Note: Descriptions are shown in the official language in which they were submitted.
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lhis invention perta:ins generally to the generation of raster images,
and more particularly to a processor and method for generating binary raster
scans fxom 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. United States Patent 4,240,119, for example, describes
a computerized laser engraving system which is particularly suitable for
producing printing plates, Canadian Patent 1,149,080, issued June 28, 1983,
describes a laser engraving system for producing artwork for printed circuit
boards either directly on the boards or on an intermediate film, and United
States Patent 4,081,842 describes a facsimile system for the transmission
and 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 ~equirement presen~s 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.
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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 inven~ion 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 ~he 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
lS 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 descriptive
data for ~he character in the character memory. When the input
command data for a given scan line has been completely assem-
2Q bled in the character store, it is transferred to a characterbu~fer, -nd 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.
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'I'hus, in accordance with one broad aspect of the invention, there
is provided, in a raster image processor :for generating serial o-utput
data from sym~olic 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 characters 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 including data indicative of the
position of a character in the cutput image and the address of the
descriptive data for the character in the character memory, a character
huffer, means for transferring the input command data for a scan line from
the character store to the character buffer, and means responsive 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.
In accordance with another broad aspect of the invention there
is provided, 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 descriptive
data for the character in the character memory, transferring the input command
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data for one scan line from the character store to a character buffer,
retrieving the descriptive data from -the character memory for each
successive 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.
In accordance with another broad aspect of the invention there
is provided, 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 des-
criptive 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
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, and means for modulating the laser beam in accordance with the
serial output data as it scans across the output medium.
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Figure 1 is a block diagram of one embodiment of a raster image
processor according to the inven-tion.
Figure 2 is a diagrammatic illustration of the descriptive data
for the characters encoded in a run length coded format 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-ll family of minicomputers
manufactured by Digital ~quipment Corporation, and it is provided with
conventional peripheral devices such as an input terminal and a magnetic
msmory disk system.
The laser engraving system can, for example, be a laser platemaker
of the type described in detail in United States Patent 4,240,119. This system
includes means for generating a reading laser beam which scans input copy in
raster fashion to provide 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 accordance with the input copy
signals to form an image of the copy on the output medium.
131.B0768
Although the invention is disclosed with specific reference
to a laser platemaking system in which the s~mbolic input
commands are typesetting commands and the output ima~e 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 systemare delivered to input bus 16 by a receiver 22, a decoder
23 and a buffer 2~. 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.
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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 organize~
in 16-bit words consisting of two run length bytes (bits
0-5 and 6-11), a color bit (bit 12), a mode bit Ibit 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~
speciied by color bit 12. ~oad 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.
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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 store.
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., whether
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 character
buffer 36, and the character store is then free to begin
assemhling the data for another line. A buffer control 37 is
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 with
decompressor 41 and line buffer 42.
A central procassing unit (CPU) 46 controls the operation of
the processor. The CPU comprises an arithmetic and logic
unit tALU) 47 and a writeable control store (WCS) 48 in which
microinstructions for the ALU are stored. The sequance in
which the microinstructions arle executed is controlled by a
microprogram sequencer 49 whic'h receives inputs through a
multiplexer 51. The instructions output from the WC~ are
stored in a pipeline register 52 so that one instruction
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
bipolax bit slice components from the Advanced Micro Devices
2900 microcomputer family, which is advantageous from the
standpoints of speed and availability of componentsO
The image processor îs 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
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 computer
in the LOAD mode for checking.
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.
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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, 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. ~he address of
the data in the scan line buffer corresponds to the x posi-
tion address of the character being decompressed~ When allof 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.
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This pr4cess continues until the end of the data in the
character buffer is reached. At this time, the processor
waits until the nex* 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.
