Method and apparatus for image signal color correction with reduced noise
View Patent ↗A method and apparatus for applying color correction to image signals provides different color corrections depending on a characterization associated with a pixel signal being processed or the gain applied to the pixel signal such as a value of a pixel signal being processed. The color corrections may be configured such that darker pixels have less color correction applied to them.
1. A method of performing a color correction with processing circuitry, comprising:
with the processing circuitry, for a plurality of pixels in an image, applying a first color correction matrix to pixels that are brighter than a first pre-determined threshold; and
with the processing circuitry, applying a second color correction matrix to pixels that are darker than said first pre-determined threshold, wherein the second color correction matrix is formed from a sum of the first color correction matrix and a unity color correction matrix.
2. The method of claim 1 further comprising:
with the processing circuitry, applying a third color correction matrix to pixels that are darker than a second pre-determined threshold, wherein said second pre-determined threshold is lower than said first pre-determined threshold.
3. The method of claim 2 further comprising:
with the processing circuitry, applying a fourth color correction matrix to pixels that are darker than a third pre-determined threshold, wherein said third pre-determined threshold is lower than said second pre-determined threshold.
4. The method of claim 3 , wherein said fourth color correction matrix is a desaturated unity color correction.
5. The method of claim 3 , wherein said third color correction matrix is a combination of a desaturated unity color correction and a unity color correction.
6. A method of performing a color correction on image signals using processing circuitry, comprising:
with the processing circuitry, determining which of the components of an RGB triplet of a pixel signal has a maximum value among the components of the RGB triplet;
with the processing circuitry, applying a first color correction to a pixel signal in response to determining that the maximum value among the components of the RGB triplet of the pixel signal is higher than a first pre-determined threshold a; and
with the processing circuitry, applying a second different color correction to said pixel signal in response to determining that the maximum value among the components of the RGB triplet of the pixel signal is lower than said first pre-determined threshold a.
7. The method of claim 6 , where said first color correction is a color correction equation of the form:
A
=
a
11
a
12
a
13
a
21
a
22
a
23
a
31
a
32
a
33
,
which is applied to said pixel signal, wherein values for a 11 . . . a 33 are predetermined.
8. The method of claim 6 further comprising:
applying a third color correction to said pixel signal if the maximum value of RGB triplet of the pixel signal in is lower than a second pre-determined threshold b, wherein said second pre-determined threshold b is lower than said first pre-determined threshold a.
9. The method of claim 8 , wherein said second color correction is a color correction equation of the form: B*(1−α)+A*α, which is applied to said pixel signal, and wherein
α
=
m
i
,
j
-
b
a
-
b
,
B
=
1
0
0
0
1
0
0
0
1
,
and
A
=
a
11
a
12
a
13
a
21
a
22
a
23
a
31
a
32
a
33
.
10. The method of claim 8 , wherein said third color correction is a color correction equation of the form C*(1−α)+B*α, which is applied to said pixel signal, wherein
α
=
m
i
,
j
-
c
b
-
c
,
C
=
V
-
1
·
0
0
0
0
1
0
0
0
0
·
V
·
B
=
0.2126
0.7152
0.0722
0.2126
0.7152
0.0722
0.2126
0.7152
0.0722
,
V
=
1
-
1
0
0
1
0
0
-
1
1
·
1
0
0
0.2126
0.7152
0.0722
0
0
1
,
B
=
1
0
0
0
1
0
0
0
1
,
and
A
=
a
11
a
12
a
13
a
21
a
22
a
23
a
31
a
32
a
33
,
and wherein values for a 11 . . . a 33 are predetermined.
11. The method of claim 10 further comprising:
applying a fourth color correction to said pixel signal if maximum value m is lower than a third pre-determined threshold c, wherein said third pre-determined threshold c is lower than said second pre-determined threshold b.
12. The method of claim 11 , wherein said fourth color correction is an equation of the form:
C
=
V
-
1
·
0
0
0
0
1
0
0
0
0
·
V
·
B
=
0.2126
0.7152
0.0722
0.2126
0.7152
0.0722
0.2126
0.7152
0.0722
,
where
V
=
1
-
1
0
0
1
0
0
-
1
1
·
1
0
0
0.2126
0.7152
0.0722
0
0
1
,
and
B
=
1
0
0
0
1
0
0
0
1
.
13. A method of performing a color correction using an image processor, comprising:
with the image processor, applying a first color correction to a pixel signal in response to determining that a characteristic associated with said pixel signal is higher than a first pre-determined threshold; and
with the image processor, applying a second different color correction to said pixel signal in response to determining that said characteristic is lower than said first pre-determined threshold, wherein the characteristic associated with said pixel signal is a gain setting applied to said pixel signal.
14. The method of claim 13 , further comprising:
with the image processor, applying a third color correction to said pixel signal in response to determining that the characteristic is lower than a second pre-determined threshold, wherein said second pre-determined threshold is lower than said first pre-determined threshold.
15. The method of claim 14 , further comprising:
with the image processor, applying a fourth color correction to said pixel signal in response to determining that the characteristic is lower than a third pre-determined threshold, wherein said third pre-determined threshold is lower than said second pre-determined threshold.
16. An image processor for performing a color correction process on image signals, said image processor comprising:
a color correction matrix multiplier configured to apply a color correction matrix to a pixel signal produced by a pixel; and
a color correction matrix mixer configured to determine a color correction matrix which is applied by said matrix multiplier based on a value of the pixel signal, wherein the color correction matrix mixer is coupled to and configured to provide the determined color correction matrix to the color correction matrix multiplier, wherein the color correction matrix mixer is configured to determine a first color correction matrix in response to determining that the pixel signal is higher than a first pre-determined threshold, and wherein the color correction matrix mixer is configured to determine a second color correction matrix in response to determining that the pixel signal is lower than the first pre-determined threshold, wherein said first color correction matrix is
a
11
a
12
a
13
a
21
a
22
a
23
a
31
a
32
a
33
,
wherein said values for a 11 . . . a 33 are predetermined, wherein said second color correction matrix is B*(1−α)+A*α, wherein
α
=
m
i
,
j
-
b
a
-
b
,
B
=
1
0
0
0
1
0
0
0
1
,
A
=
a
11
a
12
a
13
a
21
a
22
a
23
a
31
a
32
a
33
,
mij is the value of the pixel signal, a is said first pre-determined threshold, and b is said second pre-determined threshold, and wherein said third color correction matrix is C*(1−α)+B*α and wherein
α
=
m
i
,
j
-
c
b
-
c
,
C
=
V
-
1
·
0
0
0
0
1
0
0
0
0
·
V
·
B
=
0.2126
0.7152
0.0722
0.2126
0.7152
0.0722
0.2126
0.7152
0.0722
,
V
=
1
-
1
0
0
1
0
0
-
1
1
·
1
0
0
0.2126
0.7152
0.0722
0
0
1
,
B
=
1
0
0
0
1
0
0
0
1
,
and
A
=
a
11
a
12
a
13
a
21
a
22
a
23
a
31
a
32
a
33
.
17. The image processor of claim 16 , wherein said color correction matrix mixer is configured to determine a third color correction matrix in response to determining that the pixel signal is lower than a second pre-determined threshold.
18. The image processor of claim 16 , wherein said color correction matrix mixer is part of a camera system.
19. The image processor of claim 16 , wherein said color correction matrix mixer is configured to determine a fourth color correction matrix if the pixel signal is lower than a third pre-determined threshold, wherein said fourth color correction matrix is
C
=
V
-
1
·
0
0
0
0
1
0
0
0
0
·
V
·
B
=
0.2126
0.7152
0.0722
0.2126
0.7152
0.0722
0.2126
0.7152
0.0722
,
and wherein
V
=
1
-
1
0
0
1
0
0
-
1
1
·
1
0
0
0.2126
0.7152
0.0722
0
0
1
,
B
=
1
0
0
0
1
0
0
0
1
,
and c is said third pre-determined threshold.