TWI440952B - Autofocus system - Google Patents

Description

Autofocus system

The present invention relates to autofocus, and more particularly to an autofocus system that can quickly estimate the focus position.

The camera's auto focus mainly includes two parts: focus measurement and search strategy. Wherein, the focus evaluation is based on the input image to generate a corresponding focus value, and each lens position and the corresponding focus value can obtain a focus profile; the search strategy is to guide the lens according to the obtained focus value to find The position of the lens where the maximum focus value is located, that is, the in-focus position.

As far as various traditional search strategies are proposed, the following shortcomings are common. In order to resist image noise to improve the accuracy of autofocus, the focus curve produced by the focus evaluation becomes steeper near the maximum focus value, and the steep area becomes smaller. Such a focus curve will make traditional search strategies difficult to design or slow down the search speed. In addition, traditional search strategies generally require a number of parameters to determine which part of the focus curve the current lens position is. These parameters are not only difficult to determine, but often cannot be applied to different scenarios with different complexity; and, once the focus evaluation method is changed, these parameters must be re-determined. Furthermore, for some rule-oriented search strategies, such as the Fibonacci search strategy, some assumptions must be made about the starting position of the shot, thus making this type of search strategy unapplied to the autofocus of a digital camera.

Therefore, there is a need to propose a novel autofocus mechanism to solve the problems caused by the above conventional autofocus.

In view of the above, one of the objects of embodiments of the present invention is to provide an autofocus system for quickly estimating a focus position, greatly reducing the amount of computation, or reducing the use of empirical parameters.

According to an embodiment of the invention, an autofocus system includes a focus evaluation unit, a focus conversion unit, and a focus position estimating unit. The focus evaluation unit receives an image and generates a corresponding focus value accordingly. The focus conversion unit receives the focus value provided by the focus evaluation unit and converts it to obtain a corresponding converted focus value. The focus position estimating unit obtains a focus position in an analytical manner according to the plurality of converted focus values and the corresponding plurality of lens positions.

The first figure shows a block diagram of an autofocus system 100 in accordance with an embodiment of the present invention that can be applied to a general image capture device, such as a camera or camera. In this embodiment, the focus measurement unit 11 receives an image and generates a corresponding focus value. The larger the value, the clearer the image, and the smaller the focus value, the more the image is displayed. blurry. The focus evaluation unit 11 of the present embodiment can be implemented using a general focus evaluation technique, such as a high pass filter, but is not limited thereto. Since a clear image has more high-frequency components than a blurred image, a clear image will have a higher focus value after passing through the high-pass filter, and the blurred image will have a lower focus value after passing through the high-pass filter. The focus evaluation unit 11 can be implemented in a hardware or software manner, and the focus value generated can be directly calculated from the image or indirectly calculated from the frequency component of the image.

The operation of the above-described focus evaluation unit 11 can be performed in conjunction with the drive unit 10 (for example, a servo motor). The driving unit 10 can be used to move the lens of the image capturing device to a certain lens position to obtain a corresponding image, thereby enabling the focus evaluation unit 11 to obtain a corresponding focus value. If a plurality of lens positions and corresponding focus values are plotted, a focus profile can be obtained, as illustrated in the second figure. In the focus curve, the position of the lens where the maximum focus value is located is usually the clearest image. This position is called the in-focus position. On the contrary, in the area where the focus value is small, the corresponding image is relatively blurred, which is called an out-of-focus area. It is worth noting that, as shown in the second figure, the focus defocus area is much larger than the steep area near the focus position, so the information available to estimate the focus position is too small to be Quickly and accurately estimate the focus position.

In view of this, the present embodiment uses the focus conversion unit 12, which receives the focus value supplied from the focus evaluation unit 11, and converts it, thereby obtaining a corresponding converted focus value. Next, the focus position estimating unit 13 quickly obtains the focus position in an analytical manner according to the plurality of converted focus values and the corresponding number of lens positions. The focus conversion unit 12 and the focus position estimating unit 13 of the present embodiment can be implemented using a hardware or software.

The third figure shows a block diagram of the focus conversion establishing system 300 of the embodiment of the present invention for providing a basis for the focus conversion unit 12 (first image) to perform focus value conversion. In the present embodiment, the focus conversion establishing system 300 mainly includes a conversion establishing unit 31 that receives the focus curve provided by the focus evaluation unit 11 (as illustrated in the second figure), and converts it to obtain a converted focus curve ( Transformed focus profile). According to one of the features of embodiments of the present invention, the converted focus curve can be described by a resolvable mathematical formula. In the present specification, the term "analytical mathematical expression" refers to a mathematical description containing basic mathematical operations such as addition, subtraction, multiplication, division or exponentiation. The parsable mathematical description may be a closed-form mathematical description or an algebraic mathematical description, but is not limited thereto. The converted focus curve generated by the conversion establishing unit 31 is supplied to the focus conversion unit 12 (first map), whereby the conversion of the focus value is performed.

The parsable mathematical description feature of the converted focus curve can be implemented by using a programming method, or a table can be used to record the focus value before conversion and the corresponding converted focus value. The value table can be stored in the memory of the image capture device (eg, non-volatile memory).

The fourth figure illustrates the converted focus curve generated by the conversion establishing unit 31 (third map). According to one of the features of the embodiments of the present invention, the converted focus curve (fourth map) can expand the steep region of the original focus curve (second map) and reduce the original flat region. Thereby, the amount of information that can be used to estimate the focus position is increased, so that the focus position estimating unit 13 (first map) can quickly and accurately estimate the focus position using the analytical method, and can greatly reduce the amount of calculation required for the estimation. . Taking the converted focus curve illustrated in the fourth figure as an example, the focus position estimating unit 13 can obtain the minimum value using a mathematical analysis method, and the corresponding lens position indicates the focus position.

Since the embodiment of the present invention can quickly estimate the focus position, the drive unit 10 can quickly move the lens to the focus position. In addition, the present embodiment uses a mathematical analysis method to obtain a focus position, which is simple in operation, thereby greatly reducing the amount of calculation and reducing the use of empirical parameters. In addition, the focus value conversion used in the embodiment can be determined before the image capturing device leaves the factory, and once determined, it can be applied to various different scenes. Furthermore, since the embodiment of the present invention does not have any assumption of focus evaluation, it can be applied to the focus value generated by various focus evaluation techniques. Compared with the conventional autofocus method, the focus value generated by the focus evaluation is directly used to search for the focus position. In this embodiment, the focus value is first converted, and then the focus position is estimated according to the converted focus value. The converted focus curve of the present embodiment can be described by a resolvable mathematical formula, so that the lens can accurately estimate the focus position even in the defocus position to achieve the purpose of fast autofocus.

The above description is only the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention; all other equivalent changes or modifications which are not departing from the spirit of the invention should be included in the following Within the scope of the patent application.

100. . . Autofocus system

10. . . Drive unit

11. . . Focus evaluation unit

12. . . Focus conversion unit

13. . . Focusing position estimation unit

300. . . Focus conversion system

31. . . Conversion establishment unit

The first figure shows a block diagram of an autofocus system in accordance with an embodiment of the present invention.
The second figure illustrates the focus curve.
The third figure shows a block diagram of a focus conversion establishing system in accordance with an embodiment of the present invention.
The fourth figure illustrates the converted focus curve generated by the conversion establishing unit of the third figure.

100. . . Autofocus system

10. . . Drive unit

11. . . Focus evaluation unit

12. . . Focus conversion unit

13. . . Focusing position estimation unit

Claims (6)

An autofocus system comprising:
a focus evaluation unit that receives an image and generates a corresponding focus value accordingly;
a focus conversion unit receives the focus value provided by the focus evaluation unit and converts it to obtain a corresponding converted focus value; and a focus position estimation unit, according to the plurality of converted focus values and corresponding A plurality of lens positions are obtained in an analytical manner to obtain a focus position. The autofocus system as described in claim 1 of the patent scope further includes:
A conversion establishing unit receives the focus curve provided by the focus evaluation unit, converts it to obtain a converted focus curve, and supplies the focus conversion unit to the focus conversion unit to perform conversion of the focus value. The autofocus system of claim 2, wherein the converted focus curve can be described by a resolvable mathematical formula. The autofocus system of claim 2, wherein the converted focus curve records the focus value before the conversion and the corresponding converted focus value in a numerical value table. The autofocus system of claim 4, wherein the value table is stored in a memory of an image capture device. The autofocus system as described in claim 1 of the patent scope further includes:
a driving unit for moving a lens to a certain lens position to obtain a corresponding image, thereby enabling the focus evaluation unit to obtain a corresponding focus value.