METHOD OF AUTOMATICALLY CALIBRATING A VISUAL PARAMETER FOR AN IMAGING DEVICE

• US 20110261208A1
• Filed: 04/27/2010
• Published: 10/27/2011
• Est. Priority Date: 04/27/2010
• Status: Active Grant

• Current Assignee: Ability Enterprise Co., Ltd.
• Original Assignee: Ability Enterprise Co., Ltd.
• Inventors: WANG, CHIH-YUAN, WU, CHENG-CHANG
• Granted Patent: US 8,310,549 B2
• Time in Patent Office: Days
• US Class Current: 348/187
• CPC Class Codes: H04N 17/002 for television cameras
• 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 23/71 Circuitry for evaluating the brightness variation

Abstract

A method of automatically calibrating a visual parameter, such as luminance or contrast, for an imaging device is disclosed. A ratio of visual parameter difference to lens position difference between two predetermined lens positions is pre-determined for a predetermined focal length. A target visual parameter is then obtained according to the pre-determined ratio, a current visual parameter and lens position difference between a current lens position and a target lens position. Finally, the current visual parameter is updated by the target visual parameter in an automatic mode.

Claims

1. A method of automatically calibrating a visual parameter for an imaging device, comprising:

pre-determining a ratio of visual parameter difference to lens position difference between two predetermined lens positions for a predetermined focal length;

obtaining a target visual parameter according to the pre-determined ratio, a current visual parameter and lens position difference between a current lens position and a target lens position; and

updating the current visual parameter by the target visual parameter in an automatic mode.

2. The method of claim 1, wherein the step of pre-determining the ratio comprises:

directing the imaging device at a light source;

zooming the imaging device to the predetermined focal length to be calibrated;

turning off the automatic mode after the automatic mode becomes convergent;

moving the lens to a first lens position x1 and reading an associated first visual parameter y1 at least one time;

moving the lens to a second lens position x2 and reading an associated second visual parameter y2 at least one time; and

calculating the ratio m of the visual parameter difference (y2−

y1) to the lens position difference (x2−

x1).

3. The method of claim 2, wherein the first lens position corresponds to infinity focus and the second lens position corresponds to nearest-end focus.

4. The method of claim 2, wherein the first visual parameter is read a plurality of times and the readings are then averaged.

5. The method of claim 2, wherein the second visual parameter is read a plurality of times and the readings are then averaged.

6. The method of claim 1, wherein the target visual parameter Vt is obtained according to the pre-determined ratio m, the current visual parameter Vc, and the lens position difference (Pc−

Pt) between the current lens position Pc and the target lens position Pt as follows;

Vt=Vc−

(Pc−

Pt)*m.

7. The method of claim 1, wherein the target lens position corresponds to infinity focus.

8. The method of claim 1, wherein the imaging device is one of the following devices:

a digital still camera, a video camera, a mobile phone with a camera, and a web camera.

9. A method of automatically calibrating luminance for an imaging device, comprising:

pre-determining a ratio of luminance difference to lens position difference between two predetermined lens positions for a predetermined focal length;

obtaining a target luminance according to the pre-determined ratio, a current luminance and lens position difference between a current lens position and a target lens position; and

updating the current luminance by the target luminance in an automatic exposure mode.

10. The method of claim 9, wherein the step of pre-determining the ratio comprises:

directing the imaging device at a light source;

zooming the imaging device to the predetermined focal length to be calibrated;

turning off the automatic exposure mode after the automatic exposure mode becomes convergent;

moving the lens to a first lens position x1 and reading an associated first luminance y1 at least one time;

moving the lens to a second lens position x2 and reading an associated second luminance y2 at least one time; and

calculating the ratio m of the luminance difference (y2−

y1) to the lens position difference (x2−

x1).

11. The method of claim 10, wherein the first luminance is read a plurality of times and the readings are then averaged;

and the second luminance is read a plurality of times and the readings are then averaged.

12. The method of claim 9, wherein the target luminance Lt is obtained according to the pre-determined ratio m, the current luminance Lc, and the lens position difference (Pc−

Pt) between the current lens position Pc and the target lens position Pt as follows;

Lt=Lc−

(Pc−

Pt)*m.

13. The method of claim 9, wherein the target lens position corresponds to infinity focus.

14. The method of claim 9, wherein the imaging device is one of the following devices:

a digital still camera, a video camera, a mobile phone with a camera, and a web camera.

15. A method of automatically calibrating contrast for an imaging device, comprising:

pre-determining a ratio of contrast difference to lens position difference between two predetermined lens positions for a predetermined focal length;

obtaining a target contrast according to the pre-determined ratio, a current contrast and lens position difference between a current lens position and a target lens position; and

updating the current contrast by the target contrast in an automatic focus mode.

16. The method of claim 15, wherein the step of pre-determining the ratio comprises:

directing the imaging device at a light source;

zooming the imaging device to the predetermined focal length to be calibrated;

turning off the automatic exposure mode after the automatic exposure mode becomes convergent;

moving the lens to a first lens position x1 and reading an associated first contrast y1 at least one time;

moving the lens to a second lens position x2 and reading an associated second contrast y2 at least one time; and

calculating the ratio m of the contrast difference (y2−

y1) to the lens position difference (x2−

x1).

17. The method of claim 16, wherein the first contrast is read a plurality of times and the readings are then averaged;

and the second contrast is read a plurality of times and the readings are then averaged.

18. The method of claim 15, wherein the target contrast Et is obtained according to the pre-determined ratio m, the current contrast Ec, and the lens position difference (Pc−

Pt) between the current lens position Pc and the target lens position Pt as follows;

Et=Ec−

(Pc−

Pt)*m.

19. The method of claim 15, wherein the target lens position corresponds to infinity focus.

20. The method of claim 15, wherein the imaging device is one of the following devices:

a digital still camera, a video camera, a mobile phone with a camera, and a web camera.