U.S. patent number 3,729,714 [Application Number 05/155,982] was granted by the patent office on 1973-04-24 for proportional space character display including uniform character expansion.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Roderick S. Heard.
United States Patent |
3,729,714 |
Heard |
April 24, 1973 |
PROPORTIONAL SPACE CHARACTER DISPLAY INCLUDING UNIFORM CHARACTER
EXPANSION
Abstract
A system for uniformally expanding a proportionally spaced
character display in order to properly align the smallest
characters of the character set without affecting the proportional
relationship of the characters in the character set. An extra
vertical scan line is added to the displayed characters at an
escapement increment determined by the character of the character
set requiring the greatest proportion of scan line expansion per
character width in order to achieve proper character definition.
Those characters requiring an additional unit of escapement to be
properly defined utilize the added vertical scan lines and excess
added vertical scan lines are distributed in the "white space"
between characters. The added display columns have the same affect
as increasing the number of scans per unit of character
escapement.
Inventors: |
Heard; Roderick S. (Lexington,
KY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
26852746 |
Appl.
No.: |
05/155,982 |
Filed: |
June 23, 1971 |
Current U.S.
Class: |
345/25; 400/83;
400/306; 345/671 |
Current CPC
Class: |
G09G
1/18 (20130101); G09G 5/243 (20130101) |
Current International
Class: |
G09G
1/18 (20060101); G09G 1/14 (20060101); G09G
5/24 (20060101); G06f 003/14 () |
Field of
Search: |
;340/172.5,324A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Henon; Paul J.
Assistant Examiner: Chirlin; Sydney R.
Claims
What is claimed is:
1. A proportionally spaced character display system comprising:
character set selection means for selecting one of a plurality of
proportionally weighted character sets to be displayed;
storage means for storing successively addressable characters to be
displayed;
escapement decode means responsive to the character set selection
means and to the storage means for defining the relative width in
scan lines of each addressed character in the storage means in
accordance with the character set selected;
character generating means responsive to each addressed character
in the storage means for generating successive fixed vertical scan
line segments in accordance with the addressed character, the
number of vertical scan line segments generated depending upon the
addressed character;
scan line adding means responsive to the character set selection
means and to the character generating means for providing a scan
line add signal for every predetermined number of scan lines
generated when a first character set is selected and for providing
no scan line add signal when a second character set is
selected;
said character generating means being further responsive to said
scan line add signal for generating an additional vertical scan
line segment;
character termination means responsive to the escapement decode
means and the character generating means for addressing the next
successively addressable character in said storage means when the
number of vertical scan line segments generated by the character
generator means equals the defined relative width in scan
lines.
2. The proportionally spaced character display system set forth in
claim 1 wherein said character generating means distributes said
additional vertical scan line segments at the end of a generated
character.
3. The proportionally spaced character display system set forth in
claim 1 wherein said scan line adding means being further
responsive to said character set selection means for providing a
scan line add signal for a second predetermined number of scan
lines when a third character set is selected.
4. The proportionally spaced character display system set forth in
claim 1 wherein said predetermined number of scan lines corresponds
to the width in scan lines of the smallest character in the first
character set which character cannot be adequately defined by a
corresponding number of vertical scan line segments.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
The following applications are all assigned to the same assignee as
the present application.
U.S. Pat. No. 3,654,609, filed Mar. 2, 1970, entitled "Proportional
Spacing Visual Editing System," Robert G. Bluethman, et al,
inventors.
U.S. Pat. No. 3,648,271, filed Mar. 2, 1970, entitled "Visual
Editing System Incorporating Selectable Letter Spacing Display and
Associated Scale Display," Robert L. McConnell, et al,
inventors.
BRIEF BACKGROUND OF INVENTION
1. Field
This invention relates to a proportionally spaced character display
system and more particularly to means incorporated in such a system
for properly aligning and representing displayed character
symbols.
2. Description of the Prior Art
Prior Art display editing systems such as those exemplified by U.S.
Pat. No. 3,248,705 utilize standard spaced character display
representations to indicate to the system operator how printed
lines of standard spaced characters will appear on final printed
output copy. The aforereferenced copending application to Robert G.
Bluethman, et al, discloses a display editing system utilizing
proportionally spaced character representations to indicate to the
operator thereof how a final printed line of proportionally spaced
characters will appear upon printing a final copy. The
aforereferenced copending application to Robert L. McConnell, et
al, describes a display editing system wherein both standard spaced
character representations and proportionally spaced character
representations can be alternatively selected. The proportionally
spaced character display is utilized when the final output copy is
to be printed on a printer incorporating proportionally spaced or
weighted character sets. The standard display is selected when the
output printer is a standard spacing printer. In either event, the
display device is utilized to give the operator of the display
system an indication as to how the final printed copy will appear.
The operator may then actuate controls to change the appearance of
the displayed copy and hence the final output copy to achieve a
more desirable affect.
Various printing devices incorporating proportionally spaced
character sets are available to be utilized to prepare the final
output copy. The escapement increments utilized for the various
printers differ from one another. That is, for example, the
escapement of one printer system may be based on an escapement unit
of one seventy-second inch while that of another printer may be
based on an escapement unit of one-sixtieth inch. The relative
escapement values for characters of a character set utilizing a one
seventy-second inch escapement unit differ with respect to one
another as compared to the relative escapement values of characters
within a set designed for a printer using a one-sixtieth inch
escapement unit. Additionally, various printers have a print
condensation mode wherein a uniform value is subtracted from the
number of escapement units which define various ones of the
characters in order to compress the various lines of printing.
In order for the display editing system to be flexible so that it
may be used in conjunction with the various output printers
described above to provide display lines of proportionally spaced
characters which yield an accurate representation of the appearance
of a final printed line, it is necessary to display different
proportionally weighted character sets in accordance with the type
of output device to be selected. It is also desirous to utilize a
minimum character generator to generate the various character sets
in order to reduce the overall costs of the device.
Character generators of the prior art which could be utilized to
generate a proportional character display are of two types. One
prior art device is a monoscope which displays proportional
characters. Various character sets could be selected for display by
expanding the character font and selection device of prior art
monoscopes. However, the costs of such a unit would be prohibitive
for a multi-line multi-character font display. Another prior device
is one which generates a dot matrix character pattern, a unique
pattern being associated with each character of a character set.
While such a device is less costly than a monoscope type of
display, the increased number of characters which must be defined
in order to display a plurality of proportionally weighted
character sets necessitates greater costs.
In order to reduce these costs, the same matrix character generator
can be utilized to define the same character in each of the
different character sets displayed. However, in utilizing such a
scheme, some characters cannot be properly defined since the number
of scan lines necessary to define the character exceeds the number
of scan lines available when the number of scan lines is equal to
the escapement value of the character. One solution to this problem
would be to increase the number of total scan lines of the display
by a factor of two. However, by doubling the density of the scan
lines which define each character, the number of lines of display
feasible with a given circuit speed are reduced. Another solution
is to add a scan line column to each character. However, this
destroys the positional relationship of text in successive lines
since all characters are not the same width.
SUMMARY
In order to overcome the aforenoted problems of the prior art and
to provide an economical display system for displaying various
proportionally weighted character sets in a manner that lines of
displayed characters are representative of the appearance of final
printed output copy, a character generator is provided which adds
an additional vertical scan line within the line of displayed
characters at a predetermined increment thereby increasing the
number of scan lines available to define each character of a
character set without destroying the positional relationship of
characters displayed on adjacent lines. The escapement value of the
character of the character set which requires the most additional
scan lines per width value of the character for adequate character
definition is utilized to define the predetermined increment
thereby assuring that each character within the display line which
requires an additional scan line has an additional scan line
available for its use in order that the character may be properly
defined. The added scan lines enable the same character generator
to be utilized to define the characters of the various character
sets.
The foregoing and other features and advantages of the invention
will be apparent from the following more particular description of
the preferred embodiment as illustrated in the accompanying
drawings.
In the Drawings:
FIG. 1 is a schematic block diagram of the proportional space
character display system including uniform character expansion.
FIG. 2 is a pictorial illustration of proportionally spaced
characters which are displayed by the system of FIG. 1.
Referring now to FIG. 1 of the drawings, the proportional spaced
character display system including uniform character expansion is
depicted. Characters to be displayed in lines of characters on the
CRT display 11 are stored in memory 13. Each successive character
of a line of characters to be displayed is gated from the memory 13
through the And gate 15 to the character register 17. The character
in the character register provides an address input to the
character generator decode unit 19 which in turn provides
successive vertical scan line information which defines the
character to be displayed to the scan data register 21. The scan
line information stored in the scan data register 21 is serialized
by the serializer 23, the output of which is applied to the video
amplifier 25 which, in turn, provides a blank and unblank signal to
the CRT display 11.
The character located in the character register 17 is also provided
as an address input to the escapement unit decode 31. This unit
determines the number of escapement units associated with the
character located in the character register in accordance with the
character set selected. Assuming that the character in the
character register 17 is defined by a number of vertical scan lines
corresponding to the number of escapement units which define the
character, the compare unit 33 will provide an output signal when
the last vertical scan line of the character is complete. This
output signal is utilized to gate the memory address counter 35 and
the And gate 15 to cause the next successive character to be gated
to the character register 17 from the memory 13.
Referring briefly to FIG. 2 of the drawings, a pictorial
illustration of proportionally spaced characters displayed on the
CRT display 11 of FIG. 1 is shown. As can be seen, each character
is made from elements of a matrix which corresponds to a dot
pattern generated on the CRT display. Assuming a vertical character
sweep, the H character depicted would be serially generated on the
screen of the CRT a vertical scan line at a time. That is, as the
CRT beam sweeps downwardly over the leftmost portion of the
character, the beam would be unblanked for 10 successive time
intervals corresponding to the 10 vertically stacked elements of
the first column of the character matrix. Thereafter, the beam
would be returned to the uppermost position and caused to sweep
through the elements of the second column where it would be
unblanked only during its travel through the fifth vertical
element. This process is repeated until the last scan line (always
blank to assure adjacent character spacing) is complete, at which
time the beam is advanced to form the next adjacent character, the
character B.
Referring once again to FIG. 1 of the drawings, a dot clock 41 is
gated by an oscillator and caused to periodically advance. Each dot
clock time corresponds to a vertical display element so that the
first ten dot clock times correspond to the ten vertical elements
located within a single scan column of a character matrix.
Additional dot clock times are necessary to cause return of the CRT
beam back to the starting position of an adjacent vertical scan.
When the dot clock 41 reaches a zero count, it indicates that the
next successive vertical column of a character is ready to be
displayed. The "zero" output signal of the dot clock 41 advances
the column clock 43 when the dot clock reaches its zero state. The
column clock 43 is a binary counter providing an output indicative
of the count stored therein. The output of the column clock 43
provides an address input to the character generator decode unit 19
thereby controlling the scan line of information which is gated to
the scan data register 21. The foregoing description has related to
the units which are employed to generate sequential vertical column
scans to define successive characters. These units with the
exception of the escapement unit decode 31 and compare unit 33
represent a conventional character generator, as would be utilized
to generate standard spaced matrix characters and are described in
the aforereferenced U.S. Pat. No. 3,648,271 and in U.S. Pat. No.
3,618,032. As mentioned above, the escapement unit decode 31 and
the compare unit 33 operate to indicate the completion of a serial
character display and hence initiate the display of the next
character. These units are not necessary when displaying standard
space display characters since each character has the same number
of scan columns. However, since proportionally weighted characters
are displayed, it is necessary to define the completion of each
character displayed thereby necessitating the escapement unit
decode 31 and the compare unit 33. The operation of an escapement
unit decode for displaying proportionally weighted characters is
described in the afore referenced U.S. Pat. No. 3,648,271.
Assuming that the output printer has a one seventy-second inch
escapement unit and that the character unit values of the character
font vary from four units of escapement for the narrowest character
to nine units of escapement for the largest character, the mode
selection switch 51 would be placed in position A. Positioning the
switch thusly effects successive display lines of characters which
closely resemble the manner that the same lines of characters would
appear on the one seventy-second inch output printer. That is, the
relative widths of the displayed characters correspond to the
relative widths of the printed characters and the display
characters of successive lines align vertically in the same manner
as those of corresponding printed lines. This positioning is
achieved when the mode switch 51 is in position A by utilizing a
character generator which causes a one-to-one relationship to exist
between scan lines and escapement units of the characters displayed
on the CRT display 11.
Since the smallest character of the one seventy-second inch system
described above is four escapement units and, hence, four scan
lines wide, it can be readily defined. Referring briefly again to
FIG. 2 of the drawings, it can be seen that four scan lines are
necessitated to display the letter t (including the blank scan line
to the right of the character needed for inter-character
definition). This character and others such as the letters I, f, j,
and l require a minimum of four scan lines to be defined and cannot
be adequately defined with three scan lines assuming one scan line
is reserved for inter-character spacing. Hence, when an output
printer is selected having relative escapement unit values of three
escapement units to eight escapement units or one less than the
escapement units of a one seventy-second inch printer (e.g. a one
seventy-second inch printer with n- 1 print condensation) some
characters cannot be defined if the number of scan lines correspond
to the number of escapement units which define the character. For
example, a letter t would have a relative escapement value of four
units on a one seventy-second inch printer and a value of three
units on the same printer with n- 1 print condensation. It thus
becomes apparent that the number of scan lines defining the
character must be increased when it is desirous to display lines of
characters as they would appear when printed on a one
seventy-second inch printer operating in a print condensation
mode.
Referring once again to FIG. 1 of the drawings, when the mode
selector switch 51 is placed into position B thereby selecting a
one seventy-second n- 1 character display, a signal is provided to
the expansion clock 53 which is operative to cause additional scan
lines to be distributed amongst the characters in a manner to be
described. The expansion clock is a four stage binary ring counter,
with selective switching to control the number of stages utilized.
The secondary column clock 55 is responsive to the output signal of
the And gate 57 which is, in turn, responsive to the output signal
of the expansion clock 53. The And gate 57 is also responsive to
the zero output signal of the dot clock 41 and provides a counting
signal to the secondary column clock 55 whenever a signal is
provided by the expansion clock 53. The secondary column clock 55
is a binary counter which provides an output signal indicative of
the count stored therein. The expansion clock 53 provides an output
signal so long as it is not advancing to its first count. Assuming
the mode selector switch 51 to be on its B position, the expansion
clock becomes a four-stage ring counter which is advanced with each
zero output from the dot clock 41. When the counter is reset to its
first count, no signal is provided to the And gate 57 and hence the
secondary column clock 55 does not advance with the zero output of
the dot clock.
It can be readily appreciated that the count in the secondary
column clock 55 will be less than the actual number of scan lines
which have been effected for a character as represented by the
state of the column clock 43 since the secondary column clock 55 is
inhibited from advancing whenever the expansion clock resets to its
first count. Since the output signal from the secondary column
clock 55 is compared by the compare unit 33 with the true
escapement of the character in order to terminate a character
display, extra scan columns are generated under the control of the
column clock 43. That is, the number of vertical scan lines
generated by the display device 11 for a character corresponds to
the number registered by the column clock 43 which will exceed the
number registered by the secondary column clock 55. Since the
output signal of the secondary column clock 55 is utilized to halt
character generation when it corresponds to the value generated by
the escapement unit decode 31, the number of "extra scans" per
character corresponds to the difference between the value in the
column clock 43 and the secondary column clock 55. The extra scans
are utilized to further define the character. When the mode
selector switch is placed in position B, an extra scan column is
added for every three columns required by each escapement value of
the character.
Referring again to FIG. 2, it can be seen with respect to the lower
case letter t which is defined as a three-unit character for a one
seventy-second inch n- 1 display that a fourth scan will be added
thereby insuring for the white space between the characters.
Additionally, it can be appreciated that the same character
generator decode unit 19 can be utilized to produce the letter t in
both one seventy-second inch escapement display and in one
seventy-second inch n- 1 escapement display. The following table
represents the relationship of escapement units in one
seventy-second inch n- 1 to those in one seventy-second inch for a
similar character and also specifies the guaranteed minimum number
and the maximum number of columns which will be available for
display of the character when utilizing the uniform expand feature
of the present invention which adds an extra scan column for each
three scan columns.
TABLE I
Units in Equivalent Guaranteed Maximum Possible 1/72" n-1 Units in
Minimum Number Number of Excess or 1/60" 1/72" of Columns Columns
Columns 3 4 4 4 0 4 5 5 6 1 5 6 6 7 1 6 7 8 8 1 7 8 9 10 2 8 9 10
11 2
It can be seen from the above table that the guaranteed minimum
number of columns or scan lines available for displaying characters
having a one seventy-second inch n- 1 escapement is equal to or
exceeds the number of scan lines necessary to display a
corresponding character having a one seventy-second inch escapement
for which number of scan lines corresponds to the number of
escapement units. Thus, the same character generator can be
utilized for displaying characters in a one seventy-second inch
representation or in a one seventy-second inch n- 1 representation.
It can also be seen from the above table that the possible number
of excess columns associated with each character having an
escapement value of three in one seventy-second inch n- 1 is zero
when the character generator utilizes the same character set as is
utilized with a one seventy-second inch display. Where an eight
unit one seventy-second inch n- 1 character is to be displayed,
there are two possible excess columns. Additional white space may
be added to the right-hand side of the character to thus utilize
the two additional scan line columns. In the worst case, this could
cause right edge character misalignment from line to line by only
two scan lines and left edge misalignment by only one scan
line.
Referring once again to FIG. 2 of the drawings, a line of five
letter t's are depicted. Assuming that a letter t is assigned an
escapement value of three units for a one seventy-second inch n- 1
display, it will be appreciated that five of these characters
displayed adjacently on a final printed page would utilize 15
escapement units. Similarly, an eight unit letter H and a seven
unit letter B printed adjacent to one another would also take up 15
escapement units. Assuming that the five letter t's are located on
a first printed line and that the letters HB are located on the
printed line immediately below and that the left edge of the first
letter t aligns with the left edge of the letter H, the right hand
edge of the last letter t would also align with the right hand edge
of the letter B. As will be explained, this relationship is
approximately maintained with a maximum error of one scan column at
the left edge of characters and two scan columns at the right edge
of characters by utilizing the display system of the present
invention.
As noted above, an extra scan column is added for every three scan
columns when utilizing the display system of the present invention
with the mode selector switch 51 placed in position B. Thus 20 scan
columns are utilized to display the line of letter t's.
Additionally, if the H utilized the maximum number of columns noted
in the aforegoing Table I, it would require 11 scan columns to be
displayed. In a similar manner, the letter B would require a total
of 10 scan columns to be displayed. Thus, a total of 21 scan
columns would be utilized to display the letters HB of the second
line causing those characters to misalign by only one scan column
from that which would be expected with the final printed output. As
noted above, the maximum misalignment which can occur by utilizing
the identical character generator utilized for a one seventy-second
inch character display and adding the extra scan columns is one
scan column at the left edge of a character. Since the extra scan
columns are uniformly added throughout each display line, the
misalignment errors are not cumulative and an approximate
relationship is obtained without necessitating a separate character
generator for each type of escapement displayed.
Referring once again to FIG. 1 of the drawings, it can be seen that
when the mode selector switch 51 is placed in position A thereby
selecting a one seventy-second inch escapement display, a signal is
provided to the And gate 60 which inhibits the output signal of the
dot clock 41 from advancing the expansion clock 53. A signal is
also supplied to the escapement unit decode 31 which provides a
character output decode ranging from four to nine escapement units.
Since the expansion clock 53 is inhibited from advancing, it never
moves to the first count; thus each output signal of the dot clock
41 is applied to the secondary column clock 55 as well as to the
column clock 43. In this mode, there is a one-to-one relationship
between scan lines and escapement units. Thus, when the number of
columns which have been scanned as indicated by the secondary
column clock 55 equals the escapement value as determined by the
output signal from the escapement unit decode 31, the compare unit
33 provides a signal effecting the display of the next
character.
When the mode selector switch 51 is placed in position B, the
expansion clock 53 has a fours counter activated which advances
with each output signal from the dot clock 41 indicating the
completion of a scan line. When this counter resets to its first
count, the gating signal applied to the And gate 57 is removed and
the secondary column clock does not advance with the output of the
dot clock. Thus, for every three scan lines completed, a fourth
scan line is added. Since the column clock continues to advance,
the character generator decode unit 19 is provided with a signal
indicating that the next successive column is to be displayed.
Assuming that a character having an escapement value of three (e.g.
the letter t) is to be displayed and that it is the first character
of a line, the expansion clock 53 is set to a count of two with the
line start reset signal. At the completion of the first vertical
scan of the t, the dot clock 41 provides an output signal which
causes the column clock 43 to advance thereby addressing the second
column of the t in the character generator decode unit 19. The
secondary column clock 55 also advances and the expansion clock 53
advances from a count of two to a count of three. The second column
of the letter t is then displayed causing the column clock 43 to
advance to address the third column of the character in the
character generator decode unit 19. The secondary column clock also
advances to indicate that two columns have been displayed while the
expansion clock moves from a count of three to a count of four.
After the third scan line is complete, the output of the dot clock
41 causes the column clock to advance to the fourth column and
causes the expansion clock 53 to advance from a four state to a one
state. When the expansion clock 53 moves to its first count, it
provides a degating signal to the And gate 57 which prevents the
secondary column clock 55 from advancing. Since the value of the
secondary column clock 55 does not at this time equal the value
established by the escapement unit decode 31, the column clock 43
causes an additional scan to be taken. It will be noted that the
character generator is the same as that used for a one
seventy-second inch escapement display and therefore has a fourth
defined column (blank). Once this sweep is complete, the dot clock
provides a further signal causing the expansion clock to advance to
a two state and causing the secondary column clock and the column
clock to both advance. At this point, the value stored in the
secondary column clock is equal to that defined by the escapement
unit decode (three scans complete = three escapement units) thereby
causing the compare unit 33 to provide an output signal resetting
the secondary column clock 55, the column clock 43, and providing a
gating signal to the And gate 15 to cause the next data character
to be displayed. When characters such as the letter B are
displayed, it is possible to have two additional scans over that
provided by the character generator when generating that character
in a one seventy-second inch escapement display. The character
generator decode unit 19 is responsive to such additional scans
provided by the column clock to generate blank scans.
When the mode selector switch 51 is moved to position C, a threes
counter is actuated in the expansion clock 53. That is, the
expansion clock 53 counts to three before resetting to one and, in
this manner, causes an additional scan line to be provided for each
two scan lines of display. The following table is representative of
escapement values of characters when utilized in a one
seventy-second inch n- 2 or in one-sixtieth inch n- 1 display and
also represents the guaranteed minimum number of columns and
maximum number of columns and possible excess columns.
TABLE II
Units in 1/72" n-2 Equivalent Guaranteed Maximum Possible or 1/60"
Units in Minimum Number Number of Excess n-1 1/72" of Columns
Columns Columns 3 4 4 5 1 3 5 4* 5 0 4 6 6 6 0 5 7 7 8 1 6 8 9 9 1
7 9 10 11 2 *Necessitates removal of one scan line from character
generator.
In a similar manner, when the mode selector switch 51 is moved to
position D, a twos counter is actuated which provides an additional
scan line for each scan line of display and can be utilized when it
is desired to display a representation of a one-sixtieth inch n- 2
escapement system.
As is recognized by those skilled in the art, an optimum character
set can be selected for display instead of utilizing the character
set associated with a one seventy-second inch escapement display.
For example, characters having relative values defined under the
guaranteed minimum number of columns heading of Table I can be
utilized as the character set defined by the character generator
decode unit 19. If such a set were utilized, it would be necessary
to provide an additional mode input signal to the character
generator decode unit 19 to effect the reduction in scan lines of
7, 8, and 9 unit escapement characters when operating in a one
seventy-second inch escapement system. That is, for example, a 10
unit letter W as defined by the character generator decode unit 19
would be reduced to a 9 unit letter W when operating in a one
seventy-second inch escapement display. This could be effected in
designing the character such that one scan line could be removed
without affecting its overall appearance.
While the invention has been particularly shown and described with
reference to a preferred embodiment thereof, it should be
understood by those skilled in the art that the foregoing and other
changes in form and detail may be made therein without departing
from the scope of the invention.
* * * * *