Automatic focusing method and apparatus

Abstract

The invention discloses an automatic focusing method and apparatus. The method comprises: multi-frame image data are obtained continuously and focusing window division is carried out on each frame of image data among the multi-frame image data; grey level transformation processing and filtering processing are carried out on the image data in each focusing window successively; for each pixel point in the image data after filtering processing, a first gradient value and a second gradient value that correspond to the pixel point are calculated; according to the first gradient values and second gradient values corresponding to all pixel points in each focusing window, a first focusing evolution value and a second focusing evolution value that correspond to each focusing window are obtained; and a focusing direction of a motor is determined according to the first focusing evolution values and second focusing evolution values and a step length of the motor is adjusted based on a first focusing changing rate of each first focusing evaluation value and a second focusing changing rate of each second focusing evaluation value until the lens of the motor is adjusted to be at a focusing state. Therefore, the focusing speed is fast and accurate.

Description

technical field [0001] The present invention relates to the field of video monitoring, in particular to an automatic focusing method and device. Background technique [0002] At present, in terms of basic principles, the autofocus (AutoFocus, that is, the camera can automatically adjust the subject to focus on a clear position by adopting a preset method) technology used in cameras in the related art can be divided into the following Two categories: [0003] The first type, active focusing, that is, by emitting ultrasonic or infrared rays to the subject, and then detecting the reflected sound waves or light to calculate the distance between the subject and the camera lens, so that the motor drives the lens to move to the focus position ; [0004] The second type, passive focusing, does not depend on the wave source of the imaging system, but receives the light emitted by the imaging target through the lens part, and then directly uses the brightness of the imaging target (...

AI Technical Summary

Problems solved by technology

In the actual operation process, although the focus curve using the filter to calculate the focus evaluation value can show a good unimodality in most imaging scenes, there is only one extreme value, that is, the clear point, but in some lights In scenes, such as outdoor scenes with street lights, the focus curve is more complicated, and it is difficult to find a clear point

In addition, there are other related technical solutions that propose a search method with a variable step size to increase the auto-focus speed, and use the slope of the line connecting the focus evaluation values ​​of adjacent points to determine the sampling step size. However, the focus evaluation value of the image is easily affected by the circuit and Environmental impact, especially in the case of serious defocus, the slope of adjacent points is irregular at this time, and it is difficult to determine the correct sampling step size

In addition, when the focus curve is not smooth and there are glitches, this search method is easy to fall into local extrema, that is, false peaks

At this time, it is not possible to find an exact clear point

[0008] To sum up, there is a lack of a technical solution for fast focusing on the premise of ensuring focusing stability and precision in the related art

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