BACKGROUND OF THE INVENTION
1. The Field of the Invention
[0001] The present invention relates to methods and apparatus for displaying images, and
more particularly, to methods and apparatus for increasing the perceived resolution
of the displayed images and compressing image data to enable control signals to be
efficiently transmitted to display devices.
2. The Prior State of the Art
[0002] 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, typically a combination of red, green, and blue
light, which results in one or more colors being perceived by a human viewer.
[0003] In cathode ray tube (CRT) display devices, the different colors of light are generated
by phosphor coatings that may be applied as dots in a sequence on the screen of the
CRT. A different phosphor coating is normally used to generate each of the red, green,
and blue colors, resulting in repeating patterns of phosphor dots. When excited by
a beam of electrons, the phosphor dots generate the colors red, green and blue.
[0004] The term pixel is commonly used to refer to one spot in, for example, a rectangular
grid of thousands of such spots. Many computer applications and other types of applications
assume that each pixel corresponds to a square portion of a display screen. Pixels
are individually used by a computer to form an image on the display device. For a
color CRT, where a single triad of red, green and blue phosphor dots cannot be addressed,
the smallest possible pixel size will depend on the focus, alignment and bandwidth
of the electron guns used to excite the phosphors. The light emitted from one or more
triads of red, green and blue phosphor dots, in various arrangements known for CRT
displays, tends to blend together giving, at a distance, the appearance of a single
colored light source representing a pixel.
[0005] Liquid crystal displays (LCDs) and other flat panel display devices are commonly
used in portable computer devices in 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 generally consume less power than comparably sized CRT displays, making
them better suited for battery powered applications. As the quality of flat panel
color display devices increases and their cost decreases, flat panel displays continue
to replace CRT displays in desktop applications. Accordingly, flat panel displays,
and LCDs in particular, are becoming ever more common.
[0006] Color LCD displays are exemplary of display devices that utilize multiple separately
addressable and controllable elements, referred to herein as "pixel sub-components,"
to represent each pixel of an image being displayed. In many known LCD displays, each
pixel is a single square element that includes non-square red, green and blue (RGB)
pixel sub-components. When combined, the RGB pixel sub-components form the square
pixel.
[0007] Fig. 1 illustrates a portion of a known LCD device 100. The illustrated LCD device
100 includes four columns (C1-C4) and three rows (R1-R3) of pixels, each of which
has a separate red pixel sub-component 102, green pixel sub-component 104 and blue
pixel sub-component 106. Each of the three pixel sub-components 102, 104, 106 is three
times taller than it is wide. As a result of their aspect ratios of 3:1, the RGB pixel
sub-components 102, 104, 106 produce a square pixel. The RGB pixel sub-components
102, 104, 106 are arranged to form stripes along LCD device. The RGB stripes normally
run the entire length of the display in one direction. Common LCD devices used for
computer applications are wider than they are tall and tend to have RGB stripes running
in the vertical direction. For convenience, the invention is described herein primarily
in the context of LCD devices having vertical stripes, although the principles of
the invention apply to display devices having other pixel sub-component configurations.
[0008] In color displays, the intensity of the emitted red, green and blue light produced
by the corresponding pixel sub-components 102, 104, 106 can be varied to generate
the appearance of almost any desired color pixel. Emitting no light from the pixel
sub-components 102, 104, 106 produces a black pixel, whereas emitting all three colors
at 100 percent intensity results in a white pixel.
[0009] While conventional displays have proved satisfactory for many applications, there
is a need for resolution improvement. The resolution of flat panel display devices,
which is considerably lower than the resolution achieved by print media, makes it
difficult to display high quality Latin-based and similar alphanumeric characters
at small text sizes commonly used for reading. The problem of low resolution is even
more pronounced when complex script languages, such as Japanese, Chinese, Korean,
and the Indic languages, are displayed. Ideographic languages, such as Japanese, use
large numbers of Kanji characters or other characters that often rely as heavily on
vertical resolution as horizontal resolution.
[0010] The most complex Kanji character has nine horizontal lines, thus requiring 17 pixels
to represent the lines and the spaces between them. At current display resolutions
near 100 dots per inch, a true representation is not feasible at font sizes smaller
than about 14 point type (14/72 of an inch). At 100 dots per inch, display devices
simply do not have enough dots to depict complex Kanji characters at text sizes that
would be preferred for comfortable reading.
[0011] Japanese books are commonly printed in 9, 10 and 11-point type, which are similar
to those used in Western books. This is a desirable size for reading based on human
physiology. Manga comic books, hugely popular in Japan, use even smaller type sizes.
Further complicating matters is the fact that small frutigana characters used to provide
Japanese with pronunciation guidance for less-common Kanji characters are typically
displayed using 3 or 4 point type. Representing characters at these sizes on computer
screens, particularly LCDs, presents huge challenges.
[0012] One known technique to addressing the unavailability of screen pixels to represent
the full strokes of complex characters has been to use hand-tuned bitmaps at small
sizes. Unfortunately, these hand-tuned bitmaps are, at best, crude representations
of characters that cannot be drawn accurately at the desired display sizes given the
resolution of conventional displays. In such implementations, some strokes in the
true character outlines have to be run together or completely eliminated. Decisions
as to which strokes can be edited in such a manner require extensive knowledge of
the specific language and involve a great deal of time and effort. For example, it
would not be unusual for it to take over two years to produce a single typeface in
this manner, because there are upwards of 7,000 characters involved in some languages.
Embedded bitmap fonts also have the disadvantage of requiring large amounts of memory
to store. Because of such limitations, Japanese operating systems tend to ship with
very few supported typefaces. In fact, one common operating system of Microsoft Corporation
of Redmond, Washington, for Japanese personal computers currently includes only two
Japanese typefaces, MS-Gothic and MS-Mincho. Although Kanji characters represent a
particularly difficult type to render on LCD display devices, similar low resolution
problems are encountered when displaying any characters.
[0013] In view of the foregoing, it is apparent that there is a need for improved techniques
for displaying images on display devices. It would be desirable for any such techniques
to improve resolution in at least one, and more preferably, two-dimensions (i.e.,
the horizontal and vertical dimensions). It would also be desirable, from the manufacturing
standpoint, for at least some new display devices to be manufactured using existing
display technology and manufacturing equipment, thereby avoiding the expense that
would be associated with developing or obtaining new display device manufacturing
equipment.
SUMMARY OF THE INVENTION
[0014] The present invention relates to methods and systems for improving the resolution
of displayed images in the horizontal and vertical dimensions of LCD or other flat
panel display devices that have separately controllable pixel sub-components. One
factor that is responsible for at least some of the improved resolution is that the
separately controllable pixel sub-components, rather than full pixels, are treated
as individual luminous intensity sources. Each pixel sub-component represents a spatially
different portion of the image. In order to obtain such results, spatially different
sets of one or more samples of the image data are mapped to the individual pixel sub-components,
rather than to entire pixels.
[0015] Such displaced sampling is responsible for increasing the resolution of the display
device in the direction perpendicular to the stripes of the display device. Increased
resolution in the orthogonal direction (i.e., the direction parallel to the stripes)
is achieved by increasing the pixel sub-component density beyond that of conventional
display devices. For instance, each region of the display device that would ordinarily
consist of a single pixel with three pixel sub-components is configured to include
two or three full pixels, each having three pixel sub-components. The pixel sub-components
have heights 1.5 times greater than their widths if the pixel sub-component density
is doubled, or are square if the density is tripled. The pixel sub-component density
can be increased by other factors, as well, although a factor of two or three has
the advantage that the height dimension is no smaller than the width dimension, and
existing pixel sub-component manufacturing techniques can be readily adapted to construct
such display devices.
[0016] Display devices having the foregoing pixel and pixel sub-component configurations
can enable images to be displayed with resolutions that are improved both in the vertical
and horizontal dimensions compared with conventional rendering processes. The two-dimensional
improvement in resolution can be particularly advantageous for displaying complex
characters, such as Kanji characters, that rely heavily character features that have
fine detail in both the horizontal and vertical dimensions.
[0017] Many existing computers do not have the capability of transmitting luminous intensity
values in control signals to display devices at a rate great enough to support the
increased pixel sub-component densities of the display devices disclosed herein. In
order to make use of the available bandwidth of such computers, the image data processing
and image rendering processes of the invention also extend to image data compression
techniques.
[0018] The image data compression processes are adapted to encode the luminous intensity
values to be applied to a set of vertically adjacent pixels referred to as a control
element of the display device. The control element includes a set of two vertically
adjacent pixels when the pixel sub-component density is doubled and a set of three
vertically adjacent pixels when the pixel sub-component density is tripled, such that
the control element occupies a substantially square portion of the display device.
[0019] The luminous intensity values applied to the pixel sub-components in a control element
are encoded in a data structure having a length, for example, of 8, 16, or 24 bits.
The data structure includes a red luminous intensity value, a green luminous intensity
value, a blue luminous intensity value, and a bias value. The red, green, and blue
luminous intensity values correspond to the overall or average luminance to be generated
in the pixel sub-components of the control element. The bias value indicates the relative
luminance between the multiple pixels in the control element. For instance, if the
control element includes two vertically adjacent pixels, the bias value indicates
whether the luminance is to be biased toward the upper pixel, toward the lower pixel,
or to be distributed evenly.
[0020] The data compression techniques of the invention allow the control signal to be transmitted
to the display device at substantially the same rate as would be experienced if the
pixel sub-component density were not increased. In other words, if a particular display
system operating on a computer transmits 16 bits of data per square pixel in the absence
of increased pixel sub-component density, the compressed control signal for the display
device having the increased pixel sub-component density can also use 16 bits of data
per control element (i.e., square region of the display device). Of course, the cost
of the data compression is generally the loss of some resolution compared to the resolution
that would be obtained if each pixel were to be independently controlled without data
compression.
[0021] The invention also extends to display devices that are further adapted to decrease
the color artifacts that can be generated from treating each pixel sub-component as
a separate luminance source. In one implementation, the position of the red and blue
pixel sub-components in a pixel is transposed in alternating adjacent rows. This pixel
sub-component configuration breaks up the vertical stripes of same colored red and
blue pixel sub-components that are present in many conventional display devices, thereby
diminishing the color fringing effects that can be experienced. In other implementations,
successive rows of pixels have red, green, and blue pixel sub-components that are
offset by 1/3 or 2/3 the width of the full pixel, so that the stripes are not formed
from same-colored pixel sub-components, but are instead formed from alternating red,
green, and blue pixel sub-components.
[0022] Additional advantages of the invention will be set forth in the description which
follows, and in part will be obvious from the description, or may be learned by the
practice of the invention. The advantages of the invention may be realized and obtained
by means of the instruments and combinations particularly pointed out in the appended
claims. These and other features of the present invention will become more fully apparent
from the following description and appended claims, or may be learned by the practice
of the invention as set forth hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] In order that the manner in which the above-recited and other advantages of the invention
are obtained, a more particular description of the invention briefly described above
will be rendered by reference to specific embodiments thereof which are illustrated
in the appended drawings. Understanding that these drawings depict only typical embodiments
of the invention and are not therefore to be considered to be limiting of its scope,
the invention will be described and explained with additional specificity and detail
through the use of the accompanying drawings in which:
Figure 1 illustrates a portion of a conventional liquid crystal display device.
Figure 2 illustrates an exemplary system that provides a suitable operating environment
for embodiments of the present invention.
Figure 3 illustrates a display device in which the position of the red and blue pixel
sub-components is transposed on alternating rows of the display device according to
one embodiment of the present invention.
Figures 4A and 4B depict portions of a display device having a pixel sub-component
density in the vertical dimension that has been increased by a factor of two according
to one embodiment of the invention.
Figures 4C and 4D depict portions of a display device having a pixel sub-component
density in the vertical dimension that has been increased by a factor of two and that
also has the position of the red and blue pixel sub-components transposed on alternating
rows according to one embodiment of the invention.
Figures 5A and 5B illustrate portions of a display device in which the pixel sub-component
density in the vertical dimension has been increased by a factor of three.
Figures 6 and 7 qualitatively illustrate improvements in readability of various Kanji
characters that can be obtained by increasing the pixel sub-component density in the
vertical dimension.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] The present invention relates to systems and methods for increasing the resolution
of images displayed on LCD or other display devices having pixels that include separately
controllable pixel sub-components. Assuming that the display device have vertical
stripes, much of the enhanced resolution in the horizontal dimension is achieved by
performing displaced sampling on the image data and mapping the displaced samples
to individual pixel sub-components instead of mapping samples to full pixels. The
improved resolution in the vertical dimension is achieved by increasing the pixel
sub-component density in the vertical dimension. To accommodate the increased number
of pixel sub-components, the invention also relates to image data compression techniques
whereby sets of vertically adjacent pixels are controlled using a red luminous intensity
value, a green luminous intensity value, a blue luminous intensity value, and a bias
value. The red, green, and blue luminous intensity values control the overall luminance
from the sets of red, green, and blue pixel sub-components, while the bias value indicates
if, and to what extent, the luminance is to be shifted to a particular pixel in the
set of pixels.
I. Exemplary Computing and Hardware Environments
[0025] Embodiments of the present invention may comprise a special purpose or general purpose
computer including various computer hardware, as discussed in greater detail below.
Embodiments within the scope of the present invention also include computer-readable
media for carrying or having computer-executable instructions or data structures stored
thereon. Such computer-readable media can be any available media which can be accessed
by a general purpose or special purpose computer. By way of example, and not limitation,
such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical
disk storage, magnetic disk storage or other magnetic storage devices, or any other
medium which can be used to carry or store desired program code means in the form
of computer-executable instructions or data structures and which can be accessed by
a general purpose or special purpose computer.
[0026] When information is transferred or provided over a network or another communications
connection (either hardwired, wireless, or a combination of hardwired or wireless)
to a computer, the computer properly views the connection as a computer-readable medium.
Thus, any such a connection is properly termed a computer-readable medium. Combinations
of the above should also be included within the scope of computer-readable media.
Computer-executable instructions comprise, for example, instructions and data which
cause a general purpose computer, special purpose computer, or special purpose processing
device to perform a certain function or group of functions.
[0027] Figure 2 and the following discussion are intended to provide a brief, general description
of a suitable computing environment in which the invention may be implemented. Although
not required, the invention will be described in the general context of computer-executable
instructions, such as program modules, being executed by computers in network environments.
Generally, program modules include routines, programs, objects, components, data structures,
etc. that perform particular tasks or implement particular abstract data types. Computer-executable
instructions, associated data structures, and program modules represent examples of
the program code means for executing steps of the methods disclosed herein. The particular
sequence of such executable instructions or associated data structures represent examples
of corresponding acts for implementing the functions described in such steps.
[0028] Those skilled in the art will appreciate that the invention may be practiced in network
computing environments with many types of computer system configurations, including
personal computers, hand-held devices, multi-processor systems, microprocessor-based
or programmable consumer electronics, network PCs, minicomputers, mainframe computers,
and the like. The invention may also be practiced in distributed computing environments
where tasks are performed by local and remote processing devices that are linked (either
by hardwired links, wireless links, or by a combination of hardwired or wireless links)
through a communications network. In a distributed computing environment, program
modules may be located in both local and remote memory storage devices.
[0029] With reference to Figure 2, an exemplary system for implementing the invention includes
a general purpose computing device in the form of a conventional computer 20, including
a processing unit 21, a system memory 22, and a system bus 23 that couples various
system components including the system memory 22 to the processing unit 21. The system
bus 23 may be any of several types of bus structures including a memory bus or memory
controller, a peripheral bus, and a local bus using any of a variety of bus architectures.
The system memory includes read only memory (ROM) 24 and random access memory (RAM)
25. A basic input/output system (BIOS) 26, containing the basic routines that help
transfer information between elements within the computer 20, such as during start-up,
may be stored in ROM 24.
[0030] The computer 20 may also include a magnetic hard disk drive 27 for reading from and
writing to a magnetic hard disk 39, a magnetic disk drive 28 for reading from or writing
to a removable magnetic disk 29, and an optical disk drive 30 for reading from or
writing to removable optical disk 31 such as a CD-ROM, CD-R, CD-RW or other optical
media. The magnetic hard disk drive 27, magnetic disk drive 28, and optical disk drive
30 are connected to the system bus 23 by a hard disk drive interface 32, a magnetic
disk drive-interface 33, and an optical drive interface 34, respectively. The drives
and their associated computer-readable media provide nonvolatile storage of computer-executable
instructions, data structures, program modules and other data for the computer 20.
Although the exemplary environment described herein employs a magnetic hard disk 39,
a removable magnetic disk 29 and a removable optical disk 31, other types of computer
readable media for storing data can be used, including magnetic cassettes, flash memory
cards, digital video disks, Bernoulli cartridges, RAMs, ROMs, and the like.
[0031] Program code means comprising one or more program modules may be stored on the hard
disk 39, magnetic disk 29, optical disk 31, ROM 24 or RAM 25, including an operating
system 35, one or more application programs 36, other program modules 37, and program
data 38. A user may enter commands and information into the computer 20 through keyboard
40, pointing device 42, or other input devices (not shown), such as a microphone,
joy stick, game pad, satellite dish, scanner, or the like. These and other input devices
are often connected to the processing unit 21 through a serial port interface 46 coupled
to system bus 23. Alternatively, the input devices may be connected by other interfaces,
such as a parallel port, a game port or a universal serial bus (USB). A monitor 47
or another display device is also connected to system bus 23 via an interface, such
as video adapter 48. In addition to the monitor, personal computers typically include
other peripheral output devices (not shown), such as speakers and printers.
[0032] The computer 20 may operate in a networked environment using logical connections
to one or more remote computers, such as remote computers 49a and 49b. Remote computers
49a and 49b may each be another personal computer, a server, a router, a network PC,
a peer device or other common network node, and typically includes many or all of
the elements described above relative to the computer 20, although only memory storage
devices 50a and 50b and their associated application programs 36a and 36b have been
illustrated in Figure 2. The logical connections depicted in Figure 2 include a local
area network (LAN) 51 and a wide area network (WAN) 52 that are presented here by
way of example and not limitation. Such networking environments are commonplace in
office-wide or enterprise-wide computer networks, intranets and the Internet.
[0033] When used in a LAN networking environment, the computer 20 is connected to the local
network 51 through a network interface or adapter 53. When used in a WAN networking
environment, the computer 20 may include a modem 54, a wireless link, or other means
for establishing communications over the wide area network 52, such as the Internet.
The modem 54, which may be internal or external, is connected to the system bus 23
via the serial port interface 46. In a networked environment, program modules depicted
relative to the computer 20, or portions thereof, may be stored in the remote memory
storage device. It will be appreciated that the network connections shown are exemplary
and other means of establishing communications over wide area network 52 may be used.
II. LCD Display Devices with Increased Pixel Sub-Component Densities
[0034] Computer display devices are two-dimensional devices. Since display devices are normally
oriented in a vertical fashion, for convenience, the first and second dimensions of
a display device are commonly referred as vertical (y) and horizontal (x) dimensions,
respectively. By rotating the physical display device, the horizontal and vertical
dimensions can be interchanged. For purposes of explanation, the methods and apparatus
of the present invention will be explained in terms of vertical and horizontal dimensions.
However, it is to be understood that the described exemplary display devices can be
rotated to achieve the described improvement in resolution in the vertical direction
in the horizontal direction, and the described improvement in resolution in the horizontal
direction, in the vertical direction.
[0035] As discussed above, pixel elements commonly include red, green and blue pixel sub-components.
The luminous intensity of each pixel sub-component may be separately controlled by
selecting a luminous intensity control value associated with the particular pixel
sub-component. In most known devices, each R, G and B pixel sub-component is rectangular
in shape and is three times taller than it is wide. The three rectangular pixel sub-components
form a square pixel.
[0036] In accordance with one embodiment of the present invention, R, G, B luminous intensity
values are independently controlled to represent different portions of an image. This
provides an increase in the horizontal spatial resolution of up to three times over
those of conventional rendering techniques that use the entire pixel to represent
a single portion of an image.
[0037] Unfortunately, in cases where the R, G, B elements are arranged in vertical stripes
as in the case of the conventional LCD device illustrated in Fig. 1, treating the
pixel sub-components as separate luminous intensity sources can result in some color
distortions. For example, undesired red and/or green vertical stripes or fringes may
be visible in a displayed image. In one embodiment of the present invention, to decrease
the visibility of color artifacts introduced by treating pixel sub-components as independent
luminous sources, the common RGB striped display pattern is replaced with a pattern
that transposes the position of red and blue pixel sub-components in alternating rows,
as illustrated in Fig. 3. Row R1 of display device 200 includes a series of pixel
sub-components having an (R, G, B, R, G, B, ...) pattern. In contrast, row R2 includes
a series of pixel sub-components having an (B, G, R, B, G, R, ...) pattern. Stated
another way, the vertically adjacent pixel sub-components 202 and 212 have different
colors (red and blue), the vertically adjacent pixel sub-components 206 and 214 have
the same green color, and the vertically adjacent pixel sub-components 208 and 216
have different colors (blue and red).
[0038] Such pixel sub-component configurations can reduce the effect of color artifacts
by eliminating the contiguous red and blue vertical pixel sub-component stripes. It
is these contiguous vertical color strips that can produce distracting red and blue
fringing effects in an image. Rather than having vertical stripes of same-colored
red and blue pixel sub-components, LCD device 200 has vertical stripes of alternating
red and blue pixel sub-components.
[0039] The foregoing techniques of treating pixel sub-components as independent luminous
sources can result in a significant increase in spatial resolution in the dimension
perpendicular to the direction of the stripes. When the display device has vertical
stripes, this method of increasing image resolution is particularly useful for rendering
Latin-based characters or other characters that rely more heavily on vertical character
features than horizontal character features. As noted above, however, Kanji characters
generally depend as heavily on horizontal character features as they do on vertical
features. Accordingly, to increase the legibility of Kanji characters, it is important
to increase vertical as well as horizontal resolution.
[0040] In various embodiments of the present invention, resolution is increased in the vertical
dimension by increasing the number of pixel sub-components in this dimension. For
example, the number of pixel sub-components per unit distance in the direction parallel
to the stripes can be doubled with respect to the conventional display device illustrated
in Figure 1. One example of such a display device is illustrated in Figures 4A and
4B. The portion of LCD display device 320 illustrated in Figure 4B includes rows R1-R3
and columns C1-C4. Rows R1-R3 represent scanlines of the display device 320 that are
oriented perpendicularly to the vertical striping. In contrast, display devices having
horizontal striping have vertical scanlines. Each region of LCD device 320 that would
correspond to a single full pixel with three pixel sub-components in a conventional
display device instead represents two pixels containing a total of six pixel sub-components.
For instance, Figure 4A illustrates one such region 300 of display device 320, which
includes separately controllable pixel sub-components R1, G1, B1, R2, G2, and B2,
indicated by reference numbers 302, 304, 306, 312, 314, and 316, respectively.
[0041] The pixel and pixel sub-component configuration of Figures 4A and 4B results in pixel
sub-components that are approximately 1.5 times taller than they are wide. In other
words, the aspect ratio of the pixel sub-components is approximately 1.5:1. It is
noted that the aspect ratios can describe the size and relative positioning of the
pixel sub-components regardless of whether the display device has vertical or horizontal
stripes. The decreased aspect ratio of the pixel sub-components of Figures 4A and
4B has the effect of increasing the resolution in the vertical direction. The apparent
factor by which the resolution is increased depends largely on the manner in which
the pixel sub-components 302, 304, 306, 312, 314, and 316 are controlled, as will
be described in greater detail below. When the pixel and pixel sub-component configuration
of Figures 4A and 4B is combined with the above-discussed technique of increasing
the perceived resolution in the horizontal dimension, characters with increased vertical
resolution and increased horizontal resolution can be displayed.
[0042] Figures 4C and 4D depict a portion of an LCD device 350 that has pixel sub-components
that are approximately 1.5 times taller than they are wide, as in the example of Figures
4A and 4B, in combination with transposing the position of the red and green pixel
sub-components on alternating rows as has been described in reference to Figure 3.
Each region of display device 350 of Figure 4D that would correspond to a single full
pixel in conventional LCD devices instead represents two pixels that include a total
of six pixel sub-components. For instance, region 330 of Figure 4C includes pixel
sub-components R1, G1, B1, B2, G2, R2 indicated by reference numbers 332, 334, 336,
342, 344, and 346, respectively. The embodiment of Figures 4C and 4D can generate
increased resolution in the vertical and horizontal directions, as well as reducing
some of the color artifacts that could otherwise be experienced.
[0043] In other embodiments, resolution is increased by tripling the number of pixel sub-components
in the vertical dimension. For example, in Figure 5B, each region of display device
450 that would correspond to a single full pixel in conventional LCD devices instead
represents three pixels that include a total of nine pixel sub-components. For instance,
region 400 of Figure 5A includes pixel sub-components R1, G1, B1, R2, G2, B2, R3,
G3, B3 indicated by reference numbers 402, 404, 406, 408, 410, 412, 414, 416, and
418, respectively. The pixel and pixel sub-component configuration of Figures 5A and
5B results in pixel sub-components that are square or approximately square, or have
aspect ratios of approximately 1:1.
[0044] The doubling or tripling of the resolution in the vertical dimension can be implemented
using existing display device manufacturing equipment since it does not require a
finer gradation between pixel sub-components than is already found in the horizontal
dimension.
[0045] Specific examples of increasing the number of pixel sub-components in the direction
of the striping of the display device by factors of two and three have been presented.
Increasing the pixel sub-component density by factors of two and three has certain
advantages, such as maintaining generally square regions of the display device and
preserving pixel sub-component heights that are at least as great as the widths, which
enables previously-known manufacturing techniques to be adapted for constructing these
display devices. However, the invention also extends to increasing the pixel sub-component
density by other factors so as to improve the resolution in the direction parallel
to the stripes.
[0046] Each set or triad of RGB pixel sub-components produced by increasing the number of
pixel sub-components in the direction parallel to the striping can be treated as a
separate pixel. Such treatment, in the case where the pixel sub-component density
is increased by a factor of two, results in non-square pixels that are half as tall
as they are wide. In order to fully use all of the pixels, the display software generates
and transmits a signal containing twice as many luminous intensity values associated
with pixel sub-components than would be needed if the pixel sub-component density
had not been increased by a factor of two. Similarly, when the pixel sub-component
density is increased by a factor of three, the number of luminous intensity values
is also tripled if the pixel sub-components are to be fully and independently utilized
to represent different portions of the image data.
III. Image Data Compression
[0047] The large number of luminous intensity values that are to be transmitted in the control
signal for display devices, such as those illustrated in Figures 4A-5B can present
bandwidth problems in some systems. That is, some systems may not be capable of generating
and transmitting such a large number of independent luminous intensity values during
the time available for each update of the display device. In addition, as discussed
above, many existing image processing applications assume that pixels are square.
There may be some inefficiencies or complexities associated with using non-square
pixels with such applications.
[0048] In order to compensate for the limited bandwidth capabilities of many existing computer
systems, embodiments of the present invention relate to compressing the luminous intensity
values associated with the pixel sub-components of display devices having increased
pixel sub-component densities. The data compression sacrifices some resolution in
exchange for reducing the data transmission requirements to render images.
[0049] In systems capable of processing and transmitting double or triple the number of
video control signals that would otherwise be needed in the absence of increased pixel
sub-component densities, each set, or triad, of RGB pixel sub-components can be treated
as an independent pixel without using the data compression techniques disclosed herein.
However, when image data compression can be beneficial, sets of pixels are grouped
together for control purposes.
[0050] For example, in Figures 4A-4D, where the pixel sub-component density is doubled in
the vertical dimension, two sets of vertically adjacent RGB pixel sub-components can
be grouped together to form a pair of adjacent pixels that is referred to herein as
a "control element". For example, region 300 of Figure 4A and region 400 of Figure
5A are examples of control elements. In such an embodiment, each pair of pixels occupies
a generally square region of the display device and corresponds in size to a single
pixel of a conventional display device. Although the control element can consist of
adjacent pixels, control elements can, in general, consist of two or more pixels,
regardless of whether the pixels are adjacent one to another.
[0051] For data compression purposes, in accordance with one embodiment of the present invention,
the luminance generated by the pixel sub-components in each control element is controlled
using a single red luminous intensity value, a single green luminous intensity value,
a single blue luminous intensity value, and a bias value. The bias value indicates
how the light energy specified by the R, G and B luminous intensity values should
be distributed or differentially applied between the upper pixel and the lower pixel
of the control element. The bias value indicates, for example, whether the luminance
should be evenly distributed between the upper and lower pixels, or whether it should
be weighted by a specified factor to the upper or lower pixel.
[0052] Opportunity for bias depends on the specified luminous intensity of each color component.
Accordingly, in the case where the different color components are assigned different
luminous intensity values, the opportunity for bias will be different for each of
the R, G and B components. Medium gray offers a large opportunity for bias, since
the R, G and B luminous intensity values are each at their midrange point. This allows
for one pixel sub-component, in a control element that includes a pair of pixels,
each having R, G and B pixel sub-components, to be turned fully on and the corresponding
pixel sub-components in the other pixel in the control element to be turned fully
off, if desired, without affecting the overall energy output.
[0053] In order to optimize the use of the bandwidth available for transmitting luminous
intensity values to the display device, the number of bits included in the red, green,
and blue luminous intensity values and the bias value can be selected in view of empirical
observations relating to the perception of colors by humans. In general, most humans
can perceive green light far better than red or blue light. Studies have shown that,
in general, of the total perceived luminous intensity of a light source that outputs
red, green, and blue light of the same luminous intensity, approximately 60% of the
perceived luminous intensity is associated with the green light, 30% with the red
light, and 10% with the blue light. For this reason, humans tend to be able to distinguish
differences in green luminous intensity values far better than differences in red
or blue luminous intensity values.
[0054] In many conventional computer systems, the luminous intensity of the R, G, and B
pixel sub-components is controlled using a control signal that includes 8, 16 or 24
bits per pixel. Multiples of eight bits are frequently used in control signals to
efficiently use the data capacity of data words used to transmit such signals. Conventional
systems that use a total of eight bits to specify the luminous intensity values of
red, green and blue pixel sub-components of a single pixel normally allocate three
bits for specifying the red luminous intensity value, three bits for specifying the
green luminous intensity value and two bits for specifying the blue luminous intensity
value. Conventional systems that use a total of sixteen bits to specify the luminous
intensity values of red, green and blue pixel sub-components normally allocate five
bits for specifying the red luminous intensity value, six bits for specifying the
green luminous intensity value and five bits for specifying the blue luminous intensity
value.
[0055] To support the display of an extremely large number of different colors, some conventional
computer systems, including many personal computers, use twenty-four bits to specify
the luminous intensity values of red, green and blue pixel sub-components that form
a single pixel. In such systems, eight of the twenty-four available bits are usually
dedicated to specifying the luminous intensity value of each of the red, green and
blue pixel sub-components.
[0056] The allocation of bits commonly used to specify the luminous intensity values of
pixel sub-components in conventional systems is shown in Table 1:
TABLE 1
Total bits per pixel |
Bits per R component |
Bits per G component |
Bits per B component |
8 |
3 |
3 |
2 |
16 |
5 |
6 |
5 |
24 |
8 |
8 |
8 |
[0057] By using fewer bits than is commonly used in the examples presented in Table 1 to
represent the set of RGB luminous intensity values, and dedicating the unused bits
for use as the bias value, a display device having an increased pixel sub-component
density can be controlled using control signals that require no more data to transmit.
Of course, the cost of performing such data compression is often the loss of some
spatial or color resolution in the rendered image.
[0058] In the above-described manner, a display device having two pixels in each control
element can be controlled using an 8-bit signal where two bits are used for the R
luminous intensity value, two bits for the G luminous intensity value, two bits for
the B luminous intensity value, and two bits for the bias value. In the case where
16 bits are available per control element, four bits can be used to specify the red
luminous intensity value, six to specify the green luminous intensity value, four
to specify the blue luminous intensity value, and two bits to specify the bias value.
In the case of a 24-bit interface, eight bits can be used to specify the red luminous
intensity value, eight to specify the green luminous intensity value, six to specify
the blue luminous intensity value, and two bits to specify the bias value.
[0059] These ratios favor reallocation of blue and/or red luminous intensity control bits
for use as bias value bits, since humans are less sensitive to different intensity
levels of these colors than to different green intensity levels. However, alternative
allocations of control bits to luminous intensity and bias values are also possible.
For example, other embodiments of the invention use three bits to support a wider
range of luminous intensity bias values. Still other embodiments use six bias bits
so that the biasing of each pair of red, green and blue pixel sub-components can be
independently controlled. In one 6-bit bias control signal embodiment, each pair of
bias bits represents a separate red, green and blue bias signal.
[0060] A two-bit bias value can indicate whether or not a bias is to be applied, and whether
the upper or lower RGB set should be responsible for outputting the majority of the
light energy from the pixel element. For example, in one exemplary embodiment, a bias
control signal value 00 indicates that the luminous energy should be spread evenly
between the upper and lower pixels, a bias control signal value 10 indicates that
the luminous energy should be biased downward so that the lower pixel outputs more
light than the upper pixel; and a bias control signal value of 01 indicates that the
luminous energy should be biased upward so that the upper pixel outputs more light
than the lower pixel.
[0061] The luminous intensity control techniques of the present invention, which involve
the use of separate R, G, B luminous intensity values, in conjunction with a bias
value, can be used to control pixel elements comprising three or more sets of R, G
and B luminous intensity values. Such a control method is particularly well suited
to applications where the pixel sub-component density have been tripled in the vertical
dimension so that individual RGB pixel sub-components are square and have vertical
and horizontal dimensions equal to 1/3 the width of a pixel. In such embodiments,
three vertically adjacent pixels can be grouped together to form a singe square control
element.
[0062] In one such embodiment, where each control element includes three sets of RGB pixel
sub-components, a 3-bit bias control signal is used. The 3-bit bias signal supports
a large enough number of different luminous intensity energy distributions that reasonable
use of the available vertical resolution, corresponding to the three vertically adjacent
pixels, can be obtained.
[0063] The values of the bias bits can be derived by sampling image data such that the vertical
distance between vertically adjacent samples is equal to the height of the pixel sub-components.
To select the bias bits, first the two (or three) desired RGB luminous intensity values
are averaged together, component-wise, and each color is quantized to the appropriate
level for the display device. This average of the RGB luminous intensity values corresponds
to the desired overall luminance for the control element. Next, the overall luminance
that would be generated in the control element for each possible bias bit setting
is computed and compared to the averaged desired output for the control element. These
control element outputs are patterns consisting of two by three emitters or three
by three emitters, as disclosed herein. In one embodiment, the bias bits are chosen
to minimize the square of the Euclidean distance between the averaged desired control
element output and the actual control element output. Other error metrics can also
be used, including those that will be obvious to those skilled in the art upon learning
of the invention disclosed herein.
[0064] In one exemplary embodiment, the results of the resolution-enhancing filtering can
be quantized as one 8-bit value per control element. In this embodiment, the vertical
pixel sub-component density (and the corresponding rate of sampling) is increased
by a factor of two. Thus, two 8-bit filtered RGB values are to be converted into one
8-bit signal including the RGB luminous intensity values and the bias value. This
conversion can be accomplished via a lookup table, using techniques that will be understood
by those skilled in the art, upon learning of the invention disclosed herein. If the
lookup table is accomplished in software by the operating system, it does not require
a large amount of computation. Alternatively, the lookup table can be implemented
in hardware in a video card.
IV. Examples of Characters
[0065] Figures 6 and 7 qualitatively illustrate the increased resolution that can often
be obtained by displaying images according to the invention. The characters of Figures
6 and 7 are those that can be generated by independently controlling each pixel rather
than using the data compression techniques of the invention, with the bias values.
The characters illustrated in Figures 6 and 7 are presented by way of example, and
not by limitation. The results of any particular rendering process will depend on
many factors, including the size of the pixel sub-components, the sampling and filtering
processes used, etc.
[0066] Figure 6 illustrates various representations of the Japanese character "Utsu," which
is reputed as being one of the most complex Kanji characters. The characters of Figure
7 illustrate how an outline-only rendered bitmap may be rendered at different font
sizes and at different pixel sub-component densities, both in the vertical and horizontal
dimensions.
[0067] Set of characters 130 is displayed with 9-point type and corresponds to an LCD display
device having 88 dpi (i.e., 88 full pixels per inch). Character 130a is rendered using
a display device with pixel sub-components that are three times as tall as they are
wide or, in other words, with no increased pixel sub-component density. Character
130b is displayed using the same display device, but with an increase in the pixel
sub-component density by a factor of two. Character 130c is displayed with an increase
in the pixel sub-component density by a factor of three compared to that of character
130a.
[0068] Set of characters 132 is displayed with 9-point type and corresponds to an LCD display
device having 106 dpi. Character 132a is rendered using a display device with pixel
sub-components that are three times as tall as they are wide. Character 132b is displayed
using the same display device, but with an increase in the pixel sub-component density
by a factor of two. Character 132c is displayed with an increase in the pixel sub-component
density by a factor of three compared to that of character 132a.
[0069] Set of characters 134 is displayed with 6-point type and corresponds to an LCD display
device having 88 dpi. Character 134a is rendered using a display device with pixel
sub-components that are three times as tall as they are wide. Character 134b is displayed
using the same display device, but with an increase in the pixel sub-component density
by a factor of two. Character 134c is displayed with an increase in the pixel sub-component
density by a factor of three compared to that of character 134a.
[0070] Set of characters 136 is displayed with 6-point type and corresponds to an LCD display
device having 106 dpi. Character 136a is rendered using a display device with pixel
sub-components that are three times as tall as they are wide. Character 136b is displayed
using the same display device, but with an increase in the pixel sub-component density
by a factor of two. Character 136c is displayed with an increase in the pixel sub-component
density by a factor of three compared to that of character 136a.
[0071] Figure 7 illustrates various Kanji characters as they can appear when displayed according
to the invention. Row 140 includes characters that correspond to an LCD display device
having 88 dpi and where the conventional pixel sub-component density has been increased
by a factor of two. Row 142 includes characters that correspond to an LCD display
device having 106 dpi and where the conventional pixel sub-component density has been
increased by a factor of two. Row 144 represents the characters of row 140 having
been displayed with a pixel sub-component density increased by a factor of three,
rather than two. Similarly, row 146 represents the characters of row 142 having been
displayed with a pixel sub-component density increased by a factor of three, rather
than two.
[0072] As can be seen from these examples of rendered characters, the improvement in readability
and resolution can be dramatic when the characters are complex and rely heavily on
horizontal features.
[0073] The present invention may be embodied in other specific forms without departing from
its spirit or essential characteristics. The described embodiments are to be considered
in all respects only as illustrative and not restrictive. The scope of the invention
is, therefore, indicated by the appended claims rather than by the foregoing description.
All changes which come within the meaning and range of equivalency of the claims are
to be embraced within their scope.
[0074] The following is a list of further preferred embodiments of the invention:
Embodiment 1: In a computer system having a display device, the display device having
a plurality of pixels each having a plurality of pixel sub-components of different
colors, a method of displaying an image on the display device with increased resolution,
the method comprising the steps for:
obtaining image data representing the image;
based on the image data, generating a control signal that is to be applied to a control
element of the display device, the control element including at least two pixels,
the control signal including one luminous intensity value for each of the different
colors and a bias value indicating whether, and to what extent, if any, the luminous
intensity values are to be differentially applied to a particular one of the at least
two pixels; and
displaying the image on the display device by applying the luminous intensity values
and the bias value to the pixel sub-components.
Embodiment 2: A method as recited in embodiment 1, wherein the image data representing
the image includes spatially different sets of one or more samples that are mapped
to individual pixel sub-components.
Embodiment 3: A method as recited in embodiment 1, wherein the control signal that
is to be applied to the control element comprises:
a single red luminous intensity value;
a single green luminous intensity value; and
a single blue luminous intensity value.
Embodiment 4: A method as recited in embodiment 3, wherein the control signal that
is to be applied to the control element further comprises a single bias value that
is applied to the red, green, and blue luminous intensity values.
Embodiment 5: A method as recited in embodiment 3, wherein the control signal that
is to be applied to the control element further comprises three bias values, each
of the three bias values being applied to one of the red, green, and blue luminous
intensity values.
Embodiment 6: A method as recited in embodiment 1, wherein the control element occupies
a substantially square region of the display device and consists of two adjacent pixels,
each having three pixel sub-components.
Embodiment 7: A method as recited in embodiment 1, wherein the control element occupies
a substantially square region of the display device and consists of three adjacent
pixels, each having three pixel sub-components.
Embodiment 8: A method as recited in embodiment 1, wherein the step for generating
the control signal comprises the acts of:
generating a data structure for each of the at least two pixels included in the control
element, each of the data structures having a length equal to a specified number of
bits and indicating desired luminous intensity values for the pixel sub-components
of the particular pixel; and
compressing the data structures into the control signal, the control signal also having
the length equal to the specified number of bits.
Embodiment 9: A method as recited in embodiment 8, wherein the act of compressing
the data structures comprises selecting the control signal from a lookup table based
on the data structures.
Embodiment 10: A computer program product for implementing, in a computer system having
a display device, the display device having a plurality of pixels each having a plurality
of pixel sub-components of different colors, a method of displaying an image on the
display device with increased resolution, the computer program product comprising:
a computer-readable medium carrying computer-executable instructions for performing
the steps for:
obtaining image data representing the image;
based on the image data, generating a control signal that is to be applied to a control
element of the display device, the control element including at least two pixels,
the control signal including one luminous intensity value for each of the different
colors and a bias value indicating whether, and to what extent, if any, the luminous
intensity values are to be differentially applied to a particular one of the at least
two pixels; and
displaying the image on the display device by applying the luminous intensity values
and the bias value to the pixel sub components.
Embodiment 11: A computer program product as recited in embodiment 10, wherein image
data representing the image includes spatially different sets of one or more samples
that are mapped to individual pixel sub-components.
Embodiment 12: A computer program product as recited in embodiment 10, wherein the
control element occupies a substantially square region of the display device and consists
of two adjacent pixels, each having three pixel sub-components.
Embodiment 13: A computer program product as recited in embodiment 10, wherein the
control element occupies a substantially square region of the display device and consists
of three adjacent pixels, each having three pixel sub-components.
Embodiment 14: A computer program product as recited in embodiment 10, wherein the
step for generating the control signal comprises the acts of :
generating a data structure for each of the at least two pixels included in the control
element, each of the data structures having a length equal to a specified number of
bits and indicating desired luminous intensity values for the pixel sub-components
of the particular pixel; and
compressing the data structures into the control signal, the control signal also having
the length equal to the specified number of bits.
Embodiment 15: A computer program product as recited in embodiment 14, wherein the
act of compressing the data structures comprises selecting the control signal from
a lookup table based on the data structures.
Embodiment 16: A computer system for displaying images with increased resolution,
comprising:
a processing unit; and
a display device capable of being controlled by the processing unit, the display device
having a plurality of pixels each having a plurality of separately controllable pixel
sub-components of different colors, each of the plurality of pixels having a shape
other than a square.
Embodiment 17: A computer system as recited in embodiment 16, wherein the plurality
of separately controllable pixel sub-components includes a red pixel sub-component,
a green pixel sub-component, and a blue pixel sub-component, the positions of the
red pixel sub-components and the blue pixel sub-components being transposed within
the pixels in alternating rows of pixels on the display device.
Embodiment 18: A computer system as recited in embodiment 16, wherein the pixel subcomponents
have aspect ratios of approximately 1.5:1.
Embodiment 19: A computer system as recited in embodiment 16, wherein the pixel subcomponents
have aspect ratios of approximately 1:1.
Embodiment 20: A computer system as recited in embodiment 16, wherein the display
device is a liquid crystal display device.
Embodiment 21: A computer system as recited in embodiment 16, further comprising a
computer-readable medium carrying computer-executable instructions for causing an
image to be displayed on the display device, the computer-executable instructions,
when executed by the processing unit, performing the steps for:
obtaining image data representing the image; and
displaying a different portion of the image on each of the pixel sub-components of
a particular pixel as opposed to displaying a single portion of the image on the entire
particular pixel.
Embodiment 22: A computer system as recited in embodiment 21, wherein the computer-executable
instructions, when executed by the processing unit, further performs the steps for:
based on the image data, generating a control signal that is to be applied to a control
element of the display device, the control element including at least two pixels,
the control signal including one luminous intensity value for each of the different
colors and a bias value indicating whether, and to what extent, if any, the luminous
intensity values are to be differentially applied to a particular one of the at least
two pixels; and
displaying the image on the display device by applying the luminous intensity values
and the bias value to the pixel sub-components.
Embodiment 23: A display device for displaying images with increased resolution, comprising:
a plurality of pixels, each pixel having a plurality of separately controllable pixel
sub-components, including:
a red pixel sub-component;
a green pixel sub-component; and
a blue pixel sub-component;
wherein the plurality of pixels are aligned in scanlines on the display device
that are either rows or columns, and wherein the position of the red pixel sub-components
and the blue pixel sub-component in the pixels is transposed on alternating scanlines.
Embodiment 24: A display device as recited in embodiment 23, wherein the scanlines
are rows and the pixels and pixel sub-components are arranged on the display device
to form vertical stripes of same-colored green pixel sub-components and vertical stripes
of alternating red pixel sub-components and blue pixel sub-components.
Embodiment 25: A display device as recited in embodiment 23, wherein the scanlines
are columns and the pixels and pixel sub-components are arranged on the display device
to form horizontal stripes of same-colored green pixel sub-components and horizontal
stripes of alternating red pixel sub-components and blue pixel sub-components.
Embodiment 26: A display device as recited in embodiment 23, wherein the pixel subcomponents
have aspect ratios of approximately 3:1 such that the pixels have aspect ratios of
approximately 1:1.
Embodiment 27: A display device as recited in embodiment 23, wherein the pixel subcomponents
have aspect ratios of approximately 1.5:1 such that two adjacent pixels occupy a region
of the display device having an aspect ratio of approximately 1:1.
Embodiment 28: A display device as recited in embodiment 23, wherein the pixel subcomponents
have aspect ratios of approximately 1:1 such that three adjacent pixels occupy a region
of the display device having an aspect ratio of approximately 1:1.
Embodiment 29: In a computer system having a display device, the display device having
a plurality of pixels each having a plurality of pixel sub-components of different
colors, a method of displaying an image on the display device with increased resolution,
the method comprising the steps for:
mapping samples of image data representing the image to individual pixel sub-components
of a pixel, each of the pixel sub-components of the pixel having mapped thereto a
spatially different set of one or more of the samples, the pixel sub-components of
the plurality of pixels being arranged to form on the display device stripes of same-colored
green pixel sub-components and stripes of alternating red pixel sub-components and
blue pixel sub-components;
generating a separate luminous intensity value for each pixel sub-component of the
pixel based on the different set of one or more samples mapped thereto; and
displaying the image on the display device using the separate luminous intensity values,
resulting in each of the pixel sub-components of the pixel, rather than entire pixels,
representing a different portion of the image.
Embodiment 30: A method as recited in embodiment 29, further comprising, after the
step for generating the separate luminous intensity value for each pixel sub-component,
the step for compressing the separate luminous intensity values to generate a control
signal used to control a control element of the display device including at least
two pixels, the control signal including at least:
a single red pixel sub-component;
a single green pixel sub-component;
a single blue pixel sub-component; and
a bias value indicating whether, and to what extent, if any, the luminous intensity
values are to be differentially applied to a particular one of the at least two pixels.
Embodiment 31: A method as recited in embodiment 30, wherein the pixel sub-components
have aspect ratios of approximately 1.5:1 such that the control element occupies a
substantially square region of the display device and consists of two adjacent pixel
sub-components.
Embodiment 32: A method as recited in embodiment 30, wherein the pixel sub-components
have aspect ratios of approximately 1:1 such that the control element occupies a substantially
square region of the display device and consists of three adjacent pixel sub-components.