Imaging system and pixel signal readout method

1. An imaging system, comprising:

a target detector that detects a target subject from an effective pixel area of an image sensor and performs face detection;

a readout area determiner that defines a readout area within said effective pixel area, said readout area corresponding to a detected face and being smaller than the effective pixel area;

a readout processor that reads out only pixel signals within said readout area, utilizes only the pixel signals within the readout area to perform an autofocus operation, and changes a period of horizontal and vertical synchronization signals in association with a size of the readout area; and

a partial area within said readout area being redefined as said readout area when a size of an originally defined readout area is greater than a predetermined size.

2. The imaging system as in claim 1 , wherein said target detector is configured to perform automatic tracking of said target within said effective pixel area.

3. The imaging system as in claim 1 , wherein the redefined area comprises a partial area of a face-detected area including eyes at the center of the redefined area.

4. The imaging system as in claim 1 , wherein when said target detector detects a plurality of targets from said effective pixel area and when an area including all of said plurality of targets is larger than said predetermined size, an area including only a part of said plurality of targets is redefined as said readout area.

5. The imaging system as in claim 1 , wherein a preset area is set as said readout area when no target has been detected.

6. The imaging system as in claim 1 , wherein said imaging system comprises a digital camera.

7. The imaging system according to claim 1 , the readout area being configured to correspond to a face detection area enlarged on each side by a predetermined magnification.

8. The imaging system according to claim 1 , the readout processor being configured to perform the autofocus operation based only on the pixel signals within the readout area and further to focus an optical system of the imaging system on the detected face.

9. The imaging system according to claim 1 , wherein, when said target detector detects a plurality of targets from said effective pixel area, an area including only a part of said plurality of targets is redefined as said readout area, the area including only said part of said plurality of targets that includes the largest area and the smallest area corresponding to said plurality of targets.

10. A pixel signal readout method, comprising:

detecting a target subject from an effective pixel area of an image sensor, and performing face detection;

defining a readout area within the effective pixel area, the readout area corresponding to a detected face and being smaller than the effective pixel area;

reading out only pixel signals within said readout area, utilizing only the pixel signals within the readout area to perform an autofocus operation and changing a period of horizontal and vertical synchronization signals in association with a size of the readout area; and

redefining a partial area within the readout area as the readout area when a size of an originally defined readout area is greater than a predetermined size.

11. The imaging system according to claim 1 , further comprising a selector configured to select one of the original readout area, the redefined readout area or a default readout area and performing an auto focus operation based on the selected area.

12. The imaging system according to claim 1 , further comprising altering, during the autofocus operation, a frame rate of the image sensor based upon a size of the readout area.

13. The pixel signal readout method according to claim 10 , wherein the detecting comprises automatic tracking of the target within the effective pixel area.

14. The pixel signal readout method according to claim 10 , wherein the redefined area comprises a partial area of a face detected area including eyes at a center of the redefined area.

15. The pixel signal readout method according to claim 10 , wherein, when the detecting detects a plurality of targets from the effective pixel area and when an area including all of the plurality of targets is larger than the predetermined size, an area including only a part of the plurality of targets is redefined as the readout area.

16. The pixel signal readout method according to claim 10 , wherein a preset area is set as the readout area when no target has been detected.

17. The pixel signal readout method according to claim 10 , further comprising altering, during the autofocusing operation, a frame rate of the image sensor based on a size of the readout area.

18. The pixel signal readout method according to claim 10 , the readout area corresponding to a face detection area enlarged on each side by a predetermined magnification.

19. The pixel signal readout method according to claim 10 , wherein the reading out of only pixel signals comprises performing the autofocus operation based on the pixel signals within the readout area and further focusing an optical system of the imaging system on the detected face.

20. The pixel signal readout method according to claim 10 , wherein, when the detecting detects a plurality of targets in the effective pixel area, an area including only a part of the plurality of targets is redefined as the readout area, the area including only the part of the plurality of targets includes the largest area and the smallest area corresponding to the plurality of targets.