DYNAMIC DIMMING LED BACKLIGHT FOR LCD ARRAY

• US 20180047345A1
• Filed: 08/10/2017
• Published: 02/15/2018
• Est. Priority Date: 08/10/2016
• Status: Active Grant

• Current Assignee: Manufacturing Resources International, Inc.
• Original Assignee: Manufacturing Resources International, Inc.
• Inventors: Dunn, William, DeLaet, Rick
• Granted Patent: US 10,510,304 B2
• Time in Patent Office: Days
• CPC Class Codes: G02F 1/13336 Combining plural substrates to produce large-area displays, e.g. tiled displays
• CPC Class Codes: G02F 1/133601 for spatial active dimming
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/133606 including a specially adapted diffusing, scattering or light controlling members
• CPC Class Codes: G09G 2300/026 Video wall, i.e. juxtaposition of a plurality of screens to create a display screen of bigger dimensions
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2320/0686 with two or more screen areas displaying information with different brightness or colours
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 2360/18 Use of a frame buffer in a display terminal, inclusive of the display panel
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix
• CPC Class Codes: G09G 3/3607 for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels display of colours in flat matrix panels other than liquid crystal displays G09G3/2003; grey scales specific for television H04N3/127

Abstract

A LCD assembly having a dynamic dimming LCD backlight and a plurality of individual LCD displays positioned in front of the backlight, and a method for controlling a backlight of such an assembly. The backlight is divided into an array of individually controllable subsections, and adjacent edges of the LCD displays are used to define virtual boundary lines relative to the backlight subsections. Initial desired luminance values are determined for each subsection of the backlight based on incoming video data. A difference between desired luminance values for each pair of adjacent backlight subsections that border the virtual boundary lines is calculated and compared to a threshold value. Based on the comparisons, adjustments may be made to the desired luminance value of the backlight subsections.

Claims

1. A method for controlling a dynamic dimming LCD backlight of a LCD assembly having a plurality of individual LCD displays positioned in front of the backlight, the method comprising:

dividing the backlight into an array of individually controllable subsections;

using adjacent edges of the LCD displays as virtual boundary lines relative to the backlight subsections;

determining an initial desired luminance value for each subsection of the backlight based on incoming video data supplied to the LCDs;

(a) calculating the difference between desired luminance values for each pair of adjacent backlight subsections that border the virtual boundary lines;

(b) comparing the calculated difference in desired luminance values for each pair of adjacent backlight subsections to a predetermined threshold value; and

(c) when the calculated difference in desired luminance values between a pair of adjacent backlight subsections exceeds the threshold value, increasing the desired luminance value for the backlight subsection having a lower desired luminance value.

2. The method of claim 1, wherein the desired luminance value for the backlight subsection having a lower desired luminance value is also increased when the calculated difference in desired luminance values between a pair of adjacent backlight subsections is equal to the threshold value.

3. The method of claim 1, wherein all backlight subsections not having an increased desired luminance value are driven at the original desired luminance value.

4. The method of claim 1, wherein the threshold value is between 20% and 90% of the possible range of desired luminance values.

5. The method of claim 1, wherein the desired luminance value of a given subsection is increased by adding a constant value to the existing desired luminance value of said subsection.

6. The method of claim 5, wherein the constant value is some fixed percentage of the threshold value.

7. The method of claim 1, wherein the desired luminance value of a given subsection is increased by adding a value selected from a lookup table, the values in the lookup table varying with the magnitude of the calculated difference in desired luminance values.

8. The method of claim 1, wherein the desired luminance value of a given subsection is increased by multiplying the calculated difference in desired luminance values by some predetermined fraction.

9. The method of claim 1, wherein the desired luminance value for a given backlight subsection is determined by:

defining a sub-image as the portion of an overall video image displayed by the LCDs that overlies the given backlight subsection;

creating histogram data for the sub-image, the histogram data including a brightness index value and the number of pixels within the sub-image, for each color channel present;

using the histogram data to calculate the average and the standard deviation for each channel; and

setting the initial desired luminance value for each channel of the backlight subsection equal to the sum of the calculated average plus the calculated standard deviation multiplied by some factor.

10. The method of claim 9, wherein the factor is 1.5.

11. The method of claim 9, further comprising analyzing the histogram data for each channel for a bimodal distribution.

12. The method of claim 11, wherein Otsu'"'"'s Algorithm is used to determine the presence of a bimodal distribution.

13. The method of claim 11, further comprising calculating a second average and a second standard deviation for each channel having a bimodal distribution, and using the second average and the second standard deviation to calculate a final desired luminance value for each said channel.

14. The method of claim 1, further comprising performing gamma correction.

15. The method of claim 1, further comprising rescaling LCD subpixel voltage.

16. The method of claim 15, wherein subpixel voltage rescaling is accomplished by dividing the voltage of a given subpixel by the ratio of the desired luminance value for said subpixel to the maximum possible luminance value for said subpixel.

17. The method of claim 15, further comprising creating a virtual backlight that allows bleed over behavior of adjacent backlight subsections to be mathematically modeled and accounted for during rescaling of subpixel voltages.

18. The method of claim 17, wherein:

the virtual backlight is created using virtual subsections that are based on the use of a stored matrix of data that represents the appearance of a single, fully illuminated backlight subsection as seen through a diffuser;

each virtual subsection is larger than the actual backlight subsection it represents, such that adjacent subsections may be overlapped; and

the principle of additive light may be used to blend the edges of the subsections.

19. The method of claim 1, further comprising repeating steps (a)-(c) on subsequent video frames after all of any backlight subsection desired luminance value increases are completed for a current video frame.

20. A method for controlling a dynamic dimming LCD backlight of a LCD assembly, the backlight divided into an array of individually controllable subsections, and a plurality of individual LCD displays positioned in front of the backlight with adjacent edges of the LCD displays defining virtual boundary lines relative to the backlight subsections, the method comprising:

determining an initial desired luminance value for each subsection of the backlight based on incoming video data supplied to the LCDs, wherein the desired luminance value is between off and a maximum luminance value;

calculating the difference between desired luminance values for each pair of adjacent backlight subsections that border the virtual boundary lines;

comparing the calculated difference in desired luminance values for each pair of adjacent backlight subsections to a predetermined threshold value;

when the calculated difference in desired luminance values between a pair of adjacent backlight subsections exceeds the threshold value, increasing the desired luminance value for the backlight subsection having a lower desired luminance value;

driving all backlight subsections not having an increased desired luminance value at the initially determined desired luminance value;

rescaling the voltage of any LCD subpixels that overlie a backlight subsection operating at less than the maximum luminance value; and

creating a virtual backlight that allows bleed over behavior of adjacent backlight subsections to be mathematically modeled and accounted for during rescaling of the LCD subpixel voltages.

21. The method of claim 20, wherein the desired luminance value for the backlight subsection having a lower desired luminance value is also increased when the calculated difference in desired luminance values between a pair of adjacent backlight subsections is equal to the threshold value.

22. The method of claim 20, wherein the desired luminance value of a given subsection is increased by a technique selected from the group consisting of:

adding a constant value to the existing desired luminance value of said subsection;

adding a value selected from a lookup table, the values in the lookup table varying with the magnitude of the calculated difference in desired luminance values; and

multiplying the calculated difference in desired luminance values by some predetermined fraction.

23. The method of claim 20, wherein the desired luminance value for a given backlight subsection is determined by:

defining a sub-image as the portion of an overall video image displayed by the LCDs that overlies the given backlight subsection;

creating histogram data for the sub-image, the histogram data including a brightness index value and the number of pixels within the sub-image, for each color channel present;

using the histogram data to calculate the average and the standard deviation for each channel; and

setting the initial desired luminance value for each channel of the backlight subsection equal to the sum of the calculated average plus the calculated standard deviation multiplied by some factor.

24. The method of claim 20, wherein subpixel voltage rescaling is accomplished by dividing the voltage of a given subpixel by the ratio of the desired luminance value for said subpixel to the maximum possible luminance value for said subpixel.

25. The method of claim 20, wherein:

the virtual backlight is created using virtual subsections that are based on the use of a stored matrix of data that represents the appearance of a single, fully illuminated backlight subsection as seen through a diffuser;

each virtual subsection is larger than the actual backlight subsection it represents, such that adjacent subsections may be overlapped; and

the principle of additive light may be used to blend the edges of the subsections.

26. A LCD assembly having a dynamically dimmable backlight, comprising:

the dimmable backlight divided into an array of individually controllable subsections;

a plurality of LCD displays positioned in front of the backlight, with adjacent edges of the LCD displays defining virtual boundary lines relative to the backlight subsections;

a separate receiver board in electrical communication with each LCD display, each receiver board also in electrical communication with the backlight and with the other receiver boards associated with adjacent LCD displays;

a separate video source in electrical connection with each receiver board;

at least one frame buffer on each receiver board configured to receive and store data from the associated video source;

at least one histogram accumulator on each receiver board configured to sample data from the associated video source; and

a digital signal processor on each receiver board configured to receive data from the at least one histogram accumulator, to calculate the desired luminance values for the backlight subsections underlying the LCD display to which the receiver board is connected, and to output video data to the LCD display to which the receiver board is connected.

27. The LCD assembly of claim 26, further comprising a virtual backlight buffer on each receiver board, the virtual backlight buffer configured to receive updated desired luminance values from the digital signal processor and to rescale the gain of the video data output to the LCD display to which the receiver board is connected.

28. The LCD assembly of claim 26, wherein the at least one histogram accumulator samples data for each color channel present.

29. The LCD assembly of claim 26, wherein each receiver board is divided into blocks, a first block configured to receive and analyze incoming video data while a second block simultaneously scales and transmits video data to the LCD display to which the receiver board is connected.