Electronic Photocomposition System

Abstract

An electronic photocomposition system forms patterns, including characters, on an imaging device, such as a cathode ray tube, and focuses the patterns onto a photosensitive surface for recording thereon. The characters formed include ascender characters that ascend from a predetermined character baseline and descender characters that descend below the character baseline. Each character is formed by a plurality of successive vertical scans that create individual character slices. The start of each scan is positioned at the character baseline for each ascender character and is displaced to the bottommost portion of the character for each descender character. Each scan of each character is retraced immediately upon traversing the outer periphery of a character during the scan so that the length of the scans corresponds to the contour of the characters. The scans are stepped across the character as the character is scanned and, at the end of scanning a character, the scans are jumped to the position where the next character begins with no intercharacter space being scanned.

Description

BACKGROUND OF THE INVENTION

Mechanical and photographical techniques of composing type are relatively slow and the probability of increasing by a significant amount the speed of such type composition systems appears to be small. The successful transformation of type composition into an electronic art promises to increase significantly the speed of type composition. There have recently been provided electronic photocomposition systems incorporating cathode ray tubes in which a synchronous scanning pattern, such as a raster scanning pattern is utilized to form the characters. A memory is incorporated in electronic photocomposition systems to store instructions for blanking and unblanking the cathode ray tube during the scanning thereof so as to form character slices when the tube is unblanked. Such synchronous electronic photocomposition systems are relatively slow because the scanning pattern has to overscan both the top and bottom of all characters to form both ascender and descender characters in a particular type font. Such a scanning pattern not only is inefficient in the speed at which the characters are formed but also exhibits other disadvantages.

One significant disadvantage of such synchronous photocomposition systems is the large amount of storage space required in the memory to form each character. This is because there must be stored binary numbers instructing the cathode ray tube to remain blanked during the period of time the upper and lower margins are being scanned. This either increases the size of the memory required or reduces the number of characters that can be stored in the memory.

SUMMARY OF THE INVENTION

An electronic photocomposition system embodying the invention forms patterns in a imaging device by a plurality of scans which in toto creates the pattern. The patterns formed include ascender characters that ascend from a predetermined character baseline and descender characters that partially descent below the predetermined baseline. Means are provided for positioning the start of each of the scans of a character at a character scanning reference line located at the outermost point of the character and retracing the scan back to the start thereof at the end of traversing the outer periphery of the character.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an electronic photocomposition system embodying the invention;

FIG. 2 is a graphical illustration of the formation of characters in the system of FIG. 1; and

FIG. 3 is a schematic representation of the arrangement of the memory in the system of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIG. 1, there is shown a system 10 embodying the invention. Although the invention will be described in terms of a photocomposition or phototypesetting system, it is to be understood that the invention may be embodied in any alphanumeric display system. The photocomposition system 10 includes an imaging device 12, such as a cathode ray tube, that creates patterns, such as the characters 14 on the face 16 thereof. While there are a variety of techniques for forming the characters 14 on the imaging device 12, a technique that is utilized to form patterns of a high graphic quality is described. In this technique each of the characters 14 is built up by a plurality of vertical scans such as those shown in FIG. 2.

The cathode ray tube 12, in FIG. 1, includes an electron scanning beam 18 that emanates from a cathode 20 in the electron 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. It is apparent that electrostatic deflection may also be utilized in 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 28, illustrated in FIG. 1 as a single convex lens, onto a photosensitive surface, such as high gamma photographic film 30. The film 30 is supported between a pair of reels 32 in the focal plane of the lens 28. The film 30 is advanced by a drive motor 34 coupled to the reels 32 and activated when a line of print has been formed on the film 30 to move the film to a new line. The cathode ray tube 12 and the other components are enclosed in a lighttight compartment 35 shown dashed in FIG. 1, and having access doors (not shown) for changing and removing the film 30.

The characters 14 shown in FIG. 2 include a capital H and a lower case p from a sans serif font. Each character is formed by a plurality of black vertical segments 36 or character slices that comprise the portions of the scans when the electron beam 18 in the tube 12 is unblanked. The portions of the scans wherein the electron beam 18 in the tube 12 is blanked are white segments 38 and representative ones are shown dashed in FIG. 2 Of course in the tube 12 itself, the black segments 36 are actually light on a dark background whereas the segments 36 are shown dark on a light background in FIG. 2 for illustrative purposes. The black segments 36 overlap each other in actuality so that the characters are formed of a high graphic quality and a substantially uniform density.

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 characters being formed. The character baseline 37 is the nominal line on which characters sit to form the reproduced visual line of printed text. The baseline 37 is usually coincident with the bottom of nearly all the capital letters (except Q) in most fonts as well as with the bottom of many lower case letters. For the purposes of this disclosure, all characters, whether upper or lower case, that ascend from the character baseline 37, are called ascender characters. The lower case letter p in FIG. 2 has a body that sits on the character baseline 37 but which also includes a portion that descends below the baseline 37. For the purposes of this disclosure, all characters whether upper or lower case, that partially descend below the character baseline 37 are termed descender characters. The scans that form the ascender characters and descender characters are selected to start at the outermost (e.g. lowermost) point of the characters. This scan starting position is termed a "character scanning reference line " and for the character p is given the reference numeral 39 in FIG. 2. The character scanning reference line 39 determines the starting position of each scan of the associated character and, for the ascender characters, it coincides with the character baseline 37. For the descender characters, the character scanning reference line 39 may vary from character to character. The character scanning reference line 39 is defined for each character as the amount of vertical displacement from a scanning beam rest position line 40. The beam rest position line 40 comprises an overall reference for each character.

Each character is defined by a basic set of parameters that includes an em square 41 (shown in dashed lines in FIG. 2), that defines the point size of the character. The body size or overall set width 42 of a 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 thereof. 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 thereof. One character is spaced from another character by the sum of the trailing and leading side bearings of the respective successive characters. The values of typical leading and trailing side bearings for the letter H may for example 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, as stored in a storage device or memory 50, shown in FIG. 2. The memory 50 may for example comprise a magnetic core random access memory. The memory 50 is divided into at least two portions: a primary portion 52 and a secondary portion 54. The primary portion 52 includes a plurality of successive locations that correspond one-to-one with the characters and other symbols or marks in a type font. Each location in the primary portion 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 in the primary portion 52 may begin at capital A and continue through capital Z then into a lower case a, etc., until the end of the font.

As shown in FIG. 3, the contents in each one of the primary locations is actually an address for the secondary portion of the memory 50 that fixes the beginning of the stored coded representations or parameters that define the character. Thus when a character code is utilized to address a primary location, the binary number read from that location provides a secondary address for the secondary portion of the memory 50 that begins a block of secondary addresses of locations wherein all the desired coded representations of the character are stored successively. The advantage derived from such an arrangement in the memory 50 is that identical letters in each font have the same character code and thus the memory 50 can be addressed the same way for each font.

The secondary portion of the memory 50 stores the blocks of information necessary to create a character on the face of the imaging device 12. The contents of the first location in a block of data in the secondary portion of the memory 50 is a coded representation of the number of scans in the leading side bearing 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 and the trailing side bearing of the character. The data stored in the third location of the block is a coded representation of the vertical displacement, i.e. the distance from the scanning beam rest position 40 (FIG. 2) to the character scanning reference line 39 for that character. The last format data stored in the secondary portion of the memory 50 is the number of scans in the character width.

The next data stored in a block in the secondary portion of the memory 50 are the coded representations of the lengths of the black segments and white segments in each scan of the character. There may for example be one byte of stored data for to black segment 36 and one byte for each white segment 38. Thus it may be seen that by positioning the start of the scans at the character scanning reference line 39, a large saving in stored data is obtained because no white segments need be stored for scans that begin at the character scanning reference line 39 or the character baseline 37.

To attain synchronism with the scanning beam 18, the segment bytes also include data relating to starting and retracing the scanning beam, as well as turning it on and off. Thus, the least significant bit in the byte, i.e. the 2.sup.0 bit, is selected to designate the end of a scan. When a black segment has a binary 1 in this bit position, it signifies that this black segment is the last black segment in that particular scan. A binary 0 in the 2.sup.0 bit position in a black segment indicates that at least one more black segment occurs in the particular scan. Thus the stored coded representation of the black segment 41 a of FIG. 2 would contain a binary 0 in the 2.sup.0 bit position thereof, signifying that another black segment occurs in the scan. However, the stored coded representation of the black segment 41 b that occurs in the same scan would contain a binary 1 in the 2.sup.0 bit position thereof, signifying the end of the scan. Furthermore, the 2.sup.0 bit position is not only utilized to determine when a scan ends but, as will become more apparent later, when it begins.

The next to the least significant bit in the segment bytes, i.e. the 2.sup.1 bit position; signifies when the scanning beam should be turned on and when the beam should be turned off. When a binary 1 is stored in this bit position the beam is turn on and when a binary 0 is stored in this bit position the beam is turned off. Thus the segment bytes themselves control the scanning out of the character slices.

Although there are a variety of techniques for presenting editorial material to be printed to the photocomposition system 10 in FIG. 1, it will be assumed that this material is first written onto a magnetic tape 60 and read into the system 10 by a magnetic tape reader 62. The magnetic tape 60 includes not only the text material to be printed by the system 10, but also the necessary instructions for justifying, hyphenating, etc. The data read from the magnetic tape 60 is applied to an input buffer register 64, so that the data may be decoded by a decoder 66. The decoder 66 transmits the character codes to an address register 68 contained in the memory subsystem 51, and also transmits commands to initiate a timing control circuit 70 that starts the transfer of data into and through the memory subsystem 51. The decoder 66 also transmits commands to the drive motor 34 to position the film 30 for a new line of print. The timing control circuits 70 are standard timing circuits for providing timing signals for transferring data into and through the system 10. Additionally, it is to be understood that the memory 50, the memory subsystem 51 and the remaining circuits in the system 10 are standard circuits and hence will not be described in detail.

The character code in the address register 68 is applied to an X--Y decoder 72 through a plurality of transfer gates 74 that are activated by timing signals derived from the timing control circuit 70. It is assumed that all data is transferred in parallel throughout the system and hence one transfer gate is needed for each bit in the data. The contends in the location selected by the decoder 72 is read out by the read gates 76 into a data register 78. The data read from the memory 50 into the register 78 is immediately rewritten into the memory 50 by the gates 80 in all operations described in this disclosure to prevent destruction of the data.

The data in the data register 78 is transferred through gates 82 into the address register 68 since this data is the first address of the block of data in the secondary portion 54 of the memory 50 that creates the character on the imaging device 12. Consequently, this block of data is now read successively into the data register 78 from the secondary portion 54 of the memory 50. First the leading side bearing (LSB) data is read into the register 78 and coupled through transfer gates 84 to 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. As the leading side bearing (LSB) data is read out of the data register 78, an incrementer 79 increments 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 location is a binary number representing the sum of the character width (CW) and the trailing side bearing (TSB). This data is transferred through the gates 88 to the register 90. The 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 of the next character. This sum specifies the distance that the scanning beam 18 must be jumped in a horizontal direction at the end of scanning one character to the beginning of the scanning of the next successive character.

The binary adder 86 is coupled to an accumulator 87 wherein each sum is accumulated to move the scanning beam 18 across the face 16 of the tube 12. The accumulated total in the accumulator 87 is applied through transfer gates 92 to jam set a horizontal counter 94 to the accumulated total. The positional number stored in the horizontal counter 94 is transferred through transfer gates 96 to jam set a horizontal register 98 at the beginning of the scanning of a new character. The transfer gates 96 are coupled back, such as through an OR gate (not shown), to upcount the horizontal counter 94 one position at the end of every transfer so as to define the horizontal position of the next scan of the character. This gives the horizontal counter 94 time to settle down during a scan before transfer of the next scan position to the horizontal register 98. This horizontal position count is transferred through the gates 96 to the register 98 at the end of the scan. The positional number in the horizontal register 98 is coupled to a horizontal digital-to-analogue converter (DACON) 100 where the digital positional number is transformed to an analogue voltage so as to horizontally position the electron scanning beam 18. The analogue 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 incrementer 79 causes the address register 68 to read the next data, which is the vertical displacement of the character, into the data register 78. The vertical displacement data is coupled through transfer gates 104 to vertical displacement register 106. The digital positional number stored in the register 106 is converted to an analogue value in a vertical DACON 108 and applied to a summing amplifier 110. The output of the summing amplifier 110 is coupled through a driver 112 to the vertical deflection coils 24. The vertical displacement data defines the character scanning reference line 39 for the character to be scanned by the electron beam 18.

The incrementer 79 advances the address register 68 to the next successive secondary location and the character width data is then read into the data register 78. The character width data is then coupled though transfer gates 114 to a scan counter 116. The scan counter 116 is decremented by a count of one at the end of each scan so that when the counter 116 reaches zero, a zero decoder 118 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 as well as resets the displacement register 106 to zero, i.e. the scanning beam rest position.

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 coupled through transfer gates 120 to a buffer register 122. The buffer register 122 stores all the bytes of white and black segments in one complete scanline or slice of a character. More desirably the buffer register 122 may be large enough to store the segment bytes for a plurality of scans and then operated in a simultaneous read-write mode. In such operation one portion of the register 122 is receiving segment data for one scan from the memory 50 whereas the segment data for the previous scan is being read out of the register 122. Such a mode of operation avoids delay in forming the character segments on the tube 12.

The black and white segment bytes for a scan are read out of the memory 50 in sequence and into the buffer register 122. A bit detector 123 is coupled to detect a binary 1 in the 2.sup.0 bit position of the segments entering the buffer register 122. When this bit is detected in a byte entering the buffer register 122, the bit detector 123 activates a sawtooth generator 134 to begin the vertical deflection of the scanning beam 18. The sawtooth signal generated in the generator 134 is added to the vertical displacement stored in the DACON 108 by the summing amplifier 110 to cause the scanning beam 18 to scan upwardly. It is to be noted that the sawtooth generator 134 is not activated until the bytes for an entire scanline is stored in the buffer register 122. The bit detector 123 is coupled to the timing control circuits 70 to prevent segment data for the next scan from being entered into the buffer register 122. The bit detector 123 is also coupled to the transfer gates 124 to transfer the segment bytes in the register 122 through the transfer gates 124 into a video counter 126. The video counter 126 is jam set by the transfer gates 124 and counted down by a clock oscillator 128. The clock oscillator 128 may also provide the central clock pulses for the system 10 and is coupled to the timing control circuits 70 to provide the raw pulses for these circuits. When the video counter 126 equals zero, a zero decoder 130 transfers data for a new segment from the buffer register 122, into the video counter 126. When the buffer register 122 is large enough to contain scan segments from a plurality of scans, there are provided a plurality of video counters 126 so as to insure that there is no delay in processing the data.

Also coupled to 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 (i.e. a black segment), 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 (i.e. a white segment) the cathode 20 is biased off. When a binary 1 is detected in the 2.sup.0 bit position, (i.e. the last black segment in a scanline) 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 after the data in the video counter 126 has been utilized to form the last black segment in the scan. The end of scan signal is coupled to the sawtooth generator 134 to turn off the sawtooth sweep signal and retrace the scanning beam 18 back to the vertical displacement point or character scanning reference line. The end of scan signal is also coupled to the timing control circuits 70 to start the read out from the memory 50 and into the buffer register 122 the segments of data for the next scan. The end of scan signal is also coupled to down count the stroke counter 116 as well as to the transfer gates 96 to update the horizontal register 98 for the beginning of the next scan. The horizontal counter 94 is incremented by this transfer to the next successive scan position and consequently the settling time of the counter 94 is overlapped in time with a previous scan.

OPERATION

In describing the operation of the photocomposition system 10 it is assumed that the characters H and p are to be printed. The magnetic tape 60 therefore contains the character code of the character H which is a primary address for the memory 50. The content at this addressed location is the secondary address for the block of data required to form the character H. The character code is therefore first coupled into the address register 68 and the timing control circuit 70 is initiated. The contents at the location of this primary address is therefore readout of the memory 50 and into the data register 78. Since this data is a secondary address, it is transferred into the address register 68 via the transfer gates 82. The address register 68 therefore now addresses the secondary location in the memory 50 wherein the format and other data relating to the formation of the character H begins. Consequently, the leading side bearing of the character H is read out of the memory 50 and into the data register 78. The leading side bearing data is then coupled through the transfer gates 84 to the binary adder 86 where it is added to the contents of the register 90. Since the register 90 contains the sum of the character width and the trailing side bearing of the previous character, the contents thereof is zero at this time because it is assumed that the character H is the first character in a line of print. Consequently, only the leading side bearing data of the character H is applied to the accumulator 87. This value is then transferred through the transfer gates 92 to jam set the horizontal counter 94, which in turn causes the transfer gates 96 to jam set the horizontal register 98 to this value. The horizontal counter 94 is then incremented to the next successive scan position. The contents of the horizontal register 98 is converted to an analogue value in the DACON 100. The analogue value is applied through the driver 102 to position the scanning beam 28 to a point equivalent to the point 140 in the scanning beam rest position line 40 in FIG. 2. The scanning beam 18 is therefore in the correct horizontal (but not vertical) position to being scanning out the character H.

As each data word is transferred out of the data register 78, the incrementer 79 adds one to the binary number contents of the address register 68 and causes the address register 68 to address the next location in the secondary block of data in the memory 50. Therefore, the character width and trailing side bearing data is next read into the data register 78. This data is then coupled through the transfer gates 88 to the register 90 where it is stored during the scanning of the entire character H so as to be in position to add to the leading side bearing of the next character so that the scanning beam 18 may be properly positioned to begin scanning the next character

The incrementer 79 increments the address register 68 again and the vertical displacement data represented by the line 142 in FIG. 2, is read into the register 78. The data is then transferred through transfer gates 104 to the vertical displacement register 106 where it is converted into an analogue voltage by the DACON 108 to provide a vertical bias to position scanning beam 18 to the point 144 in the character baseline 37 of the character H The scanning beam 18 is now in position to start scanning out the character H. The incrementer 79 then increments the address register 68 to read out the character-width, which is the number of scans necessary to form the character H. This data is transferred through the transfer gates 114 into a stroke counter 116.

The next data read from the memory 50 is the block of bytes that specify the scan data necessary to form the character H. The bytes in each entire scan are read successively into the buffer register 122. The first byte in this data is a binary number that specifies the number of pulses from the clock 128 that are to be counted while the scanning beam is tracing out the black segment 36 between the points 144 and 146 in FIG. 2. This byte comprises an entire scan and when the number representing this byte 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 thereof. Thus the fact that an entire scan or stroke has passed into the buffer register 122 has been detected. The bit detector 123 therefore activates the transfer gates 124 to jam set the video counter 126 with the scan 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 sawtooth signal from the sawtooth generator 134 that is added to the vertical displacement bias in the summing amplifier 110, causes the scanning beam 18 to rise vertically from its position 144 as shown in FIG. 2 and the "beam on" signal causes the first black segment 36 to be formed 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 and recorded 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 clock oscillator 126 counts down the video counter 126 and when the scanning beam 18 reaches the position 146 in FIG. 2, the zero decoded 130 detects the end of the count down and the AND gate 135 is activated. The output of the AND gate 135 resets the sawtooth generator 134 and retraces the beam 18 back to the character baseline 37 in FIG. 2. The bit detector 132 may therefore include a flip-flop that is set by a binary 1 in 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 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-out state. 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. The next segment is actually the next scan and consequently the end of the scan signal from the AND gate 135 causes the timing control circuit 70 to read into the buffer register this byte. The end of scan signal is applied to count down the stroke counter 116 and transfer the count in the horizontal counter 94 to jam set the horizontal register 98 to the next horizontal position of the scanning beam along the character baseline 35. The horizontal counter 94 is then incremented to the next successive scan position.

It is to be noted that only one binary number was required to form this first black segment 36 in the character H and that the scanning beam traversed only this segment in forming the character slice. It is therefore apparent that the system 10 exhibits significant advantages in the speed of forming characters as well as in saving storage space in the memory 50.

These two segment bytes are read into the buffer register 122 in succession. The binary 1 in the 2.sup.0 bit position of the black segment starts the sawtooth sweep signal. However, each black segment of the character H in the left hand portion thereof is imaged onto the photosensitive paper 20 in a manner similar to that described above. As each segment is written, the horizontal counter 94 is counted up by one and the scan counter 116 is counted down by one. When the center of the character H is reached, each scan comprises two bytes representing a white segment and a black segment respectively, the first segment in the scan is a white segment, a binary 0 in the 2.sup.1 bit position of this segment biases the scanning beam "off" during the time the scanning beam is traversing the portion of the scan that is shown dashed in FIG. 2. Hence no character slice is formed until the end of this segment at which point the black segment begins. Otherwise, the operation of the system 10 is similar to that described previously.

When the end of the character H is reached, the scan counter 116 has been down counted to zero and the zero decoder 118 signifies that the next character should be read by the tape reader 62. The vertical displacement register 106 is also reset by the end of character signal.

The character code for the lower case p is therefore read into the address register 68 and the contents at the location of the primary address of the character p is read through the data register 78 into the address register 68. The secondary address of the beginning of the block of format and scan data is therefore positioned in the address register 68. The first format data read out is the leading side bearing of the character p. This data is added to the contents of the register 90 in the binary adder 86. It is to be recalled that the contents of the register 90 is the character width and the trailing side bearing of the character H. The output of the binary adder 86 is then added to the previous number in the accumulator 87, which is the leading side bearing of the character H, and the accumulated total is utilized to jam set the horizontal counter 94 and the horizontal register 98. The accumulated total therein is converted to an analogue value in the DACON 100 and applied through the driver 102 position the scanning beam 18 at the horizontal position 146 in FIG. 2. It is to be noted that the scanning beam 18 has been jumped to the point 146 and no time was wasted in scanning the intercharacter space between the characters H and p.

The character width and trailing side bearing for the character "p" is then entered into the register 90 and the vertical displacement is entered into the register 106. The vertical displacement when converted by the DACON 108 positions the scanning beam 18 at the point 148 in FIG. 2. The scanning beam 18 is therefore positioned at the character scanning reference line 39 for the character p and this is displaced from the character baseline 37. Thus the scanning beam is in position to scan out the character p without overscanning the character. It is to be noted that each character format includes a vertical displacement number to position the scanning beam 18 at the character scanning reference line for that character. These numbers may or may not coincide with the character baseline 35 in FIG. 2.

The character width of the character p is then read into the stroke counter 116 and the character is then scanned out in a manner similar to that described for the character H. At the end of scanning a line a print, the tape reader 62 signals through the decoder 66 for the drive motor 24 to more the photographic film 30 to the next line.

Thus a photocomposition system 10 has been described that is significantly faster than prior art systems. The increased speed is obtained by utilizing a jump scanning technique that initially positions the scanning beam at the lowest black segmental point in the character and scans to the last black segmental point at the end of the particular scan. At this point the scanning beam is retraced to its initial position. This asynchronous jump type scanning prevents "dead time" scanning from occurring, which has heretofore been typical of the prior art systems. Additionally, the amount of storage space required in the memory 50 is reduced significantly because there is no necessity for storing data relating to the scanning of a white margin above and below the character as is necessary in prior art systems. Consequently, the photocomposition system 10 prints characters extremely fast and reduces the amount of hardware to do so.

Claims

I claim:

1. An electronic composition system for forming patterns including ascender characters that ascend from a predetermined character baseline and descender characters that include regions which descend below said predetermined baseline, comprising in combination:

an imaging device;

means for providing a plurality of coded signals that define said characters, said coded signals including;

character-determining signals that correspond to linear portions of said character: and

displacement signals that determine the position of the start of said linear portions with respect to a reference position;

means for utilizing said displacement signals to position the start of the linear portions of said characters at variable character positions that are located at the outermost points of the outer periphery of said characters; and

means for scanning and selectively blanking said imaging device in response to said character determining signals to form said linear portions.

2. The combination in accordance with claim 1 wherein said reference position for each of said ascender characters comprises said predetermined character baseline.

3. The combination in accordance with claim 2 wherein said reference position for said descender characters differs from said predetermined character baseline.

4. The combination in accordance with claim 1 wherein:

said characters are separated from preceeding and succeeding characters in a line of print by leading and trailing side bearings respectively; that further includes

means for jumping the position of the start of scanning a succeeding character, at the end of scanning a preceeding character, a distance substantially equal to the sum of the leading side bearing of said succeeding character and the trailing side bearing of said preceeding character.

5. The combination in accordance with claim 1 wherein said linear portions are formed by a plurality of substantially vertical scans of said imaging device.

6. The combination in accordance with claim 5 wherein said means for scanning includes:

a sweep generator for vertically scanning said imaging device in a continuous sweep; and which combination further includes

a horizontal counter for moving said scans horizontally in discrete steps.

7. The combination in accordance with claim 6 wherein said means for scanning further includes:

means for unblanking said imaging device during a vertical sweep to form a black segment of a character in a scan; and

means for blanking said imaging device during a vertical sweep to form a white segment of a character in a scan.

8. The combination in accordance with claim 6 that further includes means for terminating a scan of a character after creating a linear portion of said character and upon reaching the outer periphery of said character.

9. The combination in accordance with claim 1 that further includes:

means for storing said coded signals of each of said characters, with each coded signal including at least one coded number for each scan of a character; and

said one coded number including a digit designating the start and end of a scan and a digit designating the blanking and unblanking of said device during said scan.

10. The combination in accordance with claim 9 wherein said means for storing said coded signals comprises;

a memory including a primary portion having a plurality of locations each successively representing a different character with each having an address corresponding to a different character code, and a secondary portion having a plurality of successive locations with each storing a coded number corresponding to a segment of said scans of said character; and

the locations in said primary portions each storing a different address of said secondary portion with said address corresponding to the beginning of the secondary portion locations that relate to a single character.

11. The combination in accordance with claim 1 wherein said outermost points comprise the lowermost edges of said characters.