Display device, display panel driver and method of driving display panel
View Patent ↗An LCD device according to the present invention has: an LCD panel; an operation and correction circuit configured to perform a correction operation with respect to an input gray-scale data of a target frame image by using an arithmetic expression to generate an output gray-scale data; a data line driver configured to drive the LCD panel in accordance with the output gray-scale data; and a correction data calculation circuit configured to generate a correction data that specifies a relationship between the input gray-scale data and the output gray-scale data of the target frame image, depending on the input gray-scale data of the target frame image or an input gray-scale data of a precedent frame image followed by the target frame image. The operation and correction circuit determines coefficients of the arithmetic expression from the correction data.
1. A display device, comprising:
a display panel;
an operation and correction circuit configured to perform a correction operation with respect to an input gray-scale data of a target frame image by using an arithmetic expression to generate an output gray-scale data;
a driver configured to drive said display panel in accordance with said output gray-scale data; and
a correction data calculation circuit configured to generate a correction data that specifies a relationship between said input gray-scale data and said output gray-scale data of said target frame image, depending on said input gray scale data of said target frame image or an input gray-scale data of a precedent frame image followed by said target frame image,
wherein said operation and correction circuit determines coefficients of said arithmetic expression from said correction data, and
wherein said arithmetic expression is switched between a plurality of arithmetic expressions in response to said input gray-scale data and said correction data.
2. The display device according to claim 1 ,
wherein said operation and correction circuit is configured to perform a gamma correction based on an approximate expression,
wherein said correction data includes a correction point data set comprising correction point data that specifies a shape of a gamma curve of said gamma correction, and
wherein said operation and correction circuit determines coefficients of said approximate expression from said correction point data set.
3. The display device according to claim 2 , wherein said correction data calculation circuit comprises:
a storage circuit configured to store a plurality of correction point data sets corresponding to different gamma values; and
a selection circuit configured to select said correction point data set supplied to said operation and correction circuit from said plurality of correction point data sets, depending on said input gray-scale data of said target frame image or said input gray-scale data of said precedent frame image followed by said target frame image.
4. The display device according to claim 2 , wherein said correction data calculation circuit calculates an Average Picture Level (APL) from said input gray-scale data of said target frame image or said precedent frame image and calculates said correction point data set supplied to said operation and correction circuit based on said calculated APL.
5. The display device according to claim 4 , wherein said correction data calculation circuit comprises:
a storage circuit configured to store a plurality of correction point data sets corresponding to different gamma values; and
a selection circuit configured to select said correction point data set supplied to said operation and correction circuit from said plurality of correction point data sets, depending on said calculated APL.
6. The display device according to claim 4 , wherein said correction data calculation circuit comprises:
a storage circuit configured to store a plurality of correction point data sets; and
an interpolation operation and selection circuit configured to select two correction point data sets from said plurality of correction point data sets depending on upper bits of said calculated APL and to generate said correction point data set supplied to said operation and correction circuit by interpolating said two correction point data sets depending on lower bits of said calculated APL.
7. The display device according to claim 4 , wherein said display panel comprises a liquid crystal display, and
wherein the display device further comprises:
a back light configured to illuminate said liquid crystal display panel; and
a back light brightness adjustment circuit configured to control a brightness of said back light depending on said calculated APL.
8. The display device according to claim 2 , wherein said correction data calculation circuit calculates a frequency distribution of said input gray-scale data of said target frame image or said precedent frame image, and calculates said correction point data set supplied to said operation and correction circuit based on said calculated frequency distribution.
9. The display device according to claim 8 , wherein said correction data calculation circuit calculates a frequency of a first class corresponding to a range in which a value of said input gray-scale data is relatively low and a frequency of a second class corresponding to a range in which a value of said input gray-scale data is relatively high, and
wherein said correction data calculation circuit calculates said correction point data set supplied to said operation and correction circuit depending on a difference in said frequency between said first class and said second class.
10. The display device according to claim 9 , wherein said correction data calculation circuit comprises:
a storage circuit configured to store a plurality of correction point data sets corresponding to different gamma values; and
a selection circuit configured to select said correction point data set supplied to said operation and correction circuit from said plurality of correction point data sets, depending on said difference in said frequency between said first class and said second class.
11. The display device according to claim 9 , wherein said display panel comprises a liquid crystal display panel, and
wherein the display device further comprises:
a back light configured to illuminate said liquid crystal display panel; and
a back light brightness adjustment circuit configured to control a brightness of said back light depending on said difference in said frequency between said first class and said second class.
12. The display device according to claim 2 , wherein said correction data calculation circuit comprises:
a frequency distribution calculation circuit configured to calculate a frequency distribution of said input gray-scale data of said target frame image or said precedent frame image;
a storage circuit configured to store a plurality of correction point data sets corresponding to different gamma values;
a selection circuit configured to select a selected correction point data set from said plurality of correction point data sets, depending on said calculated frequency distribution; and
a correction point data operation circuit configured to modify correction point data included in said selected correction point data set, depending on said calculated frequency distribution,
wherein said correction point data operation circuit determines said selected correction point data set including said modified correction point data as said correction point data set supplied to said operation and correction circuit.
13. The display device according to claim 12 , wherein each of said plurality of correction point data sets stored in said storage circuit includes correction point data CP 0 to CP 5 defined by the following equation (1a) in a case where the corresponding gamma value γ is smaller than 1 or defined by the following equation (1b) in a case where the corresponding gamma value γ is larger than 1:
CP
0
=
0
,
CP
1
=
4
·
Gamma
[
K
/
4
]
-
Gamma
[
K
]
2
,
CP
2
=
Gamma
[
K
-
1
]
,
CP
3
=
Gamma
[
K
]
,
CP
4
=
2
·
Gamma
[
(
D
IN
MAX
+
K
-
1
)
/
2
]
-
D
OUT
MAX
,
CP
5
=
D
OUT
MAX
,
(
1
a
)
CP0=0,
CP 1=2·Gamma[ K/ 2]−Gamma[ K],
CP 2=Gamma[ K− 1],
CP3=Gamma[K],
CP 4=2·Gamma[( D IN MAX +K− 1)/2 ]−D OUT MAX ,
CP5=D OUT MAX , (1b)
wherein said Gamma[x] is a function representing an accurate expression of said gamma correction and is expressed by the following equation (2):
Gamma[ x]=D OUT MAX ·( x/D IN MAX ) γ , (2)
wherein said frequency distribution calculation circuit calculates a frequency of a first class corresponding to a quarter range in which a value of said input gray-scale data is lowest, a frequency of a second class corresponding to a quarter range in which a value of said input gray-scale data is relatively higher than that of said first class, a frequency of a third class corresponding to a quarter range in which a value of said input gray-scale data is relatively higher than that of said second class, and a frequency of a fourth class corresponding to a quarter range in which a value of said input gray-scale data is relatively higher than that of said third class and is highest,
wherein said selection circuit selects said selected correction point data set from said plurality of correction point data sets stored in said storage circuit, depending on a difference between a sum of said frequency of said first class and said frequency of said second class and a sum of said frequency of said third class and said frequency of said fourth class,
wherein said correction point data operation circuit modifies said correction point data CP 1 of said selected correction point data set depending on a difference in said frequency between said first class and said second class, and modifies said correction point data CP 4 of said selected correction point data set depending on a difference in said frequency between said third class and said fourth class,
wherein when said input gray-scale data is expressed by D IN and said output gray-scale data is expressed by D OUT , said operation and correction circuit calculates said output gray-scale data based on said selected correction point data set including said modified correction point data CP 1 and CP 4 , in accordance with the following equations (3a) to (3c):
(1) in a case where D IN <D IN Center and CP 1 >CP 0 :
D
OUT
=
2
(
CP
1
-
CP
0
)
·
PD
INS
K
2
+
(
CP
3
-
CP
0
)
D
INS
K
+
CP
0.
(
3
a
)
(2) in a case where D IN <D IN Center and CP 1 <CP 0 :
D
OUT
=
2
(
CP
1
-
CP
0
)
·
ND
INS
K
2
+
(
CP
3
-
CP
0
)
D
INS
K
+
CP
0.
(
3
b
)
(3) in a case where D IN >D IN Center :
D
OUT
=
2
(
CP
4
-
CP
2
)
·
ND
INS
K
2
+
(
CP
5
-
CP
2
)
D
INS
K
+
CP
2.
(
3
c
)
wherein said K is expressed by the following equation (4):
K =( D IN MAX +1)/2, (4)
said D IN Center is expressed by the following equation (5):
D IN Center =D IN MAX /2, (5)
a parameter R is given by the following equation (6):
R=K 1/2 ×D INS 1/2 , (6)
said D INS , said PD INS and said ND INS are given by the following equations (7a) to (7d):
D INS =D IN , (in a case of D IN <D IN Center ) (7a)
D INS =D IN +1 −K , (in a case of D IN >D IN Center ) (7b)
PD INS =( K−R )× R, (7c)
ND INS =( K−D INS )× D INS . (7d)
14. The display device according to claim 13 , wherein said display panel comprises a liquid crystal display panel, and
wherein the display device further comprises:
a back light configured to illuminate said liquid crystal display panel; and
a back light brightness adjustment circuit configured to control a brightness of said back light depending on said difference between said sum of said frequency of said first class and said frequency of said second class and said sum of said frequency of said third class and said frequency of said fourth class.
15. The display device according to claim 2 , wherein when a maximum value of said input gray-scale data is D IN MAX and a maximum value of said output gray-scale data is D ouT MAX , said correction point data set generated by said correction data calculation circuit includes correction point data CP 0 to CP 5 defined by the following equation (1a) or (1b):
CP
0
=
0
,
CP
1
=
4
·
Gamma
[
K
/
4
]
-
Gamma
[
K
]
2
,
CP
2
=
Gamma
[
K
-
1
]
,
CP
3
=
Gamma
[
K
]
,
CP
4
=
2
·
Gamma
[
(
D
IN
MAX
+
K
-
1
)
/
2
]
-
D
OUT
MAX
,
CP
5
=
D
OUT
MAX
,
(
1
a
)
CP0=0,
CP 1=2·Gamma[ K/ 2]−Gamma[ K],
CP 2=Gamma[ K− 1],
CP3=Gamma[K],
CP 4=2·Gamma[( D IN MAX +K− 1)/2 ]−D OUT MAX ,
CP5=D OUT MAX , (1b)
wherein said Gamma[x] is a function representing an accurate expression of said gamma correction, and when a gamma value corresponding to said correction point data set generated by said correction data calculation circuit is γ, said Gamma[x] is expressed by the following equation (2):
Gamma[ x]=D OUT MAX ·( x/D IN MAX ) γ , (2)
wherein when said input gray-scale data is expressed by D IN and said output gray-scale data is expressed by D OUT , said operation and correction circuit calculates said output gray-scale data in accordance with the following equations (3a) to (3c):
(1) in a case where D IN <D IN Center and CP 1 >CP 0 :
D
OUT
=
2
(
CP
1
-
CP
0
)
·
PD
INS
K
2
+
(
CP
3
-
CP
0
)
D
INS
K
+
CP
0.
(
3
a
)
(2) in a case where D IN <D IN Center and CP 1 <CP 0 :
D
OUT
=
2
(
CP
1
-
CP
0
)
·
ND
INS
K
2
+
(
CP
3
-
CP
0
)
D
INS
K
+
CP
0.
(
3
b
)
(3) in a case where D IN >D IN Center :
D
OUT
=
2
(
CP
4
-
CP
2
)
·
ND
INS
K
2
+
(
CP
5
-
CP
2
)
D
INS
K
+
CP
2.
(
3
c
)
wherein said K is expressed by the following equation (4):
K =( D IN MAX +1)/2, (4)
said D IN Center is expressed by the following equation (5):
D IN Center =D IN MAX /2, (5)
a parameter R is given by the following equation (6):
R=K 1/2 ×D INS 1/2 , (6)
said D INS , said PD INS and said ND INS are given by the following equations (7a) to (7d):
D INS =D IN , (in a case of D IN <D IN Center ) (7a)
D INS =D IN +1 −K , (in a case of D IN >D IN Center ) (7b)
PD INS =( K−R )× R, (7c)
ND INS =( K−D INS )× D INS . (7d)
16. A display panel driver, comprising:
an operation and correction circuit configured to perform a correction operation with respect to an input gray-scale data of a target frame image by using an arithmetic expression to generate an output gray-scale data;
a driver configured to drive a display panel in accordance with said output gray-scale data; and
a correction data calculation circuit configured to generate a correction data that specifies a relationship between said input gray-scale data and said output gray-scale data of said target frame image, depending on said input gray-scale data of said target frame image or an input gray-scale data of a precedent frame image followed by said target frame image,
wherein said operation and correction circuit determines coefficients of said arithmetic expression from said correction data, and
wherein said arithmetic expression is switched between a plurality of arithmetic expressions in response to said input gray-scale data and said correction data.
17. The display panel driver according to claim 16 , wherein said operation and correction circuit is configured to perform a gamma correction based on an approximate expression,
wherein said correction data includes a correction point data set composed of correction point data that specifies a shape of a gamma curve of said gamma correction, and
wherein said operation and correction circuit determines coefficients of said approximate expression from said correction point data set.
18. The display panel driver according to claim 17 , wherein said correction data calculation circuit comprises:
a storage circuit configured to store a plurality of correction point data sets corresponding to different gamma values; and
a selection circuit configured to select said correction point data set supplied to said operation and correction circuit from said plurality of correction point data sets, depending on said input gray-scale data of said target frame image or said input gray-scale data of said precedent frame image followed by said target frame image.
19. The display panel driver according to claim 17 , wherein said correction data calculation circuit calculates an APL from said input gray-scale data of said target frame image or said precedent frame image and calculates said correction point data set supplied to said operation and correction circuit based on said calculated APL.
20. The display panel driver according to claim 17 , wherein said correction data calculation circuit calculates a frequency distribution of said input gray-scale data of said target frame image or said precedent frame image, and calculates said correction point data set supplied to said operation and correction circuit based on said calculated frequency distribution.
21. The display panel driver according to claim 17 , wherein said correction data calculation circuit comprises:
a frequency distribution calculation circuit configured to calculate a frequency distribution of said input gray-scale data of said target frame image or said precedent frame image;
a storage circuit configured to store a plurality of correction point data sets corresponding to different gamma values;
a selection circuit configured to select said correction point data set supplied to said operation and correction circuit from said plurality of correction point data sets, depending on said calculated frequency distribution; and
a correction point data operation circuit configured to modify correction point data included in said selected correction point data set, depending on said calculated frequency distribution.
22. A method of driving a display panel, said method comprising:
performing a correction operation with respect to an input gray-scale data of a target frame image by using an arithmetic expression to generate an output gray-scale data;
driving a display panel in accordance with said output gray-scale data; and
generating a correction data that specifies a relationship between said input gray-scale data and said output gray-scale data of said target frame image, depending on said input gray-scale data of said target frame image or an input gray-scale data of a precedent frame image followed by said target frame image,
wherein coefficients of said arithmetic expression are determined from said correction data, and
wherein said arithmetic expression is switched between a plurality of arithmetic expressions in response to said input gray-scale data and said correction data.