U.S. patent number 3,614,767 [Application Number 04/786,672] was granted by the patent office on 1971-10-19 for electronic photocomposing system that forms characters of different point sizes.
This patent grant is currently assigned to RCA Corporation. Invention is credited to Ross M. Carrell.
United States Patent |
3,614,767 |
Carrell |
October 19, 1971 |
ELECTRONIC PHOTOCOMPOSING SYSTEM THAT FORMS CHARACTERS OF DIFFERENT
POINT SIZES
Abstract
An electronic photocomposing system forms alphanumeric
characters on the face of a cathode-ray tube by a plurality of
vertical scanlines that form slices of the characters. The
characters are imaged onto photographic film for subsequent
processing into printing plates. Characters of different point
sizes are formed by changing the lengths of the scanlines, as well
as the spacing between adjacent scanlines.
Inventors: |
Carrell; Ross M. (Cinaminson,
NJ) |
Assignee: |
RCA Corporation (N/A)
|
Family
ID: |
9845353 |
Appl.
No.: |
04/786,672 |
Filed: |
December 24, 1968 |
Foreign Application Priority Data
|
|
|
|
|
Feb 19, 1968 [GB] |
|
|
08078/68 |
|
Current U.S.
Class: |
345/26;
345/213 |
Current CPC
Class: |
B41B
19/01 (20130101); B41B 27/28 (20130101); G09G
1/14 (20130101) |
Current International
Class: |
B41B
19/01 (20060101); B41B 19/00 (20060101); B41B
27/00 (20060101); B41B 27/28 (20060101); G09G
1/14 (20060101); G06f 003/14 () |
Field of
Search: |
;315/18,19
;340/324,324.1 ;178/7.8 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Curtis; Marshall M.
Claims
What is claimed is:
1. An electronic photocomposition system for composing characters
of a graphic-type font in a plurality of predetermined graphic
point sizes, comprising in combination,
an imaging device having a scanning spot for tracing out said
characters by a plurality of segments of scanlines,
first means for repeatedly deflecting said scanning spot in one
direction at a substantially constant velocity,
second means for deflecting said scanning spot in a direction
orthogonal to said one direction so as to create a plurality of
adjacent scanlines for each of said characters,
third means providing a plurality of coded character-determining
signals having code values selected to define said scanline
segments of said characters,
a plurality of oscillators each exhibiting a different
substantially fixed pulse repetition rate corresponding to a
different one of said plurality of point sizes,
fourth means coupled to count pulses from a selected oscillator and
to detect correspondence between said pulse count and said coded
values of said scanline segments,
means responding to said third and fourth means for selectively
operating said imaging device to blank and unblank said scanning
spot so as to create scanline segments of a character having a
point size that corresponds to said selected oscillator, and
means for coupling a different oscillator to drive said fourth
means at a different rate so as to create scanline segments having
lengths different from those created by said selected oscillator so
as to change the point size of the characters composed by said
system.
2. The combination in accordance with claim 1 wherein said segments
defined by said coded character-determining signals are specified
by binary numbers exhibiting values corresponding to the relative
sizes of the various segments in a character.
3. The combination in accordance with claim 2 wherein said fourth
means includes a counter into which is entered each successive
segment number.
4. The combination in accordance with claim 3 wherein said
oscillator is coupled to downcount a segment number stored in said
counter in a plurality of successive steps, and
wherein said counter is coupled to said imaging device to control
the energization of said scanning spot for the time it takes to
downcount said segment number to zero.
5. The combination in accordance with claim 1 wherein said
plurality of oscillators are crystal-controlled to exhibit and
substantially fixed pulse repetition rates to accurately control
the lengths of said segments in accordance with the point size of
the character to be created.
Description
BACKGROUND OF THE INVENTION
In some electronic photocomposing machines, characters are formed
on the face of a cathode-ray tube by modulating the intensity of
the scanning beam during a plurality of parallel scanlines and the
characters are imaged onto photographic film. In prior art systems,
the size of the characters in the direction of scanning is usually
controlled by varying the scanning beam velocity. Consequently, the
velocity is high for characters of large point sizes, whereas the
velocity is low for small point size characters.
In composing text, it is disadvantageous for the scanning beam
velocity to vary with point size because it takes longer to write
an area filled with small type than an equal area filled with large
type. Such a writing rate variation imposes a limitation in
addition to the inherent limitation on writing speed, namely the
time required for the scanning beam to expose a given area of
film.
SUMMARY OF THE INVENTION
In an electronic photocomposing system embodying the invention, the
characters of various point sizes are formed with a scanning spot
velocity that is constant and determined only by the exposure
requirements of the film. Point size changes are effected by
changing the length of the scanlines and the spacing between
scanlines.
In a specific embodiment of the invention, a memory stores binary
numbers that describe the relative lengths of the various scanlines
that in combination make up a character. These binary numbers are
converted to a scanline sweep length by a counting process that is
synchronized with the scanning beam. Each binary number is read in
succession from the memory into a counter and downcounted to zero,
with the counting beginning at the start of the scanning beam
sweep. Therefore, the length of the scanlines is determined by the
time it takes to downcount the binary numbers to zero.
The different lengths of the scanlines corresponding to the
different point sizes of the characters are obtained by changing
the counting frequency. Since character point size is specified in
discrete steps, this frequency change is conveniently done by
providing a set of crystal-controlled oscillators tuned to
appropriate and different frequencies.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram of an electronic
photocomposition system embodying the invention; and
FIG. 2 is an illustration of the formation of a character by the
system of FIG. 1.
DETAILED DESCRIPTION
In FIG. 1 a photocomposition system 10 embodying the invention
includes an imaging device 12, such as a cathode-ray tube, that
creates the characters 14 on the face 16 thereof. It is to be noted
that the cathode-ray tube 12 may also create other patterns such as
line drawings, and the invention described herein is also
applicable to such patterns. The cathode-ray tube 12 includes an
electronic scanning beam 18 that emanates from the cathode variety
in the electronic gun section (not shown) of the tube 12. The
scanning beam 18 is deflected by horizontal and vertical deflection
coils 22 and 24 that surround the neck of the tube 12. The scanning
beam 18 creates a scanning spot 26 that forms the patterns in the
phosphor on the face 16 of the tube 12. The light emanating from
the phosphor in the tube 12 is focused by a lens system, shown as a
single convex lens 28 in FIG. 1, onto a photosensitive recording
surface, such as high-gamma photographic film 30. The photographic
film 30 is supported in the focal plane of the lens 28 between a
pair of reels 32. The reels 32 are coupled to be driven by a drive
motor 34 to a new line after each line of character patterns has
been formed on the film 30. The cathode-ray tube 12 and the other
components in the light-sensitive portion of the system 10 are
enclosed in a lighttight compartment (shown dashed in FIG. 1)
having access doors (not shown) for changing and removing the film
30.
An enlarged view of a character 14 that is formed by the system 10
is shown in FIG. 2. The character 14 comprises a capital H of a
given point size from a sans serif font. The capital H, as well as
all of the other characters and patterns created by the
photocomposition system 10, are formed by a plurality of black
vertical segments 36. The segments 36 are character slices that
comprise portions of the scans, i.e., scanlines when the electron
beam 18 in the tube 12 is unblanked. A scanline is one vertical
traversal of the face 16 of the tube 12 by the scanning beam 18. Of
course horizontal scanning may also be utilized in practicing the
invention. Those portions of the scans wherein the electron beam 18
is blanked are white segments 38 and a representative one is shown
dashed in FIG. 2. In the cathode-ray tube 12 itself, the black
segments 36 are actually white on a dark background whereas the
segments 36 are shown dark on a light background in FIG. 2 for
illustrative purposes. In characters of a high graphic quality, the
blank segments 36 overlap each other and are selected to be
numerous enough such that a character of a substantially uniform
density is formed on the photographic film 30. However, for
simplicity, only 20 character slices are shown for the character H
in FIG. 2, although in actuality 80 character slices may be
utilized. The capital H is seated on a character baseline 37 and
ascends above this baseline a predetermined amount as determined by
the point size of the character. A point size twice as great as the
given point size of the character H comprises a character twice as
high and twice as wide as the character H in FIG. 2. The inverse is
true for a character one-half the point size of the character H,
etc.
Each character in a font of characters is defined by a set of
parameters that includes an EM square 41, shown dashed in FIG. 2.
The EM square defines the point size of the character. The body
size or the overall set width of the character is equal to the sum
of the character width 43 (CW) and the leading 44 and trailing 45
side bearings of the character. The leading side bearing 44 (LSB)
is defined as the distance from the leading or left outer periphery
of the character to the leading end of the set width of the
character. Similarly, the trailing side bearing 45 (TSB) is defined
as the distance from the right edge of the character to the
trailing end of the set width of the character. One character is
spaced from another character by the sum of the trailing and
leading side bearings of the respective successive characters. For
characters of a high graphic quality the values of the leading and
trailing side bearing for the capital H may comprise seven scans
each, with the character width 43 comprising 80 scans.
The parameters of a character as well as other data to be described
below are stored in a memory 50 shown in FIG. 1. The memory 50 may
for example comprise a magnetic core random-access memory that is
divided into two main portions, a primary portion 52 and a
secondary portion 54. The primary portion 52 includes a plurality
of successive storage locations that correspond one to one with the
characters and other symbols and marks in a type font. Each
multibit storage location in the primary position 52 is addressed
by a character code which may, for example, comprise a binary
number that is a coded representation of the character. The
sequence of the addresses of the storage locations in the primary
portion 52 of the memory may begin at capital A and continue
through capital Z and then into lower case a, etc. until the end of
the first font.
The contents in each one of the primary locations of the memory 50
is actually an address for the location in the secondary portion of
the memory which stores the first of the coded parameters that
define the corresponding character. Thus when the character code is
utilized to address the character in the primary portion of the
memory 50, the number read from the memory provides a secondary
address for the secondary portion of the memory 50 that begins a
block of secondary address locations wherein the coded parameters
of the character are stored successively. The advantages derived
from such an arrangement in the memory 50 is that identical letters
in different fonts have the same character code. Of course
different fonts have different secondary storage location
limits.
The secondary portion of the memory 50 stores in sequence the
blocks of information necessary to create a character pattern on
the cathode-ray tube 12. The contents of the first memory location
for a block of data in the secondary portion 54 is a coded
representation of the number of scans in the leading side bearing
(LSB) of the character. The contents of the next successive
location is a coded representation of the sum of the number of
scans in the character width (CW) and the trailing side bearing
(TSB) of the character. The next format data stored in the next
location is the number of scans in the character width. For the
sake of simplicity, it is assumed that all characters begin at the
same base line. The next data stored in the block is not format
data but rather the segment data which are the successive coded
representations of the lengths of the individual black segments and
the individual white segments in each scan of the character. Thus,
each of the lengths of the black segments 36 in the left upright
strokes of the character H in FIG. 2 would be stored. For example,
one word of binary data may be stored for each black segment 36.
The lengths of the white segment 38 and the black segment 36 for
each scan in the center portion of the character H are then stored.
One word of binary data for each white segment and one word for
each black segment 36 may be utilized to store these lengths.
Finally, the binary words representing the right upright strokes of
the character H would be stored, completing the entire
character.
To attain synchronism between the scanning beam 18 and reading
omemory 50, the stored segment words also include data relating to
the start and retracing of the scanning beam 18, as well as to
blanking and unblanking it. The least significant bit in a binary
word for a black segment 36, i.e., the 2.sup.0 bit, may be selected
to designate the end of a scan. No white segments terminate a scan
because the scanning beam 18 is retraced after finishing the last
black segment in a scanline. Thus, when a black segment includes a
binary "1 " in this 2.sup. 0 -bit position, it signifies that this
black segment is the last black segment in that particular scan. A
binary "0 " occuring in the 2.sup. o -bit position in a black
segment indicates that at least one more black segment occurs in
the particular scan. The bit in the 2.sup.0 position not only
determines when a scan ends but, as will become more apparent
later, also determines when the scan begins. Thus to sum up, the
scanning beam is retraced when a binary "1 " occurs in the 2.sup. o
-bit position of a black segment.
The next least significant bit in the segment words, i.e., the
2.sup. 1 bit indicates when the scanning beam should be turned on
(i.e., unblanked) and when the beam should be turned off (i.e.,
blanked). When a binary "1 " is stored in this position the beam is
turned on and when a binary "0 " is stored in this position, the
beam is turned off. Thus the black segment words are differentiated
from the white segment words by the binary bit (i.e., color bit)
stored in this 2.sup. 1 -bit position. It is therefore apparent
that the segment words themselves control the scanning out or
forming the character slices.
Referring back to FIG. 1, a magnetic tape 60 that contains
editorial and text data is read by a tape reader 62. The data of
the magnetic tape includes not only the text material to be printed
by the system 10, but also the necessary instructions for
justifying and hyphenating the material. The data on the magnetic
tape 60 also specifies the point size of the characters to be
created. All the data that relates to a character to be printed is
read from the tape 60 by the tape reader 62 and stored in an input
buffer register 64. The tape reader 62, after reading data from the
tape 60 into the register 64, generates a start pulse to trigger
the start of a timing control circuit 70 to start the transfer of
data into and through the system 10. The timing control circuits 70
are standard timing circuits for providing the necessary trains of
timing signal pulses (TP) for transferring data into and through
the system 10. To create the timing pulses, clock pulses from a
clock oscillator 128 may, for example, be applied to a plurality of
one-shot multivibrators to produce a series of successive timing
pulses that are selected to transfer data into and through the
system 10. Delay lines are coupled to the multivibrators to delay
selected pulses. Additionally, the memory subsystem 51 and all of
the remaining circuits to be described are standard circuits and
hence will not be described in detail.
The buffer register 64 applies the coded representation of the
point size of the character to be printed through transfer gates 71
to a point size and scanline-spacing control register 73. It is
assumed that all data is transferred in parallel throughout the
system 10 and hence there is one transfer gate for each bit in the
data transferred. The character code of the character to be printed
is shifted through transfer gates 66 into a memory address register
68 in the memory subsystem 51. The tape reader 62 also transmits a
command to the drive motor 34 to position the film 30 for a line of
print. The character code in the address register 68 is then
shifted through transfer gates 72 into an X-Y decoder 74. The
contents of the memory 50 location selected by the decoder 74 are
read out through read gates 76 into a memory data register 78. The
data register 78 immediately rewrites the data read from the memory
50 back into the same location of the memory 50 by means of write
gates 80. In all operations to be described in the disclosure, each
read operation is immediately followed by a write operation so as
to prevent the destruction of the data read out of the memory 50.
The data in the data register 78 is transferred through transfer
gates 82 to the address register 68 because the first data read
from the memory 50 in printing a character is the first address in
the secondary portion of the memory 50 of the block of data that
defines the character parameters needed to create the character on
the imaging device 12. The secondary address is coupled through
transfer gates 72 to the decoder 74. Thus the secondary portion of
the memory 50 is now addressed and is read successively.
The first data read from the memory 50 in the block of character
parameters stored in the secondary portion of the memory 50 is a
binary number representing the leading side bearing (LSB) of the
character. This data is coupled through the transfer gates 84 into
a binary adder 86. The binary adder 86 adds the contents of the
data register 78 to the contents of a register 90. The register 90
stores the sum of the character width (CW) and the trailing side
bearing (TSB) from the previous character. The sum of the data in
the register 78 and in the register 90 is the horizontal position
of the start of the new character to be created on the imaging
device 12. Since it is assumed that the character H of FIG. 2 is
the first character in a line of print, the contents of the
register 90 is zero. The sum derived by the binary adder 86 is
added to the contents of an accumulator 87 so that the accumulative
position of the beginning of the scans of each character is known,
as the characters are printed on the photographic film 30.
As the data is read out of the register 78, an incrementor 79
increments by one the address register 68 to the next successive
address in the secondary portion of the memory 50.
The data contained in this next successive secondary address is a
binary number representing the sum of the character width (CW) and
the trailing side bearing (TSB) and this data is read out of the
memory and transferred through the gates 88 into the register 90.
The new contents of the register 90 remain therein until the next
character is read and then the binary adder 86 adds these contents
to the leading side bearing (LSB) of the next character. This sum
specifies the position to which the scanning beam must be jumped at
the end of scanning one character to the beginning of the scanning
of the next successive character.
The accumulated total stored in the accumulator 87 is transferred
through transfer gates 92 to jam set a horizontal counter 94. The
count in the horizontal counter 94 is transferred through the
transfer gates 96 to the horizontal position register 98. The
positional number in the horizontal register 98 is coupled to a
horizontal digital-to-analog converter (DACON) 100 where the
digital data is transformed to an analog voltage so as to
horizontally position the electron scanning beam 18. The analog
voltage is converted to a current in a horizontal driver 102 and
applied to the horizontal deflection coils 22 in the cathode-ray
tube 12.
The horizontal counter 94 may, for example, comprise a binary
counter having a plurality of flip-flop stages for stepping the
scanning spot 26 in the imaging device 12 across the face 16
thereof as a line of characters is printed on the film 30. An
AND-gate 83 is coupled to the advance terminal A of the horizontal
counter 94 and clock pulses derived from a clock oscillator 81 are
applied to the advance terminal when the AND-gate 83 is activated.
A second input to the AND-gate 83 is derived from a flip-flop 85.
As the positional number is transferred out of the horizontal
counter 94 at the end of a scan, the flip-flop 85 is set by the
transfer. The setting of the flip-flop 85 applies an AND-gate 83
enabling signal. The third input to the AND-gate 83 is applied to
the inhibit input terminal thereof and is derived from a zero
decoder 93. The zero decoder 93 only inhibits the AND-gate 83 when
a zero is detected in a counter 91 by the zero decoder 93. The
counter 91 receives a count via transfer gates 89 from point size
and scanline-spacing control register 73.
The binary representation of the point size of the character being
printed is stored in the point size register 73 and the point size
is transferred to jam set the scanline spacing control counter 91.
The clock pulse output of the AND-gate 83 is coupled to downcount
the spacing control counter 91, and the zero decoder 93 signals the
arrival of zero in the counter 91 and deactivates the AND-gate 83
and prevents further clock pulses from upcounting the horizontal
counter 94. The output of the zero decoder 93 also activates the
transfer gates 89, and resets the flip-flop 85. The transfer gates
89 therefore cause the same point size number to jam set the
scanline-spacing control counter 91 but the counter 91 is not
downcounted until the horizontal counter 94 sets the flip-flop 85
at the end of a scan. To sum up, the horizontal counter 94 receives
the horizontal position of the first scan (i.e., point 144 in FIG.
2) of the first character in a line of print and transfers this
binary number into the horizontal register 98 where it is converted
into an analog voltage by a horizontal DACON 100. The analog
voltage is converted to a current in the horizontal driver 102 and
the scanning spot 26 is positioned to the beginning of the first
scan in the character. Previous to this, the point size of the
character is stored in the register 73 and transferred into the
counter 91. When the horizontal position number is transferred out
of the horizontal counter 94, the flip-flop 85 is set to activate
the AND-gate 83 and apply clock pulses to the horizontal counter 94
and the spacing control counter 91. The spacing control counter 91
is downcounted to zero whereas the horizontal counter is upcounted
by the same count. When the zero decoder 93 detects the zero in the
counter 91, the output of the decoder 93 deactivates the AND-gate
83 and resets the flip-flop 85. The decoder 93 also transfers the
same binary number from the register 73 back into the counter 91,
but the AND-gate 83 remains inactive due to the resetting of the
flip-flop 85. The horizontal counter 94 remains at the upcount
position. This position is actually the horizontal position of the
next scan as denoted by the point 147 in FIG. 2. The advantage
derived from such operation is that during one scanline, the
counter 94 is being stepped to the next scanline position and the
counter 94 has time to settle down before the next positional
number is transferred to the horizontal position register 98. This
eliminates any settling time delay since it occurs while the
previous scan is occurring. As stated previously, for characters of
high graphic quality, the scanlines overlap even with a narrow
aperture scanning spot 26. Thus, what is effectively controlled is
the degree of overlap of the scanlines when the point size of the
characters is changed.
It is apparent that as long as the binary representations of point
size from the magnetic tape 60 are proportional to point size, the
system 10 allows rapid change of point size. For example, if the
binary representation for a character of six points is the binary
equivalent of one quantity six and for seven points is the binary
equivalent of seven, then the horizontal counter 94 moves six
increments between scans for a six-point character and seven
increments for a seven-point character. Therefore, the horizontal
distance between scans changes in the proper proportion as the
point size is changed.
In the system 10, the point size and spacing control register 73 is
also coupled to a control switch 101. The control switch 101
couples any one of a plurality of crystal-controlled oscillators
103.sub.1 through 103.sub.n to a video counter 126 which
effectively determines the height of a scanline and consequently
the height of a character, as will be described in more detail
subsequently.
The next data readout of the memory 50 is the character width (CW).
This binary representation of the number of scanlines in the
character width is coupled through the transfer gates 114 into a
scan counter 116. The scan counter 116 is decremented by a count of
one at the end of each scanline so that when a count of zero is
reached, a zero decoder 118 coupled to the scan counter 116 signals
that the end of a character has been reached. This signal instructs
the tape reader 62 to read the next character from the tape 60.
The next data read from the memory 50 is the segment data that
actually causes the character slices to be written on the tube 12.
This data is read and transferred by appropriate segment data
timing pulses generated in a subroutine in the timing and control
circuits 70. The segment data is coupled through transfer gates 120
to a buffer register 122. The register 122 stores, at the minimum,
the entire number of white and black segments of a complete scan of
a character. The register 122 desirably stores the segment data
relating to a plurality of scans and may also be operated in a
simultaneous read-write mode, i.e., push-pull, wherein one section
of the register 122 is being written into while another secton is
being read. Such operation prevents delay in forming the segment
patterns on the imaging tube 12. A bit detector 123 is coupled to
the output of the transfer gates 120 to detect a binary "1" in the
2.sup.0 -bit position of the segments entering the buffer register
122. The bit detector 123 activates a sawtooth generator 134 when
this bit is detected to begin the vertical deflection of the
scanning beam 18. The bit detector 123 also transfers the segments
through transfer gates 124 into a video counter 126. The video
counter 126 is jam set by the gates 124 and counted down by clock
pulses derived from any one of the oscillators 103.sub.1
-103.sub.n. When the count in the video counter 126 equals zero, a
zero decoder 130 transfers a new segment from the buffer register
122, into the video counter 126.
Also coupled to the output of the transfer gates 124 is a dual bit
detector 132 which functions to detect the bits 2.sup.1 and 2.sup.0
in each segment. When the bit 2.sup.1 in a segment is a "1," the
bit detector 132 sends a signal to the cathode 20 of the tube 12 to
bias the cathode 20 to turn on the scanning beam 18. When a "0" is
detected in this 2.sup.1 -bit position, the cathode 20 is biased
off. When a binary 1 is detected in the 2.sup.0 -bit position, an
output signal is applied to an AND-gate 135 where it is gated with
the output of the zero decoder 130 to signify the "end of a scan."
This end-of-scan signal is coupled to turn off the sawtooth
generator 134 when the segment data has been utilized to form the
last black segment in the scan.
The sawtooth signal generated in the generator 134 causes the
scanning beam 18 to scan upwardly from a beam rest position (e.g.
line 37, FIG. 2). When the sawtooth generator 134 is reset, the
scanning beam is retraced back to the beam rest position line 37 in
FIG. 2. The output of the gate 135, which signals the end of a
scan, is also coupled to shift the positional count in the
horizontal counter 94 into the register 98 to move the beam 18 to
its new position as well as to downcount the scan counter 116.
Since the buffer register 122 may contain scan segments from a
variety of scans, there may also be plurality of video counters 126
so as to ensure that there is no delay in reading data from the
memory 50.
OPERATION
The system 10 forms characters of any of a variety of point sizes.
The point size of the character to be formed is read into the point
size and spacing control register 73 and this register controls
both the spacing between adjacent scanlines and the counting
frequency to downcount the video counter 126. The register 73
selects the correct one of the oscillators 103.sub.1-103.sub.n by
means of the switching circuit 101. It is assumed that the
oscillator 103.sub.1 is the oscillator selected. Let it also be
assumed that the scanning spot 26 is positioned at the point 144 in
FIG. 2 and the system 10 is ready to form the character H of a
desired point size.
The scan segment data is read from the memory 50 and the first
number read specifies the number of pulses from the oscillator
103.sub.1 that occur while the scanning beam is tracing out the
black segment 36 between the points 144 and 146 in FIG. 2. When
this number is read through the transfer gates 120 into the buffer
register 122, the bit detector 123 detects the binary "1" appearing
in the 2.sup.0 position of this number and knows that an entire
scan or stroke has passed into the buffer register 122. The bit
detector 123 therefore activates the transfer gates 124 to jam set
the video counter 126 with the segment data from the buffer
register 122 as well as activates the sawtooth generator 134 to
initiate the generation of a sawtooth signal. The bit detector 123
may for example comprise a one-shot multivibrator coupled to the
2.sup.0 position in the transfer gates 120.
Since the first stroke of the character H is a black segment, the
bit detector 132 detects the binary "1" in the 2.sup.1 position of
the segment data and generates a "beam on" scanning signal that is
coupled to the cathode 20 of the tube 12 to turn on the beam 18.
The signal from the sawtooth generator 134 is applied through the
vertical driver 112 to cause the unblanked scanning beam 18 to rise
vertically from its position 144 toward the position 146 as shown
in FIG. 2. A black segment 36 is therefore traced on the face 16 of
the cathode ray tube 12. The light emitted from phosphor on the
face 16 of the tube 12 is focused through the lens 28 onto the
high-gamma photographic film 20 and one black character slice of
the character H is exposed on the film 20.
The bit detector 132 also detects the presence of a binary "1" in
the least significant bit position 2.sup.0, which is the retrace
bit position, and applies a continuous retrace signal to the
AND-gate 135. The oscillator 103.sub.1 counts down the video
counter 126 at a frequency necessary to form a height of a given
point size. When the counter 126 is counted down to zero, the zero
decoder 130 detects the end of the countdown and the AND-gate 135
is activated. The output of the AND-gate 135 resets the sawtooth
generator 134 whereupon the beam 18 is retraced back from the
position 146 to the base line 37 in FIG. 2. The bit detector 132
may therefore include a flip-flop that is set by a binary "1" and
the 2.sup.1 -bit position of a data number to generate a scanning
"beam on" bias signal. The bit detector 132 flip-flop is then reset
by either a binary "0" in this 2.sup.1 -bit position or the end of
scan output of the AND-gate 135. Additionally, the bit detector 132
also includes a second flip-flop that is set by a binary "1" in the
2.sup.0 -bit position of the data. The flip-flop applies a retrace
signal to the input of the gate 135. This flip-flop is reset by the
output of the gate 135 which signifies the end of a scan. The
scanning beam 18 is retraced in a blanked condition.
At the end of the segment, the zero decoder 130 generates a
transfer signal that is applied to the transfer gates 124 to
transfer the next segment into the video counter 126 when the bit
detector 123 detects sufficient data for another scan. The end of
scan signal from the AND-gate 135 is also applied to count down the
scan counter 116 as well as apply to the transfer gates 96 to
transfer the position of the next scan into the horizontal register
98. This positional number is converted by the DACON 100 and driver
102 into an analog signal to position the scanning beam 18 at the
point 147 in FIG. 2. One black segment comprising an entire scan of
the character H is therefore imaged onto the film 30. The system 10
repeats the procedure until the entire character is created.
The height of the character is dependent upon the frequency of the
oscillator selected from the bank of oscillators 103.sub.1 through
103.sub.n. By selecting a different one of the oscillators a
different height is provided because the downcounting of the video
counter 126 is faster or slower depending on the frequency of the
oscillator selected. Thus the scanning beam 18 and spot 20 is
turned on for longer times for large point size characters and
shorter times for smaller point size characters. Effectively, the
oscillator frequency is converted to scanning beam spot sweep
lengths. The point size designation in the register 73 selects the
oscillator that drives the video counter 126 as well as determines
the number of clock pulses from the clock oscillator 81 that steps
the scanning spot to the next black segment scanline position. When
the point size of a character increases, the spacing between
adjacent scanlines is also increased correspondingly.
It is to be noted that the scanning beam spot moves at the same
constant rate or velocity regardless of the point sizes of the
characters being created. This velocity is selected in accordance
with the exposure requirements of the film 30.
* * * * *