Illumination device and liquid crystal display device using the same

• US 8,049,711 B2
• Filed: 07/26/2007
• Issued: 11/01/2011
• Est. Priority Date: 10/29/2002
• Status: Expired due to Fees

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Yamada, Fumiaki, Hayashi, Keiji, Kobayashi, Tetsuya, Nishido, Masanori, Suzuki, Toshihiro, Hamada, Tetsuya, Furukoshi, Yasutake, Sugawara, Mari
• Primary Examiner(s): Moon; Seokyun
• Application Number:
  US11/881,380
• Publication Number:
  US 20080018575A1
• Time in Patent Office: 1,559 Days
• Field of Search: 345 87-102, 349 61- 71
• US Class Current: 345/102
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/0076 Stacked arrangements of multiple light guides of the same or different cross-sectional area
• CPC Class Codes: G02B 6/0078 Side-by-side arrangements, e.g. for large area displays
• CPC Class Codes: G02F 1/1336 Illuminating devices
• CPC Class Codes: G09G 2310/024 Scrolling of light from the illumination source over the display in combination with the scanning of the display screen
• CPC Class Codes: G09G 2310/0245 Clearing or presetting the whole screen independently of waveforms, e.g. on power-on G09G2310/063 takes precedence
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• 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 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3666 with the matrix divided into sections
• CPC Class Codes: G09G 5/10 Intensity circuits

Abstract

A liquid crystal display device including an LCD panel modulating light transmissivities of plural pixels disposed in a matrix form on the basis of respective gradation data; an illumination device for irradiating light to the respective pixels while a ratio (duty ratio) of a lighting time in one frame period is changed; and a display data conversion part for calculating respective lightnesses and a lightness histogram from the respective gradation data, determining a threshold lightness from the lightness histogram on the basis of a previously determined ratio of pixels to be saturated in brightness, processing the respective gradation data on the basis of the threshold lightness to output them to the LCD panel, and outputting duty ratio data to change the duty ratio to the illumination device.

Claims

1. A liquid crystal display device, comprising:

an LCD panel modulating light transmissivities of plural pixels disposed in a matrix form on the basis of respective gradation data;

an illumination device for irradiating light to the respective pixels while a ratio (duty ratio) of a lighting time in one frame period is changed; and

a display data conversion part for calculating respective lightnesses and a lightness histogram from the respective gradation data, determining a threshold lightness from the lightness histogram on the basis of a previously determined ratio of pixels to be saturated in brightness, processing the respective gradation data on the basis of the threshold lightness to output them to the LCD panel, and outputting duty ratio data to change the duty ratio to the illumination device,

wherein the display data conversion part counts the lightnesses from the lightness histogram in descending order of lightness on the basis of the ratio of the pixels to be saturated in brightness and determines the threshold lightness.

2. A liquid crystal display device according to claim 1, wherein the display data conversion part judges M pixels, where M is the number of pixels in which an image is displayed, of N pixels, where N is the total number of pixels in one frame, where M≦

N, and determines the threshold lightness on the basis of a product of the number of the M pixels and the ratio of the pixels to be saturated in brightness.

4. A liquid crystal display device according to claim 1, wherein the lightness is obtained from the gradation data (R, G, B) of the respective pixels as the lightness Y=r×

R+g×

G+b×

B, where R is the gradation data of red sub-pixels;

G is the gradation data of green sub-pixels;

B is the gradation data of blue sub-pixels; and

r, g and b are real numbers and include a numerical value of 0.

3. A liquid crystal display device, comprising:

an LCD panel modulating light transmissivities of plural pixels disposed in a matrix form on the basis of respective gradation data;

an illumination device for irradiating light to the respective pixels while a ratio (duty ratio) of a lighting time in one frame period is changed; and

a display data conversion part for calculating respective lightnesses and a lightness histogram from the respective gradation data, determining a threshold lightness from the lightness histogram on the basis of a previously determined ratio of pixels to be saturated in brightness, processing the respective gradation data on the basis of the threshold lightness to output them to the LCD panel, and outputting duty ratio data to change the duty ratio to the illumination device,

wherein the display data conversion part determines the duty ratio so that a product of a maximum value which the gradation data can take and the duty ratio becomes equal to the threshold lightness, processes the gradation data of a pixel of a lightness not lower than the threshold lightness to have the maximum value, and processes the gradation data of the other pixel so that a product of the processed gradation data and the determined duty ratio becomes equal to lightness of the original gradation data of the pixel.

5. A liquid crystal display device according to claim 3, wherein the lightness is obtained from the gradation data (R, G, B) of the respective pixels as the lightness Y=r×

R+g×

G+b×

B, where R is the gradation data of red sub-pixels;

G is the gradation data of green sub-pixels;

B is the gradation data of blue sub-pixels; and

r, g and b are real numbers and include a numerical value of 0.