TWI395047B - Automatic focusing method and image capture apparatus using the same - Google Patents

Description

Autofocus method and image capturing device using the same

The present invention relates to image capture, and more particularly to an image capture device that utilizes the imaging size of a subject to perform autofocus.

Accurate focus is one of the elements that captures a clear image when shooting an image. Therefore, in addition to manual focusing, with the autofocus function provided by the camera, the user can also capture images with vivid colors and sharp outlines.

Conventionally, autofocus can measure the distance between an object and a lens through a distance measuring device, and accordingly, the mirror distance is adjusted. However, this approach requires additional hardware design and cost.

Alternatively, in some conventional techniques, the movable lens scans and captures the relevant image, and the high frequency component generated by frequency domain conversion of each image is used as a contrast, thereby analyzing according to the contrast of each image. The best focus position corresponding to the maximum contrast is taken to capture the sharpest image. However, repeatedly moving the lens is not only time consuming, but when the object to be photographed is not clear, the repeated focusing operation will also cause the focusing time to be too long.

In view of the above, the present invention provides an autofocus method and an image capture device using the above method.

Based on the above, an embodiment of the present invention provides an auto-focusing method, which is applicable to an image capturing device. The image capturing device includes a lens and an image sensing unit. First, an image is captured on the image sensing unit through the lens. Analyze the image to determine a primary subject, And obtaining identification data of the main shooting object, wherein the identification data is used to obtain an imaging setting value corresponding to one of the main shooting objects. Then, an imaging size of the main subject image formed on the image sensing unit is calculated according to the image. Determining a shooting distance according to the imaging size, a reference size of the imaging setting value, and a predetermined image distance, wherein the predetermined image distance is a distance between the lens and the image sensing unit, and the shooting distance is the The distance between the main subject and the lens. Finally, image capturing is performed on the main subject according to the shooting distance and the imaging setting value.

In addition, an embodiment of the present invention provides an image capturing device including a lens, a driving unit, an image sensing unit, and a processing unit. This lens is used to focus an image. The driving unit is coupled to the lens for driving the lens. The image sensing unit captures the image through the lens. The processing unit is coupled to the image sensing unit for determining one of the main images of the image, obtaining an identification data of the main shooting object, and obtaining an imaging setting value corresponding to one of the main shooting objects according to the identification data, Calculating an imaging size of the main imaging object on the image sensing unit, determining a shooting distance according to the imaging size and one of the imaging setting values, and a predetermined image distance, and according to the shooting distance and the imaging The set value is used to capture the image of the main subject.

The above described objects, features, and advantages of the invention will be apparent from the description and appended claims appended claims

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the first and second drawings of the accompanying drawings. Implementation provided by the specification of the present invention Examples are used to illustrate the technical features of various embodiments of the present invention. The arrangement of the various elements in the embodiments is for illustrative purposes and is not intended to limit the invention. In addition, the embodiment of the present invention is described by taking a camera as an example, but not limited thereto, any image capturing device that needs to perform a focusing process, such as a camera, is applicable to the method of the embodiment of the present invention.

1 is a block diagram of an image capture device 10 according to an embodiment of the present invention, including a lens 102, a driving unit 104, an image sensing unit 106, and a processing unit 108. In an embodiment of the invention, the image capture device comprises a camera or a camera. In one embodiment, the image capture device includes a digital camera, a digital camera, or an electronic device having an image capture function.

Referring to Figure 1, the lens 102 is used to focus an image. The driving unit 104 is coupled to the lens 102 for driving the lens 102, and the image sensing unit 106 captures the image through the lens 102. In one embodiment, the driving unit 104 includes a focus motor (not shown) for controlling the number of steps of the lens 102 and changing the distance between the lens 102 and the image sensing unit 106. The processing unit 108 is coupled to the image sensing unit 106 for receiving images captured by the image sensing unit 106. In one embodiment, the processing unit 108 can be a digital signal processing (DSP) that stores, analyzes, and calculates the image and generates associated control signals. Further, in another embodiment, the image sensing unit 106 can be a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) for sensing the image through the lens 102 and corresponding thereto. Output Image information.

As shown in FIG. 1 , after receiving the image from the image sensing unit 106 , the processing unit 108 analyzes the image to determine a main shooting object, thereby extracting one of the main shooting objects and identifying the data. In operation, the image capturing device 10 further includes a memory unit 110 having a database (not shown) for storing a plurality of image samples. In this embodiment, the processing unit 108 processes the image by using image recognition, and extracts features of the plurality of captured objects from the image as a comparison template, and uses the comparison template in the database. Each image sample is compared or paired to identify features or categories similar to the objects, such as a face or a house. Subsequently, the main subject is determined from the identification data according to a predetermined rule. For example, a priority order can be defined to specify the primary subject. For example, the main subject may be the face of the image, and if there is no face, the animal is searched in turn. In another embodiment, the location of the objects may be determined by the location of the objects. For example, when a plurality of faces are recognized, the center of the image of the image may be first determined, and then the face of the adjacent center region may be searched for as the main subject.

Further, according to the identification data, the processing unit 108 reads, from the database, an imaging setting value corresponding to one of the main shooting objects, such as an object size, wherein the object size is defined, and generally, each object The average size is defined. Then, the processing unit 108 calculates an imaging size B of the main subject image formed on the image sensing unit 106. In an embodiment, if the length and width of the main imaging object imaged on the image sensing unit 106 are N primitives, and each primitive size is P, the imaging size B = N × P. It is worth noting that the imaging size can also be calculated by other means.

Then, after calculating the imaging size, the processing unit 108 can determine a shooting distance L to indicate the relative distance between the main shooting object and the lens 102 by using one of the imaging setting values and a predetermined image distance. For example, if the main subject is a face X, the average size A corresponding to the face X can be obtained from the database as the reference size. Further, if the predetermined image distance F is the distance between the lens 102 and the image sensing unit 106, the shooting distance can be calculated according to the reference size A, the imaging size B, and the predetermined image distance F. .

In an embodiment, the image capturing device 10 further includes an aperture 112 and a shutter 114. For the main subject, such as the face X, the aperture 112 controls the amount of incident light of the lens 102 according to the aperture value determined by the imaging setting value, and the shutter 114 determines the shutter speed according to the imaging setting value. The exposure amount of the image sensing unit 106 is adjusted. The shutter 114 can be triggered by a built-in shutter button or an external control device.

In an embodiment, the driving unit 104 obtains a corresponding one of the moving steps according to the shooting distance L, directly drives the lens 102 to a focus position, and then captures an image of the main shooting object according to the imaging setting value.

More specifically, the driving unit 104 can perform a focus scanning operation according to a focus range of the shooting distance L. For example, if the shooting distance L is 10 meters, the number of moving steps corresponding to the shooting distance L is 100 steps, and the focusing range is assumed to be preset to 20 steps, then the driving unit 104 Between the 90th step and the 110th step, the lens is moved to each of the second focus positions at a fixed interval, and the image capture is performed to perform a focus scan operation, wherein the focus range is It depends on the user's settings, the characteristics of the main subject, or the specifications of the lens. After extracting the relevant image at each of the second focus positions, the processing unit 108 calculates an image contrast corresponding to each of the second focus positions to determine an optimal focus position. That is, the in-focus position corresponding to the maximum contrast is obtained within the focus range. In this way, higher focus accuracy can be achieved.

It should be noted that the image capturing device 10 further includes a flasher 116 for enabling a flash to reinforce the exposure of the image sensing unit 106 during image capture.

2 is a flow chart showing an autofocus method 20 in accordance with an embodiment of the present invention. The auto-focusing method 20 is applicable to an image capturing device (such as the image capturing device 10 of FIG. 1), wherein the image capturing device has a lens and an image sensing unit.

Referring to FIG. 2, first, an image is captured on the image sensing unit through the lens (step S202). Next, the image is analyzed to determine a main subject, and at the same time obtain one of the main subject identification data (step S204). In an embodiment, after capturing a plurality of captured objects from the image, the image samples created in a database are used to identify the captured objects to generate a plurality of identification data. After the identification data is generated, the main subject is determined from the identification data according to a predetermined rule. This part has been described in detail in FIG. 1 and its related embodiments, and will not be further described herein.

Then, based on the identification data, an imaging setting value corresponding to one of the main subjects is read from the library (step S206). In one embodiment, the imaging setpoint includes a reference size, a predetermined image distance, an aperture value, and a shutter speed. The reference size is used to indicate the average size of the main subject. The predetermined image distance is used to indicate the relative distance between the lens and the image sensing unit. This aperture value is used to control the amount of incident light of the lens. The shutter speed is used to control the exposure amount of the image sensing unit.

Further, according to the image, an imaging size of the main imaging object imaged on the image sensing unit is obtained (step S208). Through the imaging size and the imaging setting value, a shooting distance, that is, a distance between the main shooting object and the lens can be determined (step S210). The manner of calculating the shooting distance has been described above in conjunction with the embodiment of Fig. 1, and the description thereof is omitted here.

After determining the shooting distance, the lens can be directly driven to a focus position by one of the moving steps corresponding to the shooting distance, and the shutter or the aperture is controlled according to the imaging setting value to perform image detection on the main shooting object. Take (step S212).

Compared with the above-mentioned fast focus mode, the shooting distance can be adjusted according to a focus range to perform precise focusing (step S214). More specifically, according to the number of moving steps corresponding to the focus range, the lens is moved to the relevant focus position to perform an operation of capturing an image. From the captured image, look for the image with the highest contrast and its corresponding best focus position to improve focus accuracy.

Compared with the prior art, the autofocus method disclosed in the present invention and the image capturing device using the same can be selected according to different shooting objects. Like the set value, directly calculate the most suitable focus position, thus shortening the time required for focusing. In addition, a small range of focus scanning can be performed by using a focus range at the focus position, and by analyzing the contrast of the image captured by each sampling point, an optimal focus position is obtained for image capturing, and at the same time Achieve fast and accurate focus.

While the present invention has been described in its preferred embodiments, the present invention is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application.

10‧‧‧Image capture device

102‧‧‧ lens

104‧‧‧ drive unit

106‧‧‧Image sensing unit

108‧‧‧Processing unit

110‧‧‧ memory unit

112‧‧‧ aperture

114‧‧ ‧Shutter and

116‧‧‧Flash

1 is a block diagram showing an image capturing device according to an embodiment of the present invention; and FIG. 2 is a flow chart showing an automatic focusing method according to an embodiment of the present invention.

10‧‧‧Image capture device

102‧‧‧ lens

104‧‧‧ drive unit

106‧‧‧Image sensing unit

108‧‧‧Processing unit

110‧‧‧ memory unit

112‧‧‧ aperture

114‧‧ ‧Shutter and

116‧‧‧Flash

Claims (9)

An autofocus method is applicable to an image capture device. The image capture device includes a lens and an image sensing unit. The autofocus method includes: capturing an image through the lens; analyzing the image to determine a primary Taking an object and obtaining identification data of one of the main shooting objects; obtaining an imaging setting value corresponding to one of the main shooting objects according to the identification data; and calculating, according to the image, the main shooting object is imaged on the image sensing unit An imaging size; and determining a shooting distance according to the imaging size, a reference size of the imaging setting value, and a predetermined image distance, wherein the predetermined image distance is a distance between the lens and the image sensing unit, and the shooting is performed The distance is the distance between the main subject and the lens; wherein the analyzing the image comprises: capturing at least one subject from the image; using at least one of each of the plurality of image samples in a database Identifying an object to generate a plurality of identification data; and determining the master from the identification data according to a rule Shooting an object; wherein the rule is to determine the main subject according to the type of the at least one subject; wherein the main subject system is based on a type of the at least one subject and a specific order corresponding to the type of the at least one subject Determined The types of such image samples in the database include at least faces, houses and animals. The autofocus method of claim 1, further comprising: performing image capture on the main subject according to the shooting distance and the imaging setting value. The method of claim 2, wherein the step of capturing the image of the main subject comprises: driving the lens to a focus position according to a moving step corresponding to the shooting distance; Capture. The autofocus method of claim 2, further comprising: adjusting the shooting distance according to a focus range; driving the lens according to the number of moving steps corresponding to the focusing range to determine a plurality of second focusing positions; The image contrast corresponding to each of the second focus positions is calculated to determine one of the best focus positions for image capture. The autofocus method of claim 1, wherein the main subject system is determined according to the at least one photographing object located at a center of the image, the type of the at least one photographing object, and the specific order. An image capturing device includes: a lens for focusing an image; a driving unit coupled to the lens for driving the lens; and an image sensing unit for capturing the image through the lens; A processing unit is coupled to the image sensing unit for determining one of the main images of the image, obtaining an identification data of the main shooting object, and obtaining an imaging setting value corresponding to one of the main shooting objects according to the identification data. Calculating an imaging size of the main imaging object on the image sensing unit, and determining a shooting distance according to the imaging size and one of the imaging setting values and a predetermined image distance, wherein the predetermined imaging distance a distance between the lens and the image sensing unit, wherein the shooting distance is a distance between the main shooting object and the lens; and a memory unit includes a database for storing a plurality of image samples, wherein the processing unit is Taking a plurality of captured objects in the image, each of the plurality of image samples is used to identify the captured objects, to generate a plurality of identification data, and determining the main captured object from the identification data according to a rule; Wherein, the rule determines the main subject according to the type of the photographed object; wherein the main subject system root The object of at least one kind of shot, and a specific sequence corresponding to the at least one kind of object of shooting of the decision, and those kinds of images of the sample library to include at least a face, house and animals. The image capturing device of claim 6, wherein the driving unit drives the lens to a focus position according to a moving step corresponding to the shooting distance, and performs image capturing at the focusing position. The image capturing device of claim 6, wherein the driving unit is in accordance with a moving step corresponding to a focusing range of the shooting distance The number is driven to the second focus position of the plurality of pixels, and the image capture is performed, and the processing unit calculates the image contrast corresponding to each of the second focus positions, and determines one of the best focus positions for image capture. The image capturing device of claim 6, wherein the primary subject system is determined according to the at least one subject, the type of the at least one subject, and the specific order at a center of the image.