Face detection apparatus

1. A face detection apparatus for detecting a face contained in an input image comprising:

a face detection section for detecting a face contained in the input image, based on a predetermined frame rate and face detection throughput per frame;

an accuracy changing section for changing, when no face is detected by the face detection section, an accuracy in detecting a face by the face detection section by reducing the frame rate; and

a storage section for storing, when a face is detected by the face detection section, as accuracy change history, the accuracy, which is changed by the accuracy changing section, in detecting a face by the face detection section, wherein

when no face is detected by the face detection section, the accuracy changing section changes the accuracy in detecting a face by the face detection section based on the accuracy change history stored in the storage section.

2. The face detection apparatus according to claim 1 , wherein when a face is detected by the face detection section, the accuracy changing section changes the accuracy in detecting a face by the face detection section by reducing the face detection throughput per frame.

3. The face detection apparatus according to claim 2 , wherein when a face is detected by the face detection section, a face detection range to be a target of the face detection is limited in the frame to be the target of the face detection by the face detection section.

4. The face detection apparatus according to claim 2 , wherein when a face is detected by the face detection section, a size of a face to be a target of the face detection is limited in the frame to be the target of the face detection by the face detection section.

5. The face detection apparatus according to claim 2 , wherein when a face is detected by the face detection section, an orientation of a face to be a target of the face detection process is limited in the frame to be the target of the face detection by the face detection section.

6. The face detection apparatus according to claim 2 , wherein when a face is detected by the face detection section, a target of the face detection is limited in accordance with a preset priority, in the frame to be the target of the face detection by the face detection section.

7. The face detection apparatus according to claim 1 , wherein when no face is detected by the face detection section, the accuracy changing section changes the accuracy in detecting a face by the face detection section based on the accuracy change history stored in the storage section, to an accuracy at which a face has been most recently detected by the face detection section.

8. The face detection apparatus according to claim 1 , wherein

when no face is detected by the face detection section, the accuracy changing section reduces the frame rate and increases the face detection throughput per frame, and

when a face is detected by the face detection section, the accuracy changing section reduces the face detection throughput per frame and increases the frame rate.

9. The face detection apparatus according to claim 8 , wherein the accuracy changing section changes the accuracy in detecting a face by the face detection section so as to keep constant the throughput of the entire face detection by the face detection section.

10. The face detection apparatus according to claim 1 , wherein when no face is detected by the face detection section, a frame to be a target of the face detection by the face detection section is selected at a regular interval from among all frames of the input image.

11. The face detection apparatus according to claim 1 , wherein when no face is detected by the face detection section, a frame to be a target of the face detection by the face detection section is a frame having a specific picture type selected from among all frames of the input image.

12. The face detection apparatus according to claim 1 , wherein when no face is detected by the face detection section, a frame to be a target of the face detection by the face detection section is selected in accordance with a preset priority order.

13. A face detection method for detecting a face contained in an input image, which is executed by a face detection apparatus, the face detection method comprising:

a face detection step for detecting a face contained in the input image, based on a predetermined frame rate and face detection throughput per frame;

an accuracy changing step for changing, when no face is detected by the face detection step, an accuracy in detecting a face by the face detection step by reducing the frame rate; and

a storing step for storing, when a face is detected by the face detection section, as accuracy change history, the accuracy, which is changed by the accuracy changing section, in detecting a face by the face detection step, wherein

when no face is detected by the face detection step, the accuracy changing step changes the accuracy in detecting a face by the face detection step based on the accuracy change history stored in the storing step.

14. An integrated circuit used in a face detection apparatus for detecting a face contained in an input image, comprising:

a face detection section for detecting a face contained in the input image, based on a predetermined frame rate and face detection throughput per frame;

an accuracy changing section for changing, when no face is detected by the face detection section, an accuracy in detecting a face by the face detection section by reducing the frame rate; and

a storage section for storing, when a face is detected by the face detection section, as accuracy change history, the accuracy, which is changed by the accuracy changing section, in detecting a face by the face detection section, wherein

when no face is detected by the face detection section, the accuracy changing section changes the accuracy in detecting a face by the face detection section based on the accuracy change history stored in the storage section.