Auto-focusing imaging device and auto-focusing image capture method thereof

An imaging device includes a capturing module with at least one lens for capturing an image from a scene, a driving module for driving the at least one lens to different focusing positions using different driving steps, a flat-scene judging module, and a step-judging module. The flat-scene judging module divides the image into a central area and a plurality of peripheral areas, and determines whether the captured scene is a flat scene according to the divided image. The step-judging module determines whether the driving steps corresponding to a maximum focusing value of the central area of the image are same as driving steps corresponding to respective maximum focusing values of the peripheral areas of image, and changes the driving steps corresponding to the maximum focusing value of the central area to the driving steps corresponding to the greatest one of the maximum focusing values of the peripheral areas.

BACKGROUND

1. Field of the Invention

The present invention relates to an imaging device.

2. Description of the Related Art

When an imaging device, such as a digital camera, is used to capture an image from a flat scene, a central area of the image is clear while peripheral areas of the image may be blurred because the lens module in the imaging device is tilted or decentered relative to an imaging sensor during assembling of the image device.

What is needed, therefore, is to provide an imaging device, in which blurring of the peripheral areas of the image formed thereby is eliminated or at least alleviated.

SUMMARY

The present invention relates to an imaging device. The imaging device includes a capturing module with at least one lens for capturing an image of a scene, a driving module for driving the at least one lens to different focusing positions using different driving steps, a flat-scene judging module, and a step-judging module. The flat-scene judging module divides the image into a central area and a plurality of peripheral areas, and determines whether the captured scene is a flat scene according to the divided image. The step-judging module determines whether the driving steps corresponding to a maximum focusing value of the central area of the image are the same as driving steps corresponding to respective maximum focusing values of the peripheral areas of the image, and changes the driving steps corresponding to the maximum focusing value of the central area to the driving steps corresponding to the greatest one of the maximum focusing values of the peripheral areas.

Other advantages and novel features of the present invention will become more apparent from the following detailed description of exemplary embodiments when taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made to the drawings to describe the exemplary embodiments in detail.

Referring toFIG. 1, an imaging device10includes a capturing module11, a flat-scene judging module12, a step-judging module13, and a driving module14. The capturing module11is configured for capturing an image MFIG. 3from a current scene. The capturing module11includes a lens20for focusing light from the current scene into an imaging sensor (not shown) in the capturing module11. The driving module14includes a motor141for driving the lens20to different focusing positions using different driving steps of the motor141.

The flat-scene judging module12is configured for determining whether the captured scene is a flat scene according to the image M. Referring toFIG. 2, the flat-scene judging module12includes a dividing sub-module21, a curve-getting sub-module22, a focusing-position reading sub-module23, a distance-estimating sub-module24, and a comparing sub-module25.

The dividing sub-module21is configured for dividing the image M into a plurality of areas. The plurality of areas includes a central area and several peripheral areas. Referring toFIG. 3, in the exemplary embodiment, the image M is divided into nine areas by the dividing sub-module21, labeled as areas31-39, from left to right, and top to bottom of the image M, herein the area35is the central area and the other eight areas are the peripheral areas. It is to be understood that an alternative dividing fashion can be selected, but there must be a central area located in the center of the image M.

The curve-getting sub-module22is configured for getting respective auto-focusing curves of areas31to39at different driving steps of the motor141. Referring toFIG. 4, the vertical axis of a diagram represents auto-focusing values, and the horizontal axis of the diagram represents driving steps of the motor141. Auto-focusing curves L1-L9are formed from a plurality of auto-focusing values of the areas3139respectively at different driving steps of the motor141.

The focusing-position reading sub-module23is configured for reading a plurality of focusing positions i.e., a plurality of numbers of driving steps of the motor141according to the auto-focusing curves L1-L9. In the exemplary embodiment, some driving steps of the motor141are selected, as shown in Table 1.

In Table 1, AF-31through AF-39represents auto-focusing values of the auto-focusing curves L1-L9respectively at different driving steps of the motor141.

The distance-estimating sub-module24is configured for approximately calculating respective distances between the imaging device10and the captured scene according to the different driving steps of the motor141. The calculated distance can be found in a table similar to Table 1, which is provided by a manufacturer of the imaging device10. Shadowed regions in Table 1 show maximum focusing values corresponding to peaks of the auto-focusing curves L1-L9respectively.

The comparing sub-module25is configured for comparing the calculated distance corresponding to the central area35at the maximum focusing value of the auto-focusing curve L5with the calculated distances corresponding to the peripheral areas31,32,33,34,36,37,38, and39at the respective maximum focusing values of the auto-focusing curves L1, L2, L3, L4, L6, L7, L8and L9, and determining differences therebetween. If all differences are equal to or smaller than a reference difference value, the flat-scene judging module12determines the captured scene is a flat scene. If the one of the differences is greater than the reference difference value, the flat-scene judging module12determines the captured scene is not a flat scene. In the exemplary embodiment, the reference difference value is 150 millimeters (mm), which is obtained by experiments. Referring to Table 1, the calculated distance corresponding to the central area35is 471 mm at the maximum focusing value of the contrast curve L5, and all differences are smaller than 150 mm. That is, the captured scene is a flat scene.

If the captured scene is a flat scene, the step-judging module13is configured for determining whether number of driving steps corresponding to the maximum focusing value of the auto-focusing curve L5of the central area35is same as that corresponding to the respective maximum focusing values of the auto-focusing curves L1, L2, L3, L4, L6, L7, L8, L9of the peripheral areas31,32,33,34,36,37,38, and39. If not, the number of the driving steps of the motor141corresponding to the maximum focusing value AF-35of the auto-focusing curve L5of the central area35is changed to the number of the driving steps of the motor141corresponding to the greatest one of the maximum focusing values AF-31, AF-32, AF-33, AF-34, AF-36, AF-37, AF-38, AF-39of the auto-focusing curves L1, L2, L3, L4, L6, L7, L8, L9of the peripheral areas31,32,33,34,36,37,38, and39by the step-judging module13. Referring to Table 1 again, the respective number of the driving steps of the motor141corresponding to the maximum focusing values AF-31, AF-32, AF-33, AF-34, AF-35, and AF-36is the same, which herein is 20, while the respective number of the driving steps corresponding to the maximum focusing values AF-37, AF-38, and AF-39is the same, which herein are 22. Because the greatest one of the maximum focusing values AF-37, AF-38, and AF-39of the auto-focusing curves L7, L8, L9of the peripheral areas37,38, and39is 15203 (AF-39) corresponding to the peripheral area39as shown in Table 1, and the number of the driving steps of the motor141corresponding to the maximum focusing value AF-35of the auto-focusing curve of the central area35is changed from 20 to 22. Correspondingly, the focusing position corresponding to the maximum focusing value AF-35of the auto-focusing curve L5of the central area35is offset to the focusing position corresponding to the maximum focusing value AF-39of the auto-focusing curve L9of the peripheral area39of the image M by the motor141. As a result, a blurring of the peripheral areas of the image M can be avoided while a central blurring of the image M is in an acceptable range.

Referring toFIG. 5, a flowchart of an image capturing method of the imaging device10, is shown. The method includes capturing an image of a current scene (S10); dividing the image into a central area and a plurality of peripheral areas, and determining whether the captured scene is a flat scene according to the divided image (S11); if the captured scene is a flat scene, determining whether the number of driving steps of a motor corresponding to a maximum focusing value of the central area of the image is same as that corresponding to respective maximum focusing values of the plurality of peripheral areas of the image (S12); and if the number of the driving steps of the motor corresponding to the maximum focusing value of the central area is not same as the number of the driving steps of the motor corresponding to respective maximum focusing values of the plurality of peripheral areas, changing the number of the driving steps of the motor corresponding to the maximum focusing value of the central area to the number of the driving steps corresponding to the greatest one of the respective maximum focusing values of the plurality of peripheral areas (S13).

Referring toFIG. 6, the Step S11further includes getting respective auto-focusing curves of the plurality of areas (S21); reading a plurality of numbers of driving steps of the motor according to the auto-focusing curves of the plurality of areas (S22); calculating respective distances between the imaging device and the captured scene according to the numbers of the driving steps (S23); determining whether differences between the distance corresponding to the central area at a maximum focusing value of the auto-focusing curve of the central area and the distances corresponding to the peripheral areas at the respective maximum focusing values of the auto-focusing curves of the peripheral areas are greater than a reference difference value (S24); if no, the captured scene is a flat scene.

The above mentioned method can be performed by the imaging device10. In a process of capturing images by the method, the number of driving steps of the motor corresponding to the maximum focusing value of the central area is kept constant.