Better picture for inexpensive cameras
View Patent ↗A method for enhancing an image includes applying an auto-level transformation to an original image to form a first image, applying an auto-contrast transformation to the original image to form a second image, and applying an auto-brightness transformation to the original image to form a third image. The method further includes applying a color cast correction to the first, the second, and the third images to generate a first group of images, applying a gamma correction to the first group of images to generate a second group of images, applying a sharpening correction to the second group of images to generate a third group of images, and presenting the third group of images to a user to select a final result.
1. A method for enhancing an image, comprising using a processor to perform:
applying an auto-level transformation to an original image to form a first image;
applying an auto-contrast transformation to the original image to form a second image;
applying an auto-brightness transformation to the original image to form a third image;
applying a color cast correction to the first, the second, and the third images to generate a first plurality of images, said applying a color cast correction comprising:
creating a histogram Hist[Cr,Cb] of an image, wherein the histogram Hist[Cr,Cb] is defined as a count of points in the image with chromatic values (Cr,Cb); and
determining a nearest peak to an origin (0,0), wherein a peak is located at chromatic values (cr,cb) if (1) Hist(cr,cb)>Hist[cr−1,cb], (2) Hist(cr,cb)>Hist[cr+1,cb], (3) Hist(cr,cb)>Hist[cr,cb−1], and (4) Hist(cr,cb)>Hist[cr,cb+1];
applying a gamma correction to the first plurality of images to generate a second plurality of images;
applying a sharpening correction to the second plurality of images to generate a third plurality of images; and
presenting the third plurality of images to a user to select a final result.
2. A method for applying a color cast correction to an image, comprising using a processor to perform:
creating a histogram Hist[Cr,Cb] of the image, wherein the histogram Hist[Cr,Cb] is defined as a count of points in the image with chromatic values (Cr,Cb);
determining a nearest peak to an origin (0,0), wherein a peak is located at chromatic values (cr,cb) if (1) Hist(cr,cb)>Hist[cr−1,cb], (2) Hist(cr,cb)>Hist[cr+1,cb], (3) Hist(cr,cb)>Hist[cr,cb−1], and (4) Hist(cr,cb)>Hist[cr,cb+1];
setting new chromatic values of points in the image based on chromatic values of the nearest peak and original chromatic values of the points in the image; and
displaying the image to a user.
3. The method of claim 2 , wherein said setting new chromatic values of points in the image comprises:
setting color casts (Δcr,Δcb) equal to (−cr,−cb) of the nearest peak; and
setting the new chromatic values of the points in the image as follows:
Cr new =Cr old +Δcr,
Cb new =Cb old +Δcb. and
Y new=Y old ,
wherein Cr new is a new value of a channel Cr of a point in the image, Cr old is an original value of the channel Cr of the point, Δcr is a color cast of the channel Cr in the image, Cb new is a new value of a channel Cb of the point, Cb old is an original value of the channel Cb of the point, Δcb is a color cast of the channel Cb in the image, Y new is a new value of a channel Y of the point, and Y old is an original value of the channel Y of the point.
4. The method of claim 1 , wherein for each of the first plurality of images, said applying a gamma correction comprises:
calculating a parameter α that maximizes entropy of an image after the gamma correction as follows:
∑
1
≤
x
≤
256
h
(
x
)
α
(
x
256
)
α
-
1
,
wherein h(x) is a histogram of a channel Y of the image before the gamma correction, and x is a gray level of the channel Y;
calculating new Y channel values of points in the image using a following equation:
Y
new
=
255
(
Y
old
255
)
α
,
wherein Y new is a new value of the channel Y of a point in the image and Y old is an original value of the channel Y of the point.
5. The method of claim 1 , wherein for each of the second plurality of images, said sharpening correction comprises calculating new intensity values of an image as follows:
I
new
(
x
,
y
)
=
{
I
old
(
x
,
y
)
,
if
∇
I
(
x
,
y
)
≤
T
I
old
(
x
,
y
)
+
λ
∇
2
I
(
x
,
y
)
,
if
∇
I
(
x
,
y
)
>
T
,
∇
I
(
x
,
y
)
=
I
x
2
(
x
,
y
)
+
I
y
2
(
x
,
y
)
,
I
x
(
x
,
y
)
=
I
(
x
+
1
,
y
)
-
I
(
x
,
y
)
,
I
y
(
x
,
y
)
=
I
(
x
,
y
+
1
)
-
I
(
x
,
y
)
,
and
∇
2
I
(
x
,
y
)
=
I
(
x
,
y
)
-
1
8
∑
i
=
-
1
1
∑
j
=
-
1
1
I
(
x
+
i
,
y
+
j
)
,
wherein λ is a sharpness parameter, T is a threshold value that determines if there is a strong edge, I( ) is an intensity value at a point in the image, I new (x,y) is a new intensity value at a point (x,y) in the image, and I old (x,y) is an old intensity value at the point (x,y).
6. The method of claim 5 , wherein the sharpness parameter λ is equal to 0.1.
7. The method of claim 1 , wherein said auto-level transformation comprises calculating new channel values using a following formula:
g
new
(
C
)
=
255
(
g
(
C
)
-
min
(
C
)
)
max
(
C
)
-
min
(
C
)
,
wherein g new (C) is a new value of a channel C of a point in an image, g (C) is an original value of the channel C of the point, min (C) is a minimum value of the channel C in the image, and max (C) is a maximum value of the channel C in the image.
8. The method of claim 1 , wherein said auto-contrast transformation comprises calculating new channel values using a following formula:
g
new
(
C
)
=
255
(
g
(
C
)
-
min
)
max
-
min
,
wherein RGB values range [min (C) ,max (C) ], Cε{R,G,B}, min=MIN(min (R) ,min (G) ,min (B) ), max=MAX(max (R) ,max (G) ,max (B) ), g new (C) is a new value of a channel C of a point in an image, and g (C) is an original value of the channel C of the point.
9. The method of claim 1 , wherein said auto-brightness transformation comprises calculating new channel values using a following formula:
Y
new
=
255
(
Y
-
min
Y
)
max
Y
-
min
Y
,
Cr
new
=
Cr
,
Cb
new
=
Cb
,
wherein min Y is a minimum value of a channel Y, max Y is a maximum value of the channel Y, Y new is a new value of the channel Y of a point in an image, Y is an original value of the channel Y of the point, Cr new is a new value of a channel Cr of the point, Cr is an original value of the channel Cr of the point, Cb new is the a value of a channel Cb of the point, and Cb is an original value of the channel Cb of the point.
10. A method for enhancing an image, comprising using a processor to perform:
applying an auto-level transformation to an original image to form a first image;
applying an auto-contrast transformation to the original image to form a second image;
applying an auto-brightness transformation to the original image to form a third image;
applying a color cast correction to the first, the second, and the third images to generate a first plurality of images, wherein for each of the first, the second, and the third images, said applying a color cast correction comprises:
creating a histogram Hist[Cr,Cb] of an image, wherein Hist[Cr,Cb] is defined as the count of points in the image with chromatic values (Cr,Cb);
determining a nearest peak from an origin (0,0) for the image, wherein a peak is located at chromatic values (cr,cb) if (1) Hist(cr,cb)>Hist[cr−1,cb] , (2) Hist(cr,cb)>Hist[cr+1,cb], (3) Hist(cr,cb)>Hist[cr,cb−1], and (4) Hist(cr,cb)>Hist[cr,cb+1];
setting (Δcr,Δcb) equal to (−cr,−cb) of the nearest peak for the image, wherein:
Cr new =Cr old +Δcr,
Cb new =Cb old +Δcb, and
Y new =Y old ,
wherein Cr new is a new value of a channel Cr of a point in the image, Cr old is an original value of the channel Cr of the point, Δcr is a color cast of the channel Cr in the image, Cb new is a new value of a channel Cb of the point, Cb old is an original value of the channel Cb of the point, Δcb is a color cast of the channel Cb in the image, Y new is a new value of a channel Y of the point, and Y old is an original value of the channel Y of the point;
applying a gamma correction to the first plurality of images to generate a second plurality of images, wherein for each of the first plurality of images, said applying a gamma correction comprises:
calculating a parameter α that maximizes entropy of an image after correction as follows:
∑
1
≤
x
≤
256
h
(
x
)
α
(
x
256
)
α
-
1
,
wherein h(x) is a histogram of the Y channel in the image before correction, and x is a gray level of the Y channel;
calculating new Y channel values of points in the image using a following equation:
Y
new
=
255
(
Y
old
255
)
α
,
wherein Y new is a new value of the channel Y of a point in the image and Y old is an original value of the channel Y of the point;
applying a sharpening correction to the second plurality of images to generate a third plurality of images, wherein for each of the second plurality of images, said applying a sharpening correction comprises calculating new intensity values for an image as follows:
I
new
(
x
,
y
)
=
{
I
old
(
x
,
y
)
,
if
∇
I
(
x
,
y
)
≤
T
I
old
(
x
,
y
)
+
λ
∇
2
I
(
x
,
y
)
,
if
∇
I
(
x
,
y
)
>
T
,
∇
I
(
x
,
y
)
=
I
x
2
(
x
,
y
)
+
I
y
2
(
x
,
y
)
,
I
x
(
x
,
y
)
=
I
(
x
+
1
,
y
)
-
I
(
x
,
y
)
,
I
y
(
x
,
y
)
=
I
(
x
,
y
+
1
)
-
I
(
x
,
y
)
,
and
∇
2
I
(
x
,
y
)
=
I
(
x
,
y
)
-
1
8
∑
i
=
-
1
1
∑
j
=
-
1
1
I
(
x
+
i
,
y
+
j
)
,
wherein λ is a sharpness parameter, T is a threshold value that determines if there is a strong edge, I( ) is an intensity value at a point in the image, I new (x,y) is a new intensity value at a point (x,y) in the image, and I old (x,y) is an old intensity value at the point (x,y);
presenting the third plurality of images to a user to select a final result.
11. A method for applying a gamma correction to an image comprising: using a processor to perform:
calculating a parameter α that maximizes entropy of the image after the gamma correction as follows:
∑
1
≤
x
≤
256
h
(
x
)
α
(
x
256
)
α
-
1
,
wherein h(x) is a histogram of a channel Y of the image before the gamma correction, and x is a gray level of the channel Y;
calculating new Y channel values of points in the image using a following equation:
Y
new
=
255
(
Y
old
255
)
α
,
wherein Y new is a new value of the channel Y of a point in the image and Y old is an original value of the channel Y of the point;
saving the new Y channel values to the image; and displaying the image to a user.