SIGNAL GENERATION FOR LED/LCD-BASED HIGH DYNAMIC RANGE DISPLAYS

• US 20120056906A1
• Filed: 02/09/2010
• Published: 03/08/2012
• Est. Priority Date: 02/11/2009
• Status: Active Grant

• Current Assignee: InterDigital Madison Patent Holdings (InterDigital, Inc.)
• Original Assignee: InterDigital Madison Patent Holdings (InterDigital, Inc.)
• Inventors: Zhai, Jiefu, Llach, Joan
• Granted Patent: US 11,380,270 B2
• Time in Patent Office: Days
• US Class Current: 345/690
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• 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

Abstract

A method of operating a high dynamic range display device comprises the steps of: accessing an image signal; generating an intermediate backlighting driver signal for individual backlight elements for a backlighting unit responsive to the image signal; convoluting the intermediate backlighting driver signals with a point spread function of the backlighting unit; deriving at least one new backlighting driver signal responsive to the convoluting step; determining display error associated with a plurality of available light shutter signals of a front-end unit having individual light shutters and associated with the at least one new backlighting driver signal, the front-end unit having a higher resolution than the backlighting unit; driving the display device with a combination of shutter signals and new backlighting driver signals that causes a reduction in the display error with respect to other generated intermediate backlighting driver signals and other available light shutter signals.

Claims

1. A display device comprising:

a backlighting unit having a matrix of light generating elements;

a front-end unit having a plurality of light shutters grouped into a repeat arrangement which include at least two different shutters that each attenuate different color light;

a signal handling system for receiving image signals and having an algorithm to process the image signals and derive final backlight driver signals for the backlighting unit and final front-end driver signals for the front-end unit, wherein

the algorithm employing at least one difference reduction iteration to derive the final driver signals, the at least one iteration being responsive to a display target image brightness values (I);

at least one projected image brightness values (O) correlating to at least one set of intermediate driver signals; and

the difference between the brightness values.

2. The display device of claim 1, wherein the algorithm is an iterative gradient descent algorithm.

3. The display device of claim 1, wherein the algorithm employs a convolution between a point spread function of the backlighting unit and quantized backlight driver signals.

4. The display device of claim 3, wherein the algorithm is adapted to produce or access:

a backlight matrix L of the quantized backlight driver signals for the backlighting unit having M rows by N columns that correspond to the light generating elements and a point spread matrix P that corresponds to the point spread function; and

a product of L and P to yields a full resolution backlighting brightness matrix B.

5. The display device of claim 4, wherein the algorithm is adapted to generate the final front-end driver signals for a color p responsive to a product of the brightness matrix and a normalized front-end driver signal for the color p.

6. The display device of claim 5, wherein at least a term of display output brightness O_p for a given the color p is expressed as

7. The display device of claim 6, wherein the algorithm is adapted to produce a least square of the difference between the input high dynamic range image and the display output brightness for the color p and the algorithm reduces the least square.

8. The display device of claim 4, wherein the algorithm is adapted such that output error is generated and used in determining the final front-end driver signals for a color p, the output error incorporates at least a term expressed as:

9. The display device of claim 5, wherein the algorithm is adapted to be responsive to clipping error and quantization error, wherein:

the clipping error is caused by some intermediate driver signals for the backlighting unit correlating to insufficient brightness and is the difference between the insufficient brightness and the display target image brightness value, and

the quantization error is the difference between a brightness quantization level of the front-end unit and the display target image brightness value.

10. The display device of claim 4, wherein the algorithm is adapted such that a collective output error J is generated and used in determining the final front-end driver signals for at least three colors, the collective output error is reduced by the algorithm and incorporates at least a term expressed as:

J=∥

I_r−

O_r∥

₂²+∥

I_g−

O_g∥

₂²+∥

I_b−

O_b∥

₂²

where the Is are an input high dynamic range image brightness for three colors r, g, and b and Os are a display output brightness for the three colors, respectively.

11. A method comprising the steps of:

accessing an image signal;

generating an intermediate backlighting driver signal for individual backlight elements for a backlighting unit responsive to the image signal;

convoluting the intermediate backlighting driver signals with a point spread function of the backlighting unit;

deriving at least one new backlighting driver signal responsive to the convoluting step;

determining display error associated with a plurality of available light shutter signals of a front-end unit having individual light shutters and associated with the at least one new backlighting driver signal, the front-end unit having a higher resolution than the backlighting unit;

driving a display device with a combination of shutter signals and new backlighting driver signals that causes a reduction in the display error with respect to other generated intermediate backlighting driver signals and other available light shutter signals.

12. The method of claim 11 further comprising:

accessing target display output for the individual shutters from the image signal;

using a factor that includes a square root of the target display output to obtain intermediate backlighting driver signal in the generating step.

13. The method of claim 11 further comprising:

generating a backlight matrix L having M rows by N columns that correspond to the backlight elements; and

producing a full resolution backlighting brightness matrix B, at least in part, from the matrix L and the matrix P.

14. The method of claim 13 further comprising:

comparing the full resolution backlighting brightness matrix B to the image signal; and

generating diagonal matrices U and V having diagonal elements corresponding to sign(I-PL*) and sign(PL*-I), respectively, wherein matrix L* represents iterations of new backlighting driver signals and I represents the target display output of the image signal.

15. The method of claim 14 further comprising:

repeating the comparing step and generating diagonal matrices steps η

times, wherein η

is a predetermined number of iterations.

16. The method of claim 15 further comprising:

quantizing the backlight driver signals in the matrix L.

17. The method of claim 16 further comprising the steps of:

using the matrix L* after the last iteration to determine a final full resolution backlighting; and

selecting final light shutter signals responsive to the final full resolution backlighting to use in the driving step.

18. The method of claim 17 comprising:

determining clipping error and quantization error, wherein the clipping error is caused by intermediate driver signals for the backlighting unit correlating to insufficient brightness and is the difference between the insufficient brightness and the target display output, and the quantization error is the difference between a brightness quantization level of the front-end unit and the target display output;

applying the clipping error or quantization error into a cost function and using the cost function as a factor in determining the display error.

19. The method of claim 13 further comprising:

comparing the full resolution backlighting brightness matrix B to the image signal; and

using the comparison in the comparing step in determining the display error and selecting combinations of shutter signals and new backlighting driver signals.