Computer graphics processing and selective visual display system – Display peripheral interface input device – Light pen for fluid matrix display panel
Reexamination Certificate
1998-02-24
2001-04-03
Chow, Dennis-Doon (Department: 2675)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Light pen for fluid matrix display panel
Reexamination Certificate
active
06211859
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to computer displays and to liquid crystal computer displays. More particularly, the present invention relates to methods for reducing pulsing on liquid crystal displays.
2. The Prior Art
Numerous methods are known for producing grey-scale images on digital (i.e., on/off) displays with characteristics similar to super-twisted nematic (STN) liquid crystal displays (LCD). Modulating individual pixels by employing frame-rate-control (FRC) algorithms over time and by spatial dithering appear to be the preferred methods for realizing gray scale on displays with STN LCD and similar characteristics.
Prior-art methods producing such grey-scale images do not claim gray scale approaching the visible limit, but are usually limited to 16 gray shades when using FRC alone and to 64 gray shades when FRC and dithering are used in combination. The details of particular methods are not readily available in the literature.
These prior-art methods all suffer from one or more shortcomings. The disadvantages of these previous methods may be classified into three main categories: undesirable visual motion artifacts, undesirable visual static artifacts, and reduced gray shade fidelity.
Undesirable visual motion artifacts may be perceived as “shimmer,” “crawl,” “ripple,” or “waterfalling.” The terms used to describe these artifacts are descriptive of subjective perception and are not readily quantifiable. All observed implementations of previous methods (particularly FRC-based processes) have specific gray shade values (“sensitive gray shades”) for which one of these artifacts is readily perceivable.
Another undesirable visual motion artifact may be perceived as “pulsing”. Again, this is not readily quantifiable, but can be observed under certain sensitive gray shade orientations.
These sensitive gray shades will change from one specific STN LCD panel model to another as a result of differences in panel physical characteristics. Because of this variability among different displays, systems employing these displays have to be tuned to achieve the best result given a combination of the gray scale method and the physical display employed. This normally involves changing the specific FRC implementation and may optionally involve remapping from a sensitive gray shade to an adjacent one that is insensitive, i.e., a gray shade which does not have an undesirable visual motion artifact. Remapping sensitive gray shades to avoid undesirable visual motion artifacts also reduces gray shade fidelity and resolution.
FRC-based motion artifacts are caused by the cyclic nature of the FRC as applied over a small physical area. For a given frame, the FRC is used to assign a value to a pixel within a grid or matrix. This value is compared to the gray shade to determine if the pixel should be “on” or “off.” If neighboring pixels cycle harmonically in time with respect to each other, the human eye may perceive motion where none is intended. Virtually all visual motion artifacts are undesirable.
Undesirable static artifacts may be the result of sacrificing spatial resolution to achieve increased perceived gray shades by employing a spatial dithering process. The most noticeable static artifact in spatially-dithered grey scale images is “graininess.” If a source gray shade cannot be directly represented, the display system may map the gray shade alternately into the two closest gray shades by dithering. The gritty appearance is caused by high frequency transitions between physically adjacent pixels at a physical resolution the eye can distinguish.
Reduced gray shade fidelity can be manifested as “contouring”, also known as Mach banding or “cartooning.” For example, contouring causes a smoothly shaded sphere to appear as a series of concentric rings each of a single gray shade. In cartooning, an image has a narrow enough gray shade or color range that images appear to have been drawn with crayons for use in cartoons. Contouring and cartooning are all apparent in processes having a capacity of fewer gray shades than the perceivable visible limit, which is 256 grey shades.
BRIEF DESCRIPTION OF THE INVENTION
The purpose of the present invention is to provide the capability to display gray scale to the limit of human perception (256 shades) using displays having characteristics of or ones similar to super-twisted nematic (STN) liquid crystal displays (LCD), while reducing pulsing problems. The present invention may be utilized for monochromatic or color displays.
A method is provided according to the present invention for displaying gray scale up to the visible limit (two hundred and fifty-six shades) for displays such as, but not limited to, dual-scan super twisted nematic (DSTN) liquid crystal displays (LCD). The method of the present invention employs a large static matrix of values in concert with a circular queue consumption to distribute energy evenly in both space and time to achieve a large range of gray shades in digital displays with slow rates of response. The grey scale resolution of the method of the present invention depends upon the size of the matrix employed. The gray shades are realized in the present invention by cycling individual pixels on and off within a sequence of frames. The length of the sequence is equal to the gray scale resolution. For example, if the desired gray scale resolution is N, to realize gray scale shade M, a pixel is on M frames in every N frames, or the duty cycle is M/N.
A first part of the method addresses minimizing visual motion artifacts and equal distribution of energy over the viewing surface. This is accomplished by assigning values to a matrix. According to the first part of the method of the present invention, a matrix is defined wherein each position in the matrix contains a different number or value. For example, each position in a 16×16 matrix is defined by a different numbered value from 0 to 255. This matrix is repeatedly mapped into the entire pixel matrix of the display in both the horizontal and vertical directions.
Static visual artifacts may be minimized by rotating the matrix columns at the beginning of each vertically adjacent matrix. For example, in 16×16 matrix, the first matrix in a row includes in order columns 0 through 15. In an embodiment where the column offset is 4, the first row of matrices below begins with column
4
and ends with column
3
. The second row of the matrices below begins with column
8
and ends with column
7
.
The second part of the process primarily defines the consumption or use of the pixels within the matrix to realize smooth shading of an individual pixel over time. This is accomplished by using a circular queue. The circular queue causes pixel consumption in sequential matrix address order, and provides that within any given number of frames that pixels are used with an even distribution. Each color primary has an independent circular queue per shade. Circular queues for each shade of each color primary may be in arbitrary alignment with respect to each other in order to achieve optimal visual results.
The gray-scale value of the pixel and the frame number within a sequence of frames is used to select a range of matrix values from a circular queue (the “ON” range). The location of the current pixel is used to determine the matrix value of the current pixel. The matrix value of the current pixel is compared to the “ON” range. If the current pixel's matrix value is within that range, then it is switched “ON” for that frame. The default state for failing this test is “OFF.”
This method is duplicated for each color primary. The number of frames in a sequence is equal to the number of locations and values in each matrix.
The present invention provides gray shade resolution at the visible limit and therefor does not introduce gray shade infidelities. Dithering is not used, and thus its attendant artifacts do not occur. Motion artifacts are avoided in the present invention by assigning a static value to each pixel within a matrix and by mak
Chang Shih-hua
Killebrew, Jr. Carrell R.
Lin Jian
Awad Amr
Chips & Technologies, LLC
Chow Dennis-Doon
Hanish Marc S.
Thelen Reid & Priest LLP
LandOfFree
Method for reducing pulsing on liquid crystal displays does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for reducing pulsing on liquid crystal displays, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for reducing pulsing on liquid crystal displays will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2499092