Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1997-03-05
2001-09-25
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S182000, C345S182000, C345S088000, C345S182000
Reexamination Certificate
active
06295041
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a technique and device for increasing the number of colors output by an active liquid crystal display.
Active color liquid crystal (LCD) displays, also known as Thin Field Transistor (TFT) panel displays, are commonly used in laptop computers to present information to a user. Active color LCD panels and color cathode-ray tube (CRT) monitors both have a color resolution that depends upon the number of pixels in the display. Typical active color LCD display resolutions are 640 columns of pixels by 480 rows of pixels (640×480), 800×600 pixels and up to 1280×1024 pixels. However, a CRT monitor uses analog data to form images on its screen, and an active color LCD panel display uses digital data.
Each pixel in the active color LCD display consists of three primary color components: red, green and blue. The four common types of active color LCD displays are known as 3-3-3, 4-4-4, 6-6-6 and 8-8-8 TFT panels. The numbers indicate the number of bits of data that must be supplied to each of the primary color components of a pixel in the display. For example, in a 3-3-3 TFT panel, 3 bits of data are required for each of the three pixel components, and thus each pixel component is capable of 2
3
or eight levels of color. Consequently, the total color output of a pixel in the 3-3-3 panel equals 8×8×8 which is 512 colors.
New data must be supplied to the pixels of an active color LCD display periodically to refresh the image shown on the screen, and such time segments are known as frames. The required number of bits of data per pixel color component is typically supplied every {fraction (1/60)}th of a second, which corresponds to a refresh rate of sixty frames per second.
A technique known as frame modulation, which entails switching certain pixel color components ON and OFF over certain areas on the screen for a number of frames of the refresh cycle, is known for increasing the number of grey levels and thus the number of colors that can be shown on a color display. However, frame modulation has not been used to increase the number of colors output by an active LCD display because the pixel components change so quickly that using frame pattern modulation could result in noticeable flicker. A need exists, therefore, not only for increasing the number of colors that may be displayed by an active color LCD display, but also for improving the overall quality of the color and for minimizing any flicker of the screen which can be detected by the human eye.
SUMMARY OF THE INVENTION
The invention increases the number of colors output by an active liquid crystal display by providing an increased number of grey levels. In particular, the number of colors that may be displayed by 3-3-3, 4-4-4 and 6-6-6 active liquid crystal displays are increased.
In general, the invention features generating a M×N matrix pattern of pixel components on the display having a ratio of pixel components that are at a particular color level to pixel components at a different color level to achieve a particular grey level, where M and N are greater or equal to two. The M×N matrix pattern is produced for X frames, and at least one pixel component is at the particular color level in each frame.
Preferred embodiments include the following features. In the M×N matrix the same number of pixel components are at the particular color level in each frame but in different locations. In addition, at least one of the pixel components is at the particular color level in each row and in each column. Further, over a cycle of X frames, each pixel component is at the particular color level for “Y” amount of times, wherein “Y” is the number of pixel components in each row and column that are at the particular color level in any one frame.
A preferred embodiment includes M×N matrix patterns to produce three grey levels. In particular, 3×3 patterns having one pixel component at the color level in each row or column to generate grey level 4, and having three pixel components at the color level in each row or column to generate grey level 10, are utilized. In addition, a 2×2 matrix pattern having one pixel component at the color level in each row or column to generate grey level 7 is used.
In a further aspect of the invention, a grey level generator circuit is used to produce the grey level patterns. In particular, a memory stores an M×N matrix pattern. A frame counter for counting to X frames, a column counter for counting to N, and a row counter for counting to M are provided. The row counter is pre-loaded at the start of each frame with a value for a pixel component based on the data stored in memory. A comparator generates output signals to indicate whether pixel components should be at a particular color level or at a different color level depending on the frame and their location in a row or column.
In another aspect of the invention, an apparatus for increasing the color output of an active color LCD display includes a frame buffer for providing selection signals and LCD display signals. A plurality of grey level generators, a selector circuit and a subtract circuit are also provided. The selector circuit selects one of the grey level generators based on the frame buffer selection signals, and generates a grey level output signal. The subtract circuit processes the grey level output signal from the selector circuit with the LCD display signals from the frame buffer to provide an output signal for the active color LCD display. In addition, each grey level generator includes a memory for storing M×N matrix pattern data.
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Lee Keith
Leung Charles
ATI Technologies Inc.
Nelson Alecia D.
Saras Steven
Vedder Price Kaufman & Kammholz
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