RASTER IMAGE PROCESSOR AND METHOD

Abstract: Raster image processor and method for generating binary raster scans from symbolic input commands. The processor is particularly suitable for use in a computerized laser engraving system such as a laser platemaker, an artwork generator for printed circuits, or an intelligent copier. Descriptive data for the characters which make up an output image is generated by a computer and stored in a character memory, and symbolic input commands which point to the location of the descriptive data in the character memory is generated by the computer and stored on a line-by-line basis. As the output beam scans the output medium, the descriptive data for each successive character to be imaged is retrieved from the character memory and processed to provide serial output data for modulation of the output beam.

Description: RASTER IMAGE PROCESSOR AND METHOD This invention pertains generally to the generation of raster images, and more particularly to a processor and method for generating binary raster scans from symbolic input commands. In recent years, computers have been utilized with laser engraving equipment in a variety of applications, including the production of printing plates, the manufacture of printed circuit boards, and the recording and transmission of images. U.S. Patent 4,240,119, for example, describes a computerized laser engraving system which is particularly suitable for producing printing plates, application Serial No. 42,133, filed May 24, 1979, describes a laser engraving system for producing artwork for printed circuit boards either directly on the boards or on an intermediate film, and U.S. Patent 4,081,842 describes a facsimile system for the transmission the reproduction of documents. In each of these systems, a laser beam scans the output medium in raster fashion and is modulated in accordance with binary data definitive of the image to be produced. In order to provide data in the proper sequence for modulating the beam, a serial bit stream is required, and in computer driven systems the bit stream requirement presents a problem in that the computers employed in such systems cannot provide the data at a high enough rate for the remainder of the system. OI.ΪFI It is in general an object of the invention to provide a new and improved processor and method for generating serial output data from symbolic input commands. Another object of the invention is to provide a processor and method of the above character which are particularly suitable for use in a laser engraving system such as a laser platemaker, an artwork generator for direct exposure of printed circuit boards or the formation of an image on an intermediate film, or an intelligent copier, i.e. , a copier driven by a computer. These and other objects are achieved in accordance with the invention by loading descriptive data for all of the characters to be imaged in a group of scan lines into a character memory and loading symbolic input commands for the characters to be imaged in each successive scan line into a character store. The input commands define the x and y positions of each -charac¬ ter in the output image as well as the address of the descripti data for the character in the character memory. When the input command data for a given scan line has been completely assem- bled in the character store, it is transferred to a character buffer, and the character store is free to assemble the input command data for another line. As the beam scans across the output medium, the descriptive data pointed to by the data in the character buffer is retrieved from the character memory and converted to a serial format for modulation of the beam. In one preferred embodiment, the descriptive data is stored in a compressed run length encoded format and decompressed to provide a serial output bit stream. OMFI -3- Figure 1 is a block diagram of one embodiment of a raster image processor according to the invention. ' Figure 2 is a diagrammatic illustration of the descriptive data for the characters encoded in a run length coded for- mat for storage in the character memory in the embodiment of Figure 1. Figure 3 is a diagrammatic illustration of the symbolic input commands employed in the embodiment of Figure 1. Figures 4 and 5 are flow diagrams illustrating the operation of the image processor of Figure 1. In Figure 1, the raster image processor is illustrated in connection with a computer 11 and a laser engraving system 12, The computer can be any suitable digital computer such as one of the PDP-11 family of minicomputers manufactured by Digital Equipment Corporation, and it is provided with conventional peripheral devices such as an input terminal and a magnetic memory disk system. The laser engraving system can, for example, be a laser plate aker of the type described in detail in U.S. Patent 4,240,119 and the other patent(s)/application(s) referenced therein. This system includes means for generating a reading laser beam which scans input copy in raster fashion to pro¬ vide signals representative of the copy, means for generating a writing laser beam which scans an output medium in raster fashion, and means for modulating the writing beam in accord¬ ance with the input copy signals to form an image of the copy on the output medium. -4- Although the invention is disclosed with specific reference to a laser platemaking system in which the symbolic input commands are typesetting commands and the output image is • composed largely of alpha-numeric characters, the invention is equally applicable to other systems and characters such as printed circuit artwork, lineart and logotypes. Thus, it will be understood that the term "character", as used herein is not limited to alpha-numeric characters or con¬ ventional printing symbols, but includes any type of artwork or information to be included in the output image. Descrip¬ tive data for such artwork or information can be generated, for example, by scanning the same with the reading beam of the platemaker and converting the resulting signals to the desired digital format. For artwork the input commands are plotting commands, and for printed circuits the output medium can be either a layer of photoresist or other photosensitive material on the printed circuit boards themselves or a photosensitive film which is used as a master in exposing the boards. The image processor includes a data input bus 16 and a data output bus 17. Data is transferred to the input bus from the bus system of computer 11 by a transceiver 18 and an input latch 19, and data is transferred from output bus 17 to the computer bus system by an output latch 21 and trans- ceiver 18. Address signals from the computer bus system are delivered to input bus 16 by a receiver 22, a decoder 23 and a buffer 24. A controller 26 transfers control signals between the bus system of the computer and the image processor. A character memory 28 is provided for storing descriptive data for the characters which make up the image to be formed, and an address counter 29 is associated with this memory. As discussed more fully hereinafter, the descriptive data is generated by the computer and loaded into the character memory. As illustrated in Figure 2, the descriptive data for the characters is compressed and stored in a run length encoded format in the character memory. The data is organized 'in 16-bit words consisting of two run length bytes (bits 0-5 and 6-11) , a color bit (bit 12) , a mode bit (bit 13) and two op code bits (bits 14-15) . Bits 0-.11 define the length of runs to be imaged in the color (black/white) specified by color bit 12. Load bit 13 indicates whether the image bits defined by bits 0-11 are to be treated as a single run or two separate runs. If the mode bit is 0, the entire run of bits described by bits 0-11 is imaged with the color specified by the color bit. If the mode bit is 1, bits 0-11 are treated as two separate words, with the word defined by bits 0-5 being imaged with the color specified by the color bit and the word defined by bits 6-11 being imaged with the opposite color. Op code bits 14, 15 tell the decompressor how to interpret the run length code code that follows in accordance with the following table: Bit 15 Bit 14 Interpretation 1 0 Decompress this word and continue to the next word in the character description. 0 1 This is the last word for this scan line. Decompress this word and continue to the next character. 0 0 Repeat the following code by the ■ - number indicated in this word (used for vertical compression) . 1 . 1 This is the last word for the scan line and for ' this description. De¬ compress this word and continue to the next character, / D OMFI 301 -6- A character store 31 is provided for storing symbolic input commands for the characters to be imaged in a given scan line, and an address counter 32 is associated with this stor The symbolic input commands are generated by the computer and loaded into the character store. As illustrated in Figure 3, the symbolic code for each character consists of four 16-bit words. Bits 0-14 of the first word define the x position of the character in the output image, and bit 15 indicates whether the character is valid, i.e., wheth it has already been imaged. The second word points to the starting address of the character description in character memory 28, the third word is not used, and the fourth word contains a repeat code for vertical redundancy compression. When the symbolic data for a given scan line has been fully assembled in character store, it is transferred to a charact buffer 36, and the character store is then free to begin assembling the data for another line. A buffer control 37 i associated with buffer 36. A decompressor 41 is provided for converting the run length encoded data from character memory 28 to a serial bit stream format, and this serial output data is stored in a dual line buffer 42 for application to the modulator for the writing beam of platemaker. An address counter 43 is associated wit decompressor 41 and line buffer 42. A central processing unit (CPU) 46 controls the operation of the processor. The CPU comprises an arithmetic and logic unit (ALU) 47 and a writeable control store (WCS) 48 in whic microinstructions for the ALU are stored. The sequence in " O -7- which the microinstructions are executed is controlled by a microprogram sequencer 49 which receives inputs through a multiplexer 51. The instructions output from the WCS are • stored in a pipeline register 52 so that one instruction 5 can be executing while the next one is being fetched. This allows a fast instruction execution time of 126 nanoseconds. In the preferred embodiment the CPU is composed of LSI bipolar bit slice components from the Advanced Micro Devices 2900 microcomputer family, which is advantageous from the 0 standpoints of speed and availability of components. The image processor is interfaced directly to the bus system of host computer 11, -and when the processor is in the LOAD mode the WCS can be loaded by transferring microinstructions from the host computer. When the processor is in the RUN 5 mode it executes the microinstructions and has the capability of reading directly from the memory of the host computer through non-processor requests. WCS output registers 56-58 permit the contents of WCS 48 to be read into the host comput in the LOAD mode for checking. o Operation and use of the image processor and therein the method of the invention can best be described with- reference to the flow charts of Figures 4-5. Before imaging begins, computer 11 downloads the character description for each character in the output image to character memory 28, and the starting address for the data for each character in the character memroy is passed back to the computer. When the descriptive data for all of the. characters in the image has been transferred, the symbolic input commands for character codes for all of the characters having a common y address are loaded into character store 31. The y address is also transferred, and when all of the data for a given line has been transferred, a flag bit is set. At this point, the image processor can begin processing. The processor is synchronized with the scan of the output beam, and when the y scan line counter matches the character code y address, the data from the character store is trans¬ ferred to character buffer 36. At this time, the computer can begin assembling the input commands or character codes for the next scan line in the character store. CPU 46 scans the character buffer for valid character codes. When one is found r the CPU stops scanning and fetches the first word of the character description which is being pointed to by the character code. Decompressor 41 decompresses this data and places it in scan line buffer 42. The address of the data in the scan line buffer corresponds to the x posi- tion address of the character being decompressed. When all of the data for the portion of a character to be imaged in a given scan line has been decompressed, the CPU begins scanning the character buffer for the next valid character code. When the portion of a character in a given scan ' line has been completely imaged, the valid data bit for that character is cleared, and the portion of the character buffer where that character is stored is available for a new character code. OMFI This process continues until the end of the data in the character buffer is reached. At this time, the processor waits until the next scan line begins, and the process ■ repeats. At the appropriate time, the scan line data which has been loaded into the scan line buffer is output to the laser engraving system, and the output beam is modulated accordingly. Meanwhile, the computer is loading the next line of character codes into character store 31. For vertical redundancy, the number of bits defined by the run length code of the descriptive data is transferred to the repeat code in character buffer 36, and this number is decremented for each successive scan line. The image processor and method of the invention have a number of important features and advantages. They permit binary raster scans to be generated from symbolic input commands and they generate serial output data in a more efficient manner than computers heretofore provided. While the processor and method have been described with specific reference to a laser engraving system, they are equally applicable to other applications in which a serial bit stream is required. It is apparent from the foregoing that a new and improved -raster image processor and method have been provided. While only certain preferred embodiments have been described in detail, as will be apparent to those familiar with the art, certain changes and modifications can be made without departing from the scope of the invention as defined by the following claims. • ••

Claims: CLAIMS ; 1. In a raster image processor for generating serial output • data from symbolic input commands for use in the formation of an image on an output medium scanned in raster fashion by a beam modulated in accordance with said data: a character memory for storing descriptive data for a plurality of charac¬ ters to be imaged in a group of scan lines, a character store for storing symbolic input commands for characters to be imaged in a given scan line, each of said commands includ- ing data indicative of the position of a character in the output image and the address of the descriptive data for the character in the character memory, a character buffer, means for transferring the input command data for a scan line from the charater store to the character buffer, and means respon- sive to the position of the beam in the scan line and to the data in the character buffer for retrieving the descriptive data from the character memory for each successive character in the scan line and providing serial output data for the line. 2. The processor of Claim 1 wherein the descriptive data for the characters is stored in a compressed format in the character memory, and means for retrieving the descriptive data and providing the serial output data includes a decom¬ pressor for converting the data from the compressed format to a serial bit stream. 3. The processor of Claim 2 wherein the descriptive data is encoded in a run length coded format. -11- 4. The processor of Claim 1 wherein the output medium is a printing plate, and the symbolic input commands are type ¬ setting commands. 5. The processor of Claim 1 wherein the input commands are plotting commands for printed circuit artwork, and the output medium is selected from the group consisting of a photosensitive film and a photosensitive material on a printed circuit board. 6. In a method of generating serial output data from symbolic input codes for use in the formation of an image on an output medium scanned in raster fashion by a beam modulated in accordance with said data, the steps of: storing descriptive data in a character memory for a plur¬ ality of characters to be imaged in a group of scan lines, storing the symbolic input commands for the characters to be imaged in a given scan line in a character store, each of said commands including data indicative of the position of a character in the output image and the address of the descrip¬ tive data for the character in the character memory, trans- ferring the input command data for one scan line from the character store to a character buffer, retrieving the descriptive data from the character memory for each succes¬ sive character in the scan line in accordance with the position of the beam in the scan line and the data in the character buffer, and processing the data retrieved from the character memory to provide the serial output data. 7. The method of Claim 6 wherein the descriptive data. " - for the characters is stored in the character memory in a compressed format, and the data retrieved from the character memory is converted to a serial bit stream for the output data. 8. The method of Claim 7 wherein the descriptive data is encoded in a run length coded format. 9. The method of Claim 6 wherein the output medium is a printing plate, and the serial input commands are typesetting commands. 10. The method of Claim 6 wherein the input commands are plotting commands for printed circuit artwork, and the output medium is selected from the group consisting of a photo¬ sensitive film and a photosensitive material on a printed circuit board. 11. The method of Claim 6 wherein the descriptive data for the characters is generated and loaded into the character memory by a computer. 12. The method of Claim 6 wherein the symbolic input com¬ mand data is generated and loaded into the character store by a computer. 13. The method of Claim 6 wherein the symbolic input data for one scan line is loaded into the character store while the data for a previous scan line is being processed. 14. In a laser engraving system for forming an image on an output medium scanned along successive lines in raster fashion by a laser beam: a character memory, a character store, computer means for generating descriptive data for characters to be included in the image and symbolic input commands for the characters in a given line of the image, means for loading the descriptive data into the character memory and the symbolic input commands into the character . - store, each of said input commands including data defining - the position of a character in the output image and the address of the descriptive data for the character in the character memory, a character buffer, means for transferring the input command data for a scan line from the character store to the character buffer, means responsive to the position of the beam in the scan line and to the data in the • character bu fer for retrieving the descriptive data from the character memory for each successive character in the scan line and providing serial output data for the line, and means for modulating the laser beam in accordance with the serial output data as it scans across the output medium. 15. The system of Claim 14 wherein the data for the characters is stored in a compressed format in the character memory, and the means for retrieving the descriptive data and providing the serial output data includes a decompressor for converting the data from the compressed format to a serial bit stream. 16. The system of Claim 15 wherein the descriptive data is encoded in a run length coded format. 17. The system of Claim 14 wherein the output medium is a printing plate, and the symbolic input commands are type¬ setting commands. 18. The system of Claim 14 wherein the input commands are plotting commands for printed circuit artwork, and the output medium is selected from the group consisting of a photosen¬ sitive film and a photosensitive material on a printed circuit board.

Inventors: HOOGERBRUGGE GARY H, NORTON LYLE K, HOOGERBRUGGE, GARY, H., NORTON, LYLE, K.
Applicants: HOECHST CO AMERICAN, AMERICAN HOECHST CORPORATION
Application year: 1981
Main classification: G06F3
IPC codes: G03F7, G03G15, G06K15, G06T11, G09G5