 2;

FIG. 4 is an explanatory diagram illustrating an example of a subject.

FIG. 5 is an explanatory diagram showing a distribution of a luminance signal at the time of backlight in the screen of FIG. 4;

FIG. 6 is a block diagram showing a digital still video camera according to a second embodiment.

FIG. 7 is a flowchart for explaining the operation of the exposure control unit in FIG. 6;

[Explanation of symbols]

 1,11 CCD camera unit 13 signal distribution circuit 14 timing generation circuit 15 adder 16,133 (i, j) comparator 17 correction amount generation circuit 132 (i, j) integration circuit 4 frame memory 5 screen division unit 6 exposure control Department

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-96826 (JP, A) JP-A-6-86156 (JP, A) JP-A-3-32174 (JP, A) 43669 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 5/235

Claims (3)

(57) [Claims] 1. A digital still video camera for recording or recording / reproducing image information in the form of an electric signal by converting the luminance of a subject into an electric signal by a solid-state image pickup device. A comparison unit that divides a part or the whole into a plurality of blocks, and compares the average value of the luminance signal of all the blocks with the average value of the luminance signal of each block; based on the comparison result of the comparison unit, backlight or direct light and a exposure control means for controlling the exposure to determine the exposure control means, the average value of the luminance signal blocks all
A block that is lower than the average value of the
The number of blocks, and if the number of blocks is greater than
Control the exposure by judging that the light is normal.
Digital still video camera, characterized in that that. Wherein said exposure control means, according to claim 1 Symbol placement digital still video camera and controls the exposure based on the luminance signals for all blocks when it is determined that the forward light. Wherein said exposure control means, according to claim 1, characterized in that to control the exposure based on the luminance signal of a predetermined value or more lower blocks than the average value of the luminance signals of all blocks when it is determined that the backlight or 3. The digital still video camera according to any one of 2 .