Auto focusing method, recording medium for recording the method, and auto focusing apparatus

1. An auto focusing method comprising:

determining a current position of a focus lens before moving the focus lens;

determining whether a first image input at the current position of the focus lens has image blurring using a histogram distribution of the first image;

if the current position of the focus lens is a position for close range focusing and the first image has image blurring, determining that a motion direction of the focus lens is toward longer range focusing;

if the current position of the focus lens is a position for long range focusing and the first image has image blurring, determining that the motion direction of the focus lens is toward closer range focusing;

if the current position of the focus lens is the close range position and the first image does not have image blurring, determining that the motion direction of the focus lens is toward closer range focusing; and

if the current position of the focus lens is the long range position and the first image does not have image blurring, determining that the motion direction of the focus lens is toward longer range focusing.

2. The auto focusing method of claim 1 , wherein determining a current position of a focus lens comprises:

calculating a distance between the current position of the focus lens and a subject;

if the distance is smaller than a reference distance, determining that the subject is positioned at a close distance, and

if the distance is greater than the reference distance, determining that the subject is positioned at a far distance.

3. The auto focusing method of claim 2 , wherein

if the subject is determined to be positioned at the far distance, then determining that the current position of the focus lens is the long range position, and

if the subject is determined to be positioned at the close distance, then determining that the current position of the focus lens is the close range position.

4. The auto focusing method of claim 1 , further comprising:

moving the focus lens in the determined motion direction;

inputting a second image;

determining whether the second image and the first image are the same scene images;

if the second image and the first image are different scene images, determining whether the second image has image blurring;

if the determined motion direction was toward longer range focusing and the second image has image blurring, determining that a second motion direction is toward closer range focusing; and

if the determined motion direction was toward closer range focusing and the second image has image blurring, determining that a second motion direction is toward longer range focusing.

5. The auto focusing method of claim 4 , further comprising:

if the determined motion direction was toward longer range focusing and the second image does not have image blurring, determining that a second motion direction is toward longer range position; and

if the determined motion direction was toward closer range focusing and the second image does not have image blurring, determining that the second motion direction is toward closer range focusing.

6. The auto focusing method of claim 4 , further comprising:

if it is determined that the first and second images are the same scene images, moving the focus lens within a predetermined range of the moved focus lens.

7. The auto focusing method of claim 1 , further comprising:

moving the focus lens in the determined motion direction;

determining a changed position of the moved focus lens;

inputting a second image;

determining whether the second image and the first image are the same scene images;

if the second image and the first image are different scene images, determining whether the second image has image blurring;

if the changed position of the moved focus lens is for long range focusing and the second image has image blurring, determining that a second motion direction of the focus lens is toward closer range focusing; and

if the changed position of the moved focus lens is for close range focusing and the second image has image blurring, determining that the second motion direction of the focus lens is toward longer range focusing.

8. The auto focusing method of claim 7 , wherein

if the changed position of the moved focus lens is for long range focusing and the second image does not have image blurring, determining that the second motion direction is toward longer range focusing; and

if the changed position of the moved focus lens is for close range focusing and the second image does not have image blurring, determining that the second motion direction is toward closer range focusing.

9. The auto focusing method of claim 7 , further comprising:

if it is determined that the first and second images are the same scene images, moving the focus lens within a predetermined range from the changed position of the moved focus lens.

10. The auto focusing method of claim 1 , wherein the step determining whether a first image input at the current position of the focus lens has image blurring, comprises:

determining a histogram distribution for an intensity scale of pixels of the first image;

if the histogram distribution is narrower than a predetermined histogram distribution then determining that the first image has image blurring; and

if the histogram distribution is wider than a predetermined histogram distribution then determining that the first image does not have image blurring.

11. A non-transitory recording medium on which the auto focusing method of claim 1 is recorded as a computer readable program code.

12. An auto focusing apparatus comprising:

a focus lens;

a focus lens motor for driving the focus lens;

a focus lens position determination unit for determining whether a current position of the focus lens before driving the focus lens is a long range position or a close range position;

an image analyzing unit for determining whether a first image input at the current position of the focus lens has image blurring using a histogram distribution of the first image;

a focus lens motion direction determination unit for determining that the motion direction of the focus lens is a direction allowing the focus lens to be in the long range position when the current position of the focus lens is the close range position and the first image has image blurring, for determining that the motion direction of the focus lens is a direction allowing the focus lens to be in the close range position when the current position of the focus lens is the long range position and the first image has image blurring, for determining when the current position of the focus lens is the close range position and the first image does not have image blurring that the motion direction of the focus lens is a direction allowing the focus lens to be in the close range position, and for determining when the current position of the focus lens is the long range position and the first image does not have image blurring that the motion direction of the focus lens is a direction allowing the focus lens to be in the long range position.

13. The auto focusing apparatus of claim 12 , wherein the focus lens position determination unit comprises:

a subject distance deduction unit for assuming and deducing a distance between the current position of the focus lens and a subject;

a subject distance determination unit for determining that a subject is positioned at a close distance when the distance is shorter than a reference distance and determining that a subject is positioned at a far distance when the distance is longer than a reference distance.

14. The auto focusing apparatus of claim 13 , wherein the positioning of a subject at the close distance corresponds to positioning of the focus lens in the close range, and the positioning of a subject at the far distance corresponds to positioning of the focus lens in the long range.

15. The auto focusing apparatus of claim 12 , further comprising:

an image comparison/determination unit for determining whether a second image that is input after a photographing apparatus comprising the focus lens is moved, is the same scene image as the first image,

wherein if it is determined that the first and second images are different scene images, the image analyzing unit further determines whether the second image has image blurring, and

when the focus lens is moved to be in the long range position in consideration of image blurring with respect to the first image and the second image has image blurring, the focus lens motion direction determination unit determines that the motion direction of the focus lens is a direction allowing the focus lens to be in the close range position, and when the focus lens is moved to be in the close range position in consideration of image blurring with respect to the first image and the second image has image blurring, the focus lens motion direction determination unit determines that the motion direction of the focus lens is a direction allowing the focus lens to be in the long range position.

16. The auto focusing apparatus of claim 15 , wherein when the focus lens is moved to be in the long range position in consideration of image blurring with respect to the first image and the second image does not have image blurring, the focus lens motion direction determination unit determines that the motion direction of the focus lens is a direction allowing the focus lens to be in the long range position, and when the focus lens is moved to be in the close range position in consideration of image blurring with respect to the first image and the second image does not have image blurring, the focus lens motion direction determination unit determines that the motion direction of the focus lens is a direction allowing the focus lens to be in the close range position.

17. The auto focusing apparatus of claim 15 , wherein the focus lens motion direction determination unit determines whether the second image and the first image are the same scene images and determines that the first and second images are the same scene images, the focus lens is moved within a predetermined range from the changed position of the focus lens that has been made with respect to the first image or is not moved.

18. The auto focusing apparatus of claim 12 , further comprising:

an image comparison/determination unit for determining whether a second image that is input after a photographing apparatus comprising the focus lens is moved, is the same scene image as the first image,

wherein the focus lens motor moves the focus lens in a motion direction of the focus lens that is determined in consideration of image blurring of the first image, and

the focus lens position determination unit determines the changed position of the focus lens, and

if the image comparison/determination unit determines that the first and second images are different scene images, the image analyzing unit further determines whether the second image has image blurring, and

when the changed position of the focus lens is the long range position and the second image has image blurring, the focus lens motion direction determination unit determines that the motion direction of the focus lens is a direction allowing the focus lens to be in the close range position, and when the changed position of the focus lens is the close range position and the second image has image blurring, the focus lens motion direction determination unit determines that the motion direction of the focus lens is a direction allowing the focus lens to be in the long range position.

19. The auto focusing apparatus of claim 18 , wherein when the changed position of the focus lens belongs to the long range and the second image does not have image blurring, the focus lens motion direction determination unit determines that the motion direction of the focus lens is a direction allowing the focus lens to be in the long range position, and when the changed position of the focus lens is the close range position and the second image does not have image blurring, the focus lens motion direction determination unit determines that the motion direction of the focus lens is a direction allowing the focus lens to be in the close range position.

20. The auto focusing apparatus of claim 18 , wherein if the image comparison/determination unit determines that the first and second images are same scene images, the focus lens motion direction determination unit determines such that the focus lens is moved within a predetermined range from the changed position of the focus lens that has been made with respect to the first image or is not moved.