Methods and apparatuses for vignetting correction in image signals
View Patent ↗Methods and apparatuses for vignetting correction of imager pixels signals. A polynomial correction surface is determined based on a pixel array center, height, and width, surface fitting parameters, and pixel coordinates. The pixel signal is then multiplied by the corresponding value from the polynomial correction surface to create a vignetting corrected signal.
1. A method of adjusting a pixel signal of an image captured by a pixel array, the method comprising:
determining a correction value for the pixel signal as a function of a polynomial curve based on a pixel position in the array, a center, a pixel array height, a pixel array width, and at least one surface fitting parameter; and
generating a corrected pixel signal based on the correction value and the pixel signal,
wherein the correction value is determined according to:
vigCorrection
(
x
,
y
)
=
f
(
a
·
x
-
xc
width
)
·
f
(
b
·
y
-
yc
height
)
where f is a function,
a
·
x
-
xc
width
and
b
·
y
-
yc
height
are operands of the function f, a and b are surface fitting parameters, x and y are pixel coordinates for the pixel signal, xc and yc are center coordinates for the pixel array, width is the pixel array width, and height is the pixel array height.
2. The method of claim 1 , wherein the corrected pixel signal is generated by multiplying the pixel signal by the correction value.
3. The method of claim 1 , wherein the correction value is determined to correct pixel vignetting.
4. The method of claim 1 , wherein the function f comprises a hyperbolic cosine.
5. The method of claim 1 , wherein the function f comprises at least a portion of a Taylor series expansion.
6. The method of claim 1 , wherein the function f comprises a function of a portion of a modified Taylor series expansion wherein a Taylor series constant is substituted with a surface fitting parameter.
7. The method of claim 1 , wherein the center is a geometric center of the pixel array.
8. The method of claim 1 , wherein the center is an optical center of the pixel array.
9. A method of adjusting a pixel signal of an image captured by a pixel array, the method comprising:
determining a correction value for the pixel signal as a function of a polynomial curve based on a pixel position in the array, a center, a pixel array height, a pixel array width, and at least one surface fitting parameter; and
generating a corrected pixel signal based on the correction value and the pixel signal, wherein the correction value is determined according to:
vigCorrection( x,y )=ƒ( V x ( x ))·ƒ( V y ( y ))
where
V
x
(
x
)
=
a
·
x
-
xc
width
if
x
=
0
;
V
x
(
x
)
=
V
x
(
x
-
1
)
+
D
x
if
x
>
0
where
D
x
=
a
width
;
V
y
(
y
)
=
b
·
y
-
yc
height
if
y
=
0
;
and
V
y
(
y
)
=
V
y
(
y
-
1
)
+
D
y
if
y
>
0
where
D
y
=
b
height
where a and b are surface fitting parameters, x and y are pixel coordinates for the pixel signal, xc and yc are center coordinates for the pixel array, width is the pixel array width, and height is the pixel array height.
10. An imaging device comprising:
an imaging sensor comprising an array of imaging pixels; and
a signal processing circuit for adjusting signals from the array, the signal processing circuit comprising:
a correction value module configured to determine a correction value for each pixel signal as a function of a polynomial curve based on the pixel position in the array, a center, a pixel array height, a pixel array width, and at least one surface fitting parameter; and
a correction module configured to generate a corrected pixel signal for each pixel signal based on the corresponding correction value and pixel signal for the pixel position, wherein the correction value module is configured to determine the correction value according to:
vigCorrection
(
x
,
y
)
=
f
(
a
·
x
-
xc
width
)
·
f
(
b
·
y
-
yc
height
)
where f is a function,
a
·
x
-
xc
width
and
b
·
y
-
yc
height
are operands of the function f, a and b are surface fitting parameters, xc and yc are pixel coordinates for the pixel signal, xc and yc are center coordinates for the pixel array, width is the pixel array width, and height is the pixel array height.
11. The imaging device of claim 10 , wherein the correction value is determined to correct pixel vignetting.
12. The imaging device of claim 10 , wherein the function f comprises cos h,
where cos h is a hyperbolic cosine function.
13. The imaging device of claim 10 , wherein the function f is defined as:
f
(
z
)
=
SUM
{
1
+
z
2
2
!
+
z
4
4
!
+
z
6
6
!
+
z
8
8
!
+
⋯
}
where z is the operand of the function f.
14. The imaging device of claim 10 wherein the function f is defined as:
f
(
z
)
=
S
U
M
{
1
+
z
2
2
!
+
z
4
v
}
where v is a surface fitting parameter and z is the operand of the function f.
15. The imaging device of claim 10 , which is part of an image processing system.
16. The imaging device of claim 15 , wherein the image processing system is a camera system.