CA1132459A - Computerized laser engraving system and method - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

System and method utilizing a computer and a laser platemaker for the reproduction of information on photosensitive surfaces, as in the production of printing plates. The platemaker includes a reading beam for scanning data such as text, logotypes, line art and halftones from a read platen or copy board and a writing beam for imaging data on a writing surface or platen. Data from the reading beam is transferred to the computer which controls the modulation of the writing beam. The system provides high speed electronic composition or pagination of any combination of data created by the computer or scanned by the reading beam.

Description

COMPUTERIZED LASER ENGR~VING SYSTEM AND METHOD

This invention pertains generally to the reproduction of information on photosensitive surfaces, as in the production of printing plates, and more particularly to a system and method for electronic composition of a page from computer generated text and material read from a copy board or other reading surface.

1 In the offset printin~ process which has been employed ; for a number of years in the newspaper publishing and commercial printing industries, printed text, photo-graphs and other graphic materials are assembled manu-ally together to form a so-called "paste-up" of each page to be printed. A printing plate is then made from the paste-up, typically by a photographic process.
This traditional prepress process is time consuming, `~ re~uiring on the order of 40-60 minutes per page once the copy is ready to begin the paste-up ~pera-tion.

In recent years, computers have been employed in the creation, storage and editing of text and have significantly reduced the time required for this portion of the prepress operation. Another signifi-cant reduction of time in the prepress operation has , ,, ' '" ~

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resulted from the development o~ a laser plate~aker having reading and writing beams for slmultaneously scanning the paste-up and plate.
I For some time now, it has been thou~ht that even greater savings in time could be achieved by utilizing the computer in which the text is created, stored and edited to drive the plate making device. However, prior to the present invention, no one to the knowledge of the inventors has been able to provide a commercially feasible all electronic prepress system. United 10States Patent 3,949,159, issued April 6, 1976, describes a system for combining computer generated text with photographs and other materials read from a drum. However, the material from the drum can only be reproduced in real time and in the same relative position for storing data read from the drum, no provision for editing such data, and no pro~ision for forming a page with data read from the drum in another position, size or format.
The invention provides a system and method which achie~e total flexibility in an all electronic prepress system. The system includes a laser platemaker having a reading beam for scanning a read platen or copy board and a writing beam for scanning a write platen or printing plate. The system also includes a computer ~or creating, storing and editing data and converting data to raster format for presentation to the platemaker. An interface between the computer and platemaker permits data to pass either from t~e computer to the writing beam control of the platemaker or from the r~ading beam of the platemaker to the computer. Three basic modes of operation are provided: imaging of data created by the computer, imaging of data input through the reading beam, and .r ~ 2 imaging of a combination of data from the computer and reading beam. ~hether created by the computer or input from the platemaker, the data stored in the computer can be edited and :imayed in any desired order, position or manner. Da-ta is stored in the computer memory in a byte-oriented run length encoded format which is more efficient than more conventional bit-oriented compression techniques of the prior art.
It is in general an object of the invention to provide a new and improved computerized laser engraving system and method which are particularly suitable for the newspaper publishing and commercial printing industries but are not limited thereto.
Another object of the invention is to provide a system and method of the above character which can selectively image data created by a computer and data input through a reading beam in any desired combination and in any desired position, order or manner.
Another object of the invention is to provide a system and method of the above character in which data to be imaged is stored in a byte-oriented run length encoded format.
In accordance with a broad aspect of the invention, there is provided, in a system for imaging data on a writing surface: a laser platemaker having a reading beam for scanning a read platen to provide a read data signal representative of copy placed on the platen and a writing beam for scanning the writing surface to form an image, modulation means for controlling the intensity of the writing beam as it scans the writing surface, a computer having an input devlce and a memory for creating and storing input data signals, and an interface uni-t interconnecting the computer and platemaker for selectively transferring the read data signal from the pla-temaker to the compu-ter for storage therein and for applying signals from -the computer to the modulation means to permit selective imaging on the writing surface of data scanned from -the read platen and data crea-ted by the computer.
Additional objects and features of -the invention will be apparent from -the following description in which the preferred embodiments are set forth in detail in conjunction with the accompanying drawings.
Figure 1 is an overall block diagram o~ one embodiment of a computerized laser engraving system according to the invention.

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Figure 2 is a diagramatic illustion of data en-coded in accordance with a preferred run length compression technique for storage in the system of Figure 1.

S Figure 3 is a block diagram of one embodiment of an interface unit fox the system of Figure 1.

: Figure 4 is simplified circuit diagxam of a parallel-to-serial data converter for the inter face unit of Figure 3.

Figure 5 is a simplified circuit diagram of a serial-to-parallel converter for the interface unit of Figure 3~

Figure 6 is a block diagram of a second embodi ment of an interface unit for the system of Figure 1.

Figure 7 is a simplified circuit diagram of the data converter and decompressor of the interface unit of Figure 6.

Figure 8 is a schemetic diagram of a preferred laser platemaker for use in the embodiment of Figure 1.

. Figure 9 is a schemetic diagram illustrating the ; reference mask of the platemaker of Figure 8.
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Figure 10 is a circuit diagram of a circuit for selectively presenting data from either the com~-puter or the reading beam to the writing beam control of the platemaker.

: Figure 11 is a flow chart of a preferred program for generating raster scan line data in the system of Figure 1.

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Figure 12 is a flow chart of a preferred program for transferring scan line data between the com-puter and the platemaker in the system o Figure 1.
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Figure 13 is a flow chart of a preferred program for pagination or combination of data from the computer and platemaker in a single raster image.

Figures 14 and 15 are flow charts of preferr~d program routines for compression and decompression of data stored in the system of Figure 1.

~; 10 As illustrated in Figure 1, the system comprises a computer 31, a laser platemaker 32, and an interface unit 33 between the computer and platemaker.

In the preferred embodiment, the computer i5 a Digital Equipment Corpration (DEC) PDP-11/05 minicomputer - which operates in a 16-bit format and includes a 28K
internal memory. It is to be understood, however, that the invention is not limited to a particular type of computer or a particular word size. The computer is provided with a conventional input terminal 34 and a standard magnetic memory disk 36, as well as a direct me~ory access interface 37 such as a Digital Equipment Corporation Model DRllB.

A preferred laser platemaker for use in the system of Figure 1 is illustrated in Figures 8-9 and is here-inafter described in detail. Briefly, the platemakerincludes a reading laser beam which scans or traverses in raster fashion across a read platen 41, picking up reflected energy which is converted into a series of black/white ~ignals in a photomultiplier tube amplifier 42. The platemaker also includes a writing laser beam ~L3~

which scans a write platen 43 in synchronization with the scanning action of the reading beam. Interface unit 33 is connected to the platemaker in such manner that information read from read platen 41 can be transferred to the computer and data from the computer can be transferred to the platemaker to control the intensity of the writing beam.

This system can image plate in three different modes:
(1) a local mode in which data read from platen 41 is transferred directly to the plate or write platen 43,

(2) a somputer mode in which digital data from the computer is written on the plate, and (3) a merge mode in which data from the computer is imaged simultaneously with data from the read platen. In addition, data stored in the computer memory or individual files or raster images can be combined to produce a complete page or other composite raster image.

When text is entered from terminal 34, it is initi-ally written on disk 36 in a text file which contains source information and embedded type setting commands.
Since the write platen or plate is scanned in raster fashion and each text line is made up of a number of scan lines, it is necessary to convert the text file or source file to a raster image format before it is transmitted to the platemaker. For newspaper printing, the platemaker might typically have a resolution in the Y-direction of 1,000 lines per inch and 1,000 bits or points per inch in the X-direction. With this re-solution, a scan line sixteen inches wide would require 16,000 bits of black/white information. In order to generate text ten inches high, 10,000 scan lines con-sisting of 16,000 bits each would be required. As the source or text file is converted to raster image format, it is stored on the disk in the form of a raster image file. This file can then be transferred from the disk ~o the platemaker under the control of the computer. The raster file can also be combined with other raster files stored on the disk to produce a new raster file for transmission to the platemaker.
Raster files can also be ereated by transmitting data read from platen 41 to the computer for storage on the disk. Such data can include textual material, logo-types, halftones and the like.

In order to conserve space on disk 36, the raster files are stored in a compressed format. The compression scheme is illust~ated in Figure 2 and can be described - as byte-oriented run length encoding. Run Length encoding takes advantage of the fact that along a given scan line black and white bits generally occur in groups or strings, rather than alternating black/white/black~
white and so on. In standard run length encoding, the number of bits in each group or string is stored, rather than storing the data for each individual bit. With run length encoding, for example, data for up to 128 bits can be stored in only 8 bits of storage. This technique does not work well, however, where the string length is less than the word in which the length information is stored. Another disadvantage of standard run length encoding is that it requires the computer to operate at the bit level, rather than operating at the full width of its data path where it is more efficient.

In the data compression system of the invention, run lengths are encoded in terms of byte~ rather than bits.
In this system, the scan line is divided into a number of bytes of given length, e g. 8 bits, and the number of successive bytes which are all the same color is stored in the first sevQn bits of an 8-bi~ word, and the color of the string is stored in the remaining 5~

bit. In a second 8-bit word, the data is stored for the byte in which the transition occurs. In the example of Figure 2, bytes Bl-B3 are all black, and the first transition occurs after the second bit in byte B4. Thus, the binary number 0000011 is stored in the eighth bit to indic~e that the color is black.
The actual data for transition bit B4 is stored .in word 2. The next run in the scan line is whit~, and only byte B5 is all white. Therefore, the binary number 0000001 is stored in the first seven bits of count word 3, and a binary 0 is stored in the eighth bit. The actual data for byte B6 is stored in transi.-tion word 4O With this compression technique, a compression of up to 64:1 is possihle, and the maximum possible expansion is only 1:2. With standard run length encoding utili2ing 8-bit coding, the maximum B possible compression is 128~8 or 16~1 and the expan-sion can he as great as 1:8. The compression and decompression functions are performed as the raster file data is written onto and read off of the disk.

: As illustrated in Figure 3, interface unit 33 includes a parallel/serial data converter 46 which receives data from and delivers data to direct memory access interface 37 over a 16-bit bidirectional data bus 47.
The data converter delivers data in serial form to platemaker 32 via output line 48 and receives serial input data from the platemaker on input line 49. The data converter requests data for new words from the computer via line 51 and receives signals on line 5 when the computer is ready to deliver data for new words. Gther status and control signals are delivered to the data converter from the computer on lines such as line 53.

The interface unit also includes start-of-scan logic ~3~l5~
g -56 which receives an input signal from the plat~maker at the start of each scan line. In response to this signal, the start-of-scan logic delivers a properly shaped digital pulse to the data converter. The in-terface unit also includes a reference clock generator57 which receives 6 mil. pulses from the platemaker and delivers l mil pulses to the data converter. In the platemaker, the 6 mil. pulses are generated by diverting a portion of the reading beam to a reference mask having lines spaced 6 mils. apart. Each time the beam crosses a line on the reference mask, a pulse is generated, and these pulses are applied to the refer-ence clock generator as input pulses. The referencP
mask is illustrated in Figures 8 and 9 and described more fully hereinafter. The reference clock generator includes a phase locked loop which produces six output pulses for every input pulse, whereby the output of the reference clock generator is a train of pulses corresponding to a distance of 1 mil. in the travel of the laser beams.

A preferred parallel-to~serial data converter is shown in Figure 4. In this converter, the parallel input data from the computer is applied to the parallel inputs of parallel-input serial-output, shift registers 58, 59. The reference clock signal from generator 57 is applied to the clock inputs of the shift regis~ers, and the output of register 58 is connected to the serial input of register 59. The output of register 59 is connected to the inputs of a N~ND gate 61 which is connected to function as an inverter. The output of this gate is connec ed to one input from a flip~flop 63 which is toggled by the reference clock signal. The output of NAND gate 62 is connected to the input of a NAND gate 64 which is connected to function as a line driver, and the output of this gate is the serialized output data~

e~g Figure 5 illustrates a preferred serial-to-parallel data converter for use in the embodiment of Figure

3. In this converter, the serial input data from the platemaker is applied to the serial input of a serial-input, parallel-output shift register 66 through in-verters 67, 68. The last parallel output shift regis ter 69, and the reference clock signal from generator S7 is applied to the clock inpu~s of these shift regis-ters. The serial input data is converted to parallel vutput da~a which appears at the parallel outputs of shift registers 66, 69, and this data is delivered to the computer via data bus 47.

With the interface unit of Figure 3, both data com-pression or expanæion are performed by th computer.
Flow charts for preferred compression and decompres-sion routines are set forth in Figures 14-15 and discussed hereinafter. Figure 6 illustrates an - interface unit in which the data is decompressed in the interface unit as it is converted from parallel to serial format. This interface unit includes a buffer - 71 and a serial data generator and decompressor 72.
The buffer receives parallel data from the computer on data bus 73 and delivers this data on data bus 74 to the data generator and compressor which delivers - 25 serial data to the platemaker on line 76. In the preferred embodiment, the buffer has two sections each of which can hold four 16-bit words. One section is illed from the computer while data is being trans-ferred from the other to the serializer and decom-pressor. This provides somewhat fastex operation than the system of Figure 3 where the data converter can only receive data when the computer is not other-wise occupied.

The interface unit of Figure 6 also includes start-of-scan logic 77, a reference clock generator 78, and a serial-to-parallel data converter 79. The start~of-scan logic is of the type illustra~ed in Figure S, This converter receives serial input data from the platemaker on input line 81 and delivers parallel out-put data to the computer on data bus 82.

Referring now to Figure 7, serial data generator and decompressor 72 is shown in detail. The first seven bits o the count words or low order bytes (e.g~ words 1,3 in Figure 2) are applied to the inpu~s of pro-B grammable oounters 86, ~ , and the eighth bit whichcarries the color information is applied to the D
input of a flip-flop 88. The weighted outputs of counters 86, 87 are connected to the inputs of NOR
gates 89, 91, and the outputs of these gates are con-nected to the input of an AND gate 92. The outputs of flip-flop 88 and AND gate 92 are connected to the con-trol inputs of an eight stage multiplexer 93.

The transition words or high order bytes (e.g. words 2,4 in Figure 2) are applied to latches 94, 96, and the outputs of the latches are connected to the respective stages vf the multiplexer. In addition to receiving one bit of each transition word through the latches, each stage of the multiplexer also receives a logic 1 and a logic 0 input signal. The output of the multi-plexer is either all l's ~black) all 0's (white) or the bits of the transition word.

The outputs of multiplexer 93 are connecked to the parallel inputs of a parallel-input serial-ouput shift register 97. The serial output o the shift register is connected to the input of a NAND gate 98 which functions as a line driver. The data at the output of this gate is the decompressed serial output data which is de-livered to the platemaker via output line 76.

The reference clock signal is applied to the input of a divide-by-8 counter 101, and the sta~us of this counter is monitored by a NOR gate 102 and a NAND
gate 103. The output of gate 102 is high when the bit count is 0, and the output of gate 103 is low when the bit count equals 7. The output of NOR gate 102 is applied to the down counting input of counter 86 through an ~ND gate 104. The output signal from gate 102 is also inverted and applied to the shift/load in-put of serializing shift reglster 97 and to the clock input of a flip-flop 105. The Q ou put of this flip-flop is connected to a second input o AND gate 104O
-~ 15 AND gate 106 receives a second input from the output of AND gate 92, and the output of this gate is con-nected to the input of a one-shot multivibrator 107.
The Q output of this multivibrator is applied to the load inputs of 94, 96, and the x output i5 applied to the load inputs of counters 86, 87 and the clear input of flip-flop 105.

Operation and use of the decompressing serializer can be described briefly. Each time a new word is received from buffer 71 it is loaded into counters 86, 87, flip-flop 88 and latches 94, 96. Every time eight bits are output, counters 86, 87 are decremented, and the out-puts of these counters and flip-flop 88 determine what gets loaded into the multiplexer and serialized. For example, assume that the coded data comprises two all black bytes followed by a transition byteO During the first two pulses that set an output byte into the shift register, the output o~ the counters is greater than 0, the output of AND gate 92 is 0, and all l's are trans-ferred to the shift register. When the counter reaches .

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~3~5~3 O, the output of the AND ~ate 92 becomes a 1, and the multiplexer transfers the transition word to the shiEt register. Since the shift register is clocked at the reference clock rate rather than the divided down rate by which the counters are decremented, all eight bits in the data word are serialized between successive decrementin~ pulses. When all eight bits have been clocked out of the shi~t register, the next word ls loaded, and the process repeats.
In the platemaker, read platen 41 and write platen 43 are mounted ln fixed positlons on a stationary framework (not shown), and a carriage 111 is mounted on the framework for movement longitudinally or lengthwise of the platens. ~he carriage is driven in the longitudinal direction by a drive motor 112 and a lead screw 113.
The platemaker includes a helium-neon read laser 116 mounted on the carraige and a UV wrlte laser 117 mounted on the frame. The beam 118 produced by the write laser passes through a modulator 119 and a beam expander 121 to mirrors 122 and 123 which direct the beam to a beam combiner 12~. The beam co~biner is part of a scanning optical system 126 mounted on the carria~e, and it also received the beam 127 from read laser 116 via a mirror 128.
The beam combiner compxises a dichroic mirror which reflects the UV write beam and transmits the helium neon read beam.
The combined beam from beam combiner 124 is directed to scanner 131 which causes the beams to scan laterally across the width of the platens. From the scanner, the 5~

comhined beam passes through an objective lens 131 to a dichroic mirror 133 where the beams are separated.
Writing beam 118 is reflected downwardly to the write platen, and reading beam 127 is transmitted to a beam splitter 134. The beam splitter directs portions of the reading beam to read platen 141 and to a reference mask 136.

Reference mask 136 extends ~he full width of read platen 41 and includes alternately spaced opaque areas 137 and transparent areas 138. In the preferred em-bodiment, each of these areas has a width of 3 mils.
Light passing through ~he reference mask is sensed by fiber optics 139 and converted to a digitialized electrical signal by a photomultiplier tube 141. The signal from photomultiplier tube 141 is applied to B interface unit ~ and utilized in generating the re-ference clock signal as described h~reinbefore.

Light reflected by light and clark areas of copy on read platen 41 is sensed by fiber optics 142 and con-verted to a digitialized elect:rical signal by photo~multiplier tube 143. The output of photomultiplier tube 143 is connected to the serial data input of inter-face unit 33 and to one input of a merge circuit 133.
Serial output data from the computer interface is applied to a second input of the merge circuit, and the output of this circuit is connected to modulator 119 to control the write laser beam.

As illustrated in Figure 10, the merge circuik includes EXCLUSIVE OR gates 146, 147 ko which data from the read beam and the computer is applied, respectively.
Switches 148, 149 provide means for inverting the data by applying either +5 volts or 0 volts to second inputs of the EXCLUSIVE OR gates. ~he outputs of these gates ~3;~,~5~

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are connected to the inputs of NAND gates 151, 152, respectively. Means is provided for selectively enabling the NAND gates to pass either the data from the computer or the data from the reading beam or both.
This means includes pull-up resistors 153, 154 and a grounding switch 156 connected to second inputs of the NAND gates. Switch 156 is a 3-position switch having its armature connected to ground, two of its terminals connected to the enabling inputs of gates 151, 152 and an off or "merge" position in which neither of the terminals is grounded. When the switch is in the READ
BEAM position shown in Figure 10, NA~D gate 152 is dis-abled, and the data from the reading beam passes through gate 151. With the switch in the COMPUTER position, NAND gate 151 is disabled, and the computer data passes through gate 152. With the switch in the off or MERGE
position, both NAND gates are enabled, and the data from both the reading beam and the computer is passed.

The outputs of NAND gates 151, 152 are connected to the input~ an OR gate 157. The output of thi~ gate is con-nected to modulator 119. A switch 159 provides means for inverting the output data by applying a voltage of either of ~5 volts or 0 volts to a second input of EXCLUSIVE OR gate 158.

Operation and use of the platemaker of Figures 8-10 ca~ be described briefly. A pa~te-up or other copy to be xead is placed on read platen 41. The beams scan the read and write platens simultaneously in raster fashion, with scanner 131 deflecting the beams laterally across the width of the platens and the longitudinal movement of the carriage providing scanning at a slower rate along the length of the platens. Modulator 119 deflects the writing beam into or out of the optical path under the control of merge circuit 138 to effect - 16 ~-a turning on and off of the beclm. The merge circuit receives data from both the read platen and the compu-ter, and the circuit determines whether the data to be imaged on the write platen, comes from the read platen, the computer or both.

Figure ll is a flow chart for the program by which source or text data is converted to raster image data.
First, a line of text is read into the computer from the disk. That line contains both the tex~ itself and embedded type setting commands. The line is scanned to determine the type setting commands and the charac-ters which are required to typeset the line. The font descriptors which describe the patterns of bits that make up the characters are then read into the computer memory from the disk. Thus, a table is created in the showing all of the fonts needed to generate the line of text.

Next, the raster lines are gene:rated on a line by line basis, picking up all of the charac~ers which are re-quired for each lin~. After each scan line is generated,a check is made to determine whether all of the scan lines are now present for all oE the characters in the text line. The process repeats until all of the scan lines are present. When all of the scan lines are - 25 present, the next line of text is read and the pro-cess continues until the end oE the text is reached.

Figure 12 is a flow chart Eor the program by which data is transferred from the disk to the writing laser and scan information is transferred from the reading laser to the disk. Information such as the file namel mode o data (compressed or uncompressed) and direction (read or write) is input through the terminal~ The file is opened on the disk, and if data is to be read from ~3~

the platemaker, the first scan line i5 read in it^~
entirety and written on the disk in compressed form.
This process continues until all of the lines to be read I from the platemaker have been written on the disk. If data is to be transmitted to the platemaker, the first scan line to be written is read from the disk into a bufer and the mode in which it is ~o be sent to the interface unit is checked. If the interface unit in-cludes a decompressor, the da~a is sent to the in-terface unit in compressed form where it is decompressed and sent on the platemaker. If the interface unit does not include a decompressor, the data is decompressed by the computer and sent to the platemaker. When one scan line has been sent, the next is read from the disk, and the process repeats until the end of the file is reached.

The flow chart for the program for pagination or composition of an entire page image from individual raster files stored in the disk is illustrated in B ~gur~ 13. Data defining files to be combined, the size of the output file, and the location and size parameters for each of the input files is input through the terminal. The dimensional and positioning in-formation is given in scan lines in the y-direction and in bits in the x-direction. The cropping dimensions, output coordinates, and output size are then input for each of the files to be combined. The cropping dimen-sions define the number of bits to be omitted at the left side of the file. The output size defines the dimensions of the output image in units of lines and bits, and the output coordinates define the point at which the image begins in the output, e.g. the upper - left corner of the image. For text material which is not to be cropped, the parameters are defined accord-ingly.

Once the parameters are defined, the input files are opened, and the number of lines specified in the cropping dimensions are skipped. The scan line is written on an output buffer which is cleared at the beginning of each line. Each file is then examined to determine whether it is to be included in the parti-cular scan line. If it is to be includedl the next scan line from that ~ile is read into the output buffer.
If not, the file is ignored. After processing all of the files on the scan line, the line built up in the buffer is written on the disk. The process repeats and continues until all of the scan lines in the out-put image have been rewritten and transferred to the platemaker.

Referring now to the flow chart of Figure 14, the data from a scan buffer i5 compressed a byte at a time.
Consecutive bytes that are either all black or all white bytes is detected, the count is output, along with a high-order bit that indicates the color. Thereafter, the transition byte is output. These steps are repeated until the entire scan line is compress~d. Two bytes of zeros are then output to denote the end o the scan.

Figure 15 illustrates a program routine for reexpanding the compressed data to reconstruct the original scan line. The compressed data consists of a series of two byte pairs of data. The first of these is the run-count; the second is the transition byte. If both - of these are æero, ~he ~nd of the data for a scan has been reached, If not, the high-order bit of the run-count indicates the color of the next sequence to be generated. The low-order 7 bits of the runcount are used to generate the proper number of bytes that are all white or all black, as selected by the color bit.
Following these bytes, the transistion byte is output.

This process continues until the end of scan is detected~

The invention has a number of important features and advantages. It provides relativel~ high speed electronic composition Gr pagination of any combina-tion of data including text, logotypes, line art and halftones created by the computer or scanned by the reading beam of the platemaker. A substantial saving in memory size is achieved by compressing the stored data in a byte-oriented run length fsrmat which allows - the computer to operate at the word level where it is most efficient. While the invention is particularly suitable for the newpaper publishing and commerical printing industries, it also has application in a lS number of other areas, including art work generation, map production, printed circuit board desiy~ and pro-duction, intergrated circuit design and production, mechanical and architectural design and the like.

It is apparent from the foregoing that a new and im-proved computerized laser engraving system and method have been provided. While only certain presently preferred embodiments have been described in detail, as will be apparent with those familiar with the art, certain changes and modifications can b0 made without departing from the ~cope of the invention as defined by the following claims.
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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a system for imaging data on a writing surface: a laser platemaker having a reading beam for scanning a read platen to provide a read data signal representative of copy placed on the platen and a writing beam for scanning the writing surface to form an image, modulation means for controlling the intensity of the writing beam as it scans the writing surface, a computer having an input device and a memory for creating and storing input data signals, and an interface unit interconnecting the computer and platemaker for selectively transferring the read data signal from the platemaker to the computer for storage therein and for applying signals from the computer to the modulation means to permit selective imaging on the writing surface of data scanned from the read platen and data created by the computer.

2. The system of claim 1 wherein the platemaker includes means for effecting simultaneous scanning of the read platen and the writing surface together with means for applying a real time signal representative of copy on the read platen to the modulation means whereby the image formed on the writing surface includes real time data from the read platen.

3. The system of claim 1 further including means for compressing the data signals for storage in the computer memory.

4. The system of claim 3 wherein the means for compressing the data comprises means for encoding the data with a first word representative of the number of successive groups of bits of one type in the data and a second word consisting of the actual data bits for a group of bits in which a change in the bit type occurs.

5. In a method utilizing the system of claim 1 for imaging data on a surface scanned by a writing beam, the steps of: scann-ing input copy with the reading beam of the laser platemaker to form a read data signal representative of the copy, storing the read data signal in the memory of the computer, creating additional data through the computer and storing a signal representative thereof in the computer memory, scanning a writing surface with the writing beam of the laser platemaker, and modulating the writing beam in accordance with selected portions of the data scanned from the copy and the data created by the computer to form an image of the selected data from the copy and the computer on the writing surface.

6. The method of claim 5 wherein additional copy is scanned by the reading beam while the image is being formed on the writing surface to provide a signal representative of the additional copy, and the writing beam is modulated by both the additional copy signal and a signal representative of selected portions of the stored data whereby the image formed on the writing surface includes data from the additional copy in addition to the data input through the computer and the data scanned from the input copy.

7. The method of claim 5 wherein the data scanned from the input copy and the data created by the computer comprises a plurality of bytes each containing a predetermined number of data bits, including the steps of providing a binary signal representa-tive of the data, compressing the data signal by encoding it with a first word representative of the number of successive bytes in the data in which all of the bits are of one type and a second word consisting of the actual data bits for a byte in which a change in the bit type occurs, storing the words representing the compressed data in the computer memory, accessing and decompressing selected portions of the stored data, and modulating the writing beam in accordance with the decompressed data.