Automatic focusing system for a still video camera

• US 5,835,143 A
• Filed: 09/02/1997
• Issued: 11/10/1998
• Est. Priority Date: 09/02/1993
• Status: Expired due to Term

• Current Assignee: PENTAX RICOH IMAGING COMPANY, LTD.
• Original Assignee: Asahi Kogaku Kogyo Kabushiki Kaisha
• Inventors: Kakiuchi, Shinichi
• Primary Examiner(s): Faile, Andrew I.
• Assistant Examiner(s): Vu, Ngoc-Yen, VU, NGOC YEN T
• Application Number:
  US08/921,704
• Time in Patent Office: 434 Days
• Field of Search: 348/207, 348/222, 348/223, 348/224, 348/228, 348/266, 348/272, 348/273, 348/277, 348/279, 348/345, 348/349, 348/351, 348/353, 348/354, 348/355, 348/356, 396/79, 396/121, 396/124
• US Class Current: 348/349
• CPC Class Codes: H04N 23/673 based on contrast or high frequency components of image signals, e.g. hill climbing method
• CPC Class Codes: H04N 25/136 using complementary colours

Abstract

An automatic focusing system for a still video camera has a light detector for outputting an image signal corresponding to an intensity of light which is incident on the light detector. An image signal is output for each of a plurality of colors of light that are incident on the light detector. The autofocusing system also includes a processor for determining the value of an AF signal corresponding to the focus condition of each of the image signals. A controller executes the autofocus operation. The AF signal having the highest value is used by the controller to execute the autofocus operation.

Claims

1. An automatic focusing system for a still video camera, comprising:

a lens;

a driver that drives said lens along an optical axis of said lens;

a light detector that receives an optical image through said lens and outputting color signals corresponding to a plurality of color components of said received optical image, each of said color signals representing intensities of light at a plurality of positions of said optical image;

a processor that processes each of said color signals to obtain AF signals representing a contrast for each of said color signals corresponding to said color components of said received optical image;

a selector that compares said AF signals for each of said color signals to one another and selects, from among said compared AF signals for said color signals, one AF signal representing the highest contrast color signal among said color signals; and

a controller that controls said driver to locate said lens at a position where said one selected AF signal becomes greatest.

2. The automatic focusing system according to claim 1, said light detector comprising a charge coupled device having a plurality of light receiving pixels and color filters provided in front of said light receiving pixels, each of said color filters transmitting one of said plurality of color components.

3. The automatic focusing system according to claim 1, said controller further determining said position where said one selected AF signal becomes greatest by moving said lens along the optical axis to a plurality of lens positions and comparing between values of said one selected AF signal measured at said lens positions.

4. The automatic focusing system according to claim 3, wherein said driver initially moves said lens in a predetermined direction by a predetermined amount.

5. The automatic focusing system according to claim 4, further comprising:

means for comparing a value of said one selected AF signal with a previous value of said one selected AF signal, and said driver comprising;

means for moving said lens for a distance and in a direction in accordance with an increase or a decrease in said value of said one selected AF signal.

6. The automatic focusing system according to claim 5, wherein when said value of said one selected AF signal increases with respect to said previous value of said one selected AF signal, said moving means moves said lens in a same direction by a calculated amount.

7. The automatic focusing system according to claim 5, wherein when said value of said one selected AF signal decreases with respect to said previous value of said one selected AF signal, said moving means moves said lens in a reverse direction by one-half of said predetermined amount.

8. The automatic focusing system according to claim 1, further comprising a plurality of memories, each of said plurality of memories corresponding to a respective color component of said received optical image and coupled to said light detector.

9. The automatic focusing system according to claim 1, wherein said processor differentiates each of said color signals, obtains absolute values of each of said differentiated color signals, and integrates each of said absolute values to obtain said AF signals.

10. The automatic focusing system according to claim 1, wherein said selector checks each of said AF signals and stores information corresponding to said one AF signal representing said highest contrast color signal among said AF signals.

11. The automatic focusing system according to claim 1, wherein once said one AF signal is selected, said controller controls said processor to process only said color signal corresponding to said highest contrast color signal to obtain a driving AF signal for controlling said driver to locate said lens at a position where said driving AF signal becomes greatest.

12. A method of automatically locating a lens of a still video camera at an in-focus position, comprising the steps of:

receiving an optical image incident on the camera through the lens and outputting color signals corresponding to a plurality of color components of the received optical image, each of the color signals representing intensities of light at a plurality of positions of the optical image;

processing each of the color signals to obtain AF signals representing a contrast for each of said color signals corresponding to said color components of the received optical image;

comparing said AF signals for each of said color signals to one another;

selecting, from among said compared AF signals for said color signals, one AF signal representing the highest contrast color signal among said color signals; and

determining a position of the lens at which the one selected AF signal has a greatest value.

13. The method according to claim 12, wherein the determining step comprises moving the lens to a plurality of lens positions and comparing between values of the one selected AF signal measured at the lens positions.

14. The method according to claim 12, further comprising initially moving the lens in a predetermined direction by a predetermined amount.

15. The method according to claim 14, further comprising comparing a value of the one selected AF signal with a previous value of said one selected AF signal;

and

moving the lens for a distance and in a direction in accordance with an increase or a decrease in the value of the one selected AF signal.

16. The method according to claim 15, wherein when the value of the one selected AF signal increases, moving the lens in a same direction by a calculated amount.

17. The method according to claim 15, wherein when the value of the one selected AF signal decreases, moving the lens in a reverse direction by one-half of the predetermined amount.

18. The method according to claim 12, further comprising storing each color component of the received optical image in a respective memory.

19. The method according to claim 12, wherein said processing comprises:

differentiating each of the color signals;

obtaining absolute values of each of the differentiated color signals; and

integrating each of said absolute values of the differentiated color signals to obtain said AF signals.

20. The method according to claim 12, said selecting including:

checking each of said AF signals; and

storing information corresponding to said one AF signal representing said highest contrast color signal among said AF signals.

21. The method according to claim 12, wherein said controlling includes:

processing only said color signal corresponding to said highest contrast color signal to obtain a driving AF signal corresponding to said one selected AF signal.

22. An automatic focusing system for a still video camera, comprising:

a lens;

a driver that drives said lens along an optical axis of said lens;

a light detector that receives an optical image through said lens and outputting color signals corresponding to a plurality of color components of said received optical image, each of said color signals representing intensities of light at a plurality of positions of said optical image;

a processor that processes each of said color signals to obtain AF signals representing a contrast for each of said color signals corresponding to said color components of said received optical image;

a selector that selects, from among said AF signals for said color signals, one AF signal representing the highest contrast color signal among said color signals; and

a controller that controls said processor to process only said color signal corresponding to said one AF signal, representing the highest contrast color signal among said color signals, to obtain a driving AF signal for controlling said driver to locate said lens at a position where said driving AF signal becomes greatest.