Method and apparatus for chromatic adaptation
View Patent ↗A method for performing chromatic adaptation includes performing chromatic adaptation wherein corrections to tristimulous values XYZ are maximized in the regions of white and neutral and are minimized in the vicinity of non-neutral regions of colors space via piecewise linear corrections in XYZ. In one embodiment, a selective linear correction is performed using three matrices one for each sector in an RGB color space. In an alternative embodiment, selective color adjustments are made and the adjustments are partitioned for each primary and secondary color.
1. A method for performing chromatic adaptation, comprising:
performing maximum chromatic corrections to tristimulous color values in the vicinity of white and neutral colors;
performing minimum chromatic corrections to tristimulous color values in the vicinity of non-neutral colors;
wherein said corrections are piecewise liner in a tristimulous color space;
wherein the corrections to the tristimulous color space are performed in a Red-Green-Blue (RGB) color space that comprises a linear transformation of the tristimulous color space; and
further comprising:
applying a correction factor, α, which is equal to zero for all colors except colors near yellow, the correction factor is determined as follows:
α=α 0 G/R for R≧G≧B;
α=α 0 R/G for G≧R≧B;
α=0 for B≧R and B≧G; and
wherein said correction factor is calculated on a controller.
2. A method as defined in claim 1 , wherein the tristimulous color space comprises a Red-Green-Blue (RGB) color space, and further comprising:
utilizing three matrices one for each sector in the RGB color space, the three sectors lying between the boundaries between R/G, G/B and B/R.
3. A method as defined in claim 2 , wherein each of the three matrices ensures that a value of XYZ for the two most dominant primary colors is equal to the value of XYZ for those colors at a white point of a non-D50 system.
4. A method as defined in claim 1 , wherein a correction function applied to the tristimulous corrections is performed such that an adjustment for R is minimum for R=1.0, G=B=0 and scales linearly to 1 as RGB approaches the boundaries R=0, R=G=B, R=G with B=0, and R=B with G=0.
5. A method as defined in claim 4 , wherein the partitioning for G and B is performed in a similar fashion as that done for R.
6. A method as defined in claim 1 , wherein:
forming a matrix for each sector formed between the R/G, G/B and B/R boundaries, with each matrix that is formed ensuring that the value of XYZ for the two most dominant primary colors is equal to the value of XYZ for those colors at a white point for a non-D50 system.
7. A method as defined in claim 1 , wherein the corrections are performed using the following equation:
XYZ
→
adapt
=
XYZ
→
+
Δ
XYZ
→
(
RGB
→
)
Δ
XYZ
→
(
RGB
→
)
=
∑
i
=
0
i
=
5
Δ
XYZ
→
i
(
1.0
-
f
corr
(
RGB
→
,
i
)
)
defineC
=
1
-
R
,
M
=
1
-
G
,
Y
=
1
-
B
,
f
corr
(
RGB
→
,
i
)
=
R
-
max
(
G
,
B
)
for
i
=
0
and
R
≥
max
(
G
,
B
)
=
0
for
i
=
0
and
R
<
max
(
G
,
B
)
=
G
-
max
(
R
,
B
)
for
i
=
1
and
G
≥
max
(
R
,
B
)
=
0
for
i
=
1
and
G
<
max
(
R
,
B
)
=
B
-
max
(
R
,
G
)
for
i
=
2
and
B
≥
max
(
R
,
G
)
=
0
for
i
=
2
and
B
<
max
(
R
,
G
)
=
C
-
max
(
M
,
Y
)
for
i
=
3
and
C
≥
max
(
M
,
Y
)
=
0
for
i
=
3
and
C
<
max
(
M
,
Y
)
=
M
-
max
(
C
,
Y
)
for
i
=
4
and
M
≥
max
(
C
,
Y
)
=
0
for
i
=
4
and
M
<
max
(
C
,
Y
)
=
Y
-
max
(
C
,
M
)
for
i
=
5
and
Y
≥
max
(
C
,
M
)
=
0
for
i
=
5
and
Y
<
max
(
C
,
M
)
.
8. A method as in claim 1 , wherein said controller is selected from a group comprising a microprocessor, a microcontroller, a digital signal processor, application specific integrated circuits, field programmable logic arrays, or combinations thereof.
9. A method for performing chromatic adaptation, comprising:
performing maximum chromatic corrections to tristimulous color values in the vicinity of white and neutral colors;
performing minimum chromatic corrections to tristimulous color values in the vicinity of non-neutral colors;
wherein said corrections are piecewise linear in a tristimulous color space;
wherein the corrections to the tristimulous color space are performed in a Red-Green-Blue (RGB) color space that comprises a linear transformation of the tristimulous color space; and
wherein the corrections are performed using the following equation:
XYZ
→
E_adapt
=
M
iD
50
(
M
wp
-
1
XYZ
→
)
=
M
iD
50
RGB
→
where
i
=
0
for
R
≥
B
and
G
≥
B
i
=
1
for
G
≥
R
and
B
≥
R
i
=
2
for
R
≥
G
and
B
≥
G
;
and
wherein said corrections is calculated on a controller.
10. A system, comprising:
a display; and
a controller coupled to the display, wherein the controller performs a chromatic adaptation that yields a color profile for the display wherein:
XYZ
→
adapt
=
XYZ
→
+
Δ
XYZ
→
(
RGB
→
)
=
XYZ
→
+
∑
i
=
0
i
=
5
Δ
XYZ
→
i
(
1.0
-
f
corr
(
RGB
→
,
i
)
)
=
M
WP
RGB
→
+
∑
i
=
0
i
=
5
(
M
D
50
-
M
WP
)
RGB
→
i
(
1.0
-
f
corr
(
RGB
→
,
i
)
)
RGB
→
i
=
(
1
,
0
,
0
)
for
i
=
0
=
(
0
,
1
,
0
)
for
i
=
1
=
(
0
,
0
,
1
)
for
i
=
2
=
(
0
,
1
,
1
)
for
i
=
3
=
(
1
,
0
,
1
)
for
i
=
4
=
(
1
,
1
,
0
)
for
i
=
5
where M D50 is a matrix for converting RGB to XYZ for the display set to a white point of D50, and M WP is a matrix for converting RGB to XYZ for the display set to a white point of XYZ WP .
11. A system as defined in claim 10 , wherein the controller performs chromatic adaptation by:
performing maximum corrections to tristimulous color values in the vicinity of white and neutral colors;
performing minimum corrections to tristimulous color values in the vicinity of non-neutral colors; and
wherein said corrections are piecewise linear in the tristimulous color space.
12. A system as defined in claim 10 , wherein the correction by the controller is performed using the following equation:
XYZ
→
adapt
=
XYZ
→
+
Δ
XYZ
→
(
RGB
→
)
Δ
XYZ
→
(
RGB
→
)
=
∑
i
=
0
i
=
5
Δ
XYZ
→
i
(
1.0
-
f
corr
(
RGB
→
,
i
)
)
defineC
=
1
-
R
,
M
=
1
-
G
,
Y
=
1
-
B
,
f
corr
(
RGB
→
,
i
)
=
R
-
max
(
G
,
B
)
for
i
=
0
and
R
≥
max
(
G
,
B
)
=
0
for
i
=
0
and
R
<
max
(
G
,
B
)
=
G
-
max
(
R
,
B
)
for
i
=
1
and
G
≥
max
(
R
,
B
)
=
0
for
i
=
1
and
G
<
max
(
R
,
B
)
=
B
-
max
(
R
,
G
)
for
i
=
2
and
B
≥
max
(
R
,
G
)
=
0
for
i
=
2
and
B
<
max
(
R
,
G
)
=
C
-
max
(
M
,
Y
)
for
i
=
3
and
C
≥
max
(
M
,
Y
)
=
0
for
i
=
3
and
C
<
max
(
M
,
Y
)
=
M
-
max
(
C
,
Y
)
for
i
=
4
and
M
≥
max
(
C
,
Y
)
=
0
for
i
=
4
and
M
<
max
(
C
,
Y
)
=
Y
-
max
(
C
,
M
)
for
i
=
5
and
Y
≥
max
(
C
,
M
)
=
0
for
i
=
5
and
Y
<
max
(
C
,
M
)
.
13. A system as defined in claim 10 , wherein the correction by the controller is performed using the following equation:
XYZ
→
E_adapt
=
M
iD
50
(
M
wp
-
1
XYZ
→
)
=
M
iD
50
RGB
→
where
i
=
0
for
R
≥
B
and
G
≥
B
i
=
1
for
G
≥
R
and
B
≥
R
i
=
2
for
R
≥
G
and
B
≥
G
.
14. A method as defined in claim 10 , wherein the controller applies a correction factor, α, which is equal to zero for all colors except colors near yellow, the correction factor is determined as follows:
α=α 0 G/R for R≧G≧B;
α=α 0 R/G for G≧R≧B; and
α=0 for B≧R and B≧G.
15. A system for performing color adaptation, comprising:
a memory;
a processor coupled to the memory, the processor providing color adaptation by:
performing maximum corrections to tristimulous color values in the vicinity of white and neutral colors;
performing minimum corrections to tristimulous color values in the vicinity of non-neutral colors;
wherein said corrections are piecewise linear in the tristimulous color space;
further comprising:
corrections to the tristimulous color space are performed by the processor in an Red-Green-Blue (RGB) color space that is a linear transformation of the tristimulous color space; and
wherein the corrections are performed by determining:
XYZ
→
E_adapt
=
M
iD
50
(
M
wp
-
1
XYZ
→
)
=
M
iD
50
RGB
→
where
i
=
0
for
R
≥
B
and
G
≥
B
i
=
1
for
G
≥
R
and
B
≥
R
i
=
2
for
R
≥
G
and
B
≥
G
.