US3614767A

US3614767A - Electronic photocomposing system that forms characters of different point sizes

Info

Publication number: US3614767A
Application number: US786672A
Authority: US
Inventors: Ross M Carrell
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1968-02-19
Filing date: 1968-12-24
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19
Also published as: DE1908307B2; GB1254864A; DE1908307A1; FR2002206A1

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.

Description

TlniTe tallee aTenT Inventor Ross M. Carrel] Cinaminson, NJ.

Appl. No. 786,672

Filed Dec. 24, 1968 Patented Oct. 19, 1971 Assignee RCA Corporation Priority lFeb. 19, 1968 Great Britain 08073/68 ELECTRONIC PIHICTOCOMPOSTNG SYSTEM THAT FORMS CHARACTERS OF lDlllFlFlEll-XENT POINT SllZlES Primary Examiner-John W1 Caldwell Assistant Examiner-Marshall M. Curtis Att0rneyI-l. Christoffersen ABSTRACT: An electronic photocomposing system forms 5 Cuaims 2 Drawing Figs alphanumeric characters on the face of a cathode-ray tube by U.S. C1 1. 340/324 A, a plurality of vertical scanlines that form slices of the charac- 315/18 ters. The characters are imaged onto photographic film for lint. Cl G061 3/14 subsequent processing into printing plates. Characters of diflFieldl all Search 315/18, 19; ferent point sizes are formed by changing the lengths of the 340/324, 324.1; 178/78 scanlines, as well as the spacing between adjacent scanlines.

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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. ll.

DETAILED DESCRIPTION In FIG. I a photocomposition system 110 embodying the invention includes an imaging device I2, such as a cathode-ray tube, that creates the characters M 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 112 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 3A to a new line after each line of character patterns has been formed on the film 30. The

cathode-ray tube 112 and the other components in the lightsensitive portion of the system 10 are enclosed in a lighttight compartment (shown dashed in FIG. 11) 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 110 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 IS in the tube 12 is unblanked. A scanline is one vertical traversal of the face 16 of the tube 12 by the scanning beam 1S. Of course horizontal scanning may also be utilized in practicing the invention. Those portions of the scans wherein the electron beam IR is blanked are white segments 3% 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 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 I-l comprises a character twice as high and twice as wide as the character H in FIG. 2. The inverse is true for a character onehalf 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 Al, 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 MI and trailing 45 side bearings of the character. The leading side bearing Ml (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 hearing 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. ll. 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 mulltibit 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 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 l in this 2- bit position, it signifies that this black segment is the last black segment in that particular scan. A binary occuring in the 2-bit position in a black segment indicates that at least one more black segment occurs in the particular scan. The bit in the 2 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"-bit position of a black segment.

The next least significant bit in the segment words, i.e., the 2' 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 l 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 -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 (T?) 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 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 I 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 F IG. 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 911 is coupled to a horizontal digital-to-analog converter (DACON) 1119 where the digital data is transformed to an analog voltage so as to horizontally position the electron scanning beam 16. The analog voltage is converted to a current in a horizontal driver 102 and applied to the horizontal deflection coils 22 in the cathoderay 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 36. An AND-gate 33 is coupled to the advance terminal A of the horizontal counter 94 and clock pulses derived from a clock oscillator 31 are applied to the advance terminal when the AND-gate 33 is activated. A second input to the AND-gate 83 is derived from a flip-flop 35. As the positional number is transferred out of the horizontal counter 94 at the end of a scan, the flip-flop 115 is set by the transfer. The setting of the flip-flop 35 applies an AND-gate 93 enabling signal. The third input to the AND'gate 63 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 63 when a zero is detected in a counter 91 by the zero decoder 93. The counter 91 receives a count via transfer gates 99 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 ofthe AND-gate 113 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 113 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 35. The transfer gates 39 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 35 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 99 where it is converted into an analog voltage by a horizontal DACON 106. The analog voltage is converted to a current in the horizontal driver 1112 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 95 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 33 and resets the flip-flop 65. 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 99. 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 66 are proportional to point size, the system 11) 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.

ln 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 czrystal-contro1led oscillators 103, through 103,, 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 scan line 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 121) to a buffer register 122. The register 122 stores, at the minimum, the entire number of white and black segments ofa complete scan ofa 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 ofthe transfer gates 1211to detect a binary l in the 2-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 13. 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 -163 When the count in the video counter 126 equals zero, a zero decoder 131) 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 and 2 in each segment. When the bit 2 in a segment is a the bit detector 132 sends a signal to the cathode 20 of the tube 12 to bias the cathode 21) to turn on the scanning beam 111. When a 0 is detected in this 2'-bit position, the cathode 21) is biased off. When a binary l is detected in the: 2 -bit position, an output signal is applied to an AND-gate 135 where it is gated with the output of the zero decoder 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 19 to scan upwardly from a beam rest posi tion (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 93 to move the beam 13 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 by means of the switching circuit 101. lt is assumed that the oscillator 103 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, that occur while the scanning beam is tracing out the black segment 36 between the

points

144 and 146 in F IG. 2. When this number is read through the transfer gates 120 into the buffer register 122, the bit detector 123 detects the binary l appearing in the 2 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 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 l in the 2 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 l in the least significant bit position 2, which is the retrace bit position, and applies a continuous retrace signal to the AND-gate 135. The oscillator 103 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 l and the 2 -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 in this 2-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 l in the 2-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 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 through 103,,. 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.

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 charac ters,

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 cou'nter 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.

Claims

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.

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.