Liquid crystal display by means of time-division color mixing and voltage driving methods using birefringence

• US 6,115,014 A
• Filed: 12/21/1995
• Issued: 09/05/2000
• Est. Priority Date: 12/26/1994
• Status: Expired due to Term

• Current Assignee: Ortus Technology Co., Ltd. (TOPPAN Holdings, Inc.)
• Original Assignee: Casio Computer Company Limited
• Inventors: Takei, Jiro, Sato, Soichi, Yoshida, Tetsushi, Aoki, Hisashi
• Primary Examiner(s): Saras, Steven J.
• Assistant Examiner(s): Bell, Paul A.
• Application Number:
  US08/576,780
• Time in Patent Office: 1,720 Days
• Field of Search: 345/88, 345/89, 345/94, 345/105, 345/147, 345/150, 345/148, 345/154, 345/32, 345/95, 349/77, 349/78, 349/80, 349/33, 349/97, 349/181, 349/96, 359/265, 359/267
• US Class Current: 345/88
• CPC Class Codes: G09G 2300/0491 Use of a bi-refringent liquid crystal, optically controlled bi-refringence [OCB] with bend and splay states, or electrically controlled bi-refringence [ECB] for controlling the color
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 3/2059 using error diffusion
• CPC Class Codes: G09G 3/3607 for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels display of colours in flat matrix panels other than liquid crystal displays G09G3/2003; grey scales specific for television H04N3/127
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers

Abstract

One frame of a video signal is separated to a plurality of display frames. To display a color specified by the video signal by mixing display colors of a plurality of display frames, the video signal is converted to data indicative of a voltage to be applied to each pixel over the display frames by using a conversion table. A voltage corresponding to the converted data is applied to a birifringence control type liquid crystal display device to drive the liquid crystal display device multiple times in one frame period of the video signal. When the response speed of the liquid crystal is fast, a color obtained by mixing the display colors of a plurality of display frames is recognized by an observer. When the response speed of the liquid crystal is slow, a color corresponding to an average value of the voltages applied to a plurality of display frames is recognized by the observer. When the liquid crystal has an intermediate response speed, a color obtained by visually mixing a series of display colors displayed during the transition of the alignment state of the liquid crystal is recognized by the observer.

Claims

1. A liquid crystal display apparatus comprising:

a liquid crystal display device having a plurality of pixels arranged in a matrix form, each of said plurality of pixels displaying a plurality of colors, white (which is a non-colored brightest display) and black (which is a non-colored darkest display) in accordance with applied voltages, pixel by pixel;

display color designating means for designating display colors with different brightnesses for said plurality of pixels;

conversion means for converting a display color designated by said display color designating means to data indicating a combination of a plurality of voltages, each representing at least one of a selected color, the white and the black, to be displayed on each pixel over frame sequences;

wherein said conversion means includes

means for obtaining a difference between said display color designated by said display color designating means and a color actually displayed by mixing display colors of a plurality of frames, and

means for converting said display color designated by said display color designating means to data which indicates a combination of a plurality of voltages to be applied to each pixel over frame sequences, and which is revised in order to lower the obtained difference between the display color designated by said display color designating means and the color actually displayed by mixing display colors of the plurality of frames;

drive means for sequentially applying voltages, each representing said selected color, the white and the black, to said each pixel over the frame sequences in accordance with data from said conversion means;

whereby said display colors having different brightnesses designated by said display color designating means are displayed by mixing plural frames each displaying said selected color, the white and the black, pixel by pixel.

2. The liquid crystal display apparatus according to claim 1, wherein said conversion means includes means for applying a same voltage to a plurality of frames in accordance with a display color designated by said display color designating means, means for applying different voltages to a plurality of frames, and means for selectively driving both means.

3. The liquid crystal display apparatus according to claim 1, wherein said liquid crystal display device has a response speed for displaying a color designated by said display color designating means in each frame period.

4. The liquid crystal display apparatus according to claim 1, wherein said drive means displays a color designated by said display color designating means by visually combining display colors which continuously change in accordance with a change in alignment of a liquid crystal.

5. The liquid crystal display apparatus according to claim 4, wherein said liquid crystal display device has a response time by which alignment of liquid crystal molecules changes in accordance with a voltage to be applied to an associated pixel is substantially equal to a period of voltage to be sequentially applied to a pixel.

6. A method of driving a liquid crystal display device for displaying a plurality of colors having a plurality of brightnesses in accordance with applied voltages pixel by pixel, the method comprising:

a display color designating step of designating display colors with different brightnesses of individual pixels;

a conversion step of converting a display color designated by said display color designating means to data indicating a combination of a plurality of voltages each representing at least one of a selected color, white (which is a non-colored brightest display) and black (which is a non-colored darkest display) to be displayed on each pixel for frame sequences;

wherein said conversion step includes

a substep of obtaining a difference between said display color designated by said display color designating means and a color actually displayed by mixing display colors of a plurality of frames, and

a substep of converting said display color designated by said display color designating step to data which indicates a plurality of voltages to be applied to each pixel over frame sequences, and which is revised in order to lower the difference between the display color designated by said display color designating step and the color actually displayed by mixing display colors of a plurality of frames based on the obtained difference; and

a driving step of sequentially applying voltages, each representing said selected color, the white and the black, to said each pixel for the frame sequences in accordance with data output by said conversion step;

whereby said display colors having different brightnesses designated by said display color designating step are displayed by mixing plural frames each displaying said selected color, the white and the black, pixel by pixel.

7. The method according to claim 6, wherein said display color designating step designates display colors for every n display frames (n being an integer equal to or greater than 2) of individual pixels;

and

said conversion step outputs an applied voltage to each pixel in n display frames in order to display a color designated by said display color designating step.

8. The method according to claim 7, wherein each pixel of said liquid crystal display device displays image data in said designated display color by visual mixture of colors displayed in said n display frames.

9. The method according to claim 7, wherein each pixel of said liquid crystal display device displays said designated display color by visual mixture of display colors which continuously change in accordance with a change in an alignment state of a liquid crystal in said n display frames.