Method of automatically calibrating a visual parameter for an imaging device

• US 8,310,549 B2
• Filed: 04/27/2010
• Issued: 11/13/2012
• Est. Priority Date: 04/27/2010
• Status: Active Grant

• Current Assignee: Ability Enterprise Co., Ltd.
• Original Assignee: Ability Enterprise Co., Ltd.
• Inventors: Wu, Cheng-Chang, Wang, Chih-Yuan
• Primary Examiner(s): Natnael, Paulos M
• Application Number:
  US12/768,613
• Publication Number:
  US 20110261208A1
• Time in Patent Office: 931 Days
• Field of Search: 348/187, 348/189, 348/180, 348/175, 348/272, 348/345, 348/349, 348/353, 348/294, 396/104, 396/127
• 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;

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.

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 lens position corresponds to infinity focus.

7. 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.

8. 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;

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.

9. The method of claim 8, 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 in of the luminance difference (y2−

y1) to the lens position difference (x2−

x1).

10. The method of claim 9, 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.

11. The method of claim 8, wherein the target lens position corresponds to infinity focus.

12. The method of claim 8, 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.

13. 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;

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.

14. The method of claim 13, 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).

15. The method of claim 14, 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.

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

17. The method of claim 13, 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.