Method and apparatus for driving liquid crystal display

• US 7,705,814 B2
• Filed: 06/28/2004
• Issued: 04/27/2010
• Est. Priority Date: 11/17/2003
• Status: Expired due to Fees

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Display Co., Ltd.
• Inventors: Jang, Chul Sang, Baik, Seong Ho
• Primary Examiner(s): OSORIO, RICARDO
• Application Number:
  US10/879,947
• Publication Number:
  US 20050104837A1
• Time in Patent Office: 2,129 Days
• Field of Search: 345 98-100, 345/102, 345 87- 89, 345600-604, 348671-672
• US Class Current: 345/88
• 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 2340/16 Determination of a pixel data signal depending on the signal applied in the previous frame
• 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

Abstract

A driving method and apparatus for a liquid crystal display uses a comparison between the previous frame and the current frame to expand the contrast ratio and reduce the manufacturing cost. A limited amount of data from the current image may be used: either using a limited area of the image or merely the amount of green in the overall image or the limited area. In the apparatus, an image signal modulator expands the contrast of the input data when the previous image is analogous to the current image to thereby generate output data. A timing controller re-arranges the output data to apply the output data to a data driver.

Claims

1. A driving apparatus for a liquid crystal display, comprising:

an image signal modulator for expanding contrast of input data when a previous image is analogous to a current image to thereby generate output data; and

a timing controller for re-arranging the output data to apply the output data to a data driver.

wherein the image signal modulator includes;

a brightness/color separator for converting input data corresponding to the current frame into brightness components and chrominance components;

a histogram analyzer for arranging the brightness components into a histogram for each frame and for storing a previous histogram;

an image analyzer for extracting a control value from partial area brightness components of the brightness components;

a comparator for determining an analogy between the current image and the previous image using a current control value and a previous control value; and

a data processor for modulating current brightness components to have an expanded contrast ratio in correspondence with a result of the comparator to thereby generate modulated brightness components.

2. The driving apparatus of claim 1, further comprising:

a controller for changing a synchronizing signal inputted in synchronization with the input data to be synchronized with the output data.

3. The driving apparatus of claim 1, wherein, when the previous image is analogous to the current image, the current image is converted using a previous result to thereby generate the output data.

4. The driving apparatus of claim 1, wherein the control value is a most-frequent value of gray levels of the histogram or an average value of the gray levels the histogram.

5. The driving apparatus of claim 1, wherein the histogram analyzer generates a current histogram using the current brightness components supplied from the brightness/color separator and applies the previous histogram stored therein to the data processor, the current and previous histograms being of consecutive frames.

6. The driving apparatus of claim 1, wherein the image analyzer includes:

an area extractor for extracting the partial area brightness components from the brightness components;

an area histogram analyzer for dividing the extracted partial area brightness components into gray levels to generate a partial area histogram; and

a control value extractor for extracting a current frame partial area control value from the image histogram analyzer.

7. The driving apparatus of claim 6, wherein the comparator includes:

a first register for storing the current frame partial area control value;

a second register for storing a previous frame partial area control value; and

a determiner for determining an analogy between the current image and the previous image using the current frame partial area control value and the previous frame partial area control values stored in the first and second registers.

8. The driving apparatus of claim 7, wherein the determiner determines that the current image is analogous to the previous image when the current frame partial area control value is within a specific deviation from the previous frame partial area control value, and the determiner determines that the current image is not analogous to the previous image when the current frame partial area control value is not within a specific deviation from the previous frame partial area control value.

9. The driving apparatus of claim 1, wherein the data processor includes:

an image processor for generating the modulated brightness components; and

a selector for outputting the modulated brightness components or non-modulated brightness components.

10. The driving apparatus of claim 9, wherein the selector outputs the modulated brightness components when the comparator determines that the current image is analogous to the previous image and the selector outputs the non-modulated brightness components when the comparator determines that the current image is not analogous to the previous image.

11. The driving apparatus of claim 9, further comprising:

delay means for delaying the chrominance components and the brightness components during a time interval when the comparator determines the analogy between the current image and the previous image using a current frame partial area control value; and

a brightness/color mixer for generating the output data using the brightness components or the modulated brightness components and the chrominance components of the current frame supplied from the data processor.

12. The driving apparatus of claim 1, further comprising:

back light control means for controlling brightness of a back light in response to a result of the comparator.

13. The driving apparatus of claim 12, wherein the back light control means includes:

a control value extractor for extracting a control value of the previous histogram when the comparator determines that the current image is analogous to the previous image; and

a back light controller for controlling the brightness of the back light in correspondence with the extracted control value from the control value extractor.

14. The driving apparatus of claim 13, wherein the control value extractor does not extract the control value when the comparator determines that the current image is analogous to the previous image, and the back light controller controls the back light such that light of a predetermined brightness can be supplied when the control value is not applied from the control value extractor.

15. The driving apparatus of claim 1, wherein the image signal modulator includes:

a histogram analyzer for arranging green data of the input data corresponding to the current frame into gray levels for each frame to generate a histogram and for storing the generated histogram using green data of data of the previous frame;

an image analyzer for extracting a control value from green data of a partial area of the green data of the current frame;

a comparator for determining an analogy between the current image and the previous image using a current partial area control value and a previous partial area control value; and

a data processor for generating the output data obtained by an expansion in a contrast of the input data in correspondence with a result of the comparator.

16. The driving apparatus of claim 15, wherein the data processor includes:

an image processor for generating the output data having an expanded contrast; and

a selector for applying the output data or the input data to the timing controller.

17. The driving apparatus of claim 16, wherein the selector applies the output data to the timing controller when the comparator determines that the current image is analogous to the previous image, and the selector applies the input data to the timing controller when the comparator determines that the current image is not analogous to the previous image.

18. The driving apparatus of claim 15, further comprising:

delay means for delaying the input data during a time interval when the comparator determines the analogy between the current image and the previous image.

19. The driving apparatus of claim 15, further comprising:

back light control means for controlling brightness of a back light in response to a result of the comparator.

20. The driving apparatus of claim 19, wherein the back light control means includes:

a control value extractor for extracting a control value for a previous histogram when the comparator determines that the current image is analogous to the previous image; and

a back light controller for controlling the brightness of the back light in correspondence with the extracted control value from the control value extractor.

21. The driving apparatus of claim 20, wherein the control value extractor does not extract the control value when the comparator determines that the current image is analogous to the previous image, and the back light controller controls the back light such that light of a predetermined brightness can be supplied when the control value is not applied from the control value extractor.

22. A method of driving a liquid crystal display, comprising:

determining an analogy between a previous image and a current image; and

converting current input data to have an expanded contrast using a result of a previous frame when the previous image is analogous to the current image.

wherein determining the analogy include converting the current input data into brightness components and chrominance components;

arranging partial area brightness components of the brightness components for one frame into a histogram corresponding to gray levels;

extracting a control value from the histogram; and

determining that the previous image is analogous to the current image when the extracted control value is within a specific deviation from a control value extracted from the previous frame.

23. The method of claim 22, wherein the current input data is not converted when the previous image is not analogous to the current image.

24. The method of claim 22, wherein converting the current input data includes:

converting the current input data using a histogram generated from brightness components of the previous frame.

25. The method of claim 22, wherein determining the analogy includes:

arranging green data in a partial area of data for one frame into a histogram corresponding to gray levels;

extracting a control value from the histogram; and

determining that the previous image is analogous to the current image when the extracted control value is within a specific deviation from a control value extracted from the previous frame.

26. The method of claim 25, wherein converting the current input data includes:

converting the current input data using a histogram generated from green data of the previous frame.

27. The method of claim 22, further comprising:

controlling brightness of a back light when the previous image is analogous to the current image.