Methods, systems and apparatus for over-exposure correction
An aspect of present principles is directed to methods, apparatus, systems and computer readable media for image processing. The image processing may include receiving a standard dynamic range (SDR) image or a receiver for receiving a standard dynamic range (SDR) image. It may further include determining an over-exposed region of the SDR image and determining a corrected luminance value for at least a pixel of the over-exposed region, or a processor configured to determine an over-exposed region of the SDR image and a corrected luminance value for at least a pixel of the over-exposed region. The corrected luminance value is determined based on at least one of a shape of the over-exposed region, luminance information of pixels surrounding the over-exposed region, and edge information of the pixels surrounding the over-exposed region. The over-exposed region may be an irregularly shaped region.
1. An image processing method comprising:
determining a corrected luminance value for at least a pixel of an over-exposed region determined from a standard dynamic range (SDR) image;
wherein the corrected luminance value is determined based on at least one of a shape of a skeleton of pixels of the over-exposed region, and edge information of a ring of pixels surrounding the over-exposed region.
2. The method of claim 1 , wherein the over-exposed region is an irregularly shaped region.
3. The method of claim 1 , further comprising determining the type of the over-exposed region and determining the corrected luminance based on the type of the over-exposed region.
4. The method of claim 3 , wherein the type is one of a specular highlight region, diffuse, or light sources.
5. The method of claim 1 , wherein luminance is corrected based on peak luminance of pixels along the skeleton.
6. The method of claim 1 , wherein the luminance is corrected based on edges determined based on the ring of pixels.
7. The method of claim 1 , wherein the luminance is corrected based on direction vectors determined based on the ring of pixels.
8. The method of claim 7 , wherein the direction vectors are determined based on isophote vectors of the ring of pixels.
9. The method of claim 7 , wherein the direction vectors are determined based on gradients of the ring of pixels.
10. The method of claim 1 , wherein luminance is corrected based on a luminance at the edge pixel L(p j ), a gradient g j of an edge pixel, a distance between the edge pixel and the interior pixel, and a user parameter η as follows:
L ( o i )=η g j ∥p j −o i ∥+L ( p j ).
11. The method of claim 1 , wherein luminance is corrected based on a luminance at the skeleton L(s j ), a luminance at the edge pixel L(p j ), a distance between the edge pixel and the interior pixel, a distance between the edge pixel and the skeleton pixel, and a user parameter η as follows:
L
(
o
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=
η
L
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s
j
)
-
L
(
p
j
)
p
j
-
s
j
p
j
-
o
i
+
L
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p
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.
12. The method of claim 1 , further comprising refining the corrected luminance based on the optimization:
argmin
L
′
L
′
-
L
2
2
subject to one or more of the constraints
min( L ( o i ))−max( L ( p j ))> T 1
L ′( o i )− L orig ( o i )> T 2
∥ L ′( o i ( y ))∥ ∞ −L ′( s ( y ))< T 3
∥ L ′( o i ( x ))∥ ∞ −L ′( s ( x ))< T 3
L ′( p j +t 1 d j )≥ L ′( p j +t 2 d j ) if t 1 >t 2
that are based on relationships between optimized luminance values L′(o i ), the luminance of edge pixels L(p j ), luminance values of the input image L orig (o i ), optimized luminance values of skeleton pixels L′(s(y)), edge pixels p j , direction vectors d j , thresholds T 1 , T 2 , T 3 and scalars t 1 and t 2 .
13. An apparatus for image processing, the apparatus comprising
a processor configured to determine a corrected luminance value for at least a pixel of an over-exposed region determined from a standard dynamic range (SDR) image;
wherein the corrected luminance value is determined based on at least one of a shape of a skeleton of pixels of the over-exposed region, and edge information of a ring of pixels surrounding the over-exposed region.
14. The apparatus of claim 13 , wherein the over-exposed region is an irregularly shaped region.
15. The apparatus of claim 13 , further comprising determining the type of the over-exposed region and determining the corrected luminance based on the type of the over-exposed region.
16. The apparatus of claim 15 , wherein the type is one of a specular highlight region, diffuse, or light sources.
17. The apparatus of claim 13 , wherein luminance is corrected based on peak luminance of pixels along the skeleton.
18. The apparatus of claim 13 , wherein the luminance is corrected based on edges determined based on the ring of pixels.
19. The apparatus of claim 13 , wherein the luminance is corrected based on direction vectors determined based on the ring of pixels.
20. The apparatus of claim 19 , wherein the direction vectors are determined based on isophote vectors of the ring of pixels.
21. The apparatus of claim 19 , wherein the direction vectors are determined based on gradients of the ring of pixels.
22. The apparatus of claim 13 , wherein luminance is corrected based on a luminance at the edge pixel L(p j ), a gradient g j of an edge pixel, a distance between the edge pixel and the interior pixel, and a user parameter η as follows:
L ( o i )=η g j ∥p j −o i ∥+L ( p j ).
23. The apparatus of claim 13 , wherein luminance is corrected based on a luminance at the skeleton L(s j ), a luminance at the edge pixel L(p j ), a distance between the edge pixel and the interior pixel, a distance between the edge pixel and the skeleton pixel, and a user parameter η as follows:
L
(
o
i
)
=
η
L
(
s
j
)
-
L
(
p
j
)
p
j
-
s
j
p
j
-
o
i
+
L
(
p
j
)
.
24. The apparatus of claim 13 , further comprising refining the corrected luminance based on the optimization:
argmin
L
′
L
′
-
L
2
2
subject to one or more of the constraints
min( L ( o i ))−max( L ( p j ))> T 1
L ′( o i )− L orig ( o i )> T 2
∥ L ′( o i ( y ))∥ ∞ −L ′( s ( y ))< T 3
∥ L ′( o i ( x ))∥ ∞ −L ′( s ( x ))< T 3
L ′( p j +t 1 d j )≥ L ′( p j +t 2 d j ) if t 1 >t 2
that are based on relationships between optimized luminance values L′(o i ), the luminance of edge pixels L(p j ), luminance values of the input image L orig (o i ), optimized luminance values of skeleton pixels L′(s(y)), edge pixels p j , direction vectors d j , thresholds T 1 , T 2 , T 3 and scalars t 1 and t 2 .
25. An electronic device comprising the apparatus of claim 13 .
26. The electronic device of claim 25 selected from the group consisting of a set top box, a computer, a smartphone and a laptop.