Methods and Systems for Area Adaptive Backlight Management

• US 20100020003A1
• Filed: 07/22/2008
• Published: 01/28/2010
• Est. Priority Date: 07/22/2008
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Feng, Xiao-Fan
• Granted Patent: US 8,531,380 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0238 Improving the black level
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 2320/0271 Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2320/066 for control of contrast
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• 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

Elements of the present invention relate to systems and methods for generating, modifying and applying backlight array driving values.

Claims

1. A method for modifying display backlight target values, said method comprising:

a) receiving an initial backlight target value image, BL₀;

b) establishing an initial LED driving value (led₀) image comprising virtual points located between pixel elements of said input image by convolving said BL₀ image with an LED mask comprising said virtual point locations;

c) determining an approximated backlight image (bl₁) by convolving said led₀ image with a truncated point spread function (psf₂) kernel;

d) determining a backlight deficiency image (bl₂), which based on a difference between said BL₀ image and said bl₁ image;

e) creating a compensated backlight image (bl₃) by convolving said bl₂ image with a diffusion kernel; and

f) determining a modified LED target value image (BL₁) by adding said bl₃ image to said BL₀ image.

2. A method as described in claim 1 wherein said truncated point spread function (psf₂) is a 3×

3 kernel represented by;

3. A method as described in claim 1 wherein said diffusion kernel is a 3×

3 kernel represented by;

4. A method for generating a modified LED target value image for a display backlight array, said method comprising:

a) receiving a target backlight image (BL₁);

b) combining said BL₁ image with an LED mask, comprising virtual points interspersed between actual image points, to create an led₁ image;

c) convolving said led₁ image with a point spread function (PSF) to create an approximated backlight image, BL₂;

d) determining a difference image representing the difference between said target backlight image, BL₁, and said approximated backlight image, BL₂;

e) determining a scaling factor, β

;

f) scaling said difference image with said scaling factor thereby creating a scaled difference image;

g) adding said led₁ image to said scaled difference image to create a revised LED image, led_i+1; and

h) setting values in said revised, led_i+1, image to zero when said valued are less than zero.

5. A method as described in claim 4 wherein said point spread function is a 5×

7 kernel represented by;

6. A method as described in claim 4 further comprising repeating steps d through h a fixed number of times.

7. A method for post-processing backlight image driving values for a display backlight array, said method comprising:

a) receiving a backlight image comprising backlight image driving values;

b) finding a backlight image driving value, led_i,j, in said backlight image, that is greater than one;

c) calculating coefficients for neighbors of said driving value, led_i,j, with the following equations;

C<sub>i−

1,j</sub>=max(0,1−

led<sub>i−

1,j</sub>)

C_i+1,j=max(0,1−

led_i+1,j)

C<sub>i,j−

1</sub>=max(0,1−

led<sub>i,j−

1</sub>)

C_i,j+1=max(0,1−

led_i,j+1)

d) updating said backlight image driving values and the values of said neighbors, with the following equations;

led_i,j=1

led<sub>i−

1,j</sub>=led<sub>i−

1,j</sub>+k(led_i,j−

1)*C<sub>i−

1,j</sub>/Σ

(C_i,j)

led_i+1,j=led_i+1,j+k(led_i,j−

1)*C<sub>i−

1,j</sub>/Σ

(C_i,j)

led<sub>i,j−

1</sub>=led<sub>i,j−

1</sub>+k(led_i,j−

1)*C<sub>i−

1,j</sub>/Σ

(C_i,j)

led_i,j+1=led_i,j+1+k(led_i,j−

1)*C<sub>i−

1,j</sub>/Σ

(C_i,j);

wherein k is a constant used to compensate for a reduced contribution from neighboring LEDs.

8. A method for generating a backlight image for a display backlight array, said method comprising:

a) receiving an input image comprising an array of pixel values representing an image at an LCD resolution;

b) low-pass filtering said input image with a point spread function of a display diffusion screen to create a low-pass-filtered (LPF) image;

c) subsampling said LPF image to an intermediate resolution thereby creating a LED1p image;

d) low-pass filtering said input image with a kernel that is smaller than the kernel used to create said LPF image thereby creating a second low-pass-filtered (SLPF) image;

e) dividing said SLPF image into blocks wherein each block corresponds to a display backlight LED element in said display backlight array with some overlap between array elements;

f) determining a maximum value in each of said blocks of said SLPF image thereby creating LEDmax values in an LEDmax image; and

g) creating an LED1 image comprising values based on one of a corresponding LEDmax image value and a corresponding LED1p image value.

9. A method as described in claim 8 wherein said LED1 image is created by selecting values from said LED1p image and said LEDmax image such that LED1 image values are the greater of the corresponding LEDmax value and the corresponding LED1p value times two.

10. A method as described in claim 8 wherein said intermediate resolution is a multiple of the resolution of said backlight array.

11. A method as described in claim 8 wherein the size of said blocks in said SLPF image is determined with the following equation:

(1+k)*(m/M×

n/N)

wherein k is an overlap factor, M and N are dimensions of the LED backlight array and m and n are the dimensions of an LCD array.

12. A method as described in claim 8 further comprising:

a) deriving an LED backlight image from said LED1 image; and

b) performing inverse gamma correction on said LED image, thereby creating an inverse-gamma-corrected (IGC) LED image for said display backlight array

13. A method as described in claim 12 further comprising:

a) performing gamma correction on said IGC LED image, thereby creating an LED2 image;

b) upsampling said LED2 image to said LCD resolution;

c) convolving said LED2 image with the point spread function (PSF) of a diffusion layer of said display thereby creating an LED_BL image;

d) dividing said input image by said LED_BL image to create an LCD image; and

e) performing inverse gamma correction on said LCD image, thereby creating an inverse-gamma-corrected (IGC) LCD image.

14. A method as described in claim 12 wherein said deriving an LED backlight image comprises:

a) receiving an initial backlight target value image, BL₀;

b) establishing an initial LED driving value (led₀) image comprising virtual points located between pixel elements of said input image by convolving said BL₀ image with an LED mask comprising said virtual point locations;

c) determining an approximated backlight image (bl₁) by convolving said led₀ image with a truncated point spread function (psf₂) kernel;

d) determining a backlight deficiency image (bl₂), which based on a difference between said BL₀ image and said bl₁ image;

e) creating a compensated backlight image (bl₃) by convolving said bl₂ image with a diffusion kernel; and

f) determining a modified LED target value image (BL₁) by adding said bl₃ image to said BL₀ image.

15. A method as described in claim 12 further comprising performing temporal low-pass filtering on said LED1 image.

16. A method for generating a backlight image for a display backlight array, said method comprising:

a) receiving an input image comprising an array of pixel values representing an image at an LCD resolution;

b) low-pass filtering said input image with a point spread function of a display diffusion screen to create a low-pass-filtered (LPF) image;

c) subsampling said LPF image to an intermediate resolution thereby creating a LED1p image;

d) low-pass filtering said input image with a kernel that is smaller than the kernel used to create said LPF image thereby creating a second low-pass-filtered (SLPF) image;

e) dividing said SLPF image into blocks wherein each block corresponds to a display backlight LED element in said display backlight array with some overlap between array elements;

f) determining a maximum value in each of said blocks of said SLPF image thereby creating LEDmax values in an LEDmax image;

g) creating an LED1 image comprising values based on one of a corresponding LEDmax image value and a corresponding LED1p image value;

h) establishing a target LED driving value (led₀) image comprising virtual points located between pixel elements of said input image by convolving a target backlight image, BL₀, with an LED mask comprising said virtual point locations;

i) determining an approximated backlight image (bl₁) by convolving said led₀ image with a truncated point spread function (psf₂) kernel;

j) determining a backlight deficiency image (bl₂), which represents a difference between said BL₀ image and said bl₁ image;

k) creating a compensated LED driving value image (bl₃) by convolving said bl₀ image with a diffusion kernel; and

l) determining a modified LED target value image (BL₁) by adding said BL₀ image to said bl₃ image.

17. A method as described in claim 16 further comprising performing temporal low-pass filtering on said BL₁ image.

18. A method as described in claim 16 wherein said BL₁ image is created by selecting values from said LED1p image and said LEDmax image such that BL₁ image values are the greater of the corresponding LEDmax value and the corresponding LED1p value times two.

19. A method as described in claim 16 wherein said intermediate resolution is a multiple of the resolution of said backlight array.

20. A method as described in claim 16 wherein the size of said blocks in said SLPF image is determined with the following equation:

(1+k)*(m/M×

n/N)

wherein k is an overlap factor, M and N are dimensions of the LED backlight array and m and n are the dimensions of an LCD array.