Methods and systems for display source light illumination level selection
Elements of the present invention relate to systems and methods for selecting a display source light illumination level and calculating an image compensation process to compensate for source light illumination level changes.
1. A method for determining a tonescale adjustment curve parameter, said method comprising:
a) generating an image luminance histogram for an image to be displayed, said luminance histogram comprising bin values;
b) weighting said histogram bin values from said image luminance histogram with distortion weight values, wherein said distortion weight values correspond to a particular source light illumination level, thereby creating weighted histogram values;
c) combining said weighted histogram values to obtain distortion values for each of said source light illumination levels, said distortion values each estimating a sum of respective magnitude errors between each of a plurality of pixels' displayed values when illuminated at a respectively associated said source light illumination level and said pixels' displayed values if illuminated by a reference illumination level;
d) selecting a source light illumination level for said image wherein said selecting is based on said distortion values;
e) filtering said selected source light illumination level to determine a filtered source light illumination level;
f) generating a tonescale adjustment curve based on said filtered source light illumination level and a strength factor; where
g) said magnitude errors are calculated using the following equation:
d
->
(
x
,
bl
)
=
{
x
-
x
min
(
bl
)
2
x
≤
x
min
(
bl
)
0
x
min
(
bl
)
<
x
<
x
max
(
bl
)
x
-
x
max
(
bl
)
2
x
max
(
bl
)
≤
x
where x min and x max are the clipping limits, x is an image code value and bl is the source light illumination level.
2. A method as described in claim 1 wherein said selecting is based on a minimum value of said distortion values.
3. A method as described in claim 1 wherein said weighting comprises multiplying said distortion weight values by said histogram bin values.
4. A method as described in claim 1 wherein said combining comprises adding together all weighted histogram values for a given source light illumination level.
5. A method as described in claim 1 further comprising applying said tonescale adjustment curve to said image to create a compensated image.
6. A method as described in claim 1 wherein said generating a tonescale adjustment curve comprises the use of the following equation:
slope
=
(
S
·
1
+
(
1
-
S
)
·
BL
BL
)
1
γ
,
wherein S is the strength factor, BL is the filtered source light illumination level and γ is a display gamma value.
7. A method for selecting a display source light illumination level, said method comprising:
a) determining clipping limits for a display model;
b) determining display error vectors based on said clipping limits using the equation:
d
→
(
x
,
bl
)
=
{
x
-
x
min
(
bl
)
2
x
≤
x
min
(
bl
)
0
x
min
(
bl
)
<
x
<
x
max
(
bl
)
x
-
x
max
(
bl
)
2
x
max
(
bl
)
≤
x
,
wherein x min and x max are the clipping limits, x is an image code value and bl is the source light illumination level;
c) generating an image histogram for an image to be displayed, said histogram comprising bin values;
d) weighting said histogram bin values from said image histogram with said display error vectors, wherein said display error vectors correspond to a particular source light illumination level, thereby creating weighted histogram values;
e) combining said weighted histogram values to obtain distortion values for each of said source light illumination levels, said distortion values each estimating a sum of respective magnitude errors between each of a plurality of pixels' displayed values when illuminated at a respectively associated said source light illumination level and said pixels' displayed values if illuminated by a reference illumination level; and
f) selecting a source light illumination level for said image wherein said selecting is based on said distortion values.
8. A method as described in claim 7 further comprising filtering said selected source light illumination level to determine a filtered source light illumination level.
9. A method as described in claim 8 further comprising determining a tonescale slope based on said filtered source light illumination level and a strength factor, said tonescale slope defining, in part, a tonescale adjustment curve for a luminance channel of said image.
10. A method as described in claim 7 wherein said determining clipping limits comprises using the following equation:
x
min
(
bl
)
=
(
bl
CR
)
1
γ
x
max
(
bl
)
=
(
bl
)
1
γ
,
wherein x min and x max are the clipping limits, CR is the display contrast ratio, bl is the source light illumination level and γ is a display gamma value.
11. A method as described in claim 7 wherein said weighting said histogram bin values comprises using the following equation:
D
(
I
,
bl
)
=
∑
i
,
j
d
→
(
I
(
i
,
j
)
,
bl
)
=
∑
x
h
I
(
x
)
·
d
⇀
(
x
,
bl
)
wherein, bl is the source light illumination level, I(i,j) is an image pixel value and {right arrow over (d)}(x,bl) is a display error vector.
12. A method as described in claim 7 wherein said determining clipping limits is performed before image processing and said clipping limits are stored for use during processing.
13. A method as described in claim 7 wherein said determining display error vectors is performed before image processing and said display error vectors are stored for use during processing.
14. A method for determining a tonescale adjustment curve parameter, said method comprising:
a) generating an image luminance histogram for an image to be displayed, said luminance histogram comprising bin values;
b) weighting said histogram bin values from said image luminance histogram with distortion weight values, wherein said distortion weight values correspond to a particular source light illumination level, thereby creating weighted histogram values;
c) combining said weighted histogram values to obtain distortion values for each of said source light illumination levels;
d) selecting a source light illumination level for said image wherein said selecting is based on said distortion values;
e) filtering said selected source light illumination level to determine a filtered source light illumination level;
f) generating a tonescale adjustment curve based on said filtered source light illumination level and a strength factor using the equation:
slope
=
(
S
·
1
+
(
1
-
S
)
·
BL
BL
)
1
γ
,
wherein S is the strength factor, BL is the filtered source light illumination level and γ is a display gamma value.
15. A method for selecting a display source light illumination level, said method comprising:
a) determining clipping limits for a display model using the equation:
x
min
(
bl
)
=
(
bl
CR
)
1
γ
x
max
(
bl
)
=
(
bl
)
1
γ
,
wherein x min and x max are the clipping limits, CR is the display contrast ratio, bl is the source light illumination level and γ is a display gamma value;
b) determining display error vectors based on said clipping limits;
c) generating an image histogram for an image to be displayed, said histogram comprising bin values;
d) weighting said histogram bin values from said image histogram with said display error vectors, wherein said display error vectors correspond to a particular source light illumination level, thereby creating weighted histogram values;
e) combining said weighted histogram values to obtain distortion values for each of said source light illumination levels; and
f) selecting a source light illumination level for said image wherein said selecting is based on said distortion values.
16. A method for selecting a display source light illumination level, said method comprising:
a) determining clipping limits for a display model;
b) determining display error vectors based on said clipping limits;
c) generating an image histogram for an image to be displayed, said histogram comprising bin values;
d) weighting said histogram bin values from said image histogram with said display error vectors, wherein said display error vectors correspond to a particular source light illumination level, thereby creating weighted histogram values, and using the equation:
D
(
I
,
bl
)
=
∑
i
,
j
d
->
(
I
(
i
,
j
)
,
bl
)
=
∑
x
h
I
(
x
)
·
d
->
(
x
,
bl
)
,
wherein, bl is the source light illumination level, I(i,j) is an image pixel value and {right arrow over (d)}(x,bl) is a display error vector;
e) combining said weighted histogram values to obtain distortion values for each of said source light illumination levels; and
f) selecting a source light illumination level for said image wherein said selecting is based on said distortion values.