Partial lens shading compensation method

Patent metadata

Field	Value
Publication number	US-9392180-B2
Application number	US-201213661399-A
Country	US
Kind code	B2
Filing date	Oct 26, 2012
Priority date	Mar 29, 2012
Publication date	Jul 12, 2016
Grant date	Jul 12, 2016

Abstract

Method and apparatus for partial lens shading compensation are provided. An image area is divided, from the inside towards the outside of the image area, into several partial areas centered on an optical center of the image. When a target pixel is identified as being located in one of the partial areas, a corresponding compensation gain is determined according to the position of the target pixel with reference to the optical center. Another compensation gain is determined according to the position of the target pixel with reference to the optical center. A mixed compensation value is determined according to the compensation gains, so as to compensate the target pixel.

First claim

What is claimed is:

1. A partial lens shading compensation method, comprising:
dividing, from the inside towards the outside of an image area, the image area into a plurality of partial areas, the partial areas being centered on an optical center of the image area, the partial areas including a first partial area, a second partial area, and a third partial area;
determining, when a target pixel is identified as being located in the first partial area, a first compensation gain according to the position of the target pixel with reference to the optical center;
determining, when the target pixel is identified as being located in the second partial area, a second compensation gain according to the position of the target pixel with reference to the optical center;
determining, when the target pixel is identified as being located in the third partial area, a third compensation gain according to the position of the target pixel with reference to the optical center;
determining a fourth compensation gain according to the position of the target pixel with reference to the optical center; and
determining a mixed compensation value according to the sum of the first compensation gain, the second compensation gain, the third compensation gain, and the fourth compensation gain, so as to compensate the target pixel;
wherein within the first partial area, an absolute value of the first compensation gain monotonically varies or oscillates toward the border of the first partial area at which it becomes zero.

2. The partial lens shading compensation method according to claim 1 , wherein the partial areas are a plurality of concentric circles or concentric ellipses.

3. The partial lens shading compensation method according to claim 1 , wherein in the steps of determining the first to fourth compensation gains, the first to the fourth compensation gains compensation gains are determined according to SquarePos=a 0 x 2 +a 1 y 2 , where a 0 and a 1 indicate a first coordinate parameter and a second coordinate parameter, respectively, and x and y indicate a first coordinate and a second coordinate of the target pixel, respectively.

4. The partial lens shading compensation method according to claim 1 , wherein the borders of the first partial area, the second partial area, and the third partial area are defined by a first curvature radius, a second curvature radius, and a third curvature radius, respectively; wherein in the steps of determining the first to the third compensation gains according to the position of the target pixel with reference to the optical center, the first to the third compensation gains are determined further according to the first to the third curvature radii, respectively.

5. The partial lens shading compensation method according to claim 1 , wherein the first compensation gain is determined according to a first compensation function, and the first compensation function is expressed as Com_Gain 1 =Gain 1 ×(|SquarePos−R 1 2 |) N 1 where Com_Gain 1 indicates the first compensation gain, Gain 1 indicates a first gain parameter, SquarePos=a 0 x 2 +a 1 y 2 , a 0 and a 1 indicate a first coordinate parameter and a second coordinate parameter, respectively, x and y indicate a first coordinate and a second coordinate of the target pixel, respectively, R 1 indicates a first curvature radius parameter, and N 1 indicates a first polynomial degree parameter.

6. The partial lens shading compensation method according to claim 1 , wherein within the second partial area, an absolute value of the second compensation gain monotonically varies or oscillates toward the border of the second partial area at which it becomes substantially zero.

7. The partial lens shading compensation method according to claim 6 , wherein the second compensation gain is determined according to a second compensation function, and the second compensation function is expressed as Com_Gain 2 =Gain 2 ×(|SquarePos−R 2 2 ) N 2 |Factor×SquarePos where Com_Gain 2 indicates the second compensation gain, Gain 2 indicates a second gain parameter, SquarePos=a 0 x 2 +a 1 y 2 , a 0 and a 1 indicate a first coordinate parameter and a second coordinate parameter, x and y indicate a first coordinate and a second coordinate of the target pixel, respectively, R 2 indicates a second curvature radius parameter, and N 2 indicates a second polynomial degree parameter.

8. The partial lens shading compensation method according to claim 1 , wherein outside the third partial area, an absolute value of the third compensation gain is substantially zero at the border of the third partial area from which it monotonically varies or oscillates outwardly.

9. The partial lens shading compensation method according to claim 8 , wherein the third compensation gain is determined according to a third compensation function, and the third compensation function is expressed as Com_Gain 3 =Gain 3 ×(|SquarePos−R 3 2 |) N 3 where Com_Gain 3 indicates the third compensation gain, Gain 3 indicates a third gain parameter, SquarePos=a 0 x 2 +a 1 y 2 , a 0 and a 1 indicate a first coordinate parameter and a second coordinate parameter, respectively, x and y indicate a first coordinate and a second coordinate of the target pixel, R 3 indicates a third curvature radius parameter, and N 3 indicates a third polynomial degree parameter.

10. The partial lens shading compensation method according to claim 1 , wherein an absolute value of the forth compensation gain is substantially zero, at the optical center from which it monotonically increases or oscillates outwardly.

11. The partial lens shading compensation method according to claim 10 , wherein the fourth compensation gain is determined according to a fourth compensation function, and the fourth compensation function is expressed as Comp_Gain 4 =Gain 4 ×SquarePos where Com_Gain 4 indicates the fourth compensation gain, Gain 4 indicates a fourth gain parameter, Comp_Gain 4 =Gain 4 ×SquarePos, a 0 and a 1 indicate a first coordinate parameter and a second coordinate parameter, x and y indicate a first coordinate and a second coordinate of the target pixel.

12. The partial lens shading compensation method according to claim 1 , wherein the mixed compensation value is substantially equal to the sum of the first to the fourth compensation gains multiplied by a raw pixel value of the target pixel.

13. The partial lens shading compensation method according to claim 1 , wherein the target pixel, after being compensated by the mixed compensation value, has a pixel value which is equal to the sum of a raw pixel value of the target pixel and the mixed compensation value.

14. The partial lens shading compensation method according to claim 1 , wherein the first partial area is smaller than the second partial area and the third partial area.

15. The partial lens shading compensation method according to claim 1 , further comprising:
obtaining a first curvature radius, a second curvature radius, and a third curvature radius, according to the difference among different color shading curves of a corresponding lens; and
obtaining, according to the first to the third curvature radii, a first compensation function, a second compensation function, and a third compensation function so as to correct the difference among different color shading curves;
wherein in the steps of determining the first to the third compensation gains according to the position of the target pixel with reference to the optical center, the first to the third compensation gains are obtained by using the first to the third compensation functions.

1

Assignees

• Novatek Microelectronics Corp

Inventors

• Hsu Wei

Classifications

• H04N23/71 Primary

  Circuitry for evaluating the brightness variation · CPC title

• H04N25/61

  the noise originating only from the lens unit, e.g. flare, shading, vignetting or "cos4" · CPC title

• H04N5/3572

  Electricity · mapped topic

• H04N5/2351 Primary

  Electricity · mapped topic