Computer graphics processing and selective visual display system – Display peripheral interface input device – Light pen for fluid matrix display panel
Reexamination Certificate
1997-04-10
2001-05-08
Luu, Matthew (Department: 2778)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Light pen for fluid matrix display panel
C345S182000
Reexamination Certificate
active
06229521
ABSTRACT:
COPYRIGHT NOTICE PURSUANT TO 37 C.F.R. 1.7(E)
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
BACKGROUND
1. Field of the Invention
The present invention relates to the process of displaying characters on a video monitor, and more particularly to techniques for antialiasing fonts for display on an interlaced display, such as a television monitor.
2. Related Art
The standard television format in the United States is NTSC (National Television System Committee), which is encoded in an interlaced form. In NTSC, each frame consists of two interlaced fields which are alternately displayed on a television monitor. One field consists of all of the odd lines of a frame. The other field consists of all the even lines. One artifact of this arrangement is that fine details with high contrast, such as thin white lines on a black background, may be contained only within one of these fields. This causes fine details to flicker on television display, because a field which contains a fine detail is refreshed at half the frequency of the entire frame, and is alternated with the alternate field, which does not contain the fine detail. This causes detailed images such as text to be very unreadable on an interlaced television display.
Antialiasing techniques have been developed to smooth out the jagged edges which result from scan converting the edges of an object for bit-mapped display. These jagged edges are an instance of a phenomenon known as “aliasing.” Techniques which are used to reduce or eliminate aliasing are referred to as “antialiasing”, and images produced using these techniques are said to be “antialiased”. Antialiasing techniques operate by blurring the jagged edges so that they appear to the human eye to be more smooth. This blurring is accomplished by assigning intermediate shading values to the pixels surrounding the edge of an object, wherein these intermediate color values are a mixture of the color of the object and a background color against which the object appears.
Standard antialiasing techniques such as filtering effectively reduce the jagged edges in a standard non-interlaced display such as a computer monitor. However, standard anti-aliasing techniques do not adequately reduce the flickering which occurs near edges of objects in an interlaced display. This flickering makes it especially hard to read characters on an interlaced display; especially characters which are outputted using intricate fonts.
What is needed is a technique for generating antialiasing fonts for display on an interlaced monitor which more effectively reduces the flickering of character features, thereby enhancing the readability of characters on interlaced displays.
SUMMARY
The present invention provides a method for antialiasing fonts which is specifically tailored to overcome the flickering problems associated with interlaced displays. This method starts with an original bit-map of a character in a font, which is preferably a much larger than a desired font size for display. This original bitmap is subjected to a weighted filtering using coefficients which approximate a Gaussian distribution around a pixel in the original bitmap to produce a value for a corresponding pixel in a filtered bitmap. The filtered bitmap is reduced in size by downsampling the filtered bitmap to a desired character size. Finally, if necessary, the pixels in the reduced font are quantized so that the values of individual pixels in the bitmap fall within a fixed range, for example zero to eight. This process is repeated using different coefficients in the weighted filtering process to attain the best quality display for a given font. If a color display is used, the font color is blended with a background color by using the quantized values in the bitmap for display to index an entry in a color map comprising a range of blendings of the font color and the background color.
Accordingly, the present invention can be characterized as a method for antialiasing fonts comprising: obtaining an original bitmap of a character in the font which is larger than a desired font size for the character; performing a weighted filtering on the original bitmap to form a filtered bitmap by computing each pixel in the filtered bitmap as a weighted average of pixels in the neighborhood of a corresponding pixel in the original bitmap; and reducing the filtered bitmap to the desired size to form a reduced bitmap so that each pixel in the reduced bitmap corresponds to a block of pixels in the filtered bitmap, and each pixel in the reduced bitmap is a weighted average of pixels in the corresponding block in the filtered bitmap.
According to an aspect of the present invention, the method for antialiasing fonts further includes the step of quantizing the reduced bitmap to form a bitmap for display by setting pixels which exceed an upper limit to the upper limit, and if necessary, setting pixels which are below a lower limit to the lower limit.
According to another aspect of the present invention, the method for antialiasing fonts further includes the step of using pixels in the reduced bitmap to index a color map which contains a range of blendings of a font color with a background color to produce a color bitmap for display.
According to yet another aspect of the present invention, the method for antialiasing fonts further includes the step of outputting the reduced bitmap to an interlaced display, and more particularly to a television display.
According to another aspect of the present invention, the step of obtaining an original bitmap of a character includes: rasterizing the original bitmap from a vector description; manually creating an original bitmap with a graphical editing tool, or other type of graphical input device; or obtaining an original bitmap from a pre-existing bitmap description file.
According to yet another aspect of the present invention, the step of performing a weighted filtering uses a plurality of coefficients which approximate a Gaussian distribution around a corresponding pixel in the original bitmap.
According to another aspect of the present invention, the step of performing a weighted filtering uses a plurality of coefficients and includes the step of adjusting the plurality of coefficients for each font.
According to another aspect of the present invention, the step of reducing the filtered bitmap uses a plurality of equal coefficients to compute the weighted average so that the weighted average becomes an unweighted average.
Other aspects and advantages of the present invention can be seen upon review of the figures, the description, and the claims which follow.
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Finnegan Henderson Farabow Garrett & Dunner LLP
Luu Matthew
Piziali Jeff
Sun Microsystems Inc.
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