Auto focusing apparatus and control method

1. An auto focusing apparatus comprising:

a detection unit which detects a focus signal indicating a focus state to an object in a focus detection area set within a frame of a photographed image signal;

an object information acquisition unit which acquires one or a plurality of pieces of object information within the frame based on the image signal;

an extraction unit which extracts a main object as an object to be focused from the object information obtained by the object information acquisition unit;

a main area setting unit which sets, in the frame, a main area as one focus detection area within an area where the main object exists;

an auxiliary area setting unit which sets, around the main area, auxiliary area as focus detection area for capturing a part of the area where the main object exists;

a focus detection area selection unit which selects one or a plurality of focus detection areas from the main area and the auxiliary area in accordance with a comparing result of an in-focus position of a focus lens which is based on the focus signal in the main area and an in-focus position of the focus lens which is based on the focus signal in the auxiliary area; and

a control unit which controls the focus lens based on the in-focus position of the focus lens in the focus detection area selected by the focus detection area selection unit.

2. The apparatus according to claim 1 , wherein the focus detection area selection unit determines reliability of the in-focus positions of the focus lens in the respective focus detection areas based on the difference between the in-focus positions of the focus lens in the respective focus detection areas and selects the main area as a focus detection area used for detecting the in-focus position of the focus lens if the in-focus position of the focus lens in the main area is reliable.

3. The apparatus according to claim 1 , wherein the focus detection area selection unit determines reliability of the in-focus positions of the focus lens in the respective focus detection areas based on the difference between the in-focus positions of the focus lens in the respective focus detection areas and selects the auxiliary area as a focus detection area used for detecting the in-focus position of the focus lens if the in-focus position of the focus lens in the main area is unreliable and the in-focus position of the focus lens in the auxiliary area is reliable.

4. The apparatus according to claim 1 , wherein the focus detection area selection unit sets a threshold of the focus signal for determining that the in-focus position of the focus lens exists in the main area to be smaller than that of the focus signal for determining that the in-focus position of the focus lens exists in the auxiliary area.

5. The apparatus according to claim 1 , wherein the focus detection area selection unit executes selection based on a difference between the in-focus position of the focus lens in each of the focus detection areas and that of the focus lens corresponding to a distance of the object which is estimated based on a size of the object obtained by the object information acquisition unit.

6. The apparatus according to claim 1 , wherein the focus detection area selection unit executes selection further based on color information of the object within the focus detection area, which is obtained by the object information acquisition unit.

7. The apparatus according to claim 1 , wherein the focus detection area selection unit executes selection further based on a direction of the main object detected by the object information acquisition unit.

8. A control method comprising the steps of:

detecting a focus signal indicating a focus state to an object in a focus detection area set within a frame of a photographed image signal;

acquiring one or a plurality of pieces of object information within the frame based on the image signal;

extracting a main object as an object to be focused from the object information obtained in the acquiring step;

setting, in the frame, a main area as one focus detection area within an area where the main object exists;

setting, around the main area, auxiliary area as focus detection area for capturing a part of the area where the main object exists;

selecting one or a plurality of focus detection areas from the main area and the auxiliary area in accordance with a comparing result of an in-focus position of a focus lens which is based on the focus signal in the main area and an in-focus position of the focus lens which is based on the focus signal in the auxiliary area; and

controlling the focus lens based on the in-focus position of the focus lens in the focus detection area selected in the selecting step.

9. The apparatus according to claim 1 , wherein the focus detection area selection unit executes selection based on a difference between the in-focus positions of the focus lens in the respective focus detection areas.