Autofocus method and electronic device performing same

1. An electronic device comprising:

a camera including a lens assembly including one or more lenses and a driving unit capable of adjusting a focus by moving at least some of the lenses of the lens assembly;

a memory; and

a processor operatively connected to the lens assembly, the camera, and the memory,

wherein the processor is configured to:

obtain a first image corresponding to a first position of the at least some of the lenses and a second image corresponding to a second position of the at least some of the lenses with respect to an external object using the camera,

determine conditions related to contrast characteristics with respect to the external object using the first image and the second image,

determine a first movement direction and a movement amount of the at least some of the lenses using the first image, the second image, and a designated point spread function based on the conditions satisfying a designated first condition, and adjust the focus on the external object by moving the at least some of the lenses in accordance with the determined first movement direction and the determined movement amount, and

determine a second movement direction of the at least some of the lenses using a contrast difference between the external object included in the first image and the external object included in the second image based on the conditions satisfying a designated second condition, and adjust the focus on the external object at least based on a contrast change of one or more images obtained while moving the at least some of the lenses along the deter mined second movement direction.

2. The electronic device of claim 1 , wherein the processor is configured to:

determine a third movement direction of the at least some of the lenses using the first image, the second image, and the designated point spread function based on the conditions satisfying a designated third condition, and

adjust the focus on the external object at least based on the contrast change of the one or more images obtained while moving the at least some of the lenses along the determined third movement direction.

3. The electronic device of claim 1 ,

wherein the memory stores point spread function information, and

wherein the processor is configured to:

measure a DFD resultant value based on the first image and the second image,

measure a cost value corresponding to the first image and the second image based on the measured DFD resultant value and the point spread function information, and

determine reliability based on the measured cost value.

4. The electronic device of claim 3 , wherein the processor is configured to:

determine a target position according to a DFD method, and

determine a movement direction and a movement amount of the at least some of the lenses corresponding to the determined target position.

5. The electronic device of claim 4 , wherein the processor is configured to:

determine whether a difference value between a maximum value and a minimum value of the measured cost value is equal to or larger than a first threshold value,

adjust positions of the at least some of the lenses based on the determined target position in case that the difference value is equal to or larger than the first threshold value, and

adjust the positions of the at least some of the lenses using the contrast difference between the external objects in case that the difference value is smaller than the first threshold value.

6. The electronic device of claim 5 , wherein the processor is configured to:

identify the first position and the second position in case that the difference value is equal to or larger than the first threshold value,

compare a distance between the determined target position and the second position with a second threshold value,

adjust the positions of the at least some of the lenses corresponding to the target position in case that the distance is equal to or smaller than the second threshold value, and adjust the focus on the external object at least based on the contrast change of the obtained one or more images, and

determine the movement direction of the at least some of the lenses corresponding to the target position in case that the distance exceeds the second threshold value, and adjust the positions of the at least some of the lenses at least based on the contrast change of the determined movement direction and the obtained one or more images.

7. The electronic device of claim 6 , wherein the processor is configured to:

measure a first contrast value corresponding to the first position and a second contrast value corresponding to the second position, and

identify the first position and the second position based on the first contrast value and the second contrast value.

8. The electronic device of claim 1 , wherein a first movement interval at which the at least some of the lenses move based on the first condition is configured to be smaller than a second movement interval at which the at least some of the lenses move based on the second condition.

9. A method for controlling a focus of camera lenses in an electronic device, the method comprising:

obtaining a first image corresponding to a first position of at least some of the lenses and a second image corresponding to a second position of the at least some of the lenses with respect to an external object using a camera including one or more lenses;

determining conditions related to contrast characteristics with respect to the external object using the first image and the second image;

determining a first movement direction and a movement amount of the at least some of the lenses using the first image, the second image, and a designated point spread function based on the conditions satisfying a designated first condition, and adjusting the focus on the external object by moving the at least some of the lenses in accordance with the determined first movement direction and the determined movement amount; and

determining a second movement direction of the at least some of the lenses using a contrast difference between the external object included in the first image and the external object included in the second image based on the conditions satisfying a designated second condition, and adjusting the focus on the external object at least based on a contrast change of one or more images obtained while moving the at least some of the lenses along the determined second movement direction.

10. The method of claim 9 , further comprising:

determining a third movement direction of the at least some of the lenses using the first image, the second image, and the designated point spread function based on the conditions satisfying a designated third condition, and

adjusting the focus on the external object at least based on the contrast change of the one or more images obtained while moving the at least some of the lenses along the determined third movement direction.

11. The method of claim 9 , further comprising:

storing point spread function information in a memory of the electronic device;

measuring a DFD resultant value based on the first image and the second image;

measuring a cost value corresponding to the first image and the second image based on the measured DFD resultant value and the point spread function information; and

determining reliability based on the measured cost value.

12. The method of claim 11 , wherein determining the movement direction and the movement amount of the at least some of the lenses comprises:

determining a target position according to a DFD method; and

determining a movement direction and a movement amount of the at least some of the lenses corresponding to the determined target position.

13. The method of claim 12 , wherein adjusting the focus on the external object comprises:

determining whether a difference value between a maximum value and a minimum value of the measured cost value is equal to or larger than a first threshold value;

adjusting positions of the at least some of the lenses based on the determined target position in case that the difference value is equal to or larger than the first threshold value; and

adjusting the positions of the at least some of the lenses using the contrast difference between the external objects in case that the difference value is smaller than the first threshold value.

14. The method of claim 13 , further comprising:

identifying the first position and the second position in case that the difference value is equal to or larger than the first threshold value;

comparing a distance between the determined target position and the second position with a second threshold value;

adjusting the positions of the at least some of the lenses corresponding to the target position in case that the distance is equal to or smaller than the second threshold value, and adjusting the focus on the external object at least based on the contrast change of the obtained one or more images; and

determining the movement direction of the at least some of the lenses corresponding to the target position in case that the distance exceeds the second threshold value, and adjusting the positions of the at least some of the lenses at least based on the contrast change of the determined movement direction and the obtained one or more images.

15. The method of claim 9 , wherein a first movement interval at which the at least some of the lenses move based on the first condition is smaller than a second movement interval at which the at least some of the lenses move based on the second condition.