CN101232583A - Device and method for self-adaptive adjustment of camera aperture - Google Patents

Abstract

A camera aperture self-adaptive adjustment device and method, the device includes a variable aperture lens and its controller, a camera, and a host computer that controls the camera; the method uses digital image processing to adaptively adjust the camera's aperture according to the light brightness of the subject. The size of the aperture, so that the subject can get a proper exposure and enhance the clarity of the subject in the image. The present invention is especially suitable for shooting occasions where there is a significant light difference between the subject and the background and proper exposure of the subject is required. exposure adjustment.

Description

Device and method for self-adaptive adjustment of camera aperture

technical field

The invention relates to a camera aperture adaptive adjustment device and method.

Background technique

Obtaining a clear image is the basis for subsequent image processing and image analysis. In many applications, the quality of the image captured by the camera, especially the image quality of the subject, is often required to be very high. Appropriate aperture size is one of the key factors to obtain clear images in camera shooting. The aperture of the camera is divided into "automatic" and "manual" two control methods. Using the automatic iris, it can maintain the appropriate amount of incoming light and obtain the specified output signal strength. But in actual operation, it is difficult to use a fully automatic aperture.

A traditional automatic exposure system compares the average brightness of the entire image with a preset reference value for exposure control. When the brightness difference between the subject and the background in the image is small, the captured image can have a better effect. However, when the brightness difference between the subject and the background is large, due to the narrow dynamic range of CCD/CMOS in most current camera products, the high-brightness areas in the image will be overexposed, and the low-brightness areas will be underexposed, resulting in the subject in the image overexposed or underexposed. For example, in backlight shooting and frontal strong light shooting, the average brightness of the image is determined by the background brightness, and exposure control based on the average image brightness will lead to abnormal exposure of the subject of the image.

In order to carry out effective exposure control in backlight shooting and frontal strong light and shooting, the traditional automatic exposure control algorithm based on the average value of image brightness must be improved. The improvement measures proposed by Haruki and Kikiuchi (T.Haruki and K.Kikuchi, "Video camera system using fuzzy logic", IEEE Transactions on Consumer Electronics, Vol.38, No.3, pp.624-634, Aug.1992) will screen Divided into six areas, by assigning different weights to the brightness of each area of the screen and accumulating the weighted brightness values, the final result is to focus the exposure on the center of the screen. Shimizu (S.Shimizu, T.Kondo, T.Kohashi, M.Tsurata, T.Komuro, "A new algorithm for exposure control based on fuzzy logic for video cameras", IEEE Transactions on Consumer Electronics, Vol.38, No.3 , pp.617-623, Aug.1992) proposed a method to calculate three brightness thresholds for each image, and distinguish backlight and front glare according to the ratio of pixels whose brightness values are greater than different brightness thresholds in the entire image and other special scenes and perform corresponding exposure compensation. The automatic exposure control method proposed by Murakami and Honda (M. Murakami and N. Honda, "An exposure control system of video cameras based on fuzzy logic using color information", Proceedings of the Fifth IEEE International Conference on Fuzzy Systems, Vol.3, 1996) It uses the color information of the image to coordinate the brightness of the subject and the background while performing exposure compensation on the subject of the image.

The above improved automatic exposure control method has greatly improved the automatic exposure performance of the camera, but it still cannot effectively control the exposure of any scene. For example, the method for dividing an image proposed by Haruki and Kikiuchi is affected by the position of the subject in the screen, and it is difficult to properly expose the subject when the subject is not in the center of the screen. Since it does not use any form of region segmentation, although the algorithm proposed by Shimizu has nothing to do with the position of the subject in the image, it can detect the intensity of backlight or front light and perform corresponding exposure compensation, but the algorithm can only give the brightness contrast of the image It is not possible to determine whether the high brightness contrast is caused by the background light or the subject itself, so effective exposure control cannot be performed in many cases. Therefore, when there is a large difference in brightness between the subject and the background, using the automatic iris will easily lead to abnormal exposure of the subject and unsatisfactory images.

Contents of the invention

The technical problem of the present invention is: to overcome the deficiency of the prior art that the size of the aperture of the camera cannot be automatically adjusted when collecting images, and to provide a device and method for adaptively adjusting the aperture of the camera according to the brightness of the subject to be photographed, so as to meet the requirements for the aperture of the subject when shooting images. The requirements for proper exposure of the subject enhance the clarity of the subject in the image.

Technical solution of the present invention: a camera aperture adaptive adjustment device, a camera aperture adaptive adjustment device includes: a lens controller, a camera with a variable aperture lens, a host computer; a camera with a variable aperture lens to shoot The image is sent to the host; the host processes the image, judges the exposure of the image, and sends an aperture adjustment signal to the lens controller according to the judgment result; the lens controller converts the aperture adjustment signal sent by the host into the aperture adjustment signal of the variable aperture lens The control signal drives the aperture adjustment motor to realize the automatic adjustment of the aperture size of the camera, so that the subject can obtain a suitable exposure.

The camera adopts a shooting mode with fixed direction and fixed focal length.

A method for adjusting the aperture of a camera aperture adaptive adjustment device, comprising the following steps:

(1) Collect the background image A before the subject enters the scene;

(2) Collect an image B after the subject enters the scene;

(3) The background image A collected in step (1) and the image B collected in step (2) are converted into grayscale images respectively;

(4) Extract the grayscale image of the subject according to the two grayscale images converted by step (3);

(5) Calculating the gray mean value of the subject gray image;

(6) Judging whether the grayscale mean value is within the predefined ideal exposure grayscale threshold range, if within the threshold range, then no need to perform aperture adjustment, turn to step (7) and start the image acquisition process; otherwise, perform aperture adjustment, and then Go to step (2);

(7) The aperture adjustment process ends.

The beneficial effect of the present invention compared with the prior art: the present invention can extract the subject from the photographed image when the contrast between the subject and the background is large, and convert the image of the subject into a grayscale image. The average gray value of the subject in the high-resolution image determines the size of the aperture, and adaptively adjusts the aperture of the camera to achieve proper exposure of the subject and enhance the clarity of the subject in the image. The present invention is especially suitable for shooting occasions where there is an obvious light difference between the subject and the background and proper exposure of the subject is required. exposure adjustment.

Description of drawings

Fig. 1 is a structural diagram of a camera aperture self-adaptive adjustment device of the present invention;

Fig. 2 is a flow chart of the camera aperture self-adaptive adjustment method of the present invention.

Detailed ways

Hereinafter, specific aspects of the present invention will be described with reference to the drawings, but the present invention is not limited to the illustrated examples.

As shown in Figure 1, the image taken by the camera with variable aperture lens is sent to a computer host; the host processes the image, analyzes the exposure of the image, and sends an aperture adjustment signal to the lens controller according to the analysis result; the lens The controller converts the aperture adjustment signal sent by the host into a control signal that the lens can understand, and drives the aperture adjustment motor to realize the adjustment of the aperture.

As shown in Figure 2, the steps of the self-adaptive adjustment method for camera aperture of the present invention are as follows: the camera adopts a fixed direction and a fixed focal length to shoot, collects a background image A before the subject enters the shooting scene, and collects a background image A before the subject enters the shooting scene. After the scene, another image B is collected, and images A and B are sent to the host. The host converts images A and B into grayscale images A' and B' respectively according to the following steps:

(1) Calculate gray=r×0.3+g×0.59+b×0.11;

(2) Round the value of gray;

(3) Let the values of r, g, and b be equal to gray.

where r, g, b are the R, G, B values of each pixel in color images A and B, respectively. For simplicity, record the pixel value A'(x, y)=gray of the image A', and the pixel value B'(x, y)=gray of the image B', where x=1, 2,..., M, y=1 , 2, ..., N, M and N are the image height and width.

Extract the subject in B' according to A' and B': suppose the set of pixel values of the subject is H={c|c is the pixel value of the subject in B'}, then finding F includes the following two steps:

(a) Let H be the empty set;

(b) For images A' and B', calculate the value of h=|B'(x, y)-A'(x, y)| pixel by pixel, if h>7, then B'(x, y) into the set H.

According to H, the average gray value of the subject is calculated as:

$g=\frac{\underset{c\∈h}{\mathrm{\Σ}}c}{\left|h\right|}$ , where |H| represents the number of elements in the set H.

Assume that the size of the aperture is expressed by F, and F is expressed by a monotone function f(g) as F=f(g). The monotone function f(g) is approximated by a gray threshold range: if the gray average g of the subject is greater than the ideal exposure gray threshold range, the host will output to the lens controller according to the difference between g and the gray threshold range Δ Decrease the aperture control signal, and the reduction of the aperture is determined by the size of Δ; if the average gray value g of the subject is less than the ideal exposure gray threshold range, the host will send a signal to the lens controller according to the difference between g and the gray threshold range Δ The aperture increase control signal is output, and the increase amount of the aperture is determined by the size of the difference Δ.

For a lens driven by a DC motor, the aperture adjustment control signal output by the host is a digital signal and cannot be used as an electrical signal to drive the motor. The lens controller is responsible for converting the digital signal output by the host into a current signal for the DC motor. When a certain voltage is applied, the motor starts to move, and if a reverse voltage is applied, the motor runs in reverse. For example, under the control of the lens controller, every time a voltage of ±12V is applied to the DC motor for 100ms, the motor will take a step forward/backward, and the size of the aperture adjustment is determined by the polarity and duration of the voltage. For a lens driven by a stepping motor, the lens controller is responsible for converting the digital signal output by the host into an electrical pulse signal, and the size of the aperture adjustment is determined by the number of pulse signals.

Finally, it should be noted that the above descriptions are only preferred implementation modes of the present invention. , and several improvements or equivalent replacements can also be made, and these improvements and equivalent replacements should also be regarded as the protection scope of the present invention.

Claims (7)

1. A camera aperture adaptive adjustment device is characterized in that comprising: a lens controller, a camera with a variable aperture lens, a host computer; the image taken by the camera with a variable aperture lens is sent to the host computer; the host computer controls the image process, judge the exposure degree of the image, and send the aperture adjustment signal to the lens controller according to the judgment result; the lens controller converts the digital signal output by the host into a current signal, drives the aperture adjustment motor, and realizes the automatic adjustment of the aperture size of the camera. So that the subject gets the proper exposure. 2. A camera aperture self-adaptive adjustment device according to claim 1, characterized in that: the camera adopts a fixed direction and fixed focal length shooting mode. 3. A method for adjusting the aperture of a camera aperture adaptive adjustment device, characterized in that it comprises the following steps: (1) Collect the background image A before the subject enters the scene; (2) Collect an image B after the subject enters the scene; (3) The background image A collected in step (1) and the image B collected in step (2) are converted into grayscale images respectively; (4) Extract the grayscale image of the subject according to the two grayscale images converted by step (3); (5) Calculating the gray mean value of the subject gray image; (6) Judging whether the grayscale mean value is within the predefined ideal exposure grayscale threshold range, if within the threshold range, then no need to perform aperture adjustment, turn to step (7) and start the image acquisition process; otherwise, perform aperture adjustment, and then Go to step (2); (7) The aperture adjustment process ends. 4. a kind of camera aperture self-adaptive adjusting device according to claim 4 carries out the method for aperture adjustment, it is characterized in that: in described step (3) with the background image A that step (1) gathers and step (2) The methods for converting the collected image B into grayscale images A' and B' are as follows: (1) Calculate gray=r×0.3+g×0.59+b×0.11; (2) Round the value of gray and make the values of r, g, and b equal to gray; Where r, g, and b are the R, G, and B values of each pixel in the color images A and B, respectively, and the pixel value A'(x, y)=gray of the image A', and the pixel value B' of the image B' (x, y) = gray. 5. The method for adjusting the aperture of a camera aperture adaptive adjustment device according to claim 4, characterized in that: the grayscale image of the subject is extracted from the two grayscale images converted by the step (4) The method is as follows: (1) Assume that the set composed of the pixel values of the subject is H={c|c is the pixel value of the subject in B'}, and the initial value of H is defined as an empty set; (2) For images A' and B', calculate the value of h=|B'(x, y)-A'(x, y)| pixel by pixel, if h>7, then B'(x, y) into the set H. 6. a kind of camera aperture self-adaptive adjusting device according to claim 4 carries out the method for aperture adjustment, it is characterized in that: the gray scale mean of the subject of described step (5) is: $g=\frac{\underset{c\∈h}{\mathrm{\Σ}}c}{\left|h\right|}$ , where |H| represents the number of elements in the set H. 7. The method for adjusting the aperture of a camera aperture adaptive adjustment device according to claim 4, characterized in that: the aperture adjustment method of the step (6) is: if the gray mean value g of the subject is greater than the ideal Exposure to the gray threshold range, the host will output a control signal to the lens controller to decrease the aperture according to the difference between g and the gray threshold range Δ, and the reduction of the aperture is determined by the size of Δ; if the average gray value of the subject g is less than For the ideal exposure grayscale threshold range, the host will output a control signal for increasing the aperture to the lens controller according to the difference Δ between g and the grayscale threshold range, and the aperture increase is determined by the difference Δ.

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