TWI407235B - Auto focus system and method same - Google Patents

Abstract

An auto focus system including: a focusing lens configured to move in a focusing area; a judgment module configured to contrast a current position and an initial position of the focusing lens, and judging that whether the distant between the current position and the initial position greater than 48 steps; a controlling module choosing an auto focus mode according to the result of the judgment module; when the distant between the current position and the initial position greater than 48 steps, the controlling module controls the focusing lens to move toward to the initial position; a contrasting module contrasting the contrast value of the first three images from the current position to the initial position. If the contrast value of the first three images decreases in order, the controlling module controls the focusing lens to reverse move away from the initial position to find out the optimal focus position. In other conditions, the focusing lens is fast move to the initial position, then reverse move away from the initial position and find out the optimal focus position.

Description

Autofocus system and method

The invention relates to a camera technology, in particular to an auto focus system and an auto focus method.

In the prior art, when a digital camera focuses, a stepping motor is used to move the focus module in the lens back and forth (the distance moved is expressed in steps), and is received by the image sensing component (such as a charge coupled component). Focusing on the light of the module, and using the digital signal processor to calculate the focus point corresponding to the focus module when the contrast value is maximum.

When the previous digital camera performs autofocus, regardless of the number of steps between the current position and the initial position, the focus module is moved to the initial position, and then the focus module is moved away from the initial position and the image sensing element is moved. The comparison values of each frame of the image are compared to find the focus point corresponding to the focus module when the contrast value is maximum. Another method of focusing is to directly move the focus module from the current position to the next focus position, and according to the contrast value of the image acquired by the generated start position and the next focus position, continue to move the focus in the same direction when the contrast value increases. The module compares the contrast values of the acquired images. When the contrast value of the acquired images decreases, the focus module is moved in the opposite direction to find the best focus point; when the contrast value decreases, the focus module is moved in the opposite direction. And compare the collected The contrast value of the image, when the contrast value of the acquired image is reduced, the focus module is moved again in the opposite direction to find the best focus point. However, these two autofocus methods also have an advantage in autofocus speed when the current position of the focus module is different. If you only use one of the autofocus methods, it will take too long to focus, which will affect the performance of your digital camera.

In view of this, it is necessary to provide an autofocus system and an autofocus method that can select a focus mode according to the current position of the focus module.

An autofocus system includes a focus module, a determination module, a control module and a contrast module; a focus module is used for focusing; and a determination module determines a current position and a starting position of the focus module Whether the difference between the corresponding steps is greater than 48 steps; the control module selects the focus mode according to the judgment result; when the difference of the steps is greater than 48 steps, the control module controls the focus module to move toward the starting position, and the comparison module pairs are from the current The position is compared with the comparison value of the three consecutive images collected; when the contrast value is sequentially decreased, the focus module is moved away from the starting position, and the contrast values of the collected images are compared to find the maximum contrast value. The corresponding focus point is image-captured; when the contrast value of the two detected images is increased or the difference between the current position and the number of steps corresponding to the starting position is less than 48 steps, the focus mode is controlled. The group quickly returns to the starting position, then moves away from the starting position and compares the contrast values of the acquired images to find the focus of the largest contrast value for image capturing.

An autofocus method includes the steps of: determining whether a difference between a current position of a focus module and a starting position is More than 48 steps; if the difference between the steps is greater than 48 steps, the focus module moves toward the starting position and continuously acquires three frames of images from the current position; and determines whether the contrast values of the three consecutively collected images are sequentially decreased; If the contrast value is sequentially decreased, the focus module is moved away from the starting position, and the contrast value of each frame image is compared to find the focus point corresponding to the maximum contrast value for image capturing; when the collected is continuous When the contrast value of the two detected images increases before the three frames of images or the difference between the current position and the number of steps corresponding to the starting position is less than 48 steps, the focus control module is quickly returned to the starting position, and then the direction is away from the starting position. Move and compare the contrast values of the acquired images to find the focus of the largest contrast value for image capture.

Compared with the prior art, the autofocus system and method provided by the present invention selects the autofocus mode by judging the vertical synchronization period of the difference between the current position and the starting position, thereby effectively improving the focusing speed and saving the focusing time.

100‧‧‧Auto Focus System

10‧‧‧ Focus Module

20‧‧‧Judgement module

30‧‧‧Control Module

40‧‧‧Comparative module

FIG. 1 is a schematic diagram of functional modules of an autofocus system according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing the correspondence between the number of focusing steps and the contrast value of the autofocus system in FIG. 1. FIG.

3 is a flow chart of an autofocus method provided by an embodiment of the present invention.

The technical solution will be further described in detail below with reference to the accompanying drawings and embodiments.

As shown in FIG. 1 , an autofocus system 100 according to an embodiment of the present invention includes a focus module 10 , a determination module 20 , a control module 30 , and a comparison module 40 .

The focus module 10 is configured to move within the focus area to make the captured scene image the clearest on the image sensing element. The focus module 10 runs 12 steps in each vertical synchronization period. When the image sensing component captures an image, the time required for the focus module 10 to operate in a vertical synchronization period is 1/30 s; When the image is moved quickly without acquiring an image, the time required for the focus module 10 to move in one vertical synchronization period is 12 ms. The vertical synchronization period is a time when the image sensing component acquires an image signal once. It can be understood that the number of steps taken by the focus module 10 in one vertical synchronization period can also be set to other steps.

The determining module 20 is configured to determine whether the difference between the current position of the focus module 10 and the starting position is greater than 48 steps, and the 48 steps are performed by the focusing module 10 in four vertical synchronization periods. Step count.

The control module 30 is configured to select an auto focus mode according to the determination result of the determination module 20 and control the movement of the focus module 10 . When the difference between the current position of the focus module 10 and the starting position is less than 48 steps, the control module 30 controls the focus module 10 to quickly move to the starting position, and then controls the focusing module 10 The image within each vertical sync period is acquired moving away from the starting position. When the difference between the current position of the focus module 10 and the starting position is greater than 48 steps, the control module 30 controls the focus module 10 from the current position. Moving in a direction near the home position, the image sensing element captures three consecutive frames of images including the current position and two vertical sync periods from the current position.

The comparison module 40 is configured to compare the contrast values of the acquired images. When the difference between the current position of the focus module 10 and the starting position is within 48 steps, the comparison module 40 moves the focus module 10 during each vertical synchronization period from the starting position. The contrast value of the collected image is analyzed, and the number of steps corresponding to the position of the focus module 10 when the contrast value is maximum is recorded; until the contrast value of the collected image is decreased, the control module 30 directly controls the The focusing module 10 quickly returns to the maximum position of the contrast value. When the difference between the current position of the focus module 10 and the starting position is greater than 48 steps, the comparison module 40 compares the collected values of the consecutive three frames of images from the current position. When the comparison values of the current three frames of images are sequentially decreased, the control module 30 controls the focus module 10 to move away from the starting position and collect images in each vertical synchronization period, and the acquired images are The comparison value is compared. When the contrast value of the captured image is decreased, the control module 30 directly controls the focus module 10 to quickly return to the maximum position of the contrast value; two frames before the three consecutive frames are continuously acquired. When the contrast value of the image is increased, the control module 30 directly controls the focus module 10 to quickly return to the starting position, and then moves the focusing module 10 in a direction away from the starting position and collects each vertical synchronization period. The comparison value of the image in the image is analyzed, and the number of steps corresponding to the maximum position of the contrast value is recorded. When the contrast value of the captured image is decreased, the control module 30 directly controls the focus module 10 to quickly return. Maximum contrast value At home.

As shown in FIG. 2, the starting position of the focus module 10 is at position 1104, and the focus interval is between 1104-1248 steps. When the current position of the focus module 10 is at the position of step 1140, the determining module 20 compares the step 1140 corresponding to the current position of the focus module 10 with the step 1104 corresponding to the starting position, and obtains the difference between the positions. The control module 30 directly controls the focus module 10 to quickly return to the starting position 1104, and then moves the focusing module 10 in a direction away from the starting position, and the comparing module 40 pairs the focusing module 10 at each The contrast value of the images collected during the vertical synchronization period is analyzed, and the number of steps corresponding to the maximum position of the contrast value is recorded as 1212; when the position of 1236 steps is collected, the contrast value of the collected image is found. The control module 30 directly controls the focus module 10 to quickly return to the 1212 step position. When the current position of the focus module 10 is at the position of 1200, the determining module 20 compares the 1200 steps corresponding to the current position of the focus module 10 with the step 1104 corresponding to the starting position, and the difference between the positions is greater than 48 steps; moving the focus module 10 along the starting position direction, and continuously collecting images of 1200 steps, 1188 steps and 1176 steps corresponding to two vertical synchronization periods from the current position; the comparison module 40 is opposite The comparison values of the collected images are compared to determine that the contrast values are sequentially decreased, and the control module 30 controls the focus module 10 to move away from the starting position and collect images; when the position of 1236 steps is collected, the collection is found. The comparison value of the two frames of images is reduced, and the control module 30 directly controls the focus module 10 to quickly return to the position of step 1212. When the current position is at the position of 1236, the determining module 20 compares the step 1236 corresponding to the current position of the focus module 10 with the step 1104 corresponding to the starting position, and obtains that the difference between the positions is greater than 48 steps; Moving the focus module 10 in the position direction and collecting two vertical synchronization periods from the current position Corresponding to the image of step 1236, step 1224 and step 1212; the comparison module 40 compares the contrast values of the acquired images to determine the contrast value of the two detected images before the three consecutive frames are continuously acquired. When increasing, the control module 30 controls the focus module 10 to quickly move to the starting position 1104, and then moves the focusing module 10 in a direction away from the starting position and acquires an image in each vertical synchronization period; When the position of the 1236 step is found, the comparison value of the collected image is reduced, and the control module 30 directly controls the focus module 10 to quickly return to the position of step 1212.

As shown in FIG. 3, the present invention further provides an autofocus method, including the following steps: S101: determining whether a difference between a current position of a focus module 10 and a starting position is greater than 48 steps; S102: if step The difference between the numbers is greater than 48 steps, the focus module 10 moves toward the starting position direction and collects three consecutive frames of images from the current position; S103: determines whether the contrast values of the three consecutively collected images are sequentially decreased; S104: If the contrast value is sequentially decreased, the focus module 10 is moved away from the starting position direction, and the contrast value of each frame image is compared to find a focus point corresponding to the maximum contrast value; the focus module 10 During the movement away from the starting position, the comparison module 10 compares the contrast values of each frame image collected, and records the position corresponding to the maximum contrast value; when the acquired image is compared When decreasing, the focus module 10 is controlled to quickly return to the maximum position of the contrast value; S201: When the difference between the two detected images is increased or the difference between the current position and the step corresponding to the starting position is less than 48 steps, the focus module 10 is quickly returned to the starting position. And moving in a direction away from the starting position and comparing the contrast values of the collected images to find a focus point of the maximum contrast value; the contrast module moves in a direction away from the starting position, the contrast mode The group 10 compares the contrast values of each frame image collected, and records the position corresponding to the maximum contrast value; when the focus module 10 moves quickly, no image is acquired.

Compared with the prior art, the autofocus system and method provided by the embodiments of the present invention select an autofocus mode by judging a vertical synchronization period between a current position and a starting position, thereby effectively improving the focusing speed and saving the focusing time.

In summary, the present invention has indeed met the requirements of the invention patent, and has filed a patent application according to law. However, the above description is only a preferred embodiment of the present invention, and it is not possible to limit the scope of the patent application of the present invention. Equivalent modifications or variations made by persons skilled in the art in light of the spirit of the invention are intended to be included within the scope of the following claims.

100‧‧‧Auto Focus System

10‧‧‧ Focus Module

20‧‧‧Judgement module

30‧‧‧Control Module

40‧‧‧Comparative module

Claims (9)

An autofocus system includes a focus module, a determination module, a control module and a contrast module; a focus module is used for focusing; and a determination module determines a current position and a starting position of the focus module Whether the difference between the corresponding steps is greater than 48 steps; the control module selects the focus mode according to the judgment result; when the difference of the steps is greater than 48 steps, the control module controls the focus module to move toward the starting position, and the comparison module pairs are from the current The position is compared with the comparison value of the three consecutive images collected; when the contrast value is sequentially decreased, the focus module is moved away from the starting position, and the contrast values of the collected images are compared to find the maximum contrast value. Corresponding focus point; when the contrast value of the two detected images increases before the acquired three consecutive frames of images or the difference between the current position and the number of steps corresponding to the starting position is less than 48 steps, the control focus module is quickly returned. The starting position is then moved away from the starting position and the contrast values of the acquired images are compared to find the focus of the largest contrast value. The autofocus system of claim 1, wherein the control module directly controls the focus mode when the contrast value of the image acquired by the focus module after moving away from the starting position is decreased. The group quickly returns to the maximum position of the contrast value. The autofocus system of claim 1, wherein: the focus module runs 12 steps in each vertical synchronization period, and the time required for the focus module to move a vertical synchronization period when acquiring an image is 1/30 s. When the image is not captured, the time required for the focus module to move a vertical sync cycle is 12ms. The autofocus system of claim 1, wherein: the contrast module compares the contrast values of each frame image collected during the movement away from the starting position. And record the position corresponding to the maximum contrast value. The autofocus system of claim 1, wherein: when the focus module moves quickly, no image is acquired. An autofocus method includes the steps of: determining whether a difference between a current position of a focus module and a starting position is greater than 48 steps; if the difference of the steps is greater than 48 steps, the focusing module is oriented to a starting position Motion and continuously collect three frames of images from the current position; determine whether the contrast values of the three consecutively acquired images are sequentially decreased; if the contrast values are sequentially decreased, the lenses are moved away from the starting position, and each frame is moved Compare the contrast values of the images to find the focus point corresponding to the maximum contrast value; the contrast value of the two detected images increases or the number of steps corresponding to the current position and the starting position before the successive three frames of images are acquired When the difference is less than 48 steps, the control focus module quickly returns to the starting position, then moves away from the starting position and compares the contrast values of the acquired images to find the focus point of the maximum contrast value. The autofocus method according to claim 6, wherein: the focusing module compares the contrast values of each frame image collected during the movement away from the starting position, and records the maximum The position corresponding to the comparison value. The autofocus method of claim 7, wherein: the pair When the contrast value of the image captured by the focus module after moving away from the starting position is reduced, the focus module is directly controlled to quickly return to the maximum position of the contrast value. The autofocus method of claim 6, wherein: when the focus module moves quickly, no image is acquired.