LIQUID CRYSTAL DISPLAY AND IMAGE DISPLAY METHOD

• US 20080001881A1
• Filed: 06/25/2007
• Published: 01/03/2008
• Est. Priority Date: 06/30/2006
• Status: Abandoned Application

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Itoh, Goh, Baba, Masahiro
• Application Number:
  US11/767,618
• Publication Number:
  US 20080001881A1
• Time in Patent Office: Days
• US Class Current: 345/89
• CPC Class Codes: G09G 2310/063 Waveforms for resetting the whole screen at once
• CPC Class Codes: G09G 2320/0238 Improving the black level
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• 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 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers
• CPC Class Codes: G09G 5/06 using colour palettes, e.g. look-up tables

Abstract

There is provided with an image display method including: calculating black information indicating a length of a period in which a black image should be displayed in one frame period of an input image or a ratio of a period in which the black image should be displayed in the one frame period of the input image; controlling a light source luminance of the light source according to the information to suppress fluctuation of a display luminance at a maximum gray-scale level displayable by a liquid crystal panel due to variation of a length of a black display period depending on the information; correcting a gray-scale level of each pixel of the input image to obtain corrected gray-scale levels for suppressing fluctuation of a display luminance at gray-scale levels other than the maximum gray-scale level due to the control of the light source luminance of the light source.

Claims

1. A liquid crystal display comprising:

an input unit configured to input an input image;

a light source configured to emit light;

a liquid crystal panel configured to display an image by modulating a transmittance or a reflectance of light from the light source based on signals representing the image;

a black information calculator configured to calculate black information indicating a length of a period in which black should be displayed in one frame period of the input image or a ratio of a period in which black should be displayed in the one frame period of the input image;

a light-source-luminance controller configured to control a light source luminance of the light source according to the black information to suppress fluctuation of a display luminance at a maximum gray-scale level displayable by the liquid crystal panel due to variation of a length of a black display period depending on the black information;

a gray-scale level corrector configured to correct a gray-scale level of each pixel of the input image to obtain corrected gray-scale levels to suppress fluctuation of a display luminance at gray-scale levels other than the maximum gray-scale level due to controlling of the light source luminance of the light source; and

a liquid crystal panel driver configured to, in the one frame period,

(1) provide the liquid crystal panel with signals of each pixel having the corrected gray-scale levels in continuous period obtained by subtracting a black display period depending on the black information from the one frame period, and

(2) provide the liquid crystal panel with signals of each pixel indicating black in the black display period.

2. The display according to claim 1, wherein

the black information calculator calculates a black insertion ratio in a range between a minimum black insertion ratio and a maximum black insertion ratio which are a minimum value and a maximum value of a ratio of a period in which the black image is displayed in the one frame period, and

the gray-scale level corrector corrects gray-scale levels of the input image to a gray-scale level which can obtain a display luminance within a predetermined display luminance range with respect to a display luminance at the time when the input image is displayed on the liquid crystal panel at a reference black insertion ratio which is in the range between the minimum black insertion ratio and the maximum black insertion ratio.

3. The display according to claim 2, wherein the predetermined display luminance range is a range between the display luminance at the time when the input image is displayed on the liquid crystal panel at the reference black insertion ratio and a display luminance at the time when the input image is displayed on the liquid crystal panel at the black insertion ratio calculated by the black information calculator.

4. The display according to claim 2, wherein

the reference black insertion ratio is the minimum black insertion ratio, and

the gray-scale level corrector corrects the gray-scale levels of the input image to lower gray-scale levels.

5. The display according to claim 2, wherein

the reference black insertion ratio is the maximum black insertion ratio, and

the gray-scale level corrector corrects the gray-scale levels of the input image to higher gray-scale levels.

6. The display according to claim 2, wherein the gray-scale level corrector corrects the gray-scale levels of the input image to higher gray-scale levels when calculated black insertion ratio is equal to or larger than the minimum black insertion ratio and smaller than the reference black insertion ratio, and corrects the gray-scale levels of the input image to lower gray-scale levels when the calculated black insertion ratio is larger than the reference black insertion ratio and equal to or smaller than the maximum black insertion ratio.

7. The display according to claim 1, further comprising a memory to hold a gray-scale level correction data representing a relation among black information, gray-scale levels, and corrected gray-scale levels, wherein

the gray-scale level corrector corrects the gray-scale levels of the input image by referring to the memory by using the black information of the input image and the gray-scale level of each pixel in the input image.

8. The display according to claim 7, wherein

the memory holds gray-scale levels at predetermined level intervals in the gray-scale level correction data, and

the gray-scale level corrector calculates a corrected gray-scale level by performing interpolation processing using a gray-scale level held in the memory lower than the gray-scale level of the input image and a gray-scale level held in the memory higher than the gray-scale level of the input image when the gray-scale level of the input image is not held in the gray-scale level correction data.

9. The display according to claim 7, wherein

the black information is a black insertion ratio representing a ratio of a period in which black image is displayed in one frame period,

the memory holds black insertion rations at predetermined intervals in the gray-scale level correction data, and

the gray-scale level corrector calculates a corrected gray-scale level by performing interpolation processing using data of a black insertion ratio held in the memory smaller than calculated black insertion ratio and data of a black insertion ratio held in the memory larger than the calculated black insertion ratio.

10. The display according to claim 1, wherein the gray-scale level corrector corrects the gray-scale level of the input image by calculating a function having black information and a gray-scale level as variables.

11. The display according to claim 1, wherein

the black information is a black insertion ratio representing a ratio of a period in which the black image is displayed in one frame period,

the black information calculator detects whether the input image is a still image or a moving image, calculates a first black insertion ratio as the black information when a result of detection is a still image, and, calculates a second black insertion ratio larger than the first black insertion ratio when a result of detection is a moving image.

12. The display according to claim 11, wherein the black information calculator calculates a sum of absolute difference between two frames of an input image and detects whether the input image is a still image or a moving image by comparing the sum of absolute difference with a threshold value.

13. The display according to claim 1, wherein

the black information is a black insertion ratio representing a ratio of a period in which the black image is displayed in one frame period, and

the black information calculator detects a magnitude of motion of an object in the input image and calculates a larger black insertion ratio as the magnitude of motion is larger.

14. The display according to claim 13, wherein the black information calculator detects a motion vector between two frames of an input image and determines the black insertion ratio based on a magnitude of detected motion vector.

15. The display according to claim 13, wherein the black information calculator calculates a sum of absolute difference between two frames of an input image and determines the black insertion ratio based on calculated sum of absolute difference.

16. An image display method for performing in an image display device including a light source capable of adjusting a light source luminance and a liquid crystal panel displaying an image by modulating a transmittance or a reflectance of light from the light source based on signals representing the image, comprising;

inputting an input image;

calculating black information indicating a length of a period in which a black image should be displayed in one frame period of an input image or a ratio of a period in which the black image should be displayed in the one frame period of the input image;

controlling a light source luminance of the light source according to the black information to suppress fluctuation of a display luminance at a maximum gray-scale level displayable by the liquid crystal panel due to variation of a length of a black display period depending on the black information;

correcting a gray-scale level of each pixel of the input image to obtain corrected gray-scale levels to suppress fluctuation of a display luminance at gray-scale levels other than the maximum gray-scale level due to the controlling of the light source luminance of the light source;

providing the liquid crystal panel with signals of each pixel having the corrected gray-scale levels in continuous period of a length obtained by subtracting a black display period of a length depending on the black information from the one frame period, and;

providing the liquid crystal panel with signals of each pixel indicating black in the black display period.