IMAGE DISPLAY APPARATUS AND DRIVING METHOD THEREOF, AND IMAGE DISPLAY APPARATUS ASSEMBLY AND DRIVING METHOD THEREOF

• US 20090315921A1
• Filed: 06/15/2009
• Published: 12/24/2009
• Est. Priority Date: 06/23/2008
• Status: Active Grant

• Current Assignee: Japan Display West Incorporated (Japan Display Incorporated)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: IIJIMA, Yukiko, HIGASHI, Amane, SAKAIGAWA, Akira, NOGUCHI, Koji
• Granted Patent: US 8,194,094 B2
• Time in Patent Office: Days
• US Class Current: 345/694
• CPC Class Codes: G09G 2300/0452 Details of colour pixel setup, e.g. pixel composed of a red, a blue and two green components
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2340/06 Colour space transformation
• CPC Class Codes: G09G 2360/142 the light being detected by light detection means within each pixel
• CPC Class Codes: G09G 3/001 using specific devices not provided for in groups G09G3/02 - G09G3/36, e.g. using an intermediate record carrier such as a film slide; Projection systems; Display of non-alphanumerical information, solely or in combination with alphanumerical information, e.g. digital display on projected diapositive as background slide projectors per se G03B23/00 = 42 HP
• CPC Class Codes: G09G 3/2003 Display of colours specific for liquid crystal displays G09G3/3607
• CPC Class Codes: G09G 3/3208 organic, e.g. using organic light-emitting diodes [OLED]
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers

Abstract

An image display apparatus includes: an image display panel having a two-dimensional matrix with (P×Q) pixels each including first, second and third sub-pixels for displaying respective first, second and third elementary colors, and fourth sub-pixel for displaying a fourth color; and a signal processing section configured to receive first, second and third sub-pixel input signals respectively provided with signal values of x_{1-(p, q)}, x_{2-(p, q)} and x_{3-(p, q)}, and to output first, second, third and fourth sub-pixel output signals respectively provided with signal values of X_{1-(p, q)}, X_{2-(p, q)}, X_{3-(p, q)} and X_{4-(p, q)}, which used for determining the display gradations of the first, second, third, and fourth sub-pixels, respectively, with regard to a (p, q)th pixel where notations p and q are integers satisfying equations 1≦p≦P and 1≦q≦Q.

Claims

1. An image display apparatus comprising:

(A) an image display panel having a two-dimensional matrix with (P×

Q) pixels each including a first sub-pixel for displaying a first elementary color, a second sub-pixel for displaying a second elementary color, a third sub-pixel for displaying a third elementary color and a fourth sub-pixel for displaying a fourth color; and

(B) a signal processing section configured to receive

a first sub-pixel input signal provided with a signal value of x_{1-(p, q)},

a second sub-pixel input signal provided with a signal value of x_{2-(p, q)} and

a third sub-pixel input signal provided with a signal value of x_{3-(p, q)}, and to output

a first sub-pixel output signal provided with a signal value of X_{1-(p, q)} and used for determining the display gradation of said first sub-pixel,

a second sub-pixel output signal provided with a signal value of X_{2-(p, q)} and used for determining the display gradation of said second sub-pixel,

a third sub-pixel output signal provided with a signal value of X_{3-(p, q)} and used for determining the display gradation of said third sub-pixel as well as

a fourth sub-pixel output signal provided with a signal value of X_{4-(p, q)} and used for determining the display gradation of said fourth sub-pixel

with regard to a (p, q)th pixel where notations p and q are integers satisfying equations 1≦

p≦

P and 1≦

q≦

Q,

wherein a maximum lightness value V_max(S) expressed as a function of variable saturation S in an HSV color space enlarged by adding said fourth color is stored in said signal processing section, and

said signal processing section carries out the following processes of

(B-1) finding said saturation S and said lightness value V(S) for each of a plurality of pixels on the basis of the signal values of sub-pixel input signals in said pixels,

(B-2) finding an extension coefficient α

₀ on the basis of at least one of ratios V_max(S)/V(S) found in said pixels,

(B-3) finding said output signal value X_{4-(p, q)} in said (p, q)th pixel on the basis of at least said input signal values x_{1-(p, q)}, x_{2-(p, q)} and x_{3-(p, q)}, and

(B-4) finding said output signal value X_{1-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{1-(p, q)} said extension coefficient α

₀ and said output signal value X_{4-(p, q)}, finding said output signal value X_{2-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{2-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)} and finding said output signal value X_{3-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{3-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}.

2. The image display apparatus according to claim 1 wherein said signal processing section is capable of finding output signal values X_{1-(p, q)}, X_{2-(p, q)} and X_{3-(p, q)} on the basis of the following equations:

X_{1-(p, q)}=α

₀·

x_{1-(p, q)}−

χ

·

X_{4-(p, q)};

X_{2-(p, q)}=α

₀·

x_{2-(p, q)}−

χ

·

X_{4-(p, q)} and

X_{3-(p, q)}=α

₀·

x_{3-(p, q)}−

χ

·

X_{4-(p, q)},

where, in said above equations, reference notation χ

denotes a constant dependent on said image display apparatus whereas reference notations X_{1-(p, q)}, X_{2-(p, q)} and X_{3-(p, q)} each denote an output signal value in said (p, q)th pixel.

3. The image display apparatus according to claim 2 wherein said constant χ

is expressed by the following equation;

χ

=BN₄/BN_1-3

where, in said above equation, reference notation BN_1-3 denotes the luminance of a set of first, second and third sub-pixels for a case in which

a signal having a value corresponding to the maximum signal value of said first sub-pixel output signal is supplied to said first sub-pixel,

a signal having a value corresponding to the maximum signal value of said second sub-pixel output signal is supplied to said second sub-pixel, and

a signal having a value corresponding to the maximum signal value of said third sub-pixel output signal is supplied to said third sub-pixel

whereas reference notation BN₄ denotes the luminance of said fourth sub-pixel for a case in which a signal having a value corresponding to the maximum signal value of said fourth sub-pixel output signal is supplied to said fourth sub-pixel.

4. The image display apparatus according to claim 1 wherein a saturation S_{(p, q)} and a lightness value V_{(p, q)} in said HSV color space in a (p, q)th pixel are found on the basis of the following equations:

S_{(p, q)}=(Max_{(p, q)}−

Min_{(p, q)})/Max_{(p, q);}

and

V_{(p, q)}=Max_{(p, q)},

where, in said above equations,

notation Max_{(p, q)} denotes the maximum value of the signal values of said three sub-pixel input signals x_{1-(p, q)}, x_{2-(p, q)} and x_{3-(p, q)},

notation Min_{(p, q)} denotes the minimum value of the signal values of said three sub-pixel input signals x_{1-(p, q)}, x_{2-(p, q)} and x_{3-(p, q)},

said saturation S can have a value in the range 0 to 1 and said lightness value V can have a value in said range 0 to (2ⁿ−

1) whereas notation n in the expression (2ⁿ−

1) is an integer representing the number of display gradation bits.

5. The image display apparatus according to claim 4 wherein said output signal value X_{4-(p, q)} is determined on the basis of said minimum value Min_{(p, q)} and said extension coefficient α

₀.

6. The image display apparatus according to claim 1 wherein the smallest value among the values of said ratios V_max(S)/V(S) found in said pixels is taken as said extension coefficient α

₀.

7. The image display apparatus according to claim 1 wherein said fourth color is the white color.

8. The image display apparatus according to claim 1

wherein said image display apparatus is a color liquid-crystal display apparatus which includes

a first color filter placed between said first sub-pixel and the image observer to serve as a filter for passing light of said first elementary color,

a second color filter placed between said second sub-pixel and said image observer to serve as a filter for passing light of said second elementary color, and

a third color filter placed between said third sub-pixel and said image observer to serve as a filter for passing light of said third elementary color.

9. The image display apparatus according to claim 1 wherein all (P×

Q) pixels are taken as a plurality of pixels for each of which said saturation S and said lightness value V(S) are to be found.

10. The image display apparatus according to claim 1 wherein (P/P₀×

Q/Q₀) pixels are taken as a plurality of pixels for each of which said saturation S and said lightness value V(S) are to be found where notations P₀ and Q₀ represent values satisfying equations P≧

P₀ and Q≧

Q₀ whereas at least one of ratios P/P₀ and Q/Q₀ are integers each equal to or greater than 2.

11. The image display apparatus according to claim 1 wherein said extension coefficient α

₀ is determined for every image display frame.

12. An image display apparatus comprising:

(A-1) a first image display panel having a two-dimensional matrix with (P×

Q) first sub-pixels each used for displaying a first elementary color;

(A-2) a second image display panel having a two-dimensional matrix with (P×

Q) second sub-pixels each used for displaying a second elementary color;

(A-3) a third image display panel having a two-dimensional matrix with (P×

Q) third sub-pixels each used for displaying a third elementary color;

(A-4) a fourth image display panel having a two-dimensional matrix with (P×

Q) fourth sub-pixels each used for displaying a fourth color;

(B) a signal processing section configured to receive

a first sub-pixel input signal provided with a signal value of x_{1-(p, q)},

a second sub-pixel input signal provided with a signal value of x_{2-(p, q)} and

a third sub-pixel input signal provided with a signal value of x_{3-(p, q)}, and to output

a first sub-pixel output signal provided with a signal value of X_{1-(p, q)} and used for determining the display gradation of said first sub-pixel,

a second sub-pixel output signal provided with a signal value of X_{2-(p, q)} and used for determining the display gradation of said second sub-pixel,

a third sub-pixel output signal provided with a signal value of X_{3-(p, q)} and used for determining the display gradation of said third sub-pixel as well as

a fourth sub-pixel output signal provided with a signal value of X_{4-(p, q)} and used for determining the display gradation of said fourth sub-pixel

with regard to (p, q)th first, second and third sub-pixels where notations p and q are integers satisfying equations 1≦

p≦

P and 1≦

q≦

Q; and

(C) synthesis means for synthesizing images output by said first, second, third and fourth image display panels,

wherein a maximum lightness value V_max(S) expressed as a function of variable saturation S in an HSV color space enlarged by adding said fourth color is stored in said signal processing section, and

said signal processing section carries out the following processes of

(B-1) finding said saturation S and said lightness value V(S) for each of a plurality of sets each having said first, second and third sub-pixels on the basis of the signal values of sub-pixel input signals in said sets each having said first, second and third sub-pixels,

(B-2) finding an extension coefficient α

₀ on the basis of at least one of ratios V_max(S)/V(S) found in said sets each having said first, second and third sub-pixels,

(B-3) finding said output signal value X_{4-(p, q)} in said (p, q)th fourth sub-pixel on the basis of at least said input signal values x_{1-(p, q)}, x_{2-(p, q)} and x_{3-(p, q)}, and

(B-4) finding said output signal value X_{1-(p, q)} in said (p, q)th first sub-pixel on the basis of said input signal value x_{1-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}, finding said output signal value X_{2-(p, q)} in said (p, q)th second sub-pixel on the basis of said input signal value x_{2-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)} and finding said output signal value X_{3-(p, q)} in said (p, q)th third sub-pixel on the basis of said input signal value x_{3-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}.

13. An image display apparatus adopting a field sequential system, comprising:

(A) an image display panel having a two-dimensional matrix with (P×

Q) pixels; and

(B) a signal processing section configured to receive

a first input signal provided with a signal value of x_{1-(p, q)},

a second input signal provided with a signal value of x_{2-(p, q)} and

a third input signal provided with a signal value of x_{3-(p, q)}, and to output

a first output signal provided with a signal value of X_{1-(p, q)} and used for determining the display gradation of a first elementary color,

a second output signal provided with a signal value of X_{2-(p, q)} and used for determining the display gradation of a second elementary color,

a third output signal provided with a signal value of X_{3-(p, q)} and used for determining the display gradation of a third elementary color as well as

a fourth output signal provided with a signal value of X_{4-(p, q)} and used for determining the display gradation of a fourth color

with regard to a (p, q)th pixel where notations p and q are integers satisfying said equations 1≦

p≦

P and 1≦

q≦

Q.

wherein a maximum lightness value V_max(S) expressed as a function of variable saturation S in an HSV color space enlarged by adding said fourth color is stored in said signal processing section, and

said signal processing section carries out the following processes of

(B-1) finding said saturation S and said lightness value V(S) for each of a plurality of pixels on the basis of the signal values of first, second and third input signals in said pixels,

(B-2) finding an extension coefficient α

₀ on the basis of at least one of ratios V_max(S)/V(S) found in said pixels,

(B-3) finding said output signal value X_{4-(p, q)} in said (p, q)th pixel on the basis of at least said input signal values x_{1-(p, q)}, x_{2-(p, q)} and x_{3-(p, q)}, and

(B-4) finding said output signal value X_{1-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{1-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}, finding said output signal value X_{2-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{2-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)} and finding said output signal value X_{3-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{3-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}.

14. An image display apparatus assembly comprising:

an image display apparatus including

(A) an image display panel having a two-dimensional matrix with (P×

Q) pixels each including a first sub-pixel for displaying a first elementary color, a second sub-pixel for displaying a second elementary color, a third sub-pixel for displaying a third elementary color and a fourth sub-pixel for displaying a fourth color, and

(B) a signal processing section configured to receive

a first sub-pixel input signal provided with a signal value of x_{1-(p, q)},

a second sub-pixel input signal provided with a signal value of x_{2-(p, q)} and

a third sub-pixel input signal provided with a signal value of x_{3-(p, q)}, and to output

a first sub-pixel output signal provided with a signal value of X_{1-(p, q)} and used for determining the display gradation of said first sub-pixel,

a second sub-pixel output signal provided with a signal value of X_{2-(p, q)} and used for determining the display gradation of said second sub-pixel,

a third sub-pixel output signal provided with a signal value of X_{3-(p, q)} and used for determining the display gradation of said third sub-pixel as well as

a fourth sub-pixel output signal provided with a signal value of X_{4-(p, q)} and used for determining the display gradation of said fourth sub-pixel

with regard to a (p, q)th pixel where notations p and q are integers satisfying equations 1≦

p≦

P and 1≦

q≦

Q; and

a planar light-source apparatus for radiating light to the rear face of said image display apparatus,

wherein a maximum lightness value V_max(S) expressed as a function of variable saturation S in an HSV color space enlarged by adding said fourth color is stored in said signal processing section, and

said signal processing section carries out the following processes of

(B-1) finding said saturation S and said lightness value V(S) for each of a plurality of pixels on the basis of the signal values of sub-pixel input signals in said pixels,

(B-2) finding an extension coefficient α

₀ on the basis of at least one of ratios V_max(S)/V(S) found in said pixels,

(B-3) finding said output signal value X_{4-(p, q)} in said (p, q)th pixel on the basis of at least said input signal values x_{1-(p, q)}, x_{2-(p, q)} and x_{3-(p, q)}, and

(B-4) finding said output signal value X_{1-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{1-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}, finding said output signal value X_{2-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{2-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}, and finding said output signal value X_{3-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{3-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}.

15. The image display apparatus assembly in accordance with claim 14 wherein the luminance of said planar light-source apparatus is reduced on the basis of said extension coefficient α

₀.

16. A method for driving an image display apparatus including

(A) an image display panel having a two-dimensional matrix with (P×

Q) pixels each including a first sub-pixel for displaying a first elementary color, a second sub-pixel for displaying a second elementary color, a third sub-pixel for displaying a third elementary color and a fourth sub-pixel for displaying a fourth color, and

(B) a signal processing section configured to receive

a first sub-pixel input signal provided with a signal value of x_{1-(p, q)},

a second sub-pixel input signal provided with a signal value of x_{2-(p, q)} and

a third sub-pixel input signal provided with a signal value of x_{3-(p, q)}, and to output

a first sub-pixel output signal provided with a signal value of X_{1-(p, q)} and used for determining the display gradation of said first sub-pixel,

a second sub-pixel output signal provided with a signal value of X_{2-(p, q)} and used for determining the display gradation of said second sub-pixel,

a third sub-pixel output signal provided with a signal value of X_{3-(p, q)} and used for determining the display gradation of said third sub-pixel as well as

a fourth sub-pixel output signal provided with a signal value of X_{4-(p, q)} and used for determining the display gradation of said fourth sub-pixel

with regard to a (p, q)th pixel where notations p and q are integers satisfying equations 1≦

p≦

P and 1≦

q≦

Q,

wherein a maximum lightness value V_max(S) expressed as a function of variable saturation S in an HSV color space enlarged by adding said fourth color is stored in said signal processing section, and

said signal processing section carries out the following steps of;

(a) finding said saturation S and said lightness value V(S) for each of a plurality of pixels on the basis of said signal values of sub-pixel input signals in said pixels;

(b) finding an extension coefficient α

₀ on the basis of at least one of ratios V_max(S)/V(S) found in said pixels;

(c) finding said output signal value X_{4-(p, q)} in said (p, q)th pixel on the basis of at least said input signal values x_{1-(p, q)}, x_{2-(p, q)} and x_{3-(p, q)}; and

(d) finding said output signal value X_{1-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{1-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}, finding said output signal value X_{2-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{2-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)} and finding said output signal value X_{3-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{3-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}.

17. A method for driving an image display apparatus including

(A-1) a first image display panel having a two-dimensional matrix with (P×

Q) first sub-pixels each used for displaying a first elementary color,

(A-2) a second image display panel having a two-dimensional matrix with (P×

Q) second sub-pixels each used for displaying a second elementary color,

(A-3) a third image display panel having a two-dimensional matrix with (P×

Q) third sub-pixels each used for displaying a third elementary color,

(A-4) a fourth image display panel having a two-dimensional matrix with (P×

Q) fourth sub-pixels each used for displaying a fourth color,

(B) a signal processing section configured to receive

a first sub-pixel input signal provided with a signal value of x_{1-(p, q)},

a second sub-pixel input signal provided with a signal value of x_{2-(p, q)} and

a third sub-pixel input signal provided with a signal value of x_{3-(p, q)}, and to output

a first sub-pixel output signal provided with a signal value of X_{1-(p, q)} and used for determining the display gradation of said first sub-pixel,

a second sub-pixel output signal provided with a signal value of X_{2-(p, q)} and used for determining the display gradation of said second sub-pixel,

a third sub-pixel output signal provided with a signal value of X_{3-(p, q)} and used for determining the display gradation of said third sub-pixel as well as

a fourth sub-pixel output signal provided with a signal value of X_{4-(p, q)} and used for determining the display gradation of said fourth sub-pixel

with regard to (p, q)th first, second and third sub-pixels where notations p and q are integers satisfying equations 1≦

p≦

P and 1≦

q≦

Q, and

(C) synthesis means for synthesizing images output by said first, second, third and fourth image display panels,

wherein a maximum lightness value V_max(S) expressed as a function of variable saturation S in an HSV color space enlarged by adding said fourth color is stored in said signal processing section, and

said signal processing section carries out the following steps of;

(a) finding said saturation S and said lightness value V(S) for each of a plurality of sets each having said first, second and third sub-pixels on the basis of said signal values of sub-pixel input signals in said sets each having said first, second and third sub-pixels;

(b) finding an extension coefficient α

₀ on the basis of at least one of ratios V_max(S)/V(S) found in said sets each having said first, second and third sub-pixels;

(c) finding said output signal value X_{4-(p, q)} in said (p, q)th fourth sub-pixel on the basis of at least said input signal values x_{1-(p, q)}, x_{2-(p, q)} and x_{3-(p, q)}; and

(d) finding said output signal value X_{1-(p, q)} in said (p, q)th first sub-pixel on the basis of said input signal value x_{1-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}, finding said output signal value X_{2-(p, q)} in said (p, q)th second sub-pixel on the basis of said input signal value x_{2-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)} and finding said output signal value X_{3-(p, q)} in said (p, q)th third sub-pixel on the basis of said input signal value x_{3-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}.

18. A method for driving an image display apparatus adopting a field sequential system,

said image display apparatus including

(A) an image display panel having a two-dimensional matrix with (P×

Q) pixels, and

(B) a signal processing section configured to receive

a first input signal provided with a signal value of x_{1-(p, q)},

a second input signal provided with a signal value of x_{2-(p, q)} and

a third sub-pixel input signal provided with a signal value of x_{3-(p, q)}, and to output

a first output signal provided with a signal value of X_{1-(p, q)} and used for determining the display gradation of a first elementary color,

a second output signal provided with a signal value of X_{2-(p, q)} and used for determining the display gradation of a second elementary color,

a third output signal provided with a signal value of X_{3-(p, q)} and used for determining the display gradation of a third elementary color as well as a fourth output signal provided with

a signal value of X_{4-(p, q)} and used for determining the display gradation of said fourth color

with regard to a (p, q)th pixel where notations p and q are integers satisfying said equations 1≦

p≦

P and 1≦

q≦

Q.

wherein a maximum lightness value V_max(S) expressed as a function of variable saturation S in an HSV color space enlarged by adding said fourth color is stored in said signal processing section, and

said signal processing section carries out the following steps of;

(a) finding said saturation S and said lightness value V(S) for each of a plurality of pixels on the basis of the signal values of first, second and third input signals in said pixels;

(b) finding an extension coefficient α

₀ on the basis of at least one of ratios V_max(S)/V(S) found in said pixels;

(c) finding said output signal value X_{4-(p, q)} in said (p, q)th pixel on the basis of at least said input signal values x_{1-(p, q)}, x_{2-(p, q)} and x_{3-(p, q)}; and

(d) finding said output signal value X_{1-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{1-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}, finding said output signal value X_{2-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{2-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)} and finding said output signal value X_{3-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{3-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}.

19. A method for driving an image display apparatus assembly comprising

an image display apparatus including

(A) an image display panel having a two-dimensional matrix with (P×

Q) pixels each including a first sub-pixel for displaying a first elementary color, a second sub-pixel for displaying a second elementary color, a third sub-pixel for displaying a third elementary color and a fourth sub-pixel for displaying a fourth color, and

(B) a signal processing section configured to receive

a first sub-pixel input signal provided with a signal value of x_{1-(p, q)},

a second sub-pixel input signal provided with a signal value of x_{2-(p, q)} and

a third sub-pixel input signal provided with a signal value of x_{3-(p, q)} and to output

a first sub-pixel output signal provided with a signal value of X_{1-(p, q)} and used for determining the display gradation of said first sub-pixel,

a second sub-pixel output signal provided with a signal value of X_{2-(p, q)} and used for determining the display gradation of said second sub-pixel,

a third sub-pixel output signal provided with a signal value of X_{3-(p, q)} and used for determining the display gradation of said third sub-pixel as well as

a fourth sub-pixel output signal provided with a signal value of X_{4-(p, q)} and used for determining the display gradation of said fourth sub-pixel

with regard to a (p, q)th pixel where notations p and q are integers satisfying equations 1≦

p≦

P and 1≦

q≦

Q, and

a planar light-source apparatus for radiating light to the rear face of said image display apparatus,

wherein a maximum lightness value V_max(S) expressed as a function of variable saturation S in an HSV color space enlarged by adding said fourth color is stored in said signal processing section, and

said signal processing section carries out the following steps of;

(a) finding said saturation S and said lightness value V(S) for each of a plurality of pixels on the basis of the signal values of sub-pixel input signals in said pixels;

(b) finding an extension coefficient α

₀ on the basis of at least one of ratios V_max(S)/V(S) found in said pixels;

(c) finding said output signal value X_{4-(p, q)} in said (p, q)th pixel on the basis of at least said input signal values x_{1-(p, q)}, x_{2-(p, q)} and x_{3-(p, q)};

(d) finding said output signal value X_{1-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{1-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}, finding said output signal value X_{2-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{2-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)} and finding said output signal value X_{3-(p, q)} in said (p, q)th pixel on the basis of said input signal value x_{3-(p, q)}, said extension coefficient α

₀ and said output signal value X_{4-(p, q)}; and

(e) reducing the luminance of said planar light-source apparatus on the basis of said extension coefficient α

₀.