Method and apparatus for adjusting subpixel intensity values based upon luminance characteristics of the subpixels for improved viewing angle characteristics of liquid crystal displays

• US 6,801,220 B2
• Filed: 01/26/2001
• Issued: 10/05/2004
• Est. Priority Date: 01/26/2001
• Status: Active Grant

• Current Assignee: AU Optronics Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Wright, Steven L., Greier, Paul F., Millman, Steven Edward, Kaufman, Richard Ian, Wu, Chai Wah, Thompson, Gerhard R., Ho, Kenneth C.
• Primary Examiner(s): Zimmerman, Mark
• Assistant Examiner(s): WALLACE, SCOTT A
• Application Number:
  US09/771,323
• Publication Number:
  US 20020149598A1
• Time in Patent Office: 1,348 Days
• Field of Search: 345/589, 345/591, 345/613, 345/690, 345/597, 345/600, 345/601, 345/602, 345/63, 345/77, 345/50, 345/87, 345/596, 345/697, 345/694, 345/698, 345/209, 345/55
• US Class Current: 345/694
• CPC Class Codes: G09G 2300/0443 with several sub-pixels for the same colour in a pixel, not specifically used to display gradations G09G3/364 takes precedence
• CPC Class Codes: G09G 2300/0447 for multi-domain technique to improve the viewing angle in a liquid crystal display, such as multi-vertical alignment [MVA]
• 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 2320/028 by changing the viewing angle properties, e.g. widening the viewing angle, adapting the viewing angle to the view direction
• CPC Class Codes: G09G 3/2051 with use of a spatial dither pattern
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• CPC Class Codes: G09G 5/006 Details of the interface to the display terminal specific for a display terminal using a CRT G09G1/167; using a flat panel G09G3/2096; circuits for interfacing with colour displays G09G5/04

Abstract

Viewing angle characteristics of a liquid crystal display (LCD) are improved by reducing the number of subpixels in an image with mid-tone luminance values. In a preferred embodiment, a first table of entries associating subpixel intensity values and subpixel luminance values for a LCD in at least one viewing angle direction is provided. A target intensity value is determined from the first table, corresponding to the average subpixel luminance over a small number of adjacent subpixels. A second table of entries associates the target intensity values with intensity values above and below the target. The adjacent subpixel intensity values are modified according to the second table, thereby reducing the number of subpixels with mid-tone luminance values. The subpixel data is preferably processed within a portion of an application-specific integrated circuit (ASIC), contained within the display module.

Claims

1. A method for generating an image for display on a display device having a plurality of subpixels, the method comprising the steps of:

Providing, in digital form, luminance data which associates intensity values with corresponding luminance values characterizing luminance of said subpixels in at least one viewing angle direction for a range of said intensity values;

providing a group of subpixel data elements representing color of a portion of said image, wherein each of said subpixel data elements comprises an intensity value;

modifying said intensity values for said subpixel data elements in said group based upon said luminance data to reduce the number of said subpixels that have a luminance value in a range of mid-tone luminance values between a bright luminance value and a dark luminance value; and

outputting said modified intensity values for said subpixel data elements of said group for display on said display device, wherein said modifying step further comprises;

reducing perceptible variance in one of luminance and color over different viewing angles with respect to the display of the image;

evaluating said subpixel data elements for satisfaction of a set of predetermined criteria;

modifying said intensity values if said criteria are not satisfied; and

maintaining said intensity values if said criteria are satisfied.

2. The method of claim 1, wherein the modifying step further comprises the sub-steps of:

storing, in a first memory, a plurality of entries each providing an association between an intensity value and a corresponding luminance value characterizing luminance of said subpixels in at least one viewing angle direction;

storing, in a second memory, a plurality of entries each providing an association between a target intensity value and a corresponding set of intensity values that are above and below said target intensity value;

identifying particular luminance values stored in said first memory that correspond to intensity values of said subpixel data elements of said group;

generating a first luminance value based upon the particular luminance values stored in said first memory;

identifying a first target intensity value stored in said first memory corresponding to said first luminance value;

identifying a particular set of intensity values stored in said second memory that correspond to said first target intensity value; and

modifying intensity values for said subpixel data elements in said group based upon said particular set of intensity values.

3. The method of claim 1, further comprising the steps of:

performing a digital-to-analog conversion that converts the modified intensity values for said subpixel data elements of said group from digital form to data signals in analog form; and

supplying the data signals in analog form to subpixels of the display device for displaying the portion of the image represented by said subpixel data elements of said group.

4. The method of claim 3, wherein circuitry integral to the display device performs said digital-to-analog conversion and supplies the data signals in analog form to subpixels of the display device.

5. The method of claim 1, wherein display logic of a display subsystem operatively coupled to said display device:

provides said luminance data in digital form;

provides said group of subpixel data elements representing color of a portion of said image;

modifies said intensity values for said subpixel data elements in said group based upon said luminance data; and

outputs said modified intensity values for said subpixel data elements of said group for display on said display device.

6. The method of claim 1, wherein each step is performed by application software executing on a computer system.

7. The method of claim 1, wherein said subpixel data elements representing said image are logically partitioned into an array of rows and columns.

8. The method of claim 7, wherein said group of subpixel data elements comprise a pair of data elements in one of the rows of the array.

9. The method of claim 7, wherein said group of subpixel data elements comprise a pair of data elements in one of the columns of the array.

10. The method of claim 7, wherein said group of subpixel data elements are elements of full pixels which comprise a 2×

2 quad block of data elements in the array.

11. A programmable storage device readable by a digital processing apparatus and tangibly embodying a program of instructions executable by the digital processing apparatus to perform method steps for generating an image for display on a display device having a plurality of subpixels, the method steps comprising:

providing luminance data, in digital form, which associates intensity values with corresponding luminance values characterizing luminance of said subpixels in at least one viewing angle direction for a range of said intensity values;

providing a group of subpixel data elements representing color of a portion of said image, wherein each of said subpixel data elements comprises an intensity value;

modifying said intensity values for said subpixel data elements in said group based upon said luminance data to reduce the number of said subpixels that have a luminance value in a range of mid-tone luminance values between a bright luminance value and a dark luminance value; and

outputting said modified intensity values for said subpixel data elements of said group for display on said display device, wherein the modifying step further comprises the sub-steps of;

storing, in a first memory, a plurality of entries each providing an association between an intensity value and a corresponding luminance value characterizing luminance of said subpixels in at least one viewing angle direction;

storing, in a second memory, a plurality of entries each providing an association between a target intensity value and a corresponding set of intensity values that are above and below said target intensity value;

identifying particular luminance values stored in said first memory that correspond to intensity values of said subpixel data elements of said group;

generating a first luminance value based upon the particular luminance values stored in said first memory;

identifying a first target intensity value stored in said first memory corresponding to said first luminance value;

identifying a particular set of intensity values stored in said second memory that correspond to said first target intensity value; and

modifying intensity values for said subpixel data elements in said group based upon said particular set of intensity values.

12. The programmable storage device of claim 11, wherein said subpixel data elements in said group are elements of full pixels which are adjacent to each other in said image.

13. The programmable storage device of claim 11, wherein said first luminance value is derived by calculating an average luminance value of the particular luminance values stored in the first memory.

14. An apparatus for generating an image for display on a display device having a plurality of subpixels comprising:

a first memory wherein luminance data, in digital form, which associates intensity values with corresponding luminance values characterizing luminance of said subpixels in at least one viewing angle direction for a range of intensity values, are stored;

a second memory wherein a group of subpixel data elements representing color of a portion of said image are stored, wherein said subpixel data elements are logically partitioned into rows and columns and each of said subpixel data elements comprises an intensity value; and

an intensity controller which modifies said intensity values for said subpixel data elements in said group based upon said luminance data to reduce the number of said subpixels that have a luminance value in a range of mid-tone luminance values between a bright luminance value and a dark luminance value, wherein

said subpixels corresponding to said modified intensity values are arranged in pairs of subpixels, wherein for each pair of subpixels, the luminance of a first subpixel of said pair of subpixels is brighter than the average luminance of said pair of subpixels and the luminance of a second subpixel of said pair of subpixels is darker than the average luminance of said pair of subpixels, and

a pixel pattern has a periodicity of one of 2 full pixels along said rows and 2 full pixels along said columns, 2 full pixels along said rows and 4 full pixels along said columns, or 4 full pixels along said rows and 2 full pixels along said columns, wherein said pair of subpixels are elements of full pixels which are adjacent to each other in said image.

15. A computer, comprising:

a display device which displays an image; and

a processor which provides data to said display device, wherein said data is configured to control said display device in order to display said image, and wherein said data is configured so that said image is displayed as;

a plurality of subpixels logically partitioned into a first category and a second category, wherein;

the first category of subpixels are supplied with a data signal of a first polarity,

the second category of subpixels are supplied with a data signal of a second polarity opposite said first polarity, and

the subpixels are partitioned to reduce perceived flicker in the displayed image; and

wherein;

the subpixels correspond to data elements representing color of at least a portion of said image,

each of said data elements comprises an intensity value,

said data elements representing said image are logically partitioned into rows and columns,

each of said subpixels corresponds to a data element representing a particular color in a group of two or more colors,

a full pixel comprises subpixels corresponding to the colors of said group,

said intensity values have been modified to reduce the number of said data elements having a luminance value corresponding to said intensity value in a range of mid-tone luminance values between a bright luminance value and a dark luminance value,

said subpixels corresponding to said modified intensity values are arranged in pairs of subpixels, wherein for each pair of subpixels, the luminance of a first subpixel of said pair of subpixels is brighter than the average luminance of said pair of subpixels and the luminance of a second subpixel of said pair of subpixels is darker than the average luminance of said pair of subpixels, and

a pixel pattern has a periodicity of 2 full pixels along said rows and 2 full pixels alone said columns, wherein said pair of subpixels are elements of full pixels which are adjacent to each other in said image and wherein for each full pixel comprising subpixels corresponding to said modified intensity values, said subpixels comprising said full pixel are one of said second subpixels of said pair of subpixels and said first subpixels of said pair of subpixels.

16. A method for generating an image for display on a display device having a plurality of subpixels, the method comprising the steps of:

Providing, in digital form, luminance data which associates intensity values with corresponding luminance values characterizing luminance of said subpixels in at least one viewing angle direction for a range of said intensity values;

providing a group of subpixel data elements representing color of a portion of said image, wherein each of said subpixel data elements comprises an intensity value;

modifying said intensity values for said subpixel data elements in said group based upon said luminance data to reduce the number of said subpixels that have a luminance value in a range of mid-tone luminance values between a bright luminance value and a dark luminance value; and

outputting said modified intensity values for said subpixel data elements of said group for display on said display device, wherein the modifying step further comprises the sub-steps of;

storing, in a first memory a plurally of entries each providing an association between an intensity value and a corresponding luminance value characterizing luminance of said subpixels in at least one viewing angle direction;

storing, in a second memory, a plurality of entries each providing an association between a target intensity value and a corresponding set of intensity values that are above and below said target intensity value;

identifying particular luminance values stored in said first memory that correspond to intensity values of said subpixel data elements of said group;

generating a first luminance value based upon the particular luminance values stored in said first memory;

identifying a first target intensity value stored in said first memory corresponding to said first luminance value;

identifying a particular set of intensity values stored in said second memory that correspond to said first target intensity value; and

modifying intensity values for said subpixel data elements in said group based upon said particular set of intensity values.

17. The method of claim 16, wherein said subpixel data elements in said group are elements of fill pixels which are adjacent to each other in said image.

18. The method of claim 16, wherein the modifying step further comprises the step of:

setting intensity values for said subpixel data elements in said group to said particular set of intensity values.

19. The method of claim 16, wherein said first luminance value is derived by calculating an average luminance value of the particular luminance values stored in the first memory.

20. The method of claim 16, wherein said modifying step further comprises reducing perceptible variance in luminance over different viewing angles with respect to the display of the image.

21. The method of claim 16, wherein said modifying step further comprises reducing perceptible variance in color over different viewing angles with respect to the display of the image.

22. A computer, comprising:

a display device which displays an image; and

a processor which provides data to said display device, wherein said data is configured to control said display device in order to display said image, and wherein said data is configured so that said image is displayed as;

a plurality of subpixels logically partitioned into a first category and a second category, wherein;

the first category of subpixels are supplied with a data signal of a first polarity,

the second category of subpixels are supplied with a data signal of a second polarity opposite said first polarity, and

the subpixels are partitioned to reduce perceived flicker in the displayed image; and

wherein;

the subpixels correspond to data elements representing color of at least a portion of said image,

each of said data elements comprises an intensity value,

said data elements representing said image are logically partitioned into rows and columns,

each of said subpixels corresponds to a data element representing a particular color in a group of two or more colors,

a full pixel comprises subpixels corresponding to the colors of said group,

said intensity values have been modified to reduce the number of said data elements having a luminance value corresponding to said intensity value in a range of mid-tone luminance values between a bright luminance value and a dark luminance value,

said subpixels corresponding to said modified intensity values are arranged in pairs of subpixels, wherein for each pair of subpixels, the luminance of a first subpixel of said pair of subpixels is brighter than the average luminance of said pair of subpixels and the luminance of a second subpixel of said pair of subpixels is darker than the average luminance of said pair of subpixels, and

a pixel pattern has a periodicity of one of 2 full pixels along said rows and 4 full pixels along said columns or 4 full pixels along said rows and 2 full pixels along said columns, wherein said pair of subpixels are elements of full pixels which are adjacent to each other in said image.

23. The computer of claim 22, wherein for each full pixel comprising subpixels corresponding to said modified intensity values, said subpixels comprising said full pixel are one of said second subpixels of said pair of subpixels and said first subpixels of said pair of subpixels.

24. The computer of claim 22, wherein said subpixels corresponding to said modified intensity values are arranged in adjacent couples comprising one of said second subpixels of said pair of subpixels and said first subpixels of said pair of subpixels.

25. A computer, comprising:

a display device which displays an image; and

a processor which provides data to said display device, wherein said data is configured to control said display device in order to display said image, and wherein said data is configured so that said image is displayed as;

a plurality of subpixels logically partitioned into a first category and a second category, wherein;

the first category of subpixels are supplied with a data signal of a first polarity,

the second category of subpixels are supplied with a data signal of a second polarity opposite said first polarity, and

the subpixels are partitioned to reduce perceived flicker in the displayed image; and

wherein

the subpixels correspond to data elements representing color of at least a portion of said image,

each of said data elements comprises an intensity value,

said data elements representing said image are logically partitioned into rows and columns,

each of said subpixels corresponds to a data element representing a particular color in a group of two or more colors,

a full pixel comprises subpixels corresponding to the colors of said group,

said intensity values have been modified to reduce the number of said data elements having a luminance value corresponding to said intensity value in a range of mid-tone luminance values between a bright luminance value and a dark luminance value,

said subpixels corresponding to said modified intensity values are arranged in pairs of subpixels, wherein for each pair of subpixels, the luminance of a first subpixel of said pair of subpixels is brighter than the average luminance of said pair of subpixels and the luminance of a second subpixel of said pair of subpixels is darker than the average luminance of said pair of subpixels, and

a pixel pattern has a periodicity of 2 full pixels along said rows and 2 subpixels along said columns, and wherein said subpixels are arranged in rows alternating between a first row of adjacent couples comprising said first subpixels of said pair of subpixels, separated by one of said second subpixels of said pair of subpixels and a second row of adjacent couples comprising said second subpixels of said pair of subpixels, separated by one of said first subpixels of said pair of subpixels.

26. The computer of claim 25, wherein said first and second rows comprise adjacent couples of blue and red subpixels separated by one green subpixel.

27. The computer of claim 25, wherein said first and second rows comprise adjacent couples of blue and green subpixels separated by one red subpixel.

28. The computer of claim 25, wherein said first and second rows comprise adjacent couples of green and red subpixels separated by one blue subpixel.