Image analysis – Image enhancement or restoration – Image filter
Reexamination Certificate
2000-05-05
2002-03-19
Lee, Thomas D. (Department: 2724)
Image analysis
Image enhancement or restoration
Image filter
C382S266000
Reexamination Certificate
active
06360023
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to display methods and apparatus and, more particularly, to methods and apparatus for improving the contrast with which relatively small-dimension character features are displayed on display devices which have multiple separately controllable luminance elements per pixel.
2. The Prior State of the Art
The display of images, e.g., text characters, on display devices is of high importance. This is particularly the case given the ever increasing use of computers and other types of devices which rely on displays to convey information. Pixels are used to represent display images on a display device. The term pixel, which is short for picture-element, is commonly used to refer to one spot in, e.g., a rectangular grid of thousands of spots which can be used to represent an image. Pixels are normally used individually by a computer to form an image on the display device.
Color display devices have become the principal display devices of choice for most computer users. The display of color on a monitor is normally achieved by operating the display device to emit light, e.g., a combination of red, green, and blue light, which results in one or more colors being perceived by a human viewer.
In color displays, the intensity of the light emitted corresponding to the additive primary colors, red, green and blue, can be varied to get the appearance of almost any desired color pixel. Adding no color, i.e., emitting no light, produces a black pixel. Adding
100
percent of all three colors results in white.
In cathode ray tube (CRT) display devices, the different colors of light are generated via the use of phosphor coatings which may be applied as dots in a sequence on the screen of the CRT.
Liquid crystal displays (LCDs), or other flat panel display devices are commonly used in portable computer devices in the place of CRTs. This is because flat panel displays tend to be small and lightweight in comparison to CRT displays. In addition flat panel displays tend to consume less power than comparable sized CRT displays making them better suited for battery powered applications than CRT displays.
As the quality of flat panel color displays continues to increase and their cost decreases, flat panel displays are beginning to replace CRT displays in desktop applications. Accordingly, flat panel displays, and LCDs in particular, are becoming ever more common.
Unlike CRT displays, LCD displays use square or rectangular light emitters, usually positioned adjacent one another, as the source of red, green and blue light for each pixel. Due to manufacturing limitations with regard to the size of light emitters in LCD displays, it is difficult in an LCD display to achieve the same resolution commonly found in CRT displays.
Unfortunately, the limited resolution provided by commonly used flat panel displays such as LCDs tends to be less than ideal for the display of text. LCD display resolution problems are particularly noticeable when displaying text at small font sizes which are commonly used on personal data assistants and other hand held devices. When the size of a pixel is treated as the smallest unit of size which can be used to represent a position of a character or other image, the relatively large pixel size compared to the character size tends to produce characters with jagged edges.
The use of LCD displays with small characters can also produce less than desirable representations of, e.g., bold text. In the case of bold text it is desirable that bold character stems have stem weights that are 10-20% higher than the corresponding non-bold character stem. At small sizes a character stem may be only one or two pixels in width. Given such stem widths, adjustments in stem weights in one pixel size increments as is commonly done in the art, can lead to far more than the desired 10-20 percent increase in stem weight for bold characters.
FIG. 1
illustrates a known computer system
100
which comprises a housing
101
, keyboard
104
, disk drive
105
and an LCD display
102
. The LCD display comprises a plurality of pixels, two of which are identified by reference numbers
110
,
112
. Each of the pixels
110
,
112
includes separate red (R), green (G) and blue (B) pixel subcomponents which may be controlled as independent luminous intensity sources. In the computer system
100
, the R, G and B pixel subcomponents are arranged to for vertical stripes.
In known systems, in the case of text, a high resolution representation of a text character, sometimes referred to as an analytic representation, is normally sampled. The samples are then used to generate luminous intensity values, e.g., red, green and blue pixel sub-component luminous intensity values, which control the light output of the R, G and B pixel sub-components of each pixel, respectively. In conventional systems, the R, G, and B pixel sub-component luminous intensity values are normally generated from the same set of image samples.
FIG. 2
illustrates one known image rendering technique used to control the light output of a set of pixels. In
FIG. 2
, the grid
220
represents a source image, e.g., a foreground/background color representation of a text character, which has been divided into segments corresponding to 3 rows R(N), R(N+1), R(N+2) and 3 columns C(N), C(N+1), C(N+2) of source image pixel segments. Each one of the
9
segments corresponds directly to one pixel, e.g., pixel
240
, of the display screen represented by grid
230
. Red, green and blue pixel sub-components
232
,
234
,
236
are illustrated in
FIG. 2
using medium, dark and light speckling, respectively.
In the known image rendering technique, each portion of a source image corresponding to a pixel, referred to herein as a source image pixel segment, is oversampled by a factor of
4
in the vertical and horizontal dimensions. Thus, a set of
16
samples, represented by the circles
222
with x's inside, is generated for each pixel.
The 16 samples corresponding to each pixel segment are then filtered to produce the red, green and blue luminous intensity values used to control pixel sub-components
232
,
234
,
236
. The filtering of the samples is represented by the arrow extending from source image segment
223
to pixel
240
. Thus, in the illustrated system, the same portion of the source image is used to generate each of the red, green and blue pixel sub-component luminous intensity values of a pixel. In the known
FIG. 2
system, the filtering performed to generate pixel sub-component luminous intensity values does not cross pixel boundaries indicated in the image
220
by the use of solid lines. Accordingly, the luminous intensity of each pixel is not affected by neighboring source image pixel segments. As will be discussed below, this allows different images, e.g., text characters, to be sampled, filtered, stored and then subsequently concatenated without impacting the filtering since the filtering does not depend on neighboring image portions beyond a pixel boundary.
As is known in the art, there are generally two stages associated with the display of text images, e.g., characters, 1) the glyph rendering stage and 2) the glyph display phase. The glyph rendering stage involves the generation of one or more character glyphs and the storage of the glyphs in a glyph cache for subsequent use, e.g., during the display phase. The glyph display phase involves retrieving glyphs from the font cache as need, and, in many cases, combining them prior to display to form text strings.
In the glyph rendering stage one or more character glyphs are rendered, i.e., generated, from corresponding high resolution representations, e.g., outline representations, of the rendered characters. The high resolution character representations from which characters are frequently rendered include character shape and size information. The shape information is frequently in the form of lines, points, curves and/or arcs. Areas within the character outline correspond to the foreground c
Betrisey Claude
Dresevic Bodin
Platt John C.
Brinich Stephen
Lee Thomas D.
Microsoft Corporation
Workman & Nydegger & Seeley
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