Liquid crystal display backlight with variable amplitude LED

• US 7,675,500 B2
• Filed: 10/28/2004
• Issued: 03/09/2010
• Est. Priority Date: 11/09/2001
• Status: Expired due to Fees

• 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.
• Primary Examiner(s): Awad; Amr
• Assistant Examiner(s): Sherman; Stephen G
• Application Number:
  US10/977,788
• Publication Number:
  US 20050088402A1
• Time in Patent Office: 1,958 Days
• Field of Search: 345/102, 345/87, 345/82, 345/204, 345/76, 345/690, 349/61, 349/62
• 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 illuminating a backlit display having a light source illuminating a plurality of display pixels and comprising a plurality of light-emitting elements each capable of emitting light at respective intensities independent of other ones of said light emitting elements, said method comprising:

(a) spatially varying the luminance of said light source by;

(i) filtering an intensity value signal for a plurality of input image pixels and sampling the filtered said signal at respective spatial coordinate areas, each corresponding to at least one of said light-emitting elements; and

(ii) spatially varying the luminance of said light source by driving at least two of said light-emitting elements independently of each other according to a nonlinear relationship between the sampled said luminance signal at a respective said spatial coordinate area and the driven luminance of said at least one of said light-emitting elements;

(b) varying the transmittance of a light valve of said display in a non-binary manner; and

(c) rescaling a sample of said filtered intensity value to reflect said nonlinear relationship.

2. The method of claim 1 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.

3. The method of claim 2 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.

4. The method of claim 3 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.

5. The method of claim 4 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.

6. The method of claim 3 wherein said plurality of pixels comprises at least two contiguous pixels.

7. 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.

8. The method of claim 7 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.

9. A method of illuminating a backlit display, said method comprising:

(a) spatially varying the luminance of a light source illuminating a plurality of displayed pixels;

(b) varying the transmittance of a light valve of said display in a non-binary manner;

(c) rescaling image data to be displayed on said display according to the equation;

${\mathrm{LS}}_{\mathrm{attenuation}}<br><br>\left(\mathrm{CV}\right)=\frac{L_{\mathrm{CRT}}}{L_{\mathrm{LCD}}}=\frac{{\mathrm{gain}\left(\mathrm{CV}+V_d\right)}^{\mathrm{\gamma <br><br>}}+{\mathrm{leakage}}_{\mathrm{CRT}}}{{\mathrm{gain}<br><br>\left(\mathrm{CV}+V_d\right)}^{\mathrm{\gamma <br><br>}}+{\mathrm{leakage}}_{\mathrm{LCD}}}$

where;

LS_attenuation(CV)=the attenuation of the light source as a function of the digital value of the image pixel

L_CRT=the luminance of the CRT display

L_LCD=the luminance of the LCD display

V_d=an electronic offset

γ

=the cathode gamma.

10. The method of claim 9 wherein the step of varying a luminance of a light source illuminating a displayed pixel comprises the steps of:

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

11. The method of claim 10 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.

12. The method of claim 11 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.

13. The method of claim 12 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.

14. The method of claim 13 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.

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

16. A method of illuminating a backlit display, said method comprising the steps of:

(a) spatially varying the luminance of a light source illuminating a plurality of displayed pixels in response to a plurality of pixel values dependent on the spatial variance of luminance content of an input image to be displayed on said display;

(b) varying the transmittance of a light valve of said display in a non-binary manner, wherein said light source is spatially displaced at a location at least partially directly beneath said plurality of pixels, wherein regions of said image that are sufficiently dark are attenuated by reducing the luminance of said light source, wherein regions of said image that are not said sufficiently dark are not attenuated in the same manner as said sufficiently dark regions by reducing the luminance of said light source, wherein different regions of said light source provide different non-zero luminance; and

,

(c) modifying the light to be output from said display by rescaling said light to be said output from said display in such a manner to alter the tone-scale of said light to be said output from said display from a state that would have substantially non-uniform tone-scale to a state that has substantially uniform tone-scale resulting from the luminance of said light source.

17. The method of claim 16 wherein a relationship of said pixel values and said luminance of said light source is a nonlinear relationship.

18. The method of claim 16 further comprising the step of filtering pixel value for a plurality of pixels.

19. The method of claim 18 further comprising the step of sampling said filtered intensity value for a spatial location of said light source.

20. The method of claim 19 further comprising the step of rescaling a sample of said filtered intensity value to reflect a nonlinear relationship between said intensity of said light source and said intensity of said displayed pixel.

21. The method of claim 16 further comprising:

(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.

22. The method of claim 21 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 based upon of said luminance of said light source and a mean luminance of said plurality of pixels.

23. The method of claim 16 further comprising variably reducing luminance of a portion of said light source based upon a dark local spatial area of said pixel data.

24. The method of claim 16 further comprising non-linear modification of said pixel values in a manner that simulates a CRT display.

25. The method of claim 24 wherein said spatially varying the luminance is based upon low pass filtered pixel values.