Note: Descriptions are shown in the official language in which they were submitted.
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Description
Electrophoretic Display Employing Grey
Scale CaPability Utilizing Area Modulation
Technical Field
The present invention relates to electrophoretic
i~formation displays (EPID) in general and more
particularly to apparatus which operates in
conjunction with an EPID display enabling such a
display to operate with grey scale capability.
Background Art
The prior art is replete with a number of various
patents and articles concerning electrophoretic
displays. Such electrophoretic displays have been
widely described and disclosed in the prior art and
essentially the assignee herein, Copytele Inc., of
Huntington Station, New York has developed an
electrophoretic display which has an image area of
approximately 11 x 8 1/2 inches and is designed to be
used either as a separate display or to be combined
with other displays. The company has the ability to
con~ine as many as four such displays to create larger
area displays. The information on such displays can
be changed either locally or remotely and can be
viewed at an angle of nearly 180 degrees. Such
displays have been extremely high resolution and can
accommodate over 160,000 pixels within an image area
of approximately 2.8 inches diagonally.
In regard to such displays, reference is made to
U.S. Patent No. 4,655,897 issued on April 7, 1987
entitled ELECTROPHORETIC DISPLAY PANELS AND ASSOCIATED
METHODS to Frank J. DiSanto and Denis A. Krusos and
assigned to Copytele Inc., the assignee herein. In
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that patent, there is described an electrophoretic
display panel which includes a planar transparent
member having disposed on the surface a plurality of
vertical conductive lines to form a grid of wires in
the Y direction. On top of the grid of vertical
lines, there is disposed a plurality of horizontal
lines which are positioned above the vertical lines
and insulated therefrom by a thin insulating layer at
each of the intersection points. Spaced above the
horizontal and vertical line pattern is a conductive
plate. The space between the conductive plate and the
X and Y line pattern is filed with an electrophoretic
dispersion containing chargeable pigment particles.
When a voltage is impressed on the X and Y lines,
pigment particles which are located in the wells or
depressions between the X and Y pattern are caused to
migrate towards the conductive plate and deposited on
the plate in accordance with the voltage applied to
the X and Y conductors. There is described in that
patent an electrophoretic dispersion suitable for
operation with the display as well as techniques for
fabricating the display. Hence, in this manner the
displays can be fabricated to contain large effective
display areas while being relatively thin. These
displays are capable of high resolution and relatively
low power consumption.
As indicated, the above noted patent and others
include information concerning the fabrication,
operation and resolution of such displays.
As explained in U.S. Patent No. 4,833,464, issued
on May 23, 1989 and entitled ELECTROPHORETIC
INFORMATION DISPLAY (EPID) APPARATUS EMPLOYING GREY
SCALE CAPABILITY to Frank J. DiSanto, et al., it is a
problem with such displays to provide grey scale
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capability. Grey scale capability is a well known
term of the art and has been utilized for example in
regard to the description of television receivers and
various other types of data presentation, such as
facsimile and so on. In the case of television
receivers, the response of the receiver can be
visually determined by means of typical test patterns
such as those test patterns that were previously
transmitted and displayed when, for example, a
television station goes off the air. Various
television stations frequently transmit such a pattern
f~r the convenience of service technicians and so on.
The pattern apart from showing correct linearity, for
e~ample, also shows correct reproduction of the
background shading which can indicate proper frequency
response. The correct reproduction of the five color
shades in the center target area of the test pattern
indicates proper mid-frequency responses.
As one can ascertain, such test patterns are
associated with grey scale capability, namely with the
display of various grey levels as located between
black and white. Such grey scale capability is a
desirable feature in conjunction with any type of
display. An electrophoretic display either presents a
black or white type of representation of an image
which is conveniently referred to as dark or light.
Basically, the color of the image is a function of the
color of the pigment particles and the color of the
suspension that they are suspended in. The display
may be black and white, yellow and black and so on.
There is a wide variety of many potential color
combinations which can be employed in regard to such
displays. The above-noted U.S. Patent No. 4,833,464,
describes apparatus and techniques for grey scale
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operation for an electrophoretic display panel. The
apparatus includes circuitry which operates with a
timing generator which produces a plurality of
different time duration output wave forms which are
applied to the X and Y drive as associated with the
display. In this manner, by applying a set of
voltages for a given duration time interval, a display
is provided which results in the incomplete removal of
pigment from associated selected pixels. Hence, those
pixels appear darker than surrounding pixels but not
as dark as the pure dye solution as associated with
the display. Thus, the amount of pigment removed and
hence the darkness of each pixel is a function of the
time duration during which the appropriate voltage is
applied to the rows and columns of the display. The
timing generator can cause different pixels as
displayed to have different darknesses or grey scale
values by varying the time during which the voltage is
applied to the display.
As will be further explained, grey scale
operation at different shades of grey can also be
provided on the electrophoretic display by means of
area modulation. Area modulation can be used to shade
either the foreground, the background or both the
foreground and the background. Such electrophoretic
displays, as other displays, portray information by
writing in two different colors or shades of the same
color. These, of course, can be referred to as black
or white, although many other color combinations are
available as indicated above. Thus, in an
electrophoretic display, the normal background color
is the color of the pigment used in the display and
the written characters and graphics are generated by
removing pigment from the appropriate areas. In the
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reverse or inverse video mode the pigment is removed
from the background while pigment is retained in the
areas of the characters or graphics. This is the same
difference, for example, between a negative and
positive in photography. As will be explained, by
performing area modulation by writing a pattern of
either black or white pixels in either the background,
foreground or both, permits generation of shades of
grey. It is also understood that area modulation can
be used with any relatively high resolution display to
in fact provide a grey scale capability for the
display.
It is therefore an object of the present
invention to provide an electrophoretic display having
grey scale capability.
It is a further object of the present invention
to provide an electrophoretic display apparatus which
has grey scale capability and which operates to
modulate the area about each character or the area
within each character on a display.
Disclosure of the Invention
Apparatus for providing grey scale capability for
an electrophoretic information display (EPID), wherein
said electrophoretic display is an X-Y addressable
display with each X-Y coordinate indicative of a given
column and row intersection, with each X-Y coordinate
defining a pixel, which pixel when energized provides
a different intensity display as compared to a non-
energized pixel comprising of means coupled to saiddisplay for impressing upon said display a
predetermined digital pattern to cause predetermined
pixels in said display to be energized with respect to
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other pixels in said display in accordance with a desired grey
scale level.
According to a further broad aspect of the present
invention there is provided an apparatus to provide grey scale
capability for an electrophoretic display (EPID) and wherein
the electrophoretic display is an X-Y addressable display with
each X-Y coordinate indicative of a given column and row
intersection. Each X-Y coordinate defines a pixel which when
energized provides a different intensity display as compared
to a non-energized pixel. The apparatus comprises means
coupled to the display for impressing upon the display a
plurality of predetermined digital patterns that are
independent of data or an image written on the display to
cause the pixels in the display to be energized with respect
to other pixels in the display and according to a selected one
of such patterns. The energized pixels are of the same
intensity as those pixels of an image on the display and each
of the predetermined digital patterns are distinct and
arranged in repetitive configurations that produce different
grey scale levels, whereby the area about the image is
effectively modulated according to the pattern to vary the
contrast of the image with respect to the display background.
According to a still ~urther broad aspect o~ the
present invention there is provided a method which provides
grey scale capability for an electrophoretic information
display (EPID) of the type employing pixel selection. The
method comprises the steps of storing a plurality of digital
patterns with each of the digital pattern being distinct and
arranged in repetitive configurations that produce different
grey scale levels. The stored patterns are capable, when
applied to an electrophoretic display, to cause the pixels in
the display to be energized with respect to other pixels in
the display and in accordance with a desired grey scale level
and with each of the energized pixels being of the same
intensity as those pixels of an image on the display. The
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method also comprises the step of selecting a stored pattern
for application to the display by means independent of data or
an image written on the display to cause the display to
exhibit the grey scale level, whereby the area about the image
is effectively modulated according to the said pattern to vary
the contrast of the image with respect to the display
background.
Brief Description of the Drawings
Fig. 1 is a side plan view of an electrophoretic
display (EPID) employed in this invention;
Fig. 2 is a perspective plan view of an
electrophoretic display panel showing a given number of grid
and cathode lines;
Fig. 3 is a graph depicting a character block
displayed on a conventional black and white display;
Fig. 4 depicts a character displayed with a
predetermined area modulated background pattern;
Fig. 5 shows still another area modulated pattern;
Fig. 6 is a diagram showing still another pattern;
Fig. 7 is a diagram showing still another pattern;
Fig. 8 is a diagram showing an alternate pattern;
Fig. 9 is a diagram showing still another alternate
pattern;
Fig. 10 is a diagram of a character block showing an
alternate background pattern;
Fig. 11 is a diagram of a character block showing an
alternate background pattern;
Fig. 12 is a schematic diagram partially in block
form showing a circuit for deriving a grey scale value for an
electrophoretic display employing area modulation;
Fig. 13 shows an OR gate employed in this invention;
Fig. 14 shows an AND gate employed in this
invention;
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Fig. 15 shows a logic circuit for providing grey
background or characters; and
Fig. 16 shows a logic circuit for providing the
character and background features.
Best Mode for CarrYing Out The Invention
Referring to Figure 1, there is shown a side view
of a typical electrophoretic display 10. The display
of Figure 1 is filled with an electrophoretic
solution 20 which includes light colored pigment
particles suspended in a dark dye solution. For
examples of such solutions and techni~ues, reference
is made to the above cited U.S. Patent No. 4,655,897.
It is also understood that the display can
consist of a dark pigment suspended in a light
solution and so on. As seen from Figure 1, the
display contains a front glass sheet or viewing
surface 21. The eye of the viewer 15 is shown viewing
the front of the display via the glass sheet 21.
Superimposed upon the glass sheet 21 by suitable
etching techniques are columns 23 and rows 25. The
rows are made from an extremely thin layer of idium-
tin-oxide (ITO) while the columns are made from thin
layers of aluminum or other suitable metal. These
pal:terns, as indicated, are provided in extremely thin
layers and constitute an XY matrix. The layers of ITO
as can be seen by reference to the above-noted patent
are relatively thin being approximately 3000 Angstroms
thick. The grid or columns and the rows or cathodes
(XY) are spaced from one another and insulated from
one another by means of an insulating layer 22. While
the grids and cathodes have been specified in terms of
rows and columns, it is understood that the terms can
be interchanged as desired. Each of the grid and
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cathode intersections are associated with a pigment
well 24. These wells contain electrophoretic solution
which is in the cavity 20. The columns and rows are
separated from a back electrode 26 which is also
fabricated on a sheet of glass 27 and constitutes a
thin layer of ITO. The-spacers such as 12 and 23 can
be implemented in many different ways and essentially
serve to mech~n;cally separate the display or panel
10. In operation of the display, the pigment
particles contained in the electrophoretic solution 20
are brought forward towards the viewing surface in
order to fill the wells formed between the rows and
columns. Once a well such as 24 is filled, the
voltage on the tows and columns and rear cover is then
set, such that the wells remain filled, but pigment
spaced between the rear cover and the columns are
swept onto the rear cover plate 26. At viewing side
21, one sees the color of the pigment in the wells.
By selectively applying voltages to the rows and
columns, the pigment in the individual wells 24 (at
the intersection of the rows and columns selected) is
forced out of the wells exposing the dye solution and
making that intersection (pixel) dark. The removal of
the pigment from the wells is not instantaneous but
requires a period of time which depends upon the
dimension of the cell or display, the fluid
components, and the various supply voltages. The
above-noted U.S. Patent No. 4,833,464 discusses the
control of the voltages and the duration of the same
to control grey scale operation. The techniques for
performing area modulation in conjunction with an
electrophoretic display will be described in detail.
Referring to Figure 2, there is shown a plan view
of an enlarged representation of an electrophoretic
W093/02~3 PCT/US9l/04834
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display cell or panel according to Figure 1. As seen
in Figure 2, each well is accommodated between an
intersection of a column metal layer 23, which is
insulatively separated from a row layer of ITO 25.
The well 24 forms a pixel area which is indicative of
an XY intersection of the ITO display. Thus, as one
will understand, the object of the present invention
is to provide grey scale capability and this grey
scale capability is performed in a high resolution
electrophoretic display. It is noted that the
resolution of the display has to be high to
ac~ommodate area modulation and derive the particular
aspects and benefits of this technique.
Referring to Figure 3, there is shown a
representation of the letter E as for example,
displayed on a conventional electrophoretic display.
In regard to the following discussion, it will be
indicated that the states of the electrophoretic
display, for example as shown in Figure 3, are black
and white. It is understood that the letter E will be
visible if the pixels were darker than the background.
As indicated above, area modulation is
accomplished by writing a pattern of either black or
white pels in either the background, the foreground or
bot:h. The high resolution provided by an
electrophoretic display permits the use of area
modulation to generate shades of grey. Area
modulation can be employed with any relatively high
resolution display. Appearance of the grey scale due
to area modulation is a physiological consequence of
the resolution of the human eye. The effect is
obtained when the angle suspended by the black and
white pels as seen by the viewer, approaches the
resolution of the human eye. In a typical
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electrophoretic display as provided by the assignee
herein, Copytele Inc., a resolution of 200 lines per
inch in both the horizontal and vertical directions is
available.
This resolution is ideal for producing grey scale
by means of area modulation. On an electrophoretic
display with this resolution, characters are written
using a character block of 16 pixels horizontally and
24 pixels vertically. As seen in Figure 3, both the
horizontal and vertical directions are indicated by
means of gradations as 30 and 31. These gradations
encompass an area which is indicative of a pixel.
Hence, as one can see, there are essentially 16 boxes
or pixels representing the top line in the image area
32 depicted in Figure 3. Thus, again referring to
Figure 3, it is indicated that with the above-noted
resolution of 200 lines per inch in both the
horizontal and vertical directions, character blocks
consisting of 16 pixels or pels horizontally and 24
pels vertically are typical. This character block
yields a display with 25 lines of 80 characters each
on a display whose dimensions are approximately 6.4 x
3.2 inches. Thus, as one can ascertain from Figure 3,
there is shown the character E which is represented in
black on a relatively white background. It is, of
course, understood that the inverse of this image
could also be provided by the electrophoretic display.
Referring to Figure 4, there is again shown the
character E within the character block 32 having a 50
percent grey background. Essentially, the character E
is the same as shown in Figure 3 but the background
consists of alternate pixels of black and white as can
be seen, for example, from Figure 4. Across the top
line 40, the 16 pixels are indicative of white, black,
W093/02~3 PCT/US9l/048
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white, black and so on. On line 41, the pattern is
black, white, black, white and so on. This pattern
then continues to alternate down and across the
display so that it alternates as to the 16 horizontal
pixels and the 24 vertical pixels. The background
appears grey when the image is viewed at a distance
where the individual pels are unresolved. Because of
this property, the number of grey shades obtainable
via area modulation is again a function of the
display's resolution, the size of the character and
the viewing distance. As one can ascertain, the
background area is modulated accordingly to produce
patterns which have grey scale capability due to the
nature of the modulation technique.
Referring to Figure 5, there is shown the
character block which now possesses an area modulated
background which is 93.25 percent black. This is
ob1:ained by formulating each horizontal line within
the character block, all within the display area by
means of a particular Hex code. As seen in Figure 5,
line 50 is indicative of the Hex code EE where black
is equal to binary one and white is equal to binary 0.
Bac;ed on the display format shown in Figure 5, in
or~er to obtain a background which his 93.25 percent
blzck, one modulates the display lines as follows.
The first line 50 as seen is BBBWBBBWBBBWBBBW (Hex
EE). The next three lines 51, 52, and 53 are all
black or all B (Hex FF). The fourth line is
BWBBBWBBBWBBBWBB (Hex BB). At the right of each line,
there is shown the Hex code for the line. As one can
see from the Hex code notation, it is a repetitive
pattern which specifies the display background as in
Figure 5 to obtain a background which is 93.25 percent
black. The line pattern for the display of Figure 5
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is HEX, EE, FF, FF, FF, BB, FF, FF, FF and repeats for
the 24 lines.
Referring to Figure 6, there is shown an area
modulated background or character block which is 87.5
percent black. The Hex line values are shown at the
right hand side to denote the repetitive pattern. As
one can see from Figure 6, line 61 is BWBBBWBBBWBBBWBB
which is Hex code BB. Line 62 is all black which is
Hex FF. Line 63 is BBBWBBBWBBBWBBBW which is hex code
EE. Line 64 is all black as Hex code FF.
Referring to Figure 7, there is shown an area
modulated background pattern which is 62.5 percent
black. The Hex code is shown at the right and is a
relatively simple repeating code with the first line
70 being WBBBWBBBWBBBWBBB or Hex 77. Line 71 is
BBWBBBWBBBWBBBWB which is Hex DD and then the pattern
repeats as Hex 77, DD, 77, DD, 77, DD...etc.
Referring to Figure 8, there is shown a pattern
which is 50 percent black and has a simple repeat as
line 80 is ~w~w~w~W... etc. Line 81 is WBWBWB etc.
which respectively denotes the Hex code of AA and 55,
which code repeats for the 24 lines.
Referring to Figure 9, there is shown an area
modulated display or character block which is 37.5
percent black. The Hex code is shown on the right as
line 90 is Hex code AA as for example indicative of
line 80 of Figure 8, while line 91 is Hex code 44
which is w~www~www~www~ww. Line 92 is the same as
line 90 (AA) while line 93 is Hex code 11 or
www~www~www~www~. The code then alternates as seen in
Figure 9.
Referring to Figure 10, it depicts a character
block or display having 25 percent black background.
W093/0~3 PCT/US91/04834
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The Hex code is shown on the right hand side for each
line.
Referring to Figure 11; it shows a display or
character block, the Hex code again at the right
e~hibiting a 12.4 percent black background. As one
can ascertain, the above-noted figures essentially
depict six different patterns which six patterns will
yield seven different shades of grey when viewed at
normal viewing distance on a 200 x 200 line per inch
electrophoretic display. These patterns coupled with
black and white yield a system with nine shades of
grey. However, in practice, a background of 12.5
percent black can be omitted as exhibiting a small
difference from white. The patterns as one can easily
ascertain, which are distinct are shown in Figures 5-
1~. These figures represent various patterns which
yield different shades of grey when viewed at a normal
v ewing distance on a 200 x 200 line per inch
electrophoretic display.
The system as shown with a 200 line resolution
irlcluding black and white can produce eight different
effective shades of grey. The patterns used to
achieve area modulation in a character type or
graphics type display when the graphics are formed
using special characters must be a factor of the
character block. For example, in a display using a
character block which is 16 pixels wide and 24 pixels
high, the width of the area modulated pattern must be
a factor (divisor) of 24 and the height of the pattern
must be a factor (divisor) of 16. The figures shown
in the above-noted application, as indicated for
example in Figure 3, are patt~rns which are designed
for a 16 x 24 pel character block. The figures show
patterns which have increasingly more white (less
.
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grey), however, the actual grey shade that the human
eye perceives is dependent upon many factors including
display type, ambient lighting, color and other
factors. It may be necessary to have unequal
increments in the percentages of black and white in
successive patterns to generate scales which are
subjectively more and more grey.
There are many t~hn;ques as one can imagine for
accommodating area modulation which can be implemented
simply by using registers and appropriate gating
modules.
Displays using shades of grey require that an
attribute which describes the image foreground and
background colors be designed for each character. The
attribute length depends on the total number of
different color combinations required. For example,
if only one intermediate shade of grey is required
between black and white then there are only six
combinations of foreground/background colors. These
six states are most readily encoded using 4 bits. Bit
0 and 1 specify the foreground color while bits 2 and
3 define the background color. In typical display
systems, a byte is devoted to the attribute even
though not all 64 states definable by 8 bits are used.
The implementation of such a system can be done in a
variety of ways.
Simple implementation for generating a grey
background is to OR the pel data and the selected AM
pattern (Black = binary l and White = binary 0). This
can be done in real time as the pel data and the
character data is loaded into shift registers or into
the drive circuitry. In systems which use a pixel
memory it can be done as the pel data is generated or
is loaded into the pixel memory. To make the
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characters or graphics a shade of grey, the procedures
de~cribed can be used except that the "OR" function is
replaced with an "AND" function. In inverse video,
the function used to obtain a grey background is the
AND function between the pixel data and the amplitude
modulated pattern. To make the characters grey in
inverse video, one would employ the OR function.
Referring to Figure 12, there is shown a circuit
configuration in block form for an electrophoretic
display panel 10 which is associated with area
modulation as described above. Of course, it is
understood that the cathodes and grids while described
previously in the XY planes can be reversed whereby
the cathode lines can be arranged in the Y plane with
the grid lines in the X plane or vice versa. As one
can see from Figure 12, each Y line such as 30 and 31
is associated with suitable drive amplifiers 32 and
33, where each X line such as lines 34 and 35 are
associated with suitable amplifiers 36 and 37. It is
of course seen in Figure 12, that the dots or dashes
between amplifiers 36 and 37 and 32 and 33 are
employed to indicate a plurality of additional
individual amplifiers indicative of a large number of
lines. In this manner, by applying proper biasing
potentials to respective amplifiers, one can cause
pigment particles to migrate at any intersection
between the X and Y matrix as formed by the associated
grid and cathode lines. Thus, based on the X and Y
matrix, one can therefore produce any alphanumeric
character. For such displays with a large plurality
of intersections or pixels, one can provide graphic
data such as a television picture and types of other
displays on the display panel 10. The display which
is the electrophoretic display is provided with high
W093/0~3 2 1 1 3 ~ ~ ~ PCT/US91/04834
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resolution based on the technique of fabricating line
patterns and based on presently available display
techn;ques. The driver amplifiers 32 and 33 and 36
and 37 are fabricated by typical integrated circuit
techniques and may for example by CMOS devices, which
are well known and many of which are available as
conventional integrated circuits. As indicated, the
resolution of the electrophoretic display panel is
high based on modern integrated circuit techniques and
including the fabrication techniques employed in
conjunction with such displays. It is anticipated
that the resolution of such displays can be as high as
40,000 dots per square inch. As seen from Figure 12,
the Y amplifier such as 32 and 33 are coupled to a Y
address register 41. The address register 41 is a
well known component consisting of various
conventional decoding devices including buffer
registers and so on for the storage of data and
interfacing with the various columns associated with
display 10. In a similar manner the amplifiers 36 and
37 have inputs coupled to an address module 40 which
is similar to module 41 and operates to provide the
Hex address information for the XY intersections
provided by the display. Means for addressing an XY
matrix is solved by many typical circuit solutions in
the prior art and such decoders as the Y address
register 41 and the X address register 40 are well
known components in the prior art.
Both the X and the Y address registers are
coupled to master decode module 50 which operates to
decode data and to generate the X and Y addresses for
such data as is conventionally known.
Coupled to the decode module 50 which again may
be a typical microprocessor or another programmed
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device is an area modulation memory 51. The area
modulation memory 51 contains in storage suitable
digital patterns, such as for example the Hex codes as
shown in Figure 4-11 which will enable one to produce
a display according to a desired grey background. The
s~ored data as indicated is associated with 4 bits
wllich determine the darkness or content of both the
background and foreground depending upon whether one
wants to introduce the grey in the foreground or to
introduce the grey in the background. The area
modulation memory contains the patterns as shown in
the above-noted figures to enable one to provide 6 or
more levels of grey associated with a particular
display and according to the preference of the user.
It: is, of course, indicated that each line of the
display can be modulated by means of the code
contained in memory 51 to thereby produce a uniform
grey or other background for the entire display. In a
similar manner, one can also modulate each character
block in a different manner or modulate each line in a
different manner or a portion of the display to
produce various grey formats throughout the display.
This can enable one to highlight certain regions of
the display or certain areas of the displayed text
with respect to the other areas and according to the
intensity of the foreground or background. The decode
module 50 is also coupled to a character generator 52
which character generator is a conventional component.
The character generator 52 is coupled to a keyboard
53. The character generator 52, the decoder 50 and
the keyboard 53 may be part of a conventional computer
system such as a PC system. There is another path
shown in Figure 12, whereby there is a data receiver
57 which is capable of receiving data from a typical
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telephone line or other transmission medium. This
data receiver may be a conventional modem. The output
of the data receiver is coupled to an analog to
digital converter 56 for transforming the analog
signals at the input to digital signals at the output
of the analog-to-digital converter 56. The analog-to-
digital converter 56 is associated with a digital
signal pixel generator 58 which operates in
conjunction with the master decoder 50 to allow one to
perform area modulation at various pixel sites as
desired. The output of the decoder 50 is also coupled
to the X address register and the Y address register
40 and 41. The area modulation memory 51 is shown
coupled to the decoder 50, but can of course be part
of the microprocessor memory where a certain section
will be reserved for the different area modulation
background codes. As shown in Figure 12, the module
designated as grey scale select 60 is coupled to the
area modulation memory 51. The module 60 decodes the
particular grey scale request which data may be
forwarded to the module 60 by means of the character
generator 52 or by means of the decoder 50. In this
manner, the system by decoding the transmitted data
would automatically determine what grey scale is to be
utilized for a particular display. This can be
automatically done by means of suitable decoders or
can be implemented at the preference of the user. As
shown in Figure 12, the character generator 52 is also
coupled to the grey scale select module 60 and a user
while viewing an image can go ahead and select the
grey scale value desired and according to the
preference of the user. As one can immediately
ascertain from Figure 12, area modulation can be
simply implemented. One technique of implementing the
.
W093/0~3 PCT/US91/048
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axea modulation is that the decoder or microprocessor
50 combines the area modulation code as stored in the
area modulation memory with the data code. For
example, if black is equal to l and white is equal to
0 then an "AND" or "OR" function can be used. In the
OR function, whenever a pixel does not contain data,
the pixel would receive the exact binary digit
indicative of the background code. Where a pixel does
contain data, the output will be a 1 if the data is a
1. If the data is 0 and the background is a 1, the
output would also be a 1 according to the area
modulation pattern as stored. Thus, the OR function
provides a full black or dark character with the
selected grey background as stored in the area
modulation memory 51. Thus, the patterns depicted in
the above-noted Figures 5-11 can be combined with he
data pattern, to provide AND and OR functions or both
as will be further explained. To present the
characters or graphics with a desired shade of grey,
the procedures described above can be used except the
OR is replaced with an AND function.
In this manner, both the data and the area
modulation bit must be the same in order to produce a
black spot at the output. If they are not the same
then the color of the pixel remains white. As one can
see, one will produce a character having a different
grey scale which is presented on an all white or in
the case of a negative application on an all black
background. In an inverse video mode the function
used to obtain a grey background is the AND function
occurring between the pixel data and the stored area
modulation pattern. To make the characters grey in an
inverse video mode, one would employ the OR function
between a grey background pattern and a pixel data
W~93/0~3 PCT/US91/04834
211357~ ~
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pattern. As indicated above and briefly described,
either the characters (foreground) or the background
of a display can have grey scale. Both these options
and the no grey scale option can be readily generated
by means of simple combinatorial circuits.
Referring to Figure 13, no grey scale requires no
gating. The grey background is accomplished by OR
gating the character data bit stream with the grey
scale pattern bit stream as shown in Figure 13. Thus,
as indicated in Figure 13, there is shown an OR gate
70 with one input designated as CHAR representative of
the character bit stream and the other input
designated as the grey bit steam.
As one can ascertain, the grey bit stream would
be that stream or data which has been defined in
conjunction with Figures 5-11.
Referring to Figure 14, there is shown an AND
gate 71 having one input designated as by CHAR and
indicative of the character bit stream and the other
input receiving the grey bit stream as again shown in
the above-noted figures. The output of the AND gate
71 is directed to the display or to the display
drivers as is the output of gate 70. The grey
characters are generated by the AND gate 71 which will
produce grey character on a constant background.
Typically, the color of each character can be
described by a number of additional bits which are
designated as attribute bits or an attribute byte.
This set of bits or byte are normally required for
each character to be displayed. The number of bytes
of attribute data could be reduced by means of many
different schemes which are not pertinent to this
aspect of the invention. For example, an attribute
W093/0~3 PCT/US91/04834
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byte with the following bit interpretations can be
employed for generating grey scale displays.
00000000 no grey scale (black characters
on white.
00000001 grey background with black characters.
00000010 grey characters with white background.
It is noted that in the above examples only 2
bits, as for example, the first and second bits are
needed to generated the grey display. The other bits
t~Tpically are used to specify the shade of grey
desired. For simplicity, assume the desired grey
shade has been selected and will be used when grey is
re.quired. With these assumptions and the example
attribute code specified above, only a simple logic
circuit is required to generate the required bit
stream.
Referring to Figure 15, there is shown a logic
circuit capable of generating an output signal for the
display which provides a grey background or a grey
character as controlled by the attribute bits. As
seen in Figure 15, the attribute bits designated as A0
and Al define the type of display. For example, oo is
no grey, 01 is a grey background and 10 is a grey
character. As one can see, the character bit stream
is directed to a 3 input AND gate 80 and is also
directed to a 2 input AND gate 81. The grey bit
stream is directed to one input of an OR gate 82 and
to one input of the AND gate 81.
In this manner, as one can ascertain, the
attribute bits which are A0 and Al are applied to
inverters 83 and 84. The output of inverter 83 is
directed to one input of AND gate 80 and one input of
AND gate 85. The output of inverter 84 is applied to
one input of AND gate 80 and to one input of AND gate
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86. The output of OR gate 82 is coupled to one input
of AND gate 86 while the output of AND gate 81 is
coupled to input of AND gate 85. As seen, the AND
gates 85 and 86 also receive the attribute bits which
are the uninverted bits. The outputs of the three AND
gates 85, 86 and 80 are coupled to three inputs of an
output OR gate 87, which supplies the output display
bit stream. For the combination of attribute bits,
the bit streams are suitably directed through
lo appropriate gates to provide a grey background with a
black character, to provide no grey, or to provide a
grey character on a light background. The logic
implemented by the circuit should be well understood
by those skilled in the art.
Referring to Figure 16, there is shown a logic
arrangement which based on the attribute bit table
shown will produce either no grey, a grey background,
a grey character, grey background of a given intensity
or a grey background of another intensity specified as
grey No. 2. Thus, as seen in the Figure 16, the
attribute bits Al and A0 can combine to produce no
grey, a grey 1 background with black characters, grey
No. 2 with a white background, grey No. 1 background
with grey No. 2 characters. Thus, the logic circuit
shown in Figure 16 defines a simplified logic circuit
which is predicated on using either a grey pattern of
a first intensity for the background and another grey
pattern of a different intensity for the foreground
and so on. These are indicated as a grey No.
pattern and a grey No. 2 pattern. Both of these
patterns are typical of those patters, for example,
shown in Figures 5-11 as described above. Again the
character bit stream is inserted into the circuit with
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t:he attribute bits AO and A1 having the binary
characteristics depicted in the table of Figure 16.
In a similar manner, the circuit of Figure 16 has
four output AND gates designated as 9O, 91, 92 and 93
with gate 9O being a no grey gate, gate 91 producing
the grey 1 ouL~ as a background, gate 92 producing
the grey 2 character and gate 93 enabling one to
provide a grey 1 background and a grey 2 character. A
description of each of the individual gates in the
uninverted state as for example, gate 93 receives the
A1 uninverted as does gate 92, while gates 91 and 9O
receive the Al inverted signal. One can immediately
ascertain the operation of the above-described circuit
by referring to Figure 16.
