Increasing the number of colors output by a passive liquid crystal display

• US 6,388,647 B2
• Filed: 03/05/1997
• Issued: 05/14/2002
• Est. Priority Date: 03/05/1997
• Status: Expired due to Term

• Current Assignee: ATI Technologies Incorporated (Advanced Micro Devices, Inc.)
• Original Assignee: ATI Technologies Incorporated (Advanced Micro Devices, Inc.)
• Inventors: Leung, Charles, Lee, Keith
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): Laneau, Ronald
• Application Number:
  US08/811,649
• Publication Number:
  US 20010011982A1
• Time in Patent Office: 1,896 Days
• Field of Search: 345/88, 345/87, 345/89, 345/152, 345/147, 345/148, 345/149
• US Class Current: 345/88
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/2051 with use of a spatial dither pattern
• CPC Class Codes: G09G 3/3622 using a passive matrix G09G3/3674 - G09G3/3696 take precedence

Abstract

A technique to increase the number of colors output by a passive color LCD display provides an increased number of grey levels for each pixel component. An M×N matrix pattern of pixel components is generated having a ratio of pixel components that are ON to the total number of pixel components to achieve a particular grey level on the passive color LCD screen, where M and N are greater or equal to two. The M×N matrix pattern is repeated for X frames, and at least one pixel component is ON in each frame. At the end of the Xth frame, the first matrix pattern for frame zero is repeated.

Claims

1. A method for increasing the number of colors outputted by an LCD display, the method comprising the steps of:

providing a plurality of groups of pixel matrix patterns, each group of pixel matrix patterns being associated with a corresponding grey level of a plurality of grey levels, each pixel matrix pattern including a respective number of row and a respective number of columns, at least one of the respective number of rows and the respective number of columns being identical for each pixel matrix pattern within a particular group of pixel matrix patterns, but being different between groups of pixel matrix patterns that are associated with consecutive grey levels of the plurality of grey levels;

selecting one group of the plurality of groups of pixel matrix patterns to be displayed in at least a portion of the display based on a desired grey level of the plurality of grey levels to produce a selected group of pixel matrix patterns; and

for each frame of a group of frames to be displayed on the LCD display, generating signals to produce a corresponding one of the pixel matrix patterns in the selected group of pixel matrix patterns, wherein each column and each row of the corresponding one of the pixel matrix patterns in the selected group of pixel matrix patterns includes an equal number of pixels that have at least one color component turned ON to achieve a particular output color over the frame.

2. The method of claim 1, wherein each pixel matrix pattern of the selected group of pixel matrix patterns has an equal number of pixels that have at least one color component turned ON and wherein locations of pixels having at least one color component turned ON are different in each pixel matrix pattern of the selected group of pixel matrix patterns.

3. The method of claim 1, wherein the number of rows equals the number of columns in each pixel matrix pattern of the selected group of pixel matrix patterns, wherein each group of pixel matrix patterns has a respective frame repeat cycle, and wherein the frame repeat cycle for the selected group of pixel matrix patterns equals the number of rows in each pixel matrix pattern of the selected group of pixel matrix patterns.

4. The method of claim 3, wherein each group of pixel matrix patterns has a respective frame repeat cycle and wherein the frame repeat cycle of the selected group of pixel matrix patterns is not a multiple of the frame repeat cycle of another group of pixel matrix patterns associated with a grey level that precedes or succeeds the desired grey level.

5. The method of claim 1, further comprising:

selecting a second group of the plurality of groups of pixel matrix patterns to be displayed in at least a portion of the LCD display based on a second grey level of the plurality of grey levels to produce a second selected group of pixel matrix patterns, wherein the respective number of columns of each pixel matrix pattern of the second selected group of pixel matrix patterns is identical within the second selected group of pixel matrix patterns, but is different than the respective number of columns of each pixel matrix pattern of the selected group of pixel matrix patterns; and

for each frame of a group of frames to be displayed on the LCD display, generating signals to produce a corresponding one of the pixel matrix patterns in the second selected group of pixel matrix patterns, wherein each column and each row of the corresponding one of the pixel matrix patterns in the second selected group of pixel matrix patterns includes an equal number of pixels that have at least one color component turned ON.

6. The method of claim 1, wherein the number of pixels that have at least one color component turned ON equals the desired grey level plus one.

7. A grey level generator circuit comprising:

a plurality of pixel matrix pattern generators, each pixel matrix pattern generator of the plurality of pixel matrix pattern generators producing a respective group of pixel matrix patterns, each group of pixel matrix patterns being associated with a corresponding grey level of a plurality of grey levels, each pixel matrix pattern including a respective number of rows and a respective number of columns, at least one of the respective number of rows and the respective number of columns being identical for each pixel matrix pattern within particular group of pixel matrix patterns, but being different between groups of pixel matrix patterns that are associated with consecutive grey levels of the plurality of grey levels;

a grey level determiner for determining a desired grey level from the plurality of grey levels; and

a selector for selecting one group of the plurality of groups of pixel matrix patterns to be displayed in at least a portion of an LCD display based on the desired grey level to produce a selected group of pixel matrix patterns and

for generating, for each frame of a group of frames to be displayed on the LCD display, signals to produce a corresponding one of the pixel matrix patterns in the selected group of pixel matrix patterns, wherein each column and each row of the corresponding one of the pixel matrix patterns in the selected group of pixel matrix patterns includes an equal number of pixels that have at least one color component turned ON.

8. The grey level generator circuit of claim 7, wherein each of the plurality of pixel matrix pattern generators comprises:

a frame counter for counting frames to produce a frame count;

a column counter for counting pixels in a column to produce a column count;

a memory operably coupled to the frame counter and the column counter, wherein the memory includes a look-up table-of pixel color component values for a particular grey level;

a row counter that is pre-loaded with an initial pixel color component value for a pixel from the look-up table, wherein the initial pixel color component value for the pixel is based on the frame count and the column count; and

a comparator operably coupled to an output of the row counter, wherein the comparator verifies a pixel color component value received from the row counter and, based on the value, generates the signals.

9. The grey level generator circuit of claim 7, wherein the grey level determiner comprises a frame buffer.

10. The grey level generator circuit of claim 7, wherein the plurality of pixel matrix pattern generators and the selector form part of a frame modulator.