Backlit display with improved dynamic range

• US 20030090455A1
• Filed: 11/09/2001
• Published: 05/15/2003
• Est. Priority Date: 11/09/2001
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Daly, Scott J.
• Granted Patent: US 7,064,740 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/02 Improving the quality of display appearance
• CPC Class Codes: G09G 2320/0238 Improving the black level
• 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 2320/0285 using tables for spatial correction of display data
• 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

Abstract

A display is backlit by a source having spatially modulated luminance to attenuate illumination of dark areas of images and increase the dynamic range of the display.

Claims

1. A method of increasing a dynamic range of a backlit display, said method comprising the step of varying a luminance of a light source illuminating a displayed pixel in response to an intensity value of said pixel.

2. The method of claim 1 wherein the step of varying a luminance of a light source illuminating a displayed pixel in response to a intensity of value of said pixel comprises the steps of:

(a) determining a luminance of said pixel from said intensity value; and

(b) varying a luminance of said light source according to a relationship of said luminance of said pixel and said luminance of said light source.

3. The method of claim 2 wherein said relationship of said luminance of said pixel and said luminance of said light source is a nonlinear relationship.

4. The method of claim 2 wherein the step of determining a luminance of a pixel from an intensity value comprises the step of filtering an intensity value for a plurality of pixels.

5. The method of claim 4 wherein said relationship of said luminance of said pixel and said luminance of said light source is a nonlinear relationship.

6. The method of claim 4 further comprising the step of sampling a filtered intensity value at a spatial coordinate corresponding to said light source.

7. The method of claim 6 further comprising the step of resealing a sample of said filtered intensity value to reflect a nonlinear relationship between said luminance of said light source and said intensity of said displayed pixel.

8. The method of claim 2 wherein the step of varying a luminance of said light source according to a relationship of said luminance of said pixel and said luminance of said light source comprises the steps of:

(a) operating said light source at substantially a maximum luminance if a luminance of at least one displayed pixel exceeds a threshold luminance; and

(b) otherwise, attenuating said luminance of said light source according to a relationship of said luminance of said light source and a luminance of a plurality of pixels.

9. The method of claim 8 wherein the step of attenuating a luminance of a light source according to a relationship of said luminance of said light source and a luminance of a plurality of pixels comprises the step of attenuating said luminance of said light source according to a relationship of said luminance of said light source and a mean luminance of said plurality of pixels.

10. The method of claim 9 wherein the step of attenuating a luminance of a light source illuminating a pixel comprises the step of attenuating a luminance of a plurality of light sources illuminating a plurality of pixels comprising a frame in a sequence of video frames.

11. The method of claim 10 wherein the step of attenuating a luminance of a plurality of light sources illuminating a plurality of pixels comprising a frame in a sequence of video frames comprises the step of attenuating said luminance of said light sources for a subset of frames of said sequence, said subset including less than all said frames of said sequence.

12. The method of claim 9 wherein said plurality of pixels comprises at least two contiguous pixels.

13. The method of claim 1 wherein the step of varying a luminance of a light source illuminating a displayed pixel comprises the step of varying a luminance of a plurality of light sources illuminating a plurality of displayed pixels substantially comprising a frame in a sequence of video frames.

14. The method of claim 13 wherein the step of varying a luminance of a plurality of light sources illuminating a plurality of pixels substantially comprising a frame in a sequence of video frames comprises the step of varying said luminance of said light sources for less than all frames of said sequence.

15. A method of increasing the dynamic range of a backlit display, said method comprising the steps of:

(a) determining a luminance of a pixel of an image from a data value for said pixel;

(b) filtering said luminance;

(c) determining a maximum of said filtered luminance for a plurality of pixels illuminated by a light element of a backlight;

(d) determining a statistical value of said filtered luminance for a plurality of pixels illuminated said light element; and

(e) illuminating said light element according to a relationship of said maximum of said filtered luminance and said statistical value of said filtered luminance.

16. The method of claim 15 wherein said statistical value of said luminance comprises a mean luminance of said plurality of pixels.

17. The method of claim 15 wherein step of illuminating a light element according to a relationship of a maximum of a filtered luminance for a plurality of pixels and a statistical value of said filtered luminance for a plurality of pixels comprises the steps of:

(a) illuminating said light source at a maximum luminance if said maximum of said filtered luminance exceeds a threshold luminance; and

(b) otherwise, illuminating said light source at an attenuated luminance, said attenuated luminance determined by a relationship of said statistical value of said luminance of said plurality of pixels and a luminance level of said light source.

18. The method of claim 17 wherein said relationship of said statistical value of said luminance of said plurality of pixels and a luminance level of said light source is a nonlinear relationship.

19. A backlit display comprising:

(a) a plurality of light source elements;

(b) a light valve arranged for locally modulated transmittance of light from said light source elements, said locally modulated transmittance being responsive to a data value of an image pixel; and

(c) a light source controller to modulate a luminance output of a light source element according to a relationship of said luminance output and said data value of said image pixel.

20. The apparatus of claim 19 wherein said light source controller comprises:

(a) a data processing unit to determine a power to be applied to a light source element to cause said light source element to emit a luminance output satisfying said to said data value of said image pixel; and

(b) a light element driver to apply said power to said light source element.

21. A backlight for a display comprising a plurality of light sources, at least one light source being controllable to output light at a luminance level independent of a luminance level of light output by another of said light sources.

22. The apparatus of claim 21 further comprising a light source driver controlling said luminance level of light output by said at least one light source according to a relationship of said luminance level of said output light and a data value for a displayed pixel.